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Climates of the British Isles : present, past, and future
 9781315870793, 1315870797

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Climates of the British Isles Present, Past and Future

Edited by Mike Hulme and Elaine Barrow

CLIMATES OF THE BRITISH ISLES

Climates o f the British Isles com m em orates the tw enty-fifth anniversary o f the founding o f th e in te rn atio n ­ ally acclaim ed C lim atic Research U n it at the U niversity o f East A nglia. W ritte n by present and recent m em bers o f the U n it, the sixteen chapters o f this book distil m uch o f the w ork and expertise for w hich the C lim a tic Research U n it is fam ous, presenting to the reader th ro u g h the geographical lens o f the B ritish Isles an in teg rated synopsis o f w h at we know about clim ate at the end o f the tw e n tie th ccntury. T his dom ain is deliberately w ider than just the U n ited K ingdom . Yet clim ate know s no boundaries o th er than those w ro u g h t by m ountains and oceans and w hile clim ate change has becom e a political issue in recent years the clim ate system itself continues to function oblivious to political boundaries. Climates o f the British Isles com bines th e historical and geographical dim ensions o f clim ate to provide a m ore com prehensive account o f th e changing clim ate th an has previously been a tte m p te d . T h e clim ates o f past ages in th is region are reconstructed, from th e great Q uaternary Ice Ages th ro u g h to th e L ittle Ice Age o f the seventeenth century. A full description o f the clim ate o f th e present century is provided, illustrated w ith a w ealth o f graphs, p h o tograph s and colour m aps. Som e im p o rta n t clim ate datasets are also listed. T he book also addresses th e prospects for clim ate change in the B ritish Isles over th e next h undred years and fu rth er in to the future.

C L I M A T E S O F THE BRITISH ISLES Present, Past and Future

Edited by

Mike Hulme and Elaine Barrow

i London and New York

F irst publish ed 1997 by Roue ledge 2 P ark Square, M ilto n P ark, A b in g d o n , O x o n , 0 X 1 4 4 R N S im ultaneously publish ed in the USA and Canada by R outledge 2 7 0 M adison A ve, N e w York N Y 10016 T ransferred to D ig ita l P rin tin g 2007 © 1997 C lim atic Research U n it Typeset in G aram ond by Florencetype L td, S toodleigh, Devon All rig h ts reserved. N o p a rt o f rhis book may be reprinred or reproduced or utilized in any form or by any electronic, m echanical, or o th e r m eans, now know n or hereafter inven ted , in clu d in g p h otocopying and recording, or in any inform ation storage or retrieval system , w ith o u t perm ission in w ritin g from th e publishers. B ritish Library Cataloguing in Publication Data A catalogue record for this book is available from th e B ritish Library Library o f Congress Cataloging in Publication D ata C lim a te o f th e B ritish Isles: present, past and future / ed ited by M ike H u lm e & E laine Barrow, p. cm. inclu d es bibliographical references and index. 1. B ritish Isles - C lim ate. 2. Paleoclim atology — B ritish Isles. I. H u lm e , M. II. Barrow, E. Q C 9 8 9 .G 6 9 C 5 8 9 6 -3 1 9 8 0 5 5 1 .6 9 4 l-< lc 2 0 C IP ISBN 0 —4 1 5 —1 3 0 16—6 ISBN 0 - 4 1 5 - 1 3 0 1 7 - 4 (pbk) P u b l i s h e r ’s N o te T h e p u b lish e r has g o n e to g re a t len g th s to ensure th e q u a lity o f th is re p rin t b u t p o in ts o u t th a t som e im perfections in th e orig in al m ay be ap parent

This book is dedicated to Professor H .H . Lamb, Founder an d Director o f the Climatic Research Unit, 1972—1978

T his page intentionally lcli blank

CONTENTS

L ist o f Plates

xii

List o f Figures

xiii

L ist o f Tables

xix

L ist o f Contributors

xxi

Preface

xxv

Foreword

xxvii

Acknowledgments

xxx

C H A P T E R 1: IN T R O D U C IN G CLIM ATE C H A N G E

1

M ik e H u lm e a n d E la in e B a r ro w C h a n g in g Views o f C lim ate

1

O u tlin e o f th e Book

4

PART 1:

9

THE BRITISH ISLES CLIMATE

C H A F F E R 2: E X P L A IN IN G T H E CLIM ATE O F T H E B R IT ISH ISLES

11

T re v o r D a v ie s , P. M ick K e lly a n d T im O s b o r n In tro d u ctio n

11

G lobal-scale R adiation and H eat Balances

12

T h e G eneral C irculation

16

Surface Pressure P attern s

25

L inks w ith th e O cean

26

A ir Masses

29

Sm aller W eath er System s and Local Influences

30

T h e Scene is Set

31

C H A P T E R 3: D E S C R IB IN G T H E SURFACE CLIM ATE O F T H E B R IT ISH ISLES

33

E la in e B a r ro w a n d M ik e H u lm e In tro d u ctio n

33

Surface A ir T em perature P recipitation: A m o u n t and Frequency

33 41

O th e r C lim ate Variables: Sunshine, H u m id ity and W ind Speed

47

VIII

CONTENTS Regional Clim ates Sum m ary

53 61

PART 2:

63

RECONSTRUCTING THE PAST

C H A PT E R 4: T H E CLIMATES O F PAST AGES B ria n F u n n e l! Introduction C lim ate in the Pre-Ceriozoic F.ra T he A pproach to the Present Ice Age T he Present Ice Age Glacial Cycles in the B ritish Isles T he Last Im erglacial-G lacial Cycle Conclusions C H A PT E R 5: R E C O N S T R U C T IN G LATE-GI.ACIAL A N D H O LO C EN E CLIMATES K e ith B riffa a n d T im A tk in so n Introduction T he End of the Last G reat Ice Age T he Younger Dryas in the B ritish Isles

65 65 66 68 70 73 74 80 84 84 87 92

T h e Holocene Period Conclusions

98 107

C H A P T E R 6: D O C U M E N T IN G T H E MEDIEVAL CLIMATE A s trid O gilvie a n d G ra h a m F a rm e r

112

Introduction T he Im portance o f Source Analysis T h e Sources and D ata Strategy and M ethodology Presentation of the Data Sea-ice Incidence in the N orth A tlantic Conclusions

112 113 115 117 119 120 130

PART 3:

135

MONITORING THE PRESENT

C H A PT E R 7: O BSERV ING A N D M E A SU R IN G T H E W EA TH ER: A BRIEF H ISTO RY J o h n K in g to n Introduction

137 137

T he P re-instrum ental Period T he Beginning ol Instrum ental O bserving T he A dvent of the M odern Instrum ental Period Today’s W orld o f O bservations T he Role o f the A m ateur Observer

137 139 144 149 150

CONTENTS

C H A P T E R 8: CLA SSIFY IN G T H E W IN D S A N D W E A T H E R

153

P. M ick K elly, P h il J o n e s a n d K e ith B riffa In tro d u ctio n W eather Types

153 154

T h e L am b C lassification R elationships w ith T em perature, P re c ip itatio n and O th e r W eather Variables

155 157

T h e A nnual Cycle in th e C irculation over th e B ritish Isles

165

T h e Past Record of C irculation C hanges

168

Tow ards M ore D erailed C lassification

169

C H A P T E R 9: T H E C H A N G IN G T E M P E R A T U R E O F C E N T R A L E N G L A N D ’

173

P h il J o n e s a n d M ik e H u lm e In tro d u ctio n

173

H istorical V ariability of T em perature

174

R elationships B etw een C E T and A tm ospheric C irculation

183

R elationships Betw een C E T and N o rth ern H em isphere T em peratures

184

D aily T em perature V ariability

189

C onclusions

195

C H A P T E R 10: P R E C IP IT A T IO N V A RIA BILITY A N D D R O U G H T

197

P h il J o n e s , D e c la n C o n w a y a n d K e ith B riffa In tro d u ctio n

197

T h e G eographical V ariability o f P recip itatio n

198

T h e H istorical V ariability of P recipitation

199

D aily P re c ip itatio n V ariability

203

Snowfall

211

D ro u g h ts C onclusions

214 218

C H A P T E R 11: W IN D : R E SO U R C E A N D H A Z A R D

220

J e a n P a lu tik o f , T o m H o lt a n d A n d r e w S k e lle rn In tro d u ctio n

220

W in d C lim atology o f the B ritish Isles

220

W in d as a Resource: T h e Analysis o f Average W in d Speeds W in d as a H azard: Storm s and H ig h W in d Speeds

223 232

C onclusions

240

C H A P T E R 12: T H E A IR T H A T W E B R EA TH E: SM O G S, SM O K E A N D H E A L T H

243

P e te r B r im b le c o m b e a n d G r a h a m B e n th a m In tro d u ctio n

243

Early H isto ry o f A ir P ollution

243

T he T w entieth C e n tu ry

245

T h e P o llu ta n ts Indoor A ir P ollu tio n

246 253

H e alth Issues

257

T he F u tu re

259

X

CONTENTS C H A PT E R 13: 'P IIE W ! W H A T A SC O RCH ER': W EATHHR RECORDS A N D EXTREM ES M ichael D u k e s and P h ilip Eden Introduction

262 262

Pitfalls in the Study o f Extrem es Sum m er H eat Waves and W in ter W arm th Freezing W inters and Cool Sum m ers

262 265 268

D eluge and D rought Snowfalls, Blizzards and Ice-storm s

272 279

Severe Gales and Record G usts Smogs, Fogs and Record Sunshine Conclusions

285 288 293

PART

297

4:

FORECASTING THE FUTURE

C H A P T E R 14: FO R EC A ST IN G T H E B R IT ISH ISLESW EA TH E R Clive P ierce, M ichael D u k e s and G raham Parker Introduction

299

A H istorical Perspective W eather Forecasting Today N um erical W eather Prediction Models Practical W eather Forecasting: The H um an-M achine Mix

300 307 315 318

W eather Service Provision W eather Forecasting: T he Future

319 322

C H A PT E R 15: GLOBAL W A R M IN G A N D T H E BRITISH ISLES Sarah Raper, D avid Viner, M ike H ulm e and Elaine Barrow Introduction

326

T he Greenhouse Effect G lobal and Regional C lim ate Change C lim ate C hange in the British Isles H ow C lim ate C hange M ight Affect the Brirish Isles

326 330 335 335

Conclusions

338

C H A PT E R 16: CLIMATE B E Y O N D T H E T W E N T Y -FIR ST C E N T U R Y Clare G ood ess and Jean P a lu tik o f Introduction

340

Predicting C lim ate T housands o f Years into the Future T he Past as a G uide to the Future M odelling the N ext G lacial-lnterglacial Cycle A nthropogenic Effects: W hy the Future W on’t be Likethe Past C ontradictions and U ncertainties C lim ate Research: T he N ext Twenty-five Years

341 341 343 347 353 355

299

326

340

CONTENTS A P P E N D IC E S A C lim a te M aps o f th e B ritish Isles

359 360

B T h e Lam b C atalogue, 1 9 7 2 -9 5

365

C T h e D aily C entral E ngland T em perature, 1961—95

390

D L istings o f C lim ate D atasets

403

Glossary

418

Name index

427

Index o f place names

430

General index

434

PLATES

(Betw een pp. 4 8 - 9 and 336—7) 1 2

Seasonal average m ean tem p eratu re, °C,1961 to 1990 period Seasonal average m axim um tem p e ra tu re, °C, 1 9 6 1 -9 0

3 4

Seasonal average m in im u m tem p eratu re, °C, 1 9 6 1 -9 0 Seasonal average p recip itatio n , 1 9 6 1 -9 0

5 6 7 8

Seasonal average sunshine rate, 1 9 6 1 -9 0 Seasonal average relative hum id ity , 1 9 6 1 -9 0 Seasonal average w ind speed, 1 9 6 1 -9 0 E stim ated nitro g en dioxide and carbon m onoxide concentrations in G reat B ritain in 1991 (top), and a N im ro d radar netw ork im age for 1200 G M T on 10 May 1996 (b o tto m )

9

Mean surface a ir tem p eratu re change by the period 2035 to 206 4 for th e boreal w inter and su m m er seasons

10

M ean p re cip ita tio n change by th e period 2035 to 2064 for th e boreal w in ter and sum m er seasons

11

M ean observed surface air tem p eratu re for w in ter and su m m er seasons for the periods 1961 to 1990 and 2035 to 2064

12

M ean observed seasonal precip itatio n for the w in ter and su m m er seasons in th e period 1961 to 1990, and the percentage change for the period 2035 to 2064

FIGURES

T he global record o f annual near-surface tem p eratu re from 1856 to 1995 expressed as anom alies, in degrees C elsius, from the 1961 to 1990 average A representation of w hat happens to the incom ing solar radiation

mi 12

L atitu d in al averages o f solar rad iatio n , longw ave (terrestrial) radiation, net planetary rad iatio n , net radiation a t the E a rth ’s surface, and net radiation to th e atm osphere

13

Two exam ples o f infra-red satellite im ages o f th e B ritish Isles show ing th e contrast betw een w in ter (27 February 1986), and sum m er (16 May 1980)

14

Average annual tem p eratu re range at the E a rth ’s surface A latitu d in a l cross-section o f the general circulation .of th e atm osphere T he average latitu d in a l d istrib u tio n o f precip itatio n and evaporation Average h e ig h t o f th e 500 hP a surface in Jan u ary and Ju ly

16 17 18

Schem atic representation o f the developm ent o f a cyclone wave

19 21

Four idealised planetary waves

22

Convergence a t u p p e r levels in the cquatorw ard-m oving lim b o f a planetary wave com pensated by divergence closer to the E arth ’s surface Average m ean sea-level pressure (hPa) for th e N o rth ern H em isphere, 1 9 6 1 -9 0 A nnual sea-surface tem p eratu re anom alies in the N o rth A tlantic O cean Infra-red im age o f a polar low near th e Faroes, 25 N ovem ber 1978 Location o f the stations m entioned in C h ap ter 3 C o n rad ’s c o n tin e n ta lity index

23 25 28 30 34

H eavy rim e deposits around Lincoln C athedral at 1130 (G M T ) on 24 D ecem ber 1992

36 38 40

W e s t-e a s t‘ transect o f average w in ter and su m m er precip itatio n totals

42

W e st-e a st transect o f average w in ter and su m m er m axim um and m in im u m tem perature

A n early m orn in g visible satellite im age of the N o rth Sea show ing extensive snow cover over eastern E ngland and Scotland on 17 February 1978 Average n u m b er o f ‘snow days’ in w inter, 1961 to 1990

45 46

Snow ly in g on the so u th face o f C ader Idris, Snow donia N ational Park

47

Average n u m b er o f

days in each discom fort class in July, 1 9 6 1 -9 0

N u m b e r of days N u m b e r o f days

different discom fort different discom fort

49 50

in in

classes, 1 9 6 1 -8 7 O xford classes, 1 9 6 1 -8 7 Lowestoft

N u m b e r o f days in different discom fort classes, 1 9 6 1 -8 7 Stornow ay Average 1 9 6 1 -9 0 clim ate o f D urham , and its clim atic classification according to five different schem es

51 52 55

X IV

LIST O F F IG U R E S

3 .1 1 b

Average 1 9 6 1 -9 0 clim atc o f P ly m o u th and its clim atic classification according to five

3.11c

different schem es Average 1 9 6 1 -9 0 clim atc o f Santon D ow nham and its clim atic classification according

3.1 Id

Average 1 9 6 1 -9 0 clim ate o f Stornow ay and its clim atic classification according to five

3.1 le

Average 1 9 6 1 -9 0 clim atc o f G atw ick and its clim atic classification according to five

3.1 I f

Average 1 9 6 1 -9 0 clim atc o f K ilkenny and its clim atic classification according to five

4.1

G lobal track o f the B ritish Isles terrain d u rin g the last 6 0 0 m illio n years

68

4 .2

G lobal sea-level and land areas d u rin g th e last 250 m illio n years

69

4 .3

E xam ples o f C oralline Crag m ollusc shells

70

4 .4

G lobal sea-level and icc volum e changes over th e last 2.6 m illio n years

71

4.5

T h e Last In terg lac ial-G lac ial cycle as revealed from deep-sea and land-pollen records

74

to five different schemes d ifferent schem es d ifferent schem es different schem es

4 .6

Hippopotamus amphibius and its d istrib u tio n in the B ritish Isles d u rin g the Last Interglacial

4.7

C hanges in East A nglian flora d u rin g the last (Ipsw ichian) Interglacial

4 .8

Last G lacial (M iddle and Late D evcnsian) Ju ly tem p eratu re record inferred from fossil

4 .9

M odelled B ritish Isles ice-sheet a t th e Last G lacial M axim um

4 .1 0

Periglacial (perm afrost) features beyond th e lim its o f th e B ritish Isles ice-sheet at the Last

5.1

T em perature changes in th e B ritish Isles d u rin g the Late-G lacial and H olocene periods

5.2

E stim a te d annual cycle o f m o n th ly m ean tem peratures in the B ritish Isles, reconstructed

beetle rem ains

G lacial M axim um estim ated on th e basis o f beetle rem ains

56

57 58 59 60

75 76 77 78 81 90

on th e basis o f beetle assem blages identified at selected periods d u rin g th e transition from glacial to H olocene conditions

91

5.3a

C w m Idw al, Snow donia

95

5 .3 b

C w m d ’ur A rddu, Snow donia

96

5.4

'The lim its o f the ice-sheet th a t covered m uch o f th e B ritish Isles d u rin g the last

5.5

T h e ‘tra d itio n a l’ view o f ch an g in g clim ate and vegetation in no rth ern E urope and the

5.6

A schem atic sum m ary o f the palynological evidence for Iloloccnc clim atc changes in

5.7

Selected evidence in d ic a tin g ch an g in g clim ate conditions d u rin g th e H olocene in the

5.8

T ree-ring-derived Eennoscandian Ju ly /A u g u st m ean tem p eratu re estim ates

6.1

T h e N o rth A tlan tic and su rro u n d in g countries in m edieval tim es

113

6.2

An Icelandic m anuscript: th e FlaUyjarb6k

116

6.3 6.4

D ecadal indices o f su m m er w etness and w inter severity from a d 1220 to 1429 D ecadal annual tem p e ra tu re indices for Iceland and for E ngland for th e period a d 1200

121

7.1

to 1439 Tycho Brahe (1 5 4 6 —1601), in his observatory

129 138

7 .2

A page o f W illiam M erle’s w eather journal (1 3 3 7 —44)

138

(D evensian) ice age B ritish Isles d u rin g th e Late G lacial and Ilolocene Periods E n g lan d , Scotland, W ales and Ireland B ritish Isles, no rth -w est Europe and northern N o rth A m erica

97 99 102 104 106

LIST O F F IG U R E S

7 .3

A n ex am p le from th e Royal S ociety schem e for m ak in g w eath er observ atio n s, as sug g ested

7 .4

A n e x tra c t from a m eteo ro lo g ical re g iste r o f th e Société R oyale de M édecine, O c to b e r

7 .5

A n e x tra c t from th e Ephemertdes o f th e Societas M eteorologica P alatin a, J a n u a ry 1 7 8 6

7 .6

T w o pages from th e w e ath e r jo u rn al o f T h o m a s B arker, J u n e and J u ly 1783

143

7 .7

T h e D u rh a m U n iv e rsity O b serv ato ry

144

7 .8

R ear-A d m iral R o b e rt F itzR o y ( 1 8 0 5 - 6 5 )

144

7 .9

A n exam ple o f th e sy n o p tic c h a rts p u b lish ed by F itzR oy follo w in g th e ‘Royal C h a rte r S to rm ’ o f 2 5 - 2 6 O c to b e r 1 8 5 9

145

7 .1 0

T h e system o f ‘c au tio n ary sig n a ls’ in tro d u c e d by F itzR o y

146

by R o b e rt H o o k e in th e 1660s 1781

140 141 142

7.11

A n e x tra c t from a d e ta ile d ty p e o f m eteorological re g iste r k e p t in th e 1 8 6 0 s

148

7 .1 2

A n ex am p le o f an A u to m a tic W ea th e r S ta tio n

150

7 .1 3

A n e x p e rim e n ta l sk e tch o f clo u d form atio n s by J o h n C o n sta b le , 1823

151

8.1

BBC w e ath e r p re sen te r in fro n t o f a w e ath e r forecast c h a rt

154

8 .2

V isual sa te llite im age o f th e B ritish Isles on 28 F ebruary 1977 a t 0 9 2 4 G M T

156

8 .3

T ypical sy n o p tic p a tte rn s associated w ith six o f th e m o st im p o rta n t L am b w eath er types

158

8.4

Visible satellite image of the British Isles on 17 September 1978 at 0935 GM T

161

8.5

T h e frozen R iv er C am a t C a m b rid g e d u rin g th e w in te r o f 1962—3

161

8 .6

T h e c o n trib u tio n o f L am b types to p re c ip ita tio n ar S o u th a m p to n , 1921—50

163

8 .7

M ean d aily p re c ip ita tio n associated w ith an tic y clo n ic , cyclonic and w esterly types

164

8 .8

B ack trajec to rie s associated w ith d iffere n t c irc u la tio n types

165

8 .9

D aily average frequency for w esterly, a n tic y clo n ic and cyclonic L am b types, 1 8 6 1 -1 9 9 0

167

8 .1 0

D aily average C en tral E n g lan d T em p era tu re ( 1 8 6 1 - 1 9 9 0 ) an d E n g lan d and W ales

8.11

A n n u al averages for th e W ind ex , th e C index, an d th e S index d erived from th e L am b C a ta lo g u e

170

9.1

Professor G o rd o n M anley, M A , D .Sc. ( 1 9 0 2 - 8 0 )

174

9 .2

T h e R adcliffe O b serv a to ry a t O xford

175

9-3

Seasonal an d an n u al te m p e ra tu re s for ‘C e n tra l E n g la n d ', 1 6 5 9 to 1995

176

9 .4

A frost fair on th e R iver T h am es a t London d u rin g th e w in te r o f 1 6 8 3 -4

177

9.5

C o rre la tio n betw een in d iv id u a l sites over th e B ritish Isles an d th e C e n tra l E ngland

9.6 a

A n n u a l tim e -se rie s for C e n tra l E n g lan d T em p era tu re and for th e th re e p e rip h e ral sta tio n s

9 .6 b

W in te r tim e -se rie s for C e n tra l E n g la n d T em p era tu re and for th e th ree perip h eral sta tio n s

9.6 c

S u m m e r tim e -se rie s for C e n tra l E n g la n d T e m p e ra tu re an d for th e th ree perip h eral sta tio n s

9 .7 a

A nnual tim e -se rie s for C en tral E n g lan d T em p e ra tu re , th e N o rth e rn H e m isp h ere

P re c ip ita tio n ( 1 9 3 1 - 8 0 )

T e m p e ra tu re record o f V alentía, Stornow ay an d ‘L erw ick’ o f V alen tía, Stornow ay an d ‘L erw ick’ o f V a len tía, S tornow ay an d ‘L erw ick’

168

179 180 181 182

te m p e ra tu re anom aly u sin g land sta tio n s, th e N o rth A tla n tic O sc illa tio n index and th e n u m b e r o f w esterly days over th e B ritish Isles a cc o rd in g to th e L am b C atalo g u e 9 .7 b

185

W in te r tim e -se rie s for C e n tra l E n g la n d T em p era tu re, th e N o rth e rn H e m isp h e re te m p e ra tu re anom aly u sin g land sta tio n s, th e N o rth A tla n tic O scilla tio n index and th e n u m b e r o f w esterly days over th e B ritish Isles a cc o rd in g to th e L am b C atalo g u e

186

xv

xvi

LIST OF F IG U R E S

9.7c

S um m er tim e-series for C entral E ngland T em perature, the N o rth e rn H em isphere tem p e ra tu re anom aly using land stations, the N o rth A tlan tic O scillation index and the n u m b er o f w esterly days over th e B ritish Isles according to th e Lam b C atalogue

187

9.8

D ecadal values of ‘sum m er-average’ tem p eratu re anom alies for th e N o rth e rn H em isphere land area

188

9.9

D aily C entral E ngland T em peratures for nine selected years - 1816, 1868, 1879, 1921,

9 .1 0

1949, 1 9 6 3 , 1989, 1990 and 1995 T h e R iver T ham es frozen at M arlow in Jan u ary 1987

9.11

N u m b e r of days w ith m ean tem p eratu re below 0°C each w in ter and w ith m ean tem perature

190 193

equal to or in excess o f 20°C each sum m er

194

10.1

W oodcut illu stratio n from 1607 show ing the great floods w hich afflicted N o rth Devon and M o n m o u th sh ire in Ja n u a ry o f th a t year

198

10.2

G eorge Jam es Sym ons, PRS ( 1 8 3 8 -1 9 0 0 )

199

10.3

S tandard deviation o f seasonal and annual precip itatio n totals based on th e 1961 to 1990 period

200

10.4

R egions o f coherent precip itatio n variability for B ritain and Ireland

201

10.5 10.6

Seasonal tim e-series o f p re cip ita tio n totals for E ngland and W ales, 1 7 6 7 -1 9 9 5

204

Seasonal tim e-series o f p re cip ita tio n totals for the Scotland series, 1 7 5 7 -1 9 9 5

205

10.7

Seasonal tim e-series o f p re cip ita tio n totals for th e All Ireland series, 1 8 4 1 -1 9 9 5

10.8

A nnual p re cip ita tio n series for E ngland and W ales, Scotland and All Ireland

206 207

10.9

A nnual precip itatio n series for the nine regional series o f B ritain and N o rth e rn Ireland, 1 9 3 1 -9 5

208

10.10

C orrelations on an annual basis betw een each o f th e regional precip itatio n tim e-series

209

10.11

A nnual counts oí w et days for each of the nine regions o f B ritain and N o rth e rn Ireland,

10.12

M ean annual frequency o f w et and dry spells o f different len g th s for six sam ple regions

1931 to 1983 or 1988

10.13 10.14

of B ritain and N o rth e rn Ireland, 1931—95 Snowy w in ter classification for 1 8 7 5 -6 to 1994—5 A frost fair on th e R iver T ham es d u rin g February 1814

210 212 213 214

10.15

Six m ajor d ro u g h ts in th e B ritish Isles o f e ig h t to ten m o n th s’ d u ration: 1887, 1921, 1929, 1959, 1984 and 1995 Five m ajor d ro u g h ts in th e B ritish Isles o f fifteen to eighteen m o n th s’ duration:

215

10.16 10.17

1 8 5 4 -5 , 1 8 6 9 -7 0 , 1933—4, 1 9 7 5 -6 and 1 9 8 9 -9 0 A reservoir near C hurch S tre tto n , Shropshire, at th e end o f the 1976 su m m er d ro u g h t

216 217

11.1

Tree dam age to a house and car a t A ddlestone, Surrey, follow ing th e O cto b er 1987 storm

221

11.2

P ercentage of w ind observations by directio n , and m ean w ind speed by direction for H ig h Bradfield in th e Pennines

221

11.3 11.4

M ean annual w ind speed over th e B ritish Isles at 50 m above th e g round

222

O ne o f th e w ind tu rb in es a t L lidiart y W aun, Powys

222

R epresentation o f th e m ovem ent o f air over shallow and steep topography

224

C orrelations betw een m o n th ly m ean w ind speeds at neig h b o u rin g U K M et. Office an em om eter sites

226

11.7

‘T h e B eaufort Scale, revised 1906'

227

11.8

Mean M arch w ind speeds at seven stations in the U nited K ingdom w ith long in stru m e n tal records

228

11.5 11.6

LIST O F F IG U R E S

1 1 .9 1 1 .1 0

L ocations of sites in th e IJK w ith lo n g -te rm w in d d a ta

229

R e co n stru c te d ann u al m ean w ind speeds for H ig h B radfield in th e P en n in es

11.11

C o m p ariso n o f observed and re co n stru c te d an n u al m ean w in d speeds for E sk d a le m u ir

231 232

11.12

W o o d cu t illu s tra tin g th e sto rm s w h ic h ravaged E n g la n d in th e a u tu m n an d w in te r o f

11.13

G ale Index for th e n o rth e rn B ritish Isles

23 3 23 4

1 1 .1 4

A verage n u m b e r o f severe sto rm s in each m o n th betw een 1920 a n d 1990

236

11.15

T im e -serie s of in d iv id u a l sto rm scores

237

12.1

Fog in L ondon, 2 .3 0 p .m . on 3 0 N o v e m b er 1982

244

12.2

A ir p o llu tio n in L ondon since 1700

245

12.3 12.4

L ocation o f sites in th e A u to m atic U rb a n N e tw o rk w hich m o n ito r con tem p o rary air p o llu ta n ts

247

1 9 6 2 -9 3

249

12.5a

R elative im p o rta n c e o f P M .( sources in th e 1990s for th e U n ite d K in g d o m

250

1 2 .5 b

E stim a te d U n ite d K in g d o m road tra n s p o rt em issions o f P M (0

250

12.6

T ren d s in n itric oxide and n itro g e n d io x id e a t L ondon V ictoria, 1 9 7 6 -9 0

251

12.7

T ren d s in carbon m on o x id e em issio n s for G re a t B rita in , 1 9 7 0 -9 3

252

12.8

S u m m e r haze over L ondon, 1 9 8 1 , d u e to p h o to ch e m ic al p o llu tio n

254

12.9a

N u m b e r o f h ours w ith low -level ozone c o n ce n tra tio n s above 8 0 p p b , 1 9 8 7 -9 0

255

1 2 .9 b

M o n th ly average low -level ozone c o n ce n tra tio n tre n d s a t th ree ru ral sites, 1 9 8 6 91

255

1 6 1 2 -1 3

A n n u a l average c o n ce n tra tio n s o f sm oke an d s u lp h u r dio x id e for th e U n ite d K in g d o m

1 2 .10a T h e re la tiv e im p o rta n ce for th e U n ite d K in g d o m of v o latile org an ic c o m p o u n d s sources in th e 199 0 s

256

1 2 .1 0 b M easured an d e stim a te d U n ite d K in g d o m road tra n s p o rt sources o f vo latile organic c o m p o u n d s, 1 9 7 0 -2 0 1 0 1 2 .1 1

256

E m issions o f lead from a u to m o tiv e sources, 1 9 7 5 -9 3 , for th e U n ite d K in g d o m and m ean lead c o n ce n tra tio n s, 1 9 8 0 - 9 3 , m easured in c en tral London

256

12.12

H eavy traffic on the M 25 m otorw ay aro u n d L ondon

258

12.13

A d ju ste d relativ e m o rta lity rates and average P M , 5 c o n ce n tra tio n s in six c ities in the

13.1

H e a d lin e from the D a ily M irror new spaper, 4 A u g u st 1990

259 264

13.2

S y n o p tic situ a tio n a t 1200 G M T on 10 J a n u a ry 1971

266

13.3 13.4

S y n o p tic o b serv atio n s an d pressure p a tte rn a t 1200 G M T on 10 Ja n u a ry 1971

267

Frozen sea a t Pcgw ell Bay, near R am sg ate, K e n t, on th e m o rn in g o f 17 F eb ru ary 1986

271

13.5

L ord B y ro n ’s p oem ‘D a rk n ess’ w ritte n a t G eneva, 1816

2 73

13.6

S y n o p tic o b serv atio n s an d pressure p a tte rn over so u th e rn B ritain a t 1 5 0 0 G M T on 15 A u g u s t 1952 - th e L y n m o u th flood

274

13.7

T h e d is trib u tio n o f rainfall over E xm oor, 1 4 -1 5 A u g u st 1952 - th e L y n m o u th flood

275

13.8

D am ag e in th e c en tre o f L y n m o u th follo w in g th e flood o f 15 A u g u st 1952

27 6

13.9

C hew valley reservoir, G lo u c este rsh ire, in A u g u st 1 9 7 6 , follo w in g th e d riest e ig h te en

1 3 .1 0

S ynoptic situ a tio n a t 1 2 0 0 G M T on 2 6 D e ce m b er 1962

13.11 13.12

S ynoptic observ atio n s an d p ressu re p a tte rn at 1 2 0 0 G M T on 26 D e ce m b er 1962

13.13

S y n o p tic o b serv atio n s an d pressure p a tte rn over th e B ritish Isles a t 0 6 0 0 G M T on

U n ite d States

m o n th s on record in E n g la n d , a n d a year later in S e p tem b e r 1977

S y n o p tic s itu a tio n a t ()()()() G M T on 30 D ecem ber 1962 30 D e ce m b er 1962

279 281 2 83 2 84 285

X V III

LIST OF F IG U R E S

13.14 13.15 13.16 13.17

D riftin g snow a t A nnfield P lain, C ounty D u rh am , February 1963 N o rth Fleet, K e n t, after th e ‘B u rn s’ D ay’ storm o f 25 January 1990

286 287

Synoptic situ a tio n at 1200 G M T on 15 O ctober 1987 - the clay before the ‘G reat S to rm ’

287

13.18

A new spaper engraving o f a w aterspout seen off W o rth in g on Sunday 21 A ugust 1864

13.19 14.1

T h e Tower o f W in d s (A thens)

14.2

Ja m es G laisher, FRS (1 8 0 9 -1 9 0 5 )

304

14.3 14.4

A n infra-red im age from N O A A 11, taken at 0 3 4 0 G M T on 24 January 1990

308

Schem atic illu stra tio n o f m odern-day preparation of w eather forecasts P lo tte d surface w eather chart for 0 8 0 0 G M T, 4 O cto b er 1995

311

Errors in the U K M et. O ffice’s global forecasting m odel, 1 9 7 0 -9 4 G eneral illu stratio n o f th e greenhouse effect

323 327

Synoptic observations and pressure p a tte rn over so u th ern B rita in a t 0 4 0 0 G M T on 16 O cto b er 1987 - the ‘G re at S to rm ’

14.5 14.6 15.1 15.2

A C am pbell-S tokes sunshine recorder

313

328

Projections o f global-average radiative forcing from 1990 to 210 0 due to greenhouse gas em issions and su lp h ate aerosols

15.4

Schem atic representation o f th e clim ate system as m odelled by a global clim ate model

15.5

G lobal w arm ing projections from 1990 to 210 0 using a sim ple clim ate m odel, assum ing

15.6

G lobal w arm in g projections irom 1990 to 2 1 0 0 using a sim ple clim ate m odel and the

15.7

G lobal sea-level rise projections from 1990 to 2 1 0 0 using a sim ple clim ate m odel

th e IS92a em issions scenario IPC C em issions scenario a ssum ing th e IS92a em issions scenario 15.8

293 300

Schem atic representation o f th e steps involved in e stim atin g fu tu re global tem perature and sea-level change

15.3

291 292

329 330 332 332 333

G lobal-average tem p e ra tu re change from 1860 to 2 1 0 0 from the IIA D C M 2 SUL e x p erim en t and from 1860 to 1995 from the observations

334

Flooded m eadow s, Shalford, near G u ild fo rd , Surrey M ajor m echanism s o f clim ate change

337 342

16.2

G lobal ice volum e for the last 12 2 ,0 0 0 years

344

16.3 16.4

F uture co n tin e n ta l ice volum e, in clu d in g the G reenland ice sheet

345

15.9 16.1

C lim ate index show ing th e succession o f m ajor clim ate states likely to be experienced in th e B ritish Isles over th e next 125,000 years. E nhanced greenhouse effect not included

346

16.5

A tm ospheric carbon dioxide concentrations u nder various lo n g -term scenarios for fossil

16.6

Forcing scenarios and o u tp u t from three 500-year sim ulations w ith th e coupled a tm osphere-ocean G FD L G C M

350

16.7

G lobal-average tem p e ra tu re change over th e next 10,000 years

16.8

C om parison o f future greenhouse projections against th e geologic record

351 352

16.9 16.10

F u tu re c ontinental ice volum e, w ith o u t th e G reenland ice sheet

353

C lim ate index show ing th e succession o f m ajor clim ate states likely to be experienced in th e B ritish Isles over the next 125,000 years. E nhanced greenhouse effect included

354

16.11

N o rth e rn H em isphere ice volum e, 0 to 150,000 years AP

355

fuel com bustion and forest clearance

3 49

TABLES

Average 1 9 6 0 -9 0 m onthly mean tem perature Com parison o f coastal and inland m ean m onthly m axim um tem peratures Average 1 9 6 1 -9 0 seasonal num ber o f ground frostdays T he contribution of average m onthly precipitation to the average annual total, 1961-90 Average 1 9 6 1 -9 0 m onthly num ber of days o f thunder Average 1 9 6 1 -9 0 num ber of 'raindays' per season and average precipitation intensity on raindays Average 1 9 6 1 -9 0 m onthly relative hum idity Average 1 9 6 1 -9 0 m onthly wind speed Average 1 9 6 1 -9 0 annual num ber of days w ith m ean tem perature below 0 “C and -10"C for actual and w ind-chill equivalent tem perature Key features of the geological tim e-scale relating to clim atic change Selected events in the Last Interglacial-G lacial cycle, related to the global 8 lliO stages T he m ajor sources o f palaeoenvironm ental and palacoclim atic data for the Late Glacial and Holocene periods Total num bers of seasons w ith docum entary data for E ngland, a d 12 0 0 -1 4 2 9 N um bers ol unreported seasons by decade for England, AD 120 0 -1 4 2 9 T em perature and precipitation scores for England for each m onth, a d 1 2 00-1439 Average annual and seasonal frequencies of Lamb w eather types, 186 1 -1 9 9 0 Lamb Classification for w inter 19 6 2 -3 and sprin g -su m m cr 1976 and 1995 Correlations betw een seasonal indices and CET and EWP, 186 1 -1 9 9 0 T em perature change explained by a straight-line trend fitted to the CET record for three different periods M onthly and annual tem perature extrem es since 1721 in the CET record C orrelations betw een annual CET and Valentia, Stornoway and Lerwick Seasonal correlations betw een the CET and totals of the seven basic Lamb w eather types (1 8 6 1 -1 9 9 5 ) and the N o rth A tlantic O scillation (1 8 6 5 -1 9 9 5 ) N otably very' hot and very cold days in the daily CET record P recipitation regions of the B ritish Isles analysed in C hapter 10 Average inter-series correlations and the variances explained by the regional seven-gauge netw orks for daily and m onthly precipitation totals G eographical d istribution ol U K Met. Office anem om eters W ind speed predictions at G reat Dun Hell in the northern Pen nines

37 37 41 44 44 45 48 53 54

66 79 85 118 118 124 160 162 163 174 178 183 184 189 201 203 223 224

XX

LIST O F TABLES

11.3

F req u en cy d is trib u tio n o f w in d speeds over n o rth e rn E n g la n d

11.4

E xcccdence frequencies for w in d speeds o v er n o rth e rn E n g la n d

235 235

1 1.5

S to rm C a ta lo g u e, 1 9 2 0 - 9 0

238

1 1 .6

R a n k in g o f sto rm s in th e S to rm C a ta lo g u e, 1 9 2 0 -9 0

239

12.1

Sites in th e A u to m a tic U rb a n N e tw o rk w h ic h m o n ito r c o n tem p o rary a ir p o llu ta n ts

248

13.1

T h e five w a rm est, o r equal w a rm est, years an d seasons in th e C E T series

266

1 3 .2

D ays w ith a m a x im u m te m p e ra tu re o f 35°C o r over since 1900

268

13.3

Som e o f th e h o tte s t days in th e R e p u b lic o f Irelan d

268

13.4

H ig h e s t d a ily m a x im u m te m p e ra tu re since 1900 for each m o n th

269

13.5

C o ld est n ig h ts since 1 9 0 0

270

1 3 .6

L ow est d a ily m in im u m te m p e ra tu re for each m o n th since 1 9 0 0

272

13.7

Five c o ld e st, or equal co ld est, years a n d seasons in th e C E T series

272

1 3 .8

N o ta b le tw e n ty -fo u r h o u r p re c ip ita tio n to ta ls

276

13.9

N o ta b le s h o rt-d u ra tio n p re c ip ita tio n to ta ls

277

1 3 .1 0

Five w e tte st an d d rie st years and seasons in th e E W P record

278

1 3.11

L ong rainless p erio d s

280

1 3 .1 2

A selectio n o f d isru p tiv e sn o w sto rm s an d b lizzards

282

1 3 .1 3

A selection o f o ut-of-season snow falls

282

1 3 .1 4

A selectio n o f n o ta b le w in d sto rm s

288

1 3 .1 5

H ig h e s t peak g u st speeds recorded since 1 9 0 0

289

1 3 .1 6

S u n n ie st an d d u lle s t m o n th s a t K ew an d Stornow ay

289

14.1

L an d m ark s in th e e v o lu tio n o f th e science o f w e ath e r forecasting

301

1 4 .2a

C u rre n t o p e ratio n a l m ete o ro lo g ica l sa tellites as o f M ay 1995

309

1 4 .2 b

S u n -sy n ch ro n o u s m ete o ro lo g ica l sa te llite s

309

1 4 .2c

G e o sta tio n a ry m ete o ro lo g ica l sa te llite s

310

14.3

S u m m ary sta tistic s for th e U K M et. O ffice U nified an d M esoscale M odels

317

14.4

T h e ran g e o f com m ercial w e ath e r services p rovided by th e U K M et. O ffice

320

15.1

Som e re ce n t e x tre m e a n n u al an d seasonal te m p e ra tu re an om alies

336

15.2

A verage a n n u a l frequencies o f d a ily te m p e ra tu re ex trem es for six locations

336

CONTRIBUTORS

T im A tk in so n

(B.Sc. G eology, P h.D . H ydrology) is a R eader in the School o f E nvironm ental Sciences and a form er Senior Research Associate in the C lim atic Research U nit. I lis research interests vary w idely in hydrogeology and hydrology, Q uaternary geology and palaeoclim atology. H e has a special interest in th e m ethodology of inferring palaeoclim ate from geological data.

E laine Barrow

(B.Sc. E nvironm ental Sciences, M.Sc. A rm ospheric Sciences) is a Senior Research Associate in the C lim atic Research U n it specialising in the construction o f clim ate change scenarios for ag ricu ltu ral applications and is also involved in th e C lim ate Im pacts L IN K Project.

G raham B entham

(MA G eography) is L ecturer in the School o f E nvironm ental Sciences and specialises in research in to the effects o f environm ental conditions on health.

K eith Briffa

(B.Sc. B iological Sciences, Ph.D . D endroclim atology) is a R eader in th e C lim atic Research U n it specialising in tree-ring-related studies. H e also w orks w ith in stru m e n tal and o th e r proxy clim ate data, m ostly in the context o f late glacial and H olocene clim ates.

P eter B rim blecom be

(B.Sc., M .Sc., P h.D . C hem istry) is a Professor in th e School o f E nvironm ental Sciences. H e is interested in the effects o f air p o llu tio n on m aterial and the history o f atm ospheric com position. l ie also w orks on th e chem istry o f cloud d roplets both in th e troposphere and in the stratosphere.

K eith Clayton

(CBE, M .Sc., P h.D . G eom orphology, H on. D.Sc.) was the founding D ean o f the School of E nvironm ental Sciences betw een 1967 and 1971 and since 1993 has been E m eritus Professor. W hile locally know n for his radical view s on coastal m anagem ent, his d o m in a n t research interest is th e long-term evolution o f the B ritish landform .

Declan C onw ay

(B.Sc., M.Sc. G eography, P h .D . C lim atology) is a Senior Research Associate in the

X X II

LIST O F C O N T R IB U T O R S

C lim atic Research U n it specialising in clim ate change and w ater resources in Africa. H e is cu rren tly w orking on the generation o f daily rainfall tim e-series from w eather types and circulation patterns. Trevor Davies

(B.Sc. Physical G eography, Ph.D . A ir P ollution and A tm ospheric C irculation) has been D irector o f th e C lim atic Research U n it since 1993 and is Professor in the School o f E nvironm ental Sciences. H e has w orked on links betw een atm ospheric circulation and atm ospheric com position and p o llu ta n t deposition. H e is interested in th e n ature o f changing atm ospheric circulations.

M ichael D ukes

(B.Sc. G eography, M.Sc. M eteorology and C lim atology) has w orked as a Research A ssociate in the C lim atic Research U n it b u t he currently runs his ow n w eather consultancy. I lis m ain interests are in extrem e w eather events and clim ate change.

P h ilip Eden

(BA G eography, M.Sc. M eteorology and C lim atology) runs his own com m ercial w eather consultancy, p roviding services for a variety o f m edia outlets, and is the ch ief w eather presenter on BBC Radio 5 Live. H is m ain interest is in th e synoptic m eteorology o f m ajor w eather events.

G raham Farm er

(B.Sc., P h.D . G eography) is cu rrently D irector o f the FA O/SAD C Early W arning System based in H arare, Z im babw e. H e was a Senior Research Associate in the C lim atic Research U n it from 1981 to 1989 w here his research interests were the h istorical clim ate o f E ngland, A frican rainfall change and the global in stru m en tal tem p eratu re record.

B rian Funnell

(BA, P h.D . G eology) is an E m eritus Professor in th e School o f E nvironm ental Sciences, and a V isiting Professor in the C lim atic Research U n it. H is research has involved investigations o f bo th deep-sea and coastal sedim ents, covering a broad sp ectru m o f palaeocnvironm ental processes and changes, from the very long term (th e past 2 5 0 m illion years) to the shorter term (the past 10,000 years).

Clare G oodess

(B.Sc. E nvironm ental Sciences) is a Senior Research Associate in the C lim atic Research U n it specialising in th e study o f lo n g -term clim ate change and the im plications for underground radioactive w aste disposal in the U K . She has also w orked on th e construction o f clim ate change scenarios for the study o f desertifi­ cation processes in the M editerranean region.

Tom H o lt

(B.Sc., P h.D . E nvironm ental Sciences) is a Senior Research Associate in the C lim atic Research U n it w ith a particu lar interest in m id -la titu d e storm s and severe tropical cyclones. H e has also w orked on carbon-cycle m odelling and has produced several reports on clim ate variations for the insurance industry.

LIST OF CONTRIBUTORS

M ike H ulm e

(B.Sc., Ph.D . G eography) is a Senior Research Associate in the Clim atic Research U nit specialising in the construction of observed clim atologies and in the valida­ tion of global clim ate models. H e has also worked extensively on trends in African rainfall and their relationship to desertification.

Phil Jones

(BA Environm ental Sciences, M.Sc., Ph.D. H ydrology) is a Reader in the Clim atic Research U nit. H e is involved in four principal research areas: m onitoring clim ate on a global scale, palaeoclimatology, bringing the instrum ental and palaeoclim atic data together in the context o f the clim ate change detection issue and rivcrflow reconstruction in the UK.

P. M ick Kelly

(B.Sc. Physics w ith Meteorology, Ph.D . E nvironm ental Sciences-Clim atic Change) is a Reader w ith the Clim atic Research U nit and the C entre for Social and Economic Research on the G lobal E nvironm ent. An atm ospheric scientist by training, he has worked extensively on instrum ental data analysis, Arctic clim ate variability and causes of clim ate change, and is currently involved in a num ber of interdisciplinary studies of clim atc and developm ent issues.

Jo h n K ington

(B.Sc. Geography, M.Sc. Meteorology) is a Visiting Fellow in the Clim atic Research U n it w ith special interests in historical clim atology and synoptic m eteorology.

H u b ert Lamb

(MA, D.Sc., H on. D.Sc.) is an E m eritus Professor in the C lim atic Research U nit and was the founding D irector of the Clim atic Research U nit from 1972 to 1978. H is interests lie in the history of clim ate and in its interactions w ith hum an society.

A strid O gilvie

(BA European History, Ph.D . E nvironm ental Sciences) is a Senior Research Associate in the C lim atic Research U nit. However, she is currently based in the USA where she is Associate D irector of the In stitu te o f Arctic and A lpine Research at the U niversity of Colorado in Boulder. H er m ain areas of interest are the use of historical records to reconstruct past clim ate, the im pact o f clim ate on societies and the comparison of different proxy clim ate records.

Tim Osborn

(B.Sc. Geophysical Sciences, Ph.D . Environm ental Sciences) is a Senior Research Associate in the C lim atic Research U nit specialising in the analysis, sim ulation and validation o f natural clim ate variability in num erical models and in observa­ tions.

Jean P alutikof

(B.Sc., Ph.D . Geography) is a Reader in the C lim atic Research U nit specialising in clim ate change im pacts, particularly related to global w arm ing, and the

X X IV

LIST OF C O N T R IB U T O R S

ap p lication o f clim ate data to econom ic and plan n in g issues. For a n u m b er of years she has w orked on the analysis o f w ind data for the renew able energy and insurance industries in the UK. G raham Parker

(B.Sc. M athem atics and Physics) is a retired g overnm ent m eteorologist w ho founded th e N orw ich W eather C entre. H e is an ex-BBC national and regional w eatherm an and radio broadcaster.

Clive Pierce

(B.Sc. E nvironm ental Sciences, M.Sc. A pplied M eteorology and C lim atology) w orked as a Research Associate in th e C lim atic Research U n it and th e School of E nvironm ental Sciences before pursuing a career in w eather forecasting. H e is cu rren tly a research scientist in the M et. Office w orking on th e conceptual m o delling o f convective p recipitation.

Sarah R aper

(B.Sc., P h.D . E nvironm ental Sciences) is a Senior Research Associate in the C lim atic Research U n it specialising in sim ple m odels for sim u la tin g past and fu tu re g lobal-m ean tem perature change and sea-level rise.

A ndrew Skellern

(B.Sc. E nvironm ental Sciences, M.Sc. Inform ation Technology) has w orked as a Research Associate in the C lim atic Research U n it, b u t is currently com p letin g his Ph.D . on m o delling global peatland d istrib u tio n s u tilisin g b o th clim ate and topo g rap h y in th e School o f G eography, U niversity o f Leeds.

D avid Viner

(B.Sc. Physical G eography, Ph.D . C ivil E ngineering) is a Senior Research Associate in th e C lim atic Research U n it specialising in the construction o f datasets for c lim ate change scenario construction. H e runs th e U K D ep artm en t o f the E nvironm ent's C lim ate Im pacts L IN K Project w hich acts as th e interface betw een the H adley C entre and the international clim atc change research com m unity.

Tom W igley

(B.Sc., P h.D . M athem atical Physics) is a form er D irector o f the C lim atic Research U n it and is cu rren tly a Senior S cientist at the N atio n al C enter for A tm ospheric Research, Boulder, Colorado. H is m ain interests are in carbon cycle m odelling, projections o f future clim ate and sea-level change and interp retatio n o f past clim ate change p articularly w ith a view to d e te ctin g anthropogenic influences.

PREFACE

In 1997 the C lim atic Research U n it w ill have existed

aries. T h e B ritish Isles are a coherent clim atic region;

for tw enty-five years. A lth o u g h th e first m em ber of

the U n ited K ingdom is not. If there is a bias in the

staff was appo in ted by the U niversity of East A nglia in O c to b er 1971, it was in Jan u ary 1972 th at

book tow ards the U n ited K ingdom

Professor H .H . Lam b arrived a t the U niversity,

by th e restriction o f certain datasets or studies to

becom ing the founding D irecto r o f th e U n it. T he

purely national or sub-national dom ains.

in som e o f

the d ata and m aps show n, it has been forced on us

original vision was to establish a research centre

T h e rationale and organisation o f th e book draws

devoted to th e stu d y o f past, present and future

upon tw o earlier studies published d u rin g the 1970s:

clim ates, a vision inspired very largely by Professor Lam b. T w enty-five years later his foresight has

Climate;. Present, Past a n d Future w ritten by I lu b ert

proved rem arkably prescient. T he U n it has long been

L am b, and published as tw o volum es in 1972 and 1977, and The Climate o f the British Isles w ritte n by

established as one o f th e w o rld ’s o u tstan d in g centres

Tony C handler and Stan G regory and pub lish ed in

for research in to clim ate change, a research field in

1976. T h e respective historical and geographical

w hich there has been escalating in terest, especially in recent years. As a m ark o f his c o n trib u tio n , not

dim ensions o f these tw o books have been com bined in the present volum e to provide a m ore com pre­

only to th e U n it b u t to th e endeavour o f clim ate

hensive account o f th e changing clim ate o f the

change research w orld-w ide, we dedicate th is book

B ritish Isles than has previously been a tte m p ted . O u r

to Professor Lam b.

understanding of clim ate and its role in hum an

T h e book com m em orates th is tw enty-fifth a n n i­

affairs has changed m arkedly since th e 1970s, as

versary o f the C lim atic Research U n it by providing

have our clim ate observation system s and m odelling

an in tegrated synopsis o f w hat we know a t th e end

capabilities. It is tim ely, therefore, th a t th is book

o f th e tw e n tie th c entury about th e clim ates o f the B ritish Isles. W ritte n by present and recent m em bers

should appear when the prospect o f h um an-induced clim ate change is reg isterin g increasingly in the

o f th e U n it, th e sixteen chapters o f th is book d istil

m inds o f the public. Som e o f the u n d erstan d in g

m uch o f th e w ork and expertise for w hich the

o f our clim ate, and its in te rp reta tio n , w hich

C lim atic Research U n it is fam ous and present it to

offered w ith in these pages w ill doubtless be super­

th e reader th ro u g h the geographical lens o f the

seded as science advances; b u t we believe th a t this

B ritish Isles. T his dom ain is deliberately w ider th an

book, as a w hole, w ill provide a lasting, a u th o rita ­

ju st th e U n ited K ingdom . C lim ate know s no b o u n d ­

tive and accessible view o f the changing clim ate

aries o th er th an those w ro u g h t by m o untains and

resource o f the B ritish Isles as we approach the

oceans and w hile clim ate change has becom e a po litical issue in recent years th e clim ate system itself

m illen n iu m . T h e tex t is w ritte n nor as a research d ocum ent,

continues to function oblivious to po litical b o u n d ­

b u r as one intended for the non-specialist. W here

is

PREFACE necessary, we separate m ore technical details from the (low of the text by placing such m aterial in boxes. Terms th at have specific clim atic or environm ental definitions appear in bold the first tim e they occur in a chapter and are formally explained in the Glossary at the back ol the book. Each chapter is fully referenced through endnotes and provides suggestions for general reading on the subject m atter by listing a sm all selection o f key texts. W e also

four appendices, inform ation that has never before been published in single volume. N o book comes into being lightly or w ithout pain. T his one is no exception. As editors we wish to thank our colleagues in the C lim atic Research U n it, and

provide a series of clim ate m aps, graphs and data listings relating to the clim ate o f the B ritish Isles in

M ike H ulm e and Elaine Barrow Climatic Research Unit, Norwich, June 1996

our ex-colleagues outside it, both those whose names appear alongside one or more of the chapters and those whose names do not, but who nevertheless contributed to the overall effort in many ways.

FOREWORD The Climatic Research Unit at Twenty-five Years

It is te m p tin g to su g g est th a t a research u n it as o rig ­

U niversity o f East A nglia to th e support o f the late

inal, as tim ely and as successful as th e C lim atic Research U n it was designed and im p lem en ted in a

and o f Professors K eith Clayton and Brian Funnell,

co-ordinated way, th a t a fine vision was realised

D eans o f th e School o f E nvironm ental Sciences in

Lord Solly Z uckerm an, an adviser to th e U niversity,

th ro u g h careful p lan n in g and m uch hard w ork. T here

1971 and 1972 and w ith in whose School th e U n it

was o f course a founding vision and there have

was based.

u n d o u b ted ly been m any years o f hard w ork; good

T h e C lim atic Research U n it set itself four aim s,

research does not ju st happen and funds for research,

laid o u t in its first annual report. It is w orth repro­

how ever innovative, are never easy to com e by. B ut

d u cing those aim s here since, tw enty-five years on,

chance, serendipity, and sim ple good luck have also

they still effectively describe th e accom plishm ents

played

the

and m ission o f the C lim atic Research U n it as we reach the end o f th e tw e n tie th century. Indeed, these

to

aim s are even m ore p e rtin e n t today than they were in 1972:

a role alongside

th e

m ore prem editated

events, th e strong a p p o in tm en ts m ade, and successful bids for funding. H u b e rt

L am b

had

for years

been

try in g

convince th e m eteorological e stab lish m en t th a t the clim ate system in its natural state is h ighly variable on tim e-scales o f decades to centuries and longer. T h e fou n d in g o f th e C lim a tic Research U n it in 1 9 7 1 -2 gave him th e chance to concentrate on th is b a ttle, one th a t he and th e clim atological c o m m u ­ n ity ev entually won so convincingly th a t ideas of clim ate constancy have faded alm ost com pletely from scientific m em ory. T h e creation o f th e U n it was due to in itial g ra n ts from Shell International and the N uffield F o undation, follow ed in th e early years by th e beneficence o f th e Rockefeller F oundation and repeatedly from the W olfson F oundation w hich, in 1986, gave th e U n it its cu rre n t b u ild in g . T h e initial e stab lish m en t o f th e U n it also owes m uch to the advocacy o f the late Sir G raham S utton (D irectorG eneral o f the U K M et. Office from 1953 to 1965 and su b seq u en tly o f the N a tu ral E nvironm ent Research C ouncil) and its location in N o rw ich a t the

• To establish firm er know ledge of th e history of clim atc in the recent and d ista n t past. • To m o n ito r and report on c u rre n t clim atic devel­ opm ents on a global scale. • To identify the processes (natural and m an-m ade/ anthropogenic) a t w ork in clim atic fluctuations and the characteristic tim e-scalcs o f th eir evolu­ tion. • To investigate the possibilities o f m aking advisory sta te m en ts about future trends o f w eather and clim ate from a season to m any years ahead, based on acceptable scientific m ethods and in a form likely

to

be

useful

for

lo n g -term

plan n in g

purposes.1 T h a t these aim s rem ain valid is testim ony not only to an early appreciation by the founder o f th e U n it o f why clim ate research is such an im p o rtan t scien­ tific endeavour, b u t also to the successes o f th e 200

xxviii

FOREW ORD

Figure 0.1 The global record of annual near-surface temperature from 1856 to 1995 expressed as anomalies, in degrees Celsius, from the 1961 to 1990 average. The bold curve is the result of applying a filter to the yearly values which emphasises variations on time-scales longer than thirty years. The land component of this record is compiled by the Climatic Research Unit and the marine component by the Hadley Centre. The merged record, as shown here, is the one used by the Intergovernmental Panel on Climate Change in all their publications.

or so individuals w ho have been m em bers of th e U n it

clim ate observations from around th e w orld. T he

over

have

dem and cam e in itially from those involved in clim ate

researched these objectives and com m unicated th eir

reconstruction, such as Hal F ritts o f the Tree R in g

the

past

tw enty-five

years and

w ho

results to th e o utside w orld. All o f these scientists

Laboratory at th e U niversity o f Arizona in Tucson,

have m ade c o n trib u tio n s to th e in tellectual assets

and then to su p p o rt efforts to detect th e p o tential

m ain tain ed by th e U n it and should be proud o f th eir

effects on clim ate of greenhouse gas em issions. T he

achievem ents.

U n it was w ell-placed to m eet this dem and - and

T h e global near-surfacc tem p e ra tu re record is perhaps the best, b u t by no m eans th e only, exam ple

acted on the opportunity. S trong contacts in the U n ited States, such as the late J . M urray M itchell,

o f such w ork. P ain stak in g ly com piled d u rin g the

the doyen o f A m erican clim atologists, Ray Bradley

early 1980s by the U n it, then u n d e r th e directo rsh ip

at the U niversity o f M assachusetts and H enry Diaz a t N O A A , led to collaboration and fu n d in g th ro u g h

o f Professor Tom W igley, th e record is now routinely u p d a te d in c o n junction w ith th e H adley C entre (see F igure 0.1). T h is a u th o ritativ e record o f global

a series o f contracts w ith the US D e p artm en t o f Energy th a t have continued to be renew ed to the

tem p e ra tu re fluctuations over the last 140 years has

present.

p rovided the science o f clim ate change w ith an

T h is book is a com m em oration of the first q u a rte r

invaluable resource and has acted as a pow erful

c entury o f the existence o f the C lim atic Research

sym bol to th e p u b lic a t large of th e reality o f clim ate

U n it. W e are very happy to see it and p roud th at

change. T he in itial fu n d in g for this w ork provides a

the U n it has prospered d u rin g th is tim e and estab­

good exam ple o f w here serendipity u n derw rites e n te r­

lished a w orld-w ide rep u tatio n . W ith all w ho find

prise. It becam e clear, in th e second h a lf o f th e 1970s,

in terest in the clim ate o f the B ritish Isles, in its vari­

th a t th ere was a need for an im proved d a ta -b an k of

a b ility and change over tim e, and in its relationship

FOREWORD

to th e w ider global clim ate system , we join in

E m e r i t u s P r o f e s s o r H .H . L a m b

th a n k in g the a u thors and editors o f th e book. W e also express our w ishes for a c o n tin u in g successful

(F ounding D irector, C R U , 1 9 7 2 -8 )

Holt, Norfolk

future for the U n it u n d e r its c u rren t D irector,

E m e r i t u s P r o f e s s o r K .M . C l a y t o n

Professor Trevor Davies. T h e U n it, now w ith other

Norwich, Norfolk

in stitu tio n s in B ritain and abroad, m aintains its c rit­ ical w atch on the c hanging clim ate, b o th in the

(D ean, E nvironm ental Sciences, U E A , 1967—71 and 1 9 8 7 -9 3 )

B ritish Isles and w orld-w ide. Som e o f these changes

P r o f e s s o r T.M .L. W

arc shaped by h u m an actions; som e o f them are q u ite

ig l e y

n atural in o rigin. E ith e r way, clim ate change funda­

Boulder, Colorado

m en tally affects the conditions o f life in o u r w orld. Seeking to understan d and p red ict such change

(D irector, C R U , 1 9 7 8 -9 3 )

rem ains a critical endeavour deserving o u r strongest

NOTE

efforts, a w orthy and w orthw hile challenge to h u m an

1

creativity, in g en u ity and discipline.

Climatic Research Unit Monthly Bulletin, 1972, vol. I, p. 9.

A CKNO WLE DGEMEN TS

Many people whose names do not appear as chapter authors have contributed to the production of this book T hey have all provided invaluable assistance and it is no exaggeration to say th at this book would not have appeared w ithout their help. In particular we thank Ju lie Burgess, C hristine Jeffery, and Susan Boland for secretarial support; Sheila Davies, P hillip Ju d g e and A dam Jam es for their photographic, carto­ graphic and com puter graphic skills, respectively; M ick Kelly for allow ing us to use his nifty graphics package, Doodler for W indow s; M ike Bristow for help w ith com puting problem s; Mary Spence of the Royal M eteorological Society, Frankie Pullinger and G raham B artlett o f the N ational M eteorological Library, Bracknell, Andrew Joyce of the University o f D urham , Don M cK inlay of the Clim atic Research U n it and M artin Ingram o f Brasenose College, O xford, for their help in tracking down pliotos which we have used in this book. W e would also like to thank the Hadley C entre and the U K Met. Office for providing the global clim ate model data and the station norm al data w hich have been used in various chapters. These data were provided through the D epartm ent o f the F.nvironm ent’s C lim ate Impacts L IN K Project. T he daily precipitation data from the E ngland and W ales precipitation series used in C hapter 10 were m ade available by agreem ent of Tom W igley and Phil Jones ol the C lim atic Research U n it at the U niversity of East A nglia and Jo h n Cole o f the W ater Research Centre. T he assistance of the U K M et. Office in updating the various national series is acknowledged. Precipitation data for the fourteen stations in the R epublic o f Ireland were supplied by Dennis Fitzgerald o f the Irish M eteoro­ logical Service.

W e have m ade every effort to trace the copyright holders of photographic material used in this book and acknow ledgem ent is given to them below. U nfortunately, we have not been able to trace the sources of some of the figures. W e would be grateful to readers for any further inform ation they may be able to provide. The quotation from Manley, p. 9, appears cour­ tesy o f Chapm an and Ilall who, as Allen and U nw in, published this passage in 1985 in the book The Climatic Scene (eds Tooley, M .J. and Sheail, G.M .). It is translated from an articlc which originally appeared in Russian in 1963 in the magazine Anglia. All other quotations used as epigraphs were extracted from the Penguin D ictionaries of Q uotations. Chapter 2: T he U niversity of D undee for Figures 2.3 and 2.13. Chapter 3: Ronald F. Saunders for Figure 3.4 (previ­ ously published in Weather, Decem ber 1993); University of D undee for Figure 3.6; Kevin J. R ichardson - Photography for Figure 3.8 (previously published in Weather, February 1995). Chapter 4: Figure 4.5 is reproduced by perm ission of Science Reviews I.rd from D.Q. Bowen, 'The Pleistocene of N orth W est Europe', Science Progress, 1992, vol. 76, pp. 2 0 9 -2 3 ; The N ational M useum of Wales for Figure 4.6; Figure 4 .9 is reproduced by perm ission of Oxford University Press (from F.W. Shotton (ed.), British Quaternary Studies: Recent Advances, 1977). Chapter 5: Barbara Maher for Figure 5.3. Chapter 6: Stofnun Arna M agnussonar (The Arni M agnusson M anuscript In stitu te at the University of

ACKNOWLEDGEMENTS Iceland), in particular Sigurgeir Steingn'm sson, for Figure 6.2. Chapter 7: T he Mary Evans Picture Library for Figure 7.1; the Royal M eteorological Society for Figure 7.2 (previously published in Weather, 27, p. 4 95, from Symons 1891); J. K ington, The Weather o f the 1780s over Europe, 1988, C am bridge U niversity Press, for Figures 7.3, 7 .4 , 7.5; Derek Ilu d sp erh for Figure 7.7; the Royal M eteorological Society for Figure 7.8; Figures 7.9, 7 .10 and 7.11 are from Fitzroy 1863; G raham B artlett tor Figure 7.12; the Tate Gallery, London for Figure 7.13Chapter 8: Penny T ranter and the BBC W eather Centre for Figure 8.1; U niversity o f D undee for Figures 8.2 and 8.4; J.M . Cook for inform ation about Figure 8.5 (previously published in Weather, January 1992), although the photographer is unknow n; Longmans, G reen and Co. for Figure 8.6; the Royal Geographical Society w ith the In stitu te of B ritish G eographers for Figure 8.7; Figure 8.8 is reprinted from Atmospheric Environment, 24A , T.D. Davies, G . Farmer and R.J. B arthelm ie, ‘Use o f sim ple daily atm ospheric circula­ tion types for the interpretation o f precipitation com position at a site (Eskdalem uir) in Scotland, 1 9 7 8 -1 9 8 4 ’, pp. 6 3 -7 2 , copyright (1990), w ith kind perm ission o f Elsevier Science Ltd, T he Boulevard, Langford Lane, K idlington, 0 X 5 1GB, UK. Chapter 9: T he Royal M eteorological Society for Figure 9 1 ; the Bodleian Library, U niversity of Oxford for Figure 9.2; the U K M et. Office for Figure 9.4; J.F.P. G alvin, by permission o f the Royal M eteorological Society, for Figure 9.10. Chapter 10: T he Royal M eteorological .Society for Figure 10.2; the W ater Services Association for Figure 10.17. Chapter 11: Surrey Herald, News and leader Series for Figure 11.1; B etty Bosworth for Figure 11.4 (previ­ ously published in Weather, April 1996); the Royal M eteorological Society for Figure 11.7 which is reproduced courtesy of T he Met. Office. Chapter 12: the D epartm ent of the E nvironm ent for Figures 12.6, 12.9. 12.10 and Plate 8(a); David Ball for Figures 12.1 and 12.8.

Chapter 13: Figure 13.1 is reproduced courtesy o f the Daily Mirror and M irror Syndication International; M ark Davison/ Frosted Earth for Figure 13.4 (previ­ ously published in Weather, February 1990); Figure 13.8 appears courtesy o f the Western Morning News C om pany Ltd.; George D. Anderson for Figure 13.15; S.D. B urt for Figure 1.3.19. Chapter 14: Malcolm W alker for Figure 14.1; the Royal M eteorological Society and K enneth W oodley for Figure 14.2; the U niversity of D undee for Figure 14.3; the UK Met. Office for Plate 8(b) and Figures 14.5 and 14.6. Chapter 15: Julian W illiam s for Figure 15.9Chapter 16: Figure 16.2 is reprinted from the Journal o f Glaciology w ith the permission of the International G laciological Society; A ndré Berger for Figures 16.3 and 16.9; Figure 16.4 is reprinted from Palaeogeography, Palaeoclimatology, Palaeoecology (Global and Planetary C hange Section), vol. 97, W alter and K asting, ‘Effects of fuel and forest conservation on future levels of atm ospheric carbon dioxide’, pp. 1 5 1 -8 9 , copyright (1992) w ith kind permission o f the authors and Elsevier Science - NL, Sara B urgerhartstraat 25, 1055 KV A m sterdam , The N etherlands; Figure 16.6 is reprinted w ith perm is­ sion from the authors and Nature (Manabe and Stouffer, 1993), copyright (1993), M acmillan M agazines Ltd; Figure 16.7 Kim and Crowley, Geophysical Research Letters, 21(8), pp. 681—4, 1994, published by the American Geophysical U nion; Figure 16.8 Crowley and K im , Geophysical Research Letters, 22(8), pp. 933—6, 1995, published by the Am erican Geophysical Union. Appendix D: Professor H .H . Lamb. Appendix C: T he Hadley C entre of the U K Met. Office for the daily CET data. Appendices D1 and 0 5 : The Hadley Centre. Appendices D2. 0 3 and 0 4 : Phil Jones o f the Clim atic Research U nit, University of East Anglia.

T his page intentionally lcli blank

1 I N T R O D U C I N G CLIMATE C H A N G E Mike Hulme and Elaine Barrow The more things change, the more they are the same. A lp h o n s e K a rr

CHANG IN G V IEW S OF CLIMATE

d efo restatio n in th e tro p ic s causing c lim a te change - in th is case loss o f ra in fa ll1 - w as also c o n sisten t

W ith

h in d s ig h t,

c lim a te

th e

tw e n tie th -c e n tu ry

w as d o m in a te d

by

th e

view

p ersp ectiv e

of th a t

c lim a te is c o n stan t. C lim a te w as effectively sta tio n a ry for th e p u rp o ses o f h u m a n d e c isio n -m a k in g an d only varied in any sig n ific a n t w ay over geo lo g ical tim e . T h is view o f c lim a te was p a rtly c o n d itio n e d by th e d o m in a n c e o f th e d e v elo p m e n ts in w e ath e r fore­ c astin g w h ic h to o k place d u rin g th e first h a lf o f the century.

The

e x c ite m e n t

o f scientific

discoveries

w h ic h led to im p ro v e m e n ts in th e u n d e rs ta n d in g an d p re d ic tio n o f th e w e ath e r o f th e next day m a rg in ­ alised w o rk w h ic h was m o re concerned w ith va ria ­ tio n s in c lim a te over decadcs a n d c en tu rie s. T he a d o p tio n

of

‘n o rm a l’ p e rio d s

by

th e

fled g lin g

In te rn a tio n a l M eteorological O rg a n isa tio n reinforced

w ith th is view. T h u s a m ajo r E n g lish n a tio n a l new s­ p a p er could observe in 1818 th a t, a prospect far more gloomy than the mere loss of wine had begun to present itself by the increased chilliness of our sum m er months. It is too well known that there was not sufficient warmth in the summer of 1816 to ripen the grain; and it is generally thought th at if the ten or twelve days of hot weather at the end of June last had not occurred, most of the com m ust have perished. The warm and settled appearance of the weather at this early period of the season, leads us to hope that an agreeable change is about to take place in our planet; and that we shall not, as for many past years, have to deplore the deficiency of solar heat which is so necessary to ripen the productions of the earth.2

th is ra th e r sta tic view o f c lim a tc . W e a th e r sta tistics c o llected over th ir ty or th irty -fiv e years w ere th o u g h t

O n ly d u rin g th e last q u a rte r o f th e tw e n tie th

o f as a d e q u a te to define th e c lim a tc o f a re g io n , s ta tis ­

c cn tu ry - from th e 1970s o nw ards - has th is m ore

tics w h ic h c ould th e n be safely used in fu tu re d esign

d y n a m ic view o f c lim ate been rediscovered. T h e

an d

was

tw e n tic th -c c n tu ry view th a t c lim a te is c o n sta n t was

T h is was in c o n tra st to m u ch th in k in g in th e n in e ­

o f w hom H u b e rt L am b m u st rank in th is c o u n try as

te e n th century. T h e e vidence o f g lac ia tio n discovered

p erhaps th e m o st im p o rta n t. T h ey w ere follow ed by

d u r in g th e early decades o f th a t c e n tu ry an d th e

th e g ro w in g body o f c lim ate sc ien tists a n d , by th e

p la n n in g

a p p lic atio n s.

C lim a tc

ch an g e

largely irrelev a n t.

first seriously c h allen g e d by a few p io n ee rin g scholars,

em e rg en c e o f ev o lu tio n ary ideas w ere m o re consis­

tim e o f o u r p re sen t d ecade, by an increasing c o n ­

te n t w ith a d y n a m ic view o f n a tu re an d o f c lim ate

stitu e n c y o f decisio n -m ak ers. A stro n g sense o f histo ry

th a n one in w h ic h all th in g s re m a in e d c o n stan t.

was ch ara cte ristic o f th o se o rig in a lly c h a lle n g in g th e

C o n cern a m o n g s t c o lo n ia list c o n se rv a tio n ists a b o u t

tw e n tie th -c e n tu ry orthodoxy. In d eed , H u b e r t L am b

M IKE HULME A N D E LAIN E B A R R O W

and oth ers w ere alm ost as m u ch historians as they were

th e E nvironm ent, com m issioned national reviews in

clim ato lo g ists. M ore recently, events in the clim ate

1991 and again in 1996 o f th e po ten tial im pacts of clim ate change for th e country.5 T h is type o f national

system itse lf reinforced th e challenge and have now led to a re -w ritin g o f th e orthodoxy.

review o f the im portance o f clim ate change is

T h e prospect of significant global clim ate change

required o f m any c ountries under th e Fram ew ork

induced by h u m an pollu tio n o f th e atm osphere has acted as a pow erful ag en t in consolidating the revi­

C onvention and is a m ode o f re p o rtin g th at has been

sionist view of clim ate as non-stationary. T h is process

adopted around th e world. T here is a danger th at this recent political concern

of re -th in k in g has been un d erp in n ed by th e tw in

about clim ate change and its im pacts bestow s on

d evelopm ents o f m ore ab u n d an t global clim atc observations and rapid increases in co m p u ter m o d el­

clim ate an unw arranted im portance as an agent that shapes our lives. Such th in k in g has led, perhaps

lin g capability. It is now possible to describe truly

rather curiously, to a re tu rn in som e quarters to a

global changes in clim ate usin g observational data

variant o f the clim atic determ inism prevalent at the

and to explore fu tu re changes in clim ate using cred­

sta rt o f th e century. D eterm inism is a reductionist

ible clim ate m odels. T h e changed a ttitu d e tow ards

philosophy th a t sees events and behaviour as con­

c lim ate has also been in stitu tio n a lised in recent years.

trolled by a very lim ite d set o f physical factors.

In

E llsw orth H u n tin g to n , th e Yale geographer, is the

1988, for exam ple, th e W orld M eteorological

O rganisation and the U n ite d N a tio n s E nvironm ent

m ost w ell-know n

P rogram m e established an In tergovernm ental Panel

clim ate. H e argued in 1915 th at, T h e clim ate of

on C lim a tc C hange to assess th e evidence for the

m any countries seems to be one o f the great reasons

enhanced greenhouse effect, or so-called

why idleness, dishonesty, im m orality, stu p id ity , and

‘global

proponent o f such a role for

w a rm in g ’. T h is Panel continues to produce reports

weakness o f w ill prevail.

for th e w orld c o m m u n ity on th e prospect o f clim ate

strid e n t or d o ctrinaire as H u n tin g to n , th e im p o r­

A lthough nor always as

c hange3 an d they have also considered th e conse­

tance o f the clim atic influence on o u r lives has been

quences o f global c lim ate change for individuals,

stressed by num erous th in k ers, starrin g w ith the

ecosystem s and nation-states.* T h e concern about

A ncient G reeks and th e ir supposedly unin h ab itab le,

chan g in g global clim ate was sufficient to yield a

to rrid and frigid ‘c lim a ta ’. T he influence o f clim ate

U n ited N ations Fram ew ork C onvention on C lim ate

has also been in terpreted psychologically. In the

C hange. T his C onvention was signed by I 55 nations

m iddle o f this century, for exam ple, G ordon Manley

at Rio d e Ja n e iro in Ju n e 1992 and subsequently

stated th at. A ppreciation of the B ritish clim ate depends largely on tem peram ent. T har ir has nor

cam e in to force in M arch 1994. T h e B ritish and Irish g o v ern m en ts ratified the C onvention in D ecem ber

been conducive to idleness has been reflected in the

1993 and A pril 1 994, respectively, and b oth d ip lo ­ m atic d elegations have played th e ir p a rt in the

characteristics of th e people’,7 and, m ore recently, R ichard Beck argues th a t, ‘the historical record is

o ngoing n e gotiations to establish a legally b in d in g

highly suggestive . . . th a t a m ild clim ate in m id-

c lim ate protocol. T hese d evelopm ents have taken place against a

extrem e clim ate m ay predispose people tow ards

latitudes helps to foster a tolerant society or th a t an

background of a w arm ing clim ate. Since th e 1970s,

intolerance.’8 These psychological interp retatio n s of

bo th th e B ritish Isles and th e w orld have w arm ed

clim atic determ in ism m ay seem hard to defend.

by a b o u t 0.3°C. T h e reality of rhis w'arm ing, and

N evertheless, the prospect of global w arm in g , and

th e prospect of accelerated w arm ing over th e next few decades, has focused m ore a tte n tio n on the

the stu d y of the im pacts of such clim ate change, introduces a new variant to the clim atic d e te rm in -

interactio n s and interdependencies o f clim ate and

ists’ repertoire o f argum ents. Many studies o f th e possible im pact o f future clim ate change seem , im plicitly, to elevate clim atc to

society th a n was h ith e rto the case. T h u s th e U n ited K ingdom go v ern m en t, th ro u g h its D e p artm en t of

IN T R O D U C IN G CLIMATE C H A N G E

bein g th e m ajor factor th a t w ill influence future

lengcs and o p p o rtu n ities presented by clim ate change

h u m an a ctivity and welfare. T h u s th e conventional

are very m uch those th a t every colonising c o m m u ­

clim ate change im pact stu d y w ould a tte m p t to sim ­

nity

ulate th e effect o f clim ate change by, say, 2 0 5 0 on a

geographical differences in clim ate. T h is view o f

p a rticu la r aspect o f the e n v iro n m en t, say cropping

clim atc, w hether im p licit or explicit, has been tru e

p a tte rn s or forest d istrib u tio n . L ittle a tte n tio n is usually paid to w h e th er or not clim atc is the m ain

of, for exam ple, M ongols in E urope, V ikings in G reenland or E uropeans in Africa. For exam ple, one

th ro u g h

history has realised are posed by

factor b e hind observed changes in such

may view the n in ete en th -ce n tu ry history' o f th e in te r­

d istrib u tio n s. Even if it is recognised explicitly th at

action betw een clim atc and society as one about the

d riv in g

o th er factors arc involved (e.g., changes in tech n o l­

ability o f th e European colonising powers to exploit

ogy, consum er behaviour, w ork and leisure pattern s), these arc so u n p red ictab le th a t clim atc often retains

geographical differences in clim atc in the T ropics rubber in M alaysia, cocoa in W est Africa o r bananas

the appearance o f bein g the m ain co n tro llin g factor.

in the C aribbean -

C lim atc change d e te rm in ism th u s re-appcars. Some

clim atc im pacts th a t such ex ploitation m ig h t brin g

and to m anage th e regional

studies have show n, however, th a t factors such as

w ith i t . 11 A tw cnty-first-ccntury history o f such

the fu tu re o f th e C om m on A g ric u ltu ral Policy o f the E uropean U nion w ill have a m u ch larger im pact on

c om m unities or regions to exploit and m anage the

in teraction m ay well be about the a bility o f different

th e future B ritish landscape th an clim atc change.9

forthcom ing tem poral changes in clim atc bro u g h t

A nd it only takes a sim ple th o u g h t experim ent to

a bout by h um an p o llu tio n o f th e atm osphere.

realise th a t o th er considerations, too, w ill sw am p the

T aking th is view, th e U n ited N ations Fram ew ork

effects o f clim atc change on future h u m an a n d anim al welfare. For exam ple, civil conflict, technological and

C onvention on C lim atc C hangc is concerned p rim a r­ ily w ith th e regulation o f th is exploitation and

d em o g rap h ic change and global epidem ics, are all

m anagem ent process as im plied in A rticle 2,

likely to influence welfare to a g re ater e x te n t than w ill c lim atc change. T h is is not to say th a t clim atc change is u n im p o rta n t or docs not m atter. W e m erely stress th a t to assess th e tru e significance o f clim atc change it m u st be evaluated a gainst changes th a t w ill occur due to o th er environm ental con strain ts and social c onstructs. C lim ato lo g ists

talk in g

about

clim ate

changc

always ru n th e risk, therefore, o f bein g seen to be

The ultimate objective of this Convention . . . is to achieve . . . stabilisation of greenhouse gas concentra­ tions in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system. Such a level should be achieved within a time frame sufficient to allow ecosystems ro adapt naturally to climate change, to ensure that food production is not threatened and to enable economic development to proceed in a sustainable manner.12

slanted in th eir views. T hey m ay be* in te rp rete d as bein g unnecessarily alarm ist by those w ho reckon

It is unlikely, however, th a t such regulation can

th a t h um an in g en u ity and technical changc w ill

ensure th a t com m unities and n ation-states benefit or

m in im ise th e effects o f clim ate ch an g e,10 or overly

suffer equally from clim atc changc. T he p a rtitio n in g

com placcnt by those w ho see clim atc as a d o m in a n t

o f these benefits or costs betw een nations w ill depend

control on h u m an choices and action. Seeing clim ate,

on tw o things: serendipity and access to h um an and

and therefore clim ate change, as a resource to m anage

technological capital. T h e im pact of clim ate changc

and to benefit from , and as essentially n eu tral, is

on the w orld is likely to be d ictated largely by the

surely a m ore constructive view to take. T h e notion

e xisting inequalities in hum an vulnerability, w ith

o f ’g o o d ’ and ‘b a d ’ clim ates is a hard one to defend

som e luck and in stitu tio n a l regulation throw n in.

in any absolute sense. T em poral changes in clim ate, seen in th is way, present societies w ith challenges to

tw e n tie th century is, therefore, as follows. C lim ate

cope w ith and o p p o rtu n ities to exploit. These chal-

is no longer regarded as a co n stan t, b u t is continually

T h e view o f clim atc prevailing at th e end o f the

M IKE HULME A N D E LA IN E B A R R O W

subject to change. These changcs arc increasingly

includc th e p roxim ity o f the B ritish Isles to the warm

b ein g caused, inadvertently, by h u m an behaviour.

occan currents o f th e N o rth A tlantic and th e la titu ­

T h e changes in clim ate rem ain largely unprcdictablc,

dinal position o f the region in the m ain path o f the

b u t w ill have im p o rta n t consequences for hum an

m id -la titu d e westerlies. T h e outcom e o f these broad-

w elfare, d e cision-m aking and plan n in g . In ad d itio n

scalc influences is an ensem ble o f daily w eather

to th e prospect o f clim ate change, new developm ents

events th a t, w hen averaged over a suitable length

in daily, m o n th ly and seasonal w eather forecasting

o f tim e (conventionally th irty years), yield a set o f

provide an even g re ater im p etu s to take clim atc vari­

statistics th a t provide a short-hand description o f the

a b ility seriously. O rganisations, charged w ith invest­

clim atc o f the region. Such a statistical creation is

m e n t decisions, environm ental m an ag em en t and

term ed ‘a clim atology’. T h e 1961 to 1990 clim a­

fu tu re p lan n in g strateg ies, need to include clim ate in th e ir decisio n -m ak in g stru ctu res as a key variable

Barrow and M ike H u lm c in C hapter 3. R anges and

ra th e r th an as an assum ed constant. If th is book

p attern s o f a large n u m b er o f clim atc variables arc

c o n trib u tes to such an awareness w ith respect to th e B ritish Isles, th en it w ill have achieved one o f its

described in th is chaptcr w ith the help o f m aps and

purposes. It w ill, in th e process, have also co n tri­

tology for th e B ritish Isles is described by Elaine

tables. A supplem entary set o f colour m aps are also provided in A ppendix A.

b u ted to one o f th e four original aim s o f th e C lim atic

T he reconstruction o f past clim ates, p rior to the

Research U n it cited w hen it was established in 1972,

com m encem ent o f form al m eteorological observation

nam ely, ‘To in vestigate th e p ossibilities o f m aking

d u rin g the seventeenth century, is addressed in Part

advisory sta te m en ts about future tren d s o f w eather

2 o f the book, ‘R econstructing th e P ast’. T h e lan d ­

and clim ate from a season to m any years ahead, based on acceptable scientific m ethods and in a form likely

scapes o f th e B ritish Isles have been shaped over

to be useful for lo n g -term p lan n in g purposes.’15

m illen n ia by a continually c hanging c lim atc as well as, m ore recently, by the activities o f o u r ow'n d istan t ancestors. T h e response o f th e physical and biotic environm ent to these clim atc changcs has been

OUTLINE OF THE BOOK

preserved w ith differing levels o f detail and relia­ b ility in various depositories b oth on land and in the

T h is book unasham edly exploits th e title and stru c tu re o f one o f Professor L am b s m ost im p o rta n t

ocean. These

w orks — Climate: present, past and future - p ublished

stretch in g back over thousands and m illions o f years.

landscapes and depositories enable

th e forensic w ork of reconstructing past clim ates

in tw o volum es in 1972 and 1977. T his title so well

Brian Funnell takes the longest view o f all in C h ap ter

captures th e essential tem poral d im ension o f the

4 in his assessm ent o f th e clim ates o f the B ritish

study o f clim ate and also em braces so fully th e scope o f research for w hich th e U n it is renow ned, th a t we

Isles in past geologic ages, using a m ix tu re o f land­

cannot form ulate a b e tte r description o f the subject

from the w ider N o rth A tlan tic basin. T h e glacial and

m a tte r w ith w hich we are concerned. W e have

intcrglacial pulses o f the Q u a te rn a ry era do m in ate

therefore follow ed his tem p late in this anniversary volum e.

seem to be orchestrated largely by changes in the

Part 1 o f th e book is concerned w ith an overview

o rbital characteristics o f th e E arth around th e Sun.

scape and ocean corc evidence from the region and

the record on these tim c-scalcs, pulses w hich now

o f th e causes and character o f the clim ate o f the

In C haptcr 5, K eith Briffa and T im A tkinson tackle

B ritish Isles as we know it a t the end o f th e tw en­

th e reconstruction o f clim ates d u rin g th e period —

tie th century. Trevor Davies, T im O sborn and M ick K elly in C h a p te r 2 p u t th e clim ate o f th e region into

called the H o lo c e n e — since th e last glaciation o f

a global co n tex t by d escribing th e factors th a t shape

years ago. A lth o u g h closer in tim e to th e present,

and control th e clim ate o f these islands. These

the physical and biotic evidence o f clim ate fluctua­

th e B ritish Isles, w hich cam e to an end a bout 15,000

IN T R O D U C IN G CLIMATE C H A N G E

tions in th e region th ro u g h th e H olocene do not

back to 1 January 1861. Professor Lam b still updates

always allow a robust p ic tu re o f clim ate change to be draw n d u rin g th is period o f increasing h u m an

the C atalogue each m o n th and the full 135-year record is used by M ick Kelly, P hil Jones and K eith

accu ltu ratio n . T h e R om an occupation o f th e B ritish

Briffa in C hapter 8 to describe the influence of

Isles for th e four c en tu rie s follow ing th e b irth of

seasonal and decadal variations in atm ospheric circu­

C h rist coincides w ith the earliest docum entary evidence o f the B ritish e nvironm ent. T h e D ark Ages

lation on the B ritish and Irish clim atc. H u b e rt Lam b last p ublished a com plete listin g o f his C atalogue in

also left a lim ite d legacy o f w ritte n descriptions o f

1972 and we therefore include in A ppendix B an

clim ate to fu tu re g enerations, b u t the centuries follow ing th e N o rm a n invasion in 1066 possess a

u p d a te o f the C atalogue from 1972 to 1995. T he

g re at abundance o f w ritte n docu m en ts th a t contain

com piled by the late G ordon M anley, is the longest

‘C entral

E n g la n d ’ tem p eratu re

record, originally

d irec t and in d irect references to w eather and clim ate

continuous in stru m en tal clim ate record in th e w orld.

c o nditions in th e B ritish Isles. Some o f these docu­

T h is record com m enced in 1659 - the year follow ing

m en ts, d a tin g from

the death o f O liver Crom w ell and th e year before

th e m edieval period o f the

tw elfth to fifteenth centuries, are evaluated by A strid

the creation o f rhe Royal Society — and is now

O g ilv ie and G raham

Farm er in C h a p te r 6 and

updated routinely by th e U n ited K ingdom M et.

com pared

com parable docum entary sources

Office. It provides a u nique o p p o rtu n ity to evaluate

from elsew here in th e N o rth A tlan tic basin - Iceland

w ith

clim ate change in th e region and beyond on century

and G reenland.

tim e-scales and is discussed by Phil Jones and M ike

T h e B ritish Isles is a region endow ed w ith som e

H u lm e in C h ap ter 9- T h is 337-year tem perature record provides th e clearest indication o f a w arm ing

o f the richest sources o f in stru m e n tal d ata for the stu d y o f historical and contem porary clim ate varia­

clim ate for th e B ritish Isles, and th e last fifty years

tio n and change. In P art 3 o f th e book, ‘M onitoring

have been th e w arm est such period in th e entire

th e P re se n t’, th is vast store o f q u a n tita tiv e clim ate

record. T he daily values o f th is record for th e period

in form ation is used to present a selective evaluation

since 1961 are p lo tted in A ppendix C.

o f th e observed tren d s and characteristics o f B ritish

In ad d itio n

to tem p eratu re, rainfall (or m ore

and Irish clim ate in the present and recent past. T he

correctly precip itatio n ) is th e o th er prim ary clim ate

o rigins o f regular m eteorological observations in

variable. Records o f p recipitation in the B ritish Isles

the B ritish Isles are explored by Jo h n K in g to n in

extend back alm ost as far as they do for tem perature

C h a p te r 7. T h e stim u lu s given to science in general, and careful m eteorological m easurem ents in p a rtic ­

and an analysis o f over tw o hu n d red years o f m easure­ m ents is u n dertaken in C h ap ter 10 by Phil Jones,

ular, by th e se venteenth-century E n lig h te n m e n t is

Declan Conway and K eith Briffa. P recipitation is

q u ite clear and th e first d edicated m eteorological

m uch m ore variable th an tem p eratu re and it is hard

observatories in th e B ritish Isles soon follow ed in the

to discern any significant tren d s over tim e in B ritish

e ig h te en th century. By the m id d le o f th e n in eteen th

and Irish p re cip ita tio n . D ro u g h ts and floods are th e

century, a m ore regional view o f w eather was achiev­

m anifestation o f extrem e precip itatio n v ariability and

able and, p ro m p te d by th e d em ands o f the B ritish Navy, daily synoptic w eather charts w ere a regular

also described. E xtrem e w ind storm s are also a m ajor

feature o f the m eteorological enterprise. A n im p res­

hazard in the B ritish Isles, b u t equally im p o rta n t for

the frequencies o f these environm ental hazards are

sive archive o f a synoptic-scale w eather classification

th e region is the p o tential offered by w inds for energy

for th e B ritish Isles is provided by th e L am b C ata­

g eneration

logue o f circu latio n types. T his C atalogue was originally developed by H u b e rt L am b in th e 1940s

con trastin g roles for w ind are explored in C hapter

and th e u b iq u ity o f historical daily synoptic charts

as they exam ine changes over tim e in w ind as both resource and hazard.

for th e Isles enabled him to reconstruct th e C atalogue

and

recreational pu rsu its. These

tw o

11 by Jean P alutikof, Tom H o lt and A ndrew Skellern

M IK E HULME A N D E LA IN E B A R R O W

T h e atm osphere provides th e m edium by w hich

casting m ethodologies at different tim es and in

w eather and clim ate are delivered to us w ho live at

different cultures. Clive Pierce, M ichael D ukes and

th e E a rth ’s surface. T h e com position o f th e atm o s­

G raham Parker provide a short sum m ary o f som e of

phere in term s o f gaseous com pounds and p a rtic u ­ lates is im p o rta n t, not only for clim ate b u t also

before explaining the basis o f m odern w eather fore­

this history of w eather forecasting in C h ap ter 14,

because it affects th e q u a lity o f th e air th a t we and

casting techniques in th e B ritish Isles. O f course

o th er anim als and plan ts b reathe each day. N o t only

com puters are now central to th is enterprise, and

does th e B ritish Isles possess som e o f th e longest

som e o f the m ost pow erful com puters in the w orld,

c lim ate records in th e w orld, th is region also has one o f th e longest histories o f air p o llu tio n and air p o llu ­

and in the B ritish Isles, are dedicated to this activity.

tio n legislation e x ten d in g back over several centuries.

centuries

T hese in teractio n s betw een clim ate and air quality

on very pow erful m achines are necessary. M odel

in the B ritish Isles are discussed by P eter B rim ble-

com plexity and co m p u ter pow er are no guarantees

com be and G raham B entham in C h ap ter 12. O n e o f

o f acceptable predictive capacity, however, and Sarah

ihc perennial

p o p u lar in terests afforded

Sim ilarly, for p re d ic tin g clim ate m any decades or hence,

very

com plex

m odels operated

by the

Raper, D avid Viner, M ike H u lm e and Elaine Barrow

w eather is the estab lish m en t o f new records o f

discuss the problem s of und erstan d in g and m odel­

clim atic extrem ity, w h eth er h o t o r cold, w et or dry,

ling clim ate change for a region like the B ritish Isles

w indy, sun n y or cloudy. M ichael D ukes and P h ilip

in C hapter 15. A lth o u g h c u rre n t predictions suggest

Eden exam ine th is fascination w ith w eather records

th a t th e clim ate o f the tw enty-first century w ill be

in the B ritish Isles in C hapter 13 and provide exam ­

d o m inated by continued w arm ing, exactly how this

ples o f som e o f the m ore p o p u lar and th e m ore

will be m anifest in th e ensem ble o f w eather elem ents

unusual. O f course, the m ore indices one has w hich

and tim e-scales th a t com prise clim ate rem ains u n ­ clear. P lan n in g for change, however, now seems a

describe the w eather m easured at m ore and m ore places, th e m ore com m on it w ill be on purely sta tistica l g ro u n d s for new records to be established on a given day, m o n th or year. O n e m u st be cautious

m ore necessary approach for p u b lic and private sector organisations than assum ing statio n arity o f clim ate. T here are a sm all n um ber o f p lan n in g activities,

a b o u t in te rp re tin g a preponderance o f new records

however, th a t require inform ation about th e future

as necessarily indicative o f a changcd

or m ore

clim ate on m uch longer tim e-scales, tim e-scales th at extend over thousands o f years. Clare G oodess and

W h a t of the future? Can we expect o u r w eather

Jean P a lu tik o f close th e book w ith th eir analysis in

and clim ate to con tin u e to provide us w ith the same

C hapter 16 o f th e very lo n g -term o utlook for clim ate

extrem e clim ate.

environm ental conditions th a t we have experienced

in the B ritish Isles. To achieve th is goal requires a

in o u r own lifetim es or th a t w ere experienced in

re-exam ination o f som e of the evidence for past

previous g enerations or eras? In P art 4 o f the book, ‘Forecasting th e F u tu re ’, our a b ility to envision

clim ate changc presented in C hapters 4 and 5, as well as the use o f the co m p u ter m odels described in

future w eather and clim are is discussed on three different tim e-scales: sh o rt-rerm w earher forecasting,

C hapters 14 and 15, w hich sim u late regional and global clim ate. A nd here, o f course, lies th e paradox.

clim ate pred ictio n over th e next one h undred years

T he increasing h um an im p rin t on the w orld in w hich

and, finally, clim ate p rediction m any thousands of

we live is leading to a general w arm ing o f the

years in to th e future. W earher forecasting takes on

clim ate, a w arm ing w hich we expect w ill becom e

m any guises and over tim e has reflected th e cultural

increasingly dom in an t d u rin g the lifetim e o f our

changes and d iversity th a t have characterised the

children and g randchildren. From the perspective o f

history o f th e hum an species. T hus, su p erstitio n ,

th e planet and solar system , however, and recog­

legend and folklore, in tu itio n , d e te rm in istic and

nising th a t th eir tim e m etric is very different from

chaotic scicncc, have all generated th eir ow n fore­

ours, the clim ate o f the E arth seem s set to cool over

I N T R O D U C I N G CLIMATE C H A N G E

the next 10,000, 5 0 ,0 0 0 or 100,000 years. W h e th e r global w arm ing, and associated clim ate changc in regions like the B ritish Isies, w ill appear as a m inor

5

b lip on this longer-term trend, or w h eth er th e ability o f the hum an species to modify its ow n en v ironm ent is now' so great as to be able to offset these p lan et­ ary and cosm ic forces, is a question th a t we w ill probably have to leave to our evolved descendants several m illennia hence . . . or else to science fiction.

6 7

NOTES 1 See R .H . G rove, A h istorical review o f early in s titu ­ tional and conservationist responses to fears o f artifi cially induced global c lim ate change: the deforestation— d esiccation d iscourse 1 5 0 0 -1 8 6 0 ’, Chemosphere, vol. 29, pp. 1 0 0 1 -1 3 . 2 T fx Observer, 18 ] une 1818. 3 IPC C , J.T . H o u g h to n , L.G. M eiro H lh o , B.A. C allendar, N . H arris, A. K a tte n b u rg and K. M asked (eds), Climate Change 199 5: the Science o f Climate Change, 1996, C a m b rid g e , C am b rid g e U niversity Press, 572 pp. 4 IPC C , R.T. W atson, M .C. Z inyow era and R .H . Moss (eds), Climate Change ¡995: impacts. Adaptations

8 9

10 11 12 13

a n d M itigation o f Climate Change: Scientific-technical Analyses, 1996, C am bridge, C am bridge U niversity Press, 8 7 8 pp. See C C IR G , The potential effects o f climate change in the U nited Kingdom, D ep artm en t o f the E nvironm ent, L ondon, H M SO , 1991, 123 p p .; also C C IR G , Potential impacts an d adaptations o f climate change in the United Kingdom, D ep artm en t o f the E nv iro n m en t, L ondon, H M S O , 1996, 248 pp. E. H u n tin g to n , C ivilization an d climate, H a m d en , C onn. USA, Shoe S trin g Press, 1915, p. 4 1 1 . G . Manley, Climate a nd tfye British scene, L ondon, C ollins, 1952. R.A . Beck, ‘C lim ate, liberalism and intolerance’, Weather, 1993, vol. 48 , pp. 63—4. M.L. Parry, J .E . H ossell, P.J. Jones, T. R ehm an, R.B. T ranter, J.S. M arsh, C. R osenzw eig, G . Fischer, I.G . C arson and R .G .H . Bunce, in te g r a tin g global and regional analyses o f the effects o f c lim ate changc: a case stu d y of land use in E ngland and W ales’, Climatic Change, 1996, vol. 32, pp . 1 8 5 -9 8 . J . A usubcl, ‘Technical progress and c lim ate ch an g e’, Energy Polity, 1995, vol. 23, pp. 1 1 1 -1 6 . R .H . G rove, op. cit. A rticle 2, The United Nations Framework Convention on Climate Change, New York, U n ited N ations, 1992. Q u o ted in Clim atic Research U nit Monthly Bulletin, 1972, vol. 1, p .9.

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Part 1: THE BRITISH ISLES CLIMATE

So we can claim that these islands o f frequent changes, o f the terrible A tla n tic gales whose endless roar besets our coasts in winter, o f the exquisite long June days celebrated by our poets throughout the centuries, o f the harsh biting north-easter in April, the wind-driven rain day after day i f there conies a wet autumn, the occasional spell o f three weeks o f snoiu a n d frost, the persistent dryness that quite frequently leads to shortage o f water in early summer — a ll these give us much cause to grumble, but even more cause to enjoy the march o f the seasons a n d the opportunities fo r such a variety o f flowers that the poorest man can still grow them in his garden. G o rd o n M anley, 'The Weather in B rita in ’, A n g lia, 1963

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2 E X P L A IN IN G THE CLIMATE OF THE BRITISH ISLES Trevor Davies, P. Mick Kelly and Tim Osborn It’s a warm wind , the west wind, fu ll of birds' cries. J o h n M asefield , ‘T h e W e st W i n d ’

INTRODUCTION T h e clim ate o f th e B ritish Isles is th e cum ulative result o f each day s wearher. T h e w eather on a p a rtic ­ u lar day depends on th e character o f th e atm ospheric circu latio n over th e Islands and on th e s y n o p tic sy s te m - d e p r e s s io n or a n tic y c lo n e affecting the

T h e processes w hich produce the B ritish clim are are therefore enorm ously com plex. T here are in te r­ actions on all space- and tim e-scales. C onsequently, it is over-sim plistic to a tte m p t to define a ‘b e g in ­ n in g ’ and an ‘e n d ’ to the various interplays of factors. T he p ictu re g ets even m ore com plex when one considers th a t the n ature o f th e interactions in the

region: in o th er w ords, th e overall w eather ty p e ’ (see

lan d -a tm o sp h ere -o ce an

C h a p tc r 8). T h e n atu re o f th e w inds and th e char­

T h is is e ith e r because o f natural variability internal

system

varies over tim e.

a cter o f th e synoptic system d ep en d , in tu rn , on the

to th e system , or because o f outside ‘forcings’, such

interactio n s betw een th e atm osphere, th e oceans and th e land surface a t every o th e r p o in t on the globe.

as variations in th e receipt o f solar radiation a t the

T h e w eather experienced a t a p a rticu la r location in

tion o f th e atm osphere because o f volcanic activity

to p o f the atm osphere, or changes in th e com posi­

the B ritish Isles is a function o f th e precise p a rt o f the

or a n th r o p o g e n ic gas em issions.

synoptic system w hich is overhead at the tim e and o f local influences. T he w eather associated w ith a p a rtic ­

consider in th is chapter the m ost im p o rtan t processes

ular synoptic system (w hich has a typical horizontal scale o f 1 -2 ,0 0 0 km ) can have im p o rta n t variations on

H aving m ade these cautionary rem arks, we will affecting th e clim ate o f th e B ritish Isles sequentially, from th e global to th e local scale - and thereby run

scales o f 1 0 -1 0 0 km . T h e w eather w hich is ‘d elivered’

the risk o f over-sim plification. W e start by consid­

to th e B ritish Isles by th e synoptic system s is, in tu rn ,

erin g th e m anner in w hich global clim ate is shaped

m odified by th e u n d erly in g surface: hig h land may

by th e planetary-scale atm ospheric circulation, or ‘general c ircu latio n ’. T h e general circulation o f the

enhance th e p re cip ita tio n process (see C hapter 3); radiation in different ways, affecting th e near-surface

atm osphere takes the form it does because o f th e way energy from th e Sun is d istrib u te d and u tilised,

air tem p e ra tu re; local circu latio n s (on rhe scale o f one to a few tens o f km ) can be affected by topography or

because the E arth rotates, and because o f the p a rtic ­ ular geographical p attern and orography o f the land

different land surfaces w ill react to incom ing solar

by th e d isc o n tin u ity across a coastal zone. Local effects

and ocean basins. W e first look a t the radiation and

such as these can exert a stro n g influence on the

consequent heat b u d g ets o f th e surface-atm osphere

c lim ate experienced by p a rticu la r places.

system , th e d riv in g force b ehind the w ind system s

T REVOR D AV IES, P. M IC K KELLY A N D TIM O S B O R N

Planetary A lbedo 33% ^

3%

^

25%

I— I Incoming solar I I radiation 100%

5%

o f the E a rth .1 Later sections look a t links betw een

ToP of Atmosphere

c lim ate and th e oceans and at local-scale influences

T h e E arth ’s surface also receives radiation from the atm osphere, where the solar radiation has been

on clim ate.

absorbed and re -e m itted as longw ave ra d ia tio n .2 T his longw ave radiation is also absorbed at the E a rth ’s surface. A t the surface and in th e atm osphere

GLOBAL-SCALE RADIATION AND HEAT BALANCES

there is therefore a com plex p a tte rn o f longw ave radiation absorption, em ission, re-absorption and reem ission. An issue of considerable current concern is the

T h e m ain source o f energy available to the planet is th e Sun. R ad iatio n e m itte d by th e Sun is sh o rt in

change in concentration o f th e so-called ‘greenhouse

w avelength. A round 33 p e r cent of th e solar radiation

gases’ in th e atm osphere because o f hum an activi­

w hich is received by th e p lan e t from th e Sun is scat­ tered back to space (see F igure 2.1). T h e fraction lost

ties. These greenhouse gases are the co n stitu e n ts o f the atm osphere w hich play the im p o rta n t role

in this way is called th e planetary a lb e d o . M ost o f

o f absorbing longwave terrestrial radiation (w hile not

th e sc a tterin g occurs in th e atm osphere, pred o m i­

interfering significantly w ith the incom ing solar

nantly by clouds. T h e E a rth ’s surface c o n trib u tio n to

radiation) thereby trap p in g heat near th e E a rth ’s

the planetary albedo is sm all. T here are, however, con­

surface. T his g r e e n h o u s e e ffe c t m aintains tem p e r­

siderable geographical differences in surface albedo -

atures w hich m ake th e planet habitable; w ith o u t it

d esert albedos are generally g re ater th an those of

th e E arth ’s surface w ould be m uch colder th an it is.

forests and snow has a h ig h albedo, as does w ater

A n increase in the concentrations o f greenhouse gases should lead to significant global w arm ing. T his

w hen th e Sun angle is low. T h e atm osphere (gases, clouds and du st) absorbs a b o u t 22 p er cent o f the incom ing solar radiation, leaving 45 p er cent of

enhanced greenhouse effect is likely to changc global

th e original received solar radiation to arrive at the

im p o rta n t ways. T h is issue is addressed at som e

E a rth ’s surface, w here it is absorbed.

lengrh in C hapter 15, b u t we w ill neglect it for now

clim ate, and the clim atc o f the B ritish Isles, in

E X P L A IN IN G THE CLIMATE OF THE BRITISH ISLES

globally averaged latitu d in a l d istrib u tio n . Since the S un’s overhead position traverses betw een th e Tropics o f C apricorn (23.45°S) and Cancer (23.45°N ), the in p u t o f solar radiation is at a m axim um in equatorial latitudes. T he low Sun angle tow ards th e Poles, and the greater albedo o f snow and ice, m eans th a t the in p u t o f solar radiation at th e surface is m uch sm aller at these hig h latitudes (Figure 2.2a). T h e em ission of longwave radiation shows a sm aller latitu d in a l varia­ tion and exceeds the solar energy in p u t o u tsid e tro p i­ cal latitudes. T he re su ltin g planetary net radiation d istrib u tio n (Figure 2.2b) is positive betw een 30°N and 40°S and negative at h ig h er latitudes. T h e general 4>

circulation o f th e atm osphere and th e oceans is driven by this latitu d in a l energy im balance and it serves to tran sp o rt heat polew ards. W h en we consider th e net radiation d istrib u tio n for the atm osphere (Figure 2.2b), we see th a t the values arc negative at all latitudes. In term s o f radiant energy, th e atm osphere is cooling at a rate equiva­ len t to about 0 .8 CC per day. T his radiational cooling is offset by the transfer o f energy from the E a rth ’s surface w hich experiences positive net radiation at practically all latitu d es (Figure 2.2b). T h is transfer is effected th ro u g h the c o n v e c tio n o f s e n s ib le h e a t °N

L a titu d e

°S

Figure 2.2 (a) Latitudinal averages of solar radiation (S) and longwave (terrestrial) radiation (T), and (b) latitudinal averages of net planetary radiation (Np) net radiation at the Earth’s surface (NR), and net radiation to the atmosphere (N a). Adapted from Mcllveen (1992) (see p. 32 note 13).

and th e release o f la te n t h e a t th ro u g h th e con­ densation o f w ater vapour w hich was evaporated from th e surface. G lobally, late n t heat transfer from th e surface to th e atm osphere is around four tim es m ore im p o rta n t th an th e convection o f sensible heat, alth o u g h th ere are large latitu d in a l variations. For exam ple, near the E quator sensible heat accounts for only around 5 per cent o f th e total vertical heat transfer from surface to atm osphere, and yet at

as we a tte m p t to explain th e atm ospheric processes

7 0°N it accounts for about o n c -h alf o f the total

w hich give th e Islands’ ‘n o rm al’ clim atc its essential character.

transfer.

A lth o u g h th e net radiation (th e difference betw een

In term s o f polew ards heat a d v e c tio n in the atm osphere, however, sensible heat transport is m ore

th e incom ing radiation and th e o u tg o in g radiation)

im p o rta n t than th a t o f latent heat. T h is indicates

for th e p lan e t as a w hole is zero, th is is not th e case at

th a t m ost w ater vapour re-condenses in th e atm os­

all latitu d e s; n e ith e r is it th e case for th e atm osphere

phere in m uch th e same latitu d in a l zone as it was

and th e E a rth ’s surface separately. For now, we shall

evaporated from the E arth ’s surface. M ore th an h a lf

ignore geographical variations, and only consider the

o f th e atm osphere’s sensible heat originates in the

radiation b u d g e t for the p lan e t averaged over all lines

global atm ospheric ‘e n g in e ’: the tropical rain belt

o f lo n g itu d e from 9 0°N to 90°S. T h is gives us a

(betw een around ()—10°N). Polew ards sensible heat

T R E V O R D A V IE S , P. M IC K KELLY A N D TIM O S B O R N

Figure 2.3 Two examples of infra-red satellite images o f the British Isles showing the contrast between (above) winter, 27 February 1986, when the cold land shows light against a warm sea, and (p. 15) summer, 16 May 1980, when the warm land shows dark against the colder sea. The land surface cools and warms much more rapidly than the ocean surface because o f its lower heat capacity. Images courtesy of the University of Dundee.

tran sfer e x h ib its a d o u b le m a x im u m in each h e m i­

T h u s far, we have considered ann u al energy d is tr i­

sp h ere; po lew ard s o f th e tro p ical ra in b e lt a t aro u n d

b u tio n s averaged over la titu d e . T h ere are im p o rta n t

2 0 °N a n d S, an d a g ain a t a ro u n d 5 0 -6 0 ° N a n d S in

seasonal and g e o g rap h ical v ariations. W e shall com e

response to c o n d e n sa tio n o f w a ter v ap o u r in th e m id -

back to these late r b u t, a t th is p o in t, som e im p o rta n t

la titu d e c yclonic sto rm b e lts. O cean c u rre n ts account

features w ill be in tro d u c ed . T h e sp e c ific h e a t c a p a c ­

for a ro u n d o n e -th ird o f th e po lew ard s sensible heat

ity o f land surfaces is m u c h less th a n th a t o f th e oceans

tra n s p o rt.

(F ig u re 2 .3 ), so th e a d ju s tm e n t tim e of th e oceans to

E X P L A IN IN G THE CLIMATE OF THE BRITISH ISLES

Figure 2.3 Continued

any changc in energy in p u t is g reater th an o f th e land.

is m uch sm aller than the range over land and reflects

M oreover, u n lik e th e land, the oceans can transport

the ocean circulations. T h e m oderating influence

heat, so s e a -s u rfa c e t e m p e r a t u r e s are not related in

o f the N o rth A tlan tic D rift stretch in g over to the

a sim ple way to the energy balance. Figure 2.4 , w hich

B ritish Isles, for exam ple, is m ost pronounced. T he

illu strates th e annual range in tem p eratu re a t the

greater ad ju stm e n t tim e o f the oceans m eans that

E a rth ’s surface, clearly reflects the large-scale land/sea d istrib u tio n . T h e annual tem p eratu re range in the

m axim um and m in im u m sea-surface tem peratures

in te rio r o f th e hig h n o rth ern c o n tin e n ts approaches,

sea around th e B ritish Isles is m ost pleasurable late in the sum m er.

or exceeds, 50°C. T h e sea-surface tem p eratu re range

lag th e solstices by around six weeks. B athing in the

TREVOR D AVIE S, P. M IC K KELLY A N D TIM O S B O R N

Figure 2.4 Average annual temperature range at the Earth’s surface (°C). The annual temperature range is the differ­ ence in mean surface air temperature between the warmest and coldest months. Adapted from Wallace and Hobbs (1977).

THE GENERAL CIRCULATION

concentrated over a relatively sm all area in vertically extensive convective cloud clusters. A zone o f rapidly m oving air, the subtropical jet stream , travelling

Early conceptualisations o f the general circulation of th e atm osphere took the energy im balance betw een

w est-to-east,

e q u ato r and pole as a sta rtin g p o in t. T hey th en

around 30°. T h is results from a need to conserve

focused on variants o f a single, large-scale th erm ally driven circu latio n cell in bo th hem ispheres - w ith a

a n g u la r m o m e n tu m as air moves from the E quator

is located

near th e tr o p o p a u s e

at

to regions closer to th e E arth's rotational axis. Ju s t

rising lim b in tropical latitu d e s, descent in h igher

beneath th e tropopause in m id -la titu d es is another

latitu d e s, and a re tu rn flow near th e surface - as

zone o f air m oving rapidly from w est-to-east - the

a m eans o f redressing th e im balance. Such a large convective cell, w ith one d im ension m uch m ore

polar front jet stream . T h is m id -la titu d e jet stream

extensive th an th e other, is n o t stable. Im proved

the vicinity o f th e p o la r f r o n t, a transitional zone

is a consequence o f the stro n g therm al g ra d ie n t in

observations, coupled w ith b e tte r u n d erstan d in g of

betw een the relatively cold tropospheric a ir m a sse s

th e w orkings o f a very th in atm ospheric skin on a ro ta tin g E arth, produced a latitu d in a l conceptual­

o f h igh latitudes and the relatively w arm a ir masses o f subtropical latitudes. T h e latitu d es w here the

isation

polar

w hich looks so m ething

like th e schem e

front

occurs

represent

an

area o f s la n t­

show n on the rig h t-h a n d side o f th e hem isphere in

w ise c o n v e c tio n , interleaves o f descending cold air

Figure 2.5.

m oving

In tropical latitu d es th ere is the so-called H adley C ell, nam ed after the e ig h te en th -ce n tu ry E nglish

m oving polew ards. These are th e latitudes o f travel­ ling cyclones and anticyclones, synoptic system s

scien tist, G eorge H adley. T he Ilad ley C ell can be view ed as a th erm ally d irec t cell, a lth o u g h m uch of

atm ospheric general c irculation, and

the upw ards energy tran sp o rt near the E quator is

the clim atc o f the B ritish Isles.

equatorw ards

and

ascending

w arm

air

w hich play a crucial p art in the m aintenance o f the in shaping

E X P L A I N I N G THE CLIM ATE O F THE BRITISH ISL ES

Figure 2.3 A latitudinal cross-scction of the general circulation of the atmosphere (at right-hand side). STJ and PFJ are the Sub Tropical and Polar Front Je t stream s em bedded in the broad zone ot westerly flow (see left-hand side). The tropopause (left-hand side) is the top of that part o f the atmosphere where weather systems occur, representing a lid’ on the troposphere, although there is some exchange with the stra to sp h ere above. A schematic of the airflow at the E arth’s surface is also shown, indicating that the Polar Front is heavily perturbed on a day-to-day basis, and that even in the broad band of westerlies, airflow' w ith an easterly component does occur. The surface easterlies in tropical latitudes arc the trade winds.

of

a b so lu te term s, th ey are ro ta tin g in a w est-to -east

ev ap o ra tio n a n d p re c ip ita tio n (F ig u re 2.6 ) confirm s

sense a t a rate w hich is slow er th an th a t o f th e E arth's

th e role o f th e tro p ic al H ad ley C ell an d th e m id ­

surface. In broad term s easterlies o ccur in th e la ti­

la titu d e cyclones, in b o th h e m isp h e res, in g lo b al

tu d e s o f th e low er lim b s o f th e tro p ical H a d ley C ells

a tm o sp h e ric energy tra n s p o rt. T h e su b tro p ica l dry

and in a narro w er la titu d in a l band o f th e ir u p p e r

T h e average an n u al

la titu d in a l d is trib u tio n

zones (w here ev ap o ra tio n is g re a te r th a n p re c ip ita ­

lim bs; an d re stric te d regions o f h ig h la titu d e s - see

tio n ) co rresp o n d w ith th e su b s id in g and eq u ato r-

F ig u re 2.5. O n th e o th e r h an d , o f course, th e w e st­

w ard m o v in g p a rts o f th e H a d ley C ell circu latio n s.

erlies arc ro ta tin g w e st-to -ea st a t a ra te w h ic h is

T hese p ro v id e a tm o sp h e ric m o istu re tra n s p o rt in to

faster th a n th a t o f th e E arth's surface. T h e d ra g o f

th e tro p ic a l ‘e n g in e ’, w here u p lift p ro d u ces c o n d e n ­

the E a rth ’s surface e x tracts a n g u la r m o m e n tu m from

sa tio n (rele asin g la te n t h e at) and p re c ip ita tio n . T h e

th e w esterlies. In o rd e r to keep b lo w in g , th ere m u st

re la tiv e ly w et m id -la titu d e s are th e zones o f h ig h

be a reliab le m ech an ism to in je c t a n g u la r m o m e n tu m

cyclone frequency, w here fro n tal u p lift leads to co n ­

in to th e w esterlies from th e easterlies, w h ich have

d e n sa tio n o f w a ter v a p o u r e vaporated from th e ocean

a n g u la r m o m e n tu m fed in to th e m from th e E a rth ’s

surfaces.

surface.

T h e E arth ro ta te s w e st-to -e a st a n d , because th e

In tro p ical la titu d e s, th e H a d ley C ell plays an

a tm o sp h e re c lin g s to th e E a rth , it ro ta te s w ith it.

im p o rta n t role in th is polew ard a n g u la r m o m e n ­

W h e n view ed from th e E a r th s surface, how ever,

tu m tra n s p o rt. In m id -la titu d e s , how ever, it is th e

som e w in d s travel from e ast-to -w e st (i.e., th ey are

cyclones, an d th e w aves in th e w esterlies associated

e asterly re la tiv e to an o b serv er a t th e surface). In

w ith th e m , w hich p lay th e im p o rta n t role in th e

TREV O R D AV IES, P. M IC K KELLY A N D TIM O S B O R N

result in som e differences. In th e N o rth e rn H e m i­ sphere, the subtropical jet stream and th e polar front jet stream

represent th e zones o f strongest flow

w ith in the broad band o f m id -la titu d e westerlies. T he w esterlies arc m ore vigorous and extensive in w inter; th eir k inetic energy (th at energy due to m otion) is three tim es greater in w in ter th an in sum m er. T he flow in the u pper w esterlies can be p articularly stro n g , w ith w ind speeds up to 140 m s"1 near the to p o f the tr o p o s p h e r e . T his represents a jet stream in the stric t sense o f the term w hich says th a t jet stream s should be characterised by w ind speeds o f 30 m s-1 or above. T h e term is also used m ore loosely to describe the locally stronger flow of the subtropical and polar front jet stream s. A p ro m in en t feature o f the w esterlies is th eir w ave-like form . T he wave p a tte rn is m ore notice­ able, and sim pler, away from th e surface. T h e 500 Latitude

Figure 2.6 The average latitudinal distribution of precip­ itation (P) and evaporation (E) in mm per year.

h P a p r e s s u r e lev el (at a h e ig h t o f around 5.5 km at the latitu d e of the B ritish Isles) is com m only used to describe the free atm osphere w esterlies, alth o u g h w ind speeds are g reater at h ig h er levels. O n a dayto-day basis the flow can be very com plex, b u t if the flow is averaged over a few days there tends to be

polew ard tran sp o rt o f a n g u la r m o m en tu m . T hey accom plish th is by exchanging air w ith a stronger

five waves in th e w esterlies encircling the N o rth e rn

w esterly c om ponent (m oving polew ards) w ith air

called planetary waves. If the averaging period is

H em isphere. W aves w ith this sort o f w avelength are

w ith a w eaker w esterly com ponent (equatorw ards).

increased to seasonal tim e-scalcs, then th e further

I t has been calculated th a t five sim ultaneous well-

sm oothing produces th ree waves in the N o rth e rn

developed m id -la titu d e cyclones can provide all the necessary a n g u la r m o m e n tu m tran sp o rt required in

H em isphere w inter and four in th e sum m er (Figure

w inter. Since sim ilar calculations lead to sim ilar conclusions a bout polew ard heat tran sp o rt, it is clear

w esterly p a tte rn occurs relatively a b ru p tly around

th a t th e m id -la titu d e cyclone b e lt is a crucial feature o f th e general c ircu latio n o f th e atm osphere. Since

2.7). T h e changeover from th e w in ter to sum m er Ju n e

and

back again, equally abruptly, around

O ctober (see C hapter 8). T here is a general relation­ ship betw een westerly vigour and the n u m b er o f

B ritish Isles, it is a p propriate th a t we exam ine

planetary waves, even over shorter periods. T he stronger the w esterly (or zonal) flow, th e sm aller the

th e m id -la titu d e w esterlies a little m ore closcly.

nu m b er of planetary waves.

it also d eterm ines th e character o f the clim atc o f the

In reality, the planetary waves d rift slowly east­

The westerlies

w ards, b u t statistical sm oothing h ig h lig h ts the m ajor regions o f occurrence. T h e m ain planetary wave

In th e follow ing discussion, we shall focus on the

tr o u g h s are situ ated over eastern N o rth A m erica

N o rth e rn H em isphere. M uch is also p e rtin e n t to th e S outhern H em isphere, alth o u g h th e con trastin g

and over the east coast of Asia. These troughs are especially pronounced in w inter. A w eaker planetary

land and sea d istrib u tio n s of th e tw o hem ispheres do

wave tro u g h is located over E urope, betw een about

E X P L A IN IN G THE CLIMATE OF THE BRITISH ISLES

Figure 2.1 Average height (tens of metres) of the 500 hPa surface in January (left) and July (right). The mid-latitude westerlies blow' parallel to the contours - the closer the contour spacing the stronger the wind. Dashed hold lines indi­ cate the average position of ridges, continuous bold lines the position of troughs.

10 -6 0 °E . T h e position and stre n g th o f th is European

crest (rid g e ) is located to th e w est o f th e E uropean

tro u g h are m uch m ore variable than are those o f the

tro u g h , w ith a position som ew here betw een 10°E and

N o rth A m erican and East Asian troug hs, w hich have

30°W. T his ridge is less discernible in sum m er.

m ore anchored positions. T h e European tro u g h is very sensitive to changes in the w esterly circulation. T h is

m uch to the continental d istrib u tio n s o f land masses

is an im p o rta n t characteristic for th e European and

and to th e presence o f m ajor m ou n tain ranges.

T he preferred positions o f th e planetary waves owe

B ritish clim ate since, as we shall see later, th e overly­

E xperim ents using dishpans to m odel the E a rth -

in g w esterly waves exert a strong control on surface w earher p attern s. It is o f som e in terest th a t th e aver­

atm osphere system have replicated som e o f th e m ajor features o f the general circulation w ith o u t an u n d e r­

age p o sitio n o f th e E uropean tro u g h axis, w hen averaged by decade, has varied by as m uch as 20°

lying topography (see Box 2.1). T he nature o f the u nderlying surface, however, strongly conditions

lo n g itu d e over the last 2 0 0 years. A planetary wave

th e location and character o f th e planetary waves.

BOX 2.1 DISHPAN EXPERIMENTS

representing th e ’e q u ato r’ and th e centre the ‘pole’) and th e d ishpan is rotated. T h e resulting

D ishpans are physical m odels o f th e E a rth -atm o s-

circulation o f th e fluid reproduces m any features

phere system , so nam ed because th e E arth is m o d ­

observed in th e atm osphere, inclu d in g th e w est­

elled by a d ishpan and th e atm osph ere is m odelled

erly planetary waves (as well as circulations w hich

by a fluid contained

A tem perature

resem ble cyclones and anticyclones). T h e dishpan

g ra d ie n t is applied across the d ishpan (th e outside

m odels do not have th e equivalent o f m ou n tain

therein.

T REVOR D AVIE S, P. M ICK KELLY A N D TIM O S B O R N

ranges or land masses, so the planetary waves and

analogous to observed behaviour in the atm os­

other circulation features form as a consequence o f a pole-equator temperature gradient impressed on

phere. Some dishpan experiments exhibit sem i-

a rotating fluid system , irrespective o f the under­

and am plitude. The real atmosphere also tends to

lying

demonstrate this type o f behaviour; the so-called (Zonal) Index Cycle which, typically, spans several

topography.

Nevertheless,

in

the

real

Earth-atmosphere system , it is obvious that the

regular fluctuations in the westerly wavelength

location and precise character o f the planetary

weeks. O ne extreme is strong westerly flow (high

waves are strongly conditioned by the nature o f

Zonal Index) w ith small am plitude waves; the

the underlying surface. Before we return to the real atmosphere, it is worth pointing out another

other extreme is weaker westerly flow with large am plitude waves producing more north-to-south

aspect o f dishpan circulation behaviour that is

and south-to-north (meridional) flow.

An im p o rta n t property o f atm ospheric circulations

o f the

is v o rtic ity , w hich is a m easure o f sp in w ith in a

E a rth ’s surface (th e

E arth

is

‘sp in n in g ’

and therefore has vorticity). T he local value o f

fluid. If we assum e th a t an airstream , flowing w est-

th e vorticity o f th e E a rth ’s surface is know n as the

to-east, is approaching a large m o u n ta in barrier, such

C o rio lis p a r a m e te r (nam ed after G ustave-G aspard

as th e N o rth A m erican Rockies, th en as it is forced

Coriolis, see C hapter 14) and is proportional to the

to rise over the m o u n ta in range and since the

sine of the latitu d e. It is therefore at a m in im u m at

tropopause acts as a sort o f ‘lid ’, it becom es v e rti­ cally squeezed as it passes over the peaks. M eteor­

th e E quator and a m ax im u m a t the poles. T h e largescale w esterly m otion dow nstream o f the N o rth

ology textbooks show m athem atically th a t there are

A m erican tro u g h has a polew ard com ponent; hence

im p o rta n t lin k s betw een vertical squeezing (and

th e C oriolis p aram eter is increasing. To m aintain

stre tc h in g ) and vorticity. In o u r case, it leads to a

absolute vorticity, th e atm ospheric vorticity m ust

decrease in th e vo rticity o f th e airstream w hich in

decrease. T h e airstream starts to take on increasing anticyclonic curvature, eventually tu rn in g th ro u g h a

th e N o rth e rn H em isphere represents a clockwise tu rn in g - anticyclonic curvature. As it passes over th e m o u n ta in barrier, therefore, th e air starts to tu rn

ridge, and so eventually tak in g on an equatorw ard com ponent. N ow the C oriolis param eter is decreas­

equatorw ards. As th e air flows beyond th e m ountain

ing and absolute vorticity m u st be conserved by the

barrier, however, it is allow ed to stretch vertically. T h is now leads to an increase in vorticity, w hich

atm osphere ad o p tin g m ore cyclonic curvature. T h is dow nstream oscillation w ould co ntinue indefinitely

in th e N o rth e rn H em isphere leads to anticlock­

in the absence o f any oth er factors and explains the

wise tu rn in g - cyclonic curvature. T h e result is a

p oin t m ade above th a t th e N o rth A m erican tro u g h

(cyclonic) tro u g h in the w esterlies in th e lee o f the

largely controls th e

m ountains. T h is explains th e anchoring o f a p ro n ­

tro u g h . In reality, o th er factors do com e in to play

behaviour o f th e European

ounced wave tro u g h in the w esterlies over eastern

and the character o f dow nstream waves is influenced

N o rth A m erica (Figure 2.7).

by, for exam ple, surface tem p eratu re p atterns.

O nce such a large-scale wave has been in itiate d , there are good reasons why a wave form should be m ain tain ed dow nstream . In large-scale m o tio n , at

Cyclone waves in the westerlies

is a need to conserve absolute vorticity. T h is is the

O n a day-to-day basis, th e sm oothed planetary wave p a tte rn is obscured by th e supcrim position o f sm aller

sum o f atm ospheric vorticity and th e local vorticity

wavy pertu rb atio n s w hich appear, grow and decay

m id -tro p o sp h ere levels (around 5 0 0 -6 0 0 hPa), there

E X P L A I N I N G THE C LIM ATE O F THE BRITISH ISLES

Figure 2.8 Schematic representation of the development of a cyclone wave. The heavier lines represent the flow at upper levels, with the heaviest line showing the most rapidly moving air. The frontal depression at the surface is denoted by the warm (semi-circles) and cold (triangles) fronts and by the lightest lines which represent the surface isobars (lines of constant atm ospheric pressure). Adapted from Mcliveen (1992) (see p. 32 N ote 13).

over a few days. T hese w aves are th e re su lt o f in ­

conversion o f p o te n tia l energy (d e p e n d e n t on th e

sta b ilitie s in th e sm o o th , p lan e tary flow an d th ey

relativ e p o sitio n s o f w arm an d cold air) to k in e tic

g e n era lly p ro p a g a te ra p id ly eastw ards, a p p are n tly

energy m o re effective th a n th e very shallow slope ol

steered by th e flow in th e p la n e ta ry waves, a t a rate

th e exchange m ig h t su g g est. As far as energy conver­

o f a b o u t 1 0 -1 2 ° lo n g itu d e p e r day. Typically, th e ir

sion is c oncerned, w h at is h a p p e n in g is convection

a m p litu d e increases by a factor o f tw o to th ree over

(a lth o u g h we g en erally u n d e rsta n d co n v ec tio n to be

a co u p le o f days. T h e ir w a v e le n g th is o f th e o rd e r o f

a process w h ich involves g re a te r vertical exchange);

3 - 6 ,0 0 0 k m ; so rhe n u m b e r o f w aves aro u n d the

hence th e te rm ‘slantw ise c o n v ec tio n ’. T h e cyclone

h e m isp h e re is b e tw ee n 6 and 10. T hese u n sta b le

waves pass k in e tic energy in to th e w esterly w ind

p e rtu rb a tio n s are k n o w n as b a r o e l in i c w a v e s , or

b e lt, p lay in g th e cru cial role in th e m ain ten a n ce o f

cyclone waves. O n e o f th e m o st im p o rta n t d e sta b il­

th e g eneral c irc u la tio n w hich has been m e n tio n e d

isin g

factors

m ark e d

resp o n sib le

increase o f w in d

for these speed

w aves is the

w ith

h e ig h t

before. Early n o tio n s o f th e m id -la titu d e cyclones

in

w ere th a t they were ak in to tu rb u le n t ed d ies, w hich

th e p o la r fro n t jet stre am zone. T h is , c o m b in e d w ith

arc m a in ta in e d by th e energy o f th e m ean flow. T h e

th e stro n g h o rizo n tal te m p e ra tu re g ra d ie n ts co n cen ­

o p p o site is in fact th e case.

tra te d in to th is zone, p ro d u ces th e so rt o f in sta b ility w h ic h leads to cyclone w ave d e v elo p m en t.

F ro n ta l depressions o ften form in fam ilies. F ig u re 2 .9 is an idealised p ic tu re o f four p lan e tary w aves in

F ig u re 2 .8 show s th e d e v elo p m en t of a cyclone

the 5 0 0 hP a flow an d associated fro n tal depressions

w ave a t th e level o f th e p o lar fro n t jet stre am and

(or cyclone waves). Four fam ilies o f fro n tal d e p re s­

its associated fro n tal dep ressio n a t th e E arth s surface.

sions are show n w ith new depressions fo rm in g on

In o rd e r for these cyclone w aves to grow , rhe k in e tic

the tra ilin g cold fro n t o f the ‘p a r e n t’, o r o c c lu d in g ,

en erg y o f th e w ave m u st increase. T h e k in e tic energy

depression. T h e depression fam ilies are seen to lie on

is m ad e available by w arm a ir risin g a n d cold air

th e p o lew ard -m o v in g lim b s o f th e p lan e tary waves,

sin k in g . T h e u p s lid in g o f w arm air, e x ch a n g in g w ith

d o w n stre am o f the tro u g h s. T h e reason for th is is as

th e d o w n s lid in g o f cold a ir across th e p o la r fro n t

follow s.

zone, takes place a lo n g a slope o f only aro u n d 1°.

T h e p lan e tary wave tro u g h s have cyclonic c u r­

T h e h o riz o n ta l an d v ertical te m p e ra tu re g ra d ie n ts in

v a tu re a n d th e p lan e tary w ave ridges an ticy clo n ic

th is zone are su c h , how ever, th a t th e y m ak e th e

c u rv a tu re . F or reasons w e w ill nor ex p lain here, th is

T R E V O R D A V IE S , P. M IC K KELLY A N D TIM O S B O R N

Figure 2.9 Four idealised planetary waves, showing how the formation of families o f frontal depressions is favoured under the poleward-moving lim b of the waves (see text and Figure 2.10). In the real atmosphere on a day-to-day basis, the westerly wave pattern is more complex than this. The isolines represent heights of the 500 hPa pressure surface.

has th e effect o f h o rizo n tally stre tc h in g volum es o f

and

a ir p a ssin g th ro u g h th e p o le w a rd -m o v in g lim b o f the

co m p en sato ry p a tte rn s o f convergence an d d ivergence

upper

squ eezin g

(c o n v e rg e n c e )

pro duces

p lan e tary w aves a t u p p e r levels, w hereas th e effect

near th e surface (F ig u re 2 .1 0 ). T h e surfacc co n v er­

is one o f h o riz o n ta l squ eezin g on th e e q u ato rw a rd -

gence leads to an increase in cyclonic v o rticity , and

m o v in g lim b . T h is u p p e r s tre tc h in g (d iv e rg e n c e )

th e surface div erg en ce leads to an increase in a n ti-

E X P L A I N I N G THE C LIM ATE O F THE BRITISH ISL ES

Figure 2.10 Convergence at upper levels in rhe equatorward-moving lim b of a planetary wave is compensated by diver­ gence closer to the E arths surface. U nder the poleward-moving lim b, the upper divergence is compensated by surface convergence.

cyclonic v o rtic ity . C on seq u en tly , cyclone d e v elo p ­

th e p o lew ard -m o v in g lim b o f th e p lan e tary wave

m e n t is en co u rag ed d o w n stre am o f a p lan e tary wave

anchored over N o rth A m erica (and, hence, u p p e r

tro u g h , an d is in h ib ite d u p stre am o f th e tro u g h ,

divergence) over one o f th e stro n g e st fro n tal zones

w h ere a n tic y clo n e d e v e lo p m e n t is m o re favoured.

in th e N o rth e rn H e m isp h ere favours th e d ev elo p ­

'I'he u p p e r flow p a tte rn is, th erefo re, seen to be an

m e n t o f cyclonic waves. T hese are th e n steered by

im p o rta n t c o n tro l on th e d e v e lo p m e n t o f cyclones

th e

an d tra v e llin g an ticyclones.

Iceland an d n o rth ern Scandinavia. T h is depression

u p p e r flow, g ro w in g as th ey m ove tow ards

F rom o u r discussion it is p ro b a b ly q u ite easy to

trac k is m u ch w eaker in su m m e r and ten d s to tak e

g e t th e im p re ssio n th a t th e p o lar fro n t is a c o n tin ­

a m ore n o rth erly course over th e eastern N o r th

uous b an d sn a k in g ro u n d th e h e m isp h e re, c o in c id in g

A tlan tic. S o m e th in g

w ith th e p a th o f th e p o lar fro n t jet stream (a lth o u g h

follow th is trac k , a lth o u g h th ere are sig n ific a n t v ari­

like

170 d epressions a year

F ig u re s 2.5 an d 2 .9 have in d ic a te d th a t th is is a

a tio n s from year to year an d from decade to decade.

m isle a d in g sim p lic ity ). In reality, th e g e o g rap h y o f

T h ere are also v a ria tio n s in th e typ ical depression

th e E a rth ’s surfacc, in c lu d in g th e influence o f ocean

track s, d e p e n d in g on, a m o n g st o th e r factors, v aria­

c u rre n ts, favours c erta in zones o f ‘f r o n to g e n e s is '.

tio n s in th e w e ste rly wave p a tte rn . Som e o f these

O n e su ch

v a ria tio n s w ill be discussed below.

zone stre tc h es

from

th e so u th -e aste rn

U n ite d S tates, across th e N o rth A tla n tic , to w ard s th e

W e have sp e n t som e tim e discu ssin g th e w e ste r­

B ritish Isles. It is w eaker, an d less tilte d , in su m m e r

lies an d cyclonic waves and th e ir role in th e g eneral

c o m p a red to w in te r (in p a rticu la r, its easte rn en d

c irc u la tio n o f th e a tm o sp h e re. W e have c o n ce n tra ted

sh ifts n o rth w a rd s). T h e zone o ff N o rth A m erica is

on th e area o f th e N o r th A tla n tic , a lth o u g h th ere are

th e stro n g e st p a rt o f th e N o r th A tla n tic Polar F ront.

o th e r reg io n s, in b o th h e m isp h e res, o f im p o rta n t

In

te m p e ra tu re c o n tra st

fro n to g en esis an d cyclone w ave d ev elo p m en t. W e

b e tw ee n a lan d m ass w ith an e xtensive snow cover

w ill re tu rn to som e features o f th e g lobal-scale c irc u ­

and

latio n later, b u t th e reason for th e p re sen t em p h asis

w in te r w arm

th ere

is a large

offshore c u rre n ts. T h e p o sitio n in g o f

T REVOR D AVIE S, P. M IC K KELLY A N D TIM O S B O R N

is th a t th e trav ellin g cyclones, and th eir intervening

lo n g itu d in al band, there is a tendency for the large-

h ig h pressure ridges, create th e essential character o f

scale a m p litu d e p a tte rn to spread th ro u g h o u t the

th e B ritish w eather. Seasonal fluctuations in th eir

m id -la titu d es w ith in days. A chain of four positive

behaviour control m uch o f th e regional-scale clim ate,

and four negative pressure anom alies en circling the

and lo n g -term variations in behaviour - responding

globe is a com m on p a tte rn . W h en the positive anom ­

to som e o th er feature o f the circu latio n o f the atm o s­

alies becom e w ell-established and

phere and oceans — can help explain m uch o f the

stationary, they are know n as ‘blocks’. T h e longitudes

observed longer-term fluctuations in the clim ate o f th e B ritish Isles.

o f the planetary wave ridges at 150°W and 15°W

W e do not in te n d to describe in detail th e p a rtic ­ ular p a tte rn o f w eather associated w ith frontal

coastline, see Figure 2.7) are particularly favoured for

depressions. M ost readers w ill be fam iliar w ith the p re cip ita tio n bands and tem p e ra tu re changes associ­

W h en th e m id -la titu d e flow is zonal (high Zonal Index), th e vigorous w esterly flow over extensive

ated w ith th e passage of th e w a r m and c o ld fr o n ts

regions m eans th a t fast-developing cyclonic waves

in a frontal depression, w hich can sw ing over the

move quickly eastw ards. W h en th e flow is m erid ­ ional (low Zonal Index), then the developm ent

B ritish Isles even w hen th e depression centre is passing far to th e n o rth . T h e m o b ility and precise

rem ain quasi-

(the latter position being off th e west E uropean the developm ent o f blocks.

p ath o f a p a rticu la r system are im p o rta n t character­

and passage of th e cyclonic waves is ‘blocked’ over extensive regions. B lo c k in g is m ost com m on in

istics for daily w eather. T h e severe w indstorm s w hich

spring/early sum m er, alth o u g h it can occur a t any

afflicted W estern Europe in th e early 1990s are a

tim e o f year. A typical position for a block to be

g ra p h ic exam ple (sec C h ap tcr 11). T h e passage o f the

centred is a bout 15°W. In line w ith the seasonal

in terv en in g hig h pressure ridge, w ith its different w eather (w eaker w inds, clearer skies, cool w inter

shifts in th e planetary wave p a tte rn , however, there

n ig h ts, etc.; a lth o u g h h ig h pressure can also produce

axis to m ove from east o f the B ritish Isles in w inter

p ersisten tly cloudy skies in w inter) generally p ro ­

to th e west o f Ireland in May, and co ntinue o u t into

is a tendency for the preferred position o f the block

vides a clear contrast to th eir fellow travelling

th e A tlan tic to its m ost w esterly position in sum m er,

depressions. Together, they can produce a character­

w hcnce it starts its slow progress eastw ards again.

istic 2 - 3 day sequence o f w eather - a lth o u g h this

T h e hig h

sequence is regularly distu rb ed .

sum m er when averaged over 100 years is q u ite p ro ­

Blocking W h en we were discussing the w esterlies, we noted th at the wave p a tte rn e xhibits fluctuations in wave­

frequency o f blocking in spring/early

nounced. T h is com m on spring/early su m m er block allows m ore airflow from th e n o rth , so u th and cast, at the expense o f westerly, progressive, conditions. By the end o f Ju n e , w ith the block declin in g or sta rtin g to sh ift eastw ards, m ore w esterly flow has

len g th and a m p litu d e . T h is characteristic is know n

been resum ed w ith generally m ore precipitation.

as th e Index C ycle.3 T h e term is derived from the

Some clim atologists have described th is late Ju n e

param eter, th e Z onal Index, w hich is a m easure o f

period

the stre n g th o f th e m id d le -la titu d e w esterly winds.

C hapter 8 fu rth er discusses th is characteristic o f the

A t low values o f th e Z onal Index, th e westerly

as

h eralding

th e

‘E u ro p e a n

M o n s o o n ’.

annual cycle of w eather over th e B ritish Isles.

flow is weak and the wrave p a tte rn becom es so exag­

F luctuations in the Z onal Index, and the associated

g erated th a t there are large areas o f hig h er-th an average and low er-than-average atm ospheric pressure

hem ispheric-scale ad ju stm e n ts to the m id -la titu d e flow, operate on a tim e-scale such th a t a particu lar

(positive and negative pressure anom alies, respec­

re g io n s w eather over significant parts o f whole

tively) encircling m id -la titu d es. O nce the wave p a tte rn starts to becom e strongly p e rtu rb e d in one

seasons may be strongly influenced by th em . T h at being so, a t least p art o f th e year-to-year variations

E X P L A I N I N G THE CLIM ATE O F THE BRITISH ISL ES

(a) Mean pressure (hPa): Summer (1961-90)

(b) Mean pressure (hPa): Winter (1961-90)

Figure 2.11 Average mean sea-level pressure (hPa) for the N orthern Hemisphere (1961-90), sum m er (a) and winter (b). N ote rhe changc in contour interval between the seasons. Pressure gradients are stronger in winter and, as a result, the atmospheric circulation is more vigorous.

w h ic h are such a stro n g featu re o f s h o rt-te rm c lim a tic

H ig h and is an e x te n sio n o f th e p e rm a n e n t s u b ­

v a ria tio n s can be e x p la in ed by th e ‘In d ex C ycle’.

tro p ical h ig h pressure over th e A tlan tic. T h is is m atch ed by a n o th e r over th e Pacific an d w hich are broad zones o f su b sid in g a ir reflecting d escen t in the

SURFACE PRESSURE PATTERNS

H a d ley C ell (F ig u re 2.5). T h e Icelandic I-ow is really a sta tistic a l m an ifestatio n o f th e passage o f trav e l­

A verage surface airflow is parallel to th e isobars an d

lin g cyclones over th is p a rt o f th e A tlan tic. T h e

its v ig o u r is p ro p o rtio n a l to th e pressure g ra d ie n t —

e astern p a rt o f E u ro p e is influenced by th e w estern

th e tig h te r th e isobars, th e stro n g e r th e flow. T h e

e x tre m ity o f th e S iberian H ig h in w in te r; th is is a

m o st n o tic e ab le d ifference b e tw ee n

shallow h ig h pressure caused by rad iatio n al co o lin g

th e

m aps o f the

o f th e E urasian land m ass. D u rin g periods o f low

N o r th e rn H e m is p h e re (F ig u re 2 .1 1 ) is th e replace­

Z onal Index, th ere can be outflow s o f very cold air

m e n t o f w in te r h ig h p re ssu re by su m m e r low p re s­

from th e Siberian H ig h w hich lead to cold w eath er

su re over E urasia. T h is pro d u ces th e very p ro n o u n c ed

over th e B ritish Isles. In su m m er, th e h ig h pressure

seasonal reversal o f flow w h ic h is th e so u th -e ast A sian

is replaced by low pressure, caused by h e a tin g o f th e

sum m er

an d

w in te r

surface

pressure

over

M onsoon. As far as th e m o st im m e d ia te features o f

E urasian land m ass. T h e surface pressure p a tte rn s

relevance for th e B ritish Isles are c o n ce rn ed , the

confirm w h at w e already know ; w in te r flow over th e

d o m in a n t c en tres o f a ctio n are th e area o f low p res­

A tla n tic and in to th e B ritish Isles is m u ch stro n g e r

sure n ear Iceland (th e Icelandic Low), m o st m arked

th a n su m m e r flow. T h e su m m e r re d u c tio n in th e

in w in ter, an d h ig h p re ssu re to th e w est o f S pain,

Icelandic Low reflects th e declin e in cyclone v ig o u r

w h ic h e x te n d s over w e ste rn E u ro p e in su m m e r as th e

and th e n o rth w a rd s expansion o f th e A zores H ig h

Icelan d ic Low m ig ra te s w estw ards. T h e h ig h p ressu re area is k n o w n as th e A zores

reflects th e ten d e n cy o f all c o m p o n e n ts o f th e g lo b al c lim a te to ‘follow th e S u n ’.

T REVOR D AV IES, P. M IC K KELLY A N D TIM O S B O R N

Since th e tw o centres o f action —th e Icelandic Low

A tlan tic European sector. As we indicated earlier,

and th e Azores H ig h — d o m in a te th e p a tte rn of

periods o f weeks or, occasionally w hole seasons, can

surface pressure over th e eastern A tlan tic, a useful

be d o m in ated by such conditions (see Box 2.2).

index to describe cond itio n s u pw ind o f th e B ritish Isles is th e difference in pressure betw een th e Azores region and over Iceland. T h is is, in effect, a ‘local’

LINKS WITH THE OCEAN

Z onal Index. Besides d escribing p art o f th e annual variation in surface pressure over th e A tlan tic, th is

V ariations in th e N A O have been linked to sea-

A zores/Iceland

characterises

surface tem p eratu re (SST) changes in th e N o rth

changes in th e stre n g th s and positions o f th e Icelandic-

A tlantic. From year to year, th e SST p attern s are

Low and the Azores H ig h . T h e behaviour w hich the index characterises is know n as th e N o r th A tla n tic

probably caused (or forced) by th e atm ospheric circu­ lation, w ith the surface w ind influencing th e occan

O s c illa tio n

is th e link

circulation and hence the d istrib u tio n o f SST anom ­

betw een the tw o centres o f action - w hen th e Azores H ig h is m ore intense (higher pressure), th e Icelandic

alies. T h e p ictu re is not clear, however, and there is evidence th a t SST patterns in th e w estern part o f the

Low also tends to be m ore intense (lower pressure).

N o rth A tlan tic influence the B ritish w eather on

T h is N A O signal, w hen averaged over several years, is present for all seasons, a lth o u g h it changes its

tim e-scales o f m onths.'1 W arm SST anom alies in this p art o f the ocean tend to precede a greater incidence

precise character w ith th e seasons. T h e N A O is an im p o rta n t com ponent o f th e interan n u al variability

o f cyclonic circulations over the B ritish Isles in the follow ing m onths, whereas a cold SST anom aly is

o f th e w hole N o rth e rn H em isphere circulation. It w ill com e as no surprise th at there are links

cyclonic in character.

pressure

(N A O ).

index

also

T h e oscillation

frequently followed by m o nths w hich are m ore a n ti­

betw een the behaviour o f the N A O index and the

T he precise lin k in g m echanism betw een th e ocean

w eather experienced over th e B ritish Isles d u rin g a

and the atm osphere appears to be related to th e shift

p a rticu la r year (sec C haptcr 9 for its relationship w ith

in the position o f the m axim um surface tem perature

tem perature). C hangcs in the circulation p attern s

g ra d ie n t, affecting the form ation and p a th o f cyclone

over th e A tlan tic are associated w ith shifts in storm

waves. O ver tim e-scales o f several years to decades,

tracks - hig h values o f the N A O index p u sh storm s

alth o u g h tw o-w ay interactions betw een the atm o s­

fu rth er

phere and ocean still operate, there are indications

in to

N o rth e rn

E urope,

accom panied

by

h ig h er tem p eratu res th an usual. S tronger A tlan tic

th a t th e SST anom alies (this tim e over a larger area

w esterlies

o f the N o rth A tlan tic Ocean) are playing an im p o r­ ta n t role in forcing the circulation o f th e overlying

increase

th e

atm ospheric

tran sp o rt of

m o istu re in to no rth ern E urope. T h is leads to heavier p re cip ita tio n over rhe n orthern h a lf of rhe B ritish Isles, a lth o u g h indications are th a t p re cip ita tio n m ay

atm osphere, and in influencing rhe clim ate of Europe. F igure 2.12 shows th a t SSTs over th e N o rth

be reduced over th e southern half. So, even th o u g h

A tlantic were relatively low up to the 1920s, higher

th e initial control is th e N o rth A tlan tic large-scale c irculation, we still have to consider th e sub-regional

up to the 1960s, then lower thereafter. T here are indications th a t th e high SSTs in the 1940s and

scale response. T h is reflects th e sim ilarity o f scale

1950s were associated w ith th e production o f m ore

betw een th e B ritish Isles and th e synoptic system s

cyclones over the m id -N o rth A tlan tic O cean at

w hich produce th e Islands’ day-to-day weather.

around 45°N . T here are also som e hin ts o f links

O n occasions th e N A O index is negative; th a t

betw een th e SST anom alies and the frequency of

is, th e norm al so u th -to -n o rth pressure g ra d ie n t is

different types o f circulation over the B ritish Isles.

reversed. T h is is an extrem e circulation m ode, reflecting a stro n g p a tte rn o f blocking and leads to

R obert R atcliffe and Roy M urray am ongst o th ers5 have em phasised, however, th a t it is likely to be

flow w ith an easterly com p o n en t over th e N o rth

th e precise p a tte rn o f SSTs w hich is im p o rta n t for

E X P L A IN IN G THE CLIMATE OF THE BRITISH ISLES

BOX 2.2 BLOCKING AND EXTREME SEASONAL WEATHER

than usual, over th e southern h alf o f th e B ritish Isles, p roducing m uch snowfall (snow fell som e­ w here over th e B ritish

Isles every day from

O n e o f th e lowest values o f th e N A O index

22 January to 17 M arch in 1947). In th is case,

occurred in 1963. T h is w in ter (January to M arch) was one o f th e coldest in th e last 2 5 0 years in the

source for a d eep-w hite w inter, whereas the

B ritish Isles, w hen th e tem p eratu re in parts o f E ngland d id not rise above 0°C for th ree m onths,

extrem ely cold 1963 w in ter was relatively defi­ cient in snowfall because o f th e easterly flow from

the A tlantic depressions provided th e m oisture

because o f th e p ersistent easterly flow from the

the dry European m ainland. So, alth o u g h the

cold E uropean m ainland. T h e first three m onths

p rim e control on the B ritish clim ate com es from

o f 1996 w ere also ra th e r cold, as a result o f blo ck in g h ighs in th e Scandinavia to east N o rth

th e atm ospheric circulation over th e A tlan tic, and p art o f this control can be represented by sim ple

A tlan tic region, leading to persisten t easterly or

indices such as th e N A O index, we need to

northerly flow over th e B ritish Isles. T his recent

rem em ber th a t the precise configuration o f anom ­

cold w in ter was a tim e ly rem in d er to a public,

alous circulations is im p o rtan t.

w hich had been fed an oversim plified d ie t o f

Blocks can also produce anom alously hot or

g lobal w arm in g by m any p arts o f th e m edia, th at

dry sum m ers. T he prolonged d ro u g h t o f 1 9 7 5 -6

in teran n u al v ariability is still a strong character­ istic o f th e B ritish Isles clim ate. U nd erstan d in g

(one o f th e driest 18 m o n th periods on record over E ngland and W ales, see C h ap ter 10) resulted

th e regional response o f c lim ate to th e enhanced

from blocking sum m er h ighs over, or close to,

g reenhouse effect d em an d s rather m ore so p h isti­

th e B ritish Isles. T h e clear settled conditions

cated consideration (see C h a p te r 15). T h e 1963 block was centred over Iceland.

resulted

in h igh

tem peratures and

the

rain-

bearing depressions were steered to th e no rth and

Blocks do n o t have to occur over th e A tlan tic to

to th e south, around th e blocks. Persistent high

have a d o m in a tin g control on th e B ritish w eather

pressure also dom in ated in the very hot sum m er

over a season. A n o th er extrem e w inter, in 1947, was caused by a b locking hig h over Scandinavia.

o f 1995; a particularly pronounced ridge in the w esterlies occupied a position w hich stretched

T h is was less noticeable in the N A O index, b u t had th e effect o f steering depressions fu rth er south

from th e B ritish Isles to as far east as 25°E (cf.

th e B ritish clim ate, in p a rticu la r th e positio n /o rien ­

Figure 2.7).

ated w irh strong w esterly w inds and a period when

ta tio n o f th e zone o f m axim um SST g ra d ie n t across

ice was a relatively infrequent visitor to Iceland.

th e N o rth A tlan tic.

These relationships arise because, on this geo g rap h ­

SST p a tte rn s in parrs o f th e N o rth A tlan tic are in tim ate ly linked w ith sea-ice d istrib u tio n s and there are clearly established relationships betw een sea-ice e x te n t around Iceland and th e European clim ate.6

ical scale, th e atm ospheric circulation is th e prim ary cause o f the fluctuations in ice and clim ate condi­ tions. Locally, however, th e advance and retreat o f

Periods o f extensive n ortherly w inds over th e n o rth ­

the ice edge is associated w ith a m arked change in surface h eatin g and albedo and can exert a strong

east A tlan tic and w estern Europe, for exam ple, brin g

influence on the overlying atm osphere.

cooling to th e c ontinental landm ass and ice to the shores o f Iceland. T h e w arm th o f th e 1920s and

th e atm osphere over the N o rth A tlan tic, and the

1930s round th e N o rth A tlan tic sector was associ-

consequent ‘d o w nstream ’ im pact on th e w eather or

T he interactions betw een the ocean surface and

T R E V O R D A V IE S , P. M IC K KELLY A N D TIM O S B O R N

1850

1870

1890

1910

1930

1950

1970

1990

1850

1870

1890

1910

1930

1950

1970

1990

Year Figure 2.12 Annual sea-surface tem perature anomalies, with respect to the 1961-90 mean, in the N orth Atlantic Ocean from 1856 to 1995. The smooth line is the result of applying a filter which emphasises variations on time-scales greater than 30 years. The region is defined as 20° to 70°N and from 0* to 8 0 ’W.

c lim a te o f th e B ritish Isles, are com plex an d tw o-

n o rth e rn m o st p a rts o f th e ocean causes th e G u lf

way. T h e n a tu re o f th e in te ra c tio n d e p en d s on tim e -

S tream an d its exten sio n - th e N o r t h A tla n tic D r i f t

scaie a n d g e o g rap h ica l scale. W e m u s t also consider

-

rhe a rm o s p h e re -o c e a n 'in te ra c tio n s on a w ider, indeed

w ater. T h is does not h a p p en in th e Pacific O cean

g lo b a l, scale. S im ilarly, w e have to ex te n d o u r in te rest

w hich has no deep w a ter fo rm atio n . T h e s in k in g o f

to tu rn m ore n o rth w a rd to replace th e sin k in g

to d e ep ocean c irc u la tio n s, n o t o n ly in th e n o rth e rn

th e N A D W resu lts from its h ig h density, w hich is

p a rt o f th e A tla n tic B asin, b u t fu rth e r so u th a n d , as

a consequence o f its h ig h sa lin ity as m u c h as its low

for th e a tm o sp h e re, to o th e r ocean basins.

te m p e ra tu re . It is se lf-su sta in in g , to som e deg ree,

F irst, w e exam ine th e d e ep o v e rtu rn in g o f w a ter

since its h ig h sa lin ity is d u e to th e n o rth w a rd tra n s­

w h ic h is p a rtic u la rly v ig o ro u s in th e A tla n tic O cean

p o rt o f sa lin e w a ter from m ore tro p ical la titu d e s. Its

d u e to th e fo rm atio n o f N o r th A tla n tic D eep W a te r

w a rm th is also im p o rta n t, since it induces evapora­

(N A D W ). T h e s in k in g o f th is w a ter m ass in the

tio n , fu rth e r in creasing salinity.

E X P L A IN IN G THE CLIMATE OF THE BRITISH ISLES

Since

th e sin k in g

is sensitive

to changes in

atm ospheric circulation over the N o rth A tlan tic/

th e in p u t o f freshw ater to th e N o rth A tlan tic, the

E uropean

suggestion has been m ade th a t th e o v ertu rn in g in

possible linkages w ith E uropean-scale w eather p a t­

sector,

there

are

som e

indications o f

th e A tlan tic could vary in stre n g th , stop, or even

te rn s .11 T here appear to be weak links w ith som e

reverse. Such sw itches could occur over very short

aspects of the B ritish clim ate, p articularly th e fre­

tim e-scales. T h ere is evidence th a t th e w arm ing from

quency o f anticyclonic and cyclonic w eather types in w inter, and w inter precip itatio n over E ngland and

th e last Ice A ge was in te rru p te d around 1 0,000 years ago by a d ra m a tic re tu rn tow ards Ice A ge tem p era­

W ales. T he strongest links appear to be in January

tures, som etim es called th e Y o u n g e r D ry a s period,

and February.12 It is possible th a t m ore pronounced

only to be follow ed by a rapid recovery, all w ithin

E N SO signals in B ritish clim ate w ill em erge as

1 ,000 years (see C h a p te r 5). T h is rapid clim ate d e te rio ra tio n was probably caused by th e A tlan tic

research progresses.

o v e rtu rn in g bein g d istu rb e d by a large in p u t o f fresh­ w ater o f low density in to th e N o rth A tlan tic from

AIR MASSES

th e m eltin g o f ice. T h e m echanism s w hich are likely to be involved in these fluctuations are com plex.' T here

are

som e

tan ta lisin g

indications

from

c o m p u te r m odels th a t th e sinking in th e N o rth

W e have already discussed how air flowing over the N o rth A tlantic to the B ritish Isles has a different character to th a t flowing o u t o f Siberia in w in ter —

A tlan tic m ay fluctuate over shorter tim e-scales —

relatively w arm and m oist versus cold and dry. T he

possible oscillations o f around 4 0 - 6 0 years have been re p o rte d .8 T h e reason for such oscillatory behaviour

concept o f a ir masses is a useful one and u nderpins

is u ncertain, b u t som e aspects m ay be trig g e red by

(see C hapter 8), since d irection of airflow is one of

a sh o rt-term change in th e in p u t o f freshw ater in the

the bases o f identification o f m any types. W h en air

the usefulness o f the w eather type classifications

sin k in g region n o rth o f 6 0 °N (m ore or less ice m elt,

resides in a source region for weeks it starts to

or even heavy precip itatio n ). O th e r aspects m ay be

develop a hom ogeneous character, a few kilom etres

m ore self-sustaining. T h e im plicatio n for th e B ritish

deep, w hich it acquires from its source region. T he

c lim ate is th a t these m ulti-decadal oscillations may

source regions are geographically d istin c t, cover

be reflected in changes in th e N o rth A tlan tic SST

hundreds o f thousands o f square kilom etres and differ

p a tte rn s w hich, we know, have an im p o rta n t do w n ­

betw een su m m er and w inter.

stream influence. T h e reason why these c o m p u te r

Two of th e w inter land source regions are Canada

e xperim ents are tan ta lisin g is th a t clim ate recon­

and (approxim ately) th e form er Soviet U n io n , the

stru c tio n s from

parts o f Europe

o rig in o f ‘co ntinental polar’ air masses. T h e character

also e x h ib it oscillatory-type behaviour on th e sam e tim e-scale.9

of air masses from these source regions w ill clearly

W e have m entioned th e te le c o n n e c tio n character

T here are also seasonally differing source regions for

tree-rin g s from

differ considerably betw een sum m er and w inter.

o f th e N o rth A tlan tic O scillation. T h e m ost p ro ­

‘continental

nounced teleconnections globally are those associated

masses, as well as ‘m aritim e a rctic ’, ‘m aritim e po lar’

w ith th e El N in o S outhern O scillatio n (EN SO ). T his

and ‘m aritim e tro p ic al’ a ir masses. T h e p ath the

is a surface pressure oscillation across th e tropical

air m ass takes from its source region to the B ritish

Pacific, related to Pacific O cean c u rre n ts.10 T h e E N S O dom in ates intcrannual clim ate v ariability in

Isles is im p o rtan t. For exam ple, a relatively cool air

tropical latitu d e s and there is a pronounced teleconnection betw een it and surface pressure over the

convective clouds, good visibility and g u sty w inds; w arm er air flowing over a sim ilarly w arm surface may

N o rth Pacific O cean and N o rth A m erica. A lth o u g h

produce stra tu s cloud, fog and poor visibility. M any w eather features result from such m odification of

stro n g E N S O signals have n o t been d etected in the

arctic' and

‘con tin en tal tro p ical’ air

m ass flowing over a w arm er surface w ill often b rin g

TREV O R D AV IES, P. M IC K KELLY A N D TIM O S B O R N

an a ir m ass along its p a th ; th e air mass type may change from such m odification -

co n tin e n ta l p o lar’

air flow ing o u t o f Canada over th e w arm N o rth A tlan tic D rift m ay have developed in to a cool m oist ‘m aritim e p o lar’ air m ass by m id -A tla n tic, producing b rig h t periods and som e showers.

SMALLER WEATHER SYSTEMS AND LOCAL INFLUENCES A n u m b e r o f circu latio n s on a sm aller scale th an the features we have been d escribing m ake c o n trib u tio n s to th e c lim atic character o f th e B ritish Isles. T his sh o rt section is not all-inclusive. W e w ill not, for exam ple, look at th u n d ersto rm s w hich can provide a significant p ro p o rtio n o f su m m er rainfall (see C h a p te r 3), nor a t m o u n ta in and valley w ind system s w hich can influence local w ind clim atology, or cold n octurnal

d rainage

flow

w hich

m ay

fill

‘frost

hollow s’. M idw ay in scale betw een these circulations and th e cyclones and trav ellin g depressions are p o la r lo w s . W e shall refer briefly to these circulations since, a lth o u g h they are relatively sm all (often several h u n d red s o f kilom etres) and shallow (5 km ), they can produce severe w eather over parts o f the B ritish

Figure 2.13 An infra-red image of a polar low near the Faroes, 25 November 1978, observed from the NOAA 5 satellite. This day is classified as N W in the Lamb Catalogue (see Appendix B).

Isles, w ith stro n g g u sts and c o n trib u tin g to m uch o f th e heavier snowfalls. T hey represent a spccial ease o f cyclone form ation in th a t they arc generally nonfrontal. T hey usually develop over th e ocean in the n ortherly ‘m aritim e po lar’ or ‘m aritim e a rctic ’ airflow to th e rear o f a cold front, often betw een Iceland and

W ith in tens o f kilom etres o f th e coastline, th e dayto-day w eather m ay be m odified by sea-breezes.14 T hey are also caused by th e d aytim e h eating o f the

th e B ritish Isles (see Figure 2.13). T h e cold airflow

land, w hich produces a pressure g ra d ie n t betw een

across zones o f relatively hig h SST grad ien ts provides the m echanism for th e ir form ation.

th e sea (h ig h pressure) and the land (low pressure). D u rin g late m o rn in g a sea-breeze starts to blow

A n o th er type o f low, b u t o f en tirely different

inshore and penetrates inland causing m oister, cooler

orig in and type, is th e so-called heat low. Localised

conditions, frequently accom panied by cloud. Typi­

heating o f land in sum m er can produce such features,

cally, d u rin g sum m er at som e B ritish locations, sea-

usually in th e afternoon. T here arc occasions, how ­

breezes w ill blow on 2 0 - 3 0 per cent o f days, b u t

ever, w here th ey m ay survive n ig h t-tim e cooling and

there are periods w hen they are m uch m ore frequent.

persist for som e days. T hey can be relatively sm all-

Consequently, they m ay affect th e character o f a

scale (for exam ple, over East A nglia), or they may

w hole su m m er at som e near-coastal locations.

cover an area such as m ost o f E ngland. T h u n d e r­

A nother im p o rta n t factor for local clim atc is the local orography. A glance at a lo n g -term précipita-

storm s m ay develop in th e heat low s.13

E X P L A IN IN G THE CLIMATE O F THE BRITISH ISLES

n o n m ap o f th e B ritish Isles provides clear confir­

THE SCENE IS SET

m atio n o f this (see P late 4 or A ppendix A). W h en m oist a ir is forced to rise over h igh land, the air can

T he next c hapter describes the surfacc clim atology

be cooled to a p o in t w here condensation occurs and

o f th e B ritish Isles and it is necessary for th e reader

th e p re cip ita tio n process starts. T here is a d istin c t

to bear in m in d th a t local influences, such as those

w est-to-east g ra d ie n t in p re cip ita tio n over th e B ritish

wc have introduced in th e previous section, w ill be

Isles w hich largely reflects th is orographic effect on m oist a ir blo w in g in from th e A tlantic. A nother

very im p o rta n t in m odifying th e clim ates o f specific

reason for enhanced p re cip ita tio n over th e highest

forecast for a region to take account o f local condi­

land is th a t th e passage o f fronts can be slowed dow n.

tions, so the broad clim atology presented here m ust

D etailed p re cip ita tio n m aps show a dependency o f

be m odified to su it th e reader’s neighbourhood. It is

p re cip ita tio n on elevation, even w here th e orography

possible to focus on very sm all scales - w hole books

locations. J u s t as it is necessary to adapt a w eather

is n o t pronounced and even in eastern locations.

have been w ritte n on th e clim ates of a single c ity 15

M odest orographic enhancem ent o f p re cip ita tio n is

- b u t th e aim o f this chapter, and oi m uch o f this

a p p are n t, for exam ple, even in th e far-eastern and

book, has been to look outw ards from the clim ate of

relatively flat N orfolk. It goes w ith o u t saying th a t

th e B ritish Isles to th e large-scale processes w hich

cloud also is m ore com m on over h ig h er land.

deliver o u r average weather. W h en one considers rhe

W e have noted th e im portance o f rhe land surface

m yriad factors w hich shape the clim ate o f a p a rtic ­

d u rin g o u r discussion o f global-scale radiation and

ular area, it is clear why m odelling w eather and

heat balances. It is not only albedo (w hich can change

the clim ate system presents such a challenge. It is

seasonally w ith vegetation changes) w hich is im p o r­

necessary- to take account o f all the processes d is­

ta n t, b u t also heat conductivity. T h e therm al conduc­

cussed in this chapter, and m any m ore, on spatial

tiv ity o f th e soil is an im p o rta n t factor in the

scales ranging from the global to the local. C o m p u ter

response o f th e surface to changes in net radiation. Soil con d u ctiv ity is strongly influenced by w ater

pow er is lim ited , so com prom ises have to be m ade,

co n te n t. So, if th e soil is coarse, sandy and dry (thus co n ta in in g a lot o f air; a good insulator), n ig h t-tim e

skills o f those developing th e m odels and forecasts

radiational cooling will nor be offset by the conduc­

degree o f accuracy.

often in sacrificing local detail. It is testa m en t to rhe th a t, despite th e difficulties, they m anage such a

tio n o f heat from low er levels in rhe soil. An exam ple o f th is, again from East A nglia, is the sandy soil area o f th e B rcckland area o f N orfolk, w here n ig h t-tim e m in im u m tem p eratu res can be 3—4°C lower th an in th e su rro u n d in g areas w here th e soil is less freely d rain ed (e.g., Santon D ow nham - see C h ap tcr 3). O th e r im p o rta n t surface differences occur in urban areas. T h e city fabric acts as a ‘storage h e ater’ m ain ­ tain in g n ig h t-tim e tem p eratu res above those o f the su rro u n d in g regions. T he urban heat island ten d s to be m ost pronounced on calm , clear n ig h ts after sunny days b u t, for m any tow ns and cities, is ap parent even in yearly averages. O th e r clim ate variables, such as h u m id ity and w ind speed, are also m odified to such an e x te n t by som e urban areas th a t differences are ap p are n t in rhe lo n g -term statistics for urban and adjacent rural locations.

NOTES 1 The reader wishing to learn more of the global climate system and the general circulation of the atmosphere is directed to R.G. Barry and R J . Chorley, Atmosphere, Wmther and Climate (6th edn) London, Routleclge, 1995. For more technical accounts, see R. Mcllveen, Fundamentals of Weather and Climate, London, Chapman and Hall, 1992, 497 pp.,orJ.T . Houghton, The Physics of Atmospheres (2nd edn), Cambridge, Cambridge University Press, 1986, 271 pp. 2 This radiation is longer in wavelength than thar emitted by the Sun since the temperature of the Earth s atmosphere is much lower than that of the Sun hotter bodies emit shorter wavelength radiation 3 The term ‘Index Cycle’ is something of a misnomer, since ‘cycle’ does imply some regularity. In reality, the

T R E V O R D A V I E S , P. M I C K KE LL Y A N D T IM O S B O R N

4

5

6

7

8

9

cycle has a characteristic tim e-scale o f several weeks or so, b u t th e period is very variable. R.A.S. R atcliffc and R. M urray, ‘N ow lag associations betw een N o rth A tlan tic sea tem p e ra tu re and European pressure applied to long-range w eather forecasting’, Quarterly Journal o f the Royal Meteorological Society, 1 9 7 0 , vol. 9 6 , p p . 2 2 6 -4 6 . For exam ple, A .H . Perry, 'E astern N o rth A tlan tic seasurface tem p e ra tu re anom alies and con cu rren t te m p e r­ a tu re and w eather p a tte rn s over th e B ritish Isles’, Weather, 1975, vol. 30, pp. 2 5 8 -6 1 . P.M. Kelly, C.M . G oodess and B.S.G . Cherry, T h e in te rp reta tio n o f th e Icelandic sea-ice record\ Journal o f Geophysical Research, 1987, vol. 9 2 , pp. 1 0 8 3 5 -4 3 . l.M . H eld , ’Largc-Scale D ynam ics and G lobal W a rm in g ’, Bulletin o f the American Meteorological Society, 1993, vol. 74(2), pp. 2 2 8 -4 1 . T. D elw o rth , S. M anabe and R .J. Stouffer, ‘In terdecadal variations o f th e th erm o h alin e circulation in a coupled ocean-atm osphere m o d el’, Journal o f Climate, 1 9 9 3 , vol. 6, pp . 1 9 9 3 -2 0 1 1 ; R .J. G reatbach and S. Z h a n g , ‘A n interdecadal oscillation in an idealised ocean basin forced by c o n stan t heat flux’, Journal of Clim ate, 1995, vol. 8, pp . 8 1 - 9 1 . T.F. Stocker, ‘T he variable ocean’, N ature, 1994, vol. 3 6 7 , pp. 2 2 1 -2 .

10 G .R . B igg, ‘HI N in o and the Southern O scilla tio n ', Weather, 1990, vol. 4 5 , pp . 2 - 8 . 11 K. Fraedrich and K . M üller, ‘C lim ate anom alies in Europe associated w ith E N SO extrem es’. International Journal o f Climatology, 1992, vol. 12, pp . 2 5 - 3 1 . 12 R. W ilby, ‘E vidence of E N S O in the synoptic c lim ate o f th e B ritish Isles’, Weather, 1993, vol. 48(8), pp . 2 3 4 -9 13 Sec R. M cllveen, op. c it., for in te restin g descriptions o f polar lows and heat lows. 14 J.E . Sim pson, Sea Breezes an d Local W ind, C am bridge, C am bridge U niversity Press, 1994, 2 34 pp. 15 T.J. C handler, The Climate o f London, London, H utch in so n and Co. L td, 1965, 292 pp.

G EN ER A L R EA D IN G R .G . B arry and R .J. Chorley, ‘Atmosphere, Weather and Clim ate', L ondon and N ew York, R outledge 1995, 6 th edn. R. M cllveen, 'Fundamentals o f Weather an d Clim ate', London, C hapm an and H all, 1992, 497 pp. J.M . W allace and P.V. H o b b s, 'Atmospheric Science, an Introductory Surt’ey', N ew York, A cadem ic Press Inc., 1977, 4 67 pp.

3 DESCRIBING THE SURFACE CLIMATE OF THE BRITISH ISLES Elaine Barrow and Mike Hulme Wherever you go, the weather is, without exception, exceptional. K i n g s l e y M a r t in

INTRODUCTION T he B ritish Isles have a more equable clim ate than w ould be expected at a latitude o f betw een 49° and 61°N . T h eir m aritim e location, their position w ithin the m ain flow o f the m id -latitu d e westerlies and their proxim ity to the m ild waters o f the north-east A tlantic Ocean all contribute to a clim ate which knows little of the extrem es o f w inter and sum m er typical o f Moscow or the H udson Bay, places at equivalent latitude to the B ritish Isles. W hereas C hapter 2 exam ined some o f the im portant reasons for this tem perate clim ate to prevail, the present chapter describes the main features of the British clim ate. To do this we use maps, diagram s and tables containing data averaged over the m ost recent thirtyyear clim ate ‘norm al’ perio d ,1 namely 1961 to 1990. W h en averaged over three decades, clim ate statis­ tics for variables such as tem perature, precipitation and sunshine sm ooth out the year-to-year fluctua­ tions in w eather and give a better description of the clim ate experienced o v era hum an lifetim e. T he 1961 to 1990 period is the m ost relevant for contem porary applications o f clim ate data, although there will clearly be differences between the clim ate defined by these data and clim ates described by earlier normal periods, such as 1941 to 1970 and 1951 to 1980.2 How representative the clim ate o f 1961 to 1990 is o f past and future clim ates of the British Isles is

a question exam ined in later chapters, especially Chapters 9, 10, 15 and 16. T he surface features of the clim ate of the British Isles are described using m aps constructed on a reg­ ular 10' latitude by 10' longitude grid using 1961 to 1990 station data supplied by the U nited K ingdom and Irish M et. Offices (see Box 3-1). In addition to presenting these maps, data from a num ber of indi­ vidual sites are used to illustrate more specific aspects of B ritish clim ate and the locations of these sites are shown in Figure 3.1. We also examine some of the clim atic classifications which have been used to define B ritish clim ate in relation to world clim ates.

SURFACE AIR TEMPERATURE The location o f the British Isles plays a central role in governing our clim ate (see C hapter 2). O ur situation means th at we experience the com bined influences of the m id-latitude westerly w inds and the N o r th A tla n tic D rift which comprises warm w ater o f tropical origin. The British Isles are surrounded by this comparatively warm oceanic water, the tem perature of w hich varies only slowly from m onth to m onth because of the high th e rm a l in e rtia o f the oceans. This means th at in coastal areas average tem peratures are usually sim ilar to those o f the sea surface, whereas areas farther inland and away from

E L A I N E B A R R O W A N D M IK E HULM E

Figure 3.1 Location of the stations mentioned in this chapter. The latitude transect at 524N is also indicated.

th e m a ritim e influence experience larg e r te m p e ra tu re

easterly airflow, w h ilst m ild n ess in a B ritish w in te r

e x trem es. In th ese in la n d areas o f th e B ritish Isles

is ty p ic a lly a result o f airflow from th e w est o r so u th .

th e c lim a te is m o re ‘c o n tin e n ta l’ in n a tu re . In te r ­

Cool su m m ers te n d to be p ro d u c ed by w esterly or

ru p tio n o f th e p re d o m in a n tly w esterly c irc u la tio n

n o rth erly airflow s w h ilst so u th e rly o r easterly airflow

m ay re su lt in ex tre m e s o f te m p e ra tu re . F or exam ple,

over th e

cold w in te r spells are u sually a re su lt o f n o rth e rly or

episodes (see C h a p te r 8).

B ritish

Isles

resu lts

in

w arm

su m m e r

THE SU RFAC E CLIMATE OF THE BRITISH ISLES

BOX 3.1 CONSTRUCTION OF THE 1961 TO 1990 GRIDDED CLIMATOLOGY

surfaces was depen d en t on the clim ate variable in q uestion. T he n um ber o f stations ranged from to

eighty, in the case o f w ind speed, to 7 5 0 for precipitation. T he p recipitation dataset contained

c o n stru ct g rid d e d clim ate surfaces for parts o f the B ritish Isles from scattered station observations.

alm ost 2 ,5 0 0 sites, b u t only 7 5 0 o f these were used in the interpolation. T he clim atology des­

T hese have used bo th m u ltip le regression and

cribed in th is c hapter represents, to th e best of

spatial in te rp o latio n techniques, b u t have alm ost alw ays been confined to e ith e r a lim ited n u m b er

our know ledge, th e m ost contem porary, com pre­

o f clim ate variables, a sm aller d om ain than the

the B ritish Isles presently in use.b M aps extracted

A n u m b e r o f a tte m p ts

have

been

m ade

hensive and w idely available clim ate dataset for

w hole o f th e B ritish Isles, or have been based on

from th is clim atology are show n in th is chapter

sh o rt o r non-standard records o f clim ate. Partial

and also in A ppendix A.

th in -p la te sp lin e s, a tech n iq u e developed for clim ate app licatio n s by M ike H u tc h in so n , were used to co n stru ct th e clim atology show n h e r e / T h is tech n iq u e included elevation as an in d ep en ­ d e n t p re d ic to r variable, in ad d itio n to th e m ore usual latitu d e and lo ngitude. As a result o f using th is approach, th e clim atology is available at three different elevations corresponding to th e m axi­ m u m , m in im u m and m odal elevations o f each 10' g rid cell. T h is g rid resolution corresponds to an area approxim ately 19 km by 19 k m , roughly equiv alen t in size to th e city o f B irm ingham . T he n u m b er o f stations used to construct th e clim ate

V ictor C onrad5 devised a ‘c o n tin e n ta lity ind ex ’

* E.M. Barrow, M. Hulme and T. Jiang, A 1961-90 Baseline Climatology and Future Climate Change Scenarios for Great Britain and Europe. Part I: 1961-90 Great Britain Baseline Climatology•, a report accompa­ nying the datasets prepared for the Landscape Dynamics and Climate Change' TIGER IV Consortium, Norwich, Climatic Research Unit, 1993. b The 1961 to 1990 climatology may be obtained through the Climate Impacts LINK Project (contact David Viner at the Climatic Research Unit). Monthly average values for all the variables described here are available at the three elevations (minimum, maximum and modal).

w ith the index ra nging from three in coastal areas to

based on th e annual range of average tem p eratu re and

seven inland, whereas th e m ost c ontinental areas o f

th e sine o f th e latitu d e o f th e site in question. U nder th is convention th e oceanic regim e o f T horshavn in

the B ritish Isles are in eastern and south-eastern E ngland where the index has values o f betw een eleven

th e Faeroes has an index value o f zero whereas the

and twelve.

extrem e

Siberia has an index o f 100. In N o rth A m erica, where

Table 3-1 illu strates the m onthly m e a n 1 tem p e r­ atures o f a n um ber o f sites in the B ritish Isles. Lowest

values rise to m ore th an sixty, th e area w ith values less

m ean tem peratures are a t th e m ore northerly and

co n tin en tal

clim ate

o f V erkhoyansk

in

th an tw elve is restricted to th e tip o f th e Florida

h igher a ltitu d e sites, and the annual m ean tem p e r­

p en in su la and th e Pacific coast. W h en th is index is

atures range from approxim ately 7°C in n orthern

applied to th e B ritish Isles th e extrem e oceanicity o f

Scotland to in excess o f 10°C in south-w est E ngland

stations exposed to th e A tlan tic O cean, especially

and W ales. T h e annual range o f m o n th ly m ean

those o f th e H ebrides, O rkneys and th e north-w estern

tem perature, defined as th e tem perature in the w arm ­

tip o f Scotland, is ap p aren t (see Figure 3.2). Values o f

est m o nth m in u s the tem perature in th e coldest

th e index in these areas are betw een only tw o and

m o n th , is less at coastal sites com pared to those

three. T h e clim ate o f Ireland is relatively oceanic,

inland. A t Stornoway, for exam ple, the range is

E LA IN E B A R R O W A N D M IK E HULME

exam ple, the m ean tem p eratu re in February is 0.2°C lower th an in January. T he east coast o f th e B ritish

eo'N

Isles tends to be th e leeward side o f rhe country and so stations here are not affected by the influence o f the cool February m aritim e air to the sam e extent. A t D u rh am , for exam ple, th e m ean tem p eratu re in February is 0.2°C h ig h er th an in January. H ig h e st m ean tem peratures in w in ter are betw een 6°C and 8°C and are experienced along sourh-w estern coasts, w hilst in central and eastern E ngland w inter tem peratures are o f the order 2°C to 4°C. In upland and hig h lan d areas m ean tem peratures range from less th an —2°C to 2°C, w hilst in Ireland they are w arm er in the south (4°C to 6°C) com pared to the no rth (2°C to 4°C). M ean m axim um tem peratures in w in ter show a sim ilar p a tte rn to the m ean tem p eratu re (see P late 2), w ith highest values in south-w est and southern areas (8*C to 10°C) and low est values in th e Scottish H ig h lan d s (less chan 2°C). M ean m in im u m tem p e r­

50°N

atures in w in ter range from betw een 2°C and 6°C on south-w estern coasts, to betw een 0°C and 2°C in

Figure 3-2 Conrad’s concinentality index, based on the annual range of average temperature and latitude. The larger the value (and the darker the shading) the more ‘continental’ rhe sire. Index ranges from more than eleven around Greater London to less than three in the north­ west of Scotland.

central areas and to below -2 °C in the Scottish H ig h ­ lands (P late 3). T opographic features, vegetation cover and soil type probably have a larger influence on m ean m in im u m tem peratures than they do on m ean m axim um values. These s u b - g r id scale variations in tem perature are not captured by the g rid d cd clim atology and are probably m ore im por­ ta n t for m in im u m than for m axim um tem perature.

13°C at

In sum m er, coastal areas are generally cooler rhan

E lm don near B irm ingham . T h e year-to-year vari­

inland areas at sim ilar latitudes. Sea-surface tem p e r­

a b ility o f te m p e ra tu re is discussed in C h ap ter 9.

atures around th e B ritish Isles reach th eir highest values in A u g u st or early Septem ber and th is affects

approxim ately 9°C com pared

to nearly

T h e seasonal5 p a tte rn s o f m ean tem p eratu re a t the average elevation w ith in each g rid cell are illustrated

the m o n th o f h ighest m ean tem peratures at coastal

in Plate 1. In w inter, th e m aritim e influence d o m i­ nates tem p eratu res w ith coastal stations ten d in g to

stations. T h e im pact o f th is oceanic effect extends farther around the coast rhan in January, w ith

be w arm er th an inland areas, m ainly as a result of

stations on the N o rth Sea coast being affected as far

h ig h er m in im u m tem peratures in the coastal areas.

n orth as Scarborough. Table 3.2 lisrs rhe m ean

S e a -su rfa c e t e m p e r a tu r e s around the B ritish Isles

m axim um

d o not reach th eir low est values u n til February or

stations. E quivalent tem peratures for a nearby inland

early M arch w ith the result chat th e low est m ean

sta tio n arc show n for com parison. T h u s in w inter,

tem p eratu res o f those stations exposed to th e full influence o f the A tlan tic occur in February rather

E astbourne, for exam ple, experiences daytim e m axim a about 0.5°C h igher than G arw ick, whereas

th an

in sum m er E astbourne is on average 2°C cooler.

in Jan u ary

(Table

3.1).

At

P ly m o u th , for

tem peratures for a n um ber o f coastal

THE SURFACE CLIMATE OF THE BRITISH ISLES

Table 3.1 Average 1960-90 monthly mean temperature ("C). The elevation of each site above mean sea level (m) is indicated in parentheses next to the station name. J

Site

F

Kirkwall (26) 3.7 3.6 Stornoway (15) 4.2 4.1 Dyce (65) 2.7 2.9 Durham (102) 3.0 3.2 Santon Downham (24) 3.0 3.2 Elmdon (96) 3.2 3.2

M

A

M

J

J

A

4.5 5.1 4.6 5.0 5.1 5.2

6.0 6.5 6.4 7.0 7.3 7.6

8.4 9.0 9.1 10.0 10.7 10.7

11.0 11.4 12.2 13.0 13.8 14.0

12.3 12.7 13.8 14.8 15.6 15.9

12.5 12.8 13.7 14.7 15.4 15.5

10.9 9.0 5.7 11.2 9.2 5.9 11.7 9.0 5.1 12.7 9.7 5.7 13.2 10.0 5.9 13.2 10.0 6.1

4.4 4.9 3.6 3.9 3.8 4.3

7.7 8.1 7.9 8.6 8.9 9.1

8.9 8.7 11.1 11.8 12.6 12.7

S

O

N

D Annual Range

Oxford (63) Shawbury (72) Gatwick (59) Eskdalemuir (242) Ringway (75)

4.1 3.4 3.6 1.8 3.9

4.2 3.4 3.8 1.8 3.9

6.2 5.4 5.7 3.5 5.7

8.5 7.5 8.0 5.7 8.0

11.9 10.7 11.3 8.7 11.3

15.0 13.7 14.5 11.7 14.2

17.1 15.6 16.5 13.2 15.8

16.7 15.3 16.2 13.0 15.7

14.4 13.1 13.8 10.8 13.5

11.1 10.0 10.7 8.2 10.6

6.9 6.0 6.5 4.1 6.4

4.9 4.2 4.5 2.6 4.6

10.1 9.0 9.6 7.1 9.5

13.0 12.2 12.9 11.4 11.9

Valley (10) Long Ashton (51) Plymouth (50) Cork (154) Kilkenny (66) Clones (89)

5.5 4.5 6.0 5.2 4.6 4.0

5.1 4.5 5.8 5.1 4.8 4.2

6.5 6.3 7.0 6.2 6.2 5.7

8.3 8.4 8.8 7.8 7.9 7.5

11.1 11.5 11.6 10.1 10.4 10.1

13.6 14.5 14.3 12.9 13.3 12.9

15.3 16.5 16.2 14.8 15.2 14.5

15.4 16.2 16.1 14.5 14.8 14.2

13.9 14.1 14.4 12.7 12.6 12.2

11.6 11.0 12.0 10.3 10.0 9.8

8.1 7.2 8.5 7.2 6.5 5.9

6.4 5.1 7.0 6.0 5.3 4.8

10.1 10.0 10.6 9.4 9.3 8.8

10.3 12.0 10.4 9.7 10.6 10.5

Table 3.2 Comparison of coastal and inland mean monthly maximum temperatures ('C). (Bold indicates coastal sites - tne corresponding inland site is immediately below. The approximate distance (km) between the coastal and corresponding inland site is also given. Distance (km) Site 75

55

80

120

Jan

Feb

M ar

Apr M ay

Oct

Nov

Dec

Jun

Ju l

Aug

Sep

Lowestoft

6.1

6.2

8.6

10.6 14.2 17.6 19.8 20.0 18.2 14.4

9.7

7.2

Santon Downham

6.3

6.8

9.7

12.5 16.6 19.7 21.5 21.4 18.8 14.8

9.6

7.1

Eastbourne

7.3

7.1

9.1

11.5 14.9 17.8 19.7 20.0 18.1 15.0 10.8

8.5

Gatwick

6.7

7.1

9.9

12.6 16.3 19.6 21.7 214

18.8 15.0 10.1

7.7

9.0

Isle of Portland

7.7

7.3

8.8

Boscombe Down

6.4

6.8

9.4

11.0 13.8 16.5 18.5 18.8 17.3 14.7 11.0 12.3 15.8 19.1 21.2 20.8 18.2 14.3 9.7

Aberporth

7.0

6.9

8.4

10.5 13.4 16.0 17.6 17.7 16.0 13.5

9.8

8.0

Lyonshall

6.0

6.0

8.8

11.7 15.3 18.4 20.5 19.9 17.1 13.4

9.0

6.9

Mean temperatures in summer are between l4°C and 16"C in southern and central lowland Britain and between 12°C and 14°C in the north, although in higher altitude areas such as North Wales, the Lake District, Exmoor and Dartmoor, mean temper-

7.4

atures are slightly lower (Plate 1). London is relalively warm due to the urban warming effect with mean temperatures approximately 2°C higher than those in the surrounding area. Mean summer temperatures arc lowest in the Scottish Highlands (8°C to

E LAI NE B A R R O W A N D MI KE HULME

(a) West-East Temperature Transects at 52°N: Winter mean elevation

IO°W







------



max elevation — — min elevation













l°E

9 8 Maximum

. 7

(deg C)

6

Irish sea

5 4

4 ;\

3 Minimum

2

1

E

c

fj

Elevation above msl (m)

oo

700

700

600

600

500

500

400

4(X)

300

300

200

Irish sea

200

100

0

Figure 3-3 W e s t-e a s t transect o f (a) average w in ter and (b) average sum m er m axim um and m in im u m tem p e ra tu re (°C) a t 52°N . T h e bold lin e refers to the tem p e ra tu re a t the average elevation o f each 10 km g rid cell, w hereas th e th in

THE S U R F A C E CLIMATE O F THE BRITISH ISLES

(b) W est-East Temperature Transects at 52°N: Summer ------

(deg C)

10°W



mean elevation





------



max elevation — —





min elevation







1°E

20

20

18

Maximum . 18

16

16

Irish sea

14

14 M inimum

12

10

12

10

8

8

c

•—

n

-C

G op

Oij

Elevation above msl (m)



700

700

6(X)

600

500

500

400

400

300

Irish sea

200

200 100

1(K)

0 7°





lines in d ic a te th e m in im u m a n d m a x im u m ele v atio n s a n d te m p e ra tu re s o f each cell. T h e lo w er p lo ts show th e average, m in im u m and m a x im u m e le v atio n o f each 1 0 ’ ceil.

E L A I N E B A R R O W A N D M IK E HULM E

12°C). M ean

m a x im u m

s u m m e r te m p e ra tu re s in

cen tral areas exceed 20°C , w h ile coastal areas are b e tw ee n 2°C an d 4°C co o ler (see P la te 2). M ean m in im u m

sum m er

te m p e ra tu re s

are

h ig h e s t

in

so u th e rn an d eastern areas ( lO 'C to 12°C). E lev atio n has a stro n g influence on te m p e ra tu re an d th is is illu stra te d by w est—east tra n se c ts o f m ean m a x im u m an d m in im u m te m p e ra tu re s a t a la titu d e o f 5 2 °N

(see

m in im u m

F ig u re

3-3)-

te m p e ra tu re s

B oth

follow

m a x im u m

th e

and

sam e gen eral

p a tte rn in w in te r w ith h ig h e r te m p e ra tu re s in th e w est th a n in th e east an d d e cre asin g te m p e ra tu re w ith in cre asin g e lev atio n . In th e w est o f W ales (for ex am p le, a t F ish g u a rd ) m ean m in im u m te m p e ra tu re s are, in g e n e ra l, a b o u t 2.5°C h ig h e r th a n th o se in m ore e aste rn areas (for e x am p le, a t R oyston). C loser to

th e

east

coast

(for

e x am p le, a t

Felixstow e),

how ever, th is d ifference lessens because o f th e a m e lio ­ ra tin g

m a ritim e

te m p e ra tu re s .

influence

For m ean

on

m ean

m a x im u m

m in im u m

te m p e ra tu re s ,

how ever, th is lo n g itu d in a l difference is only a b o u t 1.5°C . T h e d i u r n a l t e m p e r a t u r e r a n g e , therefore, is a b o u t 1°C less in th e w est co m p ared to th e east. In su m m er, th e s itu a tio n is reversed. T h is is p a r­ tic u la rly th e case for m ean m a x im u m te m p e ra tu re s w here w est—east differences are o f th e o rd e r o f 2°C to 3°C w ith a cooler w est and w a rm er east. T h e d if­ ference b etw een w est—east m ean m in im u m te m p e r­ atu re s in s u m m e r is sm a ll, m e a n in g again th a t th e d iu rn a l te m p e ra tu re range in s u m m e r is less in

Figure 4 I leavy rime deposits (opaque, white ice crystals) around Lincoln Cathedral at 1130 (GMT) on 24 December 1992. This photograph was taken in the m iddle of a spell o ften consecutive anticyclonic days (according to the Lamb Catalogue) with calm conditions and very cold polar air.

th e w est th a n in th e east. T h e su m m e r d iu rn a l range in te m p e ra tu re is b etw een 3*C an d 4°C larg e r in th e cen tral areas o f E n g la n d c o m p a red to w estern coastal re g io n s o f th e B ritish Isles, w here th e p ro x im ity to

o f 1.4 m above g ro u n d level) falls below 0°C. G ro u n d

th e slo w -c h a n g in g sea-surface te m p e ra tu re reduces

frosts occur m ore freq u e n tly th a n a ir frosts. M any

th e d a ily range o f te m p e ra tu re s. O n th e east coast

p e o p le assum e th a t frost on rooftops and cars m eans

th e d iu rn a l ra n g e is a p p ro x im ate ly 2°C to 3°C less

th a t an air frost has o ccurred, w hen a ctu ally th is is

th a n in cen tral areas.

n o t th e case. Such surfaces are g o o d c o n d u cto rs o f

T h e seasonal p a tte rn s o f m ean m in im u m te m p e r­

heat and therefore ra d ia te away th e ir heat freely th u s

a tu re te n d to be reflected in th e average n u m b e r o f

cau sin g th e ir te m p e ra tu re , an d th a t o f th e a ir in

frostdays over a season. For o u r p u rposes, a frostday

co n ta ct w ith th e m , to fall an d frost to form . C a lm ,

is defined w hen grass m in im u m te m p e ra tu re falls

cloud-free c o n d itio n s are ideal for frosts to occur

below 0°C, i.e ., w hen a g ro u n d frost occurs. A n air

(F ig u re 3-4), especially i f th e a ir is o f p o lar o rig in .

fro st, on th e o th e r h a n d , occurs w hen th e a ir te m p e r­

In w in ter, frostdays are m o st fre q u e n t - fifty days or

a tu re recorded in th e S te v e n s o n s c r e e n (at a h e ig h t

m o re - in c en tra l an d eastern E n g lan d and S co tlan d ,

THE S U R F A C E CLIM ATE O F THE BRITISH ISLES

Table 3.3 Average 1961-90 seasonal number of ground frostdays

Kirkwall Stornoway Dyce Efmdon Oxford

W inter

Spring

42.1 41.0 60.8 51.2 52.1

28.4 27.3 41.3 36.6 29.2

Summer Autumn

1.1 2.9 5.0 3.4 0.6

13.5 17.9 28.1 24.4 18.3

Shawbury Gatwick Eskdalemuir Ringway Valley

52.4 52.4 59.6 40.3 31.5

40.8 37.3 44.7 22.9 18.2

5.6 1.6 6.2 0.2 0.2

26.7 23.7 29.9 12.7 8.4

Long Ashton Plymouth Cork Kilkenny Clones

50.6 31.9 42.0 51.0 47.1

31.1 21.4 27.9 39.9 35.1

0.8 0.1 0.0 3.0 3.0

19.4 10.8 15.0 27.9 21.9

a ir m asses are forced to rise, e ith e r by h ill an d m o u n ­ ta in b arriers o r in frontal system s, large q u a n titie s o f clo u d an d p re c ip ita tio n re su lt. T h e influence o f elevation is very m ark ed over th e h ills an d m o u n ­ tain s o f so u th e rn Irelan d , so u th -w e ste rn E n g la n d , n o rth an d so u th W ales, th e Lake D is tric t and the H ig h la n d s o f Scotland an d th ere is therefore a stro n g w e st-e a st c o n tra st in p re c ip ita tio n . T h is is illu stra te d in F ig u re 3.5

w hich show s w in te r an d su m m e r

p re c ip ita tio n to ta ls a long th e sam e w e st-e a st tran sec t at la titu d e o f 52°N as used for te m p e ra tu re . T h e effect o f th e h ills a n d m o u n ta in s is clear. In w in ter, seasonal p re c ip ita tio n to ta ls over th e h ig h e st areas o f W ales are a b o u t 6 0 0 m m co m p ared to a b o u t 150 m m

in rh e eastern

r a in - s h a d o w

areas. In

su m m er, seasonal p re c ip ita tio n totals in th e east are sim ila r to those in w in ter, b u t in w estern areas they are only a b o u t h a lf th e ir w in te r values. T h e seasonal p a tte rn o f p re c ip ita tio n d is trib u tio n over th e B ritish Isles is illu stra te d in P la te 4 . Large p re c ip ita tio n to ta ls are o b tain e d in th e h ig h e r areas

w hereas in m o re coastal areas, su ch as P ly m o u th and

o f Irela n d , W ales, so u th -w e st E n g la n d , S cotland and

Valley, th e ir n u m b e r is less th a n forty (see T able 3.3).

th e

Lake

D is tric t,

but

these g ra d u a lly

decrease

to w ard s th e so u th an d east. T h e relative p a tte rn o f p re c ip ita tio n ten d s to be sim ila r over all seasons,

PRECIPITATION: AMOUNT AND FREQUENCY

a lth o u g h th e a b so lu te m a g n itu d e o f th e g e o g ra p h ­ ical differences varies.

P re c ip ita tio n 6 over th e B ritish Isles is p ro d u c ed from

'Fhe m o n th ly c o n trib u tio n o f p re c ip ita tio n to th e

th re e m ain sources: fro n tal sy stem s, local a tm o sp h e ric

an n u al to tal for a n u m b e r o f sites is illu stra te d in

s t a ti c

th u n d e r­

T able 3-4. For m any sires p re c ip ita tio n in th e a u tu m n

show ers) an d a tm o sp h e ric u p lift by h ills an d m o u n ­

and w in te r m o n th s m akes th e largest c o n trib u tio n

ta in s (o ro g rap h ic p re c ip ita tio n ).

A verage seasonal

to th e an n u al p re c ip ita tio n to tal. T h is is especially

p re c ip ita tio n d e p e n d s on th e frequency, in te n sity and

tru e o f th e n o rth e rn and w estern areas of th e B ritish

i n s ta b ility

(th u n d e rs to rm s

an d

trac k s o f ra in -b e a rin g system s near th e B ritish Isles.

Isles and is caused by th e m o st freq u e n t and in ten se

M ore active an d m ore fre q u e n t fro n tal system s cross

d e p r e s s io n s b e in g experienced in these m o n th s. In

S cotland

from

w est to east an d

th is , c o m b in ed

m u ch o f central and eastern E n g la n d , how ever, the

w ith th e influence o f th e m o u n ta in s, leads to h ig h

an n u al cyclc is m uch

p re c ip ita tio n to ta ls in rh is reg io n . T h e w est coast o f

p re c ip ita tio n can m ake th e largest c o n trib u tio n to

less m arked and

su m m e r

Scotland receives b etw een four a n d five tim e s as

the an n u al to ta l. A t S an to n D ow n h am and E lm d o n ,

m u ch p re c ip ita tio n as rh e east coast.

for exam ple, m ore th a n 25 per c e n t of p re c ip ita tio n

T h e h ig h e s t p re c ip ita tio n to ta ls over th e B ritish

falls in sum m er. In th is reg io n a h ig h e r p ro p o rtio n

Isles are u sually p ro d u c ed by cyclonic, so u th e rly or

o f su m m e r p re c ip ita tio n is likely to be of convective

w esterly c irc u la tio n s (see C h a p te r 8). W esterly c irc u ­

o rig in th a n elsew here. In no p a rt o f th e c o u n try is

latio n s d riv e m o ist m a ritim e a ir m a s s e s o rig in a tin g

sp rin g th e w e tte st season. T h e v a ria b ility o f p re c ip ­

from th e A tla n tic over th e B ritish Isles. W h e n these

ita tio n from year to year is discussed in C h a p te r 10.

E LAI NE B A R R O W A N D MIKE HULME

(a) West-East Precipitation Transects at 52°N: Winter ------

10°W



mean elevation





------



max elevation ——







min elevation







l°E

7(X)

600

600

500

500

(mm)

700

Irish sea

400

300

300 200

100

100

£ -

•o

Elevation above msl (m)

CO)

700

700

600

600 500

400

400

300

300

200

Irish sea

200

100

100 0 2°

Figure 3-3 W e s t-e a s t transect of* (a) average w in ter and (b) sum m er p re cip ita tio n totals (m m ) a t 52*N. T h e bold line refers to the p re cip ita tio n at th e average elevation o f each 10 km g rid cell, w hereas th e th in lines indicate th e m in im u m

THE SURFACE CLIMATE OF THE BRITISH ISLES

(b) West-East Precipitation Transects at 52°N: Summer -------

10°W



------

m ean elevation







m ax elevation











m in elevation





1°E

700

700

(mm)

600

500

5(X)

4(X)

400

300

300

Irish sea

2(X)

200 100

100

E

c

Elevation above msl (m)

U.

700

7(X)

600

600

500

500

400

400

300

300

Irish sea

200

2(X)

100

100



8*>o





0

and m aximum elevations and precipitation of each grid cell. The lower plots show the average, m inim um and maximum elevation of each 10’ cell.

ELAINE B A R R O W AN D MIKE HULME

Table 3.4 The contribution, as per cent, of average monthly precipitation to the average annual total, 1961-90 period. (Bold lype indicates the wettest season.) Spring A M

D

Winter J

Kirkwall Stornoway Dyce Durham Santon Downham

11 11 9 9 9

11 10 10 9 9

7

8 9 7 8 7

6 6 7 7 8

5 5 8 8 8

5

6

7 7 6 6

5 7 8 9

6 8 8 9

8 7 10 10 9

10 10 9 9 8

11 12 10 8 9

12 11 10 10 10

Elmdon Oxford Shawbury Gatwick Eskdalemuir

10 10 10 10 11

9 9 8 10 11

7 6 6 7 7

8 8 8 8 9

7 7 7 7 5

8 9 9 7 6

9 9 8 8 6

7 7 8 6 6

10 9 9 7 8

8 9 9 9 10

8 9 9 10 11

9 9 10 10 10

Ringway Valley Long Ashton Plymouth Cork Kilkenny Clones

10 11 11 12 11 11 10

9 10 10 12 12 11 10

6 7 7 9 10 8 7

8 8 8 9 8 8 8

6 6 6 6 6 6 6

8 6 7 6 7 7 7

8 6 7 6 6 6 7

8 6 7 6 5 6 6

10 9 8 7 7 9 9

9 9 9 8 8 9 9

10 11 9 10 11 10 10

10 12 10 10 9 9 9

F

M

Summer A J

J

S

Autumn O N

Table 3.5 Average 1961-90 monthly number of days of thunder. (Bold values indicate the highest monthly frequency for each site.) J

F

M

A

M

J

J

A

S

O

N

D

Kirkwall Stornoway Dyce Efmdon Shawbury

0.7 0.6 0.1 0.3 0.1

0.5 0.4 0.0 0.3 0.1

0.3 0.4 0.0 0.6 0.2

0.1 0.0 0.1 1.1 0.4

0.3 0.2 0.6 3.0 2.3

0.3 0.2 0.8 2.5 1.7

0.6 0.2 0.6 2.6 2.1

0.4 0.3 1.0 2.2 1.7

0.1 0.2 0.3 1.1 0.9

0.4 0.4 0.2 0.3 0.3

0.7 0.5 0.1 0.2 0.1

0.4 0.5 0.1 0.2 0.1

Eskdalemuir Ringway Valley Plymouth

0.3 0.4 0.2 1.0

0.1 0.4 0.2 0.3

0.3 0.6 0.2 0.4

0.5 0.9 0.1 0.3

2.1 2.5 0.8 1.0

1.7 2.1 0.8 1.3

1.3 1.8 0.9 1.7

1.4 1.7 0.8 1.0

1.1 1.3 0.6 0.7

0.5 0.7 0.7 0.8

0.5 0.3 0.6 0.4

0.1 0.4 0.5 0.5

A lthough thunderstorm s tend to be localised and are usually o f short d uration they can produce high precipitation totals w hich may lead to local flooding (see C hapter 13). For thunderstorm s to occur a deep, m oist, unstable layer of air is needed to allow the grow th of large cum ulonim bus clouds. In eastern and

central England the num ber o f days o f thunder tends to be highest between May and A ugust, when favourable conditions occur as a result of local heating (see Table 3.5). Further north, w inter thunderstorm s, associated w ith the marked tem perature contrast in a c o ld fro n t, are more frequent. H ail tends to be

THE SU RFA C E CLIMATE OF THE BRITISH ISLES

Table 3.6 Average 1961-90 number of 'raindays' per season and average precipitation intensity (mm/day) on raindays. (Bold type indicates the season in which precipitation intensity is highest.)

Rain days

Winter Intensity (mm/day)

Spring Rain Intensity days (mm/day)

Summer Rain Intensify days (mm/day)

Autumn Rain Intensity days (mm/day)

Kirkwall Stornoway Dyce Elmdon Oxford

22.9 22.4 17.0 15.1 14.9

4.2 4.9 4.0 3.8 3.5

18.5 20.0 15.8 15.1 14.5

3.4 3.8 3.6 3.5 3.5

17.4 18.7 15.2 12.6 11.6

3.5 3.9 4.0 4.6 4.6

22.9 23.9 16.8 13.8 13.5

5.0 5.4 4.4 4.0 4.0

Shawbury Cork Kilkenny Clones

15.8 20.8 18.8 20.3

3.4 6.4 4.3 4.0

15.3 17.1 16.4 18.4

3.3 4.9 3.5 3.6

13.1 14.8 14.4 17.7

4.1 4.9 3.9 3.8

15.0 19.2 17.6 20.8

4.0 5.8 4.4 4.2

associated w ith su m m er th u n d ersto rm s in southern and eastern areas o f th e B ritish Isles, w hilst over the hills and coasts o f w estern and north ern areas it is m ost freq u en t in w in ter and tends to be associated w ith m aritim e polar and arctic airstream s. A n o th er index o f w etness is th e ‘rainday’.7 T he seasonal average n u m b er o f raindays and th e corre­ spo n d in g values o f p re cip ita tio n in te n sity on these days are show n in Table 3.6 for a n u m b er o f sites. T h e sm allest n u m b e r of raindays is recorded in the su m m er at all nine sites, b u t for central and eastern sites p re cip ita tio n in ten sity is hig h est in th is season; convective p re cip ita tio n is d o m in a n t in these areas in sum m er. Elsew here, p re cip ita tio n in ten sity is g e n ­ erally h ig h est in a u tu m n associated w ith th e arrival o f m o istu re-lad en frontal system s from the A tlan tic, p erhaps enhanced by orographic uplift. F rontal system s, p o la r lo w s or t r o u g h s and insta­ b ility show ers m ay result in snow fall over th e B ritish Isles. T he role w hich each o f these factors plays in p ro d u cin g snow fall varies th ro u g h o u t the country, b u t in general th e frequency o f snow falling increases tow ards th e n o rth and east and w ith a ltitu d e . Areas w hich are exposed to northerly, north-w esterly or easterly w in d s suffer m ost from in stab ility snow show ers especially w here h igh g ro u n d is close to the coast, for exam ple, the N o rth York M oors (Figure 3.6). A rctic air m ay b rin g sudden snowfalls from

Figure 3.6 An early morning (0950 GMT) visible satellite image (from NOAA 5) of che North Sea showing exten­ sive snow cover over eastern England and Scotland on 17 February 1978. The day was classified as ‘easterly’ in the Lamb Catalogue. Courtesy of the University of Dundee.

E L A IN E B A R R O W A N D M IK E HULME

Figure 3-7 Average number of 'snowdays’ in winter, 1961 to 1990. A snowday is defined as snow lying at 0900 GM T’. The values shown in this map are derived from observing stations mostly at low elevations; the actual number of snowdays on the hills and mountains are much greater than these.

sm all depressions, know n as polar lows, w hich develop

snow days is experienced in th e Scottish H ig h lan d s,

unexpectedly.

north-w est Ireland and N o rth W ales (Figure 3.8).

T h e average n u m b er o f ‘snow days’8 in w in ter is illu stra te d in F igure 3.7. T h e g reatest frequency of

In central and southern E ngland, an average w inter w ould

have

betw een

three

and

six

snow days

THE S U R F A C E CLIM ATE O F THE BRITISH ISLES

Figure 3.8 Snow lying on the south facc of Cadcr Idris, Snowdonia National Park. The uplands of the British Isles often experience several weeks of snow cover in contrast to lowland areas where, on average, less chan ten days of snow cover occur.

c o m p a red to b e tw ee n only one an d th re e snow days

d u ra tio n . In g en eral, th ere is a decrease in su n sh in e

in th e low er e lev atio n areas o f th e so u th -w e st. S im ilar

h ours from so u th to n o rth , from th e coast to inlan d

p a tte rn s ex ist in sp rin g an d a u tu m n , a lth o u g h to ta ls

an d w ith a ltitu d e . T h e so u th coast te n d s to b e the

are o b viously n o t as g re a t as in w in te r m o n th s. T h e

su n n ie st area o f th e B ritish Isles because it is m ost

v a ria tio n in snow days from year to year is discussed

sh eltered from th e c lo u d -b e a rin g w esterly an d e ast­

in C h a p te r

erly w inds an d is also influenced by c o n tin e n ta l h ig h

10 an d

u n u su a lly snow y w in te rs

in

C h a p te r 13.

pressure system s. P late 5 illu stra te s th e seasonal vari­ a tio n in su n sh in e receip t over th e B ritish Isles. In w in te r, m a x im u m su n sh in e to ta ls (b etw een 1.5 and

OTHER CLIMATE VARIABLES: SUNSHINE, HUMIDITY AND WIND SPEED

2.5 h o u rs p e r day) are experienced a long th e so u th coast, w hereas in sp rin g m any coastal areas o f m a in ­

Sunshine

land B rita in and Irela n d have th e ir h ig h e st su n sh in e

T h e an n u al v a ria tio n in d a y le n g th associated w ith

areas o f m a x im u m su n sh in e (m ore th an 6 h ours per

th e changcs in solar d e c lin a tio n m eans th a t th ere is

day) are in th e so u th and east w ith to ta ls a lm o st

a m ark e d a n n u a l v a ria tio n in average d a ily su n sh in e

d o u b le th o se in Scotland. In a u tu m n , su n sh in e to ta ls

to ta ls (b etw een 5 and 5.5 hours p e r day). In su m m er,

E L A IN E B A R R O W A N D M IKE HULME

Table 3.7 Average 1961-90 monthly relative humidity (per cent). (Range is the difference between the least and most humid months of the year.) J

F

/VI

A

M

J

J

A

S

O

N

D

Kirkwall Stornoway Dyce Durham Santon Downham

89 87 86 89 95

87 88 84 87 94

87 88 80 83 89

86 87 80 82 86

85 85 81 81 83

85 85 80 82 82

88 87 79 81 84

90 89 82 84 86

90 90 83 85 88

90 91 85 88 95

90 91 85 89 97

88 90 86 89 97

6 7 8 15

Elmdon Oxford Shawbury Gatwick Eskdalemuir

90 89 89 91 92

87 86 87 87 88

83 81 83 84 85

78 78 81 80 83

77 75 79 79 81

75 74 78 78 82

75 73 79 78 84

79 77 81 81 86

83 81 84 86 89

87 86 88 90 90

88 89 89 91 92

89 91 90 93 92

15 18 12 15 11

Ringway Valley Long Ashton Plymouth Cork Kilkenny Clones

86 85 89 89 92 90 92

83 83 87 86 89 86 87

78 83 82 84 86 82 83

74 80 79 80 82 79 80

70 78 77 80 82 78 79

72 80 77 81 82 79 80

74 81 77 81 82 79 81

76 82 79 83 84 81 83

79 84 83 85 87 84 86

82 84 89 87 90 89 88

84 84 89 88 92 90 92

86 86 92 89 93 92 93

16 8 15 9 11 14 14

are again largest in southern and eastern E ngland

Range 5

able tem p e ra tu re regim e in coastal areas. P late 6

(3.5 to 4 hours p er day). T he su n n iest m o n th for

illustrates the seasonal variation in relative h u m id ity

m uch o f the B ritish Isles ten d s to be May even

over the B ritish Isles.

th o u g h th e average d a y len g th is shorter th an in Ju n e .

Relative h u m id ity also affects how com fortable people feel in a p a rticu la r place and at a particu lar

Relative humidity

tim e. People are generally accustom ed to th e range o f tem peratures o f th e country w here they live, and

T h e w a ter-holding capacity of th e atm osphere is

w hether or not they feel com fortable at a given

dep en d e n t on tem p eratu re; as tem p e ra tu re increases

tem perature depends largely on the relative h u m id ­

th e a m o u n t of w ater vapour th e air can hold also

ity. If the relative h u m id ity is different from usual

increases. S aturated air at 20°C, for exam ple, holds

th en sim ilar tem peratures do not produce th e sam e feeling o f com fort or discom fort. In order to m ain­

3.6 tim es m ore w ater vapour th an a ir at 0°C. Relative h u m id ity is a m easure o f th e am o u n t o f w ater vapour in th e air com pared to th e m axim um a m o u n t the air

tain a c onstant body tem perature in w arm conditions perspiration — evaporation o f w ater from th e skin —

can hold at th a t p a rticu la r tem p e ra tu re, expressed as

occurs. As this process proceeds, energy is required

a percentage. Table 3-7 illustrates average m o n th ly

to evaporate the w ater and th e body is cooled. If

relative h u m id ity for selected sites. Coastal sites have

relative h u m id ity is low and tem peratures are high

a sm aller range of relative h u m id ity over the year (for exam ple, K irkw all 5 per cen t) than sites in

th en evaporation is rapid and perspiration evaporates

inland areas (for exam ple, O xford 18 per cent). T his is p artly because of th e c onstant supply o f m oisture

to avoid dehydration. I f relative h u m id ity is h igh,

around th e coast, b u t also because of th e less vari­

and people feel sticky and hot. As tem peratures

from the skin easily. R eplacem ent o f fluid is required however, then body sw eat does not evaporate readily

M ean T e m p e r a tu r e Winter

Spring

60*N

80°N

50*N

50*N

Sum m er

Autumn 60*N

50*N

Plate 1 Seasonal average m ean e e m p e ra tu re , ’C , 1961 to 1 9 9 0 p e rio d . O n rh is, an d all ocher m a p s, th e d a ta sh o w n are for th e av erag e elev a tio n in each 10 k m g r id cell. W in te r = D JF ; sp rin g = M A M ; s u m m e r = J J A ; a u tu m n = S O N .

M ean M ax im u m T e m p e r a tu r e Spring

Winter 60*N

d e g r e e s C e ls iu s

50*N

Autumn

Sum m er 60*N

6 0 -N

50*N

Plate 2 Seasonal average maximum temperature, °C, 1961 to 1990 period.

Mean M in im u m T e m p e r a tu r e

60"N

d e g r e e s C e ls iu s > 14 12 - 14

50-N

10

Sum m er

Autumn

60*N

60*N

50*N

50*N

Plate 3 Seasonal average minimum temperature, °C, 1%1 to 1990 period.

-

12

8-10 8 - 8 4 - 8 2 - 4 0 - 2 - 2 - 0
5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0
ridge U niversity Press, 1994, pp. 2 4 -5 4 . A .G . S m ith , D .G . S m ith and B.M. Funnell, op. cit.; B .U . H aq, J . H ardenbol and P R . Vail, ‘M esozoic and Cenozoic c h ronostratigraphy and eustatic cycles’, in C .K . W ilg u s, B.S. H astin g s, H . Posam entier, J.V. W agoner, C.A. Ross and C .G . St. C. K endall (eds). Sea level changes: an integrated approach, Socicty of Econom ic Paleontologists and M ineralogists, Special P u blication 4 2 , T ulsa, O k la., 1988, p p . 7 1 - 1 0 8 ; B.M. Funnell, ‘G lobal sea-level and the (pen-)insularity o f late Ccnozoic B rita in ’, in R.C. Preece (cd.). Island Britain: a Quaternary perspective, G eological Society Special P u blication N o. 96 , L ondon, 1995, pp. 3 -1 3 . B.M . Funnell, op. cit. Ibid. B.M . Funnell, Plio-Pleistocene Palaeogeography of th e southern N o rth Sea basin (3.75 to 0.55 M a)’, Quaternary Science Reviews, 1996, vol. 15, pp . 3 9 1 -4 0 5 . A.C. M ix, N .G . Pisias, W . R u g h , J . W ilson, A. Morey and T.K . H agelberg, 'B enthic foram inifera stable isotoj>e record from Site 8 4 9 (0 -5 Ma): Local and global clim ate changes’, in N .G . Pisias, L.A. Mayer, T.R. Pal m cr-Ju Ison and T .H . van A ndel (eds). Proceedings o f the Ocean D rilling Program. Scientific Results, O cean D rillin g P ro g ram , C ollege S tation, Tex., 1995, vol. 138, pp . 3 7 1 -4 1 2 . E.L. Sykes, L.D. K eigw in and W.B. Curry, ‘Pliocene paleoceanography: circulation and oceanographic changes associated w ith the 2.4 Ma glacial e v en t’, Paleoceanography, 1991, vol. 6 , pp. 24 5 —57. D .W . D ansgaard, S.J. Jo h n scn , H .B . C lausen, D. D ahlJensen, N .S. G u n d e rstru p . C .U . H am m er, C.S. H v id b e rg , J.P. Steffensen, A.E. S veinbjornsdottir, J. Jouzel and G . B ond, ‘E vidence for general in stability of past clim ate from a 2 50 kyr ice-core record’. Nature, 1993, vol. 364, pp. 21 8 - 20. D .Q . Bowen, ‘T he Pleistocene of N o rth W est E urope’, Science Progress, 1992, vol. 76 , p p . 2 0 9 -2 3 . A .J. Sutcliffe, ‘Insularity o f the B ritish Isles 2 5 0 ,0 0 0 3 0 ,0 0 0 years ago: the m am m alian, inclu d in g hum an, evidence’, in R.C. Preece (ed.), Island Britain: a Quaternary perspective, G eological Society Special P u b lica tio n N o. 9 6 , L ondon, 1995, pp . 127—40. R .G . W est, ‘Pleistocene forest history in East A n g lia ’, N ew Phytologist, 1980, vol. 85 , pp. 5 7 1 -6 2 2 . W .H . Z agw ijn, ‘V egetation and c lim ate d u rin g w arm er intervals in the Late Pleistocene o f W estern and C entral E urope1, Quaternary International, 1989, vols 3—4, pp. 5 7 -6 7 . G .R . Coope, Fossil coleopteran assem blages as sensitive indicators o f clim atic changes d u rin g the D evensian

THE CLIMATES OF PAST A G E S

(Last) cold sta g e ’, Philosophical Transactions o f the Royal Society o f London, 1977, vol. B 280, pp . 3 1 3 -4 0 . 19 G.S. B o u lto n , A.S. Jo n es, K .M . C layton and M.J. K e n n in g , A B ritish ice-sheet m odel and p a tte rn s o f glacial erosion and d eposition in B rita in ’, in F.W. Shorn») (ed.), B ritish Quaternary Studies: Recent Advances, O xford, O xford U n iv ersity Press, 1977, p. 234. 2 0 D . G o rdon, P.L. S m art, D.C. Ford, J .N . A ndrew s, T.C. A tk in so n , P J . Rowe and N .S .J. C hristopher, 'D a tin g o f late Pleistocene interglacial and intcrstadial periods in th e U n ite d K in g d o m from speleothem g ro w th frequency’, Quaternary Research, 1989, vol. 31, pp. 1 4 -2 6 ; A. Baker, P.L. S m art and D.C. Ford, ‘N o rth ­ w est E uropean palaeoclim ate as ind icated by grow th frequency v ariations o f secondary calcite d e p o sits’, Pa/aeogeography, Palaeoclimatology, Palaeoecology, 1993, vol. 100, pp . 2 9 1 -3 0 1 . 21 A. Baker et a l.y op. c it.; G . B ond, II. H e in ric h , W. Broecker, L. Labeyric, J . M cM anus, J . A ndrew s, S. H u o n , R. Ja n tsc h ik , S. C lasen, C. Sim et, K. Tedesco, M. K las, G . B onani and S. Ivy, ‘E vidence for massive discharges o f icebergs in to the N o rth A tlan tic ocean d u rin g th e last glacial p e rio d ’, Nature, 1992, vol. 3 6 0 , pp. 2 4 5 - 9 ; G . B ond, W. Broecker, S. Jo h n sen , J . M cM anus, L. Labeyrie, J . Jouzel and G . B onani, ‘C orrelations betw een c lim ate records from N o rth A tlan tic sed im en ts and G reenland ice’, N ature, 1993, vol. 365, pp. 143—7; G .C . Bond and R. L otti, ‘Iceberg discharges in to rlie* N o rth A tlan tic on m illennial tim e scales d u rin g the Last G la ciatio n ’, Science, 1995,

vol. 2 6 7 , pp. 1 0 0 5 -1 0 . 22 C .K . B allantyne and C. H arris, The Periglaciation o f Great B rita in , C am bridge, C am bridge U niversity Press, 1994, 330 pp.; R .G .B . W illiam s, ‘T h e B ritish clim ate d u rin g the Last G laciation: an in te rp reta tio n based on periglacial phenom ena’, in A .F. W rig h t and F. Moseley (eds), Ice Ages: Ancient a n d Modern, Liverpool, Seel H ouse Press, 1975, pp . 9 5 -1 1 7 . 23 R L. Jones and D .H . K een, Pleistocene Environments in the British Isles, L ondon, C hapm an and H all, 1993, 346 pp. 24 W. P e n n in g to n , T h e L ite D evensian flora and vege­ tatio n o f B rita in ’, Philosophical Transactions o f the Royal Society of London. Series B, 1977, vol. 280, pp . 2 4 7 -7 1 .

GENERAL READING M . Bell and M J .C . W alker, Late Quaternary Environmental Change: Physical a nd Human Perspectives, H arlow , L ong­ m an Scientific and T echnical, 1992, 273 pp. T.J. Crow ley and G .R . N o rth , Paleoclimatology, O xford, O xford U niversity Press, 1991, 33 9 pp J. Im brie and K.P. Im brie, Ice Ages: Solving the Mystery, L ondon, M acm illan, 1979, 2 24 pp. R.L. Jones and D .H . K een, Pleistocene Environments in the British Isles, L ondon, C hapm an and H all, 1993, 3 46 pp. A.E. W rig h t and F. Moseley (eds), Ice Ages: Ancient and M odem, L iverpool, Seel H ouse Press, 1975, 3 20 pp.

5 R E C O N S T R U C T I N G LATE-GLACIAL A N D H O L O C E N E CLIMATES Keith Briffa and Tim Atkinson Hear the voice of the Bard! Who present, past and future sees; Whose ears have heard The Holy Word That walked among the ancient trees. W i l l i a m B l a k e , Songs of Experience

INTRODUCTION

and full p ic tu re o f p a st c lim ates an d c lim a te change:

T h is c h a p te r is co n cern ed w ith th e c lim a te s o f the

can be d a te d , im precision in th e in te rp re ta tio n o f

lim ita tio n s in th e accuracy w ith w h ich th e evidence B ritish Isles from th e L a s t G la c ia l M a x im u m to

th e lags b etw een forcing an d response, a n d even

th e en d o f th e p re h isto ric p e rio d , w hich en d ed som e

a m b ig u ity

2 .0 0 0 years ago. All e vidence o f past c lim ates d u rin g

c lim ate variables w hose influence is recorded in these

o u r p e rio d o f in te re s t com cs from geo lo g ical accu­

rem ains.

in d efining th e precise n a tu re o f th e

m u la tio n s or se d im e n ta ry records and th e biological

W e are used to th in k in g o f c lim ate in te rm s o f

re m a in s th a t a re .c o n ta in e d w ith in th e m . E xam ples

the sta tistic a l d is trib u tio n o f a specific m ete o ro lo g ­

in clu d e ice-cores, s p e le o th e m s , m arin e, river and

ical v ariable, re p re se n tin g a m easured q u a n tity over

la c u strin e se d im e n ts, soils an d glacial m o ra in e s .

som e clearly defined p e rio d - for exam ple, m o n th ly

B iological evidence in clu d e s th e rem ains o f anim als

m ean

or p la n ts , su ch as b e etle p a rts, p o lle n , p la n t m acro-

B iological, an d even physical, proxy d a ta can rarely

fossils an d tree m egafossils (T able 5.1).

te m p e ra tu re

or to tal

ann u al

p re c ip ita tio n .

b e in te rp re te d solely in term s o f a sin g le variable

Before a tte m p tin g to describe w h a t w e k n o w o f

su ch as te m p e ra tu re or p re c ip ita tio n . R ealistically,

th e c lim a te s of th e B ritish Isles d u r in g rhe last

th ey m u st be seen as th e p ro d u c t o f a m ix tu re o f

2 0 .0 0 0 years, it is im p o rta n t to n o te a n u m b e r o f

th erm al

p ro b lem s th a t arise w hen a tte m p tin g to in te rp re t or

over som e flexible p e rio d -

and

m o istu re

c o n d itio n s

th a t

p revailed

for exam ple d u rin g

sy n th e sise th e d a ta th a t derive from these so-called

the g ro w in g season o f a tree o r in te g ra te d across the

p r o x y c li m a t e ’ s o u rc e s . T h is is p e rtin e n t because,

a cc u m u la tio n an d a b la tio n seasons o f a glacier. O fte n

w h ile we are e n tire ly d e p e n d e n t on th e m , each o f

th e evidence m ay show th e c u m u la tiv e influence o f

these sources o f in fo rm a tio n has its p a rtic u la r lim i­

c o n d itio n s

ta tio n s th a t fru stra te o u r a tte m p ts to p re se n t a clear

decades p rio r to th e fo rm atio n o f th e tre e -rin g o r th e

th a t

p revailed

d u r in g

years

or

even

R EC O N S T R U C T IN G LATE-GLACIAL A ND H O LO C E N E CLIMATES

Table 5 .1 The major sources of palaeoenvironmental and palaeoclimatic data for the Late Glacial and Holocene periods Palaeoclimate proxy

Primary character of the environment indicated

Aspects of palaeoclimate inferred

- Corrie glaciers

Altitude of permanent snowline

Integration of summer ablation (temperature and cloudiness) and winter accumulation (precipitation); directions of snow-bearing winds

- Larger glaciers and icesheets

Extent and shape of ice-sheet, flow direction of ice

General indicator of regional climate

- Protalus ramparts

Former snowfields at altitude of former snowline

Confirms evidence of former corrie glaciers

Chemical and isotopic composi­ tion of ice and occluded air (greenhouse gas composition of former atmospheres); dust content; accumulation rates

Complex combination of temper­ ature, source region of water vapour; atmospheric circulation patterns; snowfall

Profile of ice temperature with depth

General history of mean annual temperature at the surface

Depth of thaw layer

Degree-days of thaw Mean annual temperature Mean annual temperature

Isotopic composition of calcite and included groundwater; luminescence of annual lamination

Cave temperature, isotopic composition of palaeoprecipitation; complex signal related to annual variations in precipitation

Physical evidence: Extent of former glaciers

Information within present icesheets/ice caps - Ice-cores

-

Bore hole temperatures

Periglacial soil and ground ice structures - Involutions - Ice wedge casts - Open system pingos Speleothems

Biological evidence: Insect fossils (identified to species level) -

Beetles

Species range

Monthly mean temperature (with large uncertainty)

-

Chironomids

Lake temperature and food supply

Summer temperatures

- Land snails

Soil type and vegetation

Wetness, dryness

- Aquatic snails and bivalves (fresh or marine)

Water temperature, water chemistry

General warmth/cold

Mollusc fossils

KEITH BRIFFA AND TIM ATKINSON Table 5.1 continued Palaeoclimate proxy

Primary character of the environment indicated

Aspects of palaeoclimate inferred

Diatoms (in freshwater lake sediments)

Water chemistry, lake productivity

General warmth/cold

Foraminifera (marine sediments)

Water temperature, salinity and food/mineral supply

Seasonal sea-surface and lower ocean temperatures

Species ranges Biotope habitat

Seasonal temperatures Crude indicator of general climate

Altitudinal and latitudinal tree lines

Mixture of snowlie, exposure and summer and winter tempera­ tures

Former plant distributions

summer temperature thresholds (winter for a few species), moisture availability

- Mosses (in peat bogs)

Surface wetness of bog

Water balance in summer

- Aquatic plants (some species)

Character of vegetation

General warmth/cold, summer temperature thresholds

Pollens/spores (identified to genus/family level)

Character of vegetation

General warmth/cold, wetness/dryness

Tree-rings

Tree growth rate, ring density, chemical composition

Variable mixture of temperature and moisture availability

Vertebrate fossils - Cold blooded - Warm blooded Plant megafossils (tree remains)

Plant macrofossils (identified to species level) - Certain terrestrial plants (some species)

m ovem ent o f the glacier term inus. Many sources may provide evidence th at is fragm entary or discontin­ uous. Som etim es the effect', seen as some change in the proxy data record, may lag behind the ‘forcing’ clim ate change by m any decades or even centuries. Exam ples o f such delayed responses are changing tree lines or shifts in vegetation zones. Indeed, on tim e-scalcs o f centurics to m illennia, the lack of an equivalent long instrum ental-based clim ate yardstick m akes it im possible to com pare and calibrate proxy evidence to provide rigorous q uantitative estim ates o f past clim ates and their uncertainties. Some data, such as from tree-rings, may be contin­ uous, absolutely dated and o f annual or even specific seasonal resolution. Statistical problem s associated

w ith assem bling long com posite chronologies (i.e., those made up of many overlapping series from living and dead trees) can mean, however, that these data may only inform us about clim atc variability occurring on tim e-scales up to several decades or centuries. These data provide potentially unique insights into the nature of interannual clim ate variability and very rapid shifts or abrupt events, but they have lim ited potential ro inform us about the long-term differences in clim ate, such as occur between one m illennium and the next. Clearly, producing a com plete picture o f changing clim ate conditions over m any thousands o f years is a difficult task, even for an area as small as the British Isles. The diverse evidence of many disciplines m ust

R E C O N S T R U C T IN G LATE-GLACIAL A N D H O L O C E N E CLIMATES

be b ro u g h t together, in te rp rete d and reconciled. T he

at a n u m b er o f discrete periods d u rin g th e last

p roblem can be likened to th e restoration o f an old

2 2 ,0 0 0 radiocarbon years before present (i.e., 22 Ka

cine film th a t has been broken in to pieces, m any o f

bp;

w hich are lost. O n ly p arts o f th e surviving individual fram es are discernible and we are often not even sure

Like m any plants and oth er anim als, particular species of beetle thrive only w ith in certain clim ate

see Box 5.1).

lim its. A lth o u g h they m ay appear to have com plex

o f the stric t order in w hich to place them . In the follow ing pages wc describe selected parts

or diverse geographical d istrib u tio n s, it has been

o f th e ’film ’, illu stra tin g th e chan g in g clim atc o f the

discovered th a t m ost European species’ ranges, when

B ritish

Isles since th e hist m ajor glaciation, to

m apped according to tw o sim ple tem perature axes

th e e x ten t th a t it is possible to piece it to g eth e r at

(the mean tem p eratu re o f th e w arm est m o n th w hich

present.

we will call T max’, and the ranee betw een th e w arm est ° and coldest m o nths in the year, T rangr), alm ost invari­ ably represent coherent and clearly definable therm al

THE END OF THE LAST GREAT ICE AGE: THE LATE-GLACIAL PERIOD

ranges. A ccuratc inform ation on the present-day geographical ranges o f beetle species can be com pared w ith m odern m eteorological d ata to build

The evidence of beetles

up a

Perhaps o u r d e a re st p ictu rc o f seasonal tem p eratu re

library

o f tw o-dim ensional clim ate

range

‘envelopes’. W herever tw o or m ore beetles are know n

changes in th e B ritish Isles d u rin g th e tran sitio n

to co-exist, wc m ay assum e th a t the therm al clim ate

from

m u st lie w ith in the area o f overlap betw een th eir

glacial to in terglacial conditions has been

deduced from th e presence o f assem blages o f p a rtic ­

individual clim atc

ular beetle species,1 identified as fossil rem ains dated

rationale for the ‘m u tu al clim ate range’ (M CR)

BOX 5.1 RADIOCARBON AND ABSOLUTE TIME-SCALES

range envelopes. T his is the

At any one tim e, all living things w ill have the same proportion o f ,4C in their tissues, either because plants acquire it in photosynthesis or

Part o f the carbon in the atmosphere exists in

because animals eat plants or other animals that

the form o f the radioactive isotope ,4C. This is produced when cosm ic energy entering the

are alive, the ,4C is constantly replenished in their

Earth’s atmosphere

collides

with

atoms

and

have already assimilated it. For as long as they

releases free neutrons, som e o f which then collide

living tissue. As soon as they die, however, this renewal ceases and the ,4C then decays at a known

w ith nitrogen atoms substituting one o f the

exponential rate. By measuring the amount o f

nitrogen protons (which is released as hydrogen) to form l4C. T his radioactive carbon is then

radioactivity remaining in a sample o f old organic matter it is possible to estim ate the tim e that has

oxidised to form l4C O , and is rapidly mixed in

elapsed since its death. There are many problems

the atmosphere w ith the other non-radioactive

and assumptions

carbon dioxide and so enters the various carbon

dating, but they are beyond the scope o f our discussion here.

reservoirs. In tim e, the ,4C decays back to nitro­

associated

with

radiocarbon

gen through the release o f a beta particle and a

The one major assumption o f the technique is

neutrino. Over many thousands o f years (prior to

that the amount o f radiocarbon in the atmosphere

atom ic bom b tests), there has been a general

has remained constant. N ow we now know that

balance between the amount o f ,4C that decays

there have been short tim e-scale (annual-decadal)

and the renewed production in the atmosphere.

and longer (century-m illennial) variations in the

KEITH BRIFFA A N D TIM A T K IN S O N

2

4

6

8

10

12

14

16

18

20

22

24

T housands of C alender Years Before Present (Present - AD 1950)

a m o u n t o f ,4C in th e atm osphere. A gain a detailed

w hile a l4C d ate o f 2 0 ,0 0 0 years BP im plies a date

discussion is not w arranted here o th e r th an to say

2 3 ,0 0 0 years ago. T h e inset on th e figure shows

th a t they relate to changes in solar activity, the E a rth ’s carbon cycle and p articularly long-term

how the sm all-scale ‘w iggles’ in th e relatively high-precision ,4C calibration curve result in vari­

changes in th e E a rth ’s m agnetic field. By com ­

able d a tin g precision. A ,4C d ate o f 2 ,8 3 0 ± 50

p a ring th e a m o u n t o f radiocarbon in sam ples of

years BP corresponds to a calendar u n certainty o f

know n d a te , such as in tree-rings and (w ith less

about 1 0 2 0 -9 1 0 BC (2 ,9 7 0 -2 ,8 6 0 actual years

precision) lake varves4 and corals,h th e biases

before present, i.e., 1950), whereas a proxim al ,4C d ate w ith sim ilar fifty-year co u n tin g uncertainty,

betw een th e radiocarbon and actual dates can, these w hen e stim a tin g calendar dates based on

i.e., 2 ,5 0 0 ± 50 years B P, produces a larger calendar range o f 7 8 0 -5 2 0 BC (2 ,7 3 0 -2 ,4 7 0

th e ‘calib ra ted ’ radiocarbon tim e-scale.

actual years before present).

however, be calculated and allow ance m ade for

T h e figure show s how radiocarbon dates clearly becom e progressively too young as they g e t older, and ‘p lateau x ’ on th e calibration curve can result in an ap parent b u n c h in g o f ,4C dates in som e periods. For exam ple, an apparent ,4C d ate o f 10,000

years BP (th e tim e o f th e Y o u n g e r

D ry a s /H o lo c e n e

boundary -

see text) corre­

sponds to a ‘real’ d ate o f about 11,000 years ago,

Unless otherw ise stated, all th e dates in this c hapter are radiocarbon dates. • M. Stuiver, A. Long and R.S. Kra (eds), ’Calibration 1993’, Radiocarbon, 1993, vol. 35, p. 244. b E. Bard, B. Hamelin, G. Fairbanks and A. Zindler, ‘Calibration of the ,4C timescale over the past 30,000 years using mass spectrometric U-Th ages from Barbados corals’, Nature, 1990, vol. 345, pp. 404-10.

R E C O N S T R U C T IN G LATE-GLACIAL A N D H O L O C E N E CLIMATES

m eth o d o f clim ate reconstruction w hich has been

5.2. For convenience, in th e follow ing discussion we

used to produce F igure 5.1 on p. 90.

w ill refer to the probable m ean tem peratures. from

T here are few data betw een about 18,000 and

previous analyses o f tw enty-six m ostly late-glacial

15,000 years BP. Evidence from a site in G w ynedd,

In

a stu d y 2 o f beetle

faunas

identified

and H olocene sites in th e B ritish Isles, it has been

N o rth W ales, indicates th a t very cold conditions

possible to derive M C R estim ates o f T m ax and T ra n g e

(sim ilar to 2 2 ,0 0 0 years BP) existed at around 14,500 years BP and then again later a t 13,000 years BP.

r

From these, th e m ean tem p e ra tu re o f th e coldest m o n th , T min, and th e annual m ean tem p eratu re,

D ata from tw o sites in Yorkshire and C am bridgeshire

T a n n u a.,l’ has been deduced for m ore th an fifty* discrete

suggest, however, th a t sum m ers were about 3*C

tim e poin ts d u rin g the period 15,000 to 8 ,0 0 0 years

w arm er th an 2 2,000 years BP (i.e., a w arm est m onth

B P, as well as for an o th er e ig h t tim e ‘snapshots’ at

of about 10°C) and w inters up to 15°C w arm er (about

about 2 1 ,5 0 0 , 19,500, 1 8 ,4 0 0 , 4 ,8 0 0 , 3 ,0 0 0 , 2 ,100

-1 5 °C ) betw een 2 0,000 and 18,000 years B P, just

and 4 0 0 years BP (Figure 5.1). These d ata provide

at the tim e w hen the ice-sheet was probably at its

detailed q u a n tita tiv e evidence about large, and som e­ tim es very a b ru p t, tem p e ra tu re changcs th a t occurred

m axim um extent.

in th e B ritish Isles as th e D e v e n s ia n

ice-sheet

tures rose from those characteristic o f th e last ice age

retreated and th e m ore stable, w arm er clim ates o f

to those generally characteristic o f the H olocene: a sum m er change o f roughly 9°C (from about 8.5°C to

th e H olocene period finally becam e established. T hey

Betw een 13,500 and 10,000 years BP, tem pera­

significant

17.5°C), a w in ter change o f about 20°C (-2 0 'C

shorter tim c-scale fluctuations in tem p eratu re were

to 0°C) and hence a near 50 per cent reduction in

superim posed on these broader changes. T h e beetle d ata indicate th a t betw een 2 2 ,0 0 0 years

co n tin e n ta lity (i.e., the su m m e r-w in te r tem perature

also

provide

stro n g

indications

th a t

BP and 2 0 ,0 0 0 years B P, m ean annual tem peratures

range declined from about 30*C to 17°C). T his glacial/interglacial tran sitio n was, however, far from

w ere in th e range 0°C to -1 5 ° C , m ost likely near

sm ooth. O n th e contrary, th e beetle d a ta show th at

-1 2 °C . T h e m ean tem p e ra tu re o f the w arm est m o n th was betw een 5°C and 14"C, probably near 7°C, and

it was m arked by extrem e variability on m illennial

th e eoldest betw een -1 0 °C and -3 5 °C , likely near

and even perhaps on c entury tim e-scales. It is not wise to p u t too m uch faith in th e fine

-3 0 °C . T h e ranges we q u o te here are those indicated

details o f th e tem perature reconstructions show n in

by th e full e x te n t o f th e M C R for th e particu lar

Figure 5.1. W e do not know w hat calendar uncer­

beetle assem blage th a t we know existed at th at

tain ty m ig h t be attached to each radiocarbon d ate as

period. T h e m ean clim ates w ere som ew here w ith in these ranges. W c can also go som e way, however,

we have no precise absolute tim e-scale w ith w hich to calibrate the radiocarbon tim e-scale th is far back

to e stim a tin g m ore precisely w here, w ith in these

(cf. Box 5.1). Figure 5.1 also provides an illu stratio n

ranges, th e m ean clim ate lay. T hese ‘m ost likely’ values have been derived from regression equations

o f the T annuaJ change, sm oothed to take account o f th e uncertainty in th e individual radiocarbon dates.

e stim a tin g m odern observed tem p eratu res from the

T h is can be viewed as an objective, b u t conservative,

m edians o f th e tem p e ra tu re ranges indicated by

representation o f th e course o f tem perature vari­

m odern beetles living at th e sam e localities. These e quations allow us to estim ate the real tem peratures

a b ility im plied by the raw annual estim ates. M any o f the individual beetle assem blages are taken from

w ith a 1precision o f about ±2°C for T max and ±5°C

a stratig rap h ic context, particularly a t tw o sites -

for T min. T h e full estim a te d tem p e ra tu re ranges and

one in G lanllynnau in G w ynedd and one from

th e ‘m o st p ro b a b le ’ values are show n separately for

St Bees in C u m b ria / T his gives a strong indication

su m m er and w in ter in F igure 5.1 and th e changing

th a t a t least th e order, if not the precise tim ing, of

annual cycle o f tem p eratu res in th e form o f estim ated

events superim posed on th e m ajor changes may

d e g re e d a y s o f frost and thaw is show n in Figure

indeed be real.

KEITH BRI FFA A N D TIM A T K I N S O N

thousand radiocarbon years BP

Figure 5 . 1 T e m p e ra tu re c h an g e s in rhe B ritish Isles d u rin g th e L ate-G lacial an d H o lo cen e p e rio d s e stim a te d on th e basis o f b e e tle re m a in s (see p. 109 N o te 1). T h e vertical bars show rhe ran g es w ith in w h ich th e m ean te m p e ra tu re o f th e w a rm e st m o n th , th e co ld est m o n th a n d th e year lay. N o te th a t these are in d ic a te d on a rad io carb o n tim e -sc ale (see Box 5 .1 ) a n d d o n o t show th e u n c e rta in ty associated w ith each d a te . T h e d o ts in d ic a te th e ‘m o st p ro b a b le ' values w ith in th e te m p e ra tu re ran g es. T h e b o ld lin e in th e b o tto m box show s te m p o ra lly sm o o th ed e stim a te s w h ich m ay u n d e re s tim a te th e ra p id ity a n d m a g n itu d e o f som e o f th e changes. T h e values p lo tte d a t 0 years liP (i.e., today) are th e m ean (d o t) an d m a x im u m ra n g e (b a r) o f th e C c n tra l Iin g la n d T em p era tu re rccord over th e p e rio d 1 6 5 9 - 1 9 9 5 (see C h a p te r 9).

R E C O N S T R U C T I N G LATE-G LA CIA L A N D H O L O C E N E C LIM A T E S

Cold



Warm

Cold a p e rio d o f relativ e s ta b ility w hen tem p e ra tu re s •_1_________ I_________ I--------------1_________ I_I_________L 1-1- J rem ain ed above g lac ial, b u t below H olocene, levels

(su m m ers a b o u t 15“C an d w in ters a b o u t -5 °C ). A m ore a b ru p t fall occurred a t 1 1 ,3 0 0 years B P , and Temperature (9C )

b etw een 1 1 ,3 0 0 a n d 1 0 ,3 0 0 years B P , te m p e ra tu re s, especially w in te r te m p e ra tu re s, rem ained a t alm o st glacial levels. T h is in terv al is kn o w n as th e Y ounger D ryas

(or

Loch

L om ond

Stadial).

Finally,

Mean Monthly

a n o th e r a p p a re n tly rapid w a rm in g b etw een an d

after

10,300

1 0 ,0 0 0 years B P, te m p e ra tu re s a tta in e d th e ir

Reconstructed

g eneral Ilo lo c en e levels.

The evidence of foraminifera T h e gross p a tte rn o f te m p e ra tu re ch an g e revealed by be etle faunas b etw een 2 0 ,0 0 0 a n d 1 0 ,0 0 0 years BP - from glacial to in te rg lac ia l, follow ed by a b rie f re tu rn to a glacial Y ounger D ryas an d a final e sta b ­ lish m e n t o f a w arm H oloccnc - is in good g eneral a g re e m e n t w ith the scries o f s e a -s u r f a c e t e m p e r a ­ t u r e (SST) changcs re co n stru c te d from selected h ig h re so lu tio n N o r th A tla n tic sea-bed cores.4

Month

Local a b u n d an ces o f d iffere n t p l a n k t o n i c f o r a ­ Figure 5.2 An illustration o f rhe estim ated annual cycle of m onthly mean tem peratures in the British Isles recon­ structed on the basis of beetle assemblages identified at selected periods during rhe transition from glacial ro Holocene conditions. Also given for comparison are the estim ated degree «lays of thaw and frost (i.e., cumulative degree Celsius tem peratures above and below zero respec­ tively). The two sets of curves are plotted on the same scale and are separated only for reasons of clarity.

m in if e r a in ocean w aters are associated w ith varying w ater-m ass c o n d itio n s

(such as te m p e ra tu re

and

sa lin ity ) so th a t fossil foram iniferal g ro u p s, id e n ti­ fied in differen t core stra ta , p ro v id e in fo rm a tio n on p a st ocean te m p e ra tu re s .5 T h e re so lu tio n an d d a tin g c o n tro l is p o o r co m p ared to th e beetle rccord, b u t correlations betw een cores a t m any sites across the n o rth e rn N o rth A tla n tic show th a t th e tim in g and relative m a g n itu d e o f the m ain p o st-g lac ial w a rm in g varied acco rd in g to location. T h e first m ajo r w a rm in g

T he sm o o th ed a n n u a l curve in d icates th a t te m p e r­ atu re s

rose a b ru p tly

b etw een

about

occurred a t a b o u t 1 3 ,0 0 0 years B P in th e eastern

1 3 ,0 0 0 and

N o rth A tla n tic , a t 1 0 ,0 0 0 years B P in th e w est, an d

1 2 ,0 0 0 years B P , b u t th e in d iv id u a l d a ta p o in ts in d i­

even later ar 9 ,0 0 0 -7 ,0 0 0 years B P in th e n o rth -w est,

cate a m u c h faster c lim a te a m e lio ra tio n . By 1 2 ,7 0 0

near L abrador. T h e differences have been exp lain ed

years B P , seasonal te m p e ra tu re s reached levels near,

in te rm s o f th e m ig ra tio n o f th e p o l a r f r o n t th a t

an d in w in te r even s lig h tly above, m a x im u m values

m ark s th e b o u n d ary of cold p o lar w ater. T h e glacial

a tta in e d la te r d u r in g th e H o lo c en e (i.e., w in te rs were

p o sitio n o f th e p o lar fronr was in an east—w est o rie n ­

a t 4°C a n d su m m ers near l6°C ).

ta tio n at a b o u t 4 0 °N . A t aro u n d 1 3 ,0 0 0 years BP

O v e r th e fo llo w in g few th o u sa n d years (b etw een 1 2 ,7 0 0 an d 1 0 ,2 0 0 years B P ), te m p e ra tu re s o scillated

te m p e ra te

w aters

p e n e tra te d

rh e

eastern

N o rth

A tla n tic , b u t n o t th e w est, so th a t rhe p o lar front

a b o u t a g e n era lly d e c lin in g tren d . T h is w as associ­

sw u n g n o rth w a rd s, like a g a te w ith its h in g e near

ated p rim a rily w ith an early c o o lin g , follow ed by

C ape C od o p e n in g to rh e n o rth . Later, th e front

91

KEITH BRIFFA A N D TIM A T K IN S O N

sw ung so u th again, occupying a position off th e coast

A m erican and Scandinavian ice-sheets decayed. T he

o f Ireland or so u th -w est E ngland in the Younger

rate o f ice-sheet decay (as m easured by sea-level

D ryas ( 1 1 ,0 0 0 -1 0 ,0 0 0 years BP). Finally, in the early

rise) slowed ab ru p tly at 11,000 years BP and was

H olocene th e polar front m ig ra ted n o rth , th en n o rth ­

depressed for around a thousand radiocarbon years,

east into th e N orw egian Sea as first th e Scandinavian and th en th e L a u re n tid e ice-sheet w asted away. T he

before resum ing equally ab ru p tly at around 10,000 years BP and reaching a peak in th e early H olocene.

rap id ity o f th e tem p e ra tu re fluctuations show n by

T his slow ing o f ice-sheet decay coincided w ith a

th e beetles on land su p p o rt th is in te rp reta tio n o f the

m arked

m arine foram iniferal evidence. T h e m ag n itu d e o f

A tlantic region, w ith fainter effects being observed

th e w in ter te m p e ra tu re shifts on land are explicable

elsew here in the w orld. In the B ritish Isles there was

in term s o f extensive form ation o f sea-ice off the coast o f th e B ritish Isles d u rin g th e colder periods,

a regrow th o f sm all glaciers and ice-sheets. These were the last glaciers to have existed on these islands,

deterioration

in

clim ate

having

been

in

th e

N o rth

as has also been proposed on the basis o f th e m arine

th e whole country

data.

W inderm ere Interstadial (1 3 ,0 0 0 —11,000 years BP —

ice-free in

the

It w ould be unw ise to assum e th a t th e detailed

see Figure 5.1). T h is m in o r Y ounger D ryas glacia­

succession o f B ritish tem p e ra tu re changes th ro u g h th e late-glacial arc exactly representative o f changcs

tio n was m uch less extensive, however, th an th a t w hich occurred d u rin g the Last G lacial M axim um .

elsew here, even o f o th er areas in w estern Europe. Because o f th e ir position on the A tlan tic seaboard,

to corrics and valley heads in m o u n ta in districts,

T he Younger Dryas glaciers were m ostly confined

near th e m id p o in t o f th e oscillations o f the occan c irculation and polar front (see C h a p te r 2), the

except in the w estern H ig h lan d s where an ice-sheet

B ritish Isles are probably exceptionally sensitive to

still appear very fresh (Figure 5.3) w hich has allowed

these changes in regional clim ate. T h is p o in t is rein ­

th e d istrib u tio n o f Younger Dryas ice to be m apped

forced by the results o f a com parative M C R study

fairly definitively. D ircct d a tin g of th e m ajority o f features is poor, however, alth o u g h in one o r tw o eases

o f late-glacial beetle faunas in th e B ritish Isles, so u th ern Sw eden, w estern N orw ay and central P oland.6 T h is show ed

th at different p a tte rn s o f

developed. T he m oraine deposits left by these glaciers

th e fresh m oraines contain d istu rb ed peat w hich can be radiocarbon-dated to th e W inderm ere Intcrstadial,

change occurred in each o f these areas betw een

thus proving th a t the glacier th a t produced them

13,000 and 1 1,000 years B P , possibly associated w ith

was younger, i.e., o f Y ounger Dryas age. O therw ise,

th e ir specific p ro x im ity to th e w aning Scandinavian

d a tin g these latest glacial features relies upon their

ice-sheet. Interestingly, however, all areas seem ed to

fresh appearance and the fact th at the oldest sedi­

have experienced

m en ts found in lakes and tarns w ith in the recon­

a synchronous

Y ounger Dryas

betw een 1 1 ,0 0 0 and 1 0,000 years B P .7

stru cted glacier lim its are never older th an the early H olocene, 9 ,5 0 0 -1 0 ,0 0 0 years BP. T he Y ounger Dryas also saw a re tu rn o f p e ri-

THE YOUNGER DRYAS IN THE BRITISH ISLES

g lac ial conditions to the B ritish Isles. N um erous

T h e cause o f th e Y ounger Dryas episode is not fully

soil involutions, striped and polygonally patterned

un derstood. It coincides w ith a m axim um in sum m er

gro u n d , ice w edge casts, frost cracks, and pingos.8

solar insolation a t m id -la titu d es (see Box 5.2), when

T hey appear to have form ed in tw o generations since

exam ples o f structures form ed by g round-ice have been m apped from all over th e islands, in cluding

ice-sheet m eltin g should have been a t its m ost rapid.

the retreat o f the m ain B ritish ice-sheet after th e Last

Indeed, w ell-dated records from subm erged tropical

G lacial M axim um , the first being d u rin g the period

coral reefs show th a t sea-level was rising very rapidly

o f cold clim atc p rior to 13,000 years BP and the

just p rio r to th e Y ounger D ryas, as th e N o rth

second d u rin g the Y ounger Dryas (see Figure 5.1).

RECONSTRUCTING LATE-GLACIAL AND HOLOCENE CLIMATES

BOX 5.2 INSOLATION CHANGES THROUGH THE LAST 25,000 YEARS The regional and seasonal distribution of energy received from the sun at the top of the Earth's atm osphere has not remained constant during geological time. The interplay between the grav­ itational effects of the Sun, Moon and other planets continuously influence the shape of the path the Earth takes in its orbit around the Sun (eccentricity), change its axial tilt in relation to this orbital plane (obliquity), and cause it to

wobble on its rotational axis, so that its orbital position at the times of the equinoxes and solstices also changes (precession of the equinoxes; see also Box 4.2, Chapter 4). These quasi-periodic effects are manifest on relatively long time-scales (on average about 95,800, 41,000 and 21,700 years for eccentricity, obliquity and precession respectively), but they have produced significant changes in the seasonal and regional distribution of global insolation during the last 25,000 years/ In the early Holocene, about 11,000 years ago, perihelion (the tim e when the Earth is closest to

In solation changes over the B ritish Isles d u rin g the last 2 5 ,0 0 0 years

Maximum monthly insolation

Annual mean insolation

Minimum monthly insolation

Annual insolation range

KEITH BRIFFA A N D TIM A T K IN S O N

th e sun) occurred in th e N o rth e rn H em isphere su m m er (instead o f th e N o rth e rn H em isphere

T he radiation reaching th e E arth's surface is also

w in ter as it does today) and th e E arth ’s o b liq u ity

spheric conditions (e.g., in d u st loading, c lo u d i­

was greater. T h e figure, constructed using soft­

ness, and th e concentration and d istrib u tio n of

m odified by c hanging stratospheric and tro p o ­

w are provided by A ndré Berger,b show s th a t at

radiatively active gases). Also, surface clim ates are

th e

Isles, m axim um

th e p roduct o f atm ospheric circulation changes

su m m er insolation was then h igher by som e 9

w hich m ay be largely random and w hich are

latitu d e s o f th e

B ritish

per c en t, w hile th e m in im u m w in ter value was

subject to th e varying forcing (and dam p in g )

low er by about 14 per cent, com pared to today. Early H olocene m axim um insolation range

effects o f th e oceans and large ice masses and influenced by com plex feedback processes oper­

(betw een su m m er and w inter) was 13 per cent higher, b u t th e m ean insolation over th e whole

a tin g on different tim e-scales.

year was only about 2.5 per cent g re ater than today. Since th en , su m m er insolation has declined steadily and th a t in w in ter increased, so there has been a corresponding reduction in th e range and in th e annual m ean. W e w ould no t, however, expect to see a sim ple o r d irec t correspondence betw een these orbitally related insolation changes and th e evidence for surface te m p e ra tu re changes. T h e irradiance o f the Sun is variable - only slig h tly so on short tim escales (u p to a decade or so), b u t possibly m ore so on longer tim e-scales (centuries to m ille n n ia )/

T hese features give clues as to th e m ean annual air

4 A. Berger, ‘Long term variations of daily insolation and Quaternary climate changes’. Journal of the Atmospheric Sciences, 1978, vol. 35, pp. 2362-7. b A. Berger, 'A simple algorithm to compute long term variations of daily or monthly insolation'. Contribution No. 18, Institute of Astronomy and Geophysics, Université Catholique de Louvain, Louvain-La-Neuve, Belgium. c J. Lean, Reconstructions of Past Solar Variability', in P.D. Jones, R.S. Bradley and J. Jouzel (eds), Climatic Variations and Forcing Mechanisms of the Last 2000 Years, NATO ASI Series 1,41, Berlin, Springer, 1996, pp. 519-32.

q u ite so low as in the full glacial, w hich agrees

te m p e ra tu re at rhe rim e of th e ir form ation. Fossil ice

both w ith beetle estim ates (Figure 5.1) and w ith the

w edge casts indicate form er continuous p e r m a f r o s t,

presence in central E ngland and W ales o f rem ains o f

and active ice w edges do not occur today w here th e

a second type o f periglacial feature, pingos.

m ean annual air tem p e ra tu re is g re ater th an -6 °C to

Pingos are hillocks th at develop w hen g ro u n d ­

-8 °C . T h e ir occurrence in glacial sedim ent w ithin

w ater freezes to form a lens o f ice w hich m ay be ten

th e areas occupied by rhe last ice-sheet at G lacial M axim um im plies th a t tem p eratu res were as low

or m ore m etres thick. T he ice pushes u p the soil

as th is after th e ice-sheet had retreated, w hich is

hillock, exposing the ice beneath. T h is usually causes

in excellent agreem ent w ith the m ean annual air tem p eratu re estim ates from beetle evidence show n in

rhe ice-core to m elt, leaving a crater-like hollow w ith a raised rim . These p in g o scars occur in g roups in

Figure 5.1 for th e period p rior to 1 3,000 years BP.

a belt across E ngland and W ales. M odern, active

above it u n til it slips off the crest o f the g row ing

A lm ost all B ritish ice w edge casts th a t can be dated

exam ples in Alaska and Spitsbergen occur only in

belong to th is first late-glacial generation or earlier

areas where th e m ean annual a ir tem perature is

and th e very few th a t m ig h t be o f Y ounger Dryas

around —2°C to —5°C. Some East A nglian p in g o scars

age are sm all and im perfectly form ed. T h is suggests

have been radiocarbon dated to th e Y ounger Dryas

th a t Y ounger D ryas tem p eratu res m ay not have been

since older soil form ed at around 11,000 years BP

R E C O N S T R U C T IN G LATE-GLACIAL A N D H O L O C E N E CLIMATES

T he

c o ld -d im a te

geological

features

of

the

Y ounger Dryas give som e inform ation a b o u t w ind d irections and p recipitation at the tim e. From careful m apping o f form er corrie glaciers it is possible to reconstruct th eir form er eq u ilib riu m line altitu d es (ELAs). T h e ELA is the a ltitu d e of a glacier surface at w hich average su m m er ablation and average w inter snow accum ulation are in balance. W herever ELAs have been reconstructed for several form er glac­ iers in th e sam e d istric t they show a m arked rise from th e south or south-w est side to the north-cast side o f the m ou n tain massif. T his occurs despite the fact th a t ice ablation depends strongly on aspcct south-facing glaciers collect m ore solar radiation and th u s experience m ore ablation. T his p a tte rn poin ts very strongly to orographic ra in - s h a d o w effects sim ilar to those w hich occur round th e sam e m ou n tain s today. T he rise in ELAs from south-w est to north-east im plies th a t snow -bearing w inds cam e m ainly

from

th e south-w est quad ran t, as m ost

p recipitation does today. An exceptionally careful and detailed study o f Y ounger Dryas glaciers in Skye9 dem onstrated th a t m ost snow was deposited by southerly w inds, b u t strong w esterlies w ere respon­ sible for blow ing fresh snow from one p a rt o f a sm all ice-cap to another. T his difference betw een m ore southerly w inds p re cip ita tin g snow and w esterlies d riftin g it, h in ts strongly at a clim ate in w hich w inter precip itatio n was b ro u g h t to th e B ritish Isles Figure 5.3a Cwm Idwal, Snowdonia. From the vantage point of the Devil’s Kitchen Llyn Idwal can be seen, and the terminal and sinuous lateral moraines deposited by a corrie glacier some 11,000 years ago during the Younger Dryas period.

by A tlantic d e p re s s io n s , as it is today. R egional p attern s o f p recipitation d u rin g

the

Y ounger Dryas can also be guessed at on the basis o f corrie glaciers’ ELAs and o th er snow -line features. A regional m ap o f ELAs over the w hole Scottish H ig h lan d s (Figure 5.4 inset) shows a rise from 300 m above m odern sea-level in the south-w est

has been incorporated in to rh eir stru ctu re. M ost

to alm ost 9 0 0 m in th e C airngorm s. T h is p a tte rn

exam ples, however, are only p a rtially dared (in rhe

m irrors the rain-shadow s seen on individual massifs

sam e way as m any corrie glaciers are d ated) by

in n orthern E ngland and W ales. T he reality o f the

th e fact th a t th e oldest p o st-p in g o sedim ents in rhe

p a tte rn has been confirm ed by m ap p in g th e a ltitu d e s

cratcrs arc invariably early H olocene. T h e presence

of protaius ram parts, w hich are debris accum ulations

o f p ingos in southern B ritain in th e Y ounger Dryas

th a t occur from p erm anent snow patchcs a t a ltitu d e s

im plies m ean annual air tem p eratu res betw een -2 °C

very close to the perm an en t snow -linc. Figure 5.4

and —5°C w hich is once again in excellent agreem ent

shows th a t the snow -linc in St K ilda and the O u te r

w ith beetle estim ates (Figure 5.1).

H ebrides lay only a few tens o f m etres above m odern

KEITH B R IF F A A N D TIM A T K I N S O N

Figure 5.$b Cwm d u r Arddu, Snowdonia. A small glacier occupied the hollow to the left, transporting and depositing the areas of debris to the right.

sea-level. A lth o u g h th e re m ay have been a su m m e r

(from b e etle evidence) for a fossil exam ple o f a rock

te m p e ra tu re (an d a b la tio n ) g ra d ie n t from w est to east

g lacier, th e n c o n stra in ts can be placed on p re c ip ita ­

across S co tlan d , th is is u n lik e ly to have been m ore

tio n . By th is lin e o f a rg u m e n t, a rcccnt stu d y very

th a n on e or tw o d egrees a t m o st, an d c ertain ly c ould

te n ta tiv e ly co n trasts average an n u al p re c ip ita tio n on

n o t a cc o u n t for th e differences in sn o w -lin e a ltitu d e .

the Isle o f J u r a w ith th a t o f th e C a irn g o rm s d u rin g

T hese m u st be d u e to a m ark ed g ra d ie n t in snow

tim e s o f rock g lac ier fo rm atio n

a c c u m u la tio n an d th u s o f p re c ip ita tio n , in w in te r at

D ry a s.10 For J u ra , an n u al p re c ip ita tio n a t 3 5 0 m

least. T h e islands on th e A tla n tic seaboard m u st have

above m ean sca-lcvel was u n lik e ly to have been

experienced

w ith

g re a te r th a n 8 0 0 —1 2 5 0 m m , w h ic h is 5 0 - 8 0 p e r cent

easte rn S co tlan d w h ic h was m u c h drier, as it is today.

o f th e p re sen t value. By c o n tra st, th e C a irn g o rm

A m o u n ts o f p re c ip ita tio n arc far h a rd e r to e s ti­

p re c ip ita tio n was no m ore th a n 37 5 —5 5 0 m m a t

m ate th a n reg io n al g ra d ie n ts . N ev erth e le ss, som e

9 2 0 m a ltitu d e . T h is rep resen ts a m u ch g re a te r

very

h ig h

snow fall

co m p ared

in th e Y ounger

c o n stra in ts m ay be* placed on average an n u al p re c ip ­

re d u ctio n co m pared to m o d ern levels, a t a b o u t only

ita tio n

2 0 -3 0

by

th e

presence o f d e b ris

a cc u m u la tio n s

p er

c en t

of

presen t-d ay

p re c ip ita tio n .

re p re se n tin g th e rem ains o f r o c k g la c ie r s a t several

A lth o u g h ex tre m e ly te n ta tiv e , these values im p ly a

locatio n s in th e S c o ttish H ig h la n d s . A stu d y o f th e

c lim ate th a t was n o t only c older b u t d rie r th an

m o d e rn ex am p les in th e A lps has c o n clu d cd th a t th ey

p re sen t, w ith

can form only w ith in a specified range o f c o m b in a ­

p re c ip ita tio n co m pared to th e w est. T h is ste ep e r

eastern

S cotland

b e in g

starved

of

tio n s o f m ean an n u al a ir te m p e ra tu re an d average

e a s t-w e st p re c ip ita tio n g ra d ie n t co m p ared w ith th e

an n u al p re c ip ita tio n . T h is m eans th a t if th e m ean

m o d ern p a tte rn m ay have been d u e to th e effect o f

an n u a l a ir te m p e ra tu re can be independently e stim a te d

th e W est H ig h la n d ice-sheet in ‘c a p tu rin g ’ snow fall

R E C O N S T R U C T I N G LA TE-G LACIAL A N D H O L O C E N E C LIM A T E S

Figure .5.4 The lim its of the ice-sheet that covered much of the British Isles during rhe last (Devensian) ice age (based on the map in D.Q. Bowen, J. Rose, A.M. McCabe and D.G. Sutherland, 'Correlation of Quaternary Glaciations in England, Ireland, Scotland and Wales’, Quaternary Science Reviews, 1986, vol. 5, pp. 299-340). The dark-shaded regions indicate the m aximum Younger Dryas ice extent. The inset shows the altitude of protalus ramparts in Scotland and the inferred equilibrium line altitudes (ELAs) of glaciers at their most advanced positions during the Younger Dryas (after C.K. Ballantyne and M.P. Kirkbride, 'The characteristics and significance of some late glacial protalus ramparts in upland Britain’, F.arth Surface Processes and i^andfomiSy 1986, vol. 11, pp. 659 71).

KEITH BRIFFA A N D TIM A T K IN S O N

from a ir m a s s e s a rriving over Scotland from the

1870s, the N orw egian b otanist, Axel B ly tt, recog­

south-w est.

nised various horizons in peat bogs w hich he took

In sum m ary, th e Y ounger Dryas clim ate o f the

to be evidence o f clim ate sh ifts.12 T his stratig rap h y

B ritish Isles is know n in probably m ore detail than

was later refined by R. Sernander and cross-refer-

for any o th er tim e in the Late G lacial. In E ngland the

enced to pollen evidence in Sw edish bo g s.13 D uring the first h alf o f th e tw e n tie th century, as m ore pollen

low lands were around ~5°C w ith th e w arm est m o n th

evidence from around Europe becam e available, the

average about 10*C and the coldest about -2 0 °C .

vegetation

T em peratures at sea-level in Scotland were probably

frequently described in th e context o f w hat became

and

W ales,

m ean

annual

tem p eratu res

in

changes

th a t

they

represented

were

2 -5 °C colder th an this. T h e enhanced c o n tin en tality

know n as th e B lytt/S ernander schem e o f clim ate

and m uch colder w inters com pared w ith the present

subdivision for the late glacial and H olocenc (Figure

day were m ost likely due to th e presence o f c o n tin ­ uous sca-icc in th e A tlan tic w est o f th e islands. T he

periods d u rin g th e H olocene, often interpreted in

m ain w eather p a tte rn s b rin g in g precip itatio n to the

w arm th/w etness term s: the Pre-Boreal (w arm and

B ritish Isles were A tlan tic depressions arriving from

dry); the B o re a l (w arm and dry); the A tla n tic (warm

th e south-w est quad ran t. A lth o u g h th ere is som e

and wet); the Sub-Boreal (w arm and dry) and the

in dication o f hig h

precip itatio n am ounts in th e

S ub-A tlantic (cool and wet). These general clim ate

extrem e w estern isles o f Scotland, general precip ita­

descriptions, and even th eir tem poral boundaries,

tio n

are not now considered w idely representative o f

levels in Scotland were probably less than

to d ay ’s, w ith a steeper c ast-w e st contrast across the

5.5). T h is schem e recognises five general clim ate

changing bog conditions.

H ig h lan d s. Very little is know n about p recipitation p a tte rn s in E ngland, th o u g h th e evidence o f form er corric glacier ELAs in W ales suggests th a t here, too, the m ain inilucncc was m o isture-bearing so u th ­ w esterly w inds.

The pollen evidence Today, largely as a consequence o f m ore refined (and hence m ore accurate) d a tin g techniques, b u t perhaps also because ‘com m on w isdom ’ is now less inclined to

expect

w idespread

synchroneity

in

clim ate

THE HOLOCENE PERIOD

changes, it is recognised th a t th e B lytt/Sernander

Early evidence from bogs

schem e does not satisfactorily represent th e d a tin g

T here arc n o t e nough discrete and w ell-dated records

and p la n t m acrofossil d a ta from m any B ritish and

o f detailed vegetational changes evident in the pollen

o f beetle assem blages spread th ro u g h o u t th e last

European sites. W h a t is know n, however, is th at

1 0,000 years to enable a detailed B ritish H olocene

clim ate changes have occurred and are represented

rccord to be constructed from beetles. T he few d ata

in a great m any H olocene pollen profiles th a t have

th a t do exist, view ed to g eth e r w ith th e foram iniferal

been investigated this century. T his m u ltitu d e o f

d ata from th e N o rth A tla n tic ,11 suggest th a t the

localised

m ag n itu d e o f clim atc changcs w ere certainly m uch

th ro u g h o u t Europe has not led, however, to a corre­

sm aller and probably considerably less rapid th an the

spondingly detailed picture o f sm all-scale regional

large, frenetic events o f th e late glacial period.

clim ate variations. To som e extent, th is is because

site

records

in

the

B ritish

Isles and

T h e H olocene should no t, however, be th o u g h t o f

the d a tin g resolution o f m any pollen profiles (or parts

as a period o f u n ch an g in g clim atc. As early as the

o f profiles) is equivocal. T he m ain reason, however,

Figure 5.') The traditional' view of changing climate and vegetation in northern Europe and the British Isles during the Late Glacial and Holocene Periods (taken from the summary given in Lamb21).

R E C O N S T R U C T I N G LATE-GLACIA L A N D H O L O C E N E C L IM A T ES

100

KEITH BRIFFA A N D TIM A T K IN S O N

it is difficult to in te rp re t evidence for

from th e B ritish Isles. M aps o f pollen percentages

c h an g in g p la n t co m m u n ities at a local scale in term s

were constructed for m ajor plan t taxa at four discrete

of a

periods: 9 ,0 0 0 , 6,000, 3,0 0 0 and 500 years

is th a t

chan g in g

clim ate.

The

local

vegetational

bp

(i.e.,

changes, even the app aren tly larger shifts, do not

radiocarbon years before present - cf. Box 5.1). These

solely reflect local clim ate forcing.

m aps were used to infer large-scale vegetation p a t­

D u rin g th e early p art o f th e H olocene (some 1 1,000 years ago), p lan t co m m u n ities in th e B ritish

terns at these tim es and were in terpreted in term s o f w in ter and sum m er tem p eratu re and annual p recip i­

Isles, as in m uch o f no rth ern E urope, were still

tation. T his final step was achieved by relating

underg o in g changes in response to th e retreat o f the

geographical p a tte rn s o f m odern pollen percentages

ice-sheet. A n am elio ratin g clim ate allow ed p lan t taxa

for each taxon

to m ig rate and recolonise areas as they m oved no rth

relationships were th en used to m ake q u a n titativ e

to m odern

clim ate data. These

from the positions they had occupied d u rin g the

estim ates o f each o f these variables by finding the

glacial. D ifferent taxa m ig ra ted at different rates.

com bination o f values associated w ith the m odern

Som e were replaced, not because th e clim ate m ade

assem blage o f plants th a t corresponded m ost closely

th em less viable, b u t because they w ere less able to

w ith th a t reconstructed in th e past. T he logic behind constructing

com pete w ith others. H ence, v egetation com position in th e early H olocene, especially in north-w estern

such

c lim a te

re s p o n s e s u rfa c e s for different subfossil taxa in this

E urope, m ay not have been in e q u ilib riu m w ith

way is th a t the sm o o th in g over such a large spatial

clim ate. Even subsequently, local v egetation co m m u ­

scale rem oves very localised (non-clim ate) inconsis­

nities d id n o t stabilise in to the sam e assem blages in

tencies in the p attern s and b rings o u t the m ajor

response to specific regional clim ates. Local site

features of regional clim ate forcing. In general, this

ecology (soil types, exposure, drainage, etc.), d is tu r­

w ork provides only very crude clim ate results - in

bance history (drainage changes, fire, w inds) and to

th e case cited above, an indication o f the sign o f

som e e x ten t p u re seren d ip ity o f com p etitio n al in te r­

tem p eratu re anom alies in January and Ju ly and

action, produced local p la n t co m m u n ities o f subtly

effective m oisture (precipitation m inus evaporation).

varying com position. T h e differences in con tem p o ­ raneous c o m m u n ities, therefore, m ake it unw ise to

A t 9 ,0 0 0 years BP, Fennoscandia is reconstructed as w arm er th an today. T h e B ritish Isles are not

overin terp ret in term s o f clim ate som e o f th e rela­

detectably different in January, alth o u g h

tively sm all tem poral differences in p la n t c o m m u n i­

apparently som ew hat cooler in July. All o f w estern

ties at single locations. A n o th er significant problem ,

Europe, oth er th an the M editerranean, is estim ated

it was

w hen a tte m p tin g clim atic in te rp re ta tio n o f H olocene

to be drier at th is tim e. T he only d etectable change

v e g etatio n changes in E urope, is th e confounding

over the B ritish Isles at 6 ,000 and 3 ,000 years BP is

influence o f hum ans. Indeed, m any p ollen rccords

a w arm er July, a lth o u g h apparently less so d u rin g

have been stu d ied precisely in order to identify

the m ore recent period.

c u ltu ral history, such as th e tim in g o f forest clear­

Recently, an a tte m p t has been m ade to com pile a

ance or ad o p tio n o f a g ric u ltu ra l practices.14 These

com prehensive com pendium of pollen profiles from

activities disguise, or even m im ic, the effect of

m any European c o u n tries,16 including som e synthesis

clim ate change on natural vegetation.

o f th e inform ation contained in various so-called reference sites in E n g la n d ,1' S cotland,18 Irela n d 19 and

N o tw ith sta n d in g these problem s, im p o rta n t p ro ­ gress is bein g m ade in b rin g in g to g eth e r and sy n th e ­

W ales.20 A gain, there is a p o tential confounding

sising the m ajor features o f larger, regional-scale

influence o f hum an im pact on th e landscape, espe­

v egetation p a tte rn s represented in m any o f th e better-

cially d u rin g the late H olocene. Figure 5.6 su m m ar­

dated E uropean pollen profiles. O n e recent study was

ises the

based on pollen profiles from over four h u n d re d sites

contained in this w ork, again for generally im pre­

spread across w estern E u ro p e,15 o f w hich th irty are

cisely defined periods.

(qualitative)

inform ation

about

clim ate

R E C O N S T R U C T IN G LATE-GLACIAL A N D H O L O C E N E CLIMATES

T here is som e ag reem en t am ongst th e evidence, su g g estin g

generally

w arm er

cond itio n s

in

areas where stu m p s have been found preserved in

th e

boggy or alluvial situations. T h is picture seems to

B ritish Isles con sisten t w ith th e earlier concept o f a W arm /D ry Sub-B oreal period (cf. F igure 5.5) centred

su p p o rt the notion of a period o f w idespread relative sum m er w arm th , lasting perhaps un til nearly 4 ,0 0 0

on about 4 ,0 0 0 years BP. T h e Irish evidence for

years BP, b u t followed d u rin g th e next few centuries

d rier c o nditions (also consistent w ith th e cessation o f bog g ro w th in southern E ngland) is in conflict,

o f lake sedim ent chem istry or enhanced peat g ro w th

however, w ith

th e evidence o f a wet period in

Scotland at th is tim e. T here is also clear agreem ent

by a notable clim ate deterioration. O th e r evidence indicates a change to generally w etter a n d/or colder conditions shortly after 4 ,0 0 0 years B P.25

in the E nglish and Scottish evidence for d e te rio ra tin g

O n e o f the m ost detailed studies o f B ritish tree-

(i.e., cooling a n d /o r becom ing w etter) conditions years BP. T h is is consistent

lines was carried o u t in th e C airngorm s, Scotland, and involved th e collection, radiocarbon d a tin g , and

w ith early ideas o f a Sub-Boreal to S ub-A tlantic

analysis o f the d e u terium /hydrogen ratios o f the

tran sitio n occurring about 2 ,5 0 0 years ago. It has

cellulose in th irty -e ig h t subfossil pine stu m p s.26 T his study em phasised how direct interp retatio n o f the

a t, or after, 3 ,0 0 0

been suggested th a t th is d e te rio ra tio n is th e m ost com m on feature o f m any north-w est E uropean bog profiles.21

a ltitu d e o f subfossils in term s of form er tree-lines is com plicated by the need to account for changing conditions (i.e., b lanket bog form ation) w hich may

The evidence of pine growth

or m ay not be conducive to th e preservation o f the

W e have described how pollen data generally offer lim ite d p o ten tial for accurately representing changes

is problem atic to in te rp ret the m ere presence of pine trees as evidence for specific clim ate conditions.

wood. Even w ith o u t the preservation uncertainty, it

in H olocene clim ates, since these changes are rela­

N evertheless, this w ork clearly shows th at the eleva­

tively sm all in com parison w ith the clim ate to le r­

tio n o f pine subfossils fell dram atically at about

ances o f m any p lan t spccics, and especially w hen the vegetation m ay respond only slowly to these changes.

expansion in Scotland, th is is in terpreted by the

3 ,500 years BP. A lth o u g h co incident w ith p opulation

It is possible, however, to focus on m ore selcctivc

authors as unlikely to be a ttrib u ta b le to a hum an

evidence o f changes in v egetation types th a t are

cause and m ost likely to reflect a change to cooler

po ten tially m ore sensitive.22 O n e such exam ple is the

conditions, given th e w ider evidence o f clim ate

evidence o f past tree-lines, o f w hich Scots pin e is a

change. Later studies o f subfossil pines on Rannoch

good exam ple. A gain, a prccisc clim atic in te rp reta ­

M oor in w estern Scotland su p p o rt th is.2 Except for

tio n o f th is evidence is p ro b lem atic,23 b u t th e a h i-

a consistent absence o f pine rem ains a t about 5 ,0 0 0 -

tu d in a l lim its and in te rm itte n t survival o f pin e on

4 ,8 0 0 years BP (suggesting generally colder/w etter

m arginal sites seem s to reinforce som e o f th e evidence

conditions), the diversity in pine dates a t different

for clim atc shifts th a t wc have described above.

sites on R annoch shows, however, how differences in

Scots P ine (Pirns sylveslris) today grow s naturally only on poor soils in the S cottish H ig h lan d s. It is

very localised conditions preclude any sim ple in te r­

excluded from all o th er areas basically bccausc o f its

th at this poin ts to is a general survival o f pine th ro u g h o u t the H olocenc u n til about 4 ,0 0 0 years BP.

in ab ility to com pete w ith o th e r trees.24 D u rin g the

p retatio n o f detailed changes on a regional scale. All

early to m id -H o lo cen c, however, it was an im p o rta n t

A t 6 ,0 0 0 years BP the subfossil pines on the

and w idespread com p o n en t o f th e B ritish vegetation.

C airngorm s are at relatively low elevation. T h is

Pine reached its m ax im u m no rth w ard e x te n t over the

w ould appear not to accord w ith a general n o tion o f

B ritish Isles shortly before 4 ,0 0 0 years BP. Very soon

relative w arm th at th is tim e. T h e isotopic ratios o f

afterw ards, it retreated rapidly to its present range and ap parently disappeared, except for sm all isolated

ever, as evidence o f relative m oisture availability. T he

th e various wood sam ples can be in terp reted , how ­

KEITH B R IF F A A N D TIM A T K I N S O N

Cyre

Approx

BP

date

N. England (uplands)

BC

S. England (lowlands)

Scotland Cairngorms

Wales

Ireland

AD19S0

D

4

I

4

1000 A D W armer ^ W a r m 1020

t

It

Cool

change t o | 2000 AD10 present AD/ Cool BC 3000 1300- C ooler 1200

* 4000 2580- Warmer 2480

* 1

Warm

*

* Warm.

D rier/ Warmer

*

5000 39003700

D

6000 49404860

Warmish

7000 5060- W etter, 4820 flo o d s

C oolish

8000 70606740

W armish

9000 8070- Warmer 7930 and drier

C oolish

0 D rier/ Warmer

10000 9500- Rapid 9300 Warming

I ’///////////7777s

Human Impact/clearance Peat accumulation/bog growth

High treeline D = Deterioration

R E C O N S T R U C T I N G LA TE-G LACIA L A N D H O L O C E N E C LIM A T E S

w e tte s t phases w ere sta te d as o c cu rrin g so m e tim e

H olocene co o lin g th a t w c have said is cru d ely consis­

u p to 7 ,3 0 0 , b etw een 6 ,2 0 0 an d 5 ,8 0 0 , 4 ,2 0 0 and

te n t w ith th e lo n g -te rm ré d u ctio n in su m m e r solar

3 ,9 4 0 , an d from 3 ,3 0 0 years of

h ig h e r-e le v a tio n

5 ,4 5 0 years

bp

bp

s tu m p s

onw ards. T h e absence

rad iatio n is not th e w hole story. It is also clear th a t

b etw een

m illen n ia l and cen tu ry tim e -sc ale flu ctu atio n s, in

6 ,2 0 0

and

m ay have been a consequence o f w a ter­

b o th te m p e ra tu re an d effective m o istu re c o n d itio n s,

lo g g ed g ro u n d . C ertain ly , b la n k e t bo g sta rte d to

have occurred an d

d ev elo p in th is reg io n a t a b o u t th is tim e . T h e p ollen

changes can n o t be a ttrib u te d

e v id en ce d iscussed above, how ever, to g e th e r w ith th e

alone. W id esp read w a rm in g o r w a rm th an d dryness

existence o f an a p p a re n t c o n ce n tra tio n o f p in e s u b ­

occurred for a few c en tu ries before or aro u n d 4 ,0 0 0

fossils a t C la sh g o u r on R a n n o ch M oor an d evidence

years B P; th ere was a m arked d e te rio ra tio n in w a rm th

o f low er lake levels,28 is a t o d d s w ith th e n o tio n o f a

(and in creasin g w etness) b etw een 4 ,0 0 0 and 3 ,0 0 0

w et phase th ro u g h o u t S cotland a t th is tim e .

years B P; an d th e re is evidence for w h at m ig h t be a

I t is also in te re s tin g to n o te th a t, on th e tim e scalc o f th e to w ard s

w h o le

H o lo cen e, th e overall tre n d

low er o r re tre a tin g

tree -lin e s in

Fenno-

th a t these sig n ifican t c lim atc to solar inso latio n

sh o rt perio d o f very cool/w et c o n d itio n s d u rin g the first few c en tu rie s p rio r to 2 ,0 0 0 years BP. O v erall, th is

p ic tu re

is

fairly

co n sisten t

w ith

th e

early

scandia an d th e A lp s29 is c ru d ely c o n sisten t w ith

concepts o f a w arm dry S ub-B oreal and cooler, w e tte r

re d u cin g s u m m e r in so latio n (cf. Box 5.2). T hese

S u b -A tla n tic (cf.

g ra d u a l

m ark ed cool/w et tra n s itio n betw een th e m at a b o u t

changes are clearly in te rru p te d

b etw een

4 .0 0 0 an d 3 ,0 0 0 years B P , how ever, by an a p p a re n t

F igure

5.5) and

especially

the

2 ,5 0 0 years BP.

a b ru p t an d wide-spread sh ift to w ard s c lim ates m u c h less favourable for p in e g ro w th . O th e r evidence th a t is p ro b a b ly relev an t, a lth o u g h a d m itte d ly som ew hat

High-frequency climate variability

d is ta n t to th e B ritish Isles, is th e w e ll-re p lic ated

If we w ish to g a in in sig h t in to e n v iro n m en ta l or

p a tte rn o f n o rth e rn tre e -lin e ch an g e re co n stru c te d in

c lim atc change on tim e-scales less th a n a century, it

N o rth A m erica from a b o u t 6 ,0 0 0 years B P . 30 Based

is p lain th a t w c re q u ire evidence th a t is co nsiderably

on p o lle n d a ta from th e e x tre m e n o rth e rn lim it o f

b e tte r resolved th a n any w e have discussed so far. In

tree g ro w th , th is record show s a relativ ely h ig h -

th is final sectio n , w e m ake b rie f m en tio n o f p ro b ­

la titu d e tre e -lin e (i.e., w a rm th ) b etw een 6 ,0 0 0 an d

ably th e b e st-k n o w n and c ertain ly th e b e st-d ated

5 .0 0 0 y e a r s B P , a n d a s i m i l a r l y h i g h p o s i t i o n a r o u n d

hig h -freq u e n cy palaeo clim ate evidence — tre e -rin g

4 .0 0 0 years B P , follow ed by an in itia lly a b ru p t an d

d a ta .32 W h e re trees form an n u al g ro w th rin g s, tim e -

su b s e q u e n tly c o n tin u in g re tre at. T h e tre e -lin e is a t

serics o f in d iv id u a l tre e -rin g w id th m ea su re m e n ts

an e x tre m e so u th e rn p o sitio n (i.e., cold a n d /o r w et)

can be c o m b in ed to pro v id e an average record o f past

a t a b o u t 2 ,0 0 0 years B P. T h ese d a ta d e m o n stra te

g ro w th variatio n s a t a site o r in a specific region.

a su rp risin g q u a lita tiv e sim ila rity w ith th e lim ite d

C o n stru c tin g su ch c hronologies from sam ples tak e n

B ritish

o th e r E uropean

from liv in g trees allow s th e c h ronology to be firm ly

evidence such as th e g ro ss changes in g la c ie r flu ctu ­

anchored in tim e (by v irtu e o f th e kn o w n sa m p lin g

atio n s an d lake-level flu ctu atio n s in S candinavia and

date).

th e A lp s.31

g re a tly e x te n d ed c hronologies can be c o n stru c te d by

e vidence, an d

also w ith

T h is e vidence is su m m arise d in F ig u re 5.7. F rom th is , an d from F ig u re 5 .6 , it is clear th a t th e a p p are n t

G iv en

sufficiently

lo n g

r in g -w id th

series,

m a tc h in g th e u n iq u e p a tte rn s o f year-to-year g ro w th variatio n s

in

sam ples

re p re se n tin g

o v e rla p p in g

Figure 5.6 A schematic summary of the palynological evidence for Holocene climate changes in England17, Scotland18, Wales20 and Ireland.19 The evidence is basically qualitative. There is some consensus in the evidence for generally warm /dry conditions around 4,000 years RP and a deterioration in climate between 3,000 and 2,000 years BP. There is only lim ited evidence for relative warm th around 6,000 years BP.

KEITH B R IF F A A N D TIM A T K I N S O N

a g e (B P )

above

ra d io c a rb o n

a ltitu d e

104

ra d io c a rb o n

age

(B P )

R E C O N S T R U C T IN G LATE-GLACIAL A N D H O L O C E N E CLIMATES

periods, perhaps from surviving dead trees or stum ps,

and q uantify how reliable sim ilar inferences for earlier,

com bined w ith m easurem ents o f wood sam ples from

older parts o f the series w ould be.

historical stru ctu res or artefacts a n d even those from archaeological or geological contexts (e.g., wood

aspects o f b u ild in g chronologies and in te rp retin g the

T here arc m any statistical and m ethodological

preserved in bogs, sedim ents or in lakes). A great

inform ation they contain th a t are beyond the scope

a ttrib u te o f such chronologies is th a t they represent a record o f ch an g in g env iro n m en tal influences th a t

o f this discussion,33 b u t it is sufficient to say here th a t very long chronologies, stretch in g over m uch

is b o th contin u o u s and precisely dated to th e year.

o f th e H olocene, exist in N o rth e rn Ireland (oak)

T ree-ring chronologies have been constru cted for

and (alm ost continuously) in northern Sw eden and

m any tree spccics in a g re at m any areas o f the w orld

Finland (pine). Each o f these contains inform ation

and som e stre tc h back over thousands o f years. It was the p a in sta k in g assem bly o f tw o such continuous

on the com bined effcct o f tem perature and available m oisture lim ita tio n on grow th.

chronologies, m ade from sam ples o f m any genera­

Figure 5.8 illustrates th e variability in a provi­

tions o f oak trees th a t grew in N o rth e rn Ireland and in G erm any, th a t eventually enabled a high-precision

sional pin e chronology being constructed from living

E uropean radiocarbon calibration curve to be estab ­

Sw edish lakes,34 and also shows a continuous c h ro n ­

lished (cf. Box 5.1). T h e specific n a tu re o f th e environm ental influences

ology o f oak g ro w th m ainly recovered from Irish

th a t arc represented in any tree-rin g chronology

im pression o f the high-frequency variability a t bo th

trees and subfossil m aterial preserved in N o rth ern

bogs.35 T he annual values are show n to give an

depends on a great m any factors. P rincipal am ong

locations, and both curves have also been sm oothed

these influences are the location and general ecology of

and p lo tted to g eth er to h ig h lig h t the m ulti-decadal

th e source region. T hese w ill d icta te th e basic clim ate

variability. N o te th at, for th e first tim e in this

and th e n ature o f g ro w th response to th a t clim atc by

chaptcr,

th e trees. O th e r factors, however, such as trce-to-trcc

calendar and the dates refer to actual years before

c o m p e titio n , external interference or dam age (e.g., by

C hrist. T h e absence o f very long tim e-scale vari­

anim als or insects), or site disturbance (e.g., by fire) can all obscure th e clim atc ‘signal' co ntained in tree-

a bility in Figure 5.8 is a conscquencc o f the c h ro n ­

rin g p attern s. By careful selection o f sam ple region, by

view ed as evidence for th e absence o f very long period

careful choice o f m aterial and by inco rp o ratin g data

clim ate change.36

here wc arc dealing

w ith

an absolute

ology construction m ethods and should

not be

from m any trees, a robust chronology can be assem ­

T he variability o f the curves is partly influenced

bled th a t best represents th e u n d erly in g p a tte rn of c om m on environm ental forcing. T he m odern p art of

by c hanging sam ple replication. In the pine data

th e chronology can be com pared w ith m odern clim atc

3000 and 230 0

data to establish th e precise n ature o f clim atc influcncc

may also be suppressed by w et (and cool) conditions.

sam ple num bers are low before 5000 BC.

BC

and around

Pine g ro w th in som e periods

figure 5.7 Selected evidence indicating changing climate conditions during the Holocene in the British Isles, north­ west Europe and northern North America. Shown are: (a) the temporal changes in elevation of recovered pine subfos­ sils in the Cairngorms, Scotland2r>; (b) periods of very wet conditions in the Cairngorms implied by deuterium/hydrogen ratios in the subfossil pine wood26; (c) changing positions of the northern tree line in North America based on paJynological evidence at one representative site Radium A’30; (d) suggested periods of general glacier advance in the Alps anti high lake levels in the Jura, France31; (e) representative lake-level changes in southern Sweden (G. Digerfeldt, ‘Reconstruction and regional correlation of Holocene lake-level fluctuations in Lake Bysjon, Southern Sweden', Boreas, 1988, vol. 17, pp. 165—82); (f) altitudes of recovered pine subfossils in northern Sweden plotted as anomalies with respect to the local elevations today29; (g) the changes in the elevation of the highest subfossil pines dated to 500-year periods, in southern Lapland"’9; and (h) schematic summary of the advance and retreat of northern Swedish glaciers.31 This figure is adapted from the original references cited and plotted on a common radiocarbon time-scale.

KEITH B R IF F A A N D TIM A T K I N S O N

5500

5000

I

i

4500

4000

3500

3000

2500

2000

1500

1000

500

2000

1500

1000

500

I -4--*— I— I— I---------1— I— t-

i

F i f t y - y e a r - F i l t e r e d S c a n d i n a v i a n T e m p e r a t u r e s ( ---------) a n d O a k g r o w t h ( ----------)

5500

5000

4500

4000

3500

3000

2500

C a le n d a r Y e a r s B C

Figure 3.8 Tree-ring-derived Fcnnoscandian July/A ugust mean temperature estimates based on a provisional pine ringw idth chronology being constructed from subfossil remains in northern Swedish lakes,34 and a mean ring-width chronology comprised of oak samples recovered from Irish bogs” - oak data kindly supplied by Professor Mike Baillie of the Palaeoecology Centre, Queen’s University, Belfast. The temperatures are plotted as annual degrees Celsius anom­ alies from a modern base period and the oak chronology as standardised de|>artures from the mean of the whole curve. The small gap shown in the pine-based chronology near 1,100 BC: has since been closed, but the chronology is nor yet continuous to the present (see text). The dating shown is probably correct ro within about fifty years. The lowest box shows the Fennoscandian tem perature anil Irish oak data smoothed with a filter which emphasises variations on timescales greater than fifty years.

E ssentially,

how ever,

these

p in e

d a ta

rep resen t

w ith

th e

c h an g in g

age o f trees th a t

form

the

su m m e r te m p e ra tu re ch an g e in n o rth e rn Sw eden.

c h ronology a t d ifferen t tim es (rin g w id th s o f y o ung

T h e y sh o w th a t g en eral w a rm th p revailed b etw een

trees arc gen erally larger th a n those o f old trees). A

a b o u t 4 0 0 0 an d 3 3 0 0 BC and th a t m any no tab le

first-o rd er c lim atic in te rp re ta tio n o f th e oak curve

sh o rte r

w ould be th a t h ig h g ro w th reflects warm/dry* c o n d i­

w arm

p erio d s

occurred

th ro u g h o u t

th e

record: at 5 3 0 0 , 5 1 0 0 , 4 6 5 0 , 3 8 5 0 , 3 7 0 0 , 3 4 0 0 ,

tio n s an d low g ro w th a relatively cool/w et clim ate.

2 9 0 0 , 1 3 0 0 an d at 7 5 0 BC.

T hese d a ta certain ly d e m o n stra te sig n ifican t clim ate

'I he Irish oak ch ro n o lo g y show n here is a sim p le

v aria b ility on m u ltid ecad al and cen tu ry tim c-scales

average o f th e rin g -w id th m easu rem en ts averaged

in Ireland and even su g g e st th e presence o f a m u lti-

year by year, so a g ain th e v a ria b ility is affected by

cen tu ry q u asi-clim a te oscillatio n th ro u g h m u ch o f

c h a n g in g sam p le size and has som e bias associated

th e H olocenc. O v erall, w arm and dry c o n d itio n s

R E C O N S T R U C T IN G LATE-GLACIAL A N D H O L O C E N E CLIMATES

appear to have been m ore freq u en t over th e centuries

evidence th a t enhanced volcanic activity occurred in

betw een 5 0 0 0 and 4 4 0 0 BC and betw een 390 0 and

th is period and may have played a part in th e envi­

3 45 0 BC. O th e r periods o f notable w arm /dry condi­ tions are c entred on a b o u t 2 8 0 0 , 2 4 5 0 , 1800, 1250

ronm ental d isru p tio n th a t clearly occurred at this

and 7 0 0 BC. Longer cool/w et periods are suggested

on clim ate.41 A lth o u g h th e m odern d ata arc m uch

betw een 4 4 5 0 and 3 9 0 0

; 3 4 5 0 and 310 0 BC;

m ore detailed th an the peat and pollen stratigraphies

2 2 0 0 and 1900 BC; and betw een 1150 and 7 5 0 BC.

used by B lytt and Scrnandcr, it is te m p tin g to sec in

bc

tim e, th ro u g h th e effects o f volcanic d u st and aerosols

T h e pin e chronology is not yet continuous. N o

this clim atic d isru p tio n indicated by trec-rings, the

m aterial has been found th a t bridges th e g ap in the

equivalent of the Sub-B orcal/Sub A tlan tic tran sitio n

early centuries BC. T h is is th o u g h t to be only a short

(see Figure 5.5). M uch fu rth er developm ent o f these

g ap , th o u g h , because th e long, earlier ‘floating’

Irish and Scandinavian and oth er very long E uropean

chronology can be placed q u ite accurately in tim e

chronologies (such as in the A lps, G erm any, northern

(probably w ith in fifty years e ith e r way) on the basis

Russia and in Finland) needs to be com pleted, par­

o f a n u m b e r o f radiocarbon dates on sam ples o f

ticularly

know n relative age w ith in th e chronology.*7 M aterial

environm ental signals th a t each chronology contains. T his work is currently underway.

d a tin g to th e g ap period is pro v in g to be surpris­

fu rth er w ork

to

in te rp ret th e detailed

ing ly elusive, however, n o t ju st in n o rth ern Sweden b u t also in F in lan d .38 For a long tim e , th e Irish chronology was also d iscontinuous at th is tim e. Bog

CONCLUSIONS

oak d ata d o n o t exist after 2 2 9 BC (as show n in F igure 5.8). A fter th a t tim e th e chronology is m ade

W ith in the som ew hat a rbitrary confines o f th e period

up from archaeological tim b ers, and a sm all g ap in

addressed by this chapter (22,000 to 2 ,000 years BP),

th e early centuries BC was eventually only bridged

B ritish clim atic history falls in to three clear and

using n on-Irish m aterial from C arlisle.39 Also note

d istin c t epochs. These arc th e end o f th e Pleniglacial,

th e a p p are n t lack o f subfossil m aterial dated to this period in th e C airngorm and in d ep en d en t Swedish

the tem perate I Iolocene, and th e com plex tran sitio n betw een them know n as the Late-G lacial. For all

m o u n ta in tree -lin e surveys show n in Figure 5.7. It

three, we rely upon in te rp retin g the clim ate from

has been suggested th a t th e dem ise o f th e bog oaks

th e records left in geological accum ulations and in

in Ireland was associated w ith increased w etness and

th e rem ains o f plan ts and anim als. Very little o f this

th a t the Irish and Scandinavian gaps are con tem p o ­

evidence reflects clim atc dircctly. R ather, clim ate

raneous w ith large ‘wash o u t’ phases o f wood recov­

m ust be inferred a t second rem ove from w hat the

ered from riverine gravel deposits in G erm any.40 All

records tell us of glacial advances and retreats, frozen

of th is is consistent w ith a period o f enhanced precip­

gro u n d , vegetation co m m u n ities, tree g ro w th and so

itation. It is a p lausible hypothesis th a t th is could

forth. Inevitably, non-clim atic inform ation is m ixed

have caused a rapid rise in lake and bog levels, leading to severe tree g ro w th d isru p tio n and severe

up w ith the clim atic com ponent o f th e records, so

d isto rtio n of rin g -p atrern s. An in ab ility to identify

separate the climatic: ‘sig n a l’ from the non-clim atic

and

‘noise’. Paradoxically th is is often easier for the

m easure

these

sam ples

w ould

prevent

the

th a t we can see the problem as being one o f how to

chronology crossing th is ‘event* in th e last few

Pleniglacial and Late-G lacial than for th e H olocenc,

c enturies BC.

despite the m uch greater abundance and detail of the

Sw edish sam ples w ith ju st such d isto rte d ring-

records in the last few thousand years. T h e paradox

p a tte rn s do in fact exist and appear to dare to this

is resolved if we recall th a t th e a b ility o f proxy

period (around 350 B C), b u t none can as yet be

data to d e te ct clim atic change is itself lim ited . For

m easured w ith sufficient certain ty to be incorporated

exam ple, rhe M utual C lim ate R ange m ethod using

in th e chronology. T here is also strong circum stantial

beetles sim ply cannot resolve changes in sum m er

KEITH BRIFFA A N D TIM A T K IN S O N

m axim um

tem p e ra tu re o f less th an one or tw o

were so large th a t they can bc clearly pcrccivcd even

was

w ith the rather crude proxy-indicators th a t arc avail­

sm aller th an th is, w hich is one reason w hy th e beetle

able. T he signal-to-noise’ ratio is q u ite good. T his

degrees

Celsius.

H olocenc

clim atc

changc

record provides no in dication o f it (Figure 5.1). In su m m arisin g th e clim atic changes w hich have

is not because the m ethods o f reconstruction arc

affected th e B ritish Isles in th e last 2 0 ,0 0 0 years, we

sensitive (for they arc not), b u t bccausc th e clim atic sig n a l’ was so strong. T he c rudity o f th e proxy-

m u st keep the qu estio n o f ‘sig n al-to -n o ise’ ratio

indicators for these periods m eans th a t, so far, we have practically no indication at all o f the hig h -

constan tly in m ind. For the end o f the P leniglacial (2 0 ,0 0 0 -1 3 ,0 0 0

frequency variations th a t m ay have occurred from

radiocarbon years B P), d irec t evidence is rather sparse.

year to year or decade to decadc superim posed on

A lth o u g h the icc-shcct th a t had covcrcd m ost o f the B ritish Isles at th e Last G lacial M axim um was in

the m illennial tim e-scalc changcs. In the H oloccnc period proper wc can d istin g u ish

decay, the beetle and periglacial evidence show s th at

tw o types o f proxy-indicators. F irst arc those such as

th e clim atc rem ained extrem ely cold, w ith the m ean

peat bog stratigraphy, preserved pollen and tree-line data, w hich inform us m ainly o f m illennial changcs

tem p e ra tu re in the w arm est m o n th s below 10rtC, descending to -2 0 °C or even -3 0 °C in the w inters.

in clim atc and at best resolve sh o rt episodes to

T he seas to th e w est o f th e islands rem ained cold w ith

a tim e-scale o f centuries. Second, th ere are hig h -

extensive ice covering th em in w inter. Probably the

resolution records w hich can resolve intcrannual

decay o f th e ice-sheet cam e a b o u t because the clim ate

changes and give inform ation u p to a century tim c-

was too dry to sustain it as su m m er insolation (and

scalc, b u t for technical reasons cannot on th eir own

hence ablation) g radually increased (see Box 5.2). T he

tell us o f clim atc changes over m illennia.

initial decay m ay also have involved o th e r causcs.

For the first type o f evidence, th e H oloccnc ‘signal-

In th e L ate-G lacial period wc have m uch m ore

to-noisc’ ratio is poor. T here arc h in ts th a t the very

a b u n d a n t evidence, alth o u g h still sparse by H olocenc large

early H oloccnc clim atc around 9 ,0 0 0 years B P was slig h tly cooler and d rier th an today, whereas the m id-

tem p e ra tu re oscillations show n in F igure 5.1. T he d ra m a tic w arm in g at about 13,000 years BP left the

H oloccnc may have had slig h tly w arm er sum m ers. It is not possible to q uantify these changes except

standards.

Fossil

beetles

d em o n strate

the

w hole o f th e B ritish Isles free from ice w ith a therm al

to say th a t they were sm all, w ith tem perature differ­

c lim ate in itially sim ilar to th a t o f today, b u t g ra d ­

ences from the present day o f certainly no m ore than

ually cooling som ew hat over th e next 1,000 years.

about 16C, w hich is the resolving pow er o f the

B etw een 11,000 and 12,000 years BP, m ean annual

m ethods involved. D espite the fact th a t sum m er

air tem p e ra tu re oscillated around 5°C, w ith w arm est

insolation was falling th ro u g h o u t the H olocene, and

m o n th s averaging a bout 15°C and eoldest m o nths

w in ter insolation rising (Box 5.2), there is no d e a r

-5 °C . T here was then a ra th e r a b ru p t cooling a t the

evidence o f a cooling tren d in the B ritish Isles clim atc. T h a t is not to say th a t such a trend d id not

sta rt o f the Y ounger D ryas, w ith m ean annual air tem p e ra tu re d ro p p in g to a m in im u m o f around -5 °C in th e coldest p a rt o f th e interstad ial. G laciers and

occur, m erely th a t signal-to-noise' ratio is too poor to detect it properly.

a sm all ice-sheet reappeared on hig h g ro u n d and the

T he clearest evidence o f long tim e-scale change in

c lim ate appears to have been cold, w ith w inter

th e H olocene comes from peat bog stratig rap h y and

p re cip ita tio n dom in ated by w esterly storm s. L ittle is

tree-line data. T his tends to suggest th a t around

know n o f su m m er p re cip ita tio n , b u t w inters seem to

4 ,0 0 0 years BP the clim ate am eliorated for several

have been d rier th an today and e ast-w e st g radients

centuries. It is not clear w hether th is involved

o f p re cip ita tio n across th e c o u n try m u ch steeper.

w arm ing or a d im in u tio n o f p recip itatio n , or b oth,

For these tw o periods before th e H oloccnc began,

b u t in view o f th e weakness of any obvious tem p er­

th e clim atic changes and differences from th e present

ature signal, drier conditions were alm ost certainly

R E C O N S T R U C T I N G LA TE-G LACIAL A N D H O L O C E N E C LIM A TES

involved. T ree-lines w ere h ig h e r a t th is tim e and

u n a m b ig u o u sly in te rp re te d . T h is u n ra v ellin g o f th e

th e re

slo w in g o r cessation in

signals o f c lim a tc ch an g c in th e H olocene p resen ts

b la n k e t p e a t-b o g g ro w th , su g g e stin g d rie r g ro u n d

a g re a t scientific c h allen g e for th e n ex t dccadcs o f

c o n d itio n s on

palaeo clim atic research.

was a w id esp read

h ills in su m m er. T h is d rier, and

p o ssib ly w arm er, ep iso d e m ay correspond c ru d ely to th e early Sub-B oreal o f th e B ly tt a n d S crnandcr schem e (F ig u re 5.5). A fte r a b o u t 4 ,0 0 0 years B P th ere m ay have been an increase in w etness, as in d ic a te d

NOTES

by a c o u n try -w id e d e clin e in p in e pollen an d a d e clin e in th e tree -lin e . A ll o f these changes, a lth o u g h o bvious en o u g h in term s o f th e p rim a ry evidence, are very d iffic u lt to in te rp re t in clear c lim a tic term s. M o st o f th e vege­ ta tio n a n d b o g -g ro w th v ariables a p p e a r p a rticu la rly se n sitiv e to m o is tu re a b u n d an c e or deficit in the g ro w in g season. T h is su g g e sts th a t th e c lim a tic shifts th a t o ccurred m ay have involved sh ifts in su m m e r w a te r b alance w h ic h is its e lf a c o m p o site re su lt o f p re c ip ita tio n an d é v ap o tran sp ira tio n w h ich d ep en d s in tu r n on te m p e ra tu re , w in d in ess an d cloudiness. A m ajo r task for th e fu tu re is to resolve th e linkages b e tw ee n these factors an d th e p ro x y -in d ic ato rs th a t are available, so th a t th e c lim a tic sig n a l can be read m ore clearly. To som e

e x te n t

th e

H o lo cen e h ig h -re s o lu tio n

records available from tre e -rin g s in th e B ritish Isles confirm

th e

im p e rfe c t

p ic tu re

o u tlin e d

in

th e

p re c e d in g p a rag ra p h s. S ig n a l-to -n o ise ra tio is only fair (a lth o u g h it is b e tte r in F e nnoscandian c h ro n o lo ­ gies) an d th e lo n g c h ro n o lo g ies o f F ig u re 5.8 show clear episodes an d o sc illa tio n s b etw een w a rm e r an d d rie r c lim a tc s an d c o o le r/w e tte r ones. T h e re are m eth o d o lo g ic al d iffic u lties, how ever, in c o rre latin g th e tw o ty p es o f e v id en ce (in c lu d in g th e absence o f m ille n n ia l tim e -sc ale c lim a te signals in these data). 'Fhe real im p o rta n c e o f th e trc c -rin g rccord is th a t it reveals th a t v a ria tio n o f c lim a te occurs on all tim e scales from c en tu rie s d o w n to an n u al. Since even the cen tu ry -sc alc o sc illa tio n s are o n ly barely d e te c ta b le u sin g o th e r v e g e ta tio n pro x ies, th e a b so lu te m a g n i­ tu d e o f these c h an g es is p re su m ab ly n o t very g re at. T re e -rin g w id th s in th e B ritish Isles, lik e p e a t a cc u ­ m u la tio n , record a ra th e r com plex sig n a l in v o lv in g b o th te m p e ra tu re an d m o istu re availability, w hich re q u ire s m ore c a lib ra tio n in fu tu re before it can be

1 T.C. Atkinson, K.R. Briffa and G .R. Coope, Seasonal temperatures in Bricain during the past 22,000 years reconstructed using beetle remains’, Nature, 1987, vol. 325, pp. 587-92; T.C. Atkinson, K.R. Briffa, G.R. Coope, M.J. Joachim and D.W. Perry, 'Clim atic cali­ bration of coleopteran data’, in B.E. Berglund (ed.), Handbook o f Palaeoecology and Palaeohydrology, London, J. Wiley and Sons, 1985, pp. 8 5 1-8; G.R. Coope, ‘Fossil beetle assemblages as evidence for sudden and intense clim atic changes in the British Isles during the last 45,000 years’, in W.H. Berger and L.D. Labeyrie (eds). Abrupt Climatic Change: Evidence and Implications, NATO ASI Series C 216, Dordrecht, Reidel, 1987, p p . 147-50. 2 Atkinson et al.y 1987, op. cit. 3 G.R. Coope and J.A. Brophy, Late glacial environ­ mental changes indicated by a coleopteran succession from N orth W ales’, Boreas vol. 1, pp. 97 -1 4 2 ; G.R. Coope and M.J. Joachim , ‘Late Glacial environmental changes interpreted from fossil coleoptera from St. Bees, Cum bria, N.W . England’, in J.J. Lowe, J.M . Gray and J.E. Robinson (eds), Studies in the Ixite Glacial of Northwest Europe, Oxford, Pergamon, 1980, pp. 55-68. 4 W.F. Ruddiman and A. McIntyre, “Hie N orth Atlantic Ocean during the last deglaciation’, Palaeogeography. Palaeoclimatology, Palaeoecology, 1981, vol. 35, pp. 145-214. 5 J. Imbrie and N .G . Kipp, A new micropaleontological method for quantitative paleoclimatology: appli­ cation ro a late Pleistocene Caribbean core’, in K.K. Turekian (ed.), The Lite Cenozoic Glacial Ages, New Haven, Yale University Press, 1971, pp. 171-81. 6 G.R. Coope and G. Lemdahl, ‘Regional differences in the late glacial climate of northern Europe based on coleopteran analysis’, Journal of Quaternary Science, 1995, vol. 10, pp. 391-5. 7 J. Lowe, B. Am m ann, H .H . Birks, S. Björck, G.R. Coope, L. Cwynar, J.-L. De Beaulieu, R.J. Mott, D.M. Peteet and M.J.C. Walker, ‘Climatic changes in areas adjacent to the N orth Atlantic during the last glacial-interglacial transition (14—9 ka b p ): a contri­ bution to IG G P-253’, Journal o f Quaternary Science, 1994, vol. 9, pp. 185-98.

KEITH BRIFFA A N D TIM A T K I N S O N

8 C .K . B allantyne and C . H arris, The Periglaciation o f Great B ritain, C am b rid g e, C am b rid g e U niversity Press, 1994, 3 30 pp. 9 C .K . B allantyne, ‘T he L oth Lom ond Readvance on the Isle o f Skye, Scotland: glacier reconstruction and palaeoclim atic im p licatio n s'. Journal o f Quaternary Science, 1989, vol. 4 , pp . 9 5 - 1 0 8 . 10 B allantyne and H arris, 1994. op. cit. 11 W.F. R uddim an and A.C. M ix, 'T h e N o rth and E quatorial A tlantic a t 9 0 0 0 and 6 0 0 0 yr BP’, in H .E . W rig h t, J r., J.E . K u tzb ach , T. W ebb, III, W.F. R u d d im a n , F.A. S tre e t-P e rro tt and P.J. B artlein (eds), Global Climates Since the I ms I G lacial M axim um , M inneapolis, U niversity o f M innesota Press, 1993, pp. 9 4 - 1 3 5 . J 2 A. B ly tt, Essay on the Immigration o f the Nortvegian Flora, C h ristia n ia, 1876. 13 R- Sem andcr, 'D ie schw edischen Torfm oore als Z eugen postglacialer K lim aschw ankungen, in D ie Veränder ungen des Klimas seit dem maximum der letzten Firzeit, S tockholm , G eneralstabens Litografiska A n stalt, 1910, pp. 1 9 5 -2 4 6 . 14 F.M. C ham bers (ed.), Climate Change a nd Human Impact on the Landscape: Studies in Palaeoecological a n d Environ­ mental Archaeology, L ondon, C hapm an and H all, 19 9 3 j 15

16

17

18

19

3 03 pp. B. H u n tle y and I.C . P rentice, ‘H olocene vegetation and clim ates in E urope’, in H .E. W rig h t, J r., J.E . K utzbach, T. W eb b , III, W.F. R u d d im a n , F.A. StreetP e rro tt and P.J. B artlein (eds), Global Climates Since the iMSt G lacial M axim um , M inneapolis, U niversity of M innesota Press, 1993, pp. 1 3 6 -6 8 . B.E B erg lu n d , H .J.B . B irks, M. R alska-Jasiew iczow a and H .E . W rig h t (eds), Palaeoecological Events During the Last 1 5 0 0 0 Years: Regional Syntheses of Palaeo­ ecological Studies o f Lakes a nd Mires in Europe, C hichester, Jo h n W iley and Sons, 1996, 7 64 pp. J . G re ig , ‘G re at B rita in - E n g la n d ', in B.E. B erglund, H .J.B . B irks, M. R alska-Jasiew iczow a and H .E . W rig h t (eds), Palaeoecological Ei'ents During tl)e Last 1 5 0 0 0 Years: Regional Syntheses o f Palaeoecological Studies o f luikes a n d Mires in Europe, C hichester, Jo h n W iley and Sons, 1996, pp. 1 5 -9 4 . H .J.B . B irks (w ith c o n trib u tio n s by H .H . B irks, P.D. K erslake, S.M. P eglar and W. W illiam s), 'G reat B ritain - S co tlan d ’, in B.E. B erglund, H .J.B . Birks, M . R alska-Jasiew iczow a and H .E . W rig h t (eds), Palaeoecological Events During the I^ast 15000 Years: Regional Syntheses o f Palaeoecological Studies of I¿ikes and Mires in Europe, C hichester, Jo h n W iley and Sons, 1996, pp . 9 5 - 1 4 3 . F.J.G. M itch ell, R .H .W . Bradshaw, G .E. H annon, M. O ’C onnell, J .R . P ilcher and W .A. W atts, 'Ire la n d ', in B.E. B erg lu n d , H .J.B . B irks, M. Ralska-Jasiew iczow a

20

21

22

23

24

25

26

27

28

and H .E . W 'righr (eds), Palaeoecological Events During the Last 15000 Years: Regional Syntheses o f Palaeo­ ecological Studies o f Lakes a n d Mires in Europe, C hichester, J o h n W iley and Sons, 1996, pp . 1 -13. F.M. C ham bers, 'G reat B ritain - W ales’, in B.E. B erglund, H .J.B . Birks, M. Ralska-Jasiew iczow a and H .E. W rig h t (eds), Palaeoetological Events During the Last 15 0 0 0 Years: Regional Syntheses o f Palaeoecological Studies o f Lakes a nd Mires in Europe, C hichester, Jo h n W iley and Sons, 1996, pp . 7 7 -9 4 . H .J.B . B irks and H .H . Birks, Quaternary Palaeoecology, L ondon, E dw ard A rnold, 1981; H .H . Lam b, Climate: Present, Past a nd Future. Volume 2: Climatic History a nd Future, L ondon, M ethuen and Co. L td, 1977, 83 5 pp . H .J.B . Birks, ‘L ong-term ecological change in the B ritish u p lan d s’, in B.M. U sh er and D .B .A . T hom pson (eds), Ecological Change in the Uplands, O xford, Blackw ell, 1988, pp. 3 7 -5 6 ; J .J. Lowe, ‘In teg ra tio n of pollen and o th er proxy data: the H olocene palaeoclim ate o f the B ritish Isles and adjacent parts o f E urope', in B. Frenzel, A. Pons and B. G laser (eds), Evaluation o f Climate Proxy D ata in Relation to the European Holocene, P alaoklim aforschung, 1991, vol. 6 , pp. 3 7 -5 0 . N.V. Pears, ‘In terp re ta tio n problem s in the stu d y o f tree-line fluctuations’, in J.A . Taylor (ed.), Research Papers in Forest Meteorology, an Aberystwyth Symposium, U niversity C ollege W ales, 1972, pp . 3 1 -4 5 . K .D . B e n n ett, 'T h e Postglacial history o f Pinus sylvestris in the B ritish Isles', Quaternary Science Reviews, 1984, vol. 3, pp. 1 3 3 -5 5 . W. P en n in g to n , E.Y. H aw o rth , A.P. B onny and J.P. Lishm an, ‘Lake sedim ents in north ern Scotland’, Philosophical Transactions o f the Royal Society o f London, Series B, 1972, vol. 2 6 4 , pp. 1 9 1 -2 9 4 ; H .H . Birks, Studies in the vegetational history o f Scotland. IV. Pine stu m p s in Scottish b lan k et peats’, Philosophical Transactions o f the Royal Society o f London, Series B, vol. 270, pp. 1 8 1 -2 2 6 ; — the foregoing as cited by B ennett, 1984, op. cit. A .D . D ubois and D .K . Ferguson, ‘T he clim atic history of pine in the C airngorm s based on radiocarbon dates and stable isotope analysis, w ith an account o f the events leading up to its c olonization’, Ret>iew o f Palaeobotany an d Palynology, 1985, vol. 4 6 , pp. 5 5 -8 0 . M .C. B ridge, B.A. H ag g art and J .J . Lowe, ‘T h e history and palaeoclim atic significance of subfossil rem ains of Pinus sylvestris in b lan k et peats from S cotland’, Journal o f Ecology, 1990, vol. 78, pp. 7 7 -9 9 . S.P. H arrison, L. Saarse and G . D igerfeldt, ‘H olocene changes in lake levels as clim ate proxy data in E urope’, in B. Frenzel, A. Pons and B. G laser (eds), Evaluation o f C l inulte Proxy D ata in Relation to the European Holocene, P alaoklim aforschung, 1991, vol. 6, pp. 1 5 9 -6 9 .

R E C O N S T R U C T I N G LATE-GLACI AL A N D H O L O C E N E CL IMATE S

L. K u llm a n , O rb ita l fo rcin g a n d tre e -lim it history: h y p o th esis an d p re lim in a ry in te rp re ta tio n o f evidence from S w edish L a p la n d ’, T he Holocene, 1 9 9 2 , vol. 2 , pp. 1 3 1 - 7 ; W . K a rle n , ‘L ac u strin e s e d im e n ts a n d treelim it v a ria tio n s as in d ic a to rs o f H o lo c en e c lim a tic flu c tu a tio n s in L apland: n o rth e rn S w ed e n ’, Geografiska A n n a le r, 1 9 7 6 , vol. 5 8 A , p p . 1—34; M . E ro n en , ‘T h e re tre a t o f p in e forest in F in n ish L ap lan d sin c e th e H o lo c en e c lim a tic o p tim u m . A g e n era l d iscussion w ith ra d io c arb o n ev id en ce from subfossil p in e s ’, Fennia, 1 9 7 9 , vol. 157, p p . 9 3 - 1 1 4 ; V. M arkgraf, P a leo clim arie ev id e n ce d e riv e d from tim t>erline fluc­ tu a tio n s ’, in J . L abeyrie (e d .), Lei Methodes quantitatives

35 M .G .L . B aillie, A Slice Through Time: Dendrochronology a n d Precision D a tin g , L ondon, B.T. B atsford, 1995, 176

d'E tude des Variations d u C lim at a u cours du Pleistocene, P aris, C N R S , 1 9 7 4 , p p . 6 7 - 8 3 . 30 H . N ic h o ls , Palynological a n d Paleoclimatic Study o f the I*ite Quaternary Displacement oj the Boreal Forest—Tundra F.cotone in Keewatin a n d Mackenzie, N W T , C anada, U n iv e rsity o f C o lo rad o , I n s titu te o f A rc tic a n d A lp in e R esearch, O c ca sio n a l P a p e r 15. 31 W . K a rle n , 'S c a n d in a v ian g lac ial an d c lim a tic fluc­ tu a tio n s d u rin g th e H o lo c e n e ’, Quaternary Science Reviews, 1 9 8 8 , vol. 7, p p . 1 9 9 -2 0 9 ; M . M agny, 'H o lo ­ cene flu c tu a tio n s o f lak e levels in th e F ren ch J u r a an d s u b -A lp in e ra n g e s, a n d th e ir im p lic a tio n s for p a st g e n e ra l c irc u la tio n p a tte r n s ’, The Holocene, vol. 3, pp. 3 0 6 —1332 IL C . F rirts , Tree Rings a n d C lim ate, N e w Y ork,

ties betw een 165 BC and A D 1400 d e riv e d from Subfossil Scots Fines (Pinus sylvestris L.) found in a lake in IJtsjo k i, n o rth e rn m o st F in la n d ’, B ulletin o f the Geological Society o f F in la n d , vol. 66. 39 B aillie, 1995, op. c it. 40 Ib id . 41 Ib id .

A c ad e m ic P ress, 19 7 6 , 5 67 p p ., a n d F.H . S chw eing ru b e r, Tree Rings: Basics a n d Applications o f Dendro­

C .K . B allan ty n e an d C. H a rris, The Periglaciation o f Great B rita in , C a m b rid g e , C a m b rid g e U n iv e rsity Press, 19 9 4 , 3 3 0 pp. B .E. B e rg lu n d , ll.J .B . B irks, M . R alska-Jasiew iczow a and H .E . W rig h t (eds), Palaeoecological Events D uring the IsiSt

29

33

34

chronology, D o rd re c h t, K lu w er, 1 9 8 8 , 2 7 6 p p . F or a g en eral a n d reasonably u p -to -d a te in tro d u c tio n to th e scope an d m e th o d o lo g y o f tre e -rin g research see E .R . C ook and L.A . K a iriu k s ris (eds), Methods o f TreeR in g Analysis: Applications in the Environm ental Sciences, D o rd re c h t, K lu w e r, 1 9 9 0 , 3 9 4 p p . B riffa, K .R ., ‘M id and L ate H o lo c en e c lim a te change: e v id e n ce from tre e g ro w th in n o rth e rn F e n n o sc a n d ia , in B .M . F u n n e ll a n d R.L.F. K ay (eds), Palaeoclimate o f the last G lacial!Interglacial Cycle, S w in d o n , N E R C E a rth Sciences D ire c to ra te , 1994.

pp.

36 K .R . B riffa, P.D. J o n e s, F .lI. Schw ein g ru b e r, W . K arlen an d S.G . Shiyatov, ‘T re e -rin g variables as p ro x y -clim ate in d icato rs: p ro b lem s w ith low -frequency sig n a ls’, in P.D. Jo n e s, R.S. B radley an d J . Jo u z e l (eds), C lim atic Variations a n d Forcing Mechanisms o f the L ast 2 0 0 0 Years, N A T O ASI Series I, 41, B erlin , S p rin g e r-V erlag, 1996, p p . 9-41. 37 B riffa, 1994, op. c it. 38 P. Z e tte rb e rg , M . E ro n en an d K .R . B riffa, ‘E vidence on c lim a tic v a ria b ility an d p re h isto ric h u m a n a c tiv i­

G EN ERAL READING M .G .L . B aillie, A Slice Through Time: Dendrochronology a n d Precision D a tin g , L ondon, B.T. Batsforcl, 19 9 5 , 1 76 pp.

! 5 0 0 0 Years: Regional Syntheses o f Palaeoecological Studies o f Lakes a n d Mires in Europe, C hich ester, J o h n W ile y and Sons, 19 9 6 , 7 6 4 p p . R.S. Bradley, Quaternary Paleoclimatology: methodj o f paleodim atic reconstruction, B oston, A llen and U n w in , 1985, 4 7 2 pp. N . R o b e rts, ‘T he Holocene: A n Environmental History, O xfo rd , B lackw ell, 1 9 8 9 , 2 27 pp.

6

D O C U M E N T I N G THE MEDIEVAL CLIMATE Astrid Ogilvie and Graham Farmer History gets thicker as it approaches recent time. A.J.P. T aylor

INTRODUCTION

able, different kinds o f ‘p ro x y c lim a te ’ d a ta m ust

T h e focus o f th is chapter is on docum entary evidence

analysis of th e annual rings laid dow n by trees (see

for clim ate variations in E ngland d u rin g the m edieval

C hapter 5); sam ples o f pollen records; m arine sedi­

p e rio d .1 E ngland is concentrated upon since there is relatively little w ritte n evidence o f clim atc events for

m en t cores; and deep cores taken from ice-sheets (see C hapter 4). H istorical docum entary d ata can also be

this period o rig in a tin g in the m ore peripheral parts of

very useful. W here these are p len tifu l, and w hen used

the B ritish Isles - Scotland, W ales and Ireland. Some evidence from Iceland and, to a lesser extent, G reen ­

appropriately, they can give precise and accurate inform ation on past clim atic events. T he recon­

land, is also considered.2 T his w ill serve to place the

stru c tio n o f past clim atic regim es using do cu m en ­

inform ation from E ngland in a w ider geographical and clim atic context and provide a basis for the considera­

tary evidence is know n as ‘historical clim atology’. R a th e r than g oing directly to th e original sources,

bc used. These may take th e form of, for exam ple:

tio n of N o rth A tlan tic clim ate variations d u rin g this

m any earlier researchers in th e field o f historical

tim e. Figure 6.1 shows a m ap o f the N o rth A tlantic

clim atology relied on com pilations o f w eather events

region and the location o f th e relevant countries.

produced by o th er a uthors (i.e., 'secondary sources’).

T h e c h ap ter begins w ith a discussion o f th e value

These com pilations were produced as early as the

and usefulness o f d ocum entary data, as well as how

sixteenth century and becam e q u ite com m on by the

they need to bc evaluated and analysed. T h e different

eig h te en th century. In the last h undred years or so,

kinds o f historical sources th a t contain clim ate data

som e fifteen such com pilations have been published,

for the m edieval period are th en outlin ed . Finally, the available inform ation regarding clim atic c o n d i­

absorbing m uch o f the m aterial contained in earlier

tio n s in E ngland, Iceland and G reenland d u rin g the period from c. AD 1200 to 1430 is presented. T he

tion in chronological order and contain num erous

last section includes a consideration o f th e w ider

texts and secondary sources. T hey m ake accessible,

ones. These m odern com pilations list th eir inform a­ references extracted

from

a variety o f historical

perspective o f European and N o rth A tlan tic clim ate

in com paratively few volum es, inform ation th a t is

conditions in m edieval tim es and th e q uestion of

otherw ise

w h e th er th ere really was a ‘M e d iev a l W a rm P e r io d ’

volum es o f source m aterial. As such, they w ould

as som e researchers have suggested.3

appear

on

dispersed the

th ro u g h o u t

surface

to

several

bc extrem ely

hundred useful.

In order to reconstruct the clim ate in tim es before

U nfortunately, they invariably reproduce a variety o f

system atic m eteorological observations becam e avail-

errors and should only be used w ith extrem e carc.'1

D O C U M E N T I N G THE M E D IE V A L CLIM ATE

Figure 6 .1 The N orth Atlantic and surrounding countries in medieval times. The English clim ate data used here are drawn mainly from the southern part o f England. The clim ate data for Iceland come mainly from coastal areas to rhe north, west and south of Iceland.

O n e o f th e a ck n o w le d g ed p io n ee rs in th e field

tain . B oth his and L am b ’s p io n ee rin g efforts m u st be­

o f histo ric a l c lim a to lo g y is H u b e rt I-am b, fo u n d e r o f

lauded since th e y were carried o u t before th e need

th e C lim a tic R esearch U n it, and it is th e m edieval

for careful

c lim a tic index for E n g la n d deriv ed by him w hich

In d eed , it w as w o rk

has fre q u e n tly been used by o th e r researchers.5 T h is

C lim a tic R esearch U n it th a t led to th is realisation.

h istorical

analysis was fully in itia te d

realised.

by L am b in

the

index is based on d a ta o f w h ic h a t least som e have

In th e p re sen t analysis, only sources th a t have been

been found to be u n re lia b le .6 L am b ’s ind ex is, in

estab lish ed to be reliab le arc used. T h e im p o rta n ce

tu rn , based p a rtly on th e c o m p ila tio n p ro d u c ed by

o f analy sin g sourccs is discussed fu rth e r below.

C harles B r itto n 7 for th e B ritish Isles. T h is is an u n u su a lly carefu l an d a ccu rate ex am p le o f th is ty p e o f w ork. N ev erth e le ss, B ritto n , no d o u b t a im in g for c o m p le te n ess, has

in clu d e d

rem ark s d ra w n

THE IMPORTANCE OF SOURCE ANALYSIS

from

w e ath e r c h ro n o lo g ies w ritte n m u c h later th a n th e

A ll types o f proxy c lim ate d a ta need to g o th ro u g h a

events th e y d e scrib e an d w hose a u th o rity is u n c er­

process ot analysis and evalu atio n . T h is is no less tru e

ASTRID O G IL V IE A N D G R A H A M FARMER

BOX 6.1: AN EXAMPLE OF SOURCE ANALYSIS

sources were silent. In short, there is no reliable basis for the reported ice and severe w eather in I2 7 9 .d

T h e way in w hich historians need to unravel the o rig in s o f th e ir sources m ay be described by refer­ rin g to a specific exam ple. For th e year 1279, an Icelandic com piler o f w eather events, T horoddsen, notes a severe w in ter w ith m uch ice around Iceland.4 T horoddsen's source for th is is an earlier co m p ilatio n by Finnsson, p ublished originally in 1796.b Finnsson s source was a m anuscript he had found in C openhagen. T h is w ork, now know n as Setbergsarwa'll, has been analysed and edited by the Icelandic histo rian , J6hannesson.c H e was able to show

th a t

th e a u th o r o f Setbergsanndll, G isli

T horkelsson ( 1 6 7 6 -1 7 2 5 ) actually em bellished th e sources th a t w ere available to h im , and even w ent so far as to invent inform ation w hen his

* Th. Thoroddsen, Arferdi A islandi i thusund At 1-2, Copenhagen, Hinu isienzka fraedafjelagi, 1916-17, pp. 32-3. It may be noted that Thoroddsen was a geologist who did a tremendous service to the histor­ ical climatology of Iceland by collecting together a vast number of sources of climate information. b H. Finnsson, ‘Urn mannfaekkun af halkerum a islandi', J6n Eythorsson og J6hannes Nordal sau um utgafuna, Reykjavik, Almenna Bokafelagid, 1970. (This compilation was first published in 1796.) c J. J6hannesson, 'Setbergsannsiir, in Annales Islandici Posteriorum Saxularum. Annalar 1400-1800, 1922, vol. 4, pp. 19-21. d This example is explained more fully in A.E.J. Ogilvie, T h e past climate and sea-ice record from Iceland, part 1: data to A D 1780’, Climatic Change, 1984, vol. 6, pp. 131-52.

o f d ocum entary cvidencc; som e historical sources may

A reliable source should ideally be independent,

c ontain errors, m isconccptions and even forgeries,8

not derivative, and should be contem porary (i.e.,

w hile others provide accurate and reliable inform a­

w ritte n at or near the tim e o f the event). A lter­

tion. It is therefore extrem ely im p o rta n t th a t all

natively, there should be stro n g evidence regarding

sources to be used for clim ate reconstruction are care­

its reliability. In order to ensure th a t these criteria

fully analysed in order to ensure th e ir reliability. T his

apply, it is necessary to find o u t certain th in g s about

procedure is referred to as ‘source c ritic ism ’. It is a task

the evidence.11 First, who w rote it? M edieval w riters

th a t usually needs to be und ertak en by historians who

d id not always sign th eir nam es to th eir accounts,

are, by v irtu e o f th eir train in g and fam iliarity w ith the

b u t if it is know n who w rote a p a rticu la r w ork, then

su b ject, b e tte r suited to it th an clim atologists. Source

this can help to place it, bo th w ith regard to its date

c riticism is especially im p o rta n t w hen u sing m edieval

and the location w here it was w ritte n , and th u s help

sources; w riters from th is tim e d id n o t always value

in assessing the reliability o f the author. Second, when

accurate re p o rtin g in the sam e way th a t m odern

was it w ritten ? It is vital to know th e d ate o f a

researchers do.9 H istorical records from later periods

p articular w ork. If it was w ritte n close in tim e to

are often less p roblem atic; b u t later com pilations,

th e event described it is m uch m ore likely to give an accurate description th an if it were w ritte n m any

being secondary sources, frequently p ropagate earlier e rrors.10 Clearly, if a d ocum entary source gives incor­

years afterw ards (see Box 6.1). Indeed, in o rder to

rect inform ation, any clim ate reconstruction using it

ensure accuracy, it is alm ost always essential for an

w ill reproduce th is and th u s give a false p ictu re o f

account to be contem poraneous w ith th e events

clim atic

th e process o f source

described. T h ird , where was it w ritten? If an account

c riticism has been com pleted, and th e stage o f in te r­ p re ta tio n o f th e data been reached, th e expertise of

were w ritten close to th e events described by an eyew itness observer it is m uch m ore likely to be

clim ato lo g ists is clearly needed.

accurate than if it were w ritten far away from it, on

variations.

O nce

D O C U M E N T IN G THE M EDIE VAL CLIMATE

th e basis o f second-hand inform ation o r hearsay.

Abbey relating to m anors in Sussex.18 T h e account

F ourth, why was it w ritte n ? A w riter m ay have

roll

had a d id ac tic or p roselytising m ission w hich was

southern E ngland as far west as Som erset. T h e great

m ore im p o rta n t to him inform ation.

m ajority of th e narrative sources used here also come from southern E ngland, so the tw o types o f sources

th an conveying precise

evidence

is all

from

south-east or central

are com parable. T here is still som e scope for further w ork on clim atic inform ation from m anorial accounts

THE SOURCES AND DATA

in the M idlands and the N o rth . T here are, however, few narrative sources available, o utside southern

Both E ngland and Iceland have a rich m edieval l it ­

E ngland.

erature c o n ta in in g details o f m any aspects o f life

D ata first becom e com m on in th e tw elfth century,

in clu d in g the w eather and clim ate. O f particu lar

b u t occur in usable num bers only from c. 1 200. T hey

in terest

are generally less frequent in the fourteenth century

for

our

purposes

here

is

inform ation

reg ard in g tem p eratu re and p re cip ita tio n . Icelandic

than in the th irte e n th , and becam e scarcer in the

sources som etim es also refer to sea-ice reaching the

early fifteenth century. Presum ably th is was p artly as

coasts. T h is ice, o rig in a tin g o ff th e coasts o f East

a result of the d isru p tio n to political and econom ic

G reenland, is an in te restin g proxy clim ate indicator

life caused by the W ars of the Roses in th e fifteenth

in itself.12 T here are no accounts reg ard in g m edieval

century.

clim ate th a t o rig in a te specifically in G reenland, b u t

Iceland is particularly renow ned for its prose narra­

tw o sources o f N orw eg ian o rig in give very in te rest­

tives from m edieval tim es - know n as th e ‘family

ing descriptions o f th e sea-ice, as well as inform a­

sagas’ or ‘sagas o f Icelanders’. These literary, scm i-

tion on conditions o f life am o n g st th e N orse w ho

historical w orks arc ranked am ong th e finest w orks

had se ttle d in G re en la n d .13

o f lite ratu re ever w ritten. Since they are prim arily literatu re rather than history, they are generally not

T h e E nglish historical sources, ra th e r m ore prolific th an th e Icelandic ones, include m edieval annals as w ell as chronicles and th e account rolls k e p t on

relevant to a survey such as th is one. N evertheless, the in tellectual environm ent th a t fostered this

m an o rs.11 T h e latter, docu m en ts o f accounts m ade

literary endeavour is a factor th a t m ust bc considered

for th e churches w ho ow ned these large estates,

in evaluating docum entary evidence from Iceland.

derive th e ir nam e from th e fact th a t they took the

Figure 6.2 shows a fine exam ple o f a medieval

form o f long pieces of p a rch m en t rolled up. O n e of

Icelandic m anuscript.

th e earliest know n diaries specifically o f w eather events is from

E ogland. T h is

journal, k e p t by

W illiam M erle o f Lincolnshire, extends from January 1337 to Ja n u a ry 1 3 4 4 15 (see C h ap ter 7, F igure 7.2).

In ad d itio n to the fam ily sagas, m any fascinating works were also produced w hich were historical rather than literary in o rigin. These include oth er

Except for the b e g in n in g o f the period, th e c hron­

kinds o f sagas such as the ‘sagas o f Icelandic Bishops* and the ‘S turlunga sagas’, nam ed after th e family

icles’ statem en ts are o u tn u m b e red by those from the

who dom in ated events in thirteenth-century' Iceland.

o th er m ajor type o f source - m anorial account rolls

O th e r im p o rtan t sources are the medieval Icelandic annals and w orks o f geographical d e sc rip tio n .19

- and th e rolls are m ajor sources for the period after 1300. T he longest series of accounts from w hich d a ta

Iceland was settled , m ainly from Norw ay, in the

are available is the W in ch ester episcopal series from

late n in th century'. T he first references to w eather

w hich th e w eather inform ation has been collected

events

and p u b lis h e d .16 T h is has been su p p lem en ted by data

com m ence in the late tw elfth century. For the th ir­

w hich

have

som e

claim

to

reliability

from a H e rtfo rd sh ire m anor o f W estm in ster A bbey17

tee n th century th ere are a n um ber o f very in teresting

and a n u m b er o f d etails, especially useful in th e

w eather descriptions. T h e fourteenth century has

fifteenth century, from th e account rolls o f B attle

th e greatest coverage for th e w hole period from the

ASTRID

OGILVIE

AND

GRAHAM

FARM ER

D O C U M E N T I N G THE M E D IE V A L C LIM ATE

se ttle m e n t to th e la tte r p a rt o f th e six te e n th century.

c alculated acco rd in g to how m any ’w eeks o f s u m m e r’

It is in te re s tin g th a t th is is th e reverse o f th e s itu ­

had gone by. In a d d itio n , th e year was d iv id e d in to

a tio n in E n g la n d . In Iceland, c o n te m p o ra ry sources

tw elve m o n th s o f a b o u t th irty days each. T h e first

co m e to an en d in 1 4 3 0 , leaving a g a p u n til aro u n d

th ree

1560. As sta te d above, th e re is also a lack o f sources

eimnanudr. Thorri alw ays began on a Friday betw een

in

E n g la n d

from

th e

early

fo u rte e n th

m o n th s o f th e year were: thorri\ goa\ and

c en tu ry

9 an d 16 Ja n u a ry (O ld Style), and so on. S om etim es

o n w a rd s.20 As far as Iceland is c o n ce rn ed , th e reason

rcfcrcncc to th e seasons can cause p ro b lem s w hen it

for th is m ay be an e p id e m ic (p ro b a b ly th e B lack

is unclcar ju st w hen in a season an e v en t occurred.

D e ath ) w h ic h k ille d a large p e rc e n ta g e o f th e p o p u ­

T he precision freq u e n tly used in Icelandic d a tin g ,

latio n . In these k in d s o f c irc u m stan c e, th e clergy as

how ever, m eans th a t ev en ts can usually be d a te d

a class o ften suffered m an y d e ath s as th ey tra d itio n ­

u n am biguously.

ally su cco u red th e d y in g , a n d it was th e clergy w ho

In E n g la n d , t(x>, th e term in o lo g y used for th e

w ere also th e m ain class from w h ic h w riters an d

d ifferen t seasons can be p ro b lem atic. ‘A u tu m n ’, for

scribes w ere d raw n.

exam ple, n o rm ally m ea n t th e harvest season an d was tak e n to b e g in on 1 A u g u st. Its le n g th c ould vary from year to year, how ever, and a u tu m n c ould be

STRATEGY AND METHODOLOGY

‘la te ’ o r ‘long th is year’ (as de sc rib e d , for exam ple, in the Dunstable A n n a ls, 1294; Walter o f Coventry,

E ven reliab le m ed iev al na rra tiv e s pose a n u m b e r o f

1212). ‘W in te r w as also a flexible term . It could be

p ro b lem s o f in te rp re ta tio n . A n ex am p le o f th is is th e

th o u g h t

issue o f d a tin g . In b o th E n g la n d a n d Ic elan d , th e

S e p tem b e r (O ld Style; as in M a tth e w P aris, Chronica

J u lia n , o r O ld S tyle, c alen d ar was in use in m edieval

M ajora, 1253), and 28 D ecem b er (O ld Style) could

tim e s.

or

be d escribed as ’m id w in te r’ (ib id ., 1257). S p rin g was

G re g o ria n , c alen d a r in S e p te m b e r 1752 and Iceland

regarded m ore as a n ann u al biological event ra th e r

E n g la n d

c h an g e d

to

th e

N ew

Style,

o f as b e g in n in g

a b o u t M ichaelm as, 29

c h an g e d so m e w h a t earlier, in N o v e m b e r 1 7 0 0 .21 In

th a n a fixed perio d . T h is ty p e o f term in o lo g ical

o rd e r to co rre c t for th is , for th e p e rio d 2 9 F ebruary

difficulty is a ctu ally not so serious, p a rtly because

1 1 0 0 to 28 F eb ru ary 1 3 0 0 seven days sh o u ld be

our

ad d ed to th e d ate. From 2 9 F eb ru ary 1 3 0 0 to 28

m o n th s, an d p a rtly because we still have a gd

n arrativ es

m o st

freq u e n tly

refer

to

nam ed

F eb ru ary 1 4 0 0 , e ig h t days sh o u ld bc a d d e d , an d from

en o u g h idea o f th e d ates to allow an in te rp re ta tio n

29 F eb ru ary 1 4 0 0 to 2 8 F ebruary 1 5 0 0 , n in e days.

— as lo n g as w e can avoid th e te m p ta tio n to be too

In Ic elan d , th ey also used a d a tin g system th a t

precise. T h ere is e n o u g h o verlap betw een m edieval

was v irtu a lly u n iq u e to th a t country. T h e year was

and m odern term s to allow th e sim p le classification

d iv id e d

ad o p te d here.

Sum m er p re c e d in g

in to

tw o

beg an

on

halves; th e

sum m er T h u rsd a y

16 A p ril a cc o rd in g

an d

w inter.

im m e d ia tely

to th e O ld

T h e a d o p tio n o f fairly strin g e n t c rite ria for th e

Style

acceptance o f w eath er s ta te m e n ts in th e E n g lish

calendar. W in te r beg an on th e S atu rd ay im m e d ia tely

ch ro n icles has reduced th e available d a ta c o n sid er­

p re c e d in g St L u k e s day (1 8 O c to b er, O ld Style), or

ably. Table 6.1 show s th e q u a n tity and d is trib u tio n

on S t L u k e ’s day itself if th is w ere a Saturday. From

o f o u r in fo rm a tio n , an d th e n u m b ers o f u n re p o rte d

th e b e g in n in g o f su m m er, th e p a ssin g o f tim e was

seasons are show n in T able 6.2. It sh o u ld be n oted

Figure 6.2 This example of an Icelandic m anuscript comes from a magnificent vellum codex, Flateyjarbok, dating from around 1390. Its name, the ‘Flatey book’, derives from the fact that it remained for some time on an island named Flatey, in Breidafjord, off the west coast of Iceland. Flateyjarb6k contains several works, mainly sagas of Norwegian kings. The page shown here concerns the beginning of the Saga of (3lafr Tryggvason. The illuminated letter (P) depicts King I larald Fairhair and his cupbearer.

1 17

ASTRID O G IL V IE A N D G R A H A M FARMER

Table 6.1 Total numbers of seasons with documen­ tary data for England, AD 1200-1429

1200-49 1250-99 1300-49 1350-99 1400-29 Total

Narratives

Account rolls

56 64 39 22 15 196

22 76 94 85 35 312

T he different sources used pose different problem s o f interp retatio n . In rhe account rolls, for exam ple, the w eather is m entioned w hen it helps to explain an exceptional agricultural situation. T he account rolls therefore rend ro record extrem e seasons, b u t m ainly rhose th a t are a griculturally m ore sensitive. These d ata are th u s biased tow ards rep o rtin g sum m er and a u tu m n conditions, b u t com plem entary infor­ m ation on extrem e w inters can be obtained by refer­ ence to the narratives. T his bias extends to th e type

Note: Some seasons are described in both types of source.

o f w eather m ost likely to be recorded, dry sum m ers and wet au tu m n s being m ost frequently noted since

th a t, in sp ite o f th ere being m any seasons for w hich

they have the m ost obvious effect on agricultural

no reliable w eather descriptions exist, these are

routine and its incidental expenses.22 T hus, w hen

generally seasons w ith unrem arkable w eather. T he n ature o f th e sources is such th a t ‘n o rm al’ or ‘near-

all the E nglish records used here are considered for

n o rm al’ w eather w ould not be co m m ented on. As a

the period 1220—1430, they note ninety-nine dry sum m ers as against th irty -six wet ones, m any o f the

consequence, it is likely th a t alm ost all o f th e severe

latter com ing from the narratives, and seventy-six

seasons are included in o u r dataset.

wet au tu m n s as against only e ig h t dry ones, nearly

Table 6.2 Numbers of unreported seasons by decade for England,

1200-09 1210-19 1220-29 1230-39 1240-49 1250-59 1260-69 1270-79 1280-89 1290-99 Total 1300-09 1310-19 1320-29 1330-39 1340-49 1350-59 1360-69 1370-79 1380-89 1390-99 Total 1400-09 1410-19 1420-29

ad

1200-1429

Spring

Summer

Autumn

Winter

Total

10 9 9 8 6 4 10 7 10 2 75 7 6 6 9 8 5 6 7 6 8 68 10 7 9

9 10 7 4 2 5 5 1 4 1 48 1 1 5 2 1 2 1 0 2 4 19 2 4 5

10 8 6 7 3 3 7 8 6 4 62 4 5 6 5 5 4 4 3 2 7 45 7 8 5

9 8 5 4 5 4 7 5 2 3 52 5 2 6 5 6 6 8 4 8 9 59 8 5 7

38 35 27 23 16 16 29 21 22 10 17 14 23 21 20 17 19 14 18 28 27 24 26

D O C U M E N T IN G THE M EDIE VAL CLIMATE

all th e la tte r bein g also noted by chroniclers. If nearly

th o u g h proffered to explain a g ricultural circum ­

h a lf th e sum m ers in th is period are described as

stances. T he veracity o f bo th d ata sources - account

dry, we m ay begin to suspect a certain a m o u n t o f

rolls and chronicles - is fu rth er confirm ed w hen th eir

exaggeration

d ata are com pared (see Table 6.2).

in

the

re p o rtin g

or in terp retatio n .

L ong-term trends tow ards d rier or w e tte r seasons m ay therefore reflect changes in th e balance o f source m aterial, particu larly account rolls relative to oth er

PRESENTATION OF THE DATA

sources. A fu rth er difficulty arises from th e re p etitio n of

O nce unreliable data have been discarded, and useful

phrases year after year in accounts from the same

historical sources identified, the next step for clim ate

manor. A ccounts from a w ell-organised estate can be

reconstruction is to extract from these sources any

q u ite stylised d o cu m en ts, arranged in th e sam e way

contem porary references to weather. O nce these have

for decades on en d ,23 and w hen they repeat the sam e

been collated, they can be used in tw o p rincipal ways.

phrase in the sam e place one suspects th a t they are

O ne is to produce a detailed picture o f a p articular

b eing cast in com m on form .

w eather event or season. In cases w here th e d ata are

T h e best way o u t of b o th these difficulties is to

num erous enough, a second way o f p resenting them

accept a season as bein g extrem e only w hen it is

is to derive tim e-series o f clim ate indices. These

reported by a n u m b e r o f separate sources, or when

indices m ay be calculated by assigning a value to

it is isolated in the record d u rin g th e periods o f less

each m o n th or season in term s o f its w arm th/cold­

inform ation. An u nusually dry su m m er tends to bc

ness or w etness/dryness. T hese values m ay th en be

recorded by m any m anors in different areas, often

sum m ed in order to produce a decadal index (see

b e lo n g in g to d ifferent lords, and is confirm ed by the

Figure 6.3). T he indices derived for E ngland and Iceland, as well as a general picture o f w hat the

narratives. Such events arc q u ite clearly different from th e 'dry su m m ers’ m entio n ed in cliche or

clim ate may have been like in those regions from c.

am big u o u s form by only one or tw o m anors o u t o f

1200 to 1430, are presented below. Some specific

m any possible ones. T h is has led to a sm all n u m b er o f m odifications bein g m ade in th e in te rp reta tio n

events in E ngland and th eir sources are presented in

presented here o f th e W inchester series, m ost notably

found elsew here.24

Box 6.2. Full details o f the Icelandic sources may be

in th e spell o f dry sum m ers d u rin g th e 1280s, w hen only 1285 and 1288 can bc accepted as very d ry and 1287 need not have been dry a t all. A nother su sp i­ cious run o f d ty sum m ers occurs in th e 1410s, where

Weather events and decadal indices for England c. 1200-1439

1 4 16 looks d ubious (th e B urghclcre accounts sim ply

A data catalogue o f clim atic events has been com ­

repeat th e previous years’ phrases), no evidence is

piled for E ngland for the period AD 1200 to 1429. T his is too long to present here, b u t som e interestin g

p rin te d for 1417 and in

1418 only one m anor

clim atc events th a t occurred d u rin g th is period may

m entions dryness. A fu rth er difficulty w ould arise if th e inform ation

bc briefly m entioned. Severe and frosty w inters

from the rolls were sim ply dcduccd from th e su p ­ posed effects o f th e w eather on crops - our clim atic

occurred in 1205, 1210, 1234, 1254, 1261, 1271,

reconstruction could n o t th en bc ap plied to explain

and in 1282, it was reported th a t th e T ham es could

variations in yield, and th e w eather in form ation itself

be crossed on foot. T he river was frozen again in

1281, 1292, 1306, 1335, 1365 and 1408. In 1205

w ould bc suspect bccausc th e w eather/crop yield lin k

1310 and 1408. T he sum m ers o f 1236 and 1238

is not

were unusually hot and dry, w hilst th e years 1314

a sim ple one. T h e

w eather inform ation

extracted from th e accounts, however, takes th e form

to 1318 were very w et, and this led to w idespread

o f specific descriptions o f w eather conditions, even

crop failures.

120

A S T R ID O G I L V I E A N D G R A H A M FA RM ER

T h e d a ta for E n g la n d are p re sen te d here in Tables

lor th e year 1287: ‘A t th is tim e , m any severe w in ters

6.1 to 6.3 an d in F ig u res 6 .3 a n d 6.4. Table 6.1

cam e a t once and follow ing th em people d ied o f

show s th e to ta l n u m b e rs o f seasons w ith d o c u m e n ­

h u n g e r.’28 T h e first tw o decades o f th e fo u rte e n th

tary d a ta from n a rra tiv e sources an d from th e account

c e n tu ry seem to have been relatively m ild , a lth o u g h

rolls for th e years 1 2 0 0 to 1439. In T able 6 .2 , to tal

th ere was som e severe w eath er an d sea-ice in th e early

n u m b e rs o f u n re p o rte d seasons arc p re sen te d by

1320s. It is possible th a t the 1330s w ere m ild and

decade (n o te th a t lack o f r e p o rtin g is lik e ly to in d i­

also th e la tte r p a rt o f th e 1350s. T h e last p a rt o f the

cate a lack o f any ex tre m e s in th e w eather, as p o in te d

1340s seem s to have been cold. T h e

o u t earlier). T able 6 .3 gives te m p e ra tu re a n d p re cip ­

ap p ear to have been cold on th e w hole (see Figure

ita tio n e stim a te s for each m o n th from 1 2 0 0 to 1439-

6.4). T h e sources give th e im pression o f m ainly m ild

D ecadal

w e ath e r b etw een c. 1395 to 1440,

indiccs o f s u m m e r w etness and

w in te r

1370s also

sev erity d e riv e d from th e d a ta se t in T able 6 .3 are sh o w n in F ig u re 6 .3 , to g e th e r w ith indiccs d erived by L am b .25 T h e differences m ay bc exp lain ed by L a m b s use o f d a ta th a t are e ith e r u n re liab le or relate to

som e o th e r

p a rt o f E urope (or b o th ).

Events in Greenland G re en la n d was colonised from Iceland in a p p ro x i­

A lso,

m ately th e year 9 8 5 . Tw o areas o f se ttle m e n t were

a lth o u g h m any o f th e d a ta used here w ere n o ted by

e stab lish e d , th e so-called E astern and W estern s e ttle ­

B ritto n in his c o m p ila tio n ,26 these d a ta are su p p le ­

m en ts (see F ig u re 6.1). T h e W estern S e ttle m e n t

m e n te d by m an y p reviously u n p u b lis h e d d a ta and

ceased to exist aro u n d AD 1 350, w h ile th e E astern

by d a ta d ra w n from tex ts u n u se d o r unavailable to

S e ttle m e n t m ay have survived in to th e six tee n th

B ritto n . In a d d itio n , errors in B ritto n ’s c o m p ilatio n

c entury. It has been su g g e ste d th a t a d e te rio ra tio n

have been d e le te d from th e p re se n t analysis. T h e

in c lim a tc played a p a rt in th e loss o f these N orse

a n n u a l te m p e ra tu re indiccs for Icclan d and E n g lan d

se ttle m e n ts . T h is is possible, a lth o u g h th ere is no

are c o m p a red in F ig u re 6 .4 .

d ire c t evidence for th is, an d several o th e r factors are likely to have played an e q u al, o r m ore im p o r­

Weather events and decadal indices for Iceland c. 1200-1440 It is a ro u n d 1180 th a t c o n te m p o ra ry c lim a tc refer­

ta n t, parr: for exam p le; conflicts w ith th e n a tiv e In u it p o p u la tio n ; changes in th e p a tte rn s of E uropean trad e;

and

th e

s tru c tu re

o f N orse

G re en la n d ic

society.29

ences first b ecom e available in Ic e la n d .27 F rom th is tim e , an d th ro u g h to the first years o f th e th irte e n th cen tu ry , th ere are several d e sc rip tio n s w h ic h su g g e st th a t c lim a tic c o n d itio n s w ere harsh. B etw een 1211

SEA-ICE INCIDENCE IN THE NORTH ATLANTIC

an d 1232 th e re are no rcfcrenccs to w eather. O v e r th e n ex t few years th ere arc sporadic references to

T h e cause o f th e presence o f sea-ice o ff th e coasts o f

severe seasons, in c lu d in g

1233 to 1236. T h ere is

G re en la n d an d Iceland is a com plex am algam o f

v irtu a lly no w e ath e r in fo rm a tio n for th e 1240s. T he

c o n d itio n s in th e G re e n la n d Sea an d Polar B asin, th e

1250s seem to have b e en variable. T h e c lim a te o f

m o v em e n t o f ocean c u rre n ts, and also local w eath er

th e la tte r p a rt o f th e th ir te e n th c e n tu ry was alm o st

c o n d itio n s. T h ese causes can n o t be discussed here,

c e rta in ly severe. A n in te re s tin g s ta te m e n t is m ade

b u t it sh o u ld be* n oted th a t th e incidence o f sea-ice

Figure 6.3 Decadal indices of sum m er wetness (top) and w inter severity (bottom ) from a d 1220 to 1429 derived from the present analysis1 (revised index) and from H .H . Lamb.“5 The differences may be explained by Lamb s use of data that are unreliable or relate to some other parr of Europe, or both. Shaded decades are wetter (summer) or more severe (winter) than the average.

D O C U M E N T I N G THE M E D I E V A L C L IM A T E

H.H. Lamb index

1250

1200

Revised index

1350

1300

1400

Summer wetness

20

-20

I

10 o



. .M

1450

[ I . .. .

g - . W

j

-i 10 L

M

-10

H-10

-20

-20

(Index value)

-t---- 1-----1-----1----- 1—

20-

■20

10.

10

1200

1250

1300

1350

1400

Winter severity

20 r

1450 20

10^

■10

0“ -10 r

r .10 —h— I— I— I— I— I5 0

-5 -

-5 ■

1200

‘___I___ I___ > 1250

>___I___ I___I___>___ ____I___ I___ L_ 1300

1350

1400

1450

121

A ST R ID O G IL V IE A N D G R A H A M FA R M ER

BOX 6.2 DATA CATALOGUE AND SOURCES

Walteri de Coventria. W. Stubbs (ed.). Rolls Ser., 18 7 2 -3 , ii, p. 201. Spring: cold and windy, Walter of Coventry, Memoriale fratris Walteri dt Coventria. W. Stubbs (ed.), Rolls Ser.,

The following list some specific events and their sources: 1201

1205

Spring, summer and autumn: (a) Wet from 20 May to 15 September, crops harmed. Annales de Margan, sire chronica Abbreviate (1 0 6 6 -1 2 3 2 ). H.R. Luard (ed.), Annales Monastic/, Rolls Scr., 1864, i, p. 25. (b) Storm and flood damage in July. Waverley Annals. Annales Monasterii de Waverleia, a d 1 -1 2 9 1 . H.R. Luard (ed.), Annales Monastic!, Rolls Ser., 1865, ii,

1212

1215

1220

1221

Creation to 1235)- H.R. Luard (ed.). Rolls Ser., 1 8 7 2 -8 3 , ii, p. 490. (c) Severe frost 28 December 1204 to 1 April 1205. Worcester Annals. Annales Prioratus de Wigornia, A D 1 -1 3 7 7 . H.R. Luard (ed.), Annalts Monastici. Rolls Ser., 1210

1222

sogion. J. W illiams ab Ithel (ed.). Rolls Ser., 1860, p. 289. Winter: (a) Wet from Christmas (1219) all winter. Worcester Annals. Annales Prioratus de

1869, iv, pp. 4 1 1 -1 2 . Winter: January cold. Dunstable Annals. Annales prioratus de Dunstaplia, A D 33 to 1297. H.R. Luard (ed.), Annales Monastici. Rolls Ser., 1866, iii, p. 53. Spring: heavy snow, severe frost in April. Waverley Annals. Annales Monasterii de Waverleia, A D 1 -1291. H.R. Luard (ed.). Annates Monastici. Rolls Ser., 1865, ii, p. 296. Summer: dry and hot. Ralph of Cogges­

1869, iv, p. 393. Winter: (a) Frost 7 January to 21 February, Severn frozen to 4 miles beyond Gloucester. Worcester Annals. Annales Prioratus de W igornia, a d 1 -1377. H.R. Luard (ed.),

hall, Chronicon Anglicanum (1 0 6 6-1223). J. Stevenson (ed.). Rolls Ser., 1875,

Annales Monastici. Rolls Ser., 1869, iv, p. 398. (b) Frost and snow, 8 January to 21 February, ice more than one foot thick. Walter o f Coventry, Mtmoriale fratris

(ed.). Rolls Ser., 1 8 7 2 -3 , ii. p. 206. Winter: December mild. Brut y Tyuy-

Wigornia, A D 1 -1 3 7 7 . H.R. Luard (ed.), Annales Monastici. Rolls Ser., 1869, iv, pp. 4 1 1 -1 2 . (b) Wet from 16 August to end of December. Worcester Annals. Annales Prioratus de Wigornia, A D 1-1377. H.R. Luard (ed.), Annales Monastici. Rolls Ser.,

p. 253. Winter: (a) Frozen from 8 January to 1 April, Thames could be crossed on foot. Ralph o f Coggeshall, Chronicon AngHcanum (1 0 6 6 -1 2 2 3 ). J. Stevenson (ed.). Rolls Ser., 1875, p. 151. (b) Frozen from 21 January to 29 March, agriculture impossible. Roger o f Wendover, Flores historiarum (from the

1 8 7 2 -3 , ii. p. 201. Autumn: severe to 15 September, then heavy rain. Walter o f Coventry, Memoriale fratris Walteri de Coventria. W. Stubbs

1223

p. 192. Winter: wet until 9 February 1223. Roger o f Wendover, Flores historiarum (from the Creation to 1235). H.R. Luard (ed.). Rolls Ser., 1 8 7 2 -8 3 , ii, p. 74. W hole year wet. Matthew Paris, Chronica majora (from the Creation to 1259). H.R.

D O C U M E N T IN G THE M EDIE VAL CLIMATE

Luard (ed.), R olls Ser., p. 82.

1 8 7 2 -8 3 , iii,

1230

W inter: heavy snow, January. W averley Annals. Annales M onasterii de W averleia, A D 1 - 1 29I. H .R . Luard (ed.), Annales Monastici, Rolls Ser. 1865, ii, p. 421.

1 2 2 3 -4 W in ter: dry. W averley A nnals. Annales M onasterii de W averleia, A D 1 -1 2 9 1 . H .R . Luard (ed.), Annales Monastici, Rolls 1227

Ser., 1865, ii, p. 300. W in ter: rivers flood, D ecem ber 1226, Jan u ary and February. W orcester Annals. A nnales P rioratus de W ig o rn ia,

AD

1232

S p rin g -a u tu m n :

d ro u g h t,

M arch

to

O ctober. Annales Cambriae. J . W illiam s ab Ithel (ed.). Rolls Ser., I8 6 0 , p. 79Sum m er: w et. Flores historiarum (from the

1233

1-

Creation to 1326). H .R . Luard (ed.), Rolls

1377. H .R . Luard (ed.), Annales Monas-

Ser. 1890. ii, p. 209.

ticiy Rolls Ser., 1869, iv, p. 420.

is also h ighly variable on a variety o f tim e-scales (see C h a p te r 2).

can generally be assum ed to indicate sea-ice. It is possible th a t sea-ice only occurred in one o f these

N o rth

years and th a t th e o th er is th e result o f a co p y ists

A tlan tic d u rin g th e m edieval period com es from the Icelandic annals and certain sagas, as well as from

error. In 1306, sea-ice is recorded as having been present all sum m er in rhe n o rth .34 Several o f the

tw o

annals refer to sea-ice in e ith e r 1319 or 1320.35 Sea-

Evidence

for sea-icc

in te restin g

sources

variations

w hich

in

th e

were w ritte n

in

Norw ay. These la tte r are th e Konungs skuggsjd (T he

ice is said to have lain around the coast all sum m er

K in g ’s Mirror),-^0 com posed around 1250, and the

and also reached rhe south coast. T h e ice also

Grœnlandslysing fva r Bàrdarsonar (the description o f

occurred in 1321 and several o f the annals refer to

G reenland

polar bears w hich cam e on lan d .36 In th e a u tu m n of 1361, th e annal Gottskdlksanndll stares rh at a polar

according

to

Ivar Bardarson) w ritten

p robably som e tim e shortly after 136 4 .51 T h e seaice sources are discussed below in chronological

bear cam e ashore in Breidafjord even th o u g h there

order.

was no ice in the vicinity, w hich was obviously

T h e Konungs skuggsja contains detailed and accu­ rate descriptions o f th e A rctic regions. T h is infor­

th o u g h t

to

be

stran g e.37 In

1374,

the

annal

LfigmannsannalP8 notes th a t th e sea-ice lay off the

m ation was g ath ered by th e a u th o r from travellers

coasts

w ho had been to these places. A m ongst o th e r things,

the B ishops’ sagas, Gudmundar saga biskups Arasonar,

u n til

1 Septem ber (N ew

Style). O n e o f

th e w ork contains a very full account concerning sea-

includes a geographical d escription o f Iceland in

ice: ‘As soon as one has passed over th e deepest p art o f the ocean, he w ill en co u n ter such masses o f ice in

cation from th is Icelandic source is th a t sea-ice was

th e sea, th a t I know o f no equal to it anyw here else

q u ite com m on off th e n orthern coasts a t th e tim e

in all th e earth . . ,’32 T h e im pression is given from Konungs skuggsjd th a t th ere was m uch sea-ice betw een

th e saga was w ritte n , c. 1350.39 Because o f its in terestin g com m ents on sea-ice the

Iceland and G reenland a t the tim e o f w ritin g .

Granlandslysing tvar Ba'rdarsonar has been frequently

w hich glaciers and sea-ice are m entioned. T h e im p li­

For th e year 1261, the Icelandic annals state th a t

cited by those interested in the past clim ate o f the

there was sea-ice ail around Iceland. T h is is th e first

N o rth A tlantic re g io n /10 T he w ork begins by g iving

recorded reference to such an extrem e event. For

detailed sailing directions, from N orw ay to Iceland,

1274 and 1275 th e annals record th e arrival o f polar

from Iceland to G reenland, from Iceland to Svalbard

bears and sea-ice.53 Polar bears often d rifted to

(Spitsbergen), and from N orw ay direct to G reenland.

Iceland on ice floes, so a m en tio n o f th e ir presence

As regards the route from Iceland to G reenland, the

124

ASTRID O GIL VIE A N D G R A H A M FARMER

Table 6.3 Temperature and precipitation scores for England for each month from a d 1200-1439. (Negative values indicate drier or cooler conditions; positive values indicate warmer or welter conditions. The value ±2 indicates conditions which are slightly more severe than 'normal', whereas the value ±3 indicates a partic­ ularly severe season. Where the values are in parentheses there is a likelihood, rather than definite evidence, of those conditions prevailing.)

Year

Winter D J F

Precipitation: Spring Summer M A M J J A

1200 01 02

2

Autumn SO N

Winter D J F

-3 -3

1210

-

11 12

2-2

-3

-

2-2

2 2

13 14 15 16 17 18 19

Autumn SO N

2 2 2

03 04 05 06 07 08 09

-2

-2

2

(2) (2)

1220 21 22 23 24 25 26 27 28 29 1230 31 32 33 34 35 36 37 38 39 1240 41 42 43

Temperature: Spring Summer M A M J J A

2 2

2

2

2

2

2

2 2 2

2 -2 -2-2 2 2 2 2 -3-3 2

2 -2

-

2 2 2 -2-2-2

2 2 2 -2

2 22-2 2 2 2 2

-3

2 2

2 2 2 2

2 2

2

-2 -2-2-2

-2-2 3 3 -2 2 2 2 2 2 2 2 2 2 2 2 -2-2 -2 2 2 2 -2

-3-3-2 2 3 2 -2-2 -3-3-2 -3-3

3

2 2 2 -2-2-2

-2-2 3 3 -2-2 2 33

2 2 2 3 3

2 2 2 -2-2

-2

2

2 2 2

-2-2 -2-2-2 2 2

-2-2 2222222

DOCUMENTING THE MEDIEVAL CLIMATE Table 6.3 continued

Year 44 45 46 47 48 49 1250 51 52 53 54 55 56 57 58 59 1260 61 62 63 64 65 66 67 68 69 1270 71 72 73 74 75 76 77 78 79 1280 81 82 83 84 85 86 87 88 89 1290 91 92

Winter D J F

Precipitation: Spring Summer M AM J J A

Autumn SO N

-2 -2-2 (-2)1-2) 2 2 2 2 2 2 2 2 2 2 2 -3 —3(—2) (—2)(—2)(—2) (—2)(—2)(—2) (-2) -3-3 1-2) -2 3 3 3 2 2 2 2 2 2

-2 -2 -2 2 2 -2 2 2 (-2) 3(2) (2) (2) (2) 2 3-3 -2 2 3 3 3 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 -2 -2-2

Winter D J F

Temperature: Spring Summer M AM J J A

2 2 2 3 3 2

-2 -2 -2 2 3-2

-2-2

-2 -2 -2

-2 -2 -2 -2-2

Autumn SO N

2 3

2 2 2

2 2 -2--2 -2 -2 -2 -2 2

2 2-2

{—2)(—2)(—2) (-2) -2

-2-2

-2-2 -3-3 -2 -2 -2-2 2 -2-2 2

2 2 2

2 2 2 3

3 (-2)1-2) (-2) 2-2-2 3-2

2 2 (-2)(-2)(-2) 2 2 2

2 -2

2 2 2

-2 -2

2 2 2 2

(—2)(—2)(—2) -2-2 -2 -2 -2-2 (-2)1-2) -2-2-2 -2 -3 —3(—2) -2 -3 -3 (—2)(—2)(—2) 3 3 -3 -3 -3 2 2 2 2 2 -2-2 -3-3 -3 -3 -2 -2 3 3 3 3 2 -3 -3 3 3 2 2 -3 -3(2) (2) 2 2 2 2 2 2 -3-3 -2-2-2 -2 -2 -2-2 -2 -2 -2-2 (2)(2)(2) -2-2 (2) -3 2 2 2 2 2 -2-2-2 -2 2 2 2 -2 2 2 2 2 -3-3 2 2 2 2 2 2 -2-2-3 -2 2

-2 (-2)

2 3

2 2 -2 2 2

(2)

-2 2

125

ASTRID O GIL VIE A N D G R A H A M FARMER

Table 6.3 continued

2

2 2 -3 -3 -3-3

(2)(2)(2) 2 2 2 2 2 -2 -2

2

2 2 -2

-3-3

2

(2)(2)(2)

(2)

-2

-3-3 -2-2 2 2 2 2 -3 -3 -3 -3 -3 -3 -2 -2 -2 -3-3 3 3 (-2)(-2) (-2)(-2) 2 2 -3 -3 2 -3-3 (2) (2)—2 -2 -2 -2-2 -2 -2 -2 -2 -2-2 -2 -2-2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 2 2 2 2 2 2 2

2 2

-2 -2 -2-3-2

-2 -2-2

2

2 2

-3 (-2)

-2-2-2 -2 -2

-2

CN

2

2 2

-2

-2 CN

-2

CN

CN

CN

-2

CM

CN

CN

-2

-3 -3 -3

-2

1 1 1

-2 1 1 1

-3 -3 2 2 2 -2 -2-2 -3-3

-2 2 2 2

1 1 1

(—2)(—2)(—2)

1

-2 CN

2

CO

(2)(2) CN

(2)(2) (2)

1

1 1

CN

CN

(2) -3-3 -3-3 -2-2

-2

-3

CO

3 3 (2) 3 2 2 2 2 -2-2 (2) (2) (2)

(2)(2)

-2-2-2 -2

(2)(2)

1 CN 1 CN 1

2 2 3 2 2 2

(2)(2)(2) 2 -2 2 -2 -3

CO

2 2 2 -2

Autumn SO N

1

-3 2

Temperature: Spring Summer M A M J J A

CN

2 -2-2

Winter D J F

CN

2 2 2

-2 2 2 2 2 2

Autumn SO N

1

2 2 2

CN 1 CN 1 CN 1

93 94 95 96 97 98 99 1300 01 02 03 04 05 06 07 08 09 1310 11 12 13 14 15 16 17 18 19 1320 21 22 23 24 25 26 27 28 29 1330 31 32 33 34 35 36 37 38 39 1340 41

Precipitation: Spring Summer M A M J J A

1 1

Year

Winter D J F

CO

126

3

3-2 -2

-3-3 (-2) 2 3 (-2)1-2) 3 (2) -2-2

3 3 2 3 2 2 (2) 2

-2 -3 -3 -3-3

-2 -3

-2

2 2 2 2 2 -2

2 2

D O C U M EN TIN G THE M EDIEVAL CLIMATE

Table 6.3 continued Precipitation: Spring Summer M AM J J A

(2 ) (2 ) (2 ) 2

2

-2-2

2

2

2

2

2

2 3 3

-2

2

2

2

2

2

2

2

2

2

-2-2

2

2

2

2 (2 ) (2 )

2

2

(2 )(2 ) -2-2 -2 - 2 - 2

2 CN 1 CN 1 CN 1

2

- 2 -2

(- 2 )1 - 2 ) 2

(- 2 )

-2 -2

(—2 )(—2 )(—2 ) (- 2 )

-2-3 -3 -2-3-3 -2-3-3

-2 2 3 -3 2 2

(2 )

-2-2

-2 (2 )(2 )

-2

-2

3 3 2

2

2

2

CN

-2-2 (—2 )(—2 ) 2

-3-3 -3 -3 -3-3 2 2

-2 (2 )

2

2

2

2

2

-2

2

2

2

2

2

2

2

2 (2 )

-2 -2 -2

-2

-3-3-3

-3

-2

CN 1 CN 1

2 2

CN

89 1390

2

-2 -2

(2 ) (2 )

2 2 (2 )

(2 )(2 )

(- 2 ) (- 2 ) (- 2 )1 - 2 ) 2

2

2 (2 )

(2 )(2 )(2 ) -2

(2 )(2 )(2 ) CN 1 CN 1

88

2

Autumn SO N

-3-3 -3 -3

66

67 68 69 1370 71 72 73 74 75 76 77 78 79 1380 81 82 83 84 85 86 87

-2-2

Temperature: Spring Summer M AM J J A CN 1 CN 1

(- 2 )

Winter D J F

Autumn SO N

CN

42 43 44 45 46 47 48 49 1350 51 52 53 54 55 56 57 58 59 1360 61 62 63 64 65

Winter D J F

1 CJ 1 CO

Year

2

2

-2-2

2

2

2

-2-2

2

2

2

-2-2 3 -2-2 3

2 2 2

(— 2)(— 2) -3-31-2) (-2)(-2) (2) (2) (2) (—2)(—2)(— 2)(— 2)(— 2)(—2) (~2)(— 2)(— 2) (— 2)(— 2)(— 2) (— 2)(— 2)(3) (3) (3) -

( 2) ( 2)

3

-2

3 2 3 3 2

2

2 2

2 2 2 3 3(2) (2)

2-2 2

(2)

2 3 3

2

(2) ( 2)

-2

-

2-2

2 -2 -2 -2 2 2 2

3 3 3 3 -3-3-3 -3 -3-3-2 2 2 -

2-2

2 2 2

(- 2 )1- 2 ) 2

2 -

2-2

-

2-2

2

2 -2 -2

(-3)1-3)

2

2 2 2 2

2 2

-2 -2 -2

2 2 2 2 2

2) (2) (2) (2) (

127

128

ASTRID O G ILV IE AN D G R A H A M FARMER Table 6.3 continued

Year

Winter D J F

Precipitation: Spring Summer M A M J J A

Temperature: Spring Summer M A M J J A

Winter D J F

(-3)1-3) 2

91 92 93 94 95 96 97 98 99 1400

2 2 -3-3 2 2 2 2 2 2

2 2 2 2

2 2

2 2 2

2 2 2 2

2 2 3

3 3

2 2 2 (2 ) ( 2 ) 2 2 2

2 2

(2 ) (2 )

-3 -3

01

02 03 04 05 06 07 08 09 1410

Autumn SO N

2 2 2 2 2

-3-3 -3 -3 -3 (2 )

-

-3-3

2-2

11

12 13 14 15 16 17 18 19 1420 21 22 23 24 25 26 27 28 29 1430 31 32 33 34 35 36 37 38 39

-

-3-3 2 2 2 2

2 2 2 2

3 3 2 2 2

-2-2-2

22 2

2-2

-3-3 -3-3 -3-3-3 -3-3 -3-3 -3-3 -3-3 -3-3 2 2 2 -3-3 3 3 3 3-2-3 -3-3 -3-3 2 2 2 2 -3-3

333

-2 222

2 2

2

-2 -2 -2

-

2-2

Autumn SO N

D O C U M E N T IN G THE MEDIEVAL CLIMATE

1200

1220

1240

1260

1280

1300

1320

1340

1360

1380

1400

1420

1440

--10

1200

1220

1240

1260

1280

1300

1320

1340

1360

1380

1400

1420

1440

Figure 6 .4 Decadal annual tem p e ra tu re indices for Iceland (data from n o rth ern , w estern and southern Iceland) and for E n g la n d 1 (data from southern E ngland) for the period A D 1200 to 1439- T he Icelandic d ata arc indicators o f annual tem p eratu res o b tained by su b tra c tin g th e n u m b e r o f cold seasons from m ild seasons. For th e E nglish d ata, th e values show n are th e sum o f th e seasonal indices d ivided by four. Shaded decades are w arm er th an the average. N o te th at th is index is closely related to th e inverse o f th e w in ter severity index show n in F igure 6.3.

statem en t is then given: ‘T his is our old sailing route,

and, furtherm ore, it is very likely th a t the account

b u t now ice is com e o u t o f the deeps o f th e north-east . . . [and] no one sails this old route w ith o u t p u ttin g

regarding sea-ice is, in fact, a later interpolation. If th is is correct then we cannot be sure w hat period

th e ir life in danger . . .’4I T h is co m m ent on sea-ice has often been taken as a stro n g indication for an increase in sea-ice c. 1350. T he earliest tim e th at the w ork could have been w ritte n , however, is c. 1364

it refers to, or indeed if it refers to a long-term or sh o rt-term (transient) change.42 As noted above, there are b etter sources w hich do, in fact, suggest that there was high sea-ice incidence c. 1350.

ASTRID O G IL V IE A N D G R A H A M FARMER

CONCLUSIONS

appears to have been one o f relatively cold w inters

T h e clim ate o f th e N o rth A tlan tic region is driven

in E ngland (see Figure 6.3). L am b’s suggestion o f a ‘M edieval W arm P eriod’ is not supported by the

by local w inds and ocean c u rren ts as w ell as by the

docum entary data, n eith er his nor ours. T h is is not

general large-scale atm ospheric and oceanic circula­

necessarily a contradiction because his basis for a

tio n s (see C h a p tc r 2). O n longer tim e-scales of

‘M edieval W arm P eriod’ is largely biological and

centuries and m ore, a sim ilarity in clim atic regim es

phenological.

w ould be expcctcd in areas centred in th is region.

W arm Period* d id exist, it was clearly less w ell-

O n shorter tim e-scales local effects w ould be m ore

defined and clim atologically m ore com plex th an has

m arked. T h e existence o f an in te restin g ‘see-saw ’

popularly been believed.

in

w in ter

tem p eratu res

betw een

G reenland

A part

and

from

N evertheless,

th e

if such

pioneering

a

w ork

M edieval

by

Lam b

no rth ern E urope may also be noted. T h is tendency

m entioned above, work on m edieval c lim ate indices

for w in ter tem p eratu res to bc low over northern

for Europe has been u n dertaken by several oth er

E urope w hen they are h igh over G reenland and the C anadian A rctic has been d o c u m e n te d .13 O u t o f

researchers, notably by Pierre A lexandre,16 whose w ork centred on B elgium and n e ighbouring regions.

in terest, an a tte m p t to com pare d ata on m edieval

In another recent study, Z ongw ei Yan and col­

w in ter tem p eratu res for E ngland and Iceland was

leagues4, com pare reliable historical datasets from

m ade here. U nfo rtu n ately th e d a ta available w ere not

c ontinental E urope for th e m edieval period w ith , for

sufficient to do a full analysis, b u t som e years could

exam ple,

be noted

(for

glacier oscillations in th e Swiss A lps.49 In sum m ary,

exam ple, in 1254) w hile oth er w inters w ere sim ilar

they observe th a t rhe w hole o f w estern Europe seems

as corresponding

to

th is p a tte rn

tree-rin g

data

for

Fennoscandia48 and

in both c ountries in term s o f th e contem porary

to have experienced a d rying and w arm ing tren d

d escrip tio n s o f m ildness or severity. A n exam ple of

around AD 1200. T hey also suggest th a t, d u rin g the

th e la tte r is th e year 1290, w hen a very cold w inter

en tire period from AD 1200 to 1426, tem peratures

is described in bo th E ngland and Iceland.

rem ained a t a m ore or less stable level w hile precip­

T h e years from around the n in th to th e fourteenth centuries, th e ‘m edieval p e rio d ’ in European perspec­

ita tio n increased. T hey also argue strongly for caution in using th e trad itio n al term th e ‘M edieval

tive, have been characterised as having been as warm

W arm P eriod’, suggesting, as wc do here, th a t this

as, or w arm er th an , today and the period has come

conceptual scenario is being challenged as m ore

to be know n as th e M edieval W arm Period (also the

derailed data becom e available.

L ittle C lim a tic O p tim u m or M edieval W arm Epoch).

O verall, th e E nglish data analysed here show a

Follow ing this, m any researchers have discerned a

long tim e-scale cooling c. 1240 to c. 1340, w arm ing

period (e.g., th e six teen th to e ig h te en th centuries;

c.

see C h a p te r 9) m uch colder th an today w hich has

Iceland suggest a m ainly variable clim atc d u rin g the

com e to be know n as th e L ittle Ic e A ge. Forem ost

early to m id -tw e lfth century, b u t a d istin c tly colder

a m ong these researchers is H u b e rt Lam b w ho argued

clim atic regim e d u rin g the latter part o f th e tw elfth

th a t, am o n g st o th e r regions, th e B ritish Isles, Iceland

and early th irte e n th century. T h is p ictu re is not d is­

an d so u th ern G reenland were favoured by a pro­

sim ilar to th a t for E ngland. T he fo urteenth century

1510, and

thereafter cooling. T h e d ata from

longed w arm phase from around the te n th to the

in Iceland appears to have been very variable, b u t

th irte e n th centuries w hich facilitated the colonisa­

th e 1320s and 1370s, and possibly the 1340s and

tio n o f th e la tte r tw o places by N orse peoples.44

1360s, w ere alm ost certainly relatively cold (see

W h ile aspects o f th is p ictu re m ay be correct, as

Figure 6.4). In term s o f decadc-to-decade changes in

fu rth er research is done the details appear m ore

rhe fourteenth century, there appears to be an o u t-

complex.'*5 Interestingly, the c entury from 1260 to

of-phase relationship betw een Iceland and E ngland,

1360, based on o u r im proved historical dataset,

whereas th e period betw een 1395 to 1430 seems to

D O C U M E N T IN G THE MEDIEVAL CLIMATE

have been relatively m ild in Iceland, sim ilar to rhe situ atio n in England. As stated above, it has been suggested by some researchers th a t a w arm phase in medieval tim es was followed by a clim atic phase th a t was generally so cold th a t it has becom e traditio n ally know n as the ‘L ittle Ice A g e’. As m ore research is d one into

4

th e clim atic history o f the past thousand years, it becom es clearer th a t, as for th e hypothesised ‘M edieval W arm P eriod’, the situ atio n was more com plex than has been previously th o u g h t and th at th is term also should be used advisedly.

5 6 7

NOTES

8

1 T h is analysis o f d o c u m e n tary c lim ate d a ta for E ngland in th e m edieval period is based on w ork u n dertaken in the C lim atic Research U n it by a n u m b er of researchers, am ong th em T.M .L. W igley, G . Farm er, R. M o rtim er, M .J. In g ram , D .J. Stern and A.E.J. O gilvie. Tw o specific p u b licatio n s/rep o rts on th is w ork m ay be m entioned. T hese are: G . Farm er and T.M.L. W igley, 'T h e reco n stru ctio n o f E uropean clim ate on decadal and sh o rter tim e scales’, 1984, Final R eport to the C om m ission o f the European C o m m u n ities u n d e r C o n tract N o. C L -0 2 9 -8 1 -U K (H ), unp u b lish ed rep o rt, C lim atic Research U n it, N o rw ic h , U K ; T.M .L. W igley, G . Farm er and A.E.J. O gilvie, 'C lim atic reconstruction using historical sources', in A. G hazi and R . Fantechi (eds), Current Issues in Clim atic Research, P roceedings o f th e EC C lim atology Program m e S ym posium , Sophia A n tip o lis, France, 2 -5 O cto b er 1984, C om m ission o f th e E uropean C o m m u n ities, D o rd re ch t, R eidel, 1986. 2 For a fuller discussion see A .E .J. O g ilv ie, ‘C lim atic changes in Iceland A D ca. 86 5 to 1598’, in G.F. B igelow (presenter). The Norse o f the North Atlantic, Acta Archaeologica, 1991, vol. 61 , pp . 2 3 3 -5 1 ; A.E.J. O g ilv ie, ‘H istorical accounts o f w eather events, sea-ice and related m atters in Iceland and G re en la n d ,’ A D ca. 1250 to 1 4 3 0 ’, in B. Frenzel (ed.), ‘D ocum entary c lim atic evidence for 1 7 5 0 -1 8 5 0 and th e 14th c e n tu ry ', Palaeoclimatic Research!Palaoklimaforschung 23, Special Issue 15> 1997 (in press), M ainz, T h e European Science F oun d atio n a n d th e A cadem y o f Sciences and L iterature. 3 Sec, for exam ple, H .H . L am b, ‘T he early m edieval w arm epoch and its sequel’, Palaeogeography. Palaeo­ climatology, Palaeoecology> 1965, vol. 1, pp. 1 3 -3 7 ; H .H . L am b, Climate: Present, Past a n d Future. Vol. 2:

9 10

11

12

13

14

15

Climate History a nd the Future, L ondon, M eth u en , 1977. H ow ever, see also O g ilv ie, op. c it., 1991, pp . 2 4 7 - 9 , anil M .K . H u g h es and H . D iaz, ‘W as there a ‘M edieval W arm P eriod’, a n d , if so, w here and w hen?’, in M .K. H u g h e s and H .E D iaz (eds), The Medieval Warm Period, R ep rin ted from Clim atic Change, 1994, vol. 26, pp. 1 0 9 -4 2 , D ordrecht, K luw er Academ ic Publishers. For a c ritiq u e o f the m ain co m pilations see W.T. Bell and A .E J . O gilvie, W eather com pilations as a source of d a ta for the reconstruction o f E uropean clim ate d u rin g the m edieval p erio d ’, Climatic Change. 1978, vol. 1, p p . 3 3 1 -4 8 . Lam b, op. c it., 1977, A ppendix 5, Table 4. Bell and O gilvie, op. cit. C .E. B ritto n , ‘A m eteorological chronology to AD 1 450’, M eteorological Office G eophysical M em oirs, N o. 70 , 1937, L ondon, I lis M ajesty’s S tationery Office. T.F. T out, ‘M edieval Forgers and Forgeries’, in The Collected Papers o f Thomas Frederick Tout, vol. 3, H is­ torical Series no. L X V I, P ublication o f the U niversity o f M anchester, no. C C X X I, M anchester, M anchester U niversity Press, 1934, pp. 1 1 7 -4 3 . Ibid. See, e.g., A.E.J. O gilvie, ‘D ocum entary evidence for changes in th e c lim ate o f Iceland, A D 1500 to 1800', in R.S. Bradley and P.D. Jo n es (eds). Climate since A D ¡ 5 0 0 , L ondon, R ou tled g e, 1992, pp. 9 2 -1 1 7 . T he im portance o f source analysis w ith regard to historical clim atology has been discussed by e.g., T h. V ilm undarson, ‘Evaluation o f historical sources on sea ice near Iceland’, in T. K arlsson (ed.), Sea Icey P roceedings o f an International Conference, R eykjavik, N a tio n a l Research C ouncil, 1972, pp. 1 5 9 -6 9 ; W.T. Bell and A .E.J. O gilvie, op. c it., 1978; M .J. Ingram , D .J. U n d e rh ill and G . Farm er, ‘T he use o f do cu m en ­ tary sources for th e stu d y o f past clim ates', in T.M .L. W igley, M .J. Ingram and G . Farm er (eds), Climate and History, C am bridge, C am b rid g e U niversity Press, 1981, pp . 1 8 0 -2 1 3 ; O g ilv ie, op. c it., 1991. P. B ergthorsson, ‘An estim a te o f d rift ice and tem p e r­ ature in 1,000 years’, J o k u ll, 1969, vol. 19, pp. 94 101. See also A.E.J. O gilvie, T h e past c lim ate and sea-ice record from Iceland, part 1: d ata to A D 1780’, Climatic Change 1984, vol. 6, p p . 1 3 1 -5 2 (esp. pp. 133, 146). T hese sources, Konungs Skuggsjd (T he K ing's M irror) and Granlandslysing Ivar Bdnlarsonar (fvar B ardarsons D escription o f G reenland) are discussed m ore fully in O gilvie, 1996, op. cit. T h e orig in s of, and differences betw een, som e o f these sources are discussed in Bell and O gilvie, 1978, op. cit. W illiam M erle’s journal is discussed in C h ap ter 7 of th is book. See also R. M ortim er, ‘W illiam M erle’s

A S T R ID O G I L V I E A N D G R A H A M FARM ER

weather diary and the reliability o f historical evidence for m edieval clim ate,' C lim ate M onitor, 1 9 8 1 , vol.

30

1 0 (2 ), p p . 4 2 - 5 .

16 J.Z . T itow , ‘Evidence o f w eather in rhe account rolls o f the Bishopric o f W inchester 1 2 0 9 - 1 3 5 0 ’, Economic History Review, 2nd ser., I9 6 0 , vol. 12, pp. 3 6 0 -4 0 7 ; J .Z . T itow , ‘Le clim a t à travers les rôles de co m p t­ ab ilité d e l ’évêché de W inchester ( 1 3 5 0 - 1 4 5 0 ) ’, A nnales E S C , 1 9 7 0 , vol. 2 5 , pp. 3 1 2 - 5 0 . 17 D.V. Srern, A H ertfordshire m anor o f W estm inster Abbey: an exam ination o f dem esne profits, corn yields and w eather e vid en ce’, U n p u b lish ed P h.D . thesis. K in g ’s C o lleg e, London, 1978. 18 P.P. Brandon, L ate-m edieval weather in Sussex and its agricultural significan ce’, Institute o f Geographers, Transactions No. 5 4 , 19 7 1 , pp. 1—17. 19 T hese different sources are all fully discusscd in O g ilv ie , 19 9 1 , op. cit. 2 0 T h is situation im proved in E ngland after the end o f the fifteenth century w hen p olitical and social order was restored after the accession o f H enry Tudor in 21

1485. A detailed d iscussion on d atin g may bc found in Lamb, 1 9 7 7 , op. c it., p. 49. A discussion specifically on Icelandic d atin g m ay be found in A.E.J. O gilv ie,

31

32 33 34 35

Larson, 1 9 1 7 , o p .c it., p .1 3 8 . S to rm , op. c it., p . 3 32. Ib id . p p . 53, 148, 2 0 1 , 340. Ib id . pp. 1 52, 2 0 4 , 2 6 7 , 345.

36

Ib id . pp. 1 52, 2 0 5 , 2 6 7 ,

37 38 39

40 41 42 43

‘C lim ate and society in Iceland from the m edieval period to th e late eigh teen th century'. U n published P h.D . th esis, School o f E nvironm ental Sciences, U n iversity o f East A n g lia , N orw ich , 1 9 8 2 , p. 35. 22 T itow , I 9 6 0 , op. c it., p. 361. 23 J .Z . T itow , Winchester Yields, C am bridge, Cam bridge 24 25

U n iversity Press, 1 9 7 2 , pp. 5 - 7 . O g ilv ie, 19 9 1 , op. cit.; O g ilv ie , 19 9 6 , op. cit. L im b , 1 9 7 7 , op. cit.

26 27

B ritton , 19 3 7 , op. cit. A ll these data and their sources are discussed m ore fully in O g ilv ie , 1 9 9 1 , op. cit. 2 8 Translated from G . Storm , Islandske A nnaler In d til 1 5 7 8 . R eprinted by N orsk H istorisk K jeldeskrift In stitu tt, O slo, 19 7 7 . O rigin ally published in 1888, U d g iv n e for det norske historiske kildeskriftfond, C hristiania, p. 2 6 0 . 2 9 T he loss o f the N orse G reenland colon y is discussed in detail in P.C. B uckland, T. A m orosi, L.K. Barlow, A J . D u gm ore, P A . M ayew ski, T .H . M cG overn, A.E.J. O g ilv ie, J.P. Sadler and P. Skidm ore, ‘Bioarchaeological and clim atological evid en ce for the fate o f N orse farmers in m edieval G reen land’, A n tiq u ity , 1 9 9 6 , vol. 7 0 , pp. 8 8 - 9 6 . See also L.K. Barlow, J.P. Sadler, A.E.J. O g ilv ie , P C . Buckland, T. A m orosi, J .H . Ingim undarson, P. Skidm ore, A.J. D u gm ore, and T .H . M cG overn. ‘Interdisciplinary investigation s o f the end o f the N orse W estern S ettlem en t in G reenland’ (unpublished).

L.M . Larson The K ings M irror (Speculum Regale Konungs Skuggsjd), N e w Y ork, S candinavian M o n o ­ g ra p h s Vol. 3 , T h e A m e ric a n -S c a n d in a v ia n F o u n ­ d a tio n , 19 1 7 . For a discu ssio n o f th is w ork see O g ilv ie , 1 9 9 6 , op. c it. F. Jo n sso n Del garnit G rinlands beskrit/else a f lia r Bdrdarson (Iva r Bardsson), U d g iv e n e fte r H â n d sk rifte rn e , C o p e n h ag e n , 1930. F or a d iscussion o f th is w ork see O g ilv ie , 1 9 9 6 , op. c it.

44

45 46

345.

Ib id . pp. 3 5 8 - 9 . Ib id . p. 2 8 0 . T ran slated by O g ilv ie from th e tex t as p u b lish e d by G . V igfiisson and J. S igurdsson et al., Biskupa Sogur 2. I Iin u Îslenzka B ô k m en ta lfé la g i, C o p e n h ag e n , 1878, p.5. See, for ex am p le, L am b, 1 9 7 7 , op. c it., p .6. Jo n sso n , 19 3 0 , op. c it., p p . 1 7 -1 8 . For a m o re d e ta ile d d iscu ssio n o f th is see O g ilv ie , 1 996, op. c it. H . Van Loon and J.C . R ogers, ‘T h e see-saw in w in te r te m p e ra tu re s b e tw ee n G re e n la n d an d N o rth e rn E urope. P art 1: G en eral D e sc rip tio n ’, M onthly Weather Rei'ieiv, 19 7 8 , vol. 106, p p . 2 9 6 - 3 1 0 ; J.C . R ogers an d I I . V an L oon, ‘T h e see-saw in w in te r te m p e ra tu re s b e tw ee n G re e n la n d and N o rth e rn E urope. P a rt 2: S om e oceanic an d a tm o sp h e ric effects in m id d le an d h ig h la titu d e s '. M onthly Weather Review, 19 7 9 , vol. 1 07, pp. 5 0 9 - 1 9 . L am b , 19 6 5 , op. c it., L am b 19 7 7 , op. c it.; H .H . L am b, C lim ate: History1 a n d the Modern World, L ondon, M e th u e n , 1982 See, for e x am p le, O g ilv ie , 19 9 1 , op. c it.; O g ilv ie 1996, op. c it.; H u g h e s an d D iaz, 1 9 9 4 , op. c it. P. A lex an d re, Le C lim at a u Moyen A ge en Belgique et dans les régions voisines (Rhénanie, N o rd de la France), 1 9 7 6 , L iège, P u b lic a tio n N o . 50 d u C e n tre B elge

47

d ’H isto ire R urale. Z . Yan, P. A lex an d re an d G . D em arée, ’Som e seasonal c lim a tic scenarios in c o n tin e n ta l w estern E u ro p e based on a d a ta se t o f m ed iev al n a rra tiv e sources, a d 7 0 8 —1 4 2 6 ’, B russels, Institut R oyal Météorologique de

48

Belgique, Publication scientifique et technique No. 0 0 3 , 1 9 9 6 (in press). K .R . B riffa, P.D. Jo n e s, T.S. B a rth o lin , D . E ck ste in , F.H . S c h w e in g rü b er, W. K a rlen , P. Z e tte rb e rg an d M. E ro n en , F e n n o sc a n d ia n su m m e rs from A D 500:

te m p e ra tu re c h an g es on sh o rt an d long tim e sc ales’, Clim ate Dynamics, 19 9 2 , vol. 7, p p . 111 —194 9 J .M . G ro v e a n d R. S w itsu r, G lacial geological ev idence for th e M edieval W arm P e rio d ', in M .K .

D O C U M E N T I N G THE M E D IE V A L CLIM ATE

Hughes and H. Diaz (eds). The Medieval Warm Period, Reprinted from Climatic Change, 1994, vol. 26, pp. 143-70.

GENERAL READING W.T. Bell and A.E.J. Ogilvie, ‘W eather compilations as a source of data for the reconstruction of European climate

during the medieval period’, Climatic Change, 1978, vol. 1, pp. 3 3 1 ^ 8 . R.S. Bradley and P.D. Jones (eds), Climate since A D 1500, London, Routledge, 1992. M.K. Hughes and H.F. Diaz (eds), 'The Medieval Warm Period’, Climatic Change (Special Issue), 1994, vol. 26, Dordrecht, Kluwer Academic Publishers. T.M.L. Wigley, M.J. Ingram and G. Farmer (eds), Climate and History, Cambridge, Cambridge University Press, 1981 .

T his page intentionally lcli blank

Part 3 M O N I T O R I N G THE P R E S E N T

We, which now behold these present days, Have eyes to wonder, but lack tongues to praise. W illiam Shakespeare, Sonnet 106

T his page intentionally lcli blank

7 O B S E R V I N G AND M E A S U R I N G THE WEATHER A Brief History

John Kington Good order is the foundation of all things. E d m u n d B u rk e

INTRODUCTION

explanation and the establishm ent o f th e first p rin ­ ciples o f scientific w eather forecasting. T h is chapter follows the history o f w eather obser­

W eath er varies enorm ously over th e E arth and is o f the greatest geographical significance for hum an

vation and m easurem ent, w ith p articular em phasis

endeavour. Travellers and

the

on the B ritish Isles, from the Renaissance th ro u g h

earliest tim es described th e alm ost endless varieties

to the present century. D u rin g the n in eteen th cen­

o f w eather to be found from place to place, and also from tim e to tim e at the sam e place. S im ple obser­

tury, m any o f the key figures responsible for se ttin g up standardised w eather observing netw orks cam e

vations o f th e w eather, en captured in trad itio n al

from these islands. N evertheless, this innovation only

w eather lore and poetry, are as old as lite ratu re itself

cam e about due to the w ider European legacy o f new m eteorological recording in stru m en ts and in te r­

w riters have from

and th e M esopotam ian, E gyptian, G reek and I Iebrew civilisations all co ntain num erous references to th eir

national co-operation betw een learned societies and

m eteorological know ledge. As an exam ple o f how

scholars. T his b rief historical review ends in the era

th is ra th e r subjective know ledge can be used in the

o f m odern observing system s and satellites, b u t

scientific process, C h ap ter 6 exam ined in som e detail

considers along the way the co n tin u in g role o f th e

how literary sources from the M iddle A ges can be

am ateu r observer. T h e ways in w hich these evolving

used to reconstruct c lim atic variations over tens and

w eather observing system s co n trib u ted to th e devel­

hundreds o f years. Follow ing the early m eteorolog­

o p m en t o f w eather forecasts is discussed in m ore detail in C hapter 14.

ical investigations by th e G reeks - notably A ristotle and H ip p o crates - and the w ritte n records o f the m edieval scholars and travellers, the rise o f w estern science in th e w ake o f th e period o f geographical

THE PRE-INSTRUMENTAL PERIOD

exploration in th e fifteenth and six teen th centuries led to a new rh irst and rig o u r for m eteorological

D u rin g the M iddle Ages texts from G reek and

observation (see Figure 7.1). O bservation du ly led to

M uslim sources becam e accessible in w estern Europe

JO H N K IN G T O N -rrw Gr>««i pnivrft hi .fit mfmrn-

c

¥

- -fi, .

,, -

*’*•*->+"'sfc S !& £ , .S x z ?

tffesnfei>toi ff r&Mt ntf a m jtut5>

fWiWt/otu

•«rfcGi |>i»u' 65 f * »*"*

ni fic fV" & f ‘> P

• «•*•„,,.

^ r .j n i . i ,

^«BT#► «»«•«■

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-« 0fH

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«M lU

f

^ jb w ih , f t - i f a « -1«

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^.'fdii raAitift U>MIA*« intt*f#» " J- 2ÌH.'.

*?f~* p"* (ft>U af,

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t Figure 7. / O ne o f the earliest clim atologists’, Tycho Brahe (1 5 4 6 -1 6 0 1 ), in his observatory on the island o f Hveen (now Ven, Denmark) (taken from the 1602 edition o f his AitroHomiae Imtauratae Meehanica).

Figure 1.2 A page o f W illiam Merle’s weather journal (1 3 3 7 -4 4 ); the m onthly accounts, recorded in Latin, contain details about individual days.1

th ro u g h L atin tran sla tio n s. A m o n g st these volum es

heavenly

w ere m a n u s c rip ts c la im in g to p re d ic t h u m a n destiny,

m eteo ro lo g y a n d , w ith its m ystical o rig in s, cam e to

as w ell as n a tu ra l ev en ts such as th e w eather, from

enjoy th e p a tro n a g e o f m any a u th o ritie s, in c lu d in g

th e m o tio n s o f th e stars, p la n e ts, su n an d m oon.

som e n o tab le figures in th e histo ry o f science such

T h ese te x ts w ere e n th u sia stic a lly received in learned

as Jo h a n n e s o f T oledo an d J u s tu s Stoffler.

bodies.

T h is

stu d y

was

term e d

astro-

circles as b e in g novel a n d p ro m is in g for m eteorology.

D e sp ite th is false hope o f c cn tu ric s p a st, a bonus

U p to th a t tim e it had only been p ossible to forecast

for c u rre n t c lim atic research has em erged from these

th e w e a th e r for sh o rt p erio d s ahead u sin g em pirical

early a tte m p ts to p re d ic t th e w eath er by astrological

rules based on

sig n s' re la te d to th e a ppearance o f

m eth o d s: d a ily m eteorological o bservations beg an to

th e sky. T h e new astro lo g ical h y p o th eses held o u t

bc m ade on an increasing scale in E urope d u rin g th e

h o p e th a t it m ig h t be possible to m ake lo n g er-ran g e

M id d le A ges.

w e ath e r p re d ic tio n s a cc o rd in g to th e m o tio n s o f

T h e m a n n e r o f m a k in g th e e n tries, so m e tim es in

I

O B S E R V IN G AN D M E A S U R IN G THE WEATHER: A BRIEF HISTORY

the m argins of astronom ical tables and almanacs, appears to suggest th at, at first, there was not a great concern about keeping a detailed record of the w eather in its own right. Rather, an a ttem p t was made to establish possible links between certain astronom ical phenom ena (such as eclipses, planetary conjunctions and phases ol the moon) and particular types of w eather - as well as com piling m eteoro­ logical statistics to assess the success or failure of previous astrom eteorological predictions. Over the period from the thirteen th century to the early 1600s, a gradual change can be detected in the m anner of recording, w ith the astrological entries becom ing less frequent w hilst the m eteorological observations become more continuous and orderly. A good exam ple o f the latter type o f record is the journal of W illiam M erle, rector of Driby, Lincolnshire and Fellow, perhaps, o f M erton College, O xford.1 Merle has the d istinction o f being the author o f the earliest know n system atic register of the weather. H is journal, Tmperies aeris Oxoniae pro septentlio, extends over a seven-year period from January 1337 to January 1344 (see Figure 7.2). Merle's exam ple was m ore or less followed du rin g the follow ing three centuries w ith the result that even before the basic observing instru­ m ents were invented in the seventeenth century, there were m any learned people who were laying the foun­ dations o f m eteorology, as an exact science, by m aking system atic reports o f eye-observable weather elem ents such as the state o f the sky, w ind direction and precipitation.

THE BEGINNING OF INSTRUMENTAL OBSERVING T he invention oi the therm om eter by G alileo in 1597 and the barom eter by his pupil, Torricelli, in 1643 m ade it possible to begin instrum ental m ete­ orological observing in the early seventeenth century. G reat interest was shown in these new instrum ents,

o f in d u c tio n advocated by Francis Bacon in the early 1600s. It was soon realised that the value of such exact and quantifiable data would be greatly enhanced if readings at various places could be made sim ultane­ ously, and in 1653 the first attem p t to establish a network of meteorological observing stations was m ade in Italy under the patronage of the G rand Duke of Tuscany, Ferdinand 11, founder of the Accademia del Cim ento. Standardised instrum ents were dis­ patched from Florence to about a dozen stations, m ostly situated in northern Italy, and a uniform procedure for m aking the observations was devised. A lthough the netw ork ceased to function after the Academy was disbanded in 1667, it did set the pattern for later attem pts. In fact, the idea was taken up again in the 1660s by the newly founded Royal Society o f London when Robert Hooke proposed a scheme to com pile a history of the w eather (see Figure 7.3). T he aim of establishing a netw ork of m eteoro­ logical stations was further pursued by the Royal Society in 1723 when its Secretary, Jam es Ju rin , issued an invitation to the scientific com m unity at large to form a world-w ide system of w eather obser­ vations. J u rin ’s interest in this undertaking was both m eteorological and medical; earlier he had studied m edicine at I.eyden under Herm ann Boerhaave, who was interested in the association between weather and public health. Like many other early attem pts, however, the m om entum was lost after a few years and it was not un til another half-century or so had passed that the tim e was ripe for such efforts to succeed. In the 1770s, following the lead of m eteorologi­ cally inclined physicians earlier in the century, medical authorities in France decided to m ake a system atic study of weather and public health. As a result, the Société Royale de M édecine was estab­

as it was hoped that their response to changing

lished in 1778, under the patronage of Louis XVI, to m aintain a regular correspondence on m eteoro­ logical and medical m atters w ith doctors throughout the French kingdom . Felix Vicq d'Azyr, physician to

atm ospheric conditions would provide the means of predicting thp w eather using the scientific m ethod

M arie-A ntoinette, was appointed Secretary-General and, together w ith the m eteorologist-cleric, Louis

140

J O H N K IN G T O N

%0ïAL

SOCIETY.

\ 79

U nfortunately, the m eans o f tra n s m ittin g

the

observations to a ccntral forecasting office w here they could be processed rapidly enough to keep pace w ith

S

C

H

E

M

the w eather were lacking at th a t tim e, and m eteo­ rologists had to w ait several m ore decades for

E

advances

At one View repreienting to the Eye the Obfervations of the Weather for a M onth. JÊ .

K

« SI

in o aa

rSci*

3

II

fi»

1 1

M.4f if n »3.40

f

N.Moon.ÿ. i t 7. t j l A. M. £ t 1 0 .8 .

&C.

& c.

com m unications

and

w eather

the Société Royale de M édecine was suppressed in 1793 by a French R evolutionary decree. However,

General De­ ductions to The Faces or Nota- be made af­ viGble ap The ter the fide oleft Eifefts. pearanees of is fitted w ith the Sky. Obfervationst As,

19[¿dear

From the laft Q.0 f the Afoon to the Change the W eather was very tern* perate , but cold for the feafo n ; the Wind pretty conftant herwetrtN.fcW . A little before the laft great Wind .And till IgCT .'the W ind rofe Overcaft and No dew u p o iy t its higheft, very lo w r- the ground the Q u ick sil­ ing. bur very ver continu’d much upon descending til Marble* it came very &:c. &c. llones, &c. Sowjafterwch lit bc^.intore 'afeend, Sec.

1)1cw A great dew b u t ydlowirti *7 i ls * 8 in the N. E. Thunder, far a 9 . 4* Clowded to to the South *9l ward the S. A very great IO J Perigeu. Checker’d Tide. W .SW .I 13. blew. N ot hy much N. W. 3 A clear Sky 18 29ri all day, b u t a lo big a Tide »8 as yefterday little Chec­ N . ÜM-H ker’d a t 4. Thunder ir P. M. at Sun- the N oith. let red and

9 j»

bo th

th e original m anuscripts o f daily observations m ade

J

w-s

in

studies before Lavoisier’s idea could be realised. Sadly,

See. See. I

D I-

in th e 1780s have been preserved in th e archives o f the A cadém ie de M édecine in Paris, w here, after nearly tw o centuries o f oblivion, they were bro u g h t to lig h t in 1965 by Jean M eyer and E m m anuel Le Roy Ladurie a t the Sorbonnc.2 T he netw ork o f the Société Royale de M édecine was not th e only such system established in the 1780s for th e advancem ent of w eather observing. M annheim , capital o f the R hineland P alatinate, had developed in to an influential centre for the arts and sciences d u rin g the E n lig h ten m en t. In 1780 the Princc-E lector, K arl T heodor, founded th e Socictas M eteorologica Palatina and ap pointed his C ourt C haplain, Jo h an n H em m cr, as its director. Besides investigating

m edico-m eteorological

scientists

the

in

eig h te en th

relationships,

century

were

also

concerned th a t progress tow ards finding a satisfac­ tory m ethod o f p re d ic tin g the w eather had been d isapp o in tin g ly slow since the appearance o f the

Figure 7.3 An example from the Royal Society scheme for making weather observations, as suggested by Robert Hooke in the 1660s.3

b arom eter and th erm o m eter in the early 1600s. C o n ­ sequently, m em bers o f th e Socictas M ctcorologica Palatina hoped th a t th e analysis o f standardised w eather d ata by statistical m ethods w ould show th at variations o f atm ospheric behaviour were subject to a regularity com parable to th a t expressed in th e laws

C o tte , becam e actively involved in establishing a

o f nature discovered earlier by Jo h a n n K epler and

netw ork o f w eather stations w hich, by th e m id1780s, com prised over seventy stations and had been

Isaac N ew ton. Each station o f th e M annheim w eather

extended beyond France to include correspondents in

netw ork was supplied, g ra tis, w ith a set o f in stru ­ m ents to g eth er w ith detailed instructions, w ritte n in

o th er p arts o f E urope as well as in A m erica and Asia

L atin, on observational procedure. R egisters were

(see F igure 7.4). T h is was th e kin d o f organisation

dispatched annually to M annheim for p u b licatio n in

envisaged by A ntoine Lavoisier w hen he suggested

the Ephemerides o f th e Society, w hich were issued to all p a rticip a tin g observers (see Figure 7.5).

th a t in o rder to prepare a forecast a m eteorologist w ould need to have sim ultaneous daily observations o f th e prin cip al w eather elem ents.

From a nucleus o f about a dozen stations, m ostly located in ccntral Europe, th e netw ork rapidly

O B S E R V I N G A N D M E A S U R I N G THE W EA T H ER : A BRIEF HISTORY

O B S E R V A T I O N S

M É T É O R O L O G I Q U E S

ou

mois

dY

W ^ _ , 7 *i

Figure 7.4 An extract from a meteorological register of the Société Royale de Médecine including thrice-daily obser­ vations of pressure (Paris inches), temperature (degrees Réaumur), wind, state of the sky, and significant weather; recorded at Dijon in October 1781.3

expanded, so th a t by the m id -1 7 8 0 s it included over fifty

observatories e x ten d in g

from

Besides th e w eather stations organised by th e tw o

R ussia across

E uropean scientific societies discussed above, a large

E urope to eastern N o rth Am erica. T he observers,

n u m b er of private observers were also recording daily

m ostly physicists, astronom ers, and clerics, were

m eteorological observations d u rin g th e e ig h te en th

associated

various scientific academ ies,

century. In the B ritish Isles, these m ore individual

learned societies, and observatories w hich had been established in m any E uropean cities d u rin g the

efforts were m ade m ostly by physicians, clerics and country landow ners. A lth o u g h w orking in isolation,

w ith

th e

E n lig h ten m en t. A lth o u g h H e m m e r died in 1790 the

they som etim es corresponded w ith one another about

a ctivities o f th e Society continued for a fu rth er five

th eir m utual interests in m eteorology and natural

years. U nfortunately, w ith th e p u b licatio n o f the

philosophy, the Royal Society providing a centre for

tw elfth volum e o f th e Epbemericies, c o n ta in in g d ata

m ore form al discussion and exchange o f ideas. O ne

for 1792, th e series was b ro u g h t to a close. T he Society was facing increasing financial difficulties,

of the best exam ples o f these individual m eteoro­

and th e final blow w hich led to its d isb a n d m e n t was

logical observers was the R u tlan d squire, T hom as Barker, w ho, b e g in n in g in 1736, m aintained an

th e fall o f M annheim to French R evolutionary forces

instrum ental w eather register at Lyndon H all, near

in 1795.*

O akham , for over sixty years (see Figure 7.6).4

JO H N KINGTON

O B S E R V A T I O N RS B U D E N S E S Auto re

B

runa

.

H o ra e o b f ; r v a ü o r u s o rd in a n c e 7 mac. 2 p o m . 9 refj».

J a n u a r i u s . Meccora. Cj Barova, Therm. Tneriod 1400 to 1969 compared to the decade-average Central England Temperature anomalies for summer, 1660 to 1989- The anomalies are calculated from the 1861 to I960 averages.

locations as possible to establish a faithful record of hem ispheric and global tem peratures. T h e re lationship betw een proxy tem p eratu re series

variations in tem perature over a sm all region are m ore likely to conform w ith hem ispheric variations the longer th e tim e-scale considered. T h e C entral

for indiv id u al sites and larger-scale tem p e ra tu re aver­

England T em perature m ay seem to coincide fairly

ages for th e hem isphere has been addressed by a

closely w ith hem ispheric tem p eratu re tren d s d u rin g

n u m b er o f authors. T here is clearly no reason why

spring, sum m er and especially a u tu m n on a dccadc-

any region should necessarily be m ore indicative o f h em ispheric conditions th an any other, except th a t

by-decade basis since 1850, b u t it does not neces­ sarily follow th a t such a situ atio n prevailed over the

th e larger th e region is, th e m ore likely its tem p e r­

earlier period from 1650 to 1850.

atu re tre n d should follow th e hem ispheric tem p era­ tu re

trend.

Sim ilarly,

in

th e

tem poral

dom ain,

O u r m ost likely chance o f e stim a tin g robust h e m i­ spheric tem perature series p rio r to the m id -n in e te en th

THE C H A N G IN G TEMPERATURE OF 'CENTRAL E N G LA N D ' Table 9.5 Notably very hot (>23.5’C) and very cold ( ,.

58°

i

7

58°

o ? f r ? 56°

56°

I ^ o n V T -iK 54°

r\ z/>"-* ^ - - 20 2o^\ / “ IO-n

c 52°

50“

4 VC ,iU €Iff: f y ; I0 ° W











2°R

52°

50J

10°W









1989/90

u

60°N

10

p /sy

58°

O T / IZ 56c

W

®

A

¿ ^ ^ - 20- ^ ) \ \ 54° G r ^ C \l "- 44-rT v 3 2 (P , ^ j $ { - 2 0 ^ XllJ 5 2 c 'C /^ V 7^5 S ■

20-

s»‘

^

. , J \

50°

_____JL .^ .x L -lV V ^a-^. IO °W



6C







2°E

Figure 10.16 Five major droughts in the British Isles of fifteen to eighteen m onths’ duration: 1854-5, 1869-70, 1933-4, 1975-6 and 1989-90. Precipitation deficits are shown as percentage deviations from the long-term average.

PR EC IP IT A T IO N V A R IA B ILIT Y A N D D R O U G H T

an d

g ro u n d w a te r reserves in c en tral an d eastern

E n g la n d . T h e responses o f these tw o types o f system s giv e tw o c h ara cte ristic d r o u g h t types in rhe region — sh o rt d ro u g h ts o f u p to nin e m o n th s e n d in g in the a u tu m n (affecting th e u p la n d surface reservoirs as o ccu rrcd in 1 9 9 5 ) an d fifteen- to e ig h te e n -m o n th d ro u g h ts (g en erally tw o su m m e rs w ith an in te r­ ve n in g d ry w in te r w ith reduced g ro u n d w a te r re­ charge) w h ic h have th e ir g re a te s t im p a c t in the so u th -e a ste rn reg io n o f th e B ritish Isles. T h e m o st e x tre m e o f these tw o types o f d ro u g h t to have affected th e B ritish Isles since 1850 are p lo tte d in F ig u res 10.15 an d 1 0 .1 6 . T h ese m aps show th e p a tte rn s o f six sh o rte r-d u ra tio n d ro u g h ts d u r in g 1 8 8 7 , 1 9 2 1 , 1 9 2 9 , 1 9 5 9 , 1984 an d 1995, an d th e p a tte rn s o f five lo n g e r-d u ra tio n d ro u g h ts d u r in g

1 8 5 4 -5 ,

1 8 6 9 -7 0 ,

1 9 3 3 -4 ,

1 9 7 5 -6

and

1 9 8 9 —9 0 .l/ T h e d ro u g h t m aps are expressed as per c e n t d e v ia tio n s in p re c ip ita tio n from th e

1961

to

1 9 9 0 average. A ll th e sh o rte r-d u ra tio n d ro u g h ts have som e region o f th e so u th e rn B ritish Isles w ith a 4 0 p e r c e n t o r m ore p re c ip ita tio n d eficit — 1887 (so u th ­ east Irela n d ), 1921 (so u th e rn an d eastern E ng lan d ), 1 9 2 9 (cen tral an d eastern E n g la n d ), 1 9 5 9 (n o rth ­ easte rn an d eastern E n g la n d an d eastern S cotland), 1 9 8 4 (so u th -w e ste rn E n g la n d an d W ales a n d n o rth ­ w estern E n g la n d ) an d 1995 (cen tral a n d n o rth ern E n g lan d ).

10. 16)

The

lo n g e r-d u ra tio n

d ro u g h ts

(F ig u re

te n d to have som e regions w ith deficits o f

over 2 0 p e r c e n t — 1 8 5 4 —5 (so u th e rn B rita in and Irelan d ), 1 8 6 9 - 7 0 (so u th -w e stern E n g la n d ), 1 9 3 3 —4 (so u th e rn B rita in an d Irelan d ), 1 9 7 5 - 6 (E n g la n d and W ales

an d

so u th e rn

S cotland)

an d

1 9 8 9 -9 0

Figure 10.17 A reservoir near Church Stretton, Shropshire, at the end of the 1976 sum m er drought. This was the culm ination of eighteen m onths of very dry weather in England and Wales, the driest such sequence since records commenced.

(so u th e rn E n g la n d an d W ales). T h e m o st severe d ro u g h ts in th e E n g la n d and W ales P re c ip ita tio n series w ere in 1921 (sh o rt d u ra ­

It is a p p are n t th a t th e c lim ate o f E n g la n d an d

tio n ) an d 1 9 7 5 - 6 (lo n g d u ra tio n ; F ig u re 10.17). T h e

W ales is such th a t a 1-in -5 0 year ‘w ater-resources’

1921

e v en t was th e m o st severe d ro u g h t over w estern

d ro u g h t m ay o ccur som ew here in E n g la n d an d W ales

E urope th is c en tu ry .18 R e t u r n p e r io d s have been

every six to e ig h t years. Such d ro u g h ts seem to be

e stim a te d

o c cu rrin g m ore frequently, especially over th e last

for re ce n t d ro u g h ts

in

re p o rts

w hich

discuss th e ir effects in m u ch m ore d e ta il for th e

tw e n ty

regions o f E n g la n d and W ales (also lo o k in g a t riv er­

F ig u res 10.5 to 10.9 in d ic a te tren d s to less p re cip ­

years. T h e

various tim e -se rie s show n

in

flow and g ro u n d w a te r levels ).19 T h e effects o f th e

ita tio n , p a rtic u la rly in su m m er, h ig h lig h tin g th e

sh o rt, b u t e x tre m e , A p ril to A u g u s t d r o u g h t in 1995

need in a c h a n g in g c lim atc to c o n tin u a lly reassess

arc o n ly ju st b e in g assessed .20

re tu rn perio d estim a te s. Increases in th e frequency

217

PHIL J O N E S , D E C L A N C O N W A Y A N D KEITH BRIFFA

o f e x tre m e ev en ts an d in p re c ip ita tio n v a ria b ility have o ccu rred d u rin g

th is perio d w hich has p u t

tre m e n d o u s p ressu re on w a ter resource system s. O v e r th e sam e tim e , d e m a n d for w a ter has also increased, so th a t su p p ly p ro b le m s o c cu r m o re frequently, and to satisfy th is d e m a n d a d d itio n a l resources m u st c o n tin u a lly bc created.

CONCLUSIONS

6

T h e B ritish Isles is p ro b a b ly th e m o st densely g au g ed re g io n for p re c ip ita tio n m ea su re m e n ts in th e w orld. L ong h o m o g en eo u s re g io n a l series for E n g la n d and

7

W ales, S co tlan d a n d th e w hole o f Irela n d in d ic a te

8

less y ear-to-year v a ria b ility in sp rin g p re c ip ita tio n c o m p a red to th e o th e r seasons. In all th ree regions

9

th ere are ten d e n cie s for w in ters to have g o t w e tte r an d su m m e rs d rier, p a rtic u la rly in th e last tw e n ty years. T h e last te n w in te rs , except for th e w in te r o f 1 9 9 5 - 6 , have seen very little snow. T h e decrease in su m m e r p re c ip ita tio n in recent years has led to m o re fre q u e n t d ro u g h ts. W h e n

10 11 12

c o m b in e d w ith th e in creasin g d e m a n d for w a ter in m o st reg io n s o f th e B ritish Isles it is n o t su rp risin g

13

th a t w a ter resources an d hence w a te r a v ailab ility have been b adly affected. 14

NOTES 1 J.M . Craddock, ‘Annual rainfall in England since 1725’, Quarterly Journal o f tl>e Royal Meteorological Society, 1976, vol. 102, pp. 823-40. 2 G .J. Symons, ‘O n the rainfall in the British Isles', Report of the 35 th meeting o f the British Association for the Advancement of Science, 1865, pp. 192-242. 3 F.J. Nicholas and J. Glasspoole, 'General m onthly rain­ fall over England and Wales, 1727 to 1931', British Rainfall, 1931, pp. 299-306. 4 M.R. Woodley, 'A review of two national rainfall series’, International Journal of Climatology, 1996, vol. 16, pp. 67 7 -8 7 . 5 T.M.L. Wigley, J.M . Lough and P.D. Jones, 'Spatial patterns o f precipitation in England and Wales and a revised, homogeneous England and Wales precipita­ tion series’, Journal o f Climatology, 1984, vol. 4, pp. 1-25; T.M.L. W igley and P.D. Jones, England and

15 16 17

18

Wales precipitation: a discussion of recent changes in variability and an update to 1985', Journal of Climat­ ology, 1987, vol. 7, pp. 231—46; J.M. Gregory, P.D. Jones and T.M.L. Wigley, ‘Precipitation in Britain: an analysis of area-average data updated to 1989’, International Journal of Climatology, 1991, vol. 11, pp. 3 31-45; P.D. Jones and D. Conway, ‘Precipitation in the British Isles: an analysis of area-average data updated to 1995 ’, International Journal of Climatology, 1997, vol. 17, in press. R.C. Tabony, A set of homogeneous European Rainfall series’, Met. 0. 13 Branch Memorandum No. 104, Mete­ orological Office, Bracknell, 1980; R.C. Tabony, A principal component and spectral analysis of European rainfall’, Journal of Climatology, 1981, vol. 1, pp. 283-94. Tabony, 1980, 1981, op. cit. W igley et a l., op. cit.; Wigley and Jones, op. cit.; Gregory et al., op. cit.; Jones and Conway, op cit. K. Sm ith, ‘Precipitation over Scotland, 1757-1992: some aspects of temporal variability’, International Journal of Climatology, 1995, vol. 15, pp. 543-56. See references in this paper to the work of Arthur Jenkinson. Nicholas and Glasspoole, op. cit. Wigley and Jones, op. cit.; Gregory et a l., op. cit. M.C. Jackson. ‘A classification of the snowiness of 100 winters - a tribute to the late L.C.W. Bonacina', Weather, 1976, vol. 32, pp. 9 1 -7 . L.C.W Bonacina, Chief events of snowfall in the British Isles during the dccadc 1956-65’, Weather, 1966, vol. 21, pp. 42 6 (see records for earlier decades in British Rainfall in 1927, 1936, 1948 and 1955). R. W ild, G. O ’Hare and R. Wilby, ‘A historical record of blizzards/major snow events in the UK and Ireland, 1880-1989', Weather, 1996, vol. 51, pp. 82-91. Jackson, op. cit. G. Manley, ‘Snowfall in Britain over the past 300 years', Weather, 1969, vol. 24, pp. 428-37. G.J. Symons, 'Historic droughts', British Rainfall, 1887, pp. 23-35; C.E. W right and P.D. Jones, 'Long period weather records, droughts and water resources', in Optimal Allocation of Water Resources, 1AHS Publ. No. 135, 1982, pp. 8 9 -99; J.C. Doornkamp, K.J. Gregory and A.S. Bums, ‘Atlas of the drought in Britain, 1975-76’, Institute of British Geographers, 1980, 86 pp.; T.J. Marsh and M L. Lees, The 1984 drought’, Hydrological Data UK Series, Institute of Hydrology, 1985; T.J. Marsh, R.A. Monkhouse, N.W . Arnell, M.L. Lees and N.S. Reynard, ‘The 1988-92 drought’. Hydrological Data UK Series, W allingford, Institute of Hydrology, 1994, 80 pp. K.R. Briffa, P.D. Jones and M. Hulm e, ‘Summer mois­ ture variability across Europe, 1892-1991: An analysis

PR E C IP IT A T IO N V A R IA B ILIT Y A N D D R O U G H T

based on the Palmer Drought Severity Index', GENERAL READING International Journal o f Climatology, 1994, vol. 14, pp. 4 7 5 -5 0 6 . J.C . Doornkamp, K.J. Gregory and A.S. Burns, ‘Atlas of 19 Marsh and Lees, op. cit.; Marsh eta l op. cit. the drought in Britain, 1975-76’, Institute of British 20 T.J. Marsh and PS. Tur ton, T h e 1995 drought - a Geographers, 1980, 86 pp. water resources perspective’, Weather, 1996, vol. 51, T.J. Marsh, R.A. Monkhousc, N.W. Arnell, M.L. Lees and pp. 4 6 -5 3 . N.S. Reynard, T lx 1988-92 Drought, W allingford, Natural Environment Research Council, 1994, 76 pp. G. Sumner, Precipitation: Process and Analysis, Chichester, John Wiley and Sons, 1988, 455 pp.

219

11 WIND Resource and Hazard

Jean Palutikof, Tom Holt and Andrew Skellern III blows the wind that profits nobody. W illia m S h ak esp eare, Henry VI, Part III

INTRODUCTION

such disasters requires know ledge o f th e historical record o f extrem e w ind events (often expressed in

T h e w ind clim atc o f the B ritish Isles has im p o rta n t

term s of th e m axim um three-second g u s t in a one-

econom ic consequences for the region. O n th e one

hour period). T his aspect o f w ind is considered in

hand, w ind is a resource to be exploited. For exam ple,

the second p art o f this chapter.

o f th e e n ergy-hungry nations, th e U n ited K ingdom has one o f th e richest w ind resources and, under g o v e rn m e n t legislation to broaden rhe base o f non­

WIND CLIMATOLOGY OF THE BRITISH ISLES

p o llu tin g energy pro d u ctio n , p re m iu m prices are cu rren tly paid for w ind-generated electricity. As a

T he location o f the B ritish Isles, on the w est coast

result,

in

o f a large continental landm ass betw een 50°N and

E n gland and W ales rose from about 2.5 m egaw atts (M W )1 at the end o f 1991 ro 190 M W a t the end

60°N , leads to a clim ate dom inated by th e p o la r f r o n t (see C hapter 2). T h e instab ility o f th is front

o f 1 995.2 To exploit the w ind resource successfully,

causes d e p re s s io n s to form , tracking across the

inform ation

historical

N o rth A tlantic and, at the longitudes o f the B ritish

v ariability o f the average w ind (com m only specified as th e hourly m ean w ind speed and d irection) is

betw een Iceland and Scotland. As these depressions

required. T h is topic is considered in th e first p a rt o f

m ove across the A tlan tic, they follow a life cycle

th is chapter.

w hich, by the tim e they reach th e longitudes o f the

installed

on

capacity

the

for

w ind

geographical

turbines

and

O n th e o th er hand, w ind is a hazard. Large w ind

Isles, follow ing

a preferred

route

w hich

passes

B ritish Isles, m eans th a t they are usually in a phase

storm s cause extensive dam age to com m ercial and dom estic p ro p erty and trees (Figure 11.1). T he

o f m atu rity or decay, m anifest as an o c c lu sio n .

frequency and severity o f large w ind storm s is o f

constraint on the average w ind field o f th e B ritish

It is th is ‘typical’ clim atology w hich is th e prim ary

g re at concern to insurance com panies and th e forestry

Isles. A t w ell-exposed sites, both the prevailing w ind

in d u stry am ongst others. It is estim ated th a t th e cost

and th e h ighest w ind speeds generally lie in the

to th e insurance industry o f th e O ctober 1987 storm

south-w est q uadrant o f th e com pass (Figure 11.2).

was around £ 1.2 b illio n ,* and th a t around fifteen

Speeds tend to be highest in the north-w est o f the B ritish Isles (closest to th e depression tracks),

m illion trees were u p ro o ted .1A dequate p lan n in g for

W IN D : R E SO U R C E A N D H AZARD

N 10.89

N 19.26

Figure 11.1 Tree damage to a house and car at Addlestone, Surrey, following the October 1987 storm. The frequency and severity of large wind storms is of great concern to insurance companies and the forestry industry', amongst others.

decreasing tow ards th e south and east. T h e secondary co n strain t is th e geography o f th e country. First, larger d r a g c o e ffic ie n ts over land lead to th e highest w ind speeds bein g observed at th e coast, decreasing

Figure 11.2 Percentage of wind observations by direction (top), and mean wind speed by direction (tenths of a metre per second; bottom) for High Bradfield in the Pennines, a typical exposed upland site. The site location is shown in Figure 11.9.

inland. Second, acceleration effects over orography lead to w ind speeds increasing w ith a ltitu d e . These effects are clearly d em onstrated

in Figure

1 1 .3 '

w hich show s average w ind speeds over th e B ritish

A lth o u g h th is broad p a tte rn is typical, m any

Isles .6 In th is m ap, broad w ind speed bands are

perm u tatio n s o f w eather and geography exist w hich

show n and w ith in each band th e local geography

affect th e w ind regim e on a day-by-day basis. An

d icta te s th e actual w ind speed range. See A ppendix

annual cycle o f h ig h er w ind speeds in w inter and at

B for a m ore detailed m ap o f average w ind speeds.

th e equinoxes, and low er speeds in sum m er, reflects

222

JE A N PALUTIKOF, TOM HOLT AND A N D R EW SKELLERN

•5

•10

V77Z\

0

Sheltered terrain

Open plain

Sea coast

Open sea

Hills 4 ridges

>6.0 5.06.0 4.5-5.0

>7.5 6.5-7.S 5.5-65

>8.5 7.0-8.5 6.0-7.0

>9.0 8.0-9.0 7.0-8.0

>11.5 10.0-11.5 8.5-10.0

Figure 11.3 Mean annual wind speed (ms-1) over the British Isles at 50 m above the ground (modified from Troen and Petersen5).

th e seasonally varying stre n g th o f th e large-scale

Figure 11.4 One of the wind turbines at Llidiart y Waun, Powys. The typical hub height for a large wind turbine is about 50 m.

atm ospheric circulation. D epressions m ay suddenly bc rejuvenated on th e eastern side o f th e A tlan tic due, for exam ple, to a local s e a -s u rfa c e t e m p e r a ­ tu r e m axim um . Such explosive d e e p e n in g / w hich

th e progress o f depressions across th e A tlan tic is

m ay bc difficult to forecast, led to th e storm s o f

im peded by the presence of a large stationary a n ti­

1 5 -1 6 O c to b er 1987 and 25 January 1990.8 T he

c y clo n e over continental Europe, can lead to low

p a th o f depressions also varies, and th e intense dam age experienced in th e O cto b er 1987 storm was

w ind speeds over the B ritish Isles.

d u e in p a rt to the fact th a t th e depression centre

Local circulations o f therm al origin m ay develop in sheltered places w hen th e large-scale circulation

crossed th e B ritish Isles m u ch to th e south o f the

is weak. A diurnal cycle is therefore com m on, w ith

usual track. Conversely, b lo c k in g situ atio n s, w hen

h igher w ind speeds in the afternoon in response to

W IN D : RESO URCE A N D HAZARD

increased local tu rb u len ce d u e to h eatin g from the g ro u n d below. Sea-breezes close to the coast also lead

Table 11.1 Geographical distribution of UK Met. Office anemometers (AMSL = above mean sea level)

to afternoon m axim a ,9 and k a t a b a t i c w in d s on long

All

m o u n ta in slopes 10 m ay lead to n ig h t-tim e w ind

100-200 m >200 m AMSL AMSL

m axim a d u rin g periods o f otherw ise calm conditions.

WIND AS A RESOURCE: THE ANALYSIS OF AVERAGE WIND SPEEDS Geographical variability

England Wales Scotland Northern Ireland Channel Islands All UK

83 7 44 11 2 147

13 3 5 2 1 24

7

1 6 0 0 14

T he W orld M eteorological O rganisation standard m easuring h e ig h t for w ind speeds is

10 m

above the

gro u n d . T h e broad features o f th e v ariability of

T his lack o f h ig h -a ltitu d e inform ation regarding

average w ind speeds over th e U n ited K in g d o m at

th e w ind clim atology is a problem com m on to m any

50 m h e ig h t was show n in Figure 11.3. T h is h eight

countries, and researchers have sought to exploit the

was selected to be a typical h u b h e ig h t for a large

know n relationship betw een h e ig h t change and w ind

w ind tu rb in e (F igure 11.4). A t th e 10 m h eight

speed to develop num erical m odels w hich predict

speeds w ill be low er th an th is - average annual w ind

w ind speeds from an underly in g terrain elevation

speeds above open level terrain range betw een about

m ap. These m odels vary greatly in th eir sophistica­

6.5 m s

1on

th e exposed coast o f n o rth -w est Scotland

1 at

tion and consequently in the size and pow er o f the

B enbecula) to below 4 m s -1 at

c o m p u tin g facilities they require. T he sim plest are

inland sites in south-east E ngland (e.g., 3-8 m s -1

th e m ass-consistent class o f m odels .13 T h e basic

(e.g., 6 .9 m s

u nderlying theory is th a t as air is forced u p and over

at K ew G ardens). T h e n u m b er o f a n e m o m e te r s

in th e U nited

a hill, th e h e ig h t o f th e to p o f the b o u n d a ry -la y e r

K in g d o m as recorded in th e M onthly Weather Report

rises, b u t to a sm aller extent than the relative h eight

for 1 9 9 1 ,11 and th eir d istrib u tio n by a ltitu d e band

o f th e hill. T his ‘squeezes’ the layer o f a ir betw een

arc show n in Table 11.1. It is im m ediately d e a r th a t

th e g round and rhe boundary-layer top and, to m ain ­

100

tain m ass consistency, the speed o f m ovem ent m ust

m , say) is very sm all. T h is is in p art because m any

increase (see Figure 11.5 ).14 More com plex non-linear m odels sim ulate tu rb u le n t flow over hills by solving

th e n u m b er at any significant a ltitu d e (above

U K M et. Office an em om eter sites are at airports (civil and m ilitary ) w hich tend to be located in low-

the m ass-continuity equations, th e m o m e n tu m con­

lying, flat terrain. T here has been little recent change

servation equations (N avier—Stokes) and th e energy

in th e size o f the anem om eter netw ork, w hich in

conservation equations. Various sim plifications and

1978 stood a t 142 sites .12 W e have already noted

assum ptions are required

th e re lationship betw een w ind speed and a ltitu d e , and th e biased d istrib u tio n o f an em om eter sites

solution, and

causes difficulties in try in g to m o n ito r th e true

by the n u m b er o f these a ssum ptions .15

to arrive at a unique

the c o m p u tin g

requirem ents (and

sophistication) o f the m odel are d eterm ined in p art

geographical v ariability o f w ind speeds in th e B ritish

A w ind-speed p rediction m odel is o f lim ite d value

Isles. D espite this difficulty, there is a g en u in e need

if it produces inaccurate estim ates a n d/or estim ates

for inform ation on w ind speeds, in h ig h -a ltitu d c

w ith w ide confidence lim its. Table 11.2 shows som e

areas, nor only because these have hig h w ind-encrgy

results from a m ass-consistent m odel (C O M PLEX )

p o ten tial b u t also to assess th e safety o f stru ctu res

applied a t tw o sites, separated by 5 km , in the

(radio m asts, etc.) w hich require in stallation on hig h

n orthern Pennines .16 T his table dem onstrates tw o

g ro u n d for good signal reception.

features typical o f m odel results. First, the m odel

223

224

JE A N

P A L U T IK O F , T O M HOLT A N D A N D R E W S K E L L E R N

FLOW OF AIR OVER : Shallow topography

a I

S te e p

to p o g ra p h y

0

5

W in d s p e e d

15

10

m /s e c

Figure 11.5 Representation of the movement of air over shallow and steep topography (left). The effect of air move­ ment over shallow topography on the vertical wind speed profile is shown (right ).14The deformation of the wind-speed profile over steep topography is less predictable. m s -1 o f observations in all

sim ple m ass-consistent m odels and the fully non­

seasons excepr sum m er. P redictions are generally less accurate in th e slacker circulation system s o f the

Analysis and A pplication P rogram m e (W A T ) is a

su m m er m onths. Second, the p redictions are all

w ind flow m odel su itable for use on a Personal

under-estim ates. G reat D u n Fell is a h illto p site, and

C om puter. A sim ple dynam ic m odel, w idely used by

m odels com m only und er-p red ict h illto p w ind speeds

w ind engineers ,18 W A SP can sim ulate th e effects of

and over-predict valley-bottom w ind speeds .17

roughness changes, obstacles to th e flow, and changes

estim ates are w ith in

Lying

in

1

com plexity

som ew here

betw een

the

linear

tu rb u le n t

flow

m odels,

th e

W in d

A tlas

in atm ospheric stability. In a study to validate the perform ance o f this m odel at a n um ber o f sites in

Table 11.2 Wind-speed predictions (ms-1) at Great Dun Fell in the northern Pennines usina the massconsistent model COMPLEX initialised wim wind data from Moor House Winter

Spring

Summer

Autumn

12.8 11.9

8.9 8.2

8.9 7.6

11.6 11.1

the U n ited K ingdom , it was found th a t only h alf th e estim ates were w ith in value.

Particular

10

problem s

per cent o f th e true identified

were

the

assum ption o f a W e ib u ll fre q u e n c y d is tr ib u tio n o f w ind speeds, and the need to specify s u rfa c e r o u g h ­ n e ss le n g th accurately because o f the sensitivity o f

Observed Predicted

th e m odel result to this param eter .19These problem s are typical o f th is class o f m odels.

W IN D : RESO U RC E AN D HAZARD

In th e absence o f p a rtic u la rly im pressive results

a schem e over its to tal lifespan, w hich is o f th e order

from sim p le m o d els, a tte m p ts have been m ade to use

o f tw e n ty years. T hey w ill co m m o n ly have a p re d ic ­

sta tistica l tec h n iq u es for w in d -sp e ed p re d ic tio n . U n ­

tio n o f th e average ten-year w in d speed, based on a

lik e m o d e llin g approaches, these e m p irica l tech n iq u es

sh o rt record o f o n -site o bservations an d th e M C P

re q u ire som e d a ta from th e site for w h ich a p re d ic tio n

m eth o d . A lth o u g h rhis m eth o d is w idely accepted

is so u g h t.

th r o u g h o u t th e in d u stry , an d ig n o rin g th e issue o f

W in d

farm

developers w ill, typically,

m easure w in d speeds a t th e ir proposed site for periods

its accuracy, we are still left w ith th e q u e stio n as to

no lo n g er th a n a year. T h ey th e n ex tra p o la te from th is

how re p resen tativ e th e ten -y ear perio d is w ith in th e

sh o rt tim e-series to a ten -y ear perio d by developing

lo n g -te rm rccord.

regression e q u atio n s (com m only one for each com pass

Long tim e-series o f observations are a possible

sector) b etw een m ea su re m e n ts from a nearby lo n g ­

source o f in fo rm a tio n

term U K M et. O ffice a n em o m e te r record an d th eir

variability. T h e U K M et. O ffice archives, how ever,

ow n m ea su re m e n ts. T h is is k n o w n as th e m e a su re -

co n ta in very few long records o f m o n th ly m ean wincl-

c o rre ia te -p re d ic t m e th o d (M C P ).20T h e success o f th is

sp e e d .22 T h e p rin c ip a l reason is th a t, u n til recently

m eth o d is d e te rm in e d in p a rt by th e stre n g th o f the

w ith th e w idespread a d o p tio n o f a u to m a te d lo g g in g ,

c o rre latio n b etw een the d a ta from th e U K M et. Office

m ean w in d speeds had to bc calcu lated from th e

site an d th e proposed w in d tu rb in e site.

a n e m o g ra p h

on lo n g -te rm

w in d speed

tra c e . T h is w as a tim e -c o n su m in g

T h e re la tio n s h ip b e tw ee n th e se p a ra tin g d istan c e

an d sk illed o p e ra tio n , w ith associated h ig h lab o u r

an d th e s tre n g th o f th e c o rre latio n b e tw ee n m o n th ly

costs. In th e absence of an an em o g rap h , readings

m ean w in d speeds a t p a irs o f U K M et. O ffice sites

from an in d ic a tin g d ia l a n em o m eter or a B e a u f o r t

is show n in F ig u re 11.6. F or each p a ir th ere are tw elv e co rre latio n s, on e for each c alen d ar m o n th . It is clear th a t th e s tre n g th o f th e c o rre latio n d e te rio ­ rates ra p id ly w ith d istan c e, p a rtic u la rly w here th e in te rv e n in g te rra in is com plex. P airs o f sites sepa­ ra te d by m o re th a n

100

k m o f c o m p le x te rra in arc

u n lik e ly to share m ore th a n 50 p e r c en t o f th e ir v a ria b ility in m o n th ly w in d speeds in c om m on. T h e re are, th ere fo re, real d iffic u lties in try in g to p re d ic t w in d speeds a t specific sites, w h e th e r by n u m erica l

o r s ta tistic a l

m odels,

an d

th e re

is a

su b s ta n tia l research effort d ire c te d to w ard s im p ro v e ­ m ent

o f p re d ic tio n

tools,

p a rtic u la rly

n u m erical

m o d e ls . '1 Ir is essential rh a t rh e lo n g -te rm reco rd in g n e tw o rk of a n em o m eters rem ain s a t least ar its c u rre n t d en sity , an d th a t effort is d ire c te d tow ards im p ro v e m e n t o f th is n e tw o rk in u p la n d areas o f com plex terra in .

sc a le e stim a tio n o f th e effect o f th e w ind on nearby ob jects (F ig u re 11.7) w ere th e only source o f in fo r­ m atio n . F igure 11.8 show s, for th e m o n th o f M arch, th e long records for seven sites w hich could be extracted . Even w here long w in d -sp e ed series e x ist, q u e stio n s arise w ith respect to th e ir h om ogeneity, or reliability, over tim e .2' O n e o f th e sites p lo tte d in F ig u re 11 .8 is E sk d alem u ir, in th e S o u th ern U p lan d s o f S cotland, w ith a record e x te n d in g from 1911 to 1985. T h is record show s a clear dow n w ard tren d in w in d speeds from aro u n d 1 9 2 0 to th e m id -1 9 6 0 s . W h ere as the average M arch w in d speed d u rin g 1916 to 1925 is 5.6 m s“1, th e average for 1956 to 1965 is o n ly 3.6 m s-1. Is th is tre n d real, or an artefact o f th e record? The Observatories' Year Book for 1922 has th is to say a b o u t the site o f th e E sk d a le m u ir in s tru m e n t, w hich srood a t rhar tim e 7 m above rhe ro o f o f rh e m ain observatory b u ild in g :

Historical variability W h e th e r on e is in te rested in w in d as a resource, o r as a hazard , it is im p o rta n t to u n d e rsta n d how it varies over th e lo n g te rm . W in d farm d evelopers, for e x am p le, re q u ire in fo rm a tio n on th e p ro fita b ility o f

Apart from the surrounding hills the exposure of the vane-head is tolerably free in all directions save ro rhe west where at a distance of some 130 ft. (40 m) is a rather large building of which the height is somewhat greater than that of the Main Building .’4

225

226

JE A N PALUTIKOF, TOM HOLT AN D A N D R E W SKELLERN

Complex terrain

S im ple te r r a in

1.0

c

CQ m

•• ♦

0 .8 -



0.6

u

o U

r

0.4

20

40

60

80

100

120

140 160

180 200

220

d is ta n c e ( k m) Figure 11.6 Correlations between m onthly mean wind speeds at neighbouring UK Met. Office anemometer sites. Terrain classification refers to the nature of the terrain separating the site-pairs. Correlations decay with distance more rapidly over complex terrain than over simple terrain.

W IN D : RESO U RC E A N D HAZARD

0.5 and

1.0 m s"1) th a n those from p re ssu re -tu b e

a n e m o m e te rs .25 E sk d a le m u ir is th e excep tio n ra th e r th an th e rule in th e a m o u n t o f in fo rm a tio n th a t is available. For m o st lo n g records th ere is insufficient in fo rm a tio n to ju d g e w h e th e r th e observed tren d s are c lim a tic in o rig in , or w h e th e r they arise from such factors as a ch an g c in exposure or in stru m e n t type. In an a tte m p t to overcom e th is p ro b lem , an inves­ tig a tio n has been m ade o f th e p o ssib ility o f recon­ s tru c tin g surface w in d speeds from th e g e o s t r o p h ic w i n d , calcu lated in tu rn from a d a ta se t o f g rid d e d daily m ean sea-level pressure. T h e reasoning beh in d th is s tu d y was th a t the pressure d a ta sh o u ld be m ore

REVISED liJOfc

h o m o g e n e o u s , an d th a t any d isc o n tin u itie s in the rccord w ould be easier to trace. T h e pressure d a ta se t e x ten d s back to 1881 w ith few m issin g d a ta .26 T h e m ain findings o f th is stu d y are su m m arise d below. T h e m o n th ly g e o stro p h ic w in d speed w as c o m ­ p u te d

for th ir ty - e ig h t

a n em o m eter sites

in

th e

U n ite d K in g d o m for w hich surface w in d speed d a ta w ere available. T h e co rrelatio n coefficient betw een th e a n em o m eter w ind speed and th e g e o stro p h ic w ind speed was th en calculated. Sixteen sites were found to have co rrelatio n coefficients o f 0 .9 o r above, and a fu rth e r e ig h t to have coefficients b etw een 0 .8 5 and 0.9 . T h e six teen h ig h ly co rrelated sta tio n s are chiefly a t exposed locations, e ith e r on th e w est coast Figure 11.7 ‘The Beaufort Scale, revised 1906’. One of a collection of Late Victorian and Edwardian humorous glass slides o f meteorological interest held by the Royal Meteorological Society.

(e.g ., B enbecula and St M aw gan), or on inland h ill­ tops (e.g., G re a t D u n Fell and H ig h B radfield). By c o n tra st, m any o f th e fo u rteen sta tio n s w ith correla­ tio n coefficients below 0 .8 5 are a t sh eltered locations, such as inlan d sites in rhe so u th ern halt of B ritain

Yet, by

1 955, a re p o rt o f a M et. O ffice site

in sp e cto r sta te d th a t th e exposure o f th e a n em o m e te r

(e.g ., E lm d o n an d K ew ), or alo n g rhe east coast (e.g., G o rlesto n an d L ossiem outh).

was ‘e x tra o rd in a rily b a d ’ w ith ‘trees to a ll sides’. T h e

T h e tw e n ty -fo u r h ig h ly co rrelated sta tio n s (show n

d o w n w ard tre n d in w in d speeds b etw een 1 9 2 0 an d

in F ig u re 11.9) w ere used for th e re co n stru c tio n from

th e m id -1 9 6 0 s can be a t least p a rtia lly exp lain ed by

th e m ean sea-level pressure data. For each sta tio n

th e g ro w th o f su rro u n d in g trees. T h e site w as m oved

tw elve regression e q u atio n s w ere d eveloped, one for

1968,

a t w h ich tim e an electrical c u p g e n e ra to r

each m o n th , u sin g th e m o n th ly g co stro p h ic w in d

(E G G ) a n e m o m e te r was installed-, w ith an a n e m o ­

speed as th e p re d ic to r an d th e m o n th ly a n em o m eter

g ra p h . A ste p -lik e ju m p can bc seen in F ig u re 11.8

w ind speed as th e d e p e n d e n t variable. Typically,

in

a t th is p o in t. T h is is u n lik e ly to bc e n tire ly d u e to

th ere were only te n to fifteen years o f reliable surface

th e site change: m ean w in d speeds d erived from E G G

w in d speed d a ta available for c o n stru ctio n o f th e

a n em o m e te rs are c o n siste n tly h ig h e r (by betw een

regression e q u atio n s, b u t co rrelatio n coefficients o f

227

228

I860 8

1880

1900

1920

1940

1960

1980

Eskdalemuir

6

4 2

0 8

Durham

6 4

2 0 8

Southport

6 4 2l V Or-

Figure 11.8 M ean M arch w in d speeds (m s~l) a t seven sta tio n s in th e U n ite d K in g d o m w ith long in stru m e n ta l records. T h e d a sh e d lines show th e lo n g -te rm av erag e an d th e sm o o th b o ld lines re su lt from a p p ly in g a filter w h ich e m p h a ­ sises v a ria tio n s o n tim e -sc ales lo n g e r th a n te n years.

Figure 1 1 .9 L ocatio n s o f sites in rhe U K w ith lo n g -te rm w in d d a ta . T h e tw e n ty -fo u r sites w ith h ig h co rre latio n s b e tw ee n near-surface an d g e o stro p h ic m o n th ly m ean w in d speeds a re u n d e rlin e d .

230 BOX 11.1 APPLICATION OF THE RECONSTRUCTED SURFACE WIND SPEEDS

question still remains as to whether these varia­ tions have any econom ic significance, for exam ple, to wind farm developers. W ould variations in wind speeds over the lifespan o f a wind turbine invali­

T he study described has dem onstrated that lon g­

date econom ic projections based on a ten-year

term variability in wind speeds does occur. The

mean wind speed calculated by the M CP method?

1880

1900

1920

1940

I960

1980

Year

Relative Price per Kilowatt Hour at Aberporth

Reconstructed annual mean wind speed for Aberporth, 1881 to 1989, using the m id-range model parameters ( m s 1; top); and relative price per kilow att-hour required to give a 20 per cent annual return on capital invested for overlapping twenty-year periods (relative price index, per cent from average, bold line; bottom). The upper and lower price curves show the 95 per cent confidence bands based on uncertainties in the reconstructed wind field (not shown in the top graph). Location of Aberporth is shown in Figure 11.9, p. 229.

W IN D : RESO URC E A N D HAZARD

A sim ple econom ic model was constructed to

to give the required annual return on capital. The

investigate the im plications o f the long-term vari­

calculation is made for overlapping twenty-year

ability in wind speeds as shown, for example, in

periods from 1881 onwards. The last period is

Figure 11.10. The basic parameters o f the model

1970 to 1989, givin g a total o f ninety lifespans

are:

for which required price can be calculated. The figure shows some results from Aberporth, on the

turbine type:

300 kW

initial investment:

rated power £ 3 0 0 ,0 0 0

annual running cost:

£ 9 ,0 0 0

turbine life expectancy:

20 years

required annual return on capital: 20%

west coast o f Wales. At this site, for the m id­ range reconstructed wind speed, the model gives a maximum required price for any twenty-year period o f 7 per cent above the average and a m inim um required price o f 6 per cent below the average. This range doubles if the upper and lower

In fact, these parameters are o f little significance

95 per cent confidence reconstructed wind speeds

— what is important is the relative differences in

(not shown in the figure) are used in the price

tim e, not the absolute values.

calculation. These figures may be interpreted as

First, the annual power production from a

the maximum possible error - e.g ., a wind turbine

typical wind turbine is calculated from the recon­

project planned on the basis o f one required price

structed wind speeds. The model then takes these

m ight, in the worst possible scenario o f falling wind speeds, fall short o f estim ated capital return

values and calculates the price (in pence per kW h) required over the twenty-year life o f the turbine

by this amount.

10.0 9.5 Ç

c

9.0

o

articular reference to the im plications for w ind pow er p ro d u c tio n ’, in A .D . G arrad (ed.), W ind Energy Conversion 1985, L ondon, M echanical E ngineer­ ing P ublications, 1985, pp. 235 -40. J.P. P alutikof, T .D . Davies and P.M. Kelly, A data bank o f w ind speed records for the B ritish Isles and offshore w aters', in P M usgrove (ed.), W ind Energy Conversion 19 8 4 , C am bridge, C am bridge U niversity Press, 1985, pp. 4 1 4 -2 5 . U K M et. Office, The Observatories' Year Book 1922, L ondon, H M SO , 1925, 2 12 pp. S.G . S m ith, ‘C om parison o f w ind speeds recorded by p ressure-tube and M eteorological Office electrical cup g enerator anem ographs’, Meteorological M agazine, 1981, vol. 110, pp. 2 8 8 -3 0 1 . See P.D. Jo n es, T.M.L. W igley and K .R . Briffa, M onthly m ean pressure reconstructions for E urope (back to 1780) and N o rth Am erica (to 1958)’, Technical Report T R 0 3 7 , D O E /E R /6 ()3 9 7 -H l, US D ept, o f Fnergy, C arbon D ioxide Research D ivision, W ashing­ to n , D C , 1987, 9 9 p p ., and P.D. Jo n es, T he early tw e n tie th cen tu ry A rctic h ig h - fact or fiction?', Climate Dynamics, 1987, vol. 1, pp. 6 3 -7 5 . T h is w ork is fully described by J.P. Palutikof, X. G uo and J.A . H alliday, ‘C lim ate variability and th e U K w ind resource’, J . W ind Engineering a n d Industrial Aerodynamics, 1992, vol. 39, pp. 2 4 3 - 9 , and by J.P. P alutikof, J.A . H alliday, X. G uo, R .J. B arthelm ie and T.J. H itc h , T h e im pact o f clim atc variability on

242

J E A N PALUTIKOF, TOM HOLT A N D A N D R E W SKELLERN

28 29

30

31

32 33

34 35

36

the U K w ind resource’, E T S U W N 6 0 2 9 , H arw ell, E nergy Technology S u p p o rt U n it, 1 9 9 3 , 148 pp . (plus appendices). Society o f Fellows Study G ro u p , op. cit. H .H . Lam b, Historic Storms o f the North Sea. British Isles a n d Northwest Europe, C am b rid g e, C am b rid g e U n iv er­ sity Press, 1991, 2 04 pp. T h e SSI values refer to th e severity of the storm in its e ntirety, and noc w ith respect to the B ritish Isles alone. M any o f these storm s were particularly severe over th e N o rth Sea region, causing dam age in the N e th e r­ lands, D enm ark, n o rth ern G erm any and southern Scandinavia. H . S chinke, O n the occurrence o f deep cyclones over Europe* and th e N o rth A tlan tic in the period 1 9 3 0 1991 , Beitrage zur Phystk dir Almosphare, 1993, vol. 6 6 , pp. 2 2 3 -3 7 . H . S c h m id t and H . von S torch, ‘G erm an B ig h t storm s a nalysed', N ature, 1993, vol. 365, p. 791. A.F. Je n k in so n and B.P. C ollison, ‘A n in itial clim a­ tology o f gales over the N o rth Sea', Synoptic Climatology Branch Memorandum No. 62 , B racknell, U K M et. O ffice, 19 7 7 , 18 pp. Jo n es et a l., op. c it., Jo n es, op. cit. S.G . S m ith , An index o f w indiness for the U nited K in g d o m ’, Meteorological M agazine, 1982, vol. I l l , pp. 2 3 2 -4 7 ; J.M . H a m m o n d , 'T h e stro n g w inds experi­ enced d u rin g the late w in ter o f 1 9 89/90 over rhe U n ite d K ingdom : historical perspectives’, Meteor­ ological Magazine, 1990, vol. 119, pp. 2 1 1 - 1 9 ; M. H u l m e and F.D. Jo n es, ‘T em peratures and w indiness over th e U K d u rin g th e w inters o f 1988/89 and 1 9 89/90 com pared to previous years’, Weather, 1991, vol. 4 6 , pp. 1 2 6 -3 5 . T h is is taken from T. H o lt and P.M. Kelly, Western European Gales, 1 8 8 1 -1 9 9 3 : a Statistical Assessment, R eport to H arvey B ow ring and O th e rs, N orw ich, C lim atic Research U n it, U n iv ersity of East A nglia,

1995, 31 pp. 37 T h e G ale Index is calibrated in knots, and the conver­

38

39

40

41

sion in to m s 1 leads to u n tid y num bers. O ne k not 0.5 1 5 m s’ 1. J.W . H u rre ll, ‘Decadal trends in the N o rth A tlan tic O scillation: regional tem peratures and p re cip ita tio n ’, Science, 1995, vol. 269, pp . 6 7 6 -9 . J-P. P a lu tik o f and A .R. Skellern, Storm Severity over B ritain, R eport to C om m ercial U nion. N orw ich, C lim atic Research U n it, U niversity o f East A nglia, 1991, 102 pp. C .J.M . A anensen and J.S. Sawyer, T h e gale o f F ebruary 1 6th 1962 o f th e W est R iding o f Y orkshire’, Nature, 1963, vol. 197, pp. 6 5 4 -6 . T he statistics in th is paragraph are taken from D ep artm en t o f Trade and Industry, A n Assessment o f Renewable Energy fo r the UK, H M SO , L ondon, 1994, as reported in 'G overnm ent publishes renewables stra te g y ’, W ind Directions, 1993, vol. 13, no. 4 , pp. 1 5 -1 6 .

GENERAL READING N .J. C ook, The Designer's Guide to W ind Loading o f Building Structu m . Part 1: Background. Damage Survey, W ind D ata a n d Structural Classification, G arston and L ondon, B u ild in g Research E stablishm ent and B u tterw o rth s, 1985, 371 pp. M.P. C o u tts and J . G race (eds), Climate a n d Trees, C am bridge, C am bridge U niversity Press, 1995, 4 85 pp. Review — the m agazine o f new and renew able energy, published by th e D ep artm en t o f Trade and Industry, E ditorial Office: Room 8 0 3 , B ridge Place, 8 8 8 9 Eccleston Square, L ondon SW 1V 1PT. Royal M eteorological Society, W eather - special issue devoted to articles on the sto rm o f 1 5 -1 6 O cto b er 1987, Weather, 1988, vol. 43 , pp. 6 6 -1 4 2 . W indpouw M onthly, an indep en d en t w indpow er news journal p u blished by Torgny M öller, V rinners I loved, 8 4 2 0 K nebel, D enm ark.

12

THE AIR THAT W E BREATHE Smogs, Smoke and Health

Peter Brimblecombe and Graham Bentham Herein is not only a great vanity, but a great contempt of God's good gifts, That the sweetness of man’s breath, being a good gift of God, Should be wilfully corrupted by this stinking smoke. Ja m e s I o f E n gland and V I o f Scotland

INTRODUCTION T he air o f cities has been polluted for thousands o f years.1 F.arly concerns about air quality in urban areas stem m ed from the use o f wood and coal as fuels, both industrial and dom estic. D uring the years of the Industrial R evolution sm oke pollution was considered a necessary part of progress. Air quality in cities tended to bc worse in w inter m onths when cold stagnating anticyclonic conditions trapped air and resulted in a b uild-up of sm oke and associated pollutants, especially sulphur dioxide. Com bined w ith fog, this resulted in the infamous pea-souper' sm ogs o f London, where visibility was frequently drastically reduced. It was not until the 1950s, however, w hen a particularly severe smog resulted in 4 ,0 0 0 excess deaths in London, th at an im portant Act was passed by Parliam ent to force the clean-up o f urban air. A lthough these 'pea-souper sm ogs are now a th in g of the past, air quality in cities is still gener­ ally poor (Figure 12.1). T his is because vehicle exhaust em issions, due to the large am ounts o f traffic in urban areas, lead to nitrogen oxides smogs in

w inter and the b uild-up o f low-level ozone in sum m er. T he effect of these pollutants on hum an health has not been categorically identified, although air pollution from traffic has often been blam ed for the m ajor increase in the incidence o f asthm a that has occurred in recent decades. T he introduction of catalytic converters into the vehicle fleet may go some way to rem edying these problems.

EARLY HISTORY OF AIR POLLUTION Although early cities burnt large quantities of wood, contem porary com plaints were often related to odour not smoke. Nevertheless there were adverse reactions to smoke, m ost especially w ith the shift from wood to coal as a fuel. In medieval B ritain, coal became im portant as a fuel following the depletion o f conve­ niently usable wood supplies.7 T he unfam iliar smell o f coal sm oke led to early tears about its health risk through the belief that disease was carried in m alodorous air (m iasm as). The use o f coal by thirteenth-century London m ade its citizens aware of problem s of air pollution at an early date, initially,

244

PETER B R IM B L E C O M B E A N D G R A H A M BE N T H A M

Figure 12.1 Fog in London, 2.30 p.m. on 30 November 1982. Calm anticyclonic conditions caused air pollution levels to rise to unusually high concentrations for several hours during the day. Although the sources of modern pollution are largely different from forty or a hundred years ago, the quality of city air is often still poor.

coal was used by

lim e-burners and blacksm iths

focus on p o in t sources.

By th e

m id -n in e te en th

and it was not u n til the sixteenth c entury th a t the

century sm oke was generally regarded as an u nde­

w idespread construction o f chim neys allow ed its use

sirable aspect o f urban life, a lth o u g h perhaps a ‘neces­ sary ev il’.

as a dom estic fuel. A tran sitio n to coal was virtually com plete in London by th e early seventeenth century, b u t it was delayed u n til th e n in ete en th century in som e o th er cities o f the B ritish Isles.

T he

belief th at

sm oke should

bc elim inated

becam e em bodied in laws th a t arose from the sani­ tary reform o f the n in ete en th century. T he early a tte m p ts to abate air pollu tio n lacked real pow er or any clear m echanism for enforcem ent, b u t the P ublic

Industrialisation

H e alth Acts o f 1872 and 1875 tried to set up a d m in ­

T h e Industrial R evolution, and in p a rticu la r the

istrative m echanism s for th e control o f nuisance.

d evelopm ent o f th e steam engine, led to th e possi­

Even where the adm inistrative procedures w ere well

b ility o f sm oke p o llu tio n on a m u ch larger scale than

defined and enthusiastically follow ed, th e lack o f

before. T h e steam e ngine forced air p o llu tio n to

ap propriate sm oke control technology seemed to

be taken

1800 the

prevent b oth th e adm inistrators and industrialists

C om m issioners o f Police in M anchester appo in ted a

from achieving a su b stan tial im provem ent in air

nuisance c o m m itte e th a t looked at the m ethods

q u a lity .'

m ore seriously. As early as

available for a b atin g sm oke from steam engines.

Laws o f th e nineteen th century suffered not only

A lth o u g h th e steam engine provoked p rotest it also

from the weaknesses noted above b u t also lacked a

caused the early en th u siasts o f sm oke abatem en t to

scientific basis, and m o n ito rin g was rarely seen as a

THE AIR THAT W E BREATHE: S M O G S , S M O K E A N D HEALTH

Year Figure 12.2 Air pollution in London since 1700, comparing predicted smoke concentrations (arbitrary scale) with fog days and later sulphate, S (X )t and smoke measurements.

significant p a rt o f im p ro v in g th e urban atm osphere.

in the London Fog Inquiry in th e opening years of

T h e m ost w idespread observations m ade last century

this century, and later in th e form ation o f the earliest

were sim ple descriptions o f sm oke from chim neys

national air p o llution m o n ito rin g netw ork. T his

and th e reports of th e inspectors w ould suggest

netw ork was established d u rin g th e First W orld W ar

th a t such observations were not p articularly useful

using d e p o s it g a u g e s th a t were to be used for m ore

w hen try in g to gauge th e im provem ents. T h e few

th an fifty years. C ontrol passed, however, to the

q u a n tita tiv e m easurem ents th a t we have com e from

D ep artm en t o f Scientific and Industrial Research in

e n th u siasts and am ateurs, w hich m eans th a t they are

the 1930s and various g overnm ent g roups becam e

sporadic and often inaccurate.

involved in the design o f a range o f air p o llution m o n ito rin g eq u ip m en t: th e je t d u s t c o u n te r , lea d c a n d le (to m easure su lp h u r dioxide deposit) and

THE TWENTIETH CENTURY

the b u b b le r . In stru m en ts such as these form the basis o f the longest system atic record o f air p o llu ­

T h e early tw e n tie th century saw no rapid im prove­

tion in th e B ritish Isles, w hich can bc linked w ith

m e n t in perceived c onditions, b u t th ere was a

o th er surrogate inform ation such as fog frequency

gro w in g recognition o f th e need for m onitoring. T he

and concentrations m odelled from fuel use (Figure

fledgling U n ited K in g d o m M et. Office was involved

12 . 2 ).

245

246

PETER B R IM B L E C O M B E A N D G R A H A M BE N T H A M

T h e longest q u a n tita tiv e records available arc

1990s, to the creation o f a centralised real-tim e

those for th e deposit o f soot and som e soluble m a­ terials w hich beg in early this century in u rban areas.

m o n ito rin g netw ork, th e E nhanced U rban N etw o rk ,

By the 1930s there were lim ite d m easurem ents o f

and its subsequent developm ent into th e A u tom atic U rban N etw o rk . T here arc also im p o rta n t non-urban

su lp h u r dioxide and soot in the atm osphere. Such

elem ents to new netw orks (sec Table 12.1 and Figure

observations w ere m uch m ore w idespread in the years th a t follow ed th e L ondon sm og o f 1952. Early scien­

12.3)» m ost notably the rural ozone m o n ito rin g sites.

tific w ork was only just b e g in n in g to influence policy

arc vitally im p o rtan t. In m eteorology such records

w hen th e Second W orld W ar intervened and pres­

were initially established th ro u g h th e in terest o f

L ong-term

records of atm ospheric

phenom ena

sures for cleaner a ir w ere delayed. T h e London sm og

individual observers (see C h ap tcr 7), since visible

o f D ecem ber 1952, w ith its 4 ,0 0 0 excess deaths,

w eather

p ro m p te d a clear response and th e passage o f the Clean A ir Act o f 1956 th ro u g h P arliam ent. T his Act

num bers o f enthusiasts. Records o f a ir pollu tio n , by contrast, have been a victim o f changing priorities

necessitated an air p o llu tio n m o n ito rin g netw ork

w ith in m o n ito rin g agencies. T hus, in te rp retin g long­

w hich was dedicated to policing its regulations.

term change in air q u ality can be m ore o f a problem

processes

have

always

attracted

large

T h e Clean A ir A ct is often proclaim ed as a success,

than w ith classical w eather observation. T here are

b u t it m ay have sim ply reinforced broader changcs

hopes th a t the centrally controlled A utom atic U rban

in fuel used w hich were already low ering the concen­

N etw o rk will have som e degree o f sta b ility and

tratio n o f sm oke and su lp h u r dioxide in B ritish

continuity.

cities. Perhaps th e m ost notable changes were the reduction in d om estic coal use (as it was replaced by

be regulated u nder E uropean U nion directives. T he

gas and electricity) and th e gro w in g im portance of

Increasingly, air q u ality in the B ritish Isles w ill

liq u id fuels used in th e private auto m o b ile fleet.

C ouncil D irective on Ambient A ir Quality Assessment a nd Management' w ill prom ote a set o f d au g h te r

O th e r influences at w ork in th is period w ould have

directives to define the type o f m o n ito rin g or m odel­

included th e shifts o f in d u stry in to suburban and

lin g required for different air po llu tan ts, th e p rovi­

rural locations, developm ent o f large rural power

sion o f p u b lic inform ation and the se ttin g o f alert

stations w ith tall stacks, ind u strial decline, and m ore

thresholds and lim it values. A lth o u g h there is a

recently a sh ift from coal to gas for electricity g e n er­

special focus on urban centres w ith a p opulation

atio n . R eductions in trad itio n al p o llu ta n ts, nam ely

greater th an 2 5 0 ,0 0 0 , the directive hopes to consider

su lp h u r dioxide and sm oke, m asked an increase in

the effects o f air pollu tio n beyond sim ply hum an

th e new p o llu tin g com ponents o f urban air, n itrogen

health. In ad d itio n to the air p o llu ta n ts currently

oxides and ozone.5 T h e w arm dry su m m er o f 1976,

covered in directives the new regulations w ill cover

for exam ple, saw m assive tongues of ozone-rich air

benzene, polycyclic arom atic hydrocarbons, carbon

across th e

m onoxide, cadm ium , arsenic, nickel and mercury'.

B ritish

Isles, w hich

heralded a new

regional air p o llu tio n problem . O th e r issues, m ost notably a preoccupation w ith w rangles over acid r a in , focused m o n ito rin g a tte n tio n on th e rural p re cip ita tio n netw orks, w hich m eant only a lim ite d g ro w th in th e n u m b er o f urban m o n ito rin g sites.

THE POLLUTANTS Sulphur dioxide

T h e in ab ility o f the U n ited K in g d o m m o n ito rin g

S ulphur dioxide (SO ,) concentrations in urban air

n etw ork of th e 1980s to exam ine a broad range o f

have long been driven by the use o f coal in the

relevant contem porary air p o llu ta n ts was increasingly

B ritish Isles. T hus the high concentrations experi­

em barrassing and u ltim ate ly the G overnm ent W h ite

enced in coal-burning cities o f B ritain late last

Paper This Common Inheritance6 sparked off a new

century and th ro u g h the first h alf o f th is century are

in terest in th e u rban atm osphere. It led, in the

no longer found (see Figure 12.2). T h e 1956 Clean

THE A IR THAT W E BREATHE: S M O G S , S M O K E A N D HEALTH

t ------------- 1------------- 1

t

t------------- 1------------- r -------

i------------- 1

t------------- r

if*’ 6 0 °N -

T

*

t


p o

Strajth V

56° -

Eskdalemuir

Kcwc itle A

Sunt

■ cL ^ U r t i g l f K 'a w

B c5a§/

w %

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L e^ds

Ql. ^ _ . ^

*Barns.ey A ¿ S h e ffie ld

^

\J?^~'£> ,< *poo\ L a d y w

JiaooHill f

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J

W1“ " A

B o tte s fo fx T ^

4Leicester

B irm in g h a m

52° London

on H^ath Yamer l^’ood

r ^ ^ Z f 50° -

J ------------- 1_

10°W



2°E

Figure 1 2.3 L ocation o f sites in th e A u to m a tic N e tw o rk s w h ic h m o n ito r c o n te m p o ra ry a ir p o llu ta n ts . T able 12.1 lists th e p o llu ta n ts m easured.

247

248

PETER B RIM BLEC O M B E A N D G R A H A M BENTHAM

Table 12.1 Sites in the Automatic Networks which monitor contemporary air pollutants, see Figure 12.3 for a map" of locations. The • indicates sites at which the following pollutants are measured: 0 3 - ozone; NO x - nitrogen oxides; CO - carbon monoxide; S 0 2 - sulphur dioxide; PM|0 - small particles with a diameter less than 10 p.m; HC - hydrocarbons

CO

so2

PM W





• •













• •



• •





• •



No.

Site name

03

NO'

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29

Straith Vaich Edinburgh Centre Edinburgh Med S Glasgow Bush Eskdalemuir Belfast Queens Uni Newcastle Centre Sunderland Great Dun Fell Belfast Centre Belfast East W harley Croft Billingham Lough Navar Middlesbrough High Muffles Leeds Centre Hull Centre Barnsley Manchester Glazebury Liverpool Centre Sheffield Ladybower Bottesford Leicester Centre Walsall Aston Hill Birmingham Wardend Birmingham Centre Sibton Harwell London UCL London Bloomsbury London Bridge Place London Cromwell Road West London Cardiff East Cardiff Centre London Bexley London Eltham Bristol Centre Southampton Centre Lullington Heath Yarner Wood Swansea Bristol East Leeds

• •

9

30

31 32 33

34 35 36 37 38 39 40

41 42 43 44

45 46 47 48 49

HC

• • •



• • • • • • •

• •

• •





• • •

• •

• •







• •

• •

• •

• •

• •

• • • •

• • • •

• • •



• •

• •

• •

• •

• •

• • • • •

• • •

• •

• • •

• •









• • • • • • ■ • • •

• • •

• •















• • •

THE AIR THAT W E BREATHE: S M O G S , S M O K E AN D HEALTH

- Sm oke

---------------S O

2

Year b eg in n in g A p ril

Figure 12.4 Annual average concentrations of smoke and sulphur dioxide for the United Kingdom from 1962 to 1993.8

A ir A ct aim ed to co n tro l only sm o k e, b u t it is

s u lp h u r

p o ssib le to arg u e th a t pressures to reduce sm oke

p lum es. E x ten d ed p o llu tio n episodes, however, are

dio x id e

c o n cen tratio n s

from

in d u strial

em issio n s also h e lp low er th e em ission o f su lp h u r

m ore likely to be found w here large a m o u n ts o f coal

d io x id e. In p a rticu la r, th e m o v em e n t away from the

are b u rn t. Belfast is rhe m o st n o tab le ex am p le o f a

localised use o f coal in b o th th e dom estic: an d in d u s­

city w ith elevated w in ter s u lp h u r d io x id e concen­

tria l sectors can reduce su lp h u r d io x id e em issions

tra tio n s, largely because o f th e n o n -av ailab ility o f

sim u lta n eo u sly w ith sm oke.

natu ral gas as a d o m estic fuel.

T h e h ig h s u lp h u r c o n te n t in fuel a n d diesel oils has p ro v o k ed som e concern, b u t reg u la tio n s have p re ­ e m p te d any su b sta n tia l increase in s u lp h u r em issions

Smoke and particles

from th is source an d leg islativ e p ressu re now requires

Sm oke em issions, th e cen tral concern o f th e 1956

oil to have a low s u lp h u r c o n te n t. Special, low -

C lean A ir A ct, have d eclin ed considerably. It is still

s u lp h u r diesel is now m ore w id ely available, so it

m o n ito re d along w ith s u lp h u r dio x id e as p a rt o f the

appears likely th a t s u lp h u r c o n cen tratio n s in the

Basic U rb an

u rb a n atm o sp h e re over B ritish cities w ill p ro b ab ly

Im p ro v em en ts in sm oke and su lp h u r d io x id e concen­

N e tw o rk o f m ore th an

150 sites.8

rem ain reasonably low. S u lp h u r d io x id e levels are

tratio n s have b een m ark ed (see F ig u re 12.4) and

ty p ically b etw een 5 and 15 p a rts p e r b illio n (p p b ),

1 993—4 was sig n ifican t in th a t for the first tim e no

b u t cities can still experience sh o rt p erio d s o f h ig h

site in th e U n ited K in g d o m exceeded any o f the

249

2 50

PETER B R I M B L E C O M B E A N D G R A H A M B E N T H A M

Industrial Combustion 17

16

Residential Combustion

Public Power Generation

Mining, Industrial Processes

15

24

Other 3 I 2 N 0 2 NO + C>5 —» N O , + 0 2

Rate * [A]X[B? which implies that Rate = jH A ]*[B P

where k is the rate constant for this reaction at a fixed temperature. The square brackets indicate concentration. This reaction is of order x with respect to A and of order y with respect to B. The overall reaction is said to be of order x «■ y. The order of reaction is usually determined exper­ imentally. The reaction: 2NO ♦ 0 2

The first reaction usually occurs very slowly and so it is that latter reaction with ozone which usually predominates.’ If the concentration of NO is low then it is the concentration of O^ which limits the rate of production of N 0 2. If, on the other hand, concentrations of NO are high then the first reaction becomes important. As the rate of this reaction is proportional to the square of the concentration of NO, then a small increase in NO will result in a large increase in the rate of N O , production.

2N 02

is a third order reaction. The rate of the reaction is given by:

* J.S. Bower, G.F.J. Broughton, J.R . Stedman and M.L. W illiam s, ’A winter N O , sm og episode in the U K ', Atmospheric Environment, 1994, vol. 28 , pp. 4 6 1 -7 5 .

Ozone There arc no im p o rtan t em ission sources of low-level ozone so its presence in air is the result o f p h o to ­ c h e m ic a l re a c tio n s involving th e nitrogen oxides and v o la tile o rg a n ic c o m p o u n d s (VOCs), along w ith a fraction transported dow n to th e surface from the stratosphere. T h e presence of anthropogenic hydrocarbons and nitrogen oxides encourages the form ation o f ozone. These reactions take place, however, over substantial distances from source areas, m aking h igh ozone concentrations a widely d istrib -

Figure 12.7 T rends in carbon m onoxide em issions for G re at B ritain from 1970 to 1993 (data derived from the D igest o f E nvironm ental S tatistics, 1994, 1995).

THE AIR THAT W E BREATHE: S M O G S , S M O K E A N D HEALTH

uted phenom ena. O ddly en o u g h , urban concentra­

T here are now ten sites th a t m o n ito r a range of

tions o f ozone can be low er th an rural values because

volatile organic com pounds in th e air over the U nited

o f reactions involving n itric oxide th a t consum e ozone (see Box 12.1). G iven the im portance o f

K ingdom , b u t this netw ork has been in operation only a short tim e. T he site at M iddlesbrough, which

su n lig h t for ozone creation, it is understandable th a t

has been ru n n in g since 1992, gives a m ost detailed

th e h ighest ozone concentrations are observed d u rin g th e hot anticyclonic days o f sum m er (Figure 12.8).

p ictu re o f hydrocarbon behaviour at th is site. T his suggests th at th eir relative concentrations are sensi­

T he E xpert Panel on A ir Q u ality S tandards16 rec­

tive to the balance of in d u strial em issions and trans­

om m ended an e ig h t-h o u r air-quality standard o f 50

p o rt sources.21 Sharp increases in styrene and 1,3

p p b ozone. Such a standard w ould be exceeded at som e sites on m ore than e ig h ty days each year. Achieving

b utadiene concentrations, w hich were found in the

this standard w ould therefore require a reduction in the

trial em issions (Figure 12.10).

air from tim e to tim e, seem to be th e result o f in d u s­

em issions o f volatile organic com pounds by betw een 75 and 80 per cent and a 95 per cent reduction in levels o f n itrogen oxides across Europe. T h is goes far beyond reductions envisaged w ith sim ple controls. M ost rural

Metals M etals are frequently found in th e p o lluted atm os­

sites appear to show significant upw ard trends in ozone

phere, associated w ith the p a r tic u la te p h a s e . These

concentrations (Figure 12.9).17

m ay arise from in d u stria l activities and com bustion processes. A m u lti-elem e n t survey com m enced in 1976 has m onitored the concentrations o f sixteen

Organic compounds

elem ents at five sites th ro u g h to the present. In the

T here are m any sources o f b o th volatile and less

early years o f the survey the concentrations o f m ost

volatile organic com pounds being e m itte d in to the

m etals declined to a fairly stable level.22 Lead has

atm osphere. Pesticides, dioxins, polycyclic arom atic

been of special concern because o f its toxicity and

hydrocarbons and polychlorinated biphenyls (PCBs)

the large am ounts m obilised from leaded fuels. Lower

are frequently g rouped

lead concentrations in fuels, and

as toxic organic

m icro-

m ore recently

p o llu ta n ts (T O M PS). M any are c a rc in o g e n ic and

unleaded fuels, have caused a reduction in em issions

often in volatile enough to be associated w ith airborne

(Figure 12.11).

p articu late m atter. These are m on ito red on a m uch m ore lim ite d basis th an the volatile hydrocarbons.18 T hey do have com b u stio n sources, b u t th e pesticides

INDOOR AIR POLLUTION

and p olychlorinated biphenyls m ay sim ply evaporate M ost o f us spend a large p a rt o f o u r lives indoors,

from the g ro u n d surface. hum an

particularly young children and the elderly w ho are

carcinogens and air q u a lity standards have been

know n to be m ost susceptible to the effects o f air

recom m ended for bo th benzene and 1,3 b u tad ie n e.19

p ollution. T h e com position o f th e air wc breathe

O th e r organic com pounds m ay n o t be as significant

indoors is, therefore, just as im p o rta n t as th e air we

V olatile

organic

com pounds

are

also

as carcinogens, b u t th e alkcncs, toluene, xylene, alde­

breathe outdoors. M ost people probably feel th at

hydes and hydrocarbons w ith m ore th an five carbon

th eir hom e provides a refuge from the often polluted

atom s arc im p o rta n t in a id in g th e form ation o f

air th a t they have to breathe in the o utdoor envi­

photochem ical sm og since these com pounds have a high Photochem ical O zone C reation P o te n tia l.20

som e im p o rta n t pollu tan ts indoors and outdoors

V olatile organic com pounds are produced d u rin g

ronm ent. A com parison o f typical concentrations o f

co m b u stio n , b u t also evaporate from m any ind u strial

shows th a t in som e respects they are rig h t.25 C oncen­ trations o f im p o rta n t p o llu ta n ts such as su lp h u r

operations.

dioxide and ozone are typically m uch lower indoors

253

254

PETER BRIMBLECOMBE AND GRAHAM BENTHAM

THE A IR THAT W E BREATH E: S M O G S , S M O K E A N D HEALTH

Year and month

Figure 12.9(a) Num ber of hours wirh low-level ozone concentrations above 80 ppb during the period 1987 to 1990.16 Figure 12.9(h) Monthly average low-level ozone concentration trends from 1986 to 1991 ai three rural sites.17 See Figure 12.3 for locations.

th a n o u t, as is exposure to p o lle n a n d a irb o rn e lead.

hyde an d th e radioactive gas radon w here, in the

In d o o rs, how ever, we m ay be exposed to m u c h h ig h e r

w orst affected p a rts o f so u th -w e st E n g la n d , doses in

c o n c e n tra tio n s

d w e llin g

(and

for

lo n g er)

o f m an y

o th e r

houses can exceed those p e rm itte d

for

su b stan ces. T hese in clu d e n itro g e n oxides w hich m ay

w orkers in th e n u clear industry. T h e re can also be

ex acerb ate a sth m a

to

severe p ro b le m s, p a rticu la rly for a sth m a tic s, from

in fectio n s, an d carb o n m on o x id e w h ic h is lethal a t

an d

increase su s c e p tib ility

fungal spores an d a lle rg e n s such as those related to

h ig h doses an d a t low er c o n ce n tra tio n can im p a ir o u r

h o u se -d u st m ites.

a b ility to c o n ce n tra te. T h e list also in clu d es tobacco

U n lik e th e situ a tio n for o u td o o r air p o llu tio n ,

sm oke w here th e re is g ro w in g concern a b o u t th e

th ere is little in fo rm a tio n o n tre n d s in in d o o r concen­

effects o f passive sm o k in g . In d o o r air can also co n ta in

tratio n s. T h ere are stro n g reasons to believe, how ever,

p o te n tia lly c arcin o g en ic su b stan ces su c h as fo rm ald e ­

th a t exposures to in d o o r air p o llu tio n have p ro b ab ly

Figure 12.8 Sum m er haze over London, 1981, due to photochemical pollution. The top picture is a view from the roof of the old London County Hall taken on 28 August 1981, a day when ozone concentrations reached 220 p.g/m*. The bottom picture was taken a m onth later when ozone concentrations reached only 30 jjig/m3.

255

256

PETER B R I M B L E C O M B E A N D G R A H A M B E N T H A M

High------------------------------ Low Other Sectors Processes and Solvents

50

Year

Figure 12.10a The relative importance for the United Kingdom of volatile organic compounds sources in the 1990s.20

Figure 12.10b Measured and estimated U nited Kingdom road transport sources of volatile organic compounds from 1970 ro 2010.18

increased in recen t decades. O n e factor has been the e m issions from

new m ate ria ls in th e hom e. For

exam ple, fo rm aldehyde resins are p resen t in p a rticle Emissions

-------

Concentration

board w hich has been w idely used as a b u ild in g m ate ria l and in fu rn itu re . T h ere have also been p ro b ­ lem s o f em issions from som e in stallatio n s o f urcaform ald eh y d c

foam

in su latio n ,

a lth o u g h

tig h te r

re g u la tio n s arc h e lp in g in th is area. A n o th e r factor p o in tin g to increased exposure is th a t in th e search 800

600

h

u F y '.5 «

G Q. on 400

200

for low er b u ild in g costs an d g re a te r energy efficiency th e

v e n tila tio n

rates

o f b u ild in g s

have

alm o st

c ertain ly decreased over tim e . M any m o d ern houses are

now

b u ilt

w ith o u t

ch im n ey s, and

d ra u g h t-

c

proofing o f doors and w indow s is m uch m ore w id e­

§

spread. T h is m eans th a t th ere is a reduced flow o f

Il>

o u tsid e air w ith w h ic h to d ilu te chem ical em issions

(j

from

U

re su ltin g increase in th e ir in door c o n ce n tra tio n . Even

§

d o m estic

m ate ria ls

and

a ctiv itie s,

w ith

a

m ore severe are th e p ro b lem s o f so-called ‘sickb u ild in g sy n d ro m e ’. T h is has been experienced in 1975

1980

1985

1990

m any m o d ern schools, h o sp itals and offices b u ilt to achieve h ig h levels o f energy efficiency to relatively

Figure 12.11 Emissions of lead from automotive sources, from 1975 to 1993, for the U nited Kingdom and mean lead concentrations, from 1980 to 1993, measured in central London.

a irtig h t designs.

THE AIR THAT W E BREATHE: S M O G S , S M O K E A N D HEALTH

HEALTH ISSUES

B ritish cities u n til the 1960s posed serious threats to health. T he m ost dram atic o f these occurred when

A typical a d u lt breathes m ore th an 10,000 litres of air p er day. Because th is air is often p o lluted there

cold w eather and stag n an t air associated w ith w inter

is am ple o p p o rtu n ity for the sensitive tissue o f the

several days o f extrem ely hig h levels o f sm oke and

respiratory tract to com e in to contact w ith signifi­ cant q u a n titie s o f p o ten tially harm ful substances.

su lp h u r dioxide. U n doubtedly the m ost notorious of

T here has been lo n g -term concern th a t air p o llu tio n m ay have c o n trib u ted to th e extrem ely h ig h rates of chronic bro n ch itis chat have, u n til recently, been

anticyclonic conditions led to the b u ild -u p over

these incidents o f extrem e a ir p o llution was the London sm og o f D ecem ber 195 2 24 (see also C hapter 13). For several days, concentrations o f sm oke and su lp h u r dioxide were hugely in excess o f current

c haracteristic o f B ritish cities. T here has also been a

W orld H e alth O rganisation guidelines. T h e first

persisten t suspicion th a t sm oke p o llu tio n , w hich can

signs of the health im pact of th e pollu tio n crisis was

contain know n carcinogens, m ay increase the risk of

a sharp increase in th e n u m b er o f p atien ts being

lung cancer - a lth o u g h there can be no d o u b t th at

a d m itte d to hospital w ith respiratory and circulatory

sm oking c igarettes is the m ain cause. M ore recently,

problem s. An official inquiry was later to show th at

there has been g row ing concern th a t a ir p o llu tio n ,

there was also a m arked increase in the death rate,

p articu larly th a t related to m o to r vehicles, m ay be

w ith the m ain period o f pollu tio n experiencing about

an im p o rta n t c o n trib u to r to th e large increase in a sthm a th a t has occurred in the B ritish Isles and in

4 ,0 0 0 deaths m ore than w ould norm ally be expected at th a t tim e o f the year in London. T he sharpest rise

m any o th er countries.

was in deaths from bronchitis b u t there were also

T he p o ten tial health effects o f air p o llu tio n , how ­

large increases from oth er causes inclu d in g p neu­

ever, are not restricted to respiratory diseases. T here

m onia, heart attacks and strokes. T he overw helm ing

is also gro w in g evidence th a t, in individuals w ith

m ajority o f these deaths were o f elderly people,

o th er risk factors such as clogged up arteries (athero­

suggesting strongly th a t th e m ain im pact o f the

sclerosis), exposure to air p o llu tio n can increase the

p o llution episode was on the section o f the popula­

risks o f heart attacks and stroke, w hich are tw o o f the

tion who were p articularly susceptible because o f

com m onest causes o f death in th e U n ited K ingdom .

existing health problem s.

In recent years there seems to have been a grow ing

T he proportion o f elderly people in the p o p u la­ tio n has grow n substantially d u rin g the tw e n tie th

p u b lic perception, fuelled by m edia interest, th a t air p o llu tio n poses a gro w in g th re a t to health. As is often

century because o f general im provem ents in the

this, w ith div erg en t tren d s in different areas. T he p re­

health statu s o f th e population and th e consequent increases in life expectancy. Before the Second W orld

v ailing gloom y view often ignores th e m ajor progress

W ar the elderly form ed a m uch sm aller fraction o f

the case, th e real p ictu re is m ore com plicated than

th a t has been m ade in reducing urban air pollu tio n

th e p opulation than has been the case since, perhaps

by sm oke and su lp h u r dioxide th a t were form erly

ex plaining why episodes o f severe air p o llution in

m ajor p roblem s; there seem s little d o u b t th a t su b ­

earlier years do n o t seem to have been associated w ith as great an im pact on m ortality rates as they were

stantial benefits to health have ensued. It is u n d o u b t­ edly tru e, however, th a t there is cause for concern

in 1952. In sp ite o f the c o n tin u in g expansion o f the

a b o u t adverse trends o f som e o th er air p o llu ta n ts, p a r­

susceptible, elderly p opulation in the B ritish Isles

ticularly those associated w ith m o to r vehicles.

there has been no re petition o f a n y th in g approaching th e scale o f th e p o llution-related health crisis repre­

Areas of progress

sented by the I-ondon sm og o f 1952. T h is u n d e r­ lines th e enorm ous benefits th a t have been associated

T here is am ple evidence th a t th e h ig h levels o f sm oke

w ith

and su lp h u r dioxide th a t were characteristic o f m any

dioxide levels in B ritish cities since the 1950s.

the

im provem ents

in

sm oke and

su lp h u r

257

258

P ET ER B R I M B L E C O M B E A N D G R A H A M B E N T H A M

As well as th e acute health effects related to extrem e episodes o f air p o llu tio n , th ere is evidence th a t lo n g -term exposure to relatively h ig h levels of sm oke and su lp h u r dioxide also posed serious risks to health. It has been show n th a t in th e early 1950s there was a close association betw een levels o f air p o llu tio n and m o rta lity rates (especially for chronic bronchitis) in B ritish cities.25 T h is suggests th a t lo n g -te rm exposure to air p o llu tio n was having a d a m ag in g effect on health, particu larly in th e cities w ith th e w orst a ir quality. By th e early 1970s, however, by w hich tim e there had been m ajor reduc­ tions in sm oke and su lp h u r dioxide levels, th ere was little evidence o f any association betw een m ortality rates and air p o llu tio n . By th e 1970s it therefore seem s th a t u rban sm oke and su lp h u r dioxide concen­ trations had been reduced to levels w here they no longer posed th e significant th rea ts to health th a t they had done only tw en ty years earlier.

Emerging problems T he good news on u rban sm oke and su lp h u r dioxide needs to be seen in th e context o f th e possible health effects o f som e o th er air p o llu ta n ts w here tren d s are

Figure 12.12 Heavy traffic on the M25 motorway around London. Air pollution from road vehicles has increased in rcccnt years, as pollution from solid fuel burning has decreased.

less favourable, particu larly those arising from m otor vehicles (F igure 12.12). A p a rticu la r cause for concern is th a t increasing exposure to air pollu tio n from traffic m ay be a factor in the m ajor increase in

areas, inclu d in g som e Scottish islands, w here there is

th e incidence o f asthm a th a t has occurred in the

little air pollution. T his has led some observers to

U n ite d K in g d o m , Ireland and o th er w estern coun­ tries in recent decades. In su p p o rt o f th e possibility

suggest th a t the rise in asthm a may have little to do w ith trends in air pollution. O n e suggestion is th at

o f such a lin k it can be p o in ted o u t th a t d u rin g the

the increase in asthm a may result from changes in the

relevant period b o th asthm a and traffic-related air

indoor e nvironm ent, especially increased exposure to

p o llu tio n have show n rising trends. F u rth er su p p o rt

rhe house-dust m ite allergen. A nother possibility is

comes from ex perim ental evidence th a t n itrogen

thar the p opulation may have becom e m ore suscepti­

oxides and ozone can increase bronchial responsive­

ble to asthm a because o f changes in d ie t w hich have

ness to allergens and viruses w hich are com m on tr ig ­

reduced a n ti-o x id a n t status, for exam ple. It is, th ere­

gers for asthm a. W h ile there seem s little d o u b t th a t exposure to air

fore, clear th a t there are several different possible

p o llu tio n can incite asthm a attacks in som e existing asth m atics it is, however, m uch less clear th a t th is is a

there is fu rth er research, it is not possible to draw any firm conclusion on w h eth er or not air p o llu tio n from

m ajor factor in th e ind u ctio n o f asthm a in previously

traffic is a m ajor factor.

unaffected individuals.26 For exam ple, th e incidence o f asthm a has been show n to be hig h in several rural

T he oth er area th a t is cu rren tly causing a great deal o f concern is th e possibility th at th e sm all

causes for rhe c u rren t epidem ic o f asthm a and, u n til

THE AIR THAT W E BREATHE: S M O G S , S M O K E A N D HEALTH

P M l0, and especially P M ,., th an in cities w ith cleaner air. Figure 12.13 shows th e strik in g rela­ tio n sh ip betw een m o rta lity rates and P M 25 in six Am erican cities after a d ju stin g for oth er factors such as cig arette sm oking th at affect the risk o f d e ath .28 In m ost cases th e proportional rise in m ortality or m o rb id ity th a t has been found is relatively sm all bu t, since it applies to very com m on health conditions, the absolute num bers o f people affected can bc very large. T here is, therefore, grow ing concern th a t exposure to sm all particles m ay pose a real th rea t to the health o f th e p opulation, even if th e increased risk for any particu lar

individual

is

relatively

sm all.

U n fo r­

tunately, there is a dearth o f B ritish studies on this im p o rta n t subject and it is not know n w hether the U n ited States findings w ould apply in the sam e way P M 25 concentration Figure 12.13 Adjusted relative mortality rates and average

to the rather different conditions in th e B ritish Isles. Levels o f P M ,0 in som e B ritish cities, however, lie w ith in the range at w hich cffccts have been observed in N o rth A m crica. O n e study has a tte m p te d to produce an estim ate o f sm all particle-related deaths in E ngland and W ales by com bining local m easure­ m ents o f P M .0 w ith th e U n ited Statcs-bascd risk

particles e m itte d from m o to r vehicles, especially

e stim ates.29 D epending on th e assum ptions th a t arc

those w ith diesel engines (and from som e oth er

m ade th is leads to an estim ate of betw een 3 ,000 and

sources), m ay have a significant and w idespread

10,000 P M I0-related deaths per year in E ngland and

d e trim e n ta l im pact on health. T here is m uch interest

W ales. T hese findings, and th e lim ita tio n s o f the

in th e effects o f particles w ith an aerodynam ic radius

inform ation on w hich they are based, underline the

o f less th an ten m icrons (P M |0) and even m ore

need for further research on th e possible health

concern about sm aller particles (P M ,-). O n e o f the

im pacts o f particu late p ollution in th e B ritish Isles.

p rin cip al reasons for concern is th a t the sm all size o f such particles allows th em to p e n etrate deep in to th e lungs w here they can cause dam age to sensitive

THE FUTURE

tissue. T h e health effects o f exposure to sm all particles has been stu d ied extensively in th e U n ited States. Research in several A m erican cities has show n th a t ho spital adm issions for respiratory diseases rise significantly on days when P M J0 levels arc h ig h .27

T he

future

w ill see increasing

regulation

of a

w idening range o f air p o llutants. T he Council o f the E uropean U nion directive on am bient air quality assessm ent and m anagem ent w ill be influential in changing air pollu tio n policy. T he directive exam ­

Increases in th e n u m b er o f deaths from circulatory

ines the density o f m o n ito rin g sites and the need to

as well as from respiratory causes on m ore polluted

set concentration standards and alert thresholds. It

days have also been found. It has also been shown

seeks to w iden interest beyond su lp h u r dioxide,

th a t, after co n tro llin g for o th e r factors, m o rtality

n itrogen dioxide, fine particles, suspended p a rtic u ­

rates tend to be h ig h er in cities w ith h ig h levels of

late m atter, lead and ozone, to include p o llu ta n ts

259

260

PETER B R I M B L E C O M B E A N D G R A H A M B E N T H A M

such as benzene, th e polycyclic a ro m a tic h y d ro ­

NOTES

c arbons, carbon m on o x id e, c a d m iu m , arsenic, nickel an d m ercury. E m issions w ill no d o u b t declin e over th e nex t decades, b u t th e secondary p o llu ta n ts w ill c o n tin u e

to

tax

o u r re g u la to ry approaches. T h e

c o n tro l o f diesel p a rtic le em issions m ay be an im p o r­ ta n t area for tec h n o lo g ic al d e v elo p m en t. T h ere is m u c h p o litica l pressure to issue a le rts w h e n p o llu ­ ta n t c o n ce n tra tio n s becom e e x tre m e ly h ig h , b u t th e effectiveness o f a lerts in a m e lio ra tin g th e in te n sity o f episodes is far from clear. N ev erth e le ss, w in te r sm o g s are very sen sitiv e to th e c o n c e n tra tio n o f n itric oxide an d th e ir occu rren ce m ay rep resen t a good ta rg e t for em issio n re d u c tio n a le rts u n d e r sta g n a n t w in te r co n d itio n s. T h e fu tu re c o u ld also see som e in te re s tin g effects o f g lo b al e n v iro n m e n ta l changes on a ir p o llu tio n . In p a rtic u la r, th e re is a p o ss ib ility th a t th e e n v iro n m e n t in B rita in an d Irela n d w ill becom e m ore favourable for th e d e v e lo p m e n t o f su m m e r ozone p o llu tio n . It has already b een stressed th a t ozone a t th e surface is p ro d u c ed by th e actio n o f s u n lig h t on hydrocarbons and n itro g e n oxides. E pisodes o f ozone p o llu tio n in th e B ritish Isles are stro n g ly associated w ith su m m e r a n tic y clo n ic c o n d itio n s w hen th e relatively still a ir leads to a b u ild u p o f th e p re cu rso r p o llu ta n ts and th e h ig h te m p e ra tu re s an d stro n g s u n lig h t favour th e p ro d u c tio n o f ozone. If c lim a te ch an g e, as a result o f th e e n h an c ed g r e e n h o u s e e ffe c t, w ere to lead to w arm er, s u n n ie r su m m e rs in th e reg io n (and there a re o bvious u n c e rta in tie s a b o u t th is , see C h a p te r 15) th is c o u ld lead to w orse p ro b lem s o f ozone p o llu ­ tio n . R a th e r paradoxically, th e re is also a p o ssib ility th a t th e d e p le tio n o f stra to sp h e ric ozone could lead to ozone increases in th e low er atm o sp h e re. T h is is because d e p le tio n o f stra to sp h e ric ozone w o u ld lead to an increased p e n e tra tio n o f th e u ltra -v io le t ra d ia ­ tio n w h ic h is involved in th e p h o to ch e m ic al p ro d u c ­ tio n o f ozone from its precursors. A ny effects w ould be likely to be g re a te s t in p o llu te d u rb a n areas, w hereas in cleaner ru ra l areas such reactions w ould be lik ely to bc lim ite d by n itro g e n oxides. T h e effects w 'ould therefore be g re a te s t w here th e re are m ost p eo p le an d w here th ere is th e g re a te st p o te n tia l for h a rm .

1 P. Brimblecombe and KM. Nicholas, 'History and ethics of clean air’, in R.J. Berry (ed.), Ethical Dilemmas, London, Chapman and Hall, 1993, pp. 72-85. 2 P. Brimblecombe, The Big Smoke, London, Methuen, 1987, 185 pp. 3 P. Brimblecombe and C. Bowler, 'The history of air pollution in York, England’, Journal of the A ir and Waste Management Association, 1992, vol. 42, pp. 1562-6. 4 Brimblecombe, op. cit. 5 It is im portant to distinguish between the different roles of ozone in the lower and upper atmosphere. In the upper atmosphere, the stratosphere, ozone is a valuable gas since it absorbs harmful ultra-violet radi­ ation from the sun. In the lower atmosphere, ozone is a health hazard as well as being a greenhouse gas. In this chapter we are concerned primarily with low-level ozone. See Chapter 15 for a discussion about stratos­ pheric ozone. 6 This Common Inheritance: Britain's environmental strategy, London, HMSO, 1990. 7 Commission of the European Com munities, Council Directive, Ambient A ir Quality Management and Monitoring 9514/95 Annex II, 1995. 8 AEA, UK Smoke and Sulphur Dioxide Monitoring Networks, Culham, AEA, 1995. 9 D.W. Dockery, C.A. Pope, X.P. Xu, J.D . Spengler, J.H . Ware, M.E. Fay. B.G. Ferris and F.E. Speizer, ‘An association between air pollution and m ortality in six United States cities’, New England Journal of Medicine, 1993, vol. 329, pp. 1753-9. 10 Com mittee on the Medical Effects of Air Pollution, Non-biological Particles and Health, LIK Departm ent of H ealth, 1995. 11 Quality of Urban Air Review G roup, Airborne Particulate Matter in the United Kingdom, London, Departm ent of the Environment, 1996. 12 Expert Panel on Air Quality Standards, Particles, Departm ent of the Environment, London, HMSO, 1995, 38 pp. 13 Quality of Urban Air Review Group, 1996, op. cit. 14 G.W. Campbell, J.R . Stedman and K. Stevenson, A survey of nitrogen dioxide concentrations in the UK using diffusion tubes, July-D ecem ber 1991’, Atmos­ pheric Environmenty 1994, vol. 28, pp. 477—86. 15 H.R. Anderson, E.S. Limb, J.M . Bland, A.P. de Leon, D .P Strachan and J.S. Bower, The Health Effects of an A ir Pollution Episode in London, December 1991, Culham, AEA Technology, 1995. 16 Expert Panel on Air Quality Standards, Ozone, Ix^ndon, HMSO, 1994.

THE A IR THAT W E BREATH E: S M O G S , S M O K E A N D HEALTH

17 Photochcmical Oxidants Review G roup, Ozone in the United Kingdom 1993, London, D epartm ent of the Environm ent, 1993. 18 Quality of Urban Air Review G roup, 4Urban A ir Quality in the United Kingdom, London, Dept of the Environm ent, 1993. 19 Expert Panel on Air Quality Standards, Benzene, London, HM SO, 1994; Expert Panel on Air Quality Standards, 1,3-Butadiene, London, HMSO, 1994. 20 N .R . Passant, Emissions of Volatile Organic Compounds from Stationary Sources in the UK, Stevenage, Warren Spring Laboratory, 1993. 21 J. Derwent, P. D um itrean, J. Chandler, T.J. Davies, R.G. Derwent, G.J. Dollard, M. Delaney, B.M.R. Jones and P.D. Nason, A Preliminary Analysis of Hydrocarbon Monitoring Data from an Urban Site, AEA CS 18358030/005/Issue 2, Culham, AEA Technology, 1994. 22 Quality of U rban Air Review Group, 1993, op. cir. 23 J.D . Spengler and K. Sexton, ‘Indoor air pollution: a public health perspective', Science, 1983, vol. 221, pp. 9 -1 7 . 24 Brimblccombe, op. cit. 25 S. Chinn, C. du V. Florey, I.G. Baldwin and M. Gorgol, ‘The relation of m ortality in England and Wales 1969—73 to measurements of air pollution’, Journal of Epidmiology and Community Health, 1981, vol. 35, pp. 174-9.

26 D epartm ent of H ealth, Committee on Medical Aspects of A ir Pollution: Asthma and outdoor air pollution, London, HMSO, 1995. 27 J. Schwartz, ‘Air pollution and daily mortality: a review and m eta analysis’, Environmental Research, 1994, vol. 64, pp. 36-52. 28 Dockery et al., op. cir. 29 D. Pearce and T. Crowards, Assessing the Health Costs of Particulate A ir Pollution in the UK, CSERGE W orking Paper GEC 9 5 -27, Norwich, Centre for Social and Economic Research on the Global Environment, 1995.

GENERAL READING P. Brimblecombe, The Big Smoke, London and New York, Routledge 1987, 185 pp. P. Brimblecombe, A ir Composition and Chemistry, Cambridge Environmental Chemistry Series 6, Cambridge, Cambridge University Press, 1996 (2nd edn), 253 pp. D.M. Elsom, Atmospheric Pollution: a Global Problem, Oxford, Blackwell, 1992 (2nd edn). C. Kirby, ‘Urban air pollution’, Geography, 1995, vol. 80, pp. 375-92. R. Read and C. Read, ‘Breathing can be hazardous ro your health', New Scientist, 1991, 23 February, pp. 34-7.

13 'PH EW ! WHAT A SCORCHER' Weather Records and Extremes Michael Dukes and Philip Eden There are two kinds of statistics; the kind you look up and the kind you make up. R e x S to u t , Death of a Doxy

INTRODUCTION

In tru th , old F re d ’s m em ory was ra th e r m ore reliable chan th e w ater com pany statistics. All th e sta te m e n ts

T h e b lis te rin g s u m m e r o f 1995 was d ra w in g to a

a ttrib u te d to him above arc essentially correct. In

close an d th e con v ersatio n in th e ‘R ed L io n ’ had once

1 995, th e h eat an d d ro u g h t were not as p rolonged as

a g ain tu rn e d to th e heat an d th e d ro u g h t, in the

in a n u m b e r o f o th e r years, and th e w in te r o f 1 9 9 4 -5

co rn cr scat o f th e p u b lic bar old Fred was h o ld in g

had been one o f th ree w e tte st o f th e tw e n tie th century.

fo rth , as was

th e w e ath e r was

N ev er has th e capacity o f those w ith vested interests to

discussed. A fte r a ll, his m em o ry w e n t back so m u ch

p ick and choose sta tistics to su it th e ir a rg u m e n ts been

fu rth e r th a n everyone else’s.

m ore a p p are n t th a n in th e 1990s.

his

h a b it

w hen

O f course, you young fellers ain’t old enough to remember ’47. Now there was a year. We wuz snow­ bound for m onths, two feet deep it were, drifts up to the top o’ the houses even in the m iddle of March, last remnants d id n ’t vanish till April. An’ when the snow went we wuz flooded for two weeks, and to cap it all there was an ’urricane which took the roof off the village school. And then we ad the ottest sum m er in living memory, in the nineties by May, not a drop of rain through the whole of August, and that was the sum m er Denis Compton hit nigh on four thousand runs with eighteen ’undreds.

PITFALLS IN THE STUDY OF EXTREMES T h e B ritish arc obsessed w ith th e w eather, especially in its m ore ex trem e form s. In sp ite o f a g e n era lly e q u ab le

c lim ate,

wc

c o m p la in

about

w hat

we

c o n sid er to be excessive heat or a b n o rm a l cold, and wc seek scapcgoats d u rin g F o rtu n a te ly

we

have an

floods an d

d ro u g h ts.

excellent c lim ato lo g ic al

n e tw o rk w ith a h isto ry o f org an isatio n an d c o n ti­ n u ity second to none (see C h a p te r 7); th u s un u su al

T h e y o u n g professionals liste n e d politely. T hey

in d iv id u a l e v en ts, n o te w o rth y m o n th s an d seasons,

w ere used to old F re d ’s v iv id im a g in a tio n . T h ey all

an d exceptional c u m u la tiv e p h e n o m e n a can readily

knew th a t th e s u m m e r o f 1995 had been rhe h o tte st

be p u t in to som e so rt o f historical co n tex t. B u t those

an d d rie s t for c en tu rie s; a fte r all, th e w a ter com pany

c o m in g new to research in to clim ato lo g ical extrem es

sp o k esm en an d even g o v e rn m e n t m in iste rs had been

an d c lim a tc histo ry sho u ld be aw are o f som e o f th e

q u o tin g th e sta tistic s a lm o st daily.

p itfa lls th a t aw ait; in p a rtic u la r th ey sh o u ld never

W EA TH ER RECO RD S AN D EXTREMES

cake p ublished records for g ra n te d - even th e m ost

repeated by reputable clim atologists and m eteorolo­

w idely q uoted ones.

g ists can acquire a false pedigree. O n e exam ple is

In th e B ritish Isles our know ledge o f clim ate fluc­

th e w idely d ocum ented account of w idespread snow

tu atio n s over th e last th ree o r four centuries is u n d e r­

show ers over low g round in E ngland on 11 Ju ly

p inned by several com posite records. Some o f the

1888. In som e publications th e validity o f these

best

observations is queried, in others th e account is

know n

o f chese are

th e

C entral

E ngland

T em perature series o f m o n th ly m ean tem perature

repeated w ith no qualificacion, and very rarely has it

values for th e period 1659 to 1973 com piled by Professor G ordon M anley (see C hapter 9) and subse­

been seriously challenged, yet th e w eather daca avail­

q u e n tly updaced by the U K M et. Office; a catalogue

over low g round in m uch of E ngland and W ales.4

able for the tim e suggests it was too w arm for snow

o f daily C en tral E ngland m ean tem p eratu re values;

N ew spaper accounts o f interestin g w eather events

tw o E ngland and W ales P recip itatio n series b e g in ­

should always be taken w ith a large degree of caution

n ing in 1727 and 1766 respectively (see C h ap ter 10);

(see Figure 13*1) —even those penned by w ell-know n

and a L ondon p re cip ita tio n series for 1697 to d a te .1

m eteorological w riters in the serious papers. T h is is

A nyone using these series should ensure th a t they

not th eir fault; it is because new spaper articles are

are fam iliar w ith th eir origins and developm ent and

subject to the w him of a sub-editor. T h e new spaper

do noc fall inco che crap o f confusing precision w ith

su b -ed ito r is a strange breed w ith tw o goals. T he

accuracy. Sim ilarly, m any contin u o u s records from

first is to force con trib u tio n s to fit th e space avail­

individual locations are liable to be affected by

able, w hich m ay necessitate rem oving tex t, no m atter

changes o f site, o f in stru m e n ta tio n , and o f observa­

its im portance, or creating new text w ith o u t refer­

tional practice, as well as trends due to urbanisation.

ence to the original author. T h e second is to m ake

Researchers should always be aware o f these before

these sam e co n trib u tio n s fit th e style o f th e news­

they seek to explain d isc o n tin u itie s or trends. T here

paper, w hich may involve extensive re-w ritin g , again

is one w ell-know n exam ple in th e lite ratu re o f a

w ith o u t reference to th e author. F urtherm ore, eye­

paper w hich used ‘se cond-hand’ d ata to illu stra te the

w itness reports o f unusual w eather are notoriously

effects on tem p eratu re o f u rbanisation in th e G reater L ondon area betw een 1878 and 1969- T h e a u th o r

unreliable. O ne o th er source o f error in extrem e values, p a rtic ­

concluded an increase in the tem p eratu re difference

ularly w ith reference to tem perature, m ay bc m en ­

betw een K ew O bservatory and R otham sted (H e rt­

tioned. T his is the usually taboo subject o f invention.

fordshire) o f about 1°C d u e to u rbanisation o f the

T hose involved in q u ality control have always been

K ew site, dism issin g a site change a t R otham sted from a w alled garden to an open field som e 15 m

aware o f (very isolated) cases of observers who ‘m assage’ th eir figures - usually m axim um tem p e r­

h ig h er as u n im p o rta n t. A cursory exam ination o f the

atures - to m ake th em appear m ore exceptional. T he

o verlapping records for th e tw o R otham sted sites

reason is probably no m ore sinister than a desire

reveals th a t th is was not th e case.2

for th e observer’s station to appear at th e to p of

auchoricies has also varied considerably over tim e.

published lists or to be quoted regularly in the national news m edia. An off-the-record chcck w ith

For m any decades ic arguably erred on the side of

th e q u ality -co n tro llin g auchority is advised if such

generosity tow ards d o u b tfu l readings, b u t since th e

suspicions are aroused. Exaggeracion o f sunshine

T h e efficacy o f d a ta q u a lity c o n tr o l by the various

late 1970s the q u a lity control process has been au to ­

records by healch or courist resorts also falls in to this

m ated and som e people believe th a t it is now m ore likely to exclude g en u in e extrem e values than to

category. T he above list o f possible pitfalls is an extensive

include d o u b tfu l ones.*

one b u t, in fact, the vast m ajority o f w eather obser­

A ccounts o f p ast w eather events should also be

vations are trustw orthy. Invescigations in to extrem e

treated w ith caution. D ubious descriptions when

events necessarily involve exam ining data at chc- cails

263

264

M IC H AEL DUKES A N D PHILIP EDEN

■BOOKIES CATCH A H COLD IN THE BIB HEAT Sun shines on punters I as record evaporates

H eat-row is m elting

120f IS ON THE CARDS .............. .......... Boffins alert l ^ s s.»rllrr»4. s a yHr. -to Thatcher -.u w 1 h.1. kri INIH Iter

* n lr p n *» iM

' *r

uuV^TrTrTau

*!S A ,n‘

ì liai

— r**»**—

* **

*■' •»

LT"'....... — ndon, Faber and Faber L td, 1982, pp. 6 9 -7 0 . P rio r to 1961 th e U K M et. Office defined an absolute d ro u g h t as a fifteen-day period in w hich no day records m ore th an 0.2 m m of rain. In fact, d ro u g h t is also influenced by p o ten tial e v apotranspiration, and a cool dry m isty couple o f w eeks o f ‘anticyclonic g lo o m ’ in N ovem ber, for exam ple, hardly c o n stitu tes a real d ro u g h t, so th e d e finition was dropped. M eteorological Office, M onthly Weather Report February'

1947, L ondon, H M S O , 1947. 18 R. B ushell, D ro u g h ts in 1893’, B ritish R a in fa ll 1 8 9 3 , 1894, vol. 33 , pp. 1 3 7 -4 7 . 19 E .G . B ilham , The Climate o f the British Isles, London, M acm illan and Co. L td, 1938, p. 241. 20 M eteorological Office, ‘Heavy falls on rainfall days in 1929’, British R a infall 1 9 2 9 , 1930, vol. 69 , pp . 5 4 -8 2 . 21 See L.C.W . Bonacina, ‘Snowfall in the B ritish Isles d u rin g the h a lf century, 1 8 7 6 -1 9 2 5 ’, British R ainfall 1927, 1928, vol. 67 , pp. 2 6 0 -8 7 ; L.C.W . Bonacina, ’Snowfall in th e B ritish Isles d u rin g th e decade 1 9 2 5 -1 9 3 6 ’, British R ainfall 1 9 3 6 , 1937, vol. 76 , pp. 2 7 2 -9 2 ; L.C.W . Bonacina, ‘Snowfall in the B ritish Isles d u rin g the decade 1936 to 1945’, B ritish R ainfall 1 9 4 8, 1949, vol. 88 , pp. 2 0 9 -1 7 ; L.C.W . Bonacina, ’Snowfall in th e B ritish Isles d u rin g the decade 1946 to 1955’, British R a infall 1955, 1956, vol. 95 , pp. 2 19—30; L.C.W . Bonacina, ‘C h ie f events o f snow fall in th e B ritish Isles d u rin g the decade, 1 9 5 6 -1 9 6 5 , Weather, 1966, vol. 21, pp. 4 2 - 6 ; M .C. Jack so n , A classification o f th e snow iness o f 100 w inters - a trib u te to th e late L.C.W . Bonacina’, Weather, 1977, vol. 32, pp. 9 1 - 7 . 22 See G . P arker and A.A. H arrison, ‘Freezing drizzle in south-east E ngland on 20 Jan u ary 1966’, Meteorological Magazine, 1967, vol. 96 , pp. 1 0 8 -1 2 , and T .H . K irk , ‘T he synoptic situ atio n a tte n d in g an occurrence o f freezing drizzle’, Meteorological Magazine, 1967, vol. 96 , pp. 1 1 2 -1 5 . 23 J K. Page, ‘H eavy glaze in Yorkshire, M arch 1969’, Weather, 1969, vol. 24, pp. 4 8 6 -9 5 . 24 S tirlin g , op. c it., p. 209. 25 H .H . Lam b, Historic Storms o f the North Sea. British Isles a nd Northwest Europe, C am bridge, C am bridge U n iv er­ sity Press, 1991, pp. 1 8 9 -9 1 . 2 6 See G . H ill, Hurricane Force, L ondon, C ollins, 1988; B. Ogley, In the wake o f the Hurricane, W esterham , K ent, Froglets P ub licatio n L td, 1988; B. O gley, I. C urrie and M. D avison, The Kent Weather Book, W esterham , K en t, Froglets P u blication L td, 1991; Weather (Special Issue), 1988, vol. 43 , pp. 6 5 - 1 4 2 . 27 Lam b, op. c it., pp. 5 9 -7 2 . 28 C .J.M . A anensen, ‘G ales in Yorkshire February 16, 1 9 6 2 ’, Geophysical Memoir, vol. 108. 29 E. M cC allum , ‘T he B u rn s’ Day sto rm , 25 Jan u ary 1990’, Weather, 1990, vol. 45 , pp. 1 6 6 -7 3 - T h is storm is incorrectly referred to as th e ‘B urns’ D ay’ storm since the S cottish festival b ein g used as a m arker is actually ‘B u rn s’ N ig h t’. 30 C .K .M . D ouglas and K .H . Stew art, L ondon fog o f D ecem ber 5—8 1952’, The Meteorological Magazine, 1953, vol. 82 , pp. 6 7 -7 1 . 31 C .W .G . D ak in g , ‘U nusual persistence o f fog’. The Meteorological Magazine, 1942, vol. 71 , pp. 2 5 2 -3 .

W EATHER RECORDS AN D EXTREM ES

GENERAL READING

F.K. Rohan, 'I'he Climate of Ireland, Dublin, Meteorological Service, 1986, 2nd edn.

P. Eden, Weatherwise, London, Macmillan, 1995. H .H . Lamb, Historic Storms of the North Sea, British isles and Northmst Europe, Cambridge, Cambridge University Press, 1991.

R ' StirIin£> The Weather of Britain, London, Faber and Faber *982.

295

T his page intentionally lcli blank

Part 4 FO R EC A ST IN G

THE

FUTURE

I f you can look into the seeds of time, And say which grain will grow and which will not, Speak then to me. William Shakespeare, Macbeth

T his page intentionally lcli blank

14 FORECASTING THE BRITISH ISLES WEATHER Clive Pierce, Michael Dukes and Graham Parker Some are weatherwise, some are otherwise. B enjam in F ran k lin , Poor Richard's Almanac, F ebruary 1735

INTRODUCTION T he w eather has enorm ous im pact on our lives, from the relatively insignificant effects on our daily routine, to the catastrophic destruction of whole com m unities du rin g severe storm s, floods and droughts. It is therefore not surprising that from the very earliest tim es hum ans have tried to understand and predict the changing moods o f the w eather w ith, it m ust be said, varying degrees of success. In the first o f three sections in this chapter, some m ilestones in our understanding of science and m ete­ orology are reviewed in the context o f their im pact on w eather forecasts. W ritten evidence from south­ west Asia shows th at the ancient E gyptian and Babylonian civilisations were interested in weather prediction as long ago as 3000 bC. W ith a few excep­ tions, little headway was m ade in our understanding o f m eteorology, however, u n til the rebirth of science in western Europe d uring the Renaissance period. Indeed, the greatest advances in the field have come d u rin g the last one hundred years or so w ith the form ulation o f a com plete set of equations to describe the physical behaviour of the atm osphere. In the second part of the chapter the m odern-day preparation of w eather forecasts is exam ined in some detail. Today, w eather forecasting is an enor­

mously complex and costly exercise, involving the co-ordinated effort of many tens o f thousands of people world-wide. A huge num ber of weather obser­ vations from the land, sea, air and space, are collected and distributed globally on a daily basis. These data arc assim ilated into elaborate, computer-based models of the E arths atm osphere th at generate forecasts of atm ospheric behaviour for hours, days or weeks ahead. A review o f data collection and processing is followed by a look at approaches to m odelling o f the atm osphere. A discussion o f the range o f techniques employed in forecasting weather from a few m inutes to one m onth ahead is followed by a sum m ary of the range o f services supplied by the U nited K ingdom Met. Office and private w eather consultancies in the B ritish Isles. In keeping w ith the chronological organisation of the chapter, the third and final section briefly explores the future of weather forecasting from a num ber of different perspectives. T he issue of atm ospheric predictability and its im plications for Num erical W eather Prediction are reviewed in the light o f projected developm ents in science and tech­ nology, and the theoretical lim itations im posed by chaos theory'. A look to the future o f weather fore­ casting would not be com plete w ithout some refer­ ence to economic issues. Perhaps m ost notew orthy is

300

CLIVE PIERCE, MICHAEL DUKES AND GRAHAM PARKER the rising cost o f collection and d istribution of w eather data w orld-w ide, and its potential im plica­ tions for w eather service provision on both national and international scales.

A HISTORICAL PERSPECTIVE T he evolution of weather forecasting, both in theory and practice, is intim ately linked to the grow th of m eteorology as a science (see Table 14.1 for a chronology o f some key landm arks). The foundations o f the m odern science o f m eteorology were laid by the G reek civilisation in Europe betw een about 650 and 300 B C (see Figure 14.1). A ristotle (3 8 4 -3 2 2 b c ) was one o f the first G reek philosophers to apply system atic observation to the study of meteorology, work which culm inated in the oldest com prehensive treatise on the subject. In his book, Meteorologica w ritten in 340 B C , A ristotle dem onstrated ru d i­ m entary understanding of the hydrological cycle,

clouds and the vertical structure of the atm osphere. U nfortunately, this highly productive period in the early history o f m eteorology and other natural sciences was relatively short-lived. W ith the fall o f the ancient G reek civilisation in the first century B C , sci­ entific investigation generally declined. N evertheless, the w ealth o f know ledge accum ulated by the Greeks was not lost. D uring the centuries o f com parative intellectual darkness th at followed, the M uslim s translated A ristotle's Meteorologica into Arabic, whence it could later be translated into Latin by west­ ern scholars. Remarkably, about 1,500 years after the fall of the ancient G reeks, Aleteorologica was still the unquestioned authority on m eteorology in western Europe. Early in the Renaissance period, meteorology was not a form ally recognised discipline. Rather, it was the concern o f individuals whose livelihoods, in one way or another, were dependent upon the vagaries o f the weather. As such, it had m ore to do w ith accu­ m ulated weather lore, astrology and superstition than any scientifically based understanding of atm ospheric behaviour. W ith the developm ent of a scientific m ethod founded on q uantitative, rather than q ualita­ tive observation, A ristotle’s Meteorologica was g radu­

Figure 14.1 The Tower of Winds (Athens), built about 40 BC by the astronomer Andronikos of Kyrrhos.

ally superseded, and the study of w eather slowly transform ed from a philosophy to an applied physical science. Experim ents w ith prim itive therm om eters and barometers during the first half o f the seventeenth century dem onstrated th at variations in atm ospheric tem perature and pressure accompanied changes in the weather. T his inspired a good deal of conjecture regarding the behaviour of the atm osphere. T he idea of a weather observing netw ork to study these changes soon followed. As early as 1653, G rand D uke Ferdinand II of Tuscany organised a weather observ­ ing netw ork in northern Italy. D espite the trem en­ dous vision of this early scientific patron, it was not until the end o f the eighteenth century th at such net­ works were more widely introduced (see C hapter 7).

F O R E C A S T I N G THE BRIT ISH IS L ES W E A T H E R

Table 14.1 Some landmarks in the evolution of the science of weather forecasting. Dale

Description

3000 BC 650 b c 340 BC 1250 a d 1337 1550 1600

The Babylonians use astrological signs to forecast the weather. The ancient Greeks begin systematic observations of the weather. The Greek philosopher, Aristotle (384-322), publishes Meteorologica. An English scholar, Roger Bacon (1214-94), advocates experiment-based scientific method. W illiam Merle, an English rector, begins the earliest known systematic record of the weather. An Italian mathematician, Girolamo Cardano (1501-76), disputes Aristotle's work. Galileo Galilei (1564-1642) demonstrates the use of a thermoscope, theforerunner of the thermometer. A contemporary of Galileo, René Descartes (1596-1650), publishes a philosophy of scientific method. An Italian mathematician, Evangelista Torricelli (1608-47), devises the barometer. The renowned scientific patron, Grand Duke Ferdinand II of Tuscany (1610-70), establishes the first weather observing network in northern Italy. The English physicist, Robert Hooke (1635-1703), proposes a Method lor Making a History of the Weather. The German mathematician, Gottfried Wilhelm Leibnitz (1646-1716), publishes a description of a branch of mathematics known as calculus. Isaac Newton (1642-1727), an English mathematician and physicist, publishes Philosophiae Naturalis Principia Mathematica which includes the three natural laws of motion. He also demonstrates the use of calculus. The English astronomer, Edmund Hailey (1656-1742), draws a map showing wind direction between 30‘N and 30’S. George Hadley (1685-1758) publishes a theory of atmospheric motion involving a cyclic circulation, later known as the Hadley circulation. The first mathematical study of atmospheric motion by the Frenchman, Jean Le Ronde d'Alembert (1717-83). The German mathematician, Leonhard Euler (1707-83) develops equations of fluid motion using Newton's second law, and partial differential equations. Johann Heinrich Lambert (1728-77) proposes the world-wide taking of weather observations. An American, Amerigo Avoaadro (1776-1856) uses the Ideal gas equation relating pressure, volume and temperature of a gas. Siméon Denis Poisson (1781-1840), student of Pierre Simon LaPlace, derives an adiabatic equation of volume changes for gases. The German meteorologist, Wilhelm Heinrich Dove (1803-76), formulates a theory of mid­ latitude storm development ('Law of Gyration'), based upon the concept of conflicting equatorial and polar air currents. Gustave-Gaspard Coriolis (1792-1843) describes the absolute acceleration of moving bodies in a system rotating about a vertical axis. The electric telegraph, conceived by Samuel Morse in 1832, comes into operational use. James Pollard Espy (1785-1860), an American meteorologist, publishes his convective theory of storms, based upon adiabatic cooling, and latent heat release. W illiam C. Redfield (1789-1857) explains the rotary motion of storms in terms of centrifugal force. The American, Elias Loomis (1811-89), draws the first synoptic chart. James Glaisher (1809-1903) organises the first synoptic weather observing network in England. The first weather reports are published in the Daily News. Rudolph Clausius (1822-88) introduces the concept of entropy. Admiral Robert FitzRoy (1805-65) is appointed head of the Meteorological department of the Board of Trade. Professor Christophorus Buys Ballot (1817-90), a Dutch meteorologist, discovers that low atmospheric pressure is on the left of an observer standing with their back to the wind in the northern hemisphere. The opposite is true in the southern hemisphere.

1637 1643 1653 1663 1684 1687

1688 1735 1746 1755 1771 1813 1823 1827

1835 1840 1841 1843 1848 1854 1857

302

C L I V E P IE R C E , M I C H A E L D U K E S A N D G R A H A M PA RK ER

Table 14.1 Continued Date

Description

1858

A German meteorologist, Hermann von Helmholtz (1821-94), introduces the concept of vorticity. The American scientist, W illiam Ferrei (1817-91), formulates the first mathematical equations of atmospheric motion on a rotating earth. Urbain Le Verrier (1811-77), a Frenchman, draws isobars on a weather map. The British Meteorological Office publish the first weather summaries in The Times. Storm warning cones are erected in British ports early in 1861. Theodore Reye (1838-1919), a Swiss mathematician, publishes a paper on dry adiabatic and saturated adiabatic processes. Muller draws isallobars on weather charts. An American engineer, H. Peslin, constructs a thermodynamic diagram for use in tracing the motions of imaginary parcels of air undergoing dry and saturated adiabatic changes. Ralph Abercromby (1842-97), an English meteorologist, publishes his book, Principles of Weather Forecasting, in which he describes the characteristic weather associated with the passage of a depression. W ladim ir Kòppen (1846-1940), a German meteorologist, uses the thermal wind relationship to derive fields of pressure at different altitudes. A Norwegian mathematician and physicist, Vilhelm Bjerknes (1862-1951), describes his Circulation theorem, in which rotary atmospheric motion is caused by horizontal temperature contrasts (barodinicity). Sir W illiam Napier Shaw (1854-1945), director of the British Meteorological Office, describes the concept of air trajectory analysis. The invention of the Tephigram is also attributed to him. Sir William Napier Shaw publishes Forecasting Weather in which he summarises the current state of weather forecasting. The Norwegian, Vilhelm Bjerknes, and a colleague, Halvor Solberg (1895-1974), publish the wave or polar front theory of cyclone development. An English meteorologist, Lewis Fry Richardson (1881-1953), expounds the theory and practice of numerical weather prediction in his book, Weather Prediction by Numerical Process. H. Jeffreys simplifies the Primitive equations using scale analysis. A Frenchman, Robert Bureau, makes the first successful atmospheric sounding with a radiosonde. Carl-Gustav Rossby (1898-1957), a Swedish meteorologist, relates long (Rossby) wave motions in the mid-latitude troposphere to conservation of absolute vorticity. Purpose-built weather radars are used by meteorologists for the first time. Sutcliffe and Forsdyke demonstrate a relationship between jet streams and the development of cyclones and anticyclones. The UK Met. Office begins research into numerical weather prediction. The World Meteorological Organisation is born. The first meteorological satellite, TIROS 1, is launched from Cape Canaveral, Florida in North America. Numerical weather prediction in the UK Met. Office takes over from manually produced weather forecasts. The World Weather Watch programme, formulated by the W M O in 1963, commences. The plotting of synoptic weather charts is automated in the UK Met. Office. Weather observations are red automatically into its numerical models. Numerical weather forecast accuracy at the UK Met. Office is improved significantly with the introduction of a more powerful computer and a ten-layer model. Nine-member Ensemble numerical weather forecasts begin at the UK Met. Office. The UK Met. Office commence N W P operations on the Cray C90 supercomputer. This is capable of performing 16,000,000,000 floating point calculations per second.

1859

1860 1864 1868 1883

1888 1898

1906 1911 1921 1922

1929 1939 1946 1950

1960 1965 1968 1974 Early 1980s 1988 1994

FORECASTING THE BRITISH ISLES WEATHER Towards the end o f the seventeenth century, two vital scientific breakthroughs, one in physics, the other in m athem atics, were m ade by the great E nglish scientist, Isaac N ew ton. T he first of these was the invention o f m echanics, th at branch of physics concerned w ith bodies in m otion. T he second was the developm ent of a m athem atical tool known as calculus. Together, these later formed the basis for the quantitative study of fluids in m otion and thus were necessary prerequisites to the emergence of m eteorology as an applied physical science. O ne o f the earliest attem p ts to explain the m otions of the atm osphere was m ade by the English astron­ om er, E dm und Hailey. In 1688, he sum m arised the wind regim e in the tropical and sub-tropical oceans in the form o f a chart illustrating the direction of the air flow w ith w ind arrows. T his was based upon the accum ulated w eather observations of num erous ships plying established trade routes. Hailey believed this general circulation to be driven by the sun's heat and this led him to consider the role o f therm al c o n v e c tio n in atm ospheric m otion. Perhaps his most im p ortant contribution to m eteorology, however, was the introduction o f the concept of w inds as a general circulation o f air over the E arth’s surface. A lm ost fifty years later, Hailey's ideas were taken a step further by another E nglish scientist, George Hadley. In 1735, H adley published the results of his study of the atm osphere in Philosophical Transactions.1 His explanation of the atm ospheric circulation outlined by Hailey not only involved therm al convection, but also took account o f the Earth's rotation. H e envis­ aged a therm ally direct ‘cell’ in w hich warm air rising on the equator moved polewards at high a lti­ tude, later to descend in the sub-tropics and return to the equator as a cooler, near surface air current. In retrospect, H adley’s work on the general cir­ culation was one o f the m ilestones in dynamical meteorology. It generated considerable interest am ongst the early m eteorological theoreticians. O ne of these, the G erm an m athem atician, Leonhard Euler, presented the first correct m athem atical explanation of fluid flow in 1755. T his involved N ew ton’s second law of m otion and the concept of partial differential equations. E uler’s studies, and later research by

Gustave-G aspard Coriolis on the effects of the E arth’s rotation in 1835, paved the way for W illiam Ferrel’s derivation of the equations of atm ospheric m otion on a rotating Earth. First published in 1859, these formulae represented another im portant advance in the theory of meteorology. Even so, they received relatively little attention until some decades later. Ferrel’s work was overshadowed by developm ents in other areas of m eteorology which were o f some practical w orth to m eteorologists of the day. First, the grow th in popularity o f w eather obser­ ving from the late eighteenth century onwards led to the discovery that periods of bad weather in m id ­ latitudes were, more often than not, associated w ith cyclonic disturbances originating over the A tlantic Ocean. Consequently, m ost theoretical exploration in meteorology during the nineteenth century was focused on identifying the causes of cyclone devel­ opm ent. In particular, the discovery o f the first law o f therm odynam ics led to the realisation that adia­ batic changes (those in w hich sensible heat energy is neither gained nor lost) played an im portant role in atm ospheric m otion. The Am erican m eteorologist, Jam es Espy, recognised this fact in form ulating his convective theory o f cyclone developm ent during the 1830s.} Second, the introduction of the electric telegraph early in the 1840s, m ade the generation of near real­ tim e weather charts possible. T he Englishm an Jam es G laisher (see Figure 14.2), was the first person to dem onstrate this when he organised the collection of w eather reports for the Daily News in 1848.4 W ith this facility for rapid data collection came the poten­ tial for producing the first observation-based shortrange w eather forecasts. This could be achieved by sim ple linear extrapolation of current weather, the assum ption being that w eather patterns w ould move in the direction o f the prevailing wind. By the early 1860s, when the recently formed Meteorological D epartm ent o f the Board of Trade (the forerunner of the U nited K ingdom Met. Office) began the first daily w'eather report and gale warning services, weather forecasting, still in its infancy, was essentially an observation-based practice. It had no means of exploiting the com plicated theoretical work of Ferrel.

303

304

CLIVE PIERCE, MICHAEL DUKES AND GRAHAM PARKER closing decades o f the Victorian era and into the tw entieth century. In 1911, Shaw published his book, Forecasting Weather, in which he succinctly sum m arised the practice o f weather forecasting as follows, 'T he business o f the forecaster is to d eter­ m ine what type of barom etric d istribution is to be expected w ithin the next tw enty-four hours and to assign to it the appropriate weather.’5 The current surface pressure d istribution was predicted forward in tim e using a com bination of p re s s u re te n d e n c y inform ation and forecaster experience. T he w eather associated w ith this new pressure d istribution was forecast using A bercrom by’s conceptual models relating w eather to high and low pressure areas.6 From Shaw’s description it is apparent th at w eather forecasters still made little use o f the grow ing body of m eteorological theory. Yet the im portance o f both therm odynam ic and dynam ic influences on atm ospheric m otion was understood in quantitative term s well before the end o f the nine­ teenth century. W h at was m issing was a coherent theory of atm ospheric m otion em bodying both th er­

Figure 14.2 James Glaisher, FRS (1809-1905) who estab­ lished the first network of reliable weather observatories in the British Isles.

In the years following 1861, the pioneering w eather predictions m ade by the M et. Office under A dm iral R obert FitzRoy received a mixed reception. Indeed, they came in for an increasing am ount of criticism for their failing to provide tim ely warnings o f bad weather. Consequently, w eather forecasts were abandoned altogether for a num ber o f years. T heir unreliability is understandable in view o f the extrem ely lim ited inform ation and knowledge then at the disposal o f m eteorologists. D espite these setbacks however, the w ork o f Christophorus BuysB allot, R alph Abercrom by, N apier Shaw and others, together w ith im provem ents in w eather observing netw orks, saw that the im petus towards an improved w eather forecast service was m aintained through the

m odynam ic and dynam ic principles. O nly then could realistic conceptual models of m id-latitude cyclones evolve, and these formed an essential part of prac­ tical w eather forecasting. A breakthrough came in 1898 when the Norw egian m athem atical physicist, Vilhelm Bjerknes, m ade the link between therm odynam ically and dynamically forced atm ospheric m otions in a powerful theorem later know as the Bjerknes circulation theorem . The success of Bjerknes’ approach lay in his ability to recognise that the density o f the air could vary when atm ospheric pressure was constant. T his recognition led him to distinguish between two atm ospheric states. These he described as b a ro tro p ic and baro clin ic. In short, the form er represents an atm osphere in which there are no horizontal variations in tem per­ ature, w hilst in the latter the converse applies. Some tim e later, Bjerknes, and another N o r­ wegian, H alvor Solberg, w orking at the Bergen School of Meteorology, p u t forward an entirely new and innovative conceptual model of cyclone devel­ opm ent. s T his had its foundations in the earlier theo­ retical work of Bjerknes and the analysis of detailed

FORECASTING THE BRITISH ISLES WEATHER w eather observations. T heir m odel treated cyclones as transient features o f the general atm ospheric circu­ lation, formed in baroclinic zones on the p o la r fro n t. As such, they were associated w ith tw o d istin c t lines o f c o n v e rg e n c e and w eather discontinuity called c o ld and w a rm fro n ts. T he adoption of the term front' in this context has its origins in the concep­ tual sim ilarity between the m ovem ent o f weather discontinuities in the atm osphere and the troop form ations used in the First W orld War. It w ould be difficult to exaggerate the im portance o f N orw egian polar front theory in term s of its subse­ qu en t im pact on m id-latitude w eather forecasting. N o t only did it revolutionise the way m eteorologists viewed the grow th and decay o f w eather systems, but it also transform ed practical w eather forecasting. O ne o f the key tasks of the w eather forecaster soon became the identification of frontal systems on w eather charts. A llied to this, the concept of the air m ass was used to identify and d istinguish broad categories o f weather. Somewhat surprisingly, the U nited K ingdom M et. Office was slow to adopt these new techniques and it was not until 1935 that frontal and air mass analyses became tw o o f the key tasks o f B ritish w eather forecasters.9 D uring the 1920s and 1930s, the aviation-led grow th in rad io so n d e-b a se d upper air m easurem ents enabled m eteorologists to exam ine the three-dim ensional structure o f entire weather system s for the first tim e. W ind observations from the m iddle and upper troposphere revealed unforeseen wave-like m otions w ith w avelengths of the order of 2,000 km . These so called lo n g w a v es were not static features. They appeared both to move and am plify or contract over tim e. Furtherm ore, the positions of individual rid g es and tr o u g h s were shown to be intim ately related to the surface pressure d istribution. T he recognition of a clear relationship between long waves in the upper air and the grow th and decay of transient surface w eather systems was another m ajor step forward for tw entieth-century m eteo­ rology. Evidently, could bc forecast dynam ical theory, in the underlying

if the behaviour o f these waves then, through well-established so could corresponding changcs pressure fields. It was a Swedish

m eteorologist,

C arl-G ustaf

Rossby,

who

finally

dem onstrated that the propagation o f long waves was dependent on three factors: their w avelength, the poleward rate o f change o f the C oriolis p a ra m e te r, and the mean zonal flow rate. By 1945, knowledge o f upper air m otion had altered weather forecasting practice significantly. Predictions of changes in the contour patterns of a tm o sp h e ric th ic k n e ss and constant pressure charts were used, in conjunction w ith surface w eather m aps, to generate forecasts for up to forty-eight hours ahead.10 U nfortunately, these techniques were very tim e-consum ing, involving the manual analysis of large quantities o f data. Furtherm ore, there was still a large subjective com ponent to the forecasting process. N ot surprisingly, weather forecasts were fre­ quently wrong. Upon being told that the Met. Office got its forecasts right 60 per cent o f the tim e, W inston Churchill is reputed to have said th at, if he believed the opposite of the weather forecast to be true, he w ould be right alm ost as often! The Second W orld W ar also saw the first use of ground-based radar for m eteorological purposes. T hrough the operation o f m ilitary radar during periods of bad weather, it was quickly discovered that areas of m oderate or heavy precipitation gener­ ated detectable radar echoes. Later, this feature was employed to track belts o f precipitation and identify convective storm s. Since the 1950s, radars designed specifically for the detection o f precipitation have come into widespread use (see Plate 8).

Numerical weather prediction O ne of the most significant breakthroughs in w eather forecasting this century has undoubtedly been the developm ent of com puter-based N um erical W eather Prediction (N W P ) models. T he potential o f such an approach was first recognised by an E nglish m eteo­ rologist, Lewis Richardson. In 1922, Richardson published a book, Weather Prediction hy Numerical Process'' in which he dem onstrated a m ethod for predicting changcs in surface atm ospheric pressure over west G erm any from an initial d istribution of pressure over western

Europe. T his involved

a

305

30Ó

CLIVE PIERCE, MICHAEL DUKES AND GRAHAM PARKER

num erical so lu tio n o f th e p rim itiv e equations: a set

large, data-sparse regions o f the E arth was alm ost

o f fu n d am en tal equations g overning atm ospheric

im possible. In particular, very few w eather reports

m o tio n , described earlier by B jerknes (see Box 14.1). M any thousands o f calculations and m o n th s o f hard

were available from the Pacific and A tlan tic oceans, yet these were som e o f the m ost active areas in term s

w ork were necessary to produce a six-hour forecast

o f w eather. D u rin g the

- there w ere no com puters or electronic calculators

experim ents w ith rock et-m o u n ted cam eras d em o n ­

- yet th e final answ er proved to bc com pletely w rong.

strated th e enorm ous p o tential o f hig h a ltitu d e

U nknow ingly, R ichardson had used flawed m ath e ­

w eather observations for supp ly in g inform ation on

m atical techniques. N o t to be deterred however, he envisaged a tim e w hen a co-ordinated arm y o f 6 4 ,0 0 0

the m ovem ent o f hurricancs. T h is provided the

h um an co m p u ters w ould perform sim ilar calculations

program m e.

q u ick ly enough

to keep ahead o f the evolving

weather.

1950s, N o rth A m erican

im petus for the w o rld s first m ctcorological satellite Betw een I9 6 0 and 1965, N o rth A m erica launched ten Television and Infra-red O bservation Satellites

R ichardson was well ahead o f his tim e. In fact, it

(T IR O S I- X ) in to low a ltitu d e , quasi-polar o rb its .13

was not u n til the 1950s th a t th e advent o f th e elec­ tro nic c o m p u te r m ade th e realisation o f his dream

These carricd television cam cras designed to capture high resolution pictures o f the E a rth ’s cloudy atm o s­

m odel was

phere. O n board, a facility called A u tom atic P icture

in tro d u ced by th e Sw edish M ilitary W eather service

Transm ission relayed th e im ages directly back to a

in 1954 an d , w ith th e invention o f faster com puters

C om m unications and D ata A cquisition centre on the

in th e 1960s, such m odels becam e b oth m ore widely

ground. For th e first tim e, forecasters had access to

possible. T he first operational N W P

used and progressively m ore sophisticated. In the

real-tim e pictures o f th e atm osphere over hundreds

U n ited K in g d o m M et. Officc, com putcr-bascd N W P forecasts w ere com pared for accuracy and reliability

o f thousands o f square kilom etres. T h is had an enorm ous im pact on w eather fore­

a gainst h u m an forecasters before th e ir full in tro ­

casting in low and m id -latitu d es. Betw een Ju ly 1961

d u c tio n in

and

19 6 5 .12 Today, h ighly com plex baro-

D ecem ber

1964,

118 tropical

storm s were

clinic N W P m odels, ru n on extrem ely pow erful

tracked by T IR O S satellites. M any o f these w ould

supercom puters, arc used by N a tio n a l M ctcorological

previously have gone unnoticed un til they reached

C entres all over th e w orld. T h is

com p u ter-d riv en

m eteorologists from

populated land areas. Now , evasive action to save life revolution

freed

and property could be taken several days, rather than

o f m anual data

several hours, ahead. O v er Europe and th e N o rth

analysis, a task w hich had previously been an in te ­

A tlan tic, satellite pictures o f frontal wave d e p r e s ­

gral p a rt o f w eather forecasting. N ow adays, th e role

sio n s confirm ed the validity o f m any aspects o f the

o f th e w eather forecaster is m ore concerned w ith

B jerknes-S olberg

th e

o f com puter-

b ro u g h t to lig h t certain sm aller-scale features o f the

based w eather pred ictio n s and th e p reparation of

atm ospheric circulation h ith e rto unim agincd. For

in te llig ib le forecasts for th e lay person. These tasks draw on his or her experience and know ledge of

exam ple, the now fam iliar open ccll’ stru c tu re of show er clouds in polar m aritim e airstrcam s w ould

local w eather - h u m an skills w hich are, at present,

probably not have been identified were it not for

m ostly beyond the capabilities o f a p rogram m ed

such pictures.

assessm ent

and

th e ted iu m

finally

in te rp re ta tio n

m achine.

conceptual

m odel.

T hey

also

Today, global coverage o f th e E arth ’s surface and atm osphere is afforded by a host of g e o s ta tio n a ry and s u n -s y n c h ro n o u s satellites (see Figure 14.3).

The Space Age Revolution

These are m aintained by various m em ber countries

P rio r to th e launch o f th e first m eteorological satel­ lites in th e early 1960s, w eather forecasting for the

o f th e U n ited N atio n s for th e benefit o f th e W orld M eteorological O rg a n isatio n ’s W orld W eather W atch

FORECASTING THE BRITISH ISLES WEATHER

BOX 14.1 THE PRIMITIVE EQUATIONS The primitive equations are a set o f fundamental equations governing large-scale atmospheric motions, and form the theoretical basis for N W P models. They appear in a variety o f configurations according to the choice o f co-ordinate system and the mathematical notation used. Here, the equa­ tions are given in their component form. The time derivatives refer to changes at a point fixed rela­ tive to the rotating Earth. The three dimensions o f the co-ordinate system are represented by x, y (the two orthogonal horizontal dimensions) and p (the vertical dimensions, atmospheric pressure). du — dt

du du du dd> , c - u —— v - -w —------- i r + It' + F dx dy dp dx *

(la )

dv dv dv dv d , c — = - u —— v -:---- w —-------i r - - j u * F dt dx dy dp dy >

(lb )

RT

d "

( 2)

P

err err err ( r t err\ h -— ■ - a —— v — + u > \------------- s- + — dt dx dy \ c f p dp) cf

(3)

du' ~dt

du dx

(4)

dq dt

dq I dp1

dv

dq Ar

dq\ dy J

(5)

Equations la -b represent the local tim e rate of change o f horizontal wind speed in the west-east

programme (see below and Table 14.2a). Sophis­ ticated remote sensing devices, including radiom e­ ters and atm osp heric sou nd ers, afford a wealth o f information on land and sea surfaces, clouds, and the three-dimensional distribution o f atmospheric temperature, humidity and composition (see Tables 14.2b c). Such observations provide an increasingly important supplement to Earth-based weather measurements and are now routinely integrated in N W P models.

(*) and south-north (v) directions. The first two terms on the right-hand side of each equation constitute the horizontal advection of the wind field; w is the vertical wind speed; is the geo­ potential, a measure o f altitude; / is the Coriolis parameter; Fx represent the effects o f friction. Equation 2 is the hydrostatic equation. It represents the vertical component o f atmospheric acceleration as a balance between the downward acceleration due to gravity and the upward acceleration due to the decrease o f atmospheric pressure with height. R is the gas constant for dry air. Equation 3 is the thermodynamic energy equa­ tion. The local time rate o f change o f temperature, T, is given in terms o f advection of the temper­ ature field, adiabatic energy transformations, and ‘in situ- diabatic energy changes; cf is the specific heat capacity o f dry air at constant pressure; H is the diabatic (sensible) heat term. Equation 4 is the continuity equation. It implies the conservation o f mass. The sum o f the terms inside the brackets on the right-hand side represent the horizontal stretching or squeezing o f the air. This is balanced by a vertical expan­ sion or contraction term on the left-hand side. Equation 5 represents the conservation o f mois­ ture. The local time rate of change o f specific humidity, q , is described in terms o f convection, advection o f the humidity field, and 'in situ' changes in the moisture content o f the air (C).

WEATHER FORECASTING TODAY In this section, the modern preparation of weather fore­ casts is explored in some detail, including the gather­ ing of weather observations, the use of computer-based weather models, the role of the meteorologist, and the range of forecast services available in the British Isles. Throughout, rhe reader should refer to Figure 14.4, which provides an overview of the weather forecasting process in the form of a flow diagram.

307

308

CLIVE PIERCE, MICHAEL DUKES AND GRAHAM PARKER

Figure 14.3 An infra-red image from NOAA 11, taken at 0340 GMT on 24 January 1990. A westerly air How- affects the British Isles on this day, categorised as *W in the Lamb Catalogue (see Appendix B). Supplied courtesy of the University of Dundee.

FORECASTING THE BRITISH ISLES WEATHER Table 14.2a Current operational meteorological satellites as of May 1995 Orbit

Satellites

Sun-synchronous Geostationary

NOAA 12, 14 Meteosat 5 (O'W), INSAT 2 (70*E), GMS 4 (140*E), GOES 7 (135‘W), GOES 8 (75‘W)

Table 14.2b Sun-synchronous meteorological satellites Launch

Satellite

Features

Measurements

1960-65

TIROS0 1-10 North American

Daylight cloud cover. Cloud top and Earth surface temperatures. Water vapour.

1964-78

NIMBUS l-VII North American

1966-69

ESSAb 1-9 North American

1970-76

NOAA' 1-5 North American

1979-81

NOAA 6, 7

1983-86

NOAA 8-10

1988-91

NOAA 11, 12

1993-94

NOAA 13, 14

2000

METOP 1 European

TV camera, Automatic Picture Transmission, five-channel radiometer. Three TV camera system, temperature-humidity, microwave radiometers. Amalgam of features from TIROS and NIMBUS series. Very High Resolution Radiometer. Vertical Temperature Profile Radiometer. Two satellites in the same orbit, ninety degrees apart, giving two passes per day. Advanced Very High Resolution Radio­ meter. TIROS Operational Vertical Sounder. Data Collection System. Similar to NOAA 6, 7. Earth Radiation Budget Experiment. Enhanced versions of NOAA 8-10. The AVHRR on NOAA 11 failed in 1994. Enhanced versions of NOAA 11, 12. NOAA 13 failed after launch. Enhanced imaging instruments, ana a high precision sounder.

Notes.0 Television and Infra-red Observation Satellite. b Environmental Science Services Administration. ' National Oceanic and Atmospheric Administration.

Day and night cloud cover. Vertical profiles of temperature, pressure and water vapour. Daylight cloud cover. Earth-atmosphere radiation balance. Day, night cloud cover. Water vapour. Vertical temperature profiles every 12 hours. Global cloud, ice and snow cover, day and night. Cloud top, Earth and seasurface temperatures. Vertical profiles of temperature and humidity. Receipt and distribution of Earth-based observations.

Similar to NOAA 6, 7. Energy exchange measurements for Earlh-atmosphere system. svsl (ar to NOAA 8-10. Similar

Similar to NOAA 11, 12. Global cloud cover, day and night. Land and sea-surface temperatures. Cloud-top temperatures. Vertical profiles of temperature and humidity. Cloud motion winds. Estimates of precipitation.

309

310

CLIVE PIERCE, MICHAEL DUKES A ND G R A H A M PARKER

Table 14.2c Geostationary meteorological satellites Measurements

Launch

Satellite

Features

1966-74

ATS° 1-6 North American

1974-78

SM Sb l-2/G O ESc 1-3 North American

1977-95

G M Sd 1-5 Japanese

1977-96

Meteosat 1-7 European

1980-87

G O ES 4-7

1983-94

INSAT 1-2 Indian

1994 - ?

G O ES NEXT 8-12 North American

1994-95

G O M Se 1-2 Russian

2000

M SG ! 1 European

Amalgam of features from Day, night cloud cover over visible Earth disc. Cloud top, earth surface TIROS and NIMBUS temperatures. Water vapour. series. Day, night cloud cover over visible Earth Two-channel Visible-Infrared Spin-Scan Radiometer. disc. Cloud top, Earth surface temperatures. Cloud motion winds. Data Collection System. Receipt and distribution of Earth-based observations. Similar measurements to those made by Two-channel Visible-InfraG O ES 1-3 satellites. red Spin-Scan Radiometer Addition of a water vapour channel on GM S 5. Data Collection System. Day, night cloud cover over visible Earth Automatic Picture Trans­ disc. Cloud motion winds. Cloud top, mission. Three-channel sea-surface temperatures. Water vapour. imaging radiometer. Data Receipt and distribution of Earth-based Collection System. weather observations. Similar to G O ES 1-3. Vertical temperature VISSR Atmospheric and humidity profiles. Sounder. Data Collection System. Data not freely available. Multi-purpose: tele­ communications, weather forecasting, search and rescue. Eighteen-channel radiometer. Similar to G O ES 4-7. Vertical temperature and humidity profiles measured at forty levels. Similar measurements to those made by Two-channel radiometer. G O ES 1-3 satellites. Addition of a water vapour channel on G O M S 2. Cloud cover and type. Fog and snow Radiometers with 16 cover. Cloud top temperatures. Cloud channels: 4 high motion winds. Sea- and land-surface resolution visible, temperatures. Detailed vertical profiles 6 infra-red, 2 water of temperature and humidity. Earthvapour, and 4 pseudo­ atmosphere radiation budget data. sounding.

Notes: ° Applications Technology Satellite. b Synchronous Meteorological Satellite. ' Geostationary Operational Environmental Satellite. d Geostationary Meteorological Satellite. • Geostationary Operational Meteorological Satellite. 1 Meteosat Second Generation.

FO R EC A ST IN G THE BRITISH ISLES WEATHER

Global data collection la u d

Sea

A ir

S p a t»

Figure 14.4 A schematic illustration of the modern-day preparation of weather forecasts.

The collection of weather data

(W M O ), a specialised agency o f th e U n ite d N a tio n s , as p a rt o f an o p e ratio n

W ith th e in tro d u c tio n o f th e e le ctric tele g ra p h in

term e d

W o rld

W ea th e r

W a tc h .14 T h e la tte r encom passes not ju st th e collec­

th e 184 0 s cam e th e first o p p o rtu n ity for th e collec­

tio n

tio n o f near re a l-tim e w e ath e r re p o rts from w idely

d isse m in a tio n a n d th e p rovision o f regional and

sep arated observers an d th e p o ssib ility o f g e n e ra tin g

g lo b al services by in d iv id u a l m em b e r c o u n trie s of

u p -to -d a te

th e U n ite d N a tio n s.

w e a th e r

m aps.

A

g ro u p

o f w eath er

o f w e ath e r d a ta ,

but

th e ir pro cessin g

and

w a tc h in g sta tio n s c o n n ec te d by te le g ra p h was first

T h e p rim a ry aim o f W o rld W ea th e r W a tc h is to

e sta b lish e d in th e B ritish Isles a n d France aro u n d

p ro v id e a re g u la r an d c o h ere n t rccord o f th e sta te o f

I 8 6 0 a n d o th e r dev elo p ed c o u n trie s soon follow ed

th e atm o sp h e re. T h is m u s t bc sufficiently d e ta ile d and

su it. T h u s b eg an th e w e ath e r m o n ito rin g n etw o rk

a ccurate to allow th e g e n e ra tio n o f useful w e ath e r fore­

th a t now covers a large p ro p o rtio n o f th e E a rth ’s

casts for w e ath e r sensitive o p e ratio n s on lan d , sea

surface.

is co­

a n d in th e air. C onsequently, th e sta n d a rd isa tio n o f

o rd in a te d by th e W o rld M ctcorological O rg a n isatio n

observational p ra ctic e is o f th e u tm o s t im p o rta n ce .

T h is

so-called

sy n o p tic

n e tw o rk

312

CLIVE PIERCE, MICHAEL DUKES AND GRAHAM PARKER T h e W M O provide detailed g u idelines on such m a t­

relative h u m id ity

ters and these include the location o f m ctcorological in stru m e n ts and th eir use, tim es o f observation and

betw een 20 and 30 km , tw ice daily a t 0 0 0 0 and

the order in w hich in stru m e n ts should be re ad .15

arc utilised to m easure cloud base h e ig h t and hig h a ltitu d e w inds. In com m on w ith surface w eather

and

w ind

up to a ltitu d e s of

1200 GM T. Sm aller balloons, called p ilo t balloons,

reports, these so-callcd up p er a ir observations arc

Surface weather observations

also reduccd to com pact coded messages for ease of

A t land-based synoptic w eather stations, m easure­

com m unication.

m en ts o f d ry -b u lb and w e t-b u lb tem p eratu re (the

The spatial coverage o f upper air observations,

la tte r for calcu latin g h u m id ity ), cloud am o u n t and

w hilst relatively dense over the B ritish Isles and

type, h e ig h t o f cloud base, w eather type, visibility,

o th er w ealthy countries, is very poor or non-existent

w ind directio n and speed, atm ospheric pressure, pres­

over substantial areas o f land and over th e sea. These

sure tendency and past w eather arc m ade at regular

large gaps in the upper air netw ork arc p artly filled

intervals. Frequency o f observation varies according

w ith

to the type o f sta tio n in q uestion. A irports, for exam ­

attached to civilian aircraft. U nfortunately, the latter

m easurem ents

m ade

by

au tom atic

sensors

p le, rep o rt th e w eather hourly, w hilst others m ake

tend to bc concentrated along the flight path s o f

m easurem ents only at w hat are term ed the m ain

th e m ajor airlines and arc prone to errors. Today, the

synoptic hours: 0 0 0 0 , 0 6 0 0 , 1200 and 1800 G M T .16

m ain sourcc o f w eather d ata in rem ote parts o f

In ad d itio n , th ere are also clim atological w eather

th e w orld is th e m eteorological satellite. D u rin g the

statio n s, usually run by a m a teu r m eteorologists, and

past three decades, satellite-based rem ote sensing

these m ake one observation a day at 0 9 0 0 GM T. O ver the sea, th e w eather is m on itored by m er­

As a consequence, w eather observations from space

ch an t sh ip p in g , a few specialised w eather ships, and

arc now of sufficient accuracy and reliability to bc

an increasing n u m b er o f u n m an n ed , in stru m e n ted

routinely

buoys w ith radio tran sm itte rs. N o t surprisingly, the

w eather satellites form

in te rp re ta tio n o f m arine w eather reports is som ew hat different to th a t applied to land-based reports. For

G lobal T elecom m unications N e tw o rk , facilitatin g

in stru m e n tatio n has becom e everm ore sophisticated.

used

in

NW P an

m odels.

F urtherm ore,

integral p a rt o f the

the exchange o f w eather data around th e E arth.

exam ple, an observation o f w in d speed and direction m ade on board a m oving ship m ust bc corrected for th e s h ip ’s m otion. T h e scarcity and uneven d istrib ­

Weather data dissemination and processing

u tio n o f w eather observations from sea areas have

It should be apparent by now th a t an enorm ous

long posed problem s for th e w eather forecaster -

q u a n tity of data is p o tentially available to the m ete­

m ajor w eather system s such as tropical storm s form over the sea, not over th e land. T he in tro d u c tio n of

orologist from th e array of sources outlin ed above. T he task of collating these data is evidently a huge

m eteorological satellites, however, has done m uch to

one. A t th e point of observation — w hether it be on

im prove th e situ atio n .

land, at sea, or in th e air - w eather reports m u st be reduced to com pact coded messages. These are then electronically tra n sm itte d , via satellite, radio or land

Upper air weather observations

line, to centres th a t co-ordinate th eir storage and su b ­

W eath er reports above g ro u n d level com e from a

sequent processing. Box 14.2 dem onstrates how a

variety

m ake

coded num erical w eather message can be deciphered

m easurem ents o f atm ospheric pressure, tem perature,

and p lo tted in sym bolic form , and Figure 14.5 shows

of

sources.

R adiosonde

balloons

Figure ¡4-.5 A plotted surface weather chart for 0800 GMT, 4 October 1995. This day is categorised as ‘CS’ - cyclonic southerly air flow - in the Lamb Catalogue (see Appendix B). Reproduced courtesy of the UK Met. Office.

FORECASTING THE BRITISH ISLES WEATHER

313

314

CLIVE PIERCE, MICHAEL DUKES AND GRAHAM PARKER

BOX 14.2 PLOTTING WEATHER CHARTS W eather observations are transm itted to N ational M eteorological Centres in the form o f coded messages com prising strings o f five figure num bers. T he structure of these messages is internationally agreed so th at the inform ation they contain can be decoded by anyone w ith a knowledge o f the relevant codes. An excerpt from a coded message com piled by a land-based w eather station in the U nited K ingdom is shown below. A brief explanation o f each five d ig it group is provided beneath. 03853 4 1 4 8 0 62213 10106 20041 40007 52020 70381 84901 0 3 8 5 3 International index num ber 03 - B ritish Isles, 853 - station number. 4 1 4 8 0 4 - N o rainfall data included in message, 1 - present w eather included in message, 4 coded height o f lowest cloud 3 0 0 -6 0 0 m , 80 - visibility 8 0 -5 0 = 30 km. 6 2 213 6 - Total am ount o f cloud observed = 6 eighths, 22 - wind direction 220°, 13 - speed 13 m ph. 10106 1- Indicator, 0 - sign is positive, 106 - dry-bulb tem perature 10.6°C. 20041 2 - Indicator, 0 sign is positive, 41 - dew -point tem perature 4.1°C. 40007 4 - Indicator, 0007 - sea-level pressure 1000.7 hPa. 5 2020 5- Indicator, 2 - pressure characteristic 'increasing', 020 - pressure tendency = 2.0 hPa. 70381 7 - Indicator, 03 - present w eather = clouds developing, 81 - past weather = showers, partly cloudy. 84901 8 - Indicator, 4 - 4 eighths of cloud at 3 0 0 -6 0 0 m , 9 - low-level cloud = cum ulonim bus w ith anvil top, 0 - no m edium -level cloud, 1 - high-level cloud = cirrus or 'm ares' tails'. These coded w eather reports are norm ally displayed on charts in sym bolic form. T he above message would be draw n like this:

)

dry bulb tem p.

4

d ew p o in t tem p.

V

v isib ility 30km



007 * 2 0 /

» "i J

80 007

l

?

11

su r fa c e pressu re: 10 0 0 .7 hPa

6 /8 to ta l clou d w ind : 220° 13m ph > c ir ru s

a V

20/

c u m u lo -n im b u s past w eather: sh ow ers p r e ssu re ten d en cy: r isin g - 2.0 hPa

Figure 14.5 shows a plotted surface weather chart for 4 O ctober 1995. T he m eteorologist would norm ally draw isobars, and w eather fronts on this. In addition, significant features such as precipi­ tation may be h ighlighted in colour, tim e perm itting.

FORECASTING THE BRITISH ISLES WEATHER

a p lo tte d surface w eather m ap for 0 8 0 0 G M T on

and the spacing betw een successive grid points, both

4 O c to b er 1995. Each station circlc and its associated

in the horizontal and the vertical, w ill de te rm in e the

sym bols represents a separate w eather observation.

scales o f m otion th a t can be resolved. Evidently, the by

issue o f m odel resolution is o f fundam ental im p o r­

in

tance to th e w eather forecaster. I f th e spacing o f grid

tu rn , pass th e ir inform ation via the G lobal Tele­

points is too coarse, then atm ospheric disturbances

c o m m u n icatio n N e tw o rk to W orld M eteorological

having a significant im pact on daily w eather may

C entres. U n d e r W M O guidelines, th e three W orld

not bc m odelled effectively. O n the o th er hand, if

D ata N a tio n a l

collcction

ten d s

M ctcorological

to

bc

C entres

co-ordinated and

these,

M eteorological C entres - M oscow, W ashington and

th e resolution is too fine, then th e m odel m ay bc too

M elbourne — have the

responsibility o f issuing

slow or too costly to run given th e lim ita tio n s on

w eather analyses an d forecasts on a global scale.

c o m p u tin g power. In reality, th e choicc o f resolution

T hese p ro d u cts arc used by a larger n u m b er o f

is always a com prom ise, arrived at by considering

R egional and N a tio n a l M eteorological C entres in the

such factors as th e area covered by th e m odel, the

p reparation o f w eather forecasts for th e ir designated

m in im u m scale o f features th a t m ust bc resolved and

regions o f th e E a rth .17

th e pow er and affordability o f available co m p u ter resources. T he behaviour o f synoptic scale features o f the

NUMERICAL WEATHER PREDICTION MODELS

w eather, such as th e m id -la titu d e depression, is g en ­

M eteorologists first experim ented w ith com puter-

phenom ena, for exam ple p o la r lo w s, are treated less

based num erical w eather p re d ic tio n m odels in the

well, however, because they cover fewer grid points. It

1940s. Since th en , c o m p u te r technology has advanced

follows th a t atm ospheric disturbances w hose charac­

erally well represented by N W P m odels. Sm aller-scalc

to such an e x te n t th a t these h ith e rto scarce and costly

teristic dim ensions are less than the m odel grid

tools are now becom ing m ore com m onplace. T hey are

spacing w ill be unresolvable. Such features may, none

used to m ake pred ictio n s o f atm ospheric behaviour on

th e less, be im p o rta n t to th e w eather forecaster.

a w ide range o f space and tim e-scales, from the

Showers fall in to th is category. T h e effects o f these,

m in u te to m in u te g ro w th and decay o f individual

and o th er so-called sub-grid scale features o f the

clouds, to global changes in clim ate over m illennia

atm osphere, are sim ulated using an approach called

(see C hapters 15 and 16).

param eterisation. In short, this is a m eans o f e stim a t­

T h e m ajority o f operational N W P m odels used in

ing the average effects o f these processes using large-

day-to-day w eather forecasting are w h at are term ed

scale m odel variables. Some o f th e m ost im p o rta n t

g rid -p o in t m odels. In these, th e atm osphere is repre­

param eterisations are those concerned w ith b o u n d a ry

sented by a n u m b er o f vertical layers, each o f w hich

lay e r processes, the developm ent o f cloud and p re cip ­

contains a n etw ork o f g rid poin ts fixed relative to

itatio n , convection, radiation, and g ra v ity w av es.

th e E arth ’s surface. Each g rid p o in t is assigned

In order to represent the physical state o f the

certain values describ in g th e state o f th e atm osphere

atm osphere, a N W P m odel m u st be able to repre­

a t th a t location and these values arc assum ed to bc

sent three basic properties: atm ospheric m ass, m otion

representative o f th e rectangular box o f air or parcel

and m oisture. T he way these q u a n titie s are m easured

su rro u n d in g th e g rid p oint. W h en th e m odel is run,

in th e real w orld differs from th e way they are repre­

tim e advances in a series o f discrete steps. A t each

sented

step th e com plete set o f physical equations governing

observer m easures m oisture in the atm osphere w ith a w e t-b u lb th erm o m eter or hygrom eter. From this,

atm ospheric behaviour is used to de te rm in e a new

in the m odel. For exam ple, the w eather

state o f th e atm osphere. In rhe real atm osphere, m otion occurs on a wide

a d e w - p o in t te m p e r a tu r e can be derived and this

range o f scales from th e m olecular to th e synoptic

present in th e air. In N W P

is an indirect m easure o f th e a m o u n t o f w ater vapour however, m oisture

315

316

CLIVE PIERCE, MICHAEL DUKES AND GRAHAM PARKER c o n te n t is represented explicitly as specific hum id ity , th e m ass o f w ater per u n it m ass o f dry air.

th e Cray C 90 - w hich is capable o f perform ing sixteen billion floating point calculations every

T o,com plicate m atters further, a d istin c tio n m u st

second. For daily w eather forecasting, th e operational

be draw n betw een variables directly represented in

forecasting m odel can run in tw o different form ats:

a m odel and those diagnosed for use w ith in it.

G lobal and L im ited Area. These are norm ally referred

C o n tin u in g w ith the exam ple o f m oisture, cloud w ater and p re cip ita tio n are diagnosed from th e

respectively.

p rim ary m odel variable, specific hum idity. Conse­ q uently, th e form er are said to be d iagnostic vari­

As its nam e im plies, the LAM confines its repre­ sentation o f the atm osphere to a sm all fraction o f the

ables, w hilst th e la tte r is referred to as a p rim ary

globe: the n orth A tlan tic and w estern Europe. T his

p rognostic variable. T he basis o f num erical w eather

is th e area o f relevance to w eather forecasters in the B ritish Isles since the m ajority o f our w eather o rig ­

forecasting is the p red ictio n o f changes in m odel p rognostic variables over tim e. From these p redic­

to as the G lobal and L im ited Area M odels (LAM)

tions, cloud, p re cip ita tio n , surface tem p eratu re and

inates over the A tlantic. U nlike the G lobal M odel, th e LAM has clearly defined boundaries beyond

o th er q u a n titie s necessary for th e p reparation of

w hich th e state o f the atm osphere is undefined. To

w eather forecasts m ay be diagnosed. T h e com plete

prevent

set o f p rognostic and d iagnostic form ulae coded in to

m argins o f th e m odel area, it m u st be provided w ith

a N W P m odel represent a synthesis o f the equations g ov ern in g large-scale atm ospheric m otions. These

w hat are term ed boundary conditions from the latest

e quations are often referred to as the p rim itiv e equa­ tions and are sum m arised in Box 14.1. Before a N W P forecasting m odel is ru n , it m u st bc su p p lied w ith in form ation on th e cu rre n t state of

it from

behaving

unpredictably

at

the

G lobal M odel run. Table 14.3 presents som e sum m ary statistics on the tw o m odels. Both divide th e atm osphere into nineteen horizontal layers. T h e vertical resolution o f

th e atm osphere, a process referred to as d a ta assim ­

these layers is greatest at the surface for th e reason th a t m ost o f the rapid variations in atm ospheric

ilation. W eather observations collected as p a rt o f the

processes occur w ith in th e boundary layer. H o ri­

W M O W orld W eath er W atch program m e are used

zontal resolution is defined by a la titu d e -lo n g itu d c

for th is purpose. D espite th e im provem ents in data

co-ordinate system . In the G lobal M odel th is varies

coverage afforded by w eather satellites, geographical ‘holes’ in m odel-assim ilated observations still exist.

m arkedly w ith latitu d e , betw een about 70 km at

T hese are filled in w ith so-called background fields

can only resolve the largest scales o f atm ospheric

from earlier m odel runs. T h e proccss o f d a ta assim ­ ilation can bc envisaged as th e b len d in g of received

m otion w ith any degree of accuracy. In th e LAM however, th e co-ordinate system is artificially rotated

observations o f the real atm osphere w ith these back­ g ro u n d fields in such a way th a t an objective best

so th a t th e m ore evenly spaced lines o f latitu d e and long itu d e found on the E quator are positioned over

estim ate o f th e tru e sta te o f th e atm osphere is

th e m odel area. T h is feature, couplcd w ith a finer

achieved.

horizontal resolution (about 50 km ), p erm its the

60°N and 140 km on the Equator. C onsequently, it

LAM

The United Kingdom Met. Office unified model T h e U K M et. Office runs a su ite o f g rid -p o in t-

to

sim ulate

th e

day-to-day

developm ent

and decay o f synoptic-scalc w eather system s m ore effectively. W eather observations from th e W orld W eather

as the

W atch are in p u t into the U nified M odel using a

U nified M odel. T h is com prises an operational fore­ casting m odel, and ocean and clim ate m odels, and

continuous data assim ilation cycle. T h is involves repeatedly in sertin g the latest reports in to the

can be used in a variety o f m odes. T he software

evolving m odel. T h e benefit o f such an approach is

runs on an extrem ely pow erful super-com puter —

th a t th e m odel atm osphere is regularly nudged

based

NW P

m odels

collectively

know n

FORECASTING THE BRITISH ISLES WEATHER Table 14.3 Summary statistics for the UK Met. Office Unified and Mesoscale Models0 Model characteristic

Global

Limited Area

Mesoscale

Coordinate system

Lat./Long.

Rotated pôle Lat./Long.

Equatorial Lat./Long. fine mesh

Resolution: Rows/columns Grid points per level Levels/levels with moisture Total grid points Grid point spacing W-E Grid point spacing S-N Grid length at 60*N/140*W

217/288 62,496 19/16 1,187,424 1.25" longitude 0.83‘ latitude 70 km/140 km

132/229 30,228 19/16 574,332 0.4425* longitude 0.4425* latitude Average: 50 km

92/92 8,464 31/28 262,384 0.15* longitude 0.15* latitude Average: 16.8 km

Time-step: Physicsb Dynamics'

20 min. 10 min.

15 min. 5 min.

5 min. 1 min. 40 s

Notes: ° All information on this page appears courtesy of the UK Met. Office. b The time-step between model evaluation of parameterisations, e.g., convection, precipitation, etc. c The time-step between successive solutions of the fundamental equations.

towards the state o f the real atm osphere, whilst m aintaining its internal consistency. In addition, assim ilation of data on a continuous cycle obviates the need for a separate initialisation tim e-step. The Global Model runs on a six-hourly assim ilation cycle, the LAM on a three-hourly cycle. A part from the Unified M odel, the Met. Office also runs a num ber o f other w eather models, the m ost

o f the atm osphere, unlike the grid-point-based Unified Model of the U nited K ingdom Met. Office. O ne obvious drawback w ith grid point models is their representation of continuously varying fields of pressure, tem perature or hum idity by discrete points. Spectral models g et round this problem by depicting these same horizontal fields in term s of finite sums of certain functions, called sp h e ric a l

notew orthy o f which is the Mesoscale Model (see Table 14.3). T his short range, high resolution N W P m odel is designed to provide detailed weather predictions for the B ritish Isles for up to thirty hours

h a rm o n ic s. Much of the research into m edium range weather

ahead. Its use in practical w eather forecasting will be m entioned later.

The ECMWF and spectral numerical models T he European C entre for M edium -range W eather Forecasting (ECM W F) based near Reading in Berkshire is an intergovernm ental organisation whose responsibility is to undertake research into N W P , the prim ary aim being to improve weather forecasts in the m edium range (four to ten days ahead). T he C entre runs an operational weather fore­ casting model w hich uses a spectral representation

forecasting done at the ECM W F is concerned w ith ensem ble num erical weather prediction.18 T his approach involves the m ultiple running of an N W P model for the same forecast period. In each run, the m odel’s starting conditions are slightly modified and, as a result, a range of different forecasts - called an ensem ble - is produced. In this way the m eteorolo­ gist may get some idea of how sensitive is the current weather situation to subtle shifts in atm ospheric state. It is a peculiarity of the atm osphere th at in certain situations its behaviour is inherently more predictable than in others. Ensemble forecasts can help to identify these more predictable states and afford some means of assessing the reliability o f in d i­ vidual model predictions.

317

318

CLIVE PIERCE, MICHAEL DUKES AND GRAHAM PARKER PRACTICAL WEATHER FORECASTING: THE HUMAN-MACHINE MIX From th e preceding discussion one m ig h t be under th e false im pression th a t in th is age o f num erical w eather p re d ic tio n rhe h um an w eather forecaster is largely red u n d an t. Far from it. C o m p u te r m odels, for all th eir soph isticatio n , are still generally unable to produce w eather forecasts in a form th a t is both m eaningful and relevant to th e lay person. O ne o f the p rin cip al tasks o f m eteorologists is ro use th eir know ledge and experience of wearher, p articularly w ith

regard

to

its

idiosyncrasies

in th e ir local

Nowcasts W eather forecasts for the period ra nging from a few m in u tes to about six hours ahead are often referred to as nowcasts. H ere, m eteorologists tend to rely heavily upon a detailed analysis of c u rren t w eather observations (see Box 14.2 and Figure 14.5) and the visual inform ation afforded by satellite im agery and rainfall radar (if th is is available). T h e essence o f the now cast is an extrapolation-based p rediction rhar assum es areas o f significant w eather w ill co n tin u e to move at m ore or less th e sam e speed and w ith little change in th e ir e x te n t or severity in the near future.

area, to provide an in te llig ib le forecast tailored to

Such an assum ption is valid unless certain features

cu sto m ers’ needs. T hus, ideally, w eather forecasting

o f th e cu rre n t w eather, or short range num erical

is an am algam o f the q u a n tita tiv e p redictive skills

m odel guidance, indicate otherw ise. For exam ple, the

o f N W P m odels and th e accum ulated w isdom o f the

pa tte rn o f pressure tendencies occurring over th e last

train ed m eteorologist. T h is is som etim es referred to

three hours is a valuable ind icato r o f likely future

as the h u m a n -m a c h in e m ix.

changes in the d istrib u tio n o f pressure and therefore

W h e n a w eather forecaster arrives for w ork, his or

the developm ent or decay o f w eather system s. Such

her first objective is to b u ild up a com prehensive,

indicators can bc com pared w ith d etailed, sh o rt range

m ental p ic tu re o f cu rre n t w eather conditions and

w eather predictions m ade by mesoscale m odels. If

th eir recent evolution in th e relevant geographical

e ith e r suggest the rapid developm ent or decay o f a

region. T h is w ill involve close exam ination o f surface

w eather system , then the linear extrapolation fore­

(e.g., F igure 14.5) and u pper air w eather charts to identify areas o f significant w eather, for exam ple,

cast m ay have to be am ended accordingly.

cloud and rain o r stro n g w inds. These features may

Short range weather forecasts

th en be placed w ith in th e broader w eather picture afforded by satellite pictures and num erical m odel

O th e r N W P m odels, such as the M et. Office U nified

forecasts. T h e detailed m ethodology em ployed by a

M odel, arc em ployed in the preparation o f w eather

m eteorologist in th e p reparation o f a w eather fore­ cast on a given day w ill vary considerably according

forecasts for betw een one and five days ahead. T he

to th e c u rre n t w eather situ atio n , th e range o f the

m odels m u st be significantly larger to account for

extent o f th e E a rth ’s atm osphere represented by these

forecast, the custom er for w hich th e forecast is

th e g reater distances m oved by w eather system s

in ten d ed and the tim e available. For exam ple, a short

d u rin g th e period o f th e forecast. For exam ple, a

range w eather forecast for holiday-m akers on a dry,

depression form ing off the coast o f N ew foundland

sunny day in sum m er, is likely to bc m uch easier,

can be over th e B ritish Isles tw o to three days later.

and o f less significance, th an a fo rty -eig h t-h o u r pred ictio n for th e offshore oil in d u stry d u rin g a wet

T he need to m odel a larger volum e o f atm osphere poses constraints on m odel resolution. T h e latter

and storm y w inter. T here is insufficient space here

tends to be coarser in an effort to lim it th e run tim e

to give a p roper explanation o f th e p lethora o f fore­

and cost o f m odel operation. T he result is th a t m odel

casting techniques used. Instead, a general descrip­

o u tp u t is less readily transposed in to useful forecasts.

tion

p red ictio n s for one ho u r to one m o n th ahead are

It is here th a t th e know ledge and experience o f the hum an forecaster com es in to play. For exam ple, given

discussed.

forecast fields o f atm ospheric pressure, tem perature

o f m ethods

em ployed

in

m ak in g

w eather

FORECASTING THE BRITISH ISLES WEATHER

and hum id ity , and an in dication o f th e e x te n t and

tim e-scales of a season or m ore, particularly in tro p ­

severity o f any atm ospheric instability, a trained

ical latitudes.

m eteorologist w ill be able to infer the sort o f w eather th a t can be expected over th e period o f th e m odel

U n til q u ite recently, th e m ost com m on long range (up to one m o nth ahead) w eather forecasting tech­

forecast.

nique

involved

the

use

o f w eather

analogues.

Initially, th is entailed try in g to find periods o f past

Medium range weather forecasts T h e reliab ility o f indiv id u al N W P m odel forecasts

w eather th a t were analogous to th e current w eather over w estern Europe and th e no rth A tlantic. T he forecast for th e com ing weeks w ould th en bc based

falls off w ith increasing lead tim e. Beyond about

upon the w eather follow ing th e historical analogue.

three days th e ir w orth m ay only be lim ite d to general

T h e sorts o f d ata used in m aking the com parison

g uid an ce on fu tu re w eather trends, alth o u g h this is

included

not always th e case. In th e last ten years or so som e

h e ig h ts . G iven th e vast q u a n titie s of archived data,

im provem ent in th e q u a lity o f w eather forecasts

and the availability o f high-pow ered com puters, th is

betw een about four and ten days ahead (m edium

approach could generate a range o f good analogues

range forecasting) has been achieved w ith the aid of

for a variety o f current w eather situations.

ensem ble N W P techniques. T h e m u ltip le ru n n in g o f a num erical m odel to reflect a p lausible range o f

D u rin g

m ean

the

sea-lcvcl pressure and

1970s

analogue

500

techniques

hPa

were

im proved by the use o f w hat were term ed predic­

initial atm ospheric states allow s a skill score to be

tors.20 These were groups o f w eather analogues for

assigned to individual m em bers in th e ensem ble. If

particu lar types o f extrem e event. For exam ple, if one

th e forecasts so produced are seen to converge, th en som e confidence can be placed in the value o f in d i­

w anted to forecast w h eth er Ju ly was g o in g to be wet

vidual m odel predictions. O n the o th e r h and, if they

selected ‘ from a data archive. C om posite 5 0 0 hPa

appear to diverge, th en this m ay indicate a less

charts o f the preceding Ju n es were then draw n for

p redictable atm ospheric state. In this la tte r case,

each case. S ubtraction o f th e tw o com posites gave a

individual m ed iu m range forecasts arc likely to be

difference chart and these differences were tested for

view ed w ith som e scepticism and w eather forecasts

statistical significance. T h e Ju n e chart for th e current

w ill be w orded to reflect th is uncertainty.

year could then be exam ined in th e significant areas

or dry, data for ten w et and ten dry Ju ly s w ould bc

to see w hether it was m ore like a Ju n e preceding a

Long range weather forecasts G iven op tim al atm ospheric conditions, the lim it of p re d ic ta b ility o f daily w eather is theoretically about

wet or a dry July.

WEATHER SERVICE PROVISION

tw o w eeks.19 Beyond th is, objective tests indicate th a t skill is no longer present in daily forecasts. A t

M any o f our w ork and leisure activities are sensitive

first glance, it m ig h t seem som ew hat contradictory

to th e w eather, and th is susceptibility is reflected in

to suppose th a t rhe atm osphere is at all predictable

the w ide range of forecast p roducts and services avail­

beyond this d e te rm in istic threshold. T h e lim it o f

able to th e public and com m erce. In the U nited

atm ospheric p re d ic ta b ility for certain types o f c ir­

K ingdom , p ublic sector w eather forecasts and related

culatio n , however, is significantly longer than for

u tilities are provided by th e M et. Office, whose head­

others. C onsequently, on occasions, th is threshold

quarters are located in Bracknell, Berkshire. T he Irish

m ay be m u ch g re ater than th e average value o f tw o

M et. Office assum es a sim ilar role in Ireland. P ublic

weeks. A t a m ore fundam ental level, slow fluctua­

services can be grouped into three broad categories.

tions in se a -s u rfa c e te m p e r a tu r e may im p a rt a

First, there are du ties perform ed for th e public

longer range p re d ic ta b ility to th e atm osphere on

good'. T hese include essential forecasts connectcd

319

320

CLIVE PIERCE, M ICHAEL DUKES A ND G R A H A M PARKER

Table 14.4 The range of commercial weatfier services provided by the UK Met. Office Service

Media

Description

Television

Radio Newspapers

Telephone/Fax

MIST

Transport

A ir

Sea Land

Primary industry

Offshore

Water

Agriculture and forestry

Utilities

Construction/ Engineering

Energy

Regional and national weather forecasts on BBC and ITV. A business unit, International Weather Productions (IW P), is involved in the selection and training of ITV presenters, and the development of the advanced computer graphics used in the presentations. Television weather broadcasters also read forecasts on the radio for the BBC and Independent stations. The Press & Distribution Unit (PDU) at the Met. Office is responsible for the issuing of weather forecasts to the Press. Most daily Newspapers publish a weather forecast of some description, often accompanied by a weather chart. The PDU also has responsibility for preparing Telephone- and Faxbased weather forecasts. Weathercall and Marinecall are premium rate telephone services. MetFAX is a dial-up Fax forecast aimed at private aviators, mariners, and educational establishments. The Meteorological Information Self-briefing Terminal (MIST) is a PCbased weather information system for downloading and viewing up-to-the-minute actual and forecast meteorological information. AIRMET is a weather forecast aimed at aviators, Dalloon operators, gliding and parachute clubs. Other products include Terminal Aerodrome Forecasts (TAFs), Meteorological Aerodrome Reports (METARs), and Significant Weather charts (SIG W X). The last of these provides guidance on the location and strength of jet streams, cloud, and severe weather to international aviation. METROUTE is a ship routeing service intended to help shipping operators avoid damage to marine craft caused by severe weather. OpenRoad, OpenBridge, OpenRoadFreight, OpenRail, and OpenRunway are services designed to help maintain the free flow of traffic during bad weather. Advanced warning of severe weather can help the relevant authorities minimise the effects on transpor­ tation. OpenRoad makes use of a Road Ice Prediction model that forecasts minimum road surface temperatures. The extraction of oil and gas in the North Sea is highly weather sensitive. Here the requirement is for the forecast of wind, wave height and frequency, and 'weather windows' when seas will be calm enough for major operations such as the installation of rigs. Real time rainfall radar images, and forecasts (Nimrod) are used by the Environment Agency in river flow forecasting, and pollution control. Five day precipitation forecasts and heavy rainfall warnings can help minimise the risks of flooding. The Rainfall and Evaporation Calculation System (MORECS) can be used to assess water balance. Forecasts of crop yields, crop disease risk, growing days, and Lamb wind-chill are available. Other services include FARMPLAN, FARMCALL. SITEPLAN, SITESUPPORT are consultancy services geared to facili­ tating the design and construction of buildings. FORESITE and SHORESITE supply site-specific weather forecasts for inland and coastal engineering projects respectively Electricity generators use forecasts of electricity demand up to ten days ahead. These are based upon predicted maximum and minimum temperatures, wind speed and direction, and rainfall. Early warnings of lightning, snow and ice accretion, and strong winds are produced to help organise the maintenance of power lines.

FORECASTING THE BRITISH ISLES WEATHER Table 14.4 The range of commercial weather services provided by the UK Met. Office Service

Description

Manufacturing and retail distribution

Professional

Legal

Recreation

Sport, travel and tourism

The Weather Initiative (TWI) is a business unit concerned with the provision of tailored weather forecasts and consultancy services for those involved in the sale and distribution of goods. Weather Sensitivity Analysis (WSA) can identify retail products whose sales are weather dependent. This information may be used as an objective basis for stock control management. BasicProof, ExtraProof and TotalProof are services designed to produce site-specific weather information and consultancy for the legal profession. For example, the weather is often implicated in insurance claims e.g., storm damage to buildings. World and European city weather forecasts. WSA based demand forecasts for caterers. Weather forecasts, warnings, and climate statistics for those planning outdoor events. MORECS Irriplan Weatherfax for the maintenance of courses and pitches.

w ith p ublic safety, such as th e N a tio n a l Severe

Finally, there is a w ide, and expanding, range of

W eather W arning and Storm T ide W arn in g services.

services available to custom ers on a com m ercial basis.

In a d d itio n , th e Office is required to notify th e p ublic

E xcluding revenue from national and international

o f p o ten tially dangerous atm ospheric p o llu tio n inci­

aviation, the m ost lucrative com m ercial services are

dences. E nquiries and com plaints can bc addressed

those produced for th e m edia, in p articular television

to an E nquiries Officer based a t th e M et. Office head­

and radio. N ex t in order o f revenue-earning po ten tial

quarters. O th e r u tilitie s considered to be in the

arc w eather forecasts for the so-called u tilitie s —elec­

national in te rest’ also fall in to th is category. For

tricity generators, the construction industry, m an u ­

exam ple, th e M et. Office provides m ctcorological

facturers and retail distrib u to rs. Services for land

su p p o rt to th e arm ed forccs. T h e M obile M ctcoro­

tran sp o rt, th e offshore oil and gas industries and a g ri­

logical U n it supplies w eather forecasts for m ilitary

c u ltu re are also valuable incom e generators. A brief d escription of the sorts o f w eather inform ation su p ­

exercises, b oth in th e B ritish Isles and overseas, and is regularly involved in th e su p p o rt o f operations

plied by the U n ited K ingdom M et. Office to these

u nder th e directio n o f th e U nited N ations.

and oth er custom ers can bc found in Table 14.4.

A second category o f services is concerned w ith

O ne cannot present a balanced view o f w eather

the M et. O ffice’s role as a m em ber o f th e W M O .

service provision in the B ritish Isles w ith o u t som e

O n e o f its responsibilities here is th e issuing o f w arn­

m ention o f the increasingly im p o rta n t c o n trib u tio n

ings in th e event o f in te rn atio n al environm ental

m ade by the private sector. T h e largest private

disasters, such as th e nuclear accident th a t occurred

w eather consultancy in the B ritish Isles is O cean-

at C hernobyl in th e U kraine in 1986. O th e rs include

routes (U K ) L td .21 Based in A berdeen, th is A m erican-

prep arin g w eather forecasts for in tern atio n al civil

ow ned com pany is ideally located to service the needs

aviation. T h e C entral Forecast Office a t the M et.

o f the offshore oil and gas industries in th e N o rth Sea.

Office is a W orld Area Forecast C entre. O ne o f its

T his w ork, to g eth er w ith its ship ro uteing business,

m ain d u tie s in th is capacity is to producc significant

provides th e m ajority o f its revenue, a lth o u g h in

w eather (S IG W X ) charts for international flights.

recent years O ceanroutes has broadened its operations

T hese enable aircraft to avoid severe w eather — for

to include th e provision o f land-based services such

exam ple, th u n d ersto rm s — or to m ake use o f strong

as w in ter road ice p rediction. H ere, it is in direct

w inds to save fuel on long distance flights.

com petition w ith the M et. Office. T h e W eather

322

CLIVE PIERCE, MICHAEL DUKES AND GRAHAM PARKER

D e p artm en t specialises in w eather forecasting for

one, relying upon everm ore sophisticated w eather

television and holds a n u m b e r o f im p o rta n t contracts,

satellites and radars, global telecom m unications and

in clu d in g w eather p resentations for C entral Tele­

som e o f the w orld's fastest supercom puters. W h at

vision, the M idlands-based division o f th e In d ep en ­

used to be a relatively low key operation is now a

d e n t T elevision (IT V ) com pany. Its success has led it

hig h profile business affecting m illions o f people in

in to c o m p e titio n w ith th e U n ited K in g d o m M et.

tod ay ’s affluent and increasingly m obile society. T he

Office in a bid to w in im p o rta n t contracts such as national television w eather broadcasts. N obel D enton

ever-grow ing dem ands on w eather services reflect

W eath er Services is a n o th er im p o rta n t co m p e tito r in

w eather forecaster’s failure to provide tim ely and

th e com m ercial w eather forecasting sector, alth o u g h

accurate w eather predictions. In looking to th e future

m u ch o f its w ork is based o utside B ritain.

of w eather forecasting, one cannot just be concerned

A lth o u g h th e rem ain in g private sector organisa­

th e increasing costs to com m erce and industry o f the

w ith

issues such

as the

lim its

to

atm ospheric

tions have m u ch sm aller annual turnovers, they too

p red ictab ility and the c hanging role o f th e hum an

have th e ir niches in th e sphere o f w eather consul­

forecaster. From an econom ic sta n d p o in t, it is im p o r­

tancy. For exam ple, W eath er A ction specialises in long range w eather pred ictio n ; B ritish W eather Ser­

ta n t to consider the future o f an in d u stry whose rapidly rising costs d icta te its increasing involvem ent

vices and the P h ilip E den W eather C onsultancy

in com petitive com m ercial ventures, b u t w hose very

provide w eather forecasts for th e m edia; and W eather

existence depends upon a fragile g e n tle m e n ’s agree­

W atch e rs’ expertise lies in th e supply o f road w eather

m en t allow ing th e free exchange o f w eather data

in form ation in Scotland.

around the w orld.

It should be ap parent by now th a t w eather fore­ casts play a crucial role in m any aspects o f our

Figure 14.6 illustrates how errors in th e U nited K ingdom M et. O ffice’s global forecasting m odel have

daily lives. W ith o u t th em , o u r advanced civilisation,

changed over th e period. It is apparent th a t tod ay ’s

d ep en d e n t as it is on rapid, efficient com m unications,

7 2 -h o u r num erical w eather predictions are about as

could not fun ctio n as well as it does. In recent

accurate as th e ir 2 4 -h o u r counterparts were in the

decades increasing pressure on N atio n al M eteoro­

early 1970s. T he question arises w hether future tech ­

logical C entres to provide value for m oney has

nological progress w ill co ntinue to b rin g accom pa­

encouraged a tte m p ts to qu an tify th e econom ic and

nying im provem ents in th e accuracy o f num erical

social benefits o f reliable w eather forecasts. In the

w eather forecasts. T he U nited K ingdom M et. Office

U n ited K in g d o m , it has been estim ated th a t w eather

aim s to reduce present errors in 2 4-hour N W P by

forecasts save com m erce as m uch as £ 6 0 0 m illion per

a fu rth er 10 per cen t in th e next few years.23 T his

year.22 A b o u t tw o -th ird s o f th is is a ttrib u te d to

im provem ent is expected to be a consequence of

savings in th e co n stru ctio n and tran sp o rt sectors

progress in three d istin c t areas. First, cu rre n t w ork

o f th e econom y, th e rem ain in g th ird to savings in

on param eterisation schem es prom ises to refine the

ag ric u ltu re and energy production.

representation o f su b -g rid scale processes - such as radiation balance and cloud and precip itatio n form a­ tion - in num erical m odels. Second, the in tro d u ctio n

WEATHER FORECASTING: THE FUTURE

o f h ig h er resolution im agers and sounders on w eather satellites launched d u rin g th e rem aining years o f

T h e last three decades have seen enorm ous advances

th e 1990s and early next century is a n ticip ated to

in rem ote sensing, telecom m unications and elec­

im prove the accuracy and spatial coverage o f w eather

tro n ic co m p u tin g . These developm ents have radically changed th e practice o f w eather forecasting. W h a t

observations

assim ilated

in to

num erical

m odels.

Finally, the com putational capacity o f supercom ­

was once a m anually intensive, technologically p rim ­

puters is expected to increase w ith th e tran sitio n

itive process has now becom e a h ighly au tom ated

from conventional co m p u ter processors to Massively

FORECASTING THE BRITISH ISLES WEATHER

New mode! introduced

New model introduced

Figure 14.6 Errors in rhe IJK Met. Office’s global forecasting model, 1970 to 1994. T+24, T+48 and T+72 refer to forecast made for 24 hours, 48 hours and 72 hours ahead, respectively. Reproduced courtesy of the UK Met. Office.

Parallel Processors. A t th e m o m e n t, supercom puters

accuracy. H ere m eteorologists are divided. Some

used in N W P can do as m any as ten thousand

believe th a t the m ost fru itfu l way forw ard is to

m illio n ( 1 0 l°) a rith m etic operations per second. By

co ntinue the current tren d tow ards ru n n in g h igher

early next century, it has been suggested th a t this

resolution, everm ore com plex g rid -p o in t m odels.

figure could increase by five orders o f m ag n itu d e to

O th e rs th in k th a t this w ould bc a waste o f techno­

around one thousand billion (1 0 15) operations per

logical resources and th a t w eather forecasting w ould

second.2'* M eteorologists believe th a t th is g ro w th in

be b e tte r served if th e em phasis was placed on

processing pow er w ill allow ro u tin e runs o f h igher

p roviding an indication o f the reliability o f N W P

resolution g rid -p o in t m odels and th e extension o f

forecasts. T h is m ig h t bc achieved by fu rth er devel­

ensem ble-based forecasting m ethods to consider a

o ping th e ensem ble approach. G iven th a t bo th the

g reater range o f in itial atm ospheric conditions.

above approaches have th e ir lim itatio n s it w ould

D espite these foreseen advances, som e scientists have argued th a t o u r a b ility to forecast th e w eather

seem th a t an am algam o f the tw o m ethods is likely to prove the best way forward.

by num erical m ethods is fast approaching th e th eo ­

A related issue concerns th e future role o f the

retical lim its o f atm ospheric predictability. In the

m eteorologist in the h u m an -m ac h in e m ix. T h e last

past few decades the concept o f chaos and its im p li­

tw o decades have seen steady im provem ents in the reliability o f N W P . Should these continue apace, it

cations in th is area have com e very m uch to th e fore. M athem aticians have d em onstrated th a t, even in

has been suggested th a t th e role o f the m eteorologist

d e te rm in istic m odels such as those used in N W P ,

w ill gradually decline to th e poin t w here hum an

chaos theory dictates th a t th e accuracy w ith w hich

in p u t in to w eather forecasts is negligible. C ertainly

th e c u rre n t state o f th e atm osphere m u st be know n

it is tru e th a t today’s h ig h resolution mesoscale

to p re d ic t all fu tu re states exactly is in finite.25

num erical m odels can provide w eather forecasts in

C onsequently, no m a tte r how great th e im prove­

sufficient detail to w arrant m inim al in te rp reta tio n by

m ents in th e q u a n tity and q u a lity o f w eather obser­

m eteorologists. These m odels are not always reliable,

v ations, a perfect forecast w ill always be im possible.

however, and the w atchful eye o f th e m eteorologist

N evertheless, th e q u estio n rem ains how the tech ­

is im p o rta n t i f w eather forecasts, particularly in the

nological advances described above can be used to

short range, are to take account o f any divergence

o p tim ise th eir beneficial effects on w eather forecast

betw een m odel predictions and the evolution o f

323

324

CLIVE PIERCE, M ICHAEL DUKES AN D G R A H A M PARKER

w cachcr in th e real w orld. F u rth e rm o re , th e com plex

w eather d a ta from its n e ig h b o u rs. O n th e o th er, it

h u m a n skills involved in p re p a rin g w eath er forecast

m ay in creasingly be encouraged to charge for w eath er

tex ts tailo red to c u sto m e rs’ specific needs are not

services p rovided to these sam e n e ig h b o u rs, th e basis

easily a cq u ire d by an e lectro n ic co m p u ter.

for w h ic h are th e d a ta p rovided freely to it. In

D e sp ite these d iffic u lties, th e N o r th A m erican N a tio n a l

W e a th e r

Service

b eg an

u sin g

sim p le

E urope,

the

air

o f in creasing

com m ercialisatio n

and c o m p e titio n has led m e m b e r c o u n trie s o f th e

C o m p u te r W o rd ed Forecasts on an o p e ratio n a l basis

E uropean U n io n to fo rm u la te an a g ree m e n t on th e

as early as th e m id -1 9 7 0 s .26 T hese u tilise d M o d e l

p rovision o f d a ta an d w e ath e r services kn o w n as

O u t p u t S ta tis tic s from N W P m o d els to g e n e ra te a

E C O M E T .27 T h is cam e in to effect in Ja n u a ry 1996.

scries o f forecast m atrices. Each m atrix c o n ta in ed

T h e p rim a ry aim o f E C O M E T is to e stab lish an

sequences o f forecast w e ath e r e le m en ts for a given

agreed fram ew ork for co m m ercial an d

location. T h e C o m p u te r W o rd ed Forecast was g e n e r­

m ak in g N a tio n a l M eteorological C e n tre op eratio n s

no n -p ro fit

a te d by fe ed in g these forecast m atrices in to an a u to ­

w ith in

m a tic te x t g e n era to r. T h e la tte r w o u ld th e n c o n stru ct

p re v en t fu tu re conflicts o f in te rest such as th a t

c o h ere n t

o u tlin e d above.

sen ten ces

from

a

c o m b in a tio n

o f th e

E urope.

It is hoped th is a g ree m e n t w ill

w e ath e r d a ta su p p lie d an d a p re -p ro g ra m m e d k n o w l­ edge o f th e se m an tics o f w e a th e r forecast scripts. Today, m ore so p h istica ted versions o f these early

NOTES

C o m p u te r W o rd e d Forecasts are used operationally, or

e x p erim e n tally ,

by

N a tio n a l

M eteorological

C en tres across th e w orld. N o tw ith s ta n d in g su g g e s­ tio n s th a t th e role o f th e h u m a n forecaster w ill d e clin e in th e fu tu re , scien tific an d tech n o lo g ical d e v elo p m en ts such as N W P an d C o m p u te r W o rd ed Forecasts have y et to rem ove th e need for th e h u m a n c o m p o n e n t in th e h u m a n -m a c h in e m ix; ra th e r th ey have tran sfo rm e d th e d e m a n d s m ade on m ete o ro lo ­ g ists. A ssu m in g th a t c u rre n t tre n d s p e rsist, one m u st c o n clu d e th a t, in th e near fu tu re a t least, th e h u m a n forecaster w ill c o n tin u e to p lay a c ru cial p a rt in dayto -d ay w e ath e r forecasting. In re ce n t decades, th e cost o f th e g lo b al w eath er in d u stry , en co m p assin g as it does th e m ain ten a n ce o f an u p -to -d a te in fra s tru c tu re in th e face o f sc ien ­ tific an d tech n o lo g ical p rogress, hits risen sig n ifi­ cantly. T h is has led som e c o u n trie s to q u e stio n th e v a lid ity o f th e g e n tle m a n ’s a g re e m e n t p e rm ittin g th e free g lo b al e xchange o f w e ath e r d a ta as p a rt o f th e W M C ) W o rld W e a th e r W atch p ro g ram m e. In a d d itio n , th e expense e n ta ile d in ru n n in g a N a tio n a l M eteorological C e n tre has led a good m an y c o u n ­ trie s to enco u rag e co m m ercial a ctiv ities as a m eans o f o ffse ttin g th e ir overall e x p e n d itu re on w eath er services. T h is leads to a p o te n tia l conflict o f in terest. O n th e one h a n d , a c o u n try expects to receive free

1 Aristotle, Meteorologica, trans. H.D.P. Lee, Cambridge, Mass., Harvard University Press, 1926. 2 G. Hadley, ‘Concerning the cause of the general trade winds’, Philosophical Transactions, 1735, vol. 34, pp. 58-62. 3 G. Kutzbach, Tim Thermal Theory of Cyclones, A History of Meteorological Thought in the Nineteenth Century, Historical Monograph Series, American Meceorological Society, 1979, pp. 22-5. 4 W. Marriot, ‘The earliest telegraphic daily meteoro­ logical reports and weather m aps’, Quarterly Journal Royal Meteorological Society, 1903, vol. 29, p. 124. 5 W. Napier Shaw, Forecasting Weather, London, Constable and Company Ltd, 1911. 6 O.M. Ashford, ‘Development of weather forecasting in Britain 1900-1940: the vision of L.F. Richardson’, Weather, 1992, vol. 47(10), pp. 394-402. 7 Kutzbach, op. cit., p. 159. 8 V. Bjerknes and H. Solberg, 'Meteorological conditions for the formation of rain’, Geofysiske Puhlikasjoner, 1921, vol. 2, no. 3. 9 O.M. Ashford, op. cit. 10 R.A.S. Ratcliffe, ‘W eather forecasting in Britain, 1939-80’, Weather, 1993, vol. 48, no. 9, pp. 299-304. 11 L.F. Richardson, Weather Prediction ))y Numerical Process, Cambridge, Cambridge University Press, 1922. 12 Ratcliffe, op. cir., p. 302. 13 J- Fishman and R. Kalish, The Weather Revolution, Innovation and Imminent Breakthroughs in Accurate Forecasting, New York, London, Plenum Press, 1994, p p .

8 2 -5 .

F O R E C A S T IN G THE BRITISH ISLES W E A T H ER

14 G .J. Day et a l., ‘Scientific sta te m e n t o n International organisation for co-operation in m eteorology’, Weather, 1992, vol. 4 7 , no. 8, p. 310. 15 T h e M eteorological Office, The Observer's Handbook, L ondon, H M S O , 1982. 16 G M T - G reenw ich M ean T im e - is used as the universal tim e zone for m eteorological observations. G M T is som etim es replaced w ith U T C - U niversal T im e C lock; these tim e u n its are identical. 17 W orld M eteorological O rganisation, The W M O Achievement, 4 0 Years in the Service o f International Meteorology a n d Hydrology, G eneva, T h e W M O no. 729, 1990, p. 16. 18 M .J.S. H arriso n , E nsem bles, h ig h er resolution m odels and fu tu re c o m p u tin g pow er — a personal view ’, Weather, 1994, vol. 49 , no. 12, pp . 3 9 8 -4 0 6 . 19 T .N . P alm er and others, ‘Scientific sta te m en t on ex ten d ed -ran g e atm ospheric p re d ic tio n ’, Weather, 1992, vol. 4 7 , no. 8, pp. 3 0 6 -9 . 2 0 R atcliffe, op. c it., p. 303. 21 N . L ynagh, V iew point: T h e range o f w eather forecast services provided by the priv ate sector and a view on th e services provided ro th e p u b lic ’, Weather, 1995, vol. 50, no. 6, pp. 2 2 6 -8 . 22 ESA, ‘M eteosat: T here in all w e a th e r, Paris, ESA, p. 23. 23 J.C .R . H u n t, D evelopm ents in forecasting th e a tm o s­ pheric e n v iro n m en t', Weather, 1994, vol. 4 9 , no. 9, pp. 3 1 2 -1 8 .

24

H .E . Brooks and C..A. D osw ell, ‘N ew technology and num erical w eather pred ictio n - a w'asted o p p o rtu n ity ’, Weather, 1993, vol. 4 8 , no. 6, pp. 1 7 3 -7 . 25 T .N . Palm er, ‘A nonlinear dynam ical perspective on c lim ate change’, Weather, 1993, vol. 4 8 , no. 10, pp. 3 1 4 -2 6 . 26 H .R . G la h n , ‘C o m p u te r worded forecasts’, Bulletin o f the American Meteorological Society, 1979, vol. 60 , pp. 4 -1 1 . 27 A. D ouglas, F. D uvernet and R. H oerson, ‘P otential econom ic benefits from th e in tro d u c tio n o f E C O M E T ’, Conference on the Econom ic Benefits o f M eteoro­ logical and H ydrological Services, W M O , G eneva, Sw itzerland, 1 9 -2 3 S eptem ber 1995, pp . 2 0 5 -8 .

GENERAL READING R .G . Barry and R .J. Chorley, Atmosphere, Weather and Climate, L ondon and N ew York, R outledge, 6 th edn, 1995. J.F.R . M cllveen, 'Fundamentals o f Weather an d Climate, L ondon, C hapm an and H all, 1992. D .H . M cIntosh and A.S. T h o m , Essentials o f Meteorology, London, W ykeham P ublications L td, 1981. P.G. W ickham , The Practice o f Weather Forecasting, London, H M S O , T h ird Im pression, 1980.

325

15 GLOBAL W A R M I N G AND THE BRITISH ISLES Sarah Raper, David Viner, Mike Hulme and Elaine Barrow Is it not the height of silent humour to cause an unknown change in the Earth's climate? R o b e r t G raves, The Meeting

INTRODUCTION

W h a t do such predictions as have been m ade signify

T h ere is increasing evidence th a t global clim ate is chan g in g and th a t at least som e o f these changes are

for th e clim ate o f the B ritish Isles o f the next century, th e clim ate th a t o u r c hildren and gran d ch ild ren w ill experience? T hese are som e o f th e questions tackled

related to p o llu tio n o f th e atm osphere resu ltin g from

in th is chapter, b u t we begin by sum m arising some

h um an activities. T h is is one o f the conclusions reached in th e latest report from th e Intergovern­

o f the background to the g re e n h o u s e e ffe c t and how h um an activities can m odify it.

m ental Panel on C lim ate C hange p ublished in 1 9 9 6 ,1 and over th e last ten years th is concern has led to th e creation o f th e U n ited

N atio n s

Fram ew ork

THE GREENHOUSE EFFECT

C onvention on C lim ate C hange. T h is C onvention has been ratified by m ost o f th e nations o f the w orld and

T h e atm osphere contains naturally o ccurring gases

its objective is to prevent 'dangerous interference in th e clim atc system '. G lobal c lim ate change w ill have

w hich are very im p o rta n t for our clim atc because they m aintain th e E arth ’s tem perature about 30*C

a variety o f effects at c o n tin en tal and regional scales

w arm er th an it w ould be in th eir absence — th is is

and, as has been

show n in C h a p te r 9 , th ere

is

the greenhouse effect. T he m ost im p o rta n t o f these

evidence from th e B ritish Isles th a t there has been

so-called greenhouse gases is w ater vapour; others,

a general w arm in g o f clim ate in th is region over the

such as naturally occurring carbon dioxide and

last tw o or three centuries an d , in particular, over th e last tw o or three decades. Is th is clim ate change

m ethane, also c o n trib u te to the total effect. G reen ­ house gases are transparent to th e incom ing sh o rt­

in th e B ritish Isles p a rt o f a larger scale tren d and,

wave (ultra-violet) radiation o f the sun w hich heats

if so, can it be clearly related to p o llu tio n o f the global atm osphere by hum ans? H ow can our k now l­

the E a rth ’s surface. In tu rn , th e w arm ed surface

edge o f how th e clim ate system w orks be used to

em its longw ave (infra-red) radiation, som e o f w hich is absorbed and scattered in all directions by the

m ake

greenhouse gases, th u s reducing the energy escaping

p redictions,

just o f th e w eather

of

w eek (see C h a p te r 14), b u t

of

to space (see F igure 15.1). For th is reason th e gases

c lim atc over th e next ten to one hundred years?

are referred to as ra d ia tiv e ly a c tiv e . T he a m o u n t of

tom orrow or next

not

GLOBAL W A RM IN G AND THE BRITISH ISLES

Some short-wave radiation is reflected back to space by clouds, small particles and the Earth’s surface

Long-wave radiation is returned to space The radiation (both short-wave and long­ wave) absorbed by clouds and greenhouse gases is re-emiued in all directions. Some of this returns to warm the

Some short-wave radiation is absorbed by the Earth

Long-wave radiation is emitted from the Earth

Figure 15.1 A general illustration of the greenhouse effect.

longw ave radiation e m itte d from a surface increases w ith increasing te m p e ra tu re so a balance is estab ­

a ttrib u te d to anthropogenic chlorofluorocarbon em is­

lished w hen th e tem p e ra tu re is such th a t th e lo n g ­

strong controls on th e future em ission o f chloro-

wave radiation escaping to space is equal to the incom ing shortw ave radiation.

fluorocarbons are being im plem ented as laid dow n in th e latest am endm ent to th e 1987 M ontreal

T h e a n th r o p o g e n ic em issions o f greenhouse gases have altered th e n atural balance betw een incom ing

ozone is a greenhouse gas, th is ozone dep letio n in

sions, has caused great concern.2 For th is reason,

Protocol

on ozone-depleting substances.

Because

and o u tg o in g radiation causing an enhanced (or

th e s tr a to s p h e r e causes a sm all reduction in the

a n thropogenic) greenhouse effect. T h e m o st im p o r­

greenhouse effect. Significant increases in tropos­

ta n t o f these gases are carbon dioxide (e m itte d from

pheric ozone, however, due largely to tran sp o rt p o llu ­

fossil

tio n , result in a significant positive c o n trib u tio n to

fuel com bustion

and

chan g in g

land use),

m ethane (from ru m in a n ts, ru b b ish tips, rice paddies,

th e greenhouse

coal m ines and gas extraction), ozone (a chem ical

changes in th e atm osphere as a whole.

effect from

ozone concentration

derivative from car p o llution), halocarbons (from

In order to assess the clim ate change w hich m ig h t

refrigeration and o th e r in d u stria l uses) and nitrous

result from past and continued em issions o f green ­

oxide (from car pollution).

house gases there are a n um ber o f calculations w hich

N a tu ra l ozone is very im p o rta n t in th e stratos­

have to be m ade in a consistent m anner as illustrated

phere because it absorbs u ltra-violet radiation w hich

in Figure 15.2. These calculations begin w ith the

is h arm ful for life. O v er th e p ast few decades strato s­

reconstruction o f p ast em issions and, for th e future,

pheric ozone dep letio n (th e O z o n e H o le ), w hich is

the construction o f e m is s io n s sc e n a rio s. In 1992,

327

SARAH RAPER, DAVID VINER, MIKE HULME AND ELAINE BARROW

Atmospheric Concentrations of the Four Greenhouse Gas Components

1

Sulphate Aerosol Forcing

GLO BA L W A R M IN G A N D THE BRITISH ISLES

th e In te rg o v e rn m e n ta l

Panel on C lim a te C hange

defined a set o f six g re en h o u se gas em issions scenarios for th e w o rld , scenarios w h ic h p o rtray ed em issions th ro u g h th e w hole o f th e tw e n ty -first c en tu ry .3 T hese scenarios have since been m odified to acc o u n t for the ra p id phase o u t o f chlorofluorocarbons d u e to the concern

over stra to s p h e ric

ozone d e p le tio n .

T he

scenarios re p re se n t possible p ro jec tio n s o f g reenhouse gas em issio n s in th e absence o f new p olicies to reduce th em and are therefore regarded as ‘n o n -in te rv e n tio n ’ scenarios. T h ey are referred to as IS 9 2 a -f. T h e IS92a scenario falls ro u g h ly in th e m id d le o f th e range and ad o p ts in te rm e d ia te a ssu m p tio n s a b o u t fu tu re g lo b al p o p u la tio n ,

eco n o m ic

co n v en tio n al

an d

g ro w th ,

an d

th e

m ix

of

renew able energy sources. T h e

range o f p o ssib le fu tu re em issions scenarios, even in th e absence o f new co n tro l policies, is th e first o f a series o f u n c e rta in tie s w h ic h e n te r a t various stages in th e process o f try in g to d e te rm in e c lim a te and sea-level p ro je c tio n s for th e nex t century. T h e n ex t ste p is to c alcu late fu tu re a tm o sp h e ric

Figure 15.3 Projections of global-average radiative forcing from 1990 to 2100 due to greenhouse gas emissions and sulphate aerosols. The six curves represent the six IS92 emissions scenarios of the Intergovernmental Panel on Clim ate Change.

c o n c e n tra tio n s o f th e g re en h o u se gase^ for a g iv en e m issio n s scenario. G a s c y c le rru x le ls are invoked

sion o f a e ro s o ls . S u lp h a te aerosols, form ed from

to k e ep trac k o f th e sources, sinks and m o v em e n ts

su lp h u r dio x id e e m itte d d u rin g th e c o m b u stio n o f

o f th e gases. For e x am p le, to e stim a te fu tu re carbon

fossil fuels an d p a rtly responsible for p ro d u c in g a c id

d io x id e c o n c e n tra tio n s th e u p ta k e o f carbon d ioxide

r a in , have been reg ard ed as p a rtic u la rly im p o rta n t.

by th e occans and b iosphere needs to be considered.

T h e size o f th is n eg ativ e forcin g is very u n c ertain

T h e carbon cycle is c o m p lic a te d an d involves m any

a n d , u n lik e g re en h o u se gas forcing, is not g e o g ra p h ­

feedbacks,

so

e s tim a tin g

fu tu re

carbon

dio x id e

c o n c e n tra tio n s also involves som e un certain ty .

ically u n ifo rm . T h u s, d e te rm in in g th e p a tte rn o f fu tu re aerosol forcing is crucial for u n d e rsta n d in g th e

T h e e stim a te d ch an g e in th e g lo b al-av erag e r a d ia ­

regional p a tte rn s o f fu tu re c lim atc change. F or th e

tiv e f o r c i n g d u e to increases in g re en h o u se gas

g lo b al average, th e aerosol forcing is e stim a te d to bc

c o n c e n tra tio n s w hich have o ccurred since th e pre-

a b o u t —1.3 W m 2 a t p re sen t, th u s p o te n tia lly offset­

in d u stria l era — assum ed to be 1765 - is a b o u t 2.5

tin g a b o u t h a lf o f th e a n th ro p o g e n ic g reen h o u se

w a tts p e r sq u a re m e tre ( W m '2). F or th e IS 92a e m is­

effect. T h e u n c e rta in ty is large, how ever, an d fu tu re

sions scenario th e c alcu la te d ch an g e in fo rcin g over

p a tte rn s o f aerosol forcing are o f course u n k n o w n . A

th e n e x t c e n tu ry is a b o u t 5.1 W m -2, m o re th a n tw ice

fu rth e r increase in th is g lo b al aerosol forcing o f a b o u t

th a t observed to d a te .'1 O v e r th e last few years,

- 0 . 6 W m -2 m ay accom pany th e em issions scenario

how ever, it has b ecom e e v id e n t th a t w hen averaged

IS95a. U sin g m id -e stim a te s for th e aerosol forcing,

over th e g lo b al a tm o sp h e re a su b s ta n tia l p a rt o f the

th e fu tu re glo b al-av erag e to tal forcing p ro je c tio n s for

a n th ro p o g e n ic g re en h o u se effect m ay have been offset

th e six em issions scenarios IS 9 2 a - f are show n in

by a n e g ativ e forcin g d u e to th e a n th ro p o g e n ic e m is­

F ig u re 15.3.

Figure 15.2 A schematic representation of the steps involved in estim ating future global tem perature and sea level change.

329

330

SARA H RAPER, DAVID ViN ER, MIKE HULME A N D ELAIN E B A R R O W

cloud types radiatively active gases and aerosols horizontal exchange between columns of momentum, heat and moisture

j precipitation momentum, latent and sensible heat fluxes biosphere

vertical exchange between layers momentum, hes and moisture

\

orography, vegetation and surface characteristics included at surface on each grid box

vertical exchange between layers of momentum, heat and salts by diffusion, convection and upwelling

horizontal exchange between columns by diffusion and advection

Figure 15.4 Schematic representation of rhe clim ate system as modelled by a global climate model, in this case HADCM2.

GLOBAL AND REGIONAL CLIMATE CHANGE

in F ig u re 15.4), sim ila r to th e N u m e ric a l W ea th e r

T h e effect o f a ch an g e in ra d ia tiv e forcing on c lim ate

oceans play a m ajo r p a rt in th e c lim a te system

can be assessed u sin g a hierarch y o f c lim a te m odels.

because they act lik e a flywheel by d a m p in g th e

P re d ictio n m odels discussed in C h a p te r 14. T h e

T h ese range from sim p le g lo b al-av erag e box m odels

response o f th e c lim ate to a g iv en forcing. T h u s an

to co m p lex th ree -d im e n sio n al m o d els o f th e coupled

essential e le m en t in c lim a te m odels, w h e th e r sim p le

a tm o sp h e re -o c e a n system (see th e sc h e m a tic d iag ra m

or com plex, is th e ir a b ility to sim u la te th e effect o f

GLOBAL W A R M IN G AND THE BRITISH ISLES

BOX 15.1 THE CLIMATE SENSITIVITY

absorbed at th e surface, th u s causing a further

T h e clim ate sensitivity can be defined as th e e q u i­

increase in tem perature. A nother im p o rta n t posi­ lib riu m , or eventual, global-average tem p eratu re

tive feedback is th e w ater vapour feedback. W ith w arm er tem peratures and increased evaporation

c hange for a d o u b lin g o f th e carbon dioxide

th e concentration o f w ater vapour in the atm o s­

concentration. Its value depends on th e various

phere w ill increase and w ater vapour is itself an

feedbacks in th e clim ate system w hich may enhance or suppress th e d irec t response o f the

im p o rta n t greenhouse gas. A part from th e large aerosol forcing u ncertainties, th e unknow n value

clim ate system to forcing. O n e such exam ple o f

o f th e clim ate sensitivity is perhaps th e single m ost im p o rta n t u ncertainty in th e w hole process

a positive feedback is th e ice-albedo feedback. Clean ice and snow have a h ig h a lb e d o w hich m eans they reflect a large p ro p o rtio n o f the

o f calculating fu tu re clim ate change. It is best estim ated from th e com plex three-dim ensional

incom ing solar radiation d irectly back to space. Less snow and ice associated w ith w arm er tem p e r­

clim ate m odels w hich ex p licitly include the know n im p o rta n t feedbacks and is th o u g h t to

a tu res in th e fu tu re m eans a low er albedo so th a t

be in th e range 1.5*C—4 .5 #C w ith a best estim ate

m ore o f th e inco m in g solar radiation w ill be

o f 2.5*C.

oceanic th e r m a l in e r tia . If th e m odel does not repre­

in this sim ple m odel is th e c lim a te s e n s itiv ity (see

sent th e deep ocean, only th e h ypothetical eventual o f clim ate change, so-called ‘tra n s ie n t’ effects, can be

Box 15.1). Before looking at th e tem perature projections for th e next century it is advisable first to look at how

sim u lated in such m odels. Sim ple clim ate m odels are a pow erful tool for th e rapid calculation o f th e global

g lobal w arm ing since pre-in d u strial tim es d u rin g the

tem p e ra tu re response to different forcing scenarios.

m id -e ig h te en th ccntury. T h is w arm ing is estim ated

- or e q u ilib riu m - change can be assessed; no rate

well th e sim ple clim ate m odel sim ulates th e observed

If regional details and oth er clim ate variables, such

to be about 0.5°C.6 It tu rn s o u t th a t th e m odel tends

as p re cip ita tio n or w ind speed, arc required, how ­

to underestim ate th e w arm ing for all three recom ­

ever, it is necessary to use th e m uch m ore com plex

m ended values o f the clim atc sensitivity. T hus, for

th ree-dim ensional ocean-atm osphere global clim ate

clim ate sensitivities o f 1.5*C, 2.5°C and 4 .5 6C, past

m odels. R esults from bo th these types o f m odels arc

w arm ing estim ated by th e m odel is, respectively,

g iven below.

a bout 0.2*C, 0.3°C and 0.4°C. To obtain an estim ate o f 0.5°C from th e m odel requires a clim atc sensi­ tiv ity o f about 6°C, w hich is larger th an the values estim ated by m ost com plex m odels. These results

Simple model projections T h e global w arm ing

projections show n

in

this

c h ap tcr arc produced by th e sim ple clim atc m odel used by th e Intergovernm ental Panel on C lim ate

m ay indicate th a t th e value o f the negative aerosol forcing choscn in the m odel is too h ig h , o r they may reflect th e presence o f natural variability in the

C h an g e.5 In th is m odel, separate boxes for land and ocean areas in each hem isphere are distin g u ish ed .

observed record w hich the m odel cannot sim u la te.7

T h e tw o occan areas arc each m odelled w ith a single

forcing and the clim ate sensitivity, and th e unknow n

ocean c olum n sp lit in to forty layers so th a t th e heat

size o f the tren d caused by natural variability over

T he com bined effect o f uncertainties in the aerosol

p en etratio n in to th e deep ocean can be represented.

th e last century, m akes the unam biguous d etection

T h e m ost im p o rta n t p aram eter w hich has to be set

o f th e anthropogenic greenhouse effect from the

332

(deg C)

SARAH RAPER, DAVID VIN ER, MIKE HULME AN D ELAIN E B A R R O W

SO Q -o

Figure 1 5.5 Global warming projections from 1990 to 2100 using a simple clim ate model, assuming the IS92a emissions scenario and three different values of the climate sensitivity: 1.5*C (low), 2.5°C (mid) and 4.5°C (high).

Figure 15.6 Global warming projections from 1990 to 2100 using a simple climate model, assuming a value of 2.58C for the climate sensitivity and the six Inter­ governmental Panel on Climate Change emissions scenarios: IS92a-f.

g lo b al-av erag e te m p e ra tu re series alone n o t possible

o f a b o u t 0.2°C per decade - a b o u t four tim e s th a t

a t th e p re sen t tim e . T ech n iq u es w h ic h seek to d e te c t

observed over th e last 150 years. T h is e stim a te d rate

in th e o b serv atio n s th e geographical patterns o f te m p e r­

o f fu tu re w a rm in g // c o n sisten t, how ever, w ith th e

a tu re ch an g c p re d ic te d by co m p lex c lim a te m odels

glo b al w a rm in g observed since th e 196 0 s.9

are, how ever, b e g in n in g to have som e success. T hese

Sim p le m odels can also bc used to o b ta in e stim a te s

re su lts su g g e st th a t th e observed c lim a te ch an g e is

o f fu tu re glo b al-av erag e sea-level rise .10 B o th t h e r ­

u n lik e ly to be e n tire ly d u e to n a tu ra l causes.8 U s in g

m al e x p a n s io n o f th e oceans and th e n et m e ltin g o f

th e sim p le c lim a tc m o d el, forced w ith

land ice are expected to c o n trib u te to an increase

ra d ia tiv e changes c o rre sp o n d in g to em issio n s scenario

in th e ocean v o lu m e w ith g lo b al w a rm in g . F or th e

IS92a, g lo b al w a rm in g p ro je c tio n s from

calcu la tio n o f m e ltin g lan d ice, glaciers an d sm all ice­

1990 are

show n in F ig u re 15.5 for th e ra n g e o f values for th e

caps an d

c lim a tc sen sitiv ity . T h e changes to th e year 2 1 0 0 are

A n ta rctic a arc considered separately. In tere stin g ly ,

th e large ice-sheets o f G re en la n d

and

1.4°C, 2 .0°C an d 2.9°C respectively. T h e effect o f th e

A n ta rc tic a is expected to c o n trib u te a sm all fall in

six d iffere n t em issio n s scenarios on g lo b al w a rm in g ,

sea-level over th e next century. T h is is because th e

u sin g a fixed value o f 2.5°C for th e c lim a te se n si­

very cold a tm o sp h e re over A n ta rc tic a w o u ld bc able

tiv ity , is show n in F ig u re

to h o ld m o re w a te r v ap o u r if it w arm ed, w h ic h m ay

15.6. T h e differences

b e tw ee n th e scenarios are sm a ll before a b o u t 2 0 5 0 ,

re su lt in g re a te r snow fall an d hence an a cc u m u la tio n

a fte r w h ic h tim e th e re su lts d iv erg e su b stan tially . By

o f ice. A lth o u g h th e m ain c o n trib u tio n s to sea-level

2100

the

ch an g c are cxpcctcd to bc from th e rm a l e xpansion and

d iffere n t em issio n s scenarios is 1.3°C to 2.5°C . To

th e ran g e o f w a rm in g

re su ltin g from

th e m e ltin g o f glaciers an d sm all icc-caps, th e u n c e r­

p u t th e above re su lts in to recen t p ersp ec tiv e , th e e sti­

ta in tie s, especially su rro u n d in g th e response o f th e

m ate u sin g IS 92a a n d a c lim a te se n sitiv ity o f 2.5°C

icc-shects to c lim ate change, are very large. T aken

gives a rate o f g lo b a l w a rm in g over th e n e x t c en tu ry

to g eth e r, th e ice -m e lt m odel u n c e rta in tie s pro d u ce

GLOBAL W A R M IN G AND THE BRITISH ISLES

from one recent e x p erim e n t.12 T h e range o f possible future global w arm ing projections produced using th e sim ple clim ate m odel, provides a context in w hich to place this exam ple o f a com plex m odel experim ent. H A D C M 2 is a nineteen-level atm o s­

(cm)

phere m odel coupled to a tw enty-level ocean m odel and has a clim atc sensitivity o f about 2.5°C. C om m encing in I8 6 0 , the m odel was forced w ith estim ates o f the past and future (based on IS92a) greenhouse gas and aerosol forcing. T h is ex perim ent was callcd the su lp h ate experim ent, or SUL for short. T h e aerosol forcing used represents only the direct scattering effect on th e energy b u d g et o f th e atm o s­ phere and am ounts to a global average o f - 0 .6 5 W m '2 in 1990. T his is a m uch sm aller negative Figure 15.7 Global sea-level rise projections from 1990 ro 2100 using a simple climate model, assuming the IS92a emissions scenario and low, mid and high settings for the climate and sea level model parameters.

forcing th an the IPCC m id -estim ate o f —1.3 W m 2 q u o ted earlier, w hich included an estim ate o f the indirect effects o f aerosols on the radiative properties o f clouds. Also, th e effect o f tropospheric ozone increases (estim ated to be about 0.4 W m -2 in 1990)

u n c ertain tie s in rhe sea-level rise projections w hich

is ignored in the H A D C M 2 SUL experim ent. These, and oth er differences, result in a 1990 forcing th a t

are o f a sim ilar size to th e un certain ties associated

is about 0.44 W m “2 g reater th an th a t w hich was

w ith the clim ate sensitivity. W h en these tw o sets of

used for the sim ple m odel results presented in Figure

un certain ties are com bined a w ide range o f sea-level

15.5. T he resu ltin g global w arm ing projection from the

p rojections results. T his range is show n in Figure 15.7 for th e IS92a em issions scenario. T he central e stim a te for sea-level rise in 21 0 0 is ab o u t 50 cm , bur

IIA D C M 2 SUL experim ent is show n in Figure 15.8,

rhe range is from 20 to 8 6 cm . T h is result can bc

changes from I8 6 0 to 1995. In contrast to the sm ooth

to g eth er

w ith

th e observed

surface

tem perature

com pared w ith th e observed rise in sea-level over the

tem perature projections o b tained from th e sim ple

last c en tu ry o f betw een 10 and 20 cm .

clim ate m odel, th e com plex clim ate m odel results have a year-to-year variation w hich is caused by the

Complex model projections

natural variability represented in this com plex m odel. W ith th e total forcing used in the H A D C M 2 exper­

A lth o u g h sim ple clim ate m odels are pow erful t(x)ls for assessing global-average tem p eratu re changes, in

show n earlier, the com plex m odel results show n here

o rder to study th e regional p a tte rn s o f fu tu re clim ate

reproduce well th e overall observed w arm in g from

changc such as for th e B ritish Isles - it is neces­ sary to perform clim ate change experim ents using

used to justify th e lower aerosol forcing used in the

im ent being larger th an in th e sim ple m odel results

I8 6 0 to 1990. T his result should not, however, be

com plex three-dim ensional global clim ate m odels.

H A D C M 2 experim ent. T he agreem ent show n in

T h e H adley C entre, and before th a t th e U n ited

Figure 15.8 could be coincidental and som e other,

K in g d o m M et. Office, has over th e years developed

h ith e rto unknow n, factors m ay be o p erating in the

and perform ed a series o f clim ate change experim ents

real w orld. N atu ral variability m ay also have affected

w ith such m o d els.11 T he latest m odel version is

the past trends in th e observations and/or th e m odel

called H A D C M 2 and we show here som e results

results. For this H A D C M 2 SUL sim u latio n

the

333

334

SARAH RAPER, DAVID VINER, MIKE HULME AND ELAINE BARROW

Observed

------------

Model-simulated

Figure 15.8 Global-average temperature change from I860 to 2100 from the HADCM2 SUL experiment’2 and from I860 ro 19956 from the observations. The changes are plotted with respect to the average temperature of 1961 to 1990. The observed temperature data are listed in Appendix D.

overall w arm ing from th e 1961 to 1990 period to th e

IIA D C M 2 SUL experim ent for the years centred

end o f next c entury is betw een 2.5°C and 3.0°C.

around 2050 are show n in Plates 9 and 10 for the

gases,

w in ter and sum m er seasons. T h e global w arm ing by

aerosols only rem ain in th e atm osphere for a few days

th is date is about 1.5°C w ith respect to th e 1961 to

before they are washed o u t by rain. T h e g e o g rap h ­

1990 average.

U n lik e

th e

anth ro p o g en ic

greenhouse

ical d istrib u tio n o f th e aerosol forcing is therefore

It is evident from the tem p eratu re change m aps

uneven and depends on th e location o f the in dustrial

th a t th e sim ulated w arm ing is far from globally u n i­

sources o f su lp h u r dioxide. T he resu ltin g p a tte rn s of

form . A strik in g feature is th e strong w in ter w arm ing

regional a n thropogenic clim ate change are q u ite

in th e A rctic o f over 4°C, a lth o u g h th is region cools

sensitive to this d istrib u tio n . T h e p a tte rn s o f regional

slightly in sum m er. Generally, w arm ing is sim ulated

change for tem p e ra tu re and precip itatio n from the

over the land masses in bo th seasons, a lth o u g h a sm all

GLOBAL W A R M IN G AND THE BRITISH ISLES area o f cooling is evident over eastern C hina in w inter.

m ore in w inter. F u rth er south, in th e sum m er, the

T h e la tte r is d u e to a stro n g local influence o f su lp h u r d ioxide em issions. C ooling is also sim u lated in

decreases in precip itatio n - a bout 5 p er cent. T he

S outhern H em isphere su m m er over parts o f the

driest areas o f th e B ritish Isles therefore experience

w arm er tem peratures are accom panied by m odest

S outhern O cean, a lth o u g h th is is d u e to changes in

the greatest decrease in sum m er precipitation. If,

ocean processes ra th e r th an to aerosol effects. For the

w ith in one g eneration, a w arm er and d rier clim ate

E arth as a w hole, p re cip ita tio n is expected to increase

such as th is ensued in th e southern regions o f the

by a b o u t 2 p e r cen t in b o th seasons, b u t regional

B ritish Isles there w ould clearly be m ajor conse­

differences are m arked. For exam ple, increases in p re­

quences for th e v iability o f a range o f social and

c ip itatio n occur over large parts o f th e equatorial

econom ic activities. T h e next section explores som e

oceans in b o th seasons, b u t decreases p redom inate

o f the im plications o f such a clim ate change for the

elsew here in th e tropical and sub-tropical oceans.

region.

O ver land areas th e S outh A sian m onsoon weakens and p re cip ita tio n decreases over north ern A ustralia d u rin g th e ir (austral) su m m er m onsoon season. A t high n o rth ern latitu d e s, increases in p re cip ita tio n tend to d o m in a te, especially in th e w in ter season.

HOW CLIMATE CHANGE MIGHT AFFECT THE BRITISH ISLES M any environm ental assets and econom ic activities

CLIMATE CHANGE IN THE BRITISH ISLES

in the B ritish Isles are highly sensitive to w eather and clim ate — o utdoor recreation, a griculture, w ater supply, tran sp o rt and th e construction industry are

T h e B ritish Isles form only a very sm all p a rt o f the

just a few. Any change in clim ate, or in its vari­

E arth s surface and because th e global c lim ate m odels like H A D C M 2 contain only a coarse geographical

ability, w ill inevitably have consequences for such

representation, th e clim ate changes sim u la ted by

given to defining the scope and m ag n itu d e o f such

such m odels are not very detailed at such a sm all regional scale. F u rth e rm o re , d ifferent experim ents

im pacts bo th n o w 13 and in the fu tu re .14

w ith different m odels yield different p a tte rn s of change even w ith th e sam e forcing, so th e results

activities and considerable a tte n tio n is now being

C hanges in tem p eratu re and precip itatio n are not necessarily th e m ost im p o rta n t clim atic changes to affect the assets and activities o f the B ritish Isles.

described here m u st be in terp reted as only one

R eductions in snow fall w ill be im p o rtan t for tran s­

possible scenario o u t o f a range o f several. T h e results from H AD C M2 SUL for th e th irty -y e ar period

p o rt or recreation, increases in w ind speed w ill affect forestry and the construction industry, changes in

c entred on 2 0 5 0 were extracted for th e B ritish Isles

radiation will alter a gricultural p ro duction and the

and are show n in Plates 11 and 12 for m ean tem p e r­ a tu re and p re cip ita tio n for th e w in ter and su m m er

design o f b u ild in g s, and increases in poten tial évapo­

seasons. T h e te m p e ra tu re changes are added to the c u rren t clim ate, defined as th e average o f 1961 to

resource base of th e country. T here are also likely to be im p o rta n t secondary effects o f a general w arm ing

1990, whereas th e p re cip ita tio n changes are show n

o f the clim ate w hich w ill have im plications for health

as per cent change from c u rren t clim ate at th e orig ­

and tourism . H ig h e r air tem peratures (particularly

inal H A D C M 2 resolution.

transpiration w ill affect the ag ricu ltu ral and w ater

in sum m er), com bined w ith increased local em issions

T h e increase in tem p eratu re is betw een 1.2°C and

o f nitro g en oxides and hydrocarbons (particularly

1.6°C in bo th seasons and is d istrib u te d over the

from the tran sp o rt sector), w ill increase tropospheric

B ritish Isles w ith g re ater w arm ing in th e east than

ozone concentrations over urban areas, increase the

in th e w est. In Scotland, th e results show increased

form ation o f photochem ical

p re cip ita tio n in bo th seasons — u p to 5 per cent or

changes in air q u ality (see C h ap ter 12).

sm ogs and

lead

to

335

336

SARAH RAPER, DAVID VINER, MIKE HULME AND ELAINE BARROW Table 15.1 Some recent extreme annual and seasonal temperature anomalies from the 1961 to 1990 average and their approximate estimated return periods under current (1961-90) climate and under the HADCM2 SUL scenario for the years centred around 2050. The global warming by this date is about 1.5‘C. Estimates derive from statistical analysis of the Central England Temperature record Seasonal anomaly I'C ) Temperature Anomaly

Annual 1990 Summer 1976 Summer 1995 Winter 1988/9 Winter 1962/3

10.6 17.8 17.4 6.5 -0.3

+1.1 +2.5 +2.1 +2.4 -4.4

Return period (years) 1961-90 2050

65 310 90 30 230

1.6 5.5 3 4 oo

Table 15.2 Average annual frequencies of daily temperature extremes for six locations around the British Isles for current climate (1961 to 1990 average) for the years centred around 2020 and 2050 under a global warming scenario.0 Santon Downham is in Norfolk, Hillsborough is near Belfast and Fortrose is near Inverness Latitude ('N j

1961-90

2020

2050

Plymouth Oxford Santon Downham Hillsborough Durham Fortrose

Average annual frequency of frost days (T . 25‘C) 50.4 3 4 8 12 15 20 51.8 26 52.4 11 17 1 2 3 54.6 7 54.8 3 5 0 0 0 57.6

° These results are from E.M. Barrow ond M. Hulme, 'The changing probabilities of daily temperature extremes in the UK related to future global warming and changes in climate variability', Climate Research, 1996, vol. 6, pp. 21-31. The global warming by 2020 and 2050 in this example is slightly higher (about 0.1" and 0.2‘C respectively) than the HADCM2 SUL scenario used in this chapter.

T he likelihood o f extrem e seasonal tem peratures will also change in a w arm ing clim ate. Table 15.1 shows the estim ated return periods for some recent extrem e seasonal tem perature anomalies over the British Isles under conditions of clim ate change. The estim ated return period of the sum m er tem peratures of 1995 changes from about ninety years at present to,

on average, about oncc every three years by 2050. Assum ing these seasonal extrem es arc m dcpendenr events, the probability of tw o successive sum m ers like 1995 occurring during a decade in the m iddle o f next century is about 90 per cent (i.e., very likely). Such an event would have severe im plications for agriculture and water resources in many parts o f the B ritish Isles.

C hange in (b o re a l) w in te r m ean te m p e ra tu re

degrees Celsius ■ f

C hange in (b o re a l) s u m m e r m ean te m p e ra tu re

3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0

4.0 - 4.0 - 3.6 - 3 0 - 2.5 - 2.0 - 1.5 - 1.0 - 05


-a c « £C J O

50

60

70

80

100

Thousand years AP figure 16.4 A climarc index showing the succession of major climate states likely to be experienced in the British Isles over the next 125,000 years constructed from orbitally forced climate model output. The potential effects of enhanced greenhouse gas warming arc not included.

no rth ern p arts o f th e B ritish Isles over th e next 125,000 years. T h e succession w ill be som ew hat

a m ount o f w ater locked up in th e c ontinental iccsheets (C hapter 4). D u rin g the next glacial period,

different in the southern parts o f th e B ritish Isles n o t covered by ice-sheets d u rin g th e last (or next)

indicated at 5 2 ,0 0 0 to 6 2 ,0 0 0 years AP in our clim ate index, it is likely th at m uch o f the area covered by

glacial m axim um . T h is clim ate index suggests th a t

the N o rth Sea at present w ill again be dry land, and

th e next 125,000 years w ill be dom in ated by cooler

th a t th e Irish Sea w ill be reduced to a sm all channel.

and drier, boreal and periglacial conditions. C on­ d itio n s as severe as the Last G lacial M axim um (w ith

G u lf Stream w ill be absent as the th e r m o h a lin e

average annual tem peratures in th e B ritish Isles 10°C

c irc u la tio n o f the ocean shuts dow n a g ain .19 These

to 20*C low er th an present), or as w arm as the

changes will b rin g far m ore continental conditions to the B ritish Isles. D u rin g th is future glacial period,

present day, are relatively rare and are not likely to occur u n til at least 5 2 ,0 0 0 and 11 5 ,0 0 0 years AP respectively. Like th e last glacial—interglacial cycle, the next

It is also probable chat the w arm ing influence o f the

it is likely th a t the atm ospheric circulation over the B ritish Isles will be dom inated

by easterly

g lac ial-in te rg la cia l cycle is likely to be accom panied

airflow, associated w ith the re-establishm ent o f a glacial a n tic y c lo n e system over the Fennoscandian

by m ajor changes in sea-level. A t th e h e ig h t o f the

icc-sheet.20

last glaciatio n , for exam ple, global sea-level was ab o u t 130 m lower th an present because o f th e huge

O u r in te rp reta tio n o f th e m odel o u tp u t suggests th a t m ajor clim ate changes are to be expected in the

CLIMATE BEYOND THE TWENTY-FIRST CENTURY B ritish Isles over th e next few tens o f thousands o f

be no h um an intervention and no m ajor changes in

years. A t present, h u m an co m m u n ities exist in no rth ern Scandinavia, R ussia and Alaska, the

boundary conditions. T h e evidence presented in C hapter 15 indicates th a t changes in th e c ry o s p h e re

analogue regions for the boreal and periglacial clim ate states. P erm anent co m m u n ities also exist in

glaciers and snow) are likely to accom pany a n th ro p o ­

coastal G reenland, o u r glacial analogue region. So,

genic global w arm ing. Such changes m ay be critical

even w ith o u t m ajor technological advances, som e

for the future response o f th e clim ate system to orbital forcing.

h u m an se ttle m e n t should be possible in th e B ritish

(i.e., changes in the extent o f ice-sheets, sea-ice,

Isles th ro u g h o u t the next 12 5 ,0 0 0 years, a lth o u g h it

T h e polar ice-sheets are considered to play a

is likely th a t present-day p o p u latio n densities w ill

p articu larly im p o rta n t role in transform ing the rela­ tively weak in s o la tio n changes associated w ith

be unsustainable in the m ore n o rth ern areas d u rin g th e coldest periods. T echnological changes may, however, radically a lte r our p erception o f habitable

orbital forcing in to global g lacial-in terg lacial cycles.

and u n in h ab itab le clim ates.

feedback effect. I f som e external m echanism , such as

T hey are, for exam ple, involved in an ic e -a lb e d o

K now ledge o f past clim ate and th e range o f

a decrease in incom ing radiation, in itiates ice-sheet

forcing m echanism s (see Figure 16.1) tells us th a t th e real clim ate is m ore variable th an im plied by

g ro w th , then the surface albedo increases. M ore lo n g ­

o u tp u t from m odels such as the LLN palaeoclim ate

surface cools further. T h u s th e ice-albedo feedback

m odel or by th e clim ate index show n here. Evidence

is a positive feedback m echanism , reinforcing the initial forcing m echanism . Ir has been suggested th at

from pollen, beetle and ocean sed im en t records in d i­

wave radiation is reflecred back to space and the

cates th a t w arm er periods - in te r s ta d ia ls - occurred

the im pact o f global w arm ing on th e global cryos­

th ro u g h o u t th e last g lac iatio n .21 T h e causes of these

phere may seriously lim it th e effectiveness o f the

events are not fully understood, b u t th e ir rapid onset

ice-alb ed o feedback and

and sh o rt d u ra tio n suggests th a t they are related to

m echanism s. A t one extrem e, it has been proposed

m ode changes in th e th erm o h alin e circulation. It is likely th a t sim ilar events w ill occur d u rin g future

oth er positive feedback

th a t these m echanism s could be w eakened to such

periods o f g laciation. T h u s, th e colder clim ate states

an e x te n t th a t the in itiatio n o f fu rth er glaciation will be prevented. T h is is the so-called irreversible green ­

in dicated in th e clim ate index m ay be in te rru p te d

house effect’ and is one o f three possible p attern s

by w arm er periods, lastin g from a few hundred to

w hich can be used to describe the relationship

possibly a thousand years. D u rin g th e deglaciation period leading up to th e next interglacial period, it

betw een global w arm ing and orbital forcing. T h e sim plest assum ption th a t can be m ade is of

is possible th a t at least one m in o r glacial re-advance

a relatively b rief (say, 1,000-year) period o f global

m ay occur, sim ilar in m a g n itu d e to th e Y o u n g e r D ry a s a t about 1 1,000 years BP (sec C h a p te r 5).

w arm ing follow ed by a retu rn to th e ‘natural p a tte rn ’ o f g lacial-in tcrg lacial cycles. T h e second possibility is th at, follow ing a longer period o f global w arm ing (up to 10,000 years in len g th ), the next glaciation

ANTHROPOGENIC EFFECTS: WHY THE FUTURE W O N 'T BE LIKE THE PAST

w ill be delayed and w ill be less severe. T h e th ird p ossibility is the irreversible greenhouse effect. In order to de te rm in e w hich o f these p a tte rn s is m ost

So far, we have im plied th a t natural m echanism s o f

likely, we need to address tw o m ajor issues. First,

clim atc change w ill operate over the next one m illion

how high w ill atm ospheric greenhouse gas concen­

years or so in the sam e way th a t they have operated

trations rise, and for how long w ill they rem ain at

over the last m illio n years or so. W e have, however,

enhanced levels? Second, w hat can clim ate m odels

stressed th a t it is only leg itim a te to use th e past as

tell us a b o u t the relationship betw een th e enhanced

a g u id e to th e fu tu re if it is assum ed chat th ere will

greenhouse effect and orbital forcing?

347

348

CLARE G O O D E S S A N D J E A N PALUTIKOF

How high will greenhouse gas concentrations rise? T here are still m ajor un certain ties concerning the operation o f th e global carbon cycle a n d concentra­ tio n s o f th e m ain greenhouse gas, carbon dioxide.22

expected due to greenhouse gases alone because o f the offsetting cooling effect o f sulphate a e ro so ls (see C hapter 15). E stim ates o f th e present-day sulphate aerosol concentrations, th e spatial variations o f these concentrations, th eir atm ospheric lifetim e, and th e

T hese un certain ties are reflected in th e range o f

m ag n itu d e o f th eir direct and indirect radiative effects, are all h ig h ly u n c ertain .26 It is no t, therefore,

g reenhouse gas e m is s io n s s c e n a rio s produced by

possible to p redict how th e relative balance o f

th e Interg o v ern m en tal Panel on C lim atc C hangc,

sulphate aerosol forcing and greenhouse gas forcing

a lth o u g h th is panel has not a tte m p te d to produce

m ay change in th e longer-term future.

scenarios beyond AD 2 1 0 0 .23 W ith o u t a b e tte r u n d e r­

Clearly it is very difficult to m ake judgem ents

sta n d in g o f th e global carbon cycle it w ill be diffi­

about energy use over th e next few thousand years

c u lt to produce reliable estim ates o f future green ­

and thus to p red ict how greenhouse gas forcing w ill

house gas c oncentrations for th e longer-term future

operate.

or to d e te rm in e th e likely persistence o f th e enhanced

indicate th a t, unless action is taken to reduce em is­ sions and to sto p deforestation, peak carbon dioxide

greenhouse effect. D espite

the

large uncertainties, som e lim ite d

N evertheless, the results presented here

(or c a rb o n d io x id e e q u iv a le n t) concentrations o f

a tte m p ts have been m ade to investigate atm ospheric

1,000 to 2 ,000 ppm v m ay be reached w ith in a

carbon dioxide concentrations thousands of years in to th e fu tu re usin g sim ple global carbon cycle m odels.24

few centuries. G reenhouse gas concentrations could rem ain at enhanced levels for hundreds o f thousands

O ne m odel has been ru n over one m illio n years,

o f years into th e future.

assum ing th a t all recoverable fossil fuel reserves w ill be b u rn t.25 In th e ‘save fuel’ scenario, reserves are exhausted in a b o u t AD 2400, w hile in the ‘b u rn fuel’ scenario reserves run o u t after about one hundred years. Two o th er scenarios reflect contin u ed defor­ estation (th e ‘bu rn forests’ scenario), and an im m e ­ diate h alt to deforestation (th e ‘save forests’ scenario). T h e response o f atm ospheric carbon dioxide concen­

The relationship between the enhanced greenhouse effect and orbital forcing

Three-dimensional global climate models O ne o f th e longest published clim ate change exper­ im ents com prised a set o f three 500-year sim ulations

tratio n s to these four scenarios over th e next 5 ,000

perform ed w ith a coupled atm osphere-ocean global

years is show n in F igure 16.5. T h e h ighest sim u ­

clim ate m odel (Figure 16.6).27 T he first sim u latio n

lated atm ospheric carbon dioxide concentration of

was o f clim ate w ith c u rren t carbon dioxide concen­

a b o u t 2 ,1 0 0 p p m v occurs in about AD 240 0 when

trations. In th e second sim u latio n , carbon dioxide

th e

forests' scenarios are

concentrations increased by I per cent p er annum ,

com bined. In th is case, th e m odel takes over one m illio n years to re tu rn to prcscnt-day carbon dioxide

u n til they stabilised after 140 years at carbon dioxide levels four tim es those at present. In the th ird sim u ­

concentrations. T hese m odel results provide a rare

lation, carbon dioxide concentrations again increased

‘b u rn

fuel’ and

‘bu rn

and ten ta tiv e look a t how carbon dioxide concentra­

by I per cent p e r an n u m , b u t stabilised after seventy

tions m ay evolve thousands o f years in to the future.

years a t levels tw ice those o f today. O ver th e first

C arbon dioxide is not the only greenhouse gas,

140 years o f the carbon dioxide q u a d ru p lin g sim ­

b u t no a tte m p ts so far have been m ade to investi­

u lation,

g a te lo n g -term changes in o th er greenhouse gases

increased by about 5°C (Figure

global-average

surface

air

tem perature

such as m ethane. R ecently pub lish ed results from

carbon dioxide concentrations th en stabilised, global

16.6). A lth o u g h

th e global

tem perature increased by a fu rth er 1.5°C by th e end

w arm in g observed over th e last century is less than

o f th e sim ulation. T his residual w arm ing was due

global

clim ate

m odels

indicate

th a t

CLIMATE B E Y O N D THE TW ENTY-FIRST CEN TURY

Year (AD) Figure 16..5 Atmospheric carbon dioxide concentrations under various long-term scenarios for fossil fuel combustion and forest clearance (simulated using Walter and Kasting's 1992 global carbon cycle model25).

m ainly to th e th e r m a l in e r tia o f th e deep oceans. It im plies

th a t global

tem p e ra tu re is likely

sions over th e next 10,000 years, and to com pare

to

th is w ith the clim ate response to orbital forcing.28

c o n tin u e rising for hu n d red s o f years after g reenhouse

T h e global average tem p e ra tu re response to an em is­

gas c oncentrations stabilise.

sions scenario in w hich carbon dioxide concentrations six tim es those at present (i.e., a b o u t 2 ,0 0 0 ppm v) are reached by betw een A D 2 10 0 and 2 3 0 0 and in

One-dimensional climate models

w hich

subsequent carbon

dioxide

concentrations

rem ain ju st above present-day levels up to 5 0 ,0 0 0 A

energy-

years A P, is show n in Figure 16.7.29 D epending on

balance m odel (sim ilar to th a t described in C h ap ter

one-dim ensional

upw elling-diffusion

the assum ed c lim a te s e n sitiv ity , th e m axim um

15) has been used to in vestigate th e global tem p er­

increase in global-average tem perature is betw een

a tu re response to 'u n re stric te d ’ carbon dioxide em is­

4° and

13°C and occurs betw een A D 2 2 0 0 and

349

350

CLARE G O O D E S S A N D J E A N PALUTIKOF

(p p m )

any ‘n a tu ra l' tem peratures found over th e last 6 0 0 m illion years. Even w ith restricted carbon dioxide

C O >C o n c e n t r a t i o n

em issions (the com bined ‘save fuel’ and ‘save forests’ scenario o f Figure 16.5) and a low clim atc sensitivity, the sim ulated global tem p eratu re is h igher than any n a tu ra l’ tem peratures found over th e last 150 m illion years. These m odel results suggest th at future global w arm ing may generate tem perature changes over the next few centuries w hich are very

T e m p e ra tu re

(°C )

large even on th e geological tim e-scale.

2.5-dimensional Models: The LLN Palaeoclimate Model T he LLN palaeoclim ate m odel docs not have a carbon cycle. T h e effects o f anthropogenic carbon dioxide m u st, therefore, be sim ulated indirectly, or future carbon dioxide concentrations m u st be prescribed. T h e first approach was adopted in one o f the first Figure 16.6 Forcing scenarios and output from three 500year simulations with the coupled atmosphere-ocean GFDL GCM27: S, standard integration; 2 X C 0 2: C 0 2 increased by 1 per cent per annum until the concentration reaches two times the present value; 4 x C 0 2: C 0 2 increased by 1 per cent per annum until the concentration reaches four times the present value, (a) CO? concentration (ppm), (b) global temperature.

tests o f the sensitivity o f orbital forcing to global w arm ing perform ed by A ndré Berger in 1 9 9 1 ' 2 In th is 80,000-year sensitivity experim ent, th e effects o f anthropogenic carbon dioxide were prescribed by rem oving rhe G reenland ice-sheet and ru n n in g the m odel w ith present-day carbon dioxide concentra­ tions. O rb ital-rela te d insolation forcing was used in bo th the control (Figure 16.3) and pertu rb ed (Figure 16.9) sim ulations. T h e m ain results were th at, as

240 0 . A fter 10,000 years, global tem p eratu re is still

a conscquence o f anthropogenic carbon dioxide in

betw een 2° and 5°C w arm er th an present. T his

the atm osphere, ice-sheets do not reappear in the

com pares w ith a global tem p e ra tu re change sim u ­

N o rth e rn H em isphere u n til about 15,000 years

lated by the sam e m odel o f only 0.04°C a t 10,000

and the next glaciation is delayed by 2 ,0 0 0 to 3,000

years

due to o rb ital forcing alone. T h e authors,

years and is less extensive than it w ould otherw ise

K w ang-Y ul K im and T hom as Crowley, conclude th a t anth ro p o g en ic w arm ing m ay well d o m in a te orbital

be (Figure 16.9). T h e representation o f global w arm ing in the

cooling for a t least th e next 10,000 years.'0

experim ent described above is crude, a lth o u g h not

T h is one-dim ensional m odel has also been used to in vestigate th e response o f global tem p e ra tu re to the

entirely unrealistic. O th e r m odel-based studies and

lo n g -term carbon dioxide em issions scenarios show n

G reenland ice-sheet suggest th a t it w ill be m uch

in Figure 16.5, and to com pare th is response w ith te m p e ra tu re changes reconstructed from erature change over the next 10,000 years as a response to elevated CO., concentra­ tions o f 2,000 ppmv between a d 2100 and 2300, and concentrations slightly higher than today thereafter (using Kim and Crowley’s 1994 energy balance model28). The three simulations result from different values of the climate sensi­ tivity being applied: 1.5°C, 2.5°C and 4.5°C.

incorporates th e effects o f a n thropogenic global w arm in g , using

th e sam e m ethod

em ployed

re-advance o f ice-sheets over th e B ritish Isles.

to

in an as yet u n p ublished set o f sensitivity exper­

c o n stru ct F igure 16.4, and based on th e evidence

im ents for th e next 150,000 years, Paul Burgess used

discussed above. T h e new index — Figure 16.10 —

th e LLN m odel to com pare the clim ate response to

com m ences w ith a 1,000-year period o f subtropical

tw o different future carbon dioxide concentrations.34

or M editerranean c o n d itio n s representing greenhouse

T he first case o f 2 8 0 p pm v o f carbon dioxide (the

w arm ing, follow ed by a prolonged, 2 4 ,000-year,

average interglacial concentration) is com pared w ith

period o f tem p erate conditions. T h e glacial period

th e clim ate response to a stepw ise reduction in carbon dioxide concentration from 350 pp m v to

from 5 2 ,0 0 0 -6 2 ,0 0 0 years A P , seen in F igure 16.4, is replaced by a period o f periglacial conditions, from

2 80 p pm v over th e first 13,000 years o f th e m odel

5 0 ,0 0 0 —6 5 ,0 0 0 years A P. T h is period w ould be

sim u latio n and thereafter a constant 2 8 0 ppm v.

com parable w ith th e Y ounger D ryas, w ith ice-caps

A lthough carbon dioxide concentrations are equal

present only in th e h ig h est, n o rth ern m o u n ta in areas

(280 ppm v) in bo th experim ents after 1 3,000 years,

o f the B ritish Isles. T h e conclusion is th a t global

differences in ice volum e persist u n til 6 5 ,0 0 0 years

w arm ing m ay restrict and delay, b u t n o t p revent, the

AP

(Figure

16.11), and occur despite a period

352

CLARE G O O D E S S A N D J E A N PALUTIKOF

R estricted C O

2

scenario

M il l io n s o f years a go ---------------------- • ' ' - ( c e n t u r i e * ) - ** E s t i m a t e s fr o m C O 2 s c e n a r i o s : -------- A T 2i C02* 1 . 5 ° C

-------------- A T 2i CO, = 2 . 5 ° C ------------ A T 2i C 0 2 = 4 . 5 ° C

E s t i m a t e s o f g lo b a l te m p e r a tu r e c h a n g e from th e o x y g en is o t o p e record: -------------- d i f f e r e n c e s f r o m o b s e r v e d ----------- d i f f e r e n c e s f r o m t h e glob al average tem p er a tu r e H o lo c e n e corc tops

U nrestricted C O

M il l io n s o f years ago

2

scenario

— Future ( cen turies)

C LIM ATE B E Y O N D THE T W EN TY -FIRST C E N T U R Y

353

o f a b o u t 1 8 ,0 0 0 years w h e n N o rth e rn H e m isp h e re ice-sheets are a b se n t from b o th sim u la tio n s. I t is c o n d u cted th a t th e sim u la te d c lim a te system show s a

lo n g -te rm

m o d estly

m em o ry

d iffere n t

response

carb o n

to

d io x id e

th ese

q u ite

c o n ce n tra tio n

scenarios. S e n sitiv ity e x p e rim e n ts p e rfo rm e d w ith th e L LN p a la eo c lim a te m o d el in d ic a te th a t th e c lim a tic effects o f e n h an c ed g re en h o u se gas forcin g m ay p e rsist for ten s o f th o u sa n d s o f years. F ig u re 16.11 show s th a t

v

on th ese lo n g tim e-scales th e c lim a te sy ste m is very

i 25 : O

fo rcin g , and th a t even relativ ely m o d est increases in carb o n d io x id e fo rcin g (in

co m p a riso n w ith

(J

— x 30 — '---- 1----- ■-----1---- »---- 1■ 0

10

20

th e

-

se n sitiv e to d iffere n t m a g n itu d e s o f g re en h o u se gas

c

i

30

40

i

i

i______

»

50

60

70

Time (thousand years AP)

scenarios show n in F ig u re 16.5) m ay severely re stric t th e

fu tu re

lo n g -te rm

d e v e lo p m e n t

o f N o rth e rn

H e m is p h e re ice-sheets.

Figure 16.9 Future continental ice volume, wirhout rhe Greenland icc sheet, as simulated by the Louvain-la-Neuve model, assuming orbital and greenhouse gas forcing (cf. Figure 16.3).

The future pattern of change O n th e basis o f th e m o d el evidence d iscussed here,

In d e ed , it is lik ely th a t th e B ritish Isles w ill be

a n d a ssu m in g th a t g re en h o u se gas c o n c e n tra tio n s

w a rm e r th a n a t any tim e d u rin g th e Q u a tern a ry

w ill e v en tu ally re tu rn to levels close to those o f the

p e rio d by th e en d o f th e tw e n ty -first cen tu ry .35 T h e

p re se n t day, we c o n sid er th a t, of. th e th ree possible

m o st recent m o d el re su lts in d ic a te th a t th e perio d

o u tco m e s

o f g re en h o u se g a s-in d u ce d w a rm in g w ill bc lo n g er

d e sc rib in g

th e

re la tio n sh ip

b etw een

e n h an c ed g re e n h o u se w a rm in g an d o rb ita l forcing,

th an su g g e ste d by earlier stu d ies. O n th e basis o f

th e

w eakened

th e latest evidence w e c ould, for exam ple, ju stify th e

g la c ia tio n - is th e m o st likely. T h e th ird p o ssib ility

exten sio n o f th e 1 ,0 0 0 -y car p e rio d o f su b tro p ic a l or

- th e irrev e rsib le g re en h o u se effect - is considered

M e d ite rran e a n c o n d itio n s show n in F ig u re 16.10 by

to have a low, b u t n o n -z e ro ,' p ro b a b ility o f o ccur­

u p to 1 0 ,0 0 0 years.

second

p o ss ib ility

-

delayed

and

rence. T h e m odel re su lts w h ic h have becom e avail­ ab le over th e last few years im p ly th a t th e p ro b a b ility o f an irrev ersib le g re en h o u se effect is h ig h e r th a n we

CONTRADICTIONS AND UNCERTAINTIES

m ig h t have th o u g h t, say, five years ago. T h e evidence also in d ic a te s th a t th e n e x t few th o u ­ sand years w ill be very w a rm in g e o lo g ic al term s.

C lim a to lo g ists

have

so m e tim es

been

m a k in g c o n tra d ic to ry p re d ic tio n s w ith

accused

of

reg ard to

Figure 16.8 Comparison of future greenhouse projections against the geologic record (using Crowley and K im ’s 1995 energy balance m odel31). Curves to the left of zero represent estimates of past global tem perature changcs from the oxy­ gen isotope record: dashed lines represent differences from the Holocene core tops, and continuous lines represent differ­ ences from the observed global average tem perature. Crossbars indicate fitting points for calibration of oxygen isotope curves in terms of global tem perature. Labelled scale on the left-hand side represents calculated values for peak warming on the right-hand side of the figure. Curves to the right of zero represent global warming estimates assuming restricted (top) and unrestricted (bottom ) C O , emissions scenarios, using three standard values for the clim ate sensitivity. ‘Error bars' represent a generous estim ate of the range of natural variability based on records of the last 1,000 years.

80

354

CLARE G O O D E S S A N D J E A N PALUTIKOF

M editerranean (5)

T em perate (4)

Boreal (3)

Periglacial (2)

5

-o c

£ c3 E U

0 U---------------------------- ^ 0 10 20

30

40

50

60

70

80

90

100

110

----------120

Thousand years AP Figure 16.10 A climate index showing the succession of major climate states likely to bc experienced in the British Isles over the nexi 125,000 years constructed from orbirally forced model output. The potential effects of enhanced greenhouse gas warming are incorporated (cf. Figure 16.4).

future clim ate. Tw enty years ago, som e clim ato lo ­

stan d in g o f exactly how th e relatively weak insola­

g ists w ere p re d ic tin g th e onset o f th e next ice age

tion

an d now, m ost, a lth o u g h not all, c lim atologists are

translated

p re d ic tin g global w arm ing. In th is c h ap ter we have

incom plete, and som e researchers continue to argue th a t o rbital changes cannot be a m ajor cause o f these

a tte m p te d to show th a t a nother ‘Ic e A g e ' is likely to follow a period o f global w arm in g , b u t th a t th is Ice A ge is likely to be delayed and to be less extrem e th an we m ig h t expect in th e absence o f global w arm in g . Its onset is also m any h u m an generations in to the future. G reenhouse w arm in g and another

forcing

associated

w ith

orbital

changes

is

in to glacial-in tcrg lacial cycles is still

cycles.36 N one o f the m odels described in th is chapter are fully realistic. T he LLN palaeoclim ate m odel, for exam ple, does not have a Southern H em isphere, nor does it include the deep ocean circulation. A t best,

Ice A ge are not, therefore, incom patible predictions,

th e m odels described here incorporate tw o m ajor forcing m echanism s, anthropogenic greenhouse gas

b u t depend on th e fu tu re tim e-scale considered.

forcing and orbital forcing. T hey do not em ploy the

T here are clearly m ajor uncertainties in any a tte m p t to p red ict clim ate over such a long tim e

full range o f forcing m echanism s know n to operate over different tim e-scales (see Figure 16.1). A nd

horizon. Som e o f these, such as th e u n certainty

there m ay be other, as yet undiscovered, a n th ro ­

concerning

pogenic effects w hich m ay counteract or intensify the enhanced greenhouse effect.

future

atm ospheric

carbon

dioxide

concentrations, have already been noted. O u r u nder­

CLIMATE B E Y O N D THE TW ENTY-FIRST CEN TU RY

350 ppmv CO 2

280 ppmv CO 2

o > o

3c c o U

Thousand years AP Figure 16.11 Northern Hemisphere ice volume, 0 to 150,000 years a p , simulated by the Louvain-la-Neuve model for experiments with future atmospheric C 0 2 concentrations of 280 and 350 ppmv.

CLIMATE RESEARCH: THE NEXT TWENTYFIVE YEARS T h ro u g h o u r

th is

c h ap ter

we

have argued

years. Tw enty-five years ago, n either m echanism was w idely recognised or accepted by th e international research com m unity. T h e g row ing acceptance o f chat

these m echanism s is a reflection o f th e rapid advances

enhanced greenhouse w arm ing and orbital forcing

in clim ate reconstruction and m o delling over th e last

w ill be th e tw o m ajor, th o u g h not th e only, forcing

tw enty-five years. It is now possible, for exam ple, to reconstruct a h igh-resolution 2 0 0,000-year record o f

m echanism s over th e next 10 0 ,0 0 0 to one m illion

355

356

C L A R E G O O D E S S A N D J E A N PALU TIK O F

p ast c h an g cs in a tm o sp h e ric carb o n d io x id e concen­ tra tio n s from a ir b u b b le s tra p p e d in an A n ta rc tic icec o re.37 Im p ro v e m e n ts in o u r u n d e rsta n d in g o f th e c lim a te sy stem , m o re d a ta for m odel v a lid a tio n , an d

5

g re a te r c o m p u tin g pow er, m ak e it p o ssib le to run co m p lex th re e -d im e n sio n a l m o d els for u p to 1,000 years an d to run one- a n d tw o -d im e n sio n a l m odels for h u n d re d s o f th o u sa n d s o f years. D e sp ite these advances, th ere are still som e m ajor

6

u n c e rta in tie s to be resolved. A s o u r u n d e rsta n d in g oi th e c lim a te sy stem im p ro v es, it so m e tim es seem s th a t m o re q u e stio n s are raised th an answ ered. T h is m ean s th a t th e next tw e n ty -fiv e years o f c lim ate research sh o u ld be as e x c itin g as th e last tw enty-five years have been, an d th a t w c can look forw ard to

7

e q u ally ra p id advances in o u r kn o w led g e.

NOTES 1 The conventional dates and names for all the geolog­ ical periods discussed in this chaptcr are given in Table •1.1 in Chapter 4. The Last Glacial Maximum is gener­ ally assigned a ,4C date of 18,000 years B P , which, on the basis of the best present-day evidence, is equiva­ lent to a calibrated age (in calendar years) of about 21,000 years np. See Box 4.1, Chapter 4, and Box 5.1, Chapter 5, for discussions of dating techniques and problems. Clim ate conditions in the British Isles during the Last Glacial Maximum are also described in C hapter 4. 2 C M . Goodess, J.P. Palutikof and T.D. Davies, Studies o f Climatic Effects and Impacts Relevant to Deep Underground Disposal of Radioactive Waste, Nirex Safety Series, NSS/R267, 1992, 398 pp., available from UK N irex Ltd, Harwell; S.T. Adcock, M.D.G. Dukes, C.M. Goodess and J.P. Palutikof, A Critical Revieti' of the Climate Literature Relevant to the Deep Disposal of Radioactive Waste, Nirex Science Rejx>rt, 1996 (in press), 292 pp., available from U K Nirex Ltd., Harwell. 3 See Chapter 4. For a discussion of the links between global and regional British Isles climate over the last glacial-interglacial cycle see C.M. Goodess, J.P. Palutikof and T.D. Davies, The Nature and Causes of Climate Change: Assessing the long term future, London, Belhaven Press, 1992, pp. 157-73. 4 J.M . M itchell, ‘An overview of clim atic variability and its causal mechanisms’, Quaternary Research, 1976, vol. 6, pp. 4 8 1 -9 4 ; A. Berger, ‘Spectrum of climatic variations and their causal mechanisms’, Geophysical

8

9 10 11

12

13

Surveys, 1979, vol. 3, pp 351-402; T.M.L. Wigley, ‘Climate and paleoclimate: what we can learn about solar luminosity variations’, Solar Physics, 1981, vol. 74, pp. 435-71. A.B. Pittock, Solar variability, weather and climate: an update’, Quarterly Journal of the Royal Meteorological Society, 1983, vol. 109, pp. 23 -5 5 ; P.M. Kelly and T.M.L. Wigley, Solar cycle length, greenhouse forcing and global clim ate’, Nature, 1992, vol. 360, pp. 328-30. See Box 4.2, Chapter 4; J. Imbrie, ‘A theoretical frame­ work for the Pleistocene ice ages’, Journal o f the Geological Society, 1985, vol. 142, pp. 4 1 7 -3 2 ; A. Berger and C. Tricot, ‘Global climatic changes and astronomical theory of paleoclimates’, in A. Cazenave (ed.), Earth Rotation: Solved and Unsolved Problems, Dordrecht, Reidel, 1986, pp. 111—29. J. Imbrie, J.D . Hays, D.G. Martinson, A. McIntyre, A.C. Mix, J.J. Morley, N .G . Pisias, W.L. Prcll and N.J. Shackleton, The orbital theory of Pleistocene climatc: support from a revised chronology of the marine ,80 record', in A. Berger, J. Imbrie, J. Hays, G. Kukla and B. Saltzman (eds), Milankovitch and Climate, Dordrecht, Reidel, 1984, pp. 269-306; P.L. de Boer and D.G. Smith (eds), Orbital Forcing and Cyclic Sequences, Oxford, Blackwell, 1994, 559 pp. See Box 4.2, Chapter 4 and reviews in Goodess et al., Nature and Causes of Climate Change, pp. 11-50, and Adcock et al., 1995, op. cit., pp. 7-81. Goodcss et al.. Studies of Climatic Effects, pp. 228—46. J. Im brie and K.P. Im brie, Ice Ages, Solving the Mystery, London, Macmillan Press, 1979, p. 178. For reviews of the range of orbital-based models see the following. A. Berger, J. Imbrie, G. Kukla and B. Saltzman (eds), Milankovitch and Climate, Parts 1-2. Understanding the Response to Orbital Forcing, Dordrecht, Reidel, 1984, two volumes; J. Imbrie, 1985, op. cit; A. Berger, ‘Milankovitch theory and clim ate’, Reviews of Geophysics, 1988, vol. 26, pp. 62 4 -5 7 ; Goodess et al., Nature and Causes o f Climate Change, pp. 25-34. H. Gallée, J.P. van Ypcrsele, T. Fichefet, C. Tricot and A. Berger, 'Simulation of the last glacial cycle by a coupled, sectorially averaged clim ate-ice sheet model. 1. The clim ate m odel\ Journal o f Geophysical Research, 1991, vol. 96, pp. 13,139—61; H. Gallée, J.P. van Ypersele, T. Fichefet, I. Marsiat, C. Tricot and A. Berger, ‘Simulation of the last glacial cycle by a coupled, sectorially averaged clim ate-ice sheet model. 2. Response to insolation and C 0 2 variations’, Journal of Geophysical Research, 1992, vol. 97, pp. 15,713—40. A. Berger, 'Long-term variations of caloric insolation resulting from the Earth’s orbital elem ents’. Quaternary Research, 1978, vol. 9, pp. 139-67.

CLIMATE B E Y O N D THE TWENTY-FIRST CENTURY

14 T he m odel has been forced by th e record o f atm o s­ p heric carbon dioxide reconstructed from air bubbles trap p ed in the V ostok ice core from A n tarctica, as described by A. Berger, H . G allée and C. T ricot, ‘G laciation and d eglaciation m echanism s in a coupled 2 -dim ensional c lim a te -ic e sheer m o d el', Journal o f Glaciology, 1993, vol. 39, pp. 4 5 -9 - I t has also been forced by a 2 0 0 ,000-year long C O , rccord reconstruc­ ted from ocean core d ata, as described by A. Berger, C. T ricot, H . G allée and M.F. L outre, ‘W ater-vapour, C 0 2 and insolation over th e last g la c ial-in te rg la cia l cycles’, Philosophical Transactions o f the Royal Society of London B , 1993, vol. 341, pp . 2 5 3 -6 1 . 15 L.D . Labeyrie, J.C . D uplessy and P.L. Blanc, ‘V ariations in th e m ode o f form ation and tem p eratu re o f oceanic deep w aters over the p a st 1 25,000 years’, Nature, 1987, vol. 3 2 7 , pp. 477- 82. 16 N a tu ra l variations in atm ospheric carbon dioxide c oncentrations accom panied past g lac ial-in te rg la cia l cycles and arc one o f th e m ost p lausible m echanism s for reinforcing th e relatively w eak insolation forcing associated w ith th e o rb ita l changes. See Box 4.2, C h a p te r 4 , and reviews in G oodess et a l., Nature and Causes o f Climate Change, pp. 35—4 0 , and A dcock et a l., 1995, op. c it., pp . 4 0 - 5 3 . 17 B erger et a l., ‘G laciation and deglaciation m echa­ n ism s’. 18 W e use a m odified version o f th e K o p p e n -T re w a rth a classification system . G .T. T rew artha, A n Introduction to Clim ate, M c G ra w -H ill, 4 th e d itio n , 1968; W. R udloff, "World Climates, S tu ttg a rt, W issenschaftliche V erlagsgesellschaft, 1981, 6 32 pp. 19 W .S. Broecker, ‘U npleasant surprises in th e g reen ­ house?’, N ature, 1987, vol. 328, pp . 123—6; J.C . D uplessy, L. Labeyrie, N . K allel and A. Juillet-L eclerc, ‘In term ed ia te and deep w ater characteristics d u rin g the Last G lacial M a x im u m ’, in A. Berger, S. Schneider and J.C . D uplessy (eds), Climate a nd Geo-Sciences, D o rd re ch t, K luw er, 1989, pp- 1 0 5 -2 0 . 20 C O H M A P M em bers, ‘C lim a tic changes o f the last 1 8 ,000 years: observations and m odel sim u la tio n s’, Science, 1988, vol. 2 4 1 , pp . 1,043—52. 21 For evidence from th e B ritish Isles, see th e follow ing: G .R . Coope, ‘C lim atic fluctuations in northw est E urope since the last interglacial, indicated by fossil assem blages o f C oleoptera', in A.E. W rig h t and E M oseley (eds), Ice Ages: Ancient a n d Modem, Liverpool, Seel H ouse Press, 1975, p p . 1 5 3 -6 8 ; T.C. A tkinson, K .R . Briffa and G .R . Coopc, ‘Seasonal tem peratures in B ritain d u rin g th e past 2 2 ,0 0 0 years, reconstructed u sin g beetle rem ains’, N ature, 1987, vol. 325, pp. 5 8 7 -9 2 . For evidence from th e N o rth A tlan tic and G reen lan d see the follow ing: G . B ond, W. Broecker, S. Jo h n sen , J . M cM anus, L. Labeyrie, J . Jouzel and G .

22

23

24

25 26

B onani, ‘C orrelations betw een clim ate records from N o rth A tlan tic sedim ents and G reenland ice’, Nature, 1993, vol. 365, pp . 1 4 3 -7 . R.A. Kerr, ‘G lobal change - fugitive C .0 2: i t ’s not h id in g in th e ocean’, Science, 1992, vol. 2 5 6 , p. 35; C.B. Field, ‘C arbon cycle: A rctic c hill for C 0 2 u p ta k e ’, Nature, 1994, vol. 371, pp . 4 7 2 -3 . J.T . H o u g h to n , B.A. C allander and S.K. Varney (eds), Climate Change 1992: The Supplementary Report to the IPCC Scientific Assessment, C am bridge, C am bridge U niversity Press, 1992, 2 00 pp. E.T. S u n d q u ist, ‘L ong-term aspects o f future a tm o s­ pheric C O , and sea level changes’, in R. Revelle (ed.), Sea-level Change, N a tu ral Research Council S tudies in G eophysics, N atio n al Academ y Press, 1990, pp. 1 9 3 -2 0 7 ; J.C .G . W alker and J.F. K asting, ‘Effects o f fuel and forest conservation on future levels o f a tm o s­ pheric C O ,’, Palaeogeography, Palaeoclimatology, Palaeo­ ecology (Global and Planetary Change Section), 1992, vol. 97 , pp. 1 5 1 -8 9 . W alker and K asting, 1992, op. cit. A. Jones, D.L. R oberts and A. Slingo, ‘A clim ate m odel stu d y o f in d irect radiative forcing by a n th ro ­ pogenic sulphate aerosols’, Nature, 1994, vol. 3 7 0 , pp.

4 5 0 -3 27 S. M anabe and R .J. Stouffer, ‘C cntury-scale effects o f increased atm ospheric C 0 2 on th e ocean atm osphere sy stem ’, Nature, 1993, vol. 364, pp . 2 1 5 -1 8 . 28 K.Y. K im and T.J. Crowley, ‘M odeling the clim atic effect o f u n restricted greenhouse em issions over the next 10,000 years’, Geophysical Research Letters, 1994, vol. 21 , pp. 6 8 1 —4. 29 H . Perry and H .H . L andsberg, ‘Projected w orld energy c o n su m p tio n ’, in N a tu ral Research C ouncil (ed.), Energy a nd Climate, W ashington, D C , N ational A cadem y Press, 1977, pp. 3 5 -5 0 ; S u n d q u ist, 1990, op. cir. 30 K im and Crowley, 1994, op. cit. 31 T.J. Crow ley and K.Y. K im , ‘C om parison o f lo n g -term greenhouse projections w ith th e geologic record’, Geophysical Research Letters, 1995, vol. 22 , pp . 9 3 3 - 6 . 32 A. Berger, H . G allée and J.L . M elice, ‘T he E arth s future clim ate a t the astronom ical tim escale’, in C.M . G oodess and J.P. P a lu tik o f (eds), Future Climate Change a nd Radioactive Waste Disposal, N irex Safety Series N S S /R 257, H arw ell, U K N irex L td, 1991, pp. 1 4 8 -6 5 . 33 A. L ctréguilly, P. H u y b rech ts and N . R eeh, Steadystate characteristics o f the G reenland ice sheet under different clim ate states', Journal of Glaciology, 1991, vol. 37 , pp . 1 4 9 -5 7 ; T.J. Crow ley and S.K. B aum , ‘Is the G reenland Ice Sheet b istable?’, Paleoceanography, 1995, vol. 10, pp. 3 5 7 -6 3 . 34 T hese sim ulations have been perform ed by Paul Burgess, a P h.D . stu d e n t in rhe C lim atic Research

357

CLARE G O O D E S S A N D J E A N PALUTIKOF

U n it, in collaboration w ith colleagues from the U n iv ersity o f L ouvain-la-N cuve. T he w ork is funded by U K N ire x L td u n d e r C o n trac t SCRS 0 2 6 8 . 35 T h e Ipsw ichian and H olocene th erm al m axim a were no m ore th an 2°C w arm er th an present in th e B ritish Isles (see C hapters 4 and 5). W arm in g o f th is m ag n i­ tu d e m ay occur in the B ritish Isles by th e end o f the next c en tu ry (see C h ap ter 15). 3 6 I.J. W in o g rad , T.B. C oplen, J.M . Landw ehr, A.C. R iggs, K .R . L udw ig, B.J. Szabo, P.T. K olesar and K .M . Revesz, ‘C o n tin u o u s 5 0 0 ,000-year clim ate record from vein calcite in D evils-H ole, N evada’, Science, 1992, vol. 2 5 8 , pp . 2 5 5 -6 0 . 37 J . Jo u z e l, N .I. Barkov, J.M . Barnola, M. Bender, J . C happellaz, C. G e n th o n , V.M. K otlyakov, V. Lipenkov, C . L orius, J.R . P e tit, D. R aynaud, G . R aisbeck, C. R itz , T. Sowers, M . Stievenard, F. Y iou and P. Yiou, ‘E x ten d in g th e V ostok ice-core record o f palaeoclim ate to th e p e n u ltim a te glacial p e rio d ’, Nature, 1993, vol. 364, p p . 4 0 7 -1 2 .

GENERAL READING A.

B erger and M-F. L outre, 'M odelling the clim ate response to astronom ical and C 0 2 forcings’, Comptes Rendus de I ’Acadeniie des Sciences, 1996, vol. 323, pp- 1 -1 6 . T.J. Crowley and K.Y. K im , ‘C om parison o f long-term greenhouse projections w ith the geologic record’, Geophysical Research Letters, 1995, vol. 22 , pp. 9 3 3 —6. C.M . Goodess, J.P. P a lu tik o f and T .D . Davies, Studies o f Glinuztic Effects a n d Impacts Relevant to Deep Underground Disposal o f Radioactive Waste, N irex Safety Series, N S S /R 267, 1992, 398 p p ., available from U K N irex L td, H arw ell. C.M . Goodess, J.P. P a lu tik o f and T.D . Davies, The Nature a n d Causes o f Climate Change: Assessing the long term future, London, Belhaven Press, 1992, 248 pp. K.Y. K im and T.J. Crowley, ‘M odeling the clim ate effect o f un restricted greenhouse em issions over th e next 10,000 years’. Geophysical Research Letters, 1994, vol. 21, pp. 6 81—4.

APPENDICES

Appendix A CLIMATE MAPS OF THE BRITISH ISLES

C h a p te r 3 described the clim atology o f th e B ritish

tem perature range, m ean m axim um and m ean m in i­

Isles using sta tistics from rhe period 1961 to 1990 and show ed a series of colour m aps d e p ic tin g average

m um surface air tem perature. D iurnal tem perature

seasonal conditions for tem p eratu re, p recipitation and a few o th er clim ate variables. In th is appendix,

and m in im u m tem perature, and m ean tem perature is th e average of m ean m axim um and m in im u m

wc present a fu rth er selection o f colour m aps show ing

tem perature.

range is th e difference betw een m ean m axim um

average annual conditions over th e B ritish Isles for

Plate A .2: P recipitation total (liquid plus solid),

a m ore com prehensive selection o f fifteen surface

daily precip itatio n in ten sity (the average d e p th of

clim ate variables. T hese clim atc m aps are p lo tte d

p re cip ita tio n on ‘raindays’), ‘rainday’ frequency (days

using d a ta on a ten m in u te latitu d e /lo n g itu d e grid

w ith g reater th an 0.1 m m precip itatio n ) and ‘snow -

and are derived from 1961 to 1990 station averages.

days’ frequency (days w ith snow lying on the g round

T h e co n stru ctio n o f th e clim atologies is described in th e follow ing p ublication: E.M . Barrow, M. H u lm e

at 0 9 0 0 G M T).

and T. J ia n g , A 1 9 6 1 -9 0 Baseline Climatology and

Plate A .3: D aily sunshine in ten sity (average n u m b er o f hours o f sunshine per day), daily solar

Future Climate Change Scenarios fo r Great Britain an d Europe. Part I: 1 9 6 1 -9 0 Great B ritain baseline climatology, A R ep o rt Prepared for th e Landscape

expressed as m ega Joules per square m etre, M Jm -2), cloud cover (proportion o f sky covered) and w ind

radiation in ten sity (derived from sunshine hours and

D ynam ics and C lim ate C hange T IG E R IV Consor­ tiu m , C lim a tic Research U n it, N o rw ich , 34 pp. T he

speed (10 m equivalent).

variables p lo tte d are as follows:

‘frostday’ frequency

Plate A . l : M ean surface air tem p e ra tu re, diurnal

Plate A .4: V apour pressure, relative h u m id ity and (days

tem perature below 0°C).

w ith

grass

m in im u m

CLIMATE MAPS OF THE BRITISH ISLES

Annual m e a n t e m p e r a t u r e

A nn u a l m e a n d iu r n a l t e m p e r a t u r e r a n g e

60°N

60°N

degrees Celsius > 12 11 - 12 10 - 1 1 9 - 10 8 9 7 - 8 7 6 5 - 6 4 - 5 4
90 8.5 - 9 0 8.0 - 8 5 75 - 8 0 7.0 - 7.5 65 - 7.0 6.0 - 6.5 5.5 - 6.0 5.0 - 5.5 5.0

50°N

Annual mean m axim u m tem perature

Plate A I

Annual m ean m inim um tem perature

36 1

362

APPENDIX A

A nn u al m e a n d a il y p r e c i p i t a t i o n i n t e n s i t y

A n n u a l m e a n p r e c i p i t a t i o n total •Y

60\

60° N I

T

1

if

m illim etres > 2100 1900 ■ ■ 1700 1500 1300 1100 WM 900 ■ i 700
4 25

4.00 3.75 3.50 3.25 3.00 2.75 2.50 2.25
76 75 74 73 72 71 70 69 “


o°w

-

363

364

APPENDIX A

Annual m ean vapour pressure

Annual m ean relative h um id ity

60°N

60°N

h e c to P a sc a ls >

11.0

10.5 10.0 9.5 9.0 8.5 8.0 7.5 7.0
130 120 no 100 90 80 70 60
88 87 - 8 8 8 6 - 87 85 - 8 6 84 - 85 83 - 84 82 - 83 81 - 82 80 - 81 < 80

Appendix B THE LAMB CATALOGUE, 1972-95

O ne o f the m ost widely used daily synoptic classifi­ cations for the B ritish Isles is that developed by Professor H .H . Lamb. T he full Catalogue runs from 1 January 1861 to the present day, and its applica­ tion to the understanding o f weather in the British Isles has been discussed in C hapter 8. T he Catalogue was published in full in 1972 in Geophysical Memoirs (London), vol. 16 (116), 85 pp., and is updated in

Climate Monitor, the quarterly publication o f the C lim atic Research U nit. W e publish here the Cata­ logue from 1972 to 1995, ensuring continuity from the 1972 publication. In addition to the eight direc­ tional com ponents (N E , E, SE, S, SW, W, N W and N ), there are the two vorticity com ponents (A, anticyclonicity, and C, cyclonicity) and also an unclassifiable type (U).

366

APPENDIX B Lamb Catalogue for 1972

1 2 3 4 5 6

7

8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Jan

Feb

Mar

Apr

M ay

Jun

AE E E E U SE SE S SE S CS S C S

S S S

C SW C SW C C C E SE AE A A ASE S AS ASE ASE ASE U A A A A A U W NW NW W CW CW

W W W CW CW CW C CN W C C NW CW C ANW A ANW AN ANE A AN ANE ANE AE A AN AN W C C

C C N NE CE C C S CS W C C NE NE N A A C CS S S

W W W S C CS

s cs c u

w w w

w w

w w

c

N AE AE E SE

S SE C C CSW SW SW SW C C AW C C E E A U U A A AE SE S S SW SW

s s

SW w

c

N W CW C NW

Ju l

W W W C CW W W c W c W c W CN AW C A C N A A A AN A ANW A W A W AE W ANE W A W ANE W AE NW C W N SW AN SW A A C A C A AS SW C C

Aug

CN N A C W SW CSW

Sep

A A AN A A A W c U CW C AW NW A NW ANW S A CNW A ANE A A ANW AW NW AN ANW AN ANE A ANW A ANW AW A A A A AE A A A A A AE A AE A AE A A S A

Oct

Nov

Dec

C E A A A E S ASW W C ANE A A A A A ANE A ANE N ANW NW NW AW ASW S S W SW SW

U AW AW AW W W W AW W W NW C CN N AW C N A CS C C NW N A ANW A W W W W

W CW W CW CW SW C C W CW SW SW SW SW

U

s s

SE AS A A A A W A S S SE C

u

A ASW

1 2 3 4 5 6

7

8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

THE LAMB WEATHER CATALOGUE, 1972-95

Lamb Catalogue for 1973

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Jan

Feb

M ar

Apr

M ay

Jun

Ju l

Aug

Sep

ASW W A A A A A A A A AS AS CSE S C U A A S C C W W ASW AW CW NW ANW AW W NW

ANW A A AW W W W CW NW NW W W NW C C A U A NW AW NW NW NW CN U U A AW

W W W W W NW AW A A A A AE A A A A A AN A A A A ASW SE CW AW AS U A W W

W C AW W W CNW N N N N N N NW ANW ANW ANW A AN N N CN CNE E E ANE A N CN C C

NW A E C C C C NW W NW ANW AW W AN A ASE E SE CE E E CSE C U A AS SE C CS C N

W SW CW A A A A A NW NW AW CW NW A AS AS W A CW CNW A A A A A A A U W ASW

SW ASW A A A C ANW A A W NW A W C CE C C NW C C CN CNW CNW NW N AN AN AN A A A

A W CW CW C C W AW W CW A A A A AE U NW A U A AE ASE A A A A W A W NW W

W W W SW A AW A A A ANE A A A A ASE S C C C N NW N N U U

Oct

A A A AE E C U AW W U ANE A E CE CE NE N NW C C ANW AW A A A w A CW S CW A CNW A N A ASE

Nov

Dec

S S S C N ANW AW W W C NW W NW NW NW N A W AN A A U AW CNW N AN A C N U

E A NW NW W NW C N A W W NW NW N A NW NW W SE CE C C

c E

A W W W W W A

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

367

368

APPENDIX B Lamb Catalogue for 1974 Jan

Feb

M ar

Apr

M ay

1 2 3 4 5 6 7 8

A S S S S SW SW

CS CSW CW W C C

10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

SW SW SW SW

C NW N E E S AS SE E E E CE E U W

E CSE A A A A AE AE AE C CE E AE A ANE A A A A A A A ANE ANE ANE AE E E C U

C C E E NE AE A AS S CS CS

9

c u

w w c w w

AW AW ASW SW W W W W SW SW SW SW SW

u w

CW SW

c

CW

c w c c u A A A W W ANW A A A A S

c w w c c A ASE E E E E E E A A A

Jun

AW W AW A U CNW W NW NW NW NW s A A s A A ANE ASE S A S C S W A ASW AW AS W ASE CNW AE N E E N AN E A NE NW NE CNW U AN C A CSW U

Ju l

Aug

Sep

Oct

Nov

Dec

C C CNW CW C U AW ASW W W CW W CN W C C NW NW W NW W W W NW W W W W W CW CW

NW NW A U A AS S C C C W C ASW CSW CSW W NW AN A A A AW SW W W W AW AS CSE CE CSE

C C C W W W C W W ASW S

AN CN NE N N C CN N N N N ANW A A U C

C SW

W W ASW W NW W W W W W N NW NW W W W NW NW AW W SW SW SW W W W W W NW AW AW

s w

ASW C AW W A A AW W W C C C NW C N N N

u w

CW NW N N AN NW NW NW NW N N AN C

c u A U SW W CW

w

CW

w s c

CW

u u CNE A C C C C C NW W NW NW W W

1 2 3 4 5 6 7 8

9

10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

THE LAMB WEATHER CATALOGUE, 1972-95

Lamb Catalogue lor 1975

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Jan

Feb

W ASW W AW AW W NW W W SW SW SW SW SW CSW SW C C W W w w w w c w c c w SW w

AW A A ASE A AE AE E ASE SE SE C C SE ASE S W A A A A S AS AS ASE ASE A AS

M ar

Apr

M ay

Jun

Ju l

Aug

Sep

Oct

Nov

Dec

S

N N N N CN A N N N CNW NW NW W C C W SW S c w SW u A A A A A A W W

W AW A A A E AE CNE CN N U C c c NE U A A A ANE ANE ANE AN ANE AE AE E NE NE N NE

N C CN A S S A ASE E A A A ANW NW CN CN CNW SW SW A AE A A A A AN ANE A A A

A A A NE AN A AE CE C C C CSW S S C u c A s w w w CW NW AW AW A A A A A

A A A SE S S A CE C U A C A U C c CNW A SW WW NW W W A A A A U NE A

A A NW NW NW C A W W W C C N CN ANW U W C AS W AW ASW W W C U C W s cs

CSW c CNW W W ANW A A A NE A A A CS C C A AE ASE SE E SE S ASW A ASW ASW AS S S S

CW CW W AW CW NW A A A E SE E E A C N N ANW NW AN A AW SW W W W C CW W W

C CN NW ANW ANW A ANW A A A A N A A A AN ANE A A A AW AW W NW NW ANW AW W W W W

S CS C C W W C C CN ANE AE AE ANE N AE AE AE AE AE A CW NW N ANW U CNE CN N N N

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

369

370

APPENDIX B Lamb Catalogue for 1976

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Jan

Feb

M ar

Apr

M ay

Jun

Ju l

Aug

Sep

Oct

Nov

Dec

C C NW AW W AW W W W NW NW AW AW ANW A AW A AW W W NW CNW NW N N NW U CS S E E

AE E E AE E SE S W W W NW C U A A A SE S S S S S SW w w AW A SW SW

A A AS S SE SE E E A ASW W C CE U C C A U ASE S S U A A W W W AW W W CW

C CN W W NW NW N A A AW U A U CN A A A A AE AE AE E ANE NE ANE NE ANE A A A

AW W CW U E A A A A NW CW C W ASW SW SW SW C C C W ASW A S c u A SE C C u

C AN A A AW AW A S W AW ASW AW AW AW A A A W CW U A AS ASW A A A A A A A

ASE AE E AE A E E E C A AS S CS SW SW C AW u w NW NW ANW ANW NW NW A A AN ANW N N

NW NW ANW ANW A A A A A A A A A A AE A A A A A A E SE E A ANE ANE AE E C NW

N N NW NW A A A C CN C C CN CNW C CNE U C SE S S S CSE E E E SE SE CSE C CE

CE C W CW SW W CW A U S C C w c c c cs c c c SW s c s u c E E E ANE A

W W W W W CS CSW s u c c CNE A U ASW ANW U U A A AN N AN ANW AW CW W W W C

C

CNW C CN W SW C CW NW ANW A A A ASE ASE SE SE E SE E C SE SE E ANE A N N U CS C

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

THE LAMB WEATHER CATALOGUE, 1972-95 Lamb Catalogue h r 1977

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Jan

Feb

M ar

Apr

M ay

Jun

Ju l

Aug

Sep

Oct

Nov

Dec

C

W SW W W W W C U S C C C CS C u c c c c c c c CE CE U A AE A

S SW W W AW AS SW s w s w SW cs u s s s c c CNE E E E U A ASE CNE AN A A SW

CW NW N AN ANW N N CN N NW NW NW NW AN A U NE A A AW W C C CW w w w CW c c

CNE NE C C C W c u c CW c c N A E NE A A A AE A A AE AE E E AE A N ANE A

A A A NW N C CN U NE C C C NE NE ANE ANE ANE N N ANE AN AE A U W NW W W NW W

AW AS A ASE AE AE ANE NE NE ANE ANE NE N ANE A W C C CW NW W W w CW N N NW N A ANW A

A AW W C N A U A A A AE E E E E CE E CNE C C NE NE A CS c c N A W C w

W W AW AW W CW AW U AW W W ANW A A AN NE NE AE ANE ANE ANE AE ASE SE S W U CW w w

NW NW W W c CE E CSE C w AS SW AS S S S S S S S S S SW w AW ASW W W SW SW W

W C CW W W W SW W w SW w NW NW NW NW N N ANW W CN N NW NW N AN A A A A A

A ASE SE SE SE CE CE C CS S C w w AW A A A U A S S S CSW W AW W NW N NW NW NW

A A AW W A ANW NW CN CN CN C C C CN A A S SW CS cs cs c s c c c u A A U

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

372

A PPEN D IX B

Lamb Catalogue for 1978

1 2 3 4 5 6 7

8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Jan

Feb

Mar

Apr

M ay

Jun

Ju l

Aug

Sep

Oct

Nov

Dec

AW W NW A W SW W A W W C A A A A C C CW C C SW W C C W CNW C C CN A CW

C U W SW w CNW U E AE NE CE NE N U A CE E AE E E SE SE S S S CS S S

C CS C AN A AS ASW W AW AW ASW W SW C C C N w w w NW W CNW W W CW W SW SW SW S

C E E E AE A A A N N N C C N A A A U CS C C AS ASE E E CE C CE E CE

CE E E E NE CNE U E ANE A A CNW CNW C C A ASE E E A A A N AN A A A A A ASE AE

S A ASE SE S W W NW NW NW NW AN AE A C CE NE A NW CW C C C N NW NW W W NW CW

W W CNW N CN N NW NW W A AE E A AN AN AN A NW NW N W SW SW W S SW

CE C C C C C N N N A A U W SW CW w AW AS S w AW W A A AN A AN A AN AN NW

AN A A A U CS U W W W W AW AW W W AW ANW A A A A AW AW W W W NW W CNW CNW

A A W AW W ASW S S C C CS S ASE U C NW NW NW AW ANW AW NW AW W AW ANW A A A ASW W

SW W SW SW SW S CS w A U AS W W W C W SW w w

SE SE SE U SE SE SE C S S S S C C C N A A A E CE SE SE C C C SE C C CE E

s

SW A CNE CNE

w

w w w w NW A ANE A A A

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

THE LAMB WEATHER CATALOGUE, 1972-95 Lamb Catalogue for 1979

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Jan

Feb

M ar

Apr

M ay

A A S U A U W W W C N A A AS S U ANE E E C SE E CNE N C CN W C C C CW

C A ANW U A A C ANE E E E CE CE E AE E E U A SE U A A A A A W W

W W W W W W W W W W W ANW CN CNE NE CNE C CE U CW c NW A AS C C C CN CN N NW

W C C CN N C C C E E C C CS E NE A A A AW W NW W c CN N N ANW NW NW N

CN A N AE N E NW C N C CW C c C c C u A A A A U AW U ASW NW ASW CNW A CNW C ANW A C A C A A A CS C CW W S W C CSW C C NW W C W C W S CSW NW c NW c

Jun

Jul

Aug

Sep

Oct

Nov

Dec

NW ANW A A A AW W W AW A A A NW W A AW AW NW NW NW NW NW NW AW U A AS CSW CW C C

C C N A SW SW CW CW c w A SW SW C w c c U N CW NW CW C C C NE A A A A S

S W W AW AS SW S C U A AW W NW ANW A ASW W W W C N A NW A W W A A A SE

CS SE C C C SE S S S S S S E CNE NE AN A AW W A A U SE S S CE E U W W W

W AW W W NW NW CW CW NW W C U U c c c w NW U A A AW W AW CSW AW A SW SW W

W W W W CW ASW C S C C C U CSW C C W C NW N AN A A C W ASW SW C C CNW N A

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

373

374

A PPEN D IX B

Lamb Catalogue for 1980

1 2 3 4 5 6 7

8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Jan

Feb

M ar

Apr

M ay

Jun

Ju l

Aug

Sep

Oct

Nov

Dec

ANE A SW W CNW CN U SE C A A A A N AN A A A CS CS C C C C U ANE A S S c c

U C C C C CE C S C W AW S CSW W A W SW C U C S C U A U A A A A

A AN A A C C C CN W C W W CNW U E A C CE E NE CNE C SE CS S S C C C AW SW

CW ANW A A A A ANW N NW ANW A S U A U A NW NW N N ANW NW NW A A A A A ANE AE

E E E E E E CNE A A ASE SE CSE SE SE ASE A AE A A CN NE AN AN AN NW C C CN CN C C

W AW A AS U C CN C E E CNE CNE CE C C CSW C W W CNW CW CW C C N N NW C N C

CN A W C C C C CNE N N NW NW C C N A W C C CN AW ASW SW A S C C SE CE C S

S ASE S C C C CE AE A ASW C C SW s c u SW NW ANW W NW ANW A A A ASE U SW C C A

A U U SW W W SW W W C w c CW u s SW s w s u c cs SW AW A A U A A A

W A A A AW CW CW NW NW C CNE A U C NE CNE CN N A A S C C C A S SW CW AW A SE

S E E AE AE E E E NE A N N AW SW C C C U S SW SW SW SW C C NW NW N A A

A N N N NW N A A SW SW W SW W C CNW W W W W C U W CW CW W CNW A W W W W

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

THE LAMB WEATHER CATALOGUE, 1972-95

Lamb Catalogue for 1981

1

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

17

18 19 20 21 22 23 24 25 26 27 28 29 30 31

Jan

Feb

M ar

Apr

M ay

Jun

NW NW NW N NW CNW A AW NW AN A N NW NW NW CW C U NW U W AW A AW ANW AW A A A A A

AW W CW NW NW W W C C N A AS A A A A A A A A U C CE A A SE SE CS

C C

A A AE A AE A A A A A CS U ANE AE AE AE AE AE NE ANE N N U C C CNE NE NW NW NW

N N C CN U C S

AS S SW W SW CW CSW

CNE A A SW W CW W SW W W C CN N N N NW C C C C C C S W

s s

U U U

cs

E CE CE C C U S CSE C CS CS S CS CS S SW

c c c c s s s

Ju l

W C C SW SW SW ASW U c U c c U c C A C ASW W AW NW NW W NW W NW N A NW CNW W N W A W NW A A C CNW N N W N W N ANW N A NW A NW A A

Aug

Sep

Oct

AN A A A A A A A A A A A U ANW ANW AN A AW CW N NW NW A A A A A A U E AE

AE A A A A A CS W ASW S SW

W ASW W CN A A C A c CW A c A c A CW AW NW CW NW NW NW ANW AW U ASW N A W A W CW U W W NW CW W N N W NW W NW W CNW AW W W W W NW CW CW AW W C CW

s c A U AW SW C C C

w w w

SW CS

c c c

SW

c

c c c

Nov

Dec A ANW ANW N CNW NW NW CN CN W CNE A U C C CE E A A S CSE CE E U A S

s

SE CSE SE SE

1

2 3 4 5 6 7 8 9 10 11

12

13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

375

376

A P P E N D IX B

Lamb Catalogue for 1982

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Jan

Feb

M ar

C S u

ASW S S

c c

s s

u A CE A A ANE A A A S

SW w w SW SW SW SW SW ASW A A AE SE ASE SE U U A U

CW W C NW AW W U SW SW C W

s SW

s s s CSW

c w w

w u A NW NW NW AW

w

SW ASW W

Apr

E SW S SE SE C C N ANW NW N c AN w A w A CSW A c A CNW A A U A c c A A u AW A A ANW A A A A A A A A ANW A N NW A NW A

M ay

Jun

Ju l

Aug

Sep

Oct

Nov

Dec

NW W C NW C C U A A A AE A ASE SE CSE S U U S C S SW C W SW U U AW A A

S A ASE SE SE C A A E E C C N ANE U C AE C U A E CE C U SE C C C W W

SW C CNW CW W C AW A C U A AE E CE C W AW A A A A AN A AN ANW ANW A A A U E

C

W AW W U CSE U W AW A A A W A A A A A A C CS C W SW SW S C C SW U A

S SW u

CSW A A S S S SE C CW w SW w w

A

u

CE CE C C C A W W AW ASW W W W C W W C W NW W CW CW W W

w w w

ASW W W

c c CNE N NE N C C C C CN W S S SW SW W W C U W A SW ASW AS S S CS

A A U AW A U C C C C C U W c W NW W W CNW w w W W w CW w CSW N SW NW W c W c W c W c W c CNW AW ASW A ASW A W

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

THE LAMB WEATHER CATALOGUE, 1972-95 Lamb Catalogue for 1983

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Jan

Feb

M ar

Apr

M ay

Jun

Jul

Aug

Sep

Oct

Nov

Dec

W W CW W W W W W W W SW W W NW NW NW W NW ANW AW AW ASW AS SW W W W W W W C

C NW A W A N N A A N AN A A A AE E ASE A A AE ASE SE SE S S U CW W

A S W A AW AW AW A A AW A S S SW w w w c u w w CNW c N NW U C N W W C

NE N W C C C C C C C C N AW AW A W CW CN CN C C C C SE CSE E E C C E

C C C u SE C C C C C C c c cs s SE CSE C C C N W u u A AN N CN CN E E

C C U u ANE A SE C W AW W W W C A A A A A AE AE A N A A NW NW NW NW AN

W W AW A A A E SE A AE AE ANE AN A AW U C NW A A A A C C U A AN A ANW A A

CN NW A AW A A A A A A A NW ANW A SW U A AS SE CE C A C A A A A A A A S

C C C C C AW A C C C N N C S C C W SW W W C AS S U A ASW A E E E

S SW SW SW w AW W W w w w SW SW w SW c w w w A A A A A A AW W AN A AW W

W A A A A A S CS E E E SE A A A AN AN A A N ANE A A S SW C C C U A

S ASW A SW W A A CW C U A U SW SW CS SE SE SE C C C C u s c w w AW AW AW W

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

377

378

A P PE N D IX B

Lamb Catalogue for 1984

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Jan

Feb

M ar

Apr

M ay

Jun

Ju l

Aug

Sep

Oct

Nov

Dec

W W CW W W W NW NW W W C W C C W C CW C U A SE W c c u E CE C SW W W

CW C W W W W W CNW AW AW A ASE A A A AS S S SE C C C U A A A A A A

W CN ANW AW A A A A A AN C C E E E E A A A A SE SE CSE C C C C C N CN ANE

AE AE AE SE A CN NE AN A A W AW ASW CW CNW ANW A ASW ASW ASW AW A A ASE AE AE ASE ASE SE SE

E E U U ANE ANE ANE A A CN ASE A A A U CN CNE N A C N C CNE N N AN AN N A A S

SE CS C CSE C C NE N CN A A AW W AW A A A A A A W CW NW NW NW ANW ANW N N AN

A AN AN A A A A S SE CS S W W W NW ANW ANW AN A A A A A A A A ANW AW SW C C

U C C CE W W CNW A A AN A ANE

U C C N AN A A W C NW W AW SW C A U C U W CW c c CN N U U S S CS C

C CS c c CN W W W W W AW ASW ASW ASW A ASW SW C C CNW W CW W C C W ASW S SW SW S

SW C CN N ANE E E C C U S SW s c c E CE CE C C C C CSW CW CW AW SW SW S CS

C C s s s SW SW AW A A A S C C C C C w w w AW SW CSW W w c u AS A U ANW

A A A A ASW A ASE E E C E AE A A AW W W W

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

THE LAMB WEATHER CATALOGUE, 1972-95

Lamb Catalogue for 1985

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Jan

Feb

Mar

Apr

M ay

Jun

Ju l

Aug

Sep

Oct

Nov

Dec

AN A ANE ANE NE N ANE AN N A A A E AE AE E E E E SE C c NW C C U U C w w w

W W AS A SE E E E E E E E E AE A A A A U AW A A SW A SE A A ASE

C C C C W SW AW A ASW A A A NW NW CNW CN A A AE SE C CE C C C CNE N AW U C C

C U SE SE SE C C C C C C W c NW AW AW A A U N ANE ANE A A AN ANW N W C W

NW CN N C C C A U N AN A AE E C C ASE A CE E E CE CNE C C U CS C AW A A A

A A AE U NE NE N W CW NW C C N AN ANW A AW W C U C C C C CW C W CW W SW

AW A A U C W A U ANW AW W W C C W W SW W W W W C AW A CSE C C C C C NW

W W W C C W W W SE SW C C SE C C C C SE SE CSW CW W C C C W SW ASW A CS C

C C C C U A AW A A A A U W W W W W ASW W ASW C U U A AS A A ASE AS SE

SE SE SE SW SW SE SW W W SW A A A A A A A A A A A AE SE A AE AE A A A A CNE

N N A CS C W C SE C N N A A U C W A A A AE AE ANE ANE NE ANE N CN C A SE

SE SE CSW SW C c c c c u A SW W SW w ASW W W W SW SW SW CSW c CSE CE N AN A U C

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

379

380

APPENDIX B Lamb Catalogue for 1986

1 2 3 4

5

6

7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Jan

Feb

M ar

Apr

M ay

C C NE U C C C C U SW W W W CNW NW W W W CW W W W C N A A W W C CE E

E E E E CE CE AE ANE A A A SE SE E E E E E E A U C NE ANE AE A A A

A A A W W W AW ASW W AW S SE SE S S

C C N AN ANE AE AE E NE NE AN N C C C C C W

W W W NW N A NW W CSW C A A A A AE E C A AE E s w AE SW E SW E SW C SW S SW ASE c AE w AE ANW E AW A W

s s c w

w CSW c w c w c w c c c NW u w A w c CW w CW

c c

AW ASW

A C CE CE CSE CSE C CS S SW CW CS C CSW CW A SE SW AS

Jun

Ju l

Aug

Sep

Oct

Nov

Dec

A A AW W W NW W NW W NW A A A AW AW SW W AW AW W W NW NW W W W SW C C C C

C C C C SW C C A A E A A U CS

W CW U AW AW AW A AN A AN ANE A U CNE NE AN AN A A A AW AW A A A A AW AW A A

A A A ASE ASW AW AW AW SW W A A S W A A A W W CW W W W CSW C W W W W CW C

U A AW AW W A W W S SW

W SW SW SW

c c

N N N A U C CN AN C C N N N NW A

c

c ASW S

c u

SW SW

s s c

SW SW

s

SW SW SW CW

CW CW

w w

c

w

CW

NW N AN A ASW W W W W U C C

c c

CW

w

SW

w

SW SW ASW SW

1 2 3 4

5 6 7 8 9 10 11 12

13 14

15 16

17

18 19 20 21 22 23 24 25 26 27 28 29 30

31

THE LAMB WEATHER CATALOGUE, 1972-95

Lamb Catalogue for 1987

1 2 3 4 5

6 7

8 9

10 11 12 13 14 15 16 17 18 19

20 21 22 23 24 25 26 27 28 29 30 31

Jan

Feb

M ar

C U A W W N A A C u E E E E AE AE ASE ASE AS A A A A A A A A ANE A A A

S S W A SW C AW SW C C C C CE NE A ANE AN AN AN A A ANE A ASE SE SE SW W

SW u A u A S S SE E E E A A A NW NW W CNW N NW W SW C C C CSW C N NW AW W

Apr

M ay

Jun

Ju l

Aug

Sep

Oct

C

U CNW AN ANW A A A A A ANW CNW N NW C CN W C N N AN N NE NE E E E CNE U AW SW W

W S C C C C C N N CNE CN N N CNE N U NW C C U C C C C C U U SW SW W

AW A A A A A NW ANW A U C A A S CS C C C C NE NE ANE AN N N CNW NW W CW W W

W W N AN. AN N N N N A S S SW AW AW A W W AW U C C C NE C N A W A A ASE

U A S

SE E E SE S W C C C C U C C CS C C S S CS C C C A A A

c

E CE E CSE C C C CW C A AW A A A S

s

SW

w

AW AS AS ASE E A A A S u

s w CW

w AW W W SW

w w w

AW A SW A

s c s

SW SW

w

NW AN A A A SE

s c

A ASE E U

Nov

Dec

A

A AE A A E NE A A A A A ASE A A SE S S W W W AW A AS S SW SW CSW

A A A ASE A A U C U

c c c w S

w w SW

w

NW NW NW N N ANE A A A U A

s

SW SW SW

1 2 3 4 5

6 7

8 9

10 11 12 13 14 15 16 17 18 19

20 21 22 23 24 25 26 27 28 29 30 31

381

382

A PPEN D IX B

Lamb Catalogue for 1988

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Jan

Feb

M ar

Apr

M ay

Jun

Ju l

Aug

Sep

Oct

Nov

Dec

W W W C CS C W S SW W W S S S A A AW U CS SW W C U C C C NE E C C C

C CW C C CW NW W W C CNW W W S S SW A A AW A A A A AN N N ANW N N N

N W N N NW NW NW A W ANW NW NW U U C C A AS SW CSW C C C C CW C W W C C U

W C A A A A A AN A A A ANE A AS S CS C SE SE C A AE AE A U

SE CE C C AW A E CE A A E E E E E E N N N A A ASE U S S CSE S S C C C

C C C N A A CNE NE NE ANE AE A A A A A ANE A A A W A A A A A AE N C C

C C C C C C c c w SW CW CSW

A A AW W AW A A SE S U CSW C SW C AW A A CS C C NW W W W W W W CW W SW CSW

C C W SW ASW AS S W A AW W CW N AN A ANW ANW A A A AS SW CW CW W W SW AW NW A

A A A CS C W NW C C U CE C CE A A A E E E CSE SE SE SE SE S S C AN A A A

A A AS ASE A A SE SE S SW ASW AW A A A AS C AN N N A A A A A A A W U C

E E C C NW ANW AW AW W AW AW A A A A A A W W W W W W W SW W W ASW ASW ASW A

c

AE E CE E

c CN A W W AW W A CSW C C CSW SW w

w c CW

c w

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

THE LAMB WEATHER CATALOGUE, 1972-95

Lamb Catalogue for 1989

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Jan

Feb

M ar

Apr

M ay

Jun

Ju l

Aug

Sep

Oct

Nov

Dec

A A S w CW c w w w AW SW w SW w w w A A ASW CSW CW AW SW S S SW S AW AW AW A

ASW ASW SW W W W W ASW S AW AW W W W W A SW SW W W A W W C C C NW CN

U CSE C SW S S AW SW SW SW ASW U C

SE CSE E E E C C U s c c

ASW ASW A A A A A A N A C C w w ASW AW A A A ASE SE E U A A A A A AN N N

N C CN N C C N A CS S S S S A A A A ASE A U A A ANW AW W W C CW A C

C A A A A A C U A AW AW ANW ANW NW ANW A A A A ASE SE U C A U A AW W W NW NW

ANW A ANW A A CSW W W W W W W SW SW SW SW W AW ASW SW ASW AW AW AW U C N A AW W A

NW ANW A A AW A A A ANE AE AE U W CW W W SW SW SW SW

A A A ASE W NW NW NW NW NW W W W W AW SW ASW S S SW CSW SW

A A A A A A A ANE A A A U C C C SE C C U SE C w

SW ASW AW AW A A A A

w

SW SW W CW CNW W W C W CSW CS A A A ASE SE SE SE E E E NE A ANE A A A A A A

c c

CNE A W W W W W W W SW S C A A AW A

c c CN U E N AN ANE NE NE N N N N C C C U SW

c c

w w A SE C C W W

w s SW A A A SE SE SE

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

383

384

APPENDIX B Lamb Catalogue for 1990 Jan

Feb

M ar

Apr

May

Jun

Ju l

Aug

Sep

Oct

Nov

Dec

1 2 3 4

S S S S

C

s c c w w

ASE ASE A A U C C C C N AN ANE AE U SE C U AE AE ANE N A NW N ANE A A A ASW W AS

SW C CW CW SW C C C N N N AN AN A A AS S CS S C C C CW CW W C C U U

A A A AW NW NW ANW AW AW AW W W W W C C

U

s

U C N A AW A AE A A W W CW C W

C NW W C

5 6 7 8

CNW ANW AW W W W W W W SW AW A S ASW SW ASW S

W W W W W C N A W W SW S S S C S CE CE E E E E E CSE CSE C C C C C C

NW N N N ANE A A ASE SE C U S CS CW W W W W W C N A W C CE NE A A A A

A A ANW AN A A C C U A N N A A A A ASE A ANW C W W SW SW W CW W W W W CW

9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

24 25 26 27 28 29 30 31

SW

w w w w SW

w w w w w w w

SW SW SW SW

w w c w c c s s

SW

C W S

SW

c

CW

w w u u

SW SW SW SW ASW

s

SW

c

SW

c w c

s SW SW

w w w NW A A

u A A A A

w w w w c E E A A A A AW A A A A

c

c w w w w

AW AW A A ASE A A A AS A A A A A A ASE SE C S

s

SW A

AW W W W C NW ANW A A A A A A A A w NW W u c NW W w AW NW AW C A C CN U A N A AN ASW A S ASW W U W C W

1 2 3 4

5 6 7 8 9 10 11 12

13 14

15 16

17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

THE LAMB WEATHER CATALOGUE, 1972-95

Lamb Catalogue for 1991

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Jan

Feb

M ar

Apr

M ay

Jun

Ju l

Aug

Sep

Oct

Nov

Dec

W W W W C W C C SW SW C U A ASE SE SE S s SW AW A A A A A A A AS C U U

SE SE SE E E E E E E N U CN A NW C N U A A SW C C SW W A S S A

A S S SE S E E CE C C S S s SW s c c SW w c NW N N A A AE A A A A AW

W W W C C SW W W SW S S C ANE A AE NE AN N N ANW NW U ASW S C A ASE AE C C

N N N N N NW CN A A A W W C ANW AN N A AW W W AW A A A A A A A ANE ANE NE

NE U CN U C C NE A C C W C C C C N N CNW C C C C C C C C C ANW AW C

C CE E AE E E E C U AS S W W CW W W AW C C U A ASE C C N NW ASW A E E C

C S ASW ASW SW C A A ASW W W AW AW A W W W A AW AW S CE C W A A A A A A ASE

C NE A A ANE A A A A A ANE A S SW W W SW W AW A SW W W W C N U E CNE U

W AW W CW W AW S S E E E E C CN U W NW N AN ANW ANW ANW ANW A A SE SE CE S S S

CSW W CW C N W W W NW W W C W CN C C c c CNE A A ASW S S S SW SW SW S A

A A A A AE A AS A A ASE A A A A S SW W W W W C w NW A A W A AW A A W

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

385

386

A PPEN D IX B

Lamb Catalogue for 1992

1 2 3 4 5 6 7

8 9 10 11 12 13 14 15 16 17 18 19

20

21 22 23 24 25 26 27 28 29 30 31

Jan

Feb

M ar

Apr

May

Jun

Ju l

Aug

Sep

Oct

Nov

Dec

W W W U SW SW C C U A A A A A A A A A A A A A ASE AS A A A A A A A

A A W W W AW SW S W SW CSW S W SW W NW A U A A AW SW W SW A SW SW A SW

W W W ASW CSW CSW C A SW W W W W NW W W ASW CSW W W W NW N N NW N N W C CE C

CE NE N A W CS C U A A A W W C C W

NW ANW ASW AW AW W W W C C CSW SW S S A A A AE A A E AE E E E E E E E CE C

C C C U NE NE E E CE E AE A A AW NW A A AN A A A A A A AW AW A A U C

CE AE C C AN A A A A W C CW CW A A S SW SW SW SW C W SW SW SW SW

W W CW W W A A A C

CW

C C C E AE AN A A AN AN NE A A N N N N CN C CNE CNW CNW W W C W C C CN NW AW

W C CW

SW C

w w

A AS U A S S SW CSW CW NW W W

w A A A A

w

SW

c c

A ASW W W A A

u

c cs CSW SW

c c c c

CSW

c c

c

NW NW A S W W SW

s c

CSW CW

w

CW A CE C C CS E C C C U AE E SE S C

w w

AW AW A W W C NW A SE C C NW W W AW

c c s

SW CSW

w w A

s

CSW

w w w cs c u

A A AW W W W C

w s w

A A A A A A A A A A A ASE ASW

1 2 3 4

5 6 7 8 9 10 11 12 13 14 15 16 17

18 19

20 21 22 23 24 25 26 27 28 29 30 31

THE LAMB WEATHER CATALOGUE, 1972-95

Lamb Catalogue for 1993

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Jan

Feb

M ar

Apr

M ay

Jun

Ju l

Aug

Sep

Oct

Nov

Dec

A A A SW W W W W W W W W CW W W W W CW W W W W W W NW W W CW U A A

A

E E AE A ANW A A A ASE S S S S S W W W W AW AW W W W ANW A A ASW S S S CS

C

CNW NW A A A A A A AE E E NE C C C CSW C C C U C SE E E E E E C C C C

U C A A A A AW A SE C C C C C AW W W C C ANW NW N N AN A AW A A A A

A AW W NW ANW ANW ANW W CNW NW NW AW C C C C C C C CNW W W C CW CNW W CW W CW CW W

SW C C C NW AW W W NW NW C NW ASW C C ANW A A AW AW ANW N N N N A A A A A A

A AN AN ANE A ASE SE CE C C C CE E NE CNE C A ASE S S CSW U A U NW AN A C C C

C C C C C CE C CE C C CNE CNE CNE NE N AN A A A N AN A A A A A A AE A A AE

A SE SE SE SE E U A W C W W C U A AS SE S SE ASE E CE E CS ASW A ASE SE S W

W W W W W W W C C C CNW C C U c NW W W NW c CNW C CNW CNW C AE A W W W W

A A A A A A A AS ASE AS AS AS AS A ANW A NW NW NW N A A AW W N N ANE

C C C CS C U S c cs CE CE E A A W W W U CS W SW CS C CNE NE AE AE A C

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

387

388

AP PE N D IX B

Lamb Catalogue for 1994 Jan

Feb

M ar

Apr

8

S

W W C C U S SW W A U U ASE SE SE E AS S S SE E E E E E SE SE C C

C W W W W W W W W AW W W W W W W NW C CNW U

C W W W

7

W C C C C C AN

1 2 3 4

5 6 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

S S S C CW C AE N A W W W W W NW W W W W AW W W AW

u w w w w

A S W W SW

c

M ay

A AS S C w W SW c c U c C U c SE u A E ANW E E AN AN E ANE NE NE A A NE A ANE AE U E C C CE C C SE ANE E CS SW E SW E SW ANE ASW A ASW A A A A

Jun

Ju l

U SW C CNW W W W NW NW ANW A A A ANW NW NW W W W W W W A C U W ASW S

A SE SE C C C C U ASW SW A U A A W A ASE ASE A A A A A ASE S S SW A A CS C

w A

Aug

Sep

Oct

A C N AN NW A A ASW A ASW A A A A NE AS NE A NW c A ANW c A A A CE AW CNE ANE SW AE N AN C AE W A SE CW CW SE W CSE C A A CS A SE C C A C CW C U C A C W A C W ANW C CW CW U ANW A C A U C E C C

c c c

CNE A U W W SW S C C C C

Nov

Dec

W AS CS CS C S S SE SE CE U C SW W CW W SW ASW SW SW ASW SW W A AW AW A A A AS

S S SW

c CSW SW SW CSW

w w w

CW N A ASW AW SW W W NW A A A ASW W W U W SW C N

1 2 3 4

5 6 7

8 9 10 11 12 13 14

15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

THE LAMB WEATHER CATALOGUE, 1972-95 Lamb Catalogue for 1995

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Jan

Feb

M ar

Apr

M ay

Jun

Ju l

Aug

Sep

Oct

Nov

Dec

N A A S SW W AW W W NW N A AW W SW SW CS SW C CSW C C CNW W C CN U C C C A

W A W AW AW W U U A C C C C CSW CW c CW w w w w w w c CNW NW W W

W CW C w c w c c SW s AW A W CNW CNW W CW W NW A A A ASW W NW N N C A ASW W

W W U A W W ANW A A AW AW A A NW NW NW C N N N C NE C E E NE A A AE A

AS A A A A A U CN N ANE NE N N N A CNE CNE N CNW A AS S S C CS S s s c c NW

NW U C C ANW NW N N N N N ANE NE N N W W w SW AW A A A A A AE AE A A A

A N N AN W W AW A ASE E SE S S C C C CSW U ASW SW W A AW A ASE CSE C ASW S U E

AE A ANE ANE A AN A A A ASE S SW W AW A A A A AE A A A NW W CW C NW N NW AN A

A CN C N N C E C C C C C C C CN CN A E NE C CW W W W W W NW NW A U

W SW SW CS SW SW SW s CSW ASW A A ASE S SW S SW AW W ANW A SW S CS CSW SW w A A AS A

ANE A A A AS A AW AW CNW C CE E SE C C C N A A S S SW SW C C CS C CE E SE

S S U A A E E CS A A A A ANE AE AE AE E NE NE NE A CSE C C CN N A A ASE E E

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

389

Appendix C THE DAILY CENTRAL EN G LA N D TEMPERATURE, 1961-95

T h e ‘C entral E n g lan d ' tem p eratu re was originally

present in a form w hich allows easy visual in te rp re ­

devised and pub lish ed in 1953 by th e late G ordon

tation. O n each o f th e graphs th a t follow, th e daily

M anley and th e record represents th e m ean m onthly te m p e ra tu re o f th e E nglish M idlands. T he series

mean tem p eratu re d u rin g th e respective year is show n as a histogram (the th in ‘blocky’ line), w hile

com m ences

E ngland

th e th irty -d ay average for th a t year is show n as the

te m p e ra tu re record was constru cted by th e H adley

heavy black curve. To com pare each year w ith the

C entre, p a rt o f th e U K M et. Office, a few years ago

long-term average, also show n (the bolder dashed

and th is is now routinely u p d a te d by th em . Some

line) is th e average daily tem p e ra tu re for the period

ap plications o f the C entral E ngland tem p eratu re

1961 to 1990.

in

1659-

A daily

C entral

record have been discussed in C h ap ter 9, w here plots o f th e seasonal data from 1659 to th e present have been show n. These seasonal m ean tem p eratu res from 1659 to 1995 are listed in A ppendix D. H ere, we present graphs o f th e daily d ata from 1961 to the

Reference: D.E. Parker, T.P. Legg and C.K. Folland, ‘A new daily Central England Temperature series, 1772-1991’, International Journal of Climatology, 1992, vol. 12, pp. 317-42.

Mean temperature

(”C)

DAILY CENTRAL E N G LA N D TEMPERATURE, 1961-95

30-day average

------

1961-90 daily average

391

A P P E N D IX C

25

25

1964 20

20

15 10

5 0

-5 25

-5 25

1965 20

20

(°C )

15

Mean temperature

392

10

5 0

-5 25

—5

25

1966 20

20

15 -

15 10

5 0

-5

-5

30-day average

.....

1961-90 daily average

DAILY CENTRAL ENGLAND TEMPERATURE, 1961-95 Jon

Feb

Mor

Apr

Moy

Jun

Jul

Aug

Sep

Oct

Nov

Dec

25

1967 20 15 10 5 0 -5 25 20 15 10 5 0 -5 25 20 15 10 5 0 -5

30-doy overage

1961-90 doily average

393

A P P E N D IX C

25

25

1970 20

20

15

15

10

10

5

5

0

0

-5 25

-5 25

1971

Meon temperature ( 9C)

394

20

20

15

15

10

10

5

5

0

0

-5 25

-5 25

1972 20

20

15

15

10

10

5

5

0

0

-5

-5

30-day average

-------

1961-90 dally average

DAILY CENTRAL EN G LA N D TEMPERATURE, 1961-95 Jon

Feb

Mor

Apr

Moy

Jun

Jul

Aug

Sep

Oct

Nov

Dec

25

25

1973 -I 20

,1

20

■*

15

15

10

10

5

5

0

0

-5 25

-5 25

1974 20

20

15

15

10

10

5

5

0

0

-5 25

-5 25

20

20

15

15

10

10

5

5

0

0

-5

-5 Jan

Feb

Mar

30-doy average

Apr

May

Jun

Jul

Aug

Sep

Oct

1961-90 doily average

Nov

Dec

395

A P P E N D IX C

25

25

1976 20

20

15

15

10

10

5

5

0

0

-5 25

-5 25

20

15

15

10

10

5

5

0

0

-5 25

(PC)

20

temperature

1977

Meon

396

-5 25

1978 20

20

15

15

10

10

5

5

0

0

-5

30-day average

.... 1961-90 daily average

DAILY CENTRAL EN G LA N D TEMPERATURE, 1961-95 Jan

Feb

Mor

Apr

Moy

Jun

Jul

Auq

Sep

Oct

Nov

Dee

25

1979 20 15 10 5 0 -5 25 20 15 10 5 0 -5 25 20 15 10 5 0 -5 Jan

Feb

Mar

30-doy average

Apr

Moy

Jun

Jul

Aug

Sep

Oct

1961-90 daily overage

Nov

Dee

397

AP P E N DI X C

25

25

1982 20

20

15

15

10

10

5

5

0

0

-5 25

—5 25

(CC)

1983

Meon temperature

398

20

20

15

15

10

10

5

5

0

0

-5 25

—5

25

1984 20

20

15

15

10

10

5

5

0

0

-5

-5

3 0-day average

-------

1961-90 daily overage

DAILY CENTRAL EN G LA N D TEMPERATURE, 1961-95

25

25

1985 20

20

15

15

10

10

5

5

0

0

-5 25

-5 25

Mean temperature

(°C)

1986 20

20

15

15

10

10

5

5

0

0

-5 25

-5 25

1987 20

20

15

15

10

10

5

5

0

0

-5

-5 Jan

Feb

Mar

30-day average

Apr

May

------

Jun

Jul

Aug

Sep

Oct

1961-90 daily average

Nov

Dec

399

A P P E N D IX C

25

25

1988 20

20

15

15

10

10

5

5

0

0

-5 25

-5 25

1989

Mean temperature (°C)

400

20

20

15

15

10

10

5

5

0

0

-5 25

-5 25

1990 20

20

15

15

10

10

5

5

0

0

-5

-5

30-day average

-------

1961-90 daily average

DAILY CENTRAL ENGLAND TEMPERATURE, 1961-95

25 20

20

15

15

10

10

5

5

0

0

-5 25

-5 25

1992 20

20

15

15

10

10

5

5

0

0

-5 25

-5 25

1993 20

20

15

15

10

10

5

5

0

0

-5

-5

30-day average

1961-90 dally overage

401

APPENDIX C

25

25

temperature

( CC)

1994

Mean

402

20

20

15

15

10

10

5

5

0

0

-5 25

-5 25 1995

20

20

15

15

10

10

5

5

0

0

-5

-5 Jan

Feb

Mar

30-day average

Apr

May

Jun

Jul

Aug

Sep

Oct

1961—90 daily average

Nov

Dec

Appendix D LISTINGS OF CLIMATE DATASETS

In this appendix are listed seasonal and annual values

Table D .3: North A tlantic Oscillation index. These

o f five com m only used clim ate datasets, relevant to

seasonal and annual values represent th e sea-level

B ritish Isles and global clim ate. T h e d a ta are co m ­

pressure difference betw een the Azores and Iceland,

plete from the first year o f th e respective records,

m easured in hectopascals (hPa). N early all values are

th ro u g h 1996. T h e sources o f th e d a ta are acknow l­

positive indicatin g h ig h er pressure in th e Azores

edged and scientific papers are cited w hich contain

than Iceland; the exception is the w in ter o f 1880/1

a d etailed discussion on how they are constructed.

w hen the N A O index was negative. T h e w in ter of

‘Central England' temperature. These

1962/3 also had a very sm all positive value. T he tw o

seasonal and annual m ean tem p eratu res arc expressed

stations used to generate these data were Ponta

Table D .l:

in degrees Celsius from 1659 to 1996. T h e series

D elgada, on the Azores, and Stykkisholm ur, Iceland.

was orig in ally

Professor G ordon

T he data are supplied by D r Phil Jones o f the

M anley, b u t is now u p d a te d by the H adley C entre. T h e d a ta are discussed in the follow ing tw o papers:

C lim atic Research U n it. See the follow ing paper for

G . M anley, ‘C entral E ngland T em peratures: m o n th ly

J.W . H u rre ll, ‘D ecadal trends in the N o rth A tlan tic

constructed

by

m eans 16 5 9 to 1973', Quarterly Journal o f the Royal Meteorological Society, 1974, vol. 100, pp. 3 8 9 -4 0 5 ;

a discussion about the N o rth A tlan tic O scillation: O scillation; regional tem peratures and p re cip ita tio n ’,

D.E. Parker, T.P. Legg and C .K . Folland, ‘A new

Science, 1995, vol. 269, pp. 6 7 6 -9 . Table D .4: Northern Hemisphere (land areas only)

daily C entral E ngland T em perature series, 1 7 7 2 -

surface air temperature anomaly. These seasonal and

19 9 1 ’, International Journal o f Climatology, 1992, vol.

annual tem perature anom alies from 1851 to 1995 / are expressed as differences in degrees Celsius from

12, pp. 3 1 7 -4 2 . Table D .2: England and Wales precipitation. These

the 1961 to 1990 average. T h e source o f the d ata is

seasonal and annual p re cip ita tio n totals are expressed in m m from 1766 to 1995. T h e source o f th e d ata is

D r P hil Jones o f th e C lim atic Research U n it and the d ata set is discussed in the follow ing paper: P.D.

D r P h il Jo n es o f the C lim atic Research U n it, and the

Jones, ‘H em ispheric surface air tem perature vari­

con stru ctio n o f th e record is discussed in the follow ­

ability - a reanalysis and an u pdate to 199 3 \ Journal

in g papers: J.M . G regory, P.D. Jones and T.M .L.

o f Climate, 1994, vol. 7, pp. 1 7 9 4 -8 0 2 .

W igley, ‘P re c ip itatio n in B ritain: an analysis of area-

Table D.5: Global-average (land and marine areas)

average data u p d ated to 19 8 9 ’, international Journal of

surface a ir temperature anomaly. These seasonal and

Climatology, 1991, vol. 11, pp. 3 3 1 -4 5 ; T.M .L. W igley, J.M . L ough and P.D. Jones, ‘Spatial patterns

annual tem perature anom alies from 1856 to 1995

o f p re cip ita tio n in E ngland and W ales and a revised

the 1961 ro 1990 average. T h e data are those used

are expressed as differences in degrees Celsius from

precip itatio n

by the Intergovernm ental Panel on C lim ate C hange

series’, Journal o f Climatology, 1984, vol. 4, pp. 1 -2 6 .

and are supplied by the H adley C entre. T he d ata are

hom ogeneous

E ngland

and

W ales

404

APPENDIX D

discusscd in numerous papers, but see D.E. Parker, P.D. Jones, C.K. Folland and A. Bevan, 'Interdecadal changes of surface temperature since the late ninetcenth century', Journal of Geophysical Research, 1994, vol. 99, pp. 14,373—99; N. Nicholls, G.V. Gruza, J. Jouzel, T.R. Karl, L.A. Ogallo and D.E. Parker,

‘Observed climate variability and change', in J.T. Houghton, L.G. Meiro Filho, B.A. Callendar, A. Kattenburg and K. Maskell (eds), Climate Change 199}: the science of climate change, Cambridge, Cambridge University Press, 1996, pp. 133—92.

Table D. 1 'Central England' mean surface air temperature (*C) Year

Win

1659

Spr

Sum

Aul

Ann

Year

Win

Spr

Sum

Aut

Ann

8.0

15.0

9.3

8.8

1660 1661 1662 1663 1664 1665 1666 1667 1668 1669

2.0 5.0 5.7 1.7 4.7 2.0 3.7 2.3 4.3 3.3

8.7 8.3 8.3 7.3 8.0 7.3 8.3 6.3 7.7 7.7

15.0 14.7 15.0 14.7 15.7 15.0 16.7 16.0 15.3 16.0

9.7 10.7 10.0 10.0 9.3 9.3 10.3 9.3 10.0 10.0

9.1 9.8 9.5 8.6 9.3 8.3 9.8 8.5 9.5 9.0

1700 1701 1702 1703 1704 1705 1706 1707 1708 1709

3.3 3.2 5.1 3.5 3.5 3.4 3.8 3.7 4.5 1.2

7.3 6.1 7.4 8.6 8.4 7.8 9.2 8.2 8.8 8.0

14.5 16.2 14.8 15.4 16.0 15.1 16.1 16.3 15.3 15.2

8.9 9.5 9.6 8.5 8.9 8.2 9.9 9.7 10.2 10.3

8.6 8.7 9.3 9.1 9.1 8.7 9.8 9.4 9.7 8.7

1670 1671 1672 1673 1674 1675 1676 1677 1678 1679

2.0 3.5 2.3 3.7 2.5 2.8 5.0 2.0 1.8 1.0

8.0 8.0 8.0 7.8 6.5 6.8 7.7 8.2 7.2 7.8

15.3 15.0 15.0 15.2 13.7 13.7 16.8 15.3 15.3 16.2

10.0 9.3 9.7 8.0 8.7 7.7 7.5 8.7 9.8 9.2

8.9 9.0 8.8 8.3 8.1 7.8 8.8 8.8 8.4 8.7

1710 1711 1712 1713 1714 1715 1716 1717 1718 1719

3.2 4.8 3.8 4.2 4.5 4.3 0.8 3.3 3.2 3.8

8.0 8.7 7.8 6.8 7.5 9.0 8.0 7.7 8.0 7.8

15.0 15.3 15.3 14.2 15.8 14.8 15.0 14.8 16.2 16.7

10.3 9.8 9.5 9.3 9.8 10.3 9.2 9.5 9.8 9.8

9.5 9.4 9.1 8.6 9.4 9.4 8.4 9.0 9.3 9.5

1680 1681 1682 1683 1684 1685 1686 1687 1688 1689

3.2 1.0 3.7 3.8 -1.2 2.7 6.3 4.7 3.7 2.7

7.7 7.5 7.5 8.8 7.5 8.7 9.3 7.3 6.5 8.0

14.7 15.0 14.5 15.0 15.5 14.3 15.5 14.5 14.5 14.3

10.5 10.7 9.3 8.0 8.7 10.0 9.5 9.3 7.7 8.7

8.9 8.7 9.0 8.5 7.9 9.1 10.1 9.0 7.8 8.5

1720 1721 1722 1723 1724 1725 1726 1727 1728 1729

4.0 3.8 4.5 3.1 5.2 3.7 3.1 3.7 3.3 1.7

7.5 7.2 8.0 9.4 7.8 8.0 8.7 9.3 9.3 6.7

14.7 15.2 14.7 15.3 15.5 13.1 16.0 16.2 16.4 15.9

9.5 9.7 10.4 10.6 9.4 9.7 10.3 10.0 9.7 11.6

9.1 8.9 9.4 9.8 9.3 8.7 9.3 9.9 9.5 9.3

1690 1691 1692 1693 1694 1695 1696 1697 1698 1699

4.3 2.2 1.8 3.8 2.7 0.7 4.7 1.3 1.0 3.4

7.3 7.2 6.8 6.2 6.7 6.0 6.5 8.0 6.5 6.8

14.7 15.2 14.5 14.8 13.7 13.2 14.7 14.3 14.0 15.5

9.3 8.3 7.7 9.2 7.8 8.7 8.7 8.3 8.7 9.4

8.9 8.1 7.7 8.5 7.7 7.3 8.5 8.0 7.6 8.8

1730 1731 1732 1733 1734 1735 1736 1737 1738 1739

4.6 2.5 4.7 5.0 6.1 4.1 5.0 5.6 4.7 5.6

9.1 8.3 8.8 9.0 9.5 8.5 8.7 9.1 8.9 8.0

15.2 16.2 15.7 16.5 15.5 14.8 16.6 15.7 15.5 15.3

11.8 11.8 10.6 9.5 9.3 10.3 10.6 9.7 9.7 8.8

10.0 9.9 9.7 10.5 9.8 9.5 10.3 9.9 9.8 9.2

LISTINGS OF CLIMATE DATASETS Table D. 1 (cont.)

Year

Win

Spr

Sum

Win

Spr

Sum

Aut

Ann

1740 1741 1742 1743 1744 1745 1746 1747 1748 1749

-0.4 2.8 3.1 3.4 3.1 3.2 2.2 4.8 3.2 5.0

6.3 6.9 7.1 8.0 7.4 7.8 7.6 7.6 6.2 8.1

14.3 15.8 15.5 15.8 15.4 14.4 15.3 16.6 15.3 14.9

7.5 11.2 8.6 10.8 9.7 10.1 8.4 10.2 10.2 10.2

6.8 9.3 8.4 9.8 8.8 8.8 8.6 9.8 8.8 9.4

1780 1781 1782 1783 1784 1785 1786 1787 1788 1789

1.4 3.4 4.2 3.2 1.2 1.4 3.0 4.1 3.8 2.1

9.0 9.3 6.1 7.9 7.3 7.3 7.1 8.6 8.9 7.3

16.2 17.0 14.9 16.5 14.3 15.4 15.4 15.1 15.7 15.3

9.7 10.4 7.7 9.6 9.4 9.3 7.5 9.0 9.8 8.8

9.1 10.2 8.0 9.3 7.8 8.5 8.3 9.3 9.2 8.9

1750 1751 1752 1753 1754 1755 1756 1757 1758 1759

5.1 3.2 3.1 3.3 3.5 2.3 4.3 2.4 3.2 5.2

8.9 7.5 7.6 8.5 7.4 7.8 7.3 7.9 8.7 8.9

15.5 14.9 15.4 15.2 14.7 15.1 14.9 15.9 15.1 16.5

9.5 8.4 10.3 9.2 10.0 8.9 9.0 9.5 8.6 9.8

9.7 8.4 9.2 9.1 8.8 8.5 8.8 8.9 8.9 10.0

1790 1791 1792 1793 1794 1795 1796 1797 1798 1799

5.7 4.4 2.6 3.9 4.8 0.5 6.2 2.6 4.1 2.0

8.1 8.9 8.7 7.1 9.5 7.5 8.2 7.7 9.5 6.1

15.0 15.3 15.1 15.4 16.4 15.0 14.8 15.6 16.5 14.6

9.5 9.5 9.2 9.7 9.4 10.7 9.1 8.5 9.4 8.9

9.4 9.3 9.2 9.1 9.9 8.7 9.0 9.0 9.6 7.9

1760 1761 1762 1763 1764 1765 1766 1767 1768 1769

2.7 5.8 4.4 2.6 4.6 2.7 1.4 2.9 3.0 3.3

9.2 9.4 8.9 8.2 7.8 8.0 7.3 7.3 8.3 8.0

16.0 15.5 16.7 15.1 15.1 14.9 15.3 14.4 15.2 14.8

10.2 9.9 8.7 9.1 8.6 8.8 9.9 10.1 8.8 8.9

9.8 10.0 9.6 8.9 8.7 8.5 8.6 8.7 8.9 8.8

1800 1801 1802 1803 1804 1805 1806 1807 1808 1809

2.1 4.2 2.3 2.9 4.4 2.8 4.0 4.4 2.4 3.3

8.5 9.0 8.4 8.6 8.3 8.2 8.0 7.5 7.6 8.1

16.1 16.0 14.8 15.8 15.9 15.2 15.5 16.1 16.6 14.5

9.5 9.7 9.7 8.6 10.5 9.2 10.6 8.3 8.6 9.2

9.2 9.6 8.9 9.1 9.6 9.0 9.8 8.6 8.8 8.9

1770 1771 1772 1773 1774 1775 1776 1777 1778 1779

4.4 2.6 2.9 3.8 2.9 4.7 2.2 2.9 2.6 5.6

6.0 6.9 7.0 8.4 8.6 9.5 8.9 8.5 7.8 9.7

14.7 14.8 16.4 15.9 15.6 16.4 15.2 14.9 16.5 16.6

9.4 9.2 10.6 9.2 9.2 9.5 9.8 10.6 8.8 10.6

8.5 8.6 9.1 9.2 9.1 10.1 9.0 9.1 9.2 10.4

1810 1811 1812 1813 1814 1815 1816 1817 1818 1819

3.3 3.1 3.7 3.1 0.4 3.7 2.4 4.7 3.2 4.1

7.4 9.6 6.6 8.7 7.2 9.3 6.8 7.3 7.6 9.0

14.8 14.9 13.8 14.4 14.3 14.8 13.4 14.3 16.6 15.7

9.7 11.2 9.1 8.3 8.5 9.0 8.7 9.6 11.6 8.9

8.8 9.7 8.2 8.7 7.8 9.1 7.9 8.9 9.8 9.2

Aut

Ann

Year

405

406

APPENDIX D Table D. 1 (co n ti

Year

Win

Spr

Sum

1820 1821 1822 1823 1824 1825 1826 1827 1828 1829

1.4 3.5 5.8 1.5 4.6 4.3 3.8 2.7 5.7 3.9

8.3 8.2 9.6 8.0 7.6 8.6 8.8 8.9 9.1 7.8

14.7 14.5 16.0 13.6 14.8 15.9 17.6 15.2 15.6 14.8

1830 1831 1832 1833 1834 1835 1836 1837 1838 1839

1.1 2.7 4.1 4.0 6.5 4.7 3.4 3.8 1.4 3.6

9.5 9.3 8.4 8.9 9.3 8.6 8.0 5.6 7.2 6.9

1840 1841 1842 1843 1844 1845 1846 1847 1848 1849

3.8 1.6 3.1 4.4 4.3 1.5 5.8 1.7 4.1 5.1

1850 1851 1852 1853 1854 1855 1856 1857 1858 1859

3.5 5.0 4.8 4.5 3.1 1.9 3.8 3.8 4.2 5.1

Aut

Ann

Year

Win

Spr

Sum

Aut

Ann

8.7 11.3 10.4 9.3 10.1 10.4 9.7 10.7 10.6 8.0

8.6 9.5 10.1 8.4 9.3 9.7 10.1 9.5 10.3 8.2

1860 1861 1862 1863 1864 1865 1866 1867 1868 1869

2.3 2.7 4.3 5.7 3.7 2.7 5.3 4.7 4.5 6.8

7.4 8.1 8.9 8.6 8.6 8.7 7.8 7.9 9.7 7.8

13.5 15.2 13.8 14.8 14.4 15.8 15.2 15.1 16.9 15.3

8.5 9.7 8.8 9.6 9.5 10.9 10.1 9.2 9.2 10.0

7.9 9.1 9.2 9.7 8.9 9.7 9.6 9.0 10.4 9.6

14.2 16.3 15.5 14.9 16.2 16.1 15.1 16.0 15.0 14.6

9.7 10.7 10.1 9.6 10.4 9.6 8.5 9.4 9.0 9.7

8.7 10.1 9.5 9.5 10.5 9.6 8.9 8.8 8.1 8.7

1870 1871 1872 1873 1874 1875 1876 1877 1878 1879

3.0 2.4 5.2 4.1 4.9 2.8 4.1 5.9 5.0 0.7

8.5 9.1 8.2 7.7 8.8 8.7 7.3 7.0 8.7 6.4

16.1 15.1 15.5 15.3 15.4 15.0 16.0 15.0 16.0 13.7

9.0 8.6 9.5 8.9 9.9 9.7 10.0 9.2 9.0 8.5

9.0 9.1 9.8 9.0 9.3 9.4 9.5 9.2 9.2 7.4

8.3 9.3 8.5 8.2 8.4 6.7 8.7 8.2 9.3 8.2

14.6 13.8 15.7 14.3 14.5 14.2 17.1 15.5 14.6 15.0

8.1 9.1 8.6 9.3 9.5 9.2 10.4 10.0 9.4 9.7

8.5 8.7 9.2 9.1 8.6 8.3 10.1 9.2 9.4 9.3

1880 1881 1882 1883 1884 1885 1886 1887 1888 1889

2.5 2.3 5.1 4.8 5.5 4.4 2.4 2.7 2.5 3.7

8.2 8.1 9.1 6.9 8.3 7.0 7.4 6.3 6.7 8.2

15.2 14.6 14.4 14.6 15.9 14.6 15.1 16.1 13.7 15.1

9.0 9.6 9.2 9.6 9.7 8.5 10.5 7.8 9.3 9.4

9.1 8.6 9.4 9.0 9.8 8.6 8.7 8.3 8.2 9.0

7.9 7.9 8.0 7.3 8.7 6.4 7.3 8.0 7.8 8.8

15.4 14.8 15.9 14.6 14.6 15.3 15.2 16.5 15.8 16.4

9.2 8.9 9.5 9.2 9.6 9.4 9.3 11.0 9.5 9.1

9.1 9.1 9.8 8.4 9.3 8.0 9.1 10.1 9.1 9.6

1890 1891 1892 1893 1894 1895 1896 1897 1898 1899

4.0 1.5 3.3 2.9 4.4 1.2 4.4 3.8 5.4 5.8

8.3 6.5 7.2 10.2 8.5 8.6 9.2 7.9 7.7 7.6

14.0 14.6 14.3 16.5 14.5 15.3 15.6 15.9 15.1 16.9

9.9 9.7 8.6 9.3 9.6 10.0 8.1 9.9 11.2 10.2

8.7 8.5 8.2 10.0 9.3 8.6 9.3 9.4 10.1 9.7

LISTINGS OF CLIMATE DATASETS Table D. 1 (conl.)

Year

Win

Spr

Sum

Aut

Ann

1900 1901 1902 1903 1904 1905 1906 1907 1908 1909

3.1 4.3 3.2 5.3 3.6 4.2 4.4 3.1 4.1 3.4

7.4 8.1 7.7 8.2 8.0 8.3 7.6 8.1 7.6 7.8

15.8 15.8 14.3 14.2 15.2 15.5 15.6 13.6 14.9 13.9

10.2 9.5 9.7 10.0 9.1 8.1 10.7 10.0 10.7 9.0

9.6 9.1 8.8 9.3 9.0 9.1 9.4 8.8 9.3 8.6

1940 1941 1942 1943 1944 1945 1946 1947 1948 1949

1910 1911 1912 1913 1914 1915 1916 1917 1918 1919

4.2 5.0 5.1 5.3 5.2 4.3 5.5 1.5 4.2 3.9

8.2 8.5 9.4 8.6 8.9 8.0 7.7 7.1 8.5 8.1

14.7 17.0 14.3 14.7 15.5 14.8 14.5 15.5 14.9 14.6

8.8 9.8 8.5 11.1 10.1 8.4 10.1 9.8 8.9 7.8

9.2 10.1 9.4 9.8 9.9 8.9 9.2 8.5 9.5 8.5

1950 1951 1952 1953 1954 1955 1956 1957 1958 1959

1920 1921 1922 1923 1924 1925 1926 1927 1928 1929

5.6 5.4 4.9 5.7 3.9 5.8 4.7 4.2 4.4 1.7

9.1 9.0 7.6 7.8 7.5 8.0 8.6 8.8 8.6 8.1

14.0 16.2 13.7 15.1 14.4 15.7 15.6 14.7 14.8 14.9

10.1 10.5 8.8 8.5 10.2 8.5 9.5 9.7 10.2 10.5

1930 1931 1932 1933 1934 1935 1936 1937 1938 1939

4.6 3.8 4.8 4.1 3.2 6.1 3.0 5.4 4.6 4.7

8.1 7.8 7.4 9.4 8.0 8.2 8.3 8.3 9.1 8.7

15.4 14.7 15.8 17.0 16.2 16.3 15.4 15.7 15.3 15.4

10.1 9.4 9.4 10.2 10.4 10.0 9.8 9.6 11.2 10.4

Year

Win

Spr

Sum

Aut

Ann

1.5 2.6 2.2 5.9 4.3 3.7 4.5 1.1 5.1 5.6

9.1 7.0 8.5 9.6 8.9 10.1 8.6 8.6 9.6 8.8

15.7 15.7 15.5 15.6 15.7 15.7 14.7 17.0 14.8 16.5

9.8 10.5 9.6 10.1 9.3 11.2 10.6 10.9 10.4 11.5

9.1 9.1 9.1 10.0 9.6 10.3 9.4 9.6 10.0 10.6

5.1 2.9 3.9 3.5 4.1 3.5 2.9 5.5 4.2 3.6

8.8 7.0 9.9 8.5 8.2 7.4 8.3 9.5 7.4 9.8

15.9 15.0 15.7 15.4 14.1 16.5 14.1 15.6 15.3 16.6

9.4 10.7 7.9 10.7 10.5 10.1 9.9 9.9 10.8 11.5

9.4 9.3 9.1 9.8 9.2 9.3 8.8 10.0 9.4 10.5

9.6 10.5 8.7 9.1 9.3 9.2 9.7 9.2 9.6 9.0

1960 4.6 1961 4.9 1962 3.6 1963 -0.3 1964 3.5 1965 3.4 1966 4.4 1967 5.1 1968 3.5 1969 3.2

9.4 9.7 6.9 8.4 8.8 8.3 8.2 8.4 8.1 7.3

15.4 15.0 14.4 14.8 15.1 14.6 15.0 15.5 15.1 15.7

10.2 10.7 9.5 10.7 10.1 9.2 9.8 9.9 11.0 10.8

9.7 9.9 8.6 8.5 9.5 8.9 9.4 9.6 9.3 9.3

9.4 9.0 9.4 9.8 10.0 9.7 9.3 9.6 10.2 9.7

1970 1971 1972 1973 1974 1975 1976 1977 1978 1979

7.8 8.1 8.4 8.2 8.3 7.7 8.3 8.2 8.3 7.5

15.9 15.0 14.2 15.7 14.8 16.9 17.8 14.4 14.5 15.0

11.0 10.4 9.5 9.7 8.9 9.9 10.1 10.6 11.5 10.5

9.6 9.7 9.2 9.5 9.6 10.0 10.1 9.5 9.4 8.8

3.3 4.4 4.9 4.8 5.4 6.4 5.2 3.3 4.1 1.6

407

408

APPENDIX D Table D. I (conf.) Year

Win

Spr

Sum

Aut

Ann

Year

1980 1981 1982 1983 1984 1985 1986 1987 1988 1989

4.6 4.5 2.6 4.3 4.2 2.7 2.9 3.5 5.3 6.5

8.2 9.0 8.8 7.8 7.6 8.0 7.3 8.2 8.8 9.0

14.8 15.0 15.9 17.1 16.3 14.5 14.8 14.8 14.8 16.5

10.1 10.3 10.8 10.6 10.9 9.9 10.0 9.9 9.6 10.9

9.4 9.2 9.8 10.0 9.7 8.9 8.7 9.1 9.8 10.5

1990 1991 1992 1993 1994 1995 1996

Win

Spr

Sum

Aut

Ann

6.2 3.0 4.6 4.7 4.7 5.9 3.0

9.6 8.9 9.9 9.2 8.8 8.8 7.4

16.2 15.5 15.7 14.9 16.2 17.4 15.8

10.7 10.6 9.5 8.5 11.0 11.5

10.6 9.5 9.9 9.5 10.2 10.5

LISTINGS OF CLIMATE DATASETS Table D.2 'England and Wales' precipitation (mm) Year

Win

Spr

Sum

Aul

Ann

Year

Win

Spr

Sum

Aul

Ann

1766 1767 1768 1769

200 275 268 259

217 192 145 160

249 271 362 279

201 241 399 276

806 941 1247 951

1770 1771 1772 1773 1774 1775 1776 1777 1778 1779

190 218 277 183 309 240 203 127 145 137

217 129 200 226 215 116 119 220 138 164

234 207 215 186 257 347 294 291 225 279

402 252 401 379 250 335 226 229 309 284

1079 793 1032 1034 995 1012 847 860 888 901

1810 1811 1812 1813 1814 1815 1816 1817 1818 1819

173 273 235 166 115 194 216 238 272 243

204 233 241 193 175 211 206 162 326 186

254 227 225 175 227 204 312 346 103 190

300 281 268 289 219 222 261 132 303 236

973 950 923 828 829 799 1007 883 943 902

1780 1781 1782 1783 1784 1785 1786 1787 1788 1789

213 157 199 231 132 138 231 182 226 207

203 101 363 155 209 55 144 180 113 200

124 197 338 226 294 227 184 268 229 296

293 217 244 237 147 272 313 276 146 308

699 734 1109 834 811 719 889 918 614 1109

1820 1821 1822 1823 1824 1825 1826 1827 1828 1829

208 149 261 252 215 219 240 172 315 180

170 248 192 166 196 197 124 226 210 166

204 200 236 261 218 160 122 173 356 396

218 346 329 245 388 293 267 310 224 245

776 1038 905 991 1027 840 730 935 1073 913

1790 1791 1792 1793 1794 1795 1796 1797 1798 1799

201 320 207 241 177 168 269 158 236 209

165 137 270 166 182 164 155 219 137 179

233 216 315 173 169 237 232 329 259 324

239 294 298 235 378 293 215 339 306 397

856 928 1117 777 895 878 863 1090 869 1079

1830 1831 1832 1833 1834 1835 1836 1837 1838 1839

133 225 180 275 331 185 165 262 181 184

223 189 188 151 111 199 210 118 169 142

321 229 270 215 316 157 225 216 262 351

283 323 251 232 170 368 362 237 298 358

1006 1005 865 914 835 900 1015 828 894 1076

1800 1801 1802 1803 1804 1805 1806 1807 1808 1809

157 248 219 196 313 184 259 227 127 275

229 194 102 137 216 161 123 157 175 179

92 193 252 167 210 222 230 171 229 267

352 308 203 184 243 139 219 271 282 180

902 948 757 751 883 735 892 746 809 941

1840 1841 1842 1843 1844 1845 1846 1847 1848 1849

270 156 208 204 167 129 242 157 307 225

114 187 155 258 102 157 227 200 212 192

213 269 198 256 189 272 256 152 344 179

283 385 300 269 258 234 262 255 299 267

801 1064 820 955 718 874 927 848 1130 867

409

410

APPENDIX D Table D.2 (conl.j

Year

Win

Spr

Sum

Aul

Ann

Year

Win

Spr

Sum

Aut

Ann

1850 1851 1852 1853 1854 1855 1856 1857 1858 1859

218 211 232 267 151 132 194 217 92 193

177 191 99 159 117 139 208 197 188 201

216 237 337 289 185 269 224 242 190 228

229 168 456 247 185 233 225 253 217 311

801 781 1213 874 673 745 901 845 739 939

1890 1891 1892 1893 1894 1895 1896 1897 1898 1899

194 105 244 214 263 191 151 290 205 287

174 187 128 72 177 147 142 218 187 186

264 288 248 205 264 247 185 232 166 133

219 319 288 231 285 259 314 201 233 254

826 997 829 756 980 856 839 916 770 840

1860 1861 1862 1863 1864 1865 1866 1867 1868 1869

243 210 154 212 164 229 280 270 230 381

215 153 276 120 177 152 151 246 169 226

371 254 223 230 118 257 261 209 143 99

247 273 260 308 250 268 320 191 247 299

1083 848 929 862 703 903 1049 891 907 943

1900 1901 1902 1903 1904 1905 1906 1907 1908 1909

323 222 225 227 284 153 246 165 223 151

121 179 173 252 171 197 171 216 228 217

245 197 222 310 190 224 170 232 216 255

236 195 202 391 165 236 290 253 174 252

975 805 758 1180 815 765 926 899 807 933

1870 1871 1872 1873 1874 1875 1876 1877 1878 1879

253 203 287 299 167 266 192 418 197 250

117 167 220 161 127 118 208 249 226 191

131 251 304 246 180 303 186 291 271 409

276 271 394 241 308 399 324 302 295 168

733 869 1285 834 852 1037 1057 1144 984 983

1910 1911 1912 1913 1914 1915 1916 1917 1918 1919

329 240 338 270 185 423 374 186 194 324

160 142 184 274 205 141 226 183 159 212

260 150 410 114 218 238 215 303 204 173

244 276 225 268 227 195 303 245 325 193

997 839 1099 868 971 990 1028 863 963 926

1880 1881 1882 1883 1884 1885 1886 1887 1888 1889

138 268 235 332 231 265 192 241 147 172

147 169 217 132 153 193 260 140 183 253

279 288 303 228 187 148 189 112 317 209

379 261 370 356 169 373 307 252 228 230

1028 967 1146 974 792 918 1051 669 878 849

1920 1921 1922 1923 1924 1925 1926 1927 1928 1929

298 210 275 333 222 330 293 200 320 171

273 138 184 193 233 204 159 186 158 106

250 133 267 192 284 177 223 337 253 185

187 164 162 312 320 282 304 327 286 344

953 629 928 1013 1083 967 905 1108 1023 894

LISTINGS OF CLIMATE DATASETS Table D.2 (cont.)

Year

Win

Spr

Sum

Aut

Ann

Year

Win

Spr

Sum

Aut

Ann

1930 1931 1932 1933 1934 1935 1936 1937 1938 1939

330 256 145 213 119 328 290 362 246 319

198 213 272 168 187 164 144 248 95 159

247 318 184 154 173 189 266 149 226 260

331 246 317 205 216 424 259 195 315 318

1025 982 923 718 850 1015 956 962 892 1008

1970 1971 1972 1973 1974 1975 1976 1977 1978 1979

288 201 214 205 295 236 146 340 297 335

177 176 220 177 102 200 129 179 187 316

195 267 160 219 243 136 74 216 210 164

308 197 183 184 378 218 397 221 129 222

934 824 853 740 1028 759 792 959 897 1023

1940 1941 1942 1943 1944 1945 1946 1947 1948 1949

210 265 193 292 174 233 277 235 308 193

183 197 215 148 111 159 162 314 161 174

148 238 183 199 213 235 298 146 259 122

354 184 209 239 378 188 323 150 206 321

907 867 840 832 894 847 1052 833 963 789

1980 1981 1982 1983 1984 1985 1986 1987 1988 1989

327 185 216 253 318 186 272 236 293 186

152 310 175 290 140 203 258 211 218 205

288 141 251 111 128 293 218 251 268 156

284 337 331 234 373 166 247 329 216 207

967 992 989 885 930 893 1013 945 982 857

1950 1951 1952 1953 1954 1955 1956 1957 1958 1959

272 285 209 170 179 239 259 282 293 218

168 269 204 165 173 190 96 127 166 177

273 221 194 250 307 138 331 265 310 154

320 295 303 224 378 187 182 260 262 219

1015 1095 901 755 1093 773 865 904 1057 828

1990 1991 1992 1993 1994 1995

421 258 143 208 388 415

85 159 210 211 241 147

157 202 262 212 157 67

231 230 336 290 298 258

842 802 980 1013 1050 841

1960 1961 1962 1963 1964 1965 1966 1967 1968 1969

374 310 257 145 89 221 363 272 212 255

147 154 184 231 226 205 216 244 207 252

283 192 186 251 182 247 274 185 274 198

439 261 215 299 159 287 264 348 317 197

1195 905 814 878 725 1032 1061 1010 1015 905

41 1

412

A PPEN DIX D

Table D.3 North Atlantic Oscillation index (hPa units) Year

W in

1865 1866 1867 1868 1869

13.2 25.9 15.2 29.4 31.3

1870 1871 1872 1873 1874 1875 1876 1877 1878 1879

13.7 17.2 23.4 20.5 28.2 14.1 20.3 22.4 24.5 8.5

1880 1881 1882 1883 1884 1885 1886 1887 1888 1889

18.6 -2 . 0 30.1 26.4 26.1 19.8 16.9 27.4 5.9 25.3

1890 1891 1892 1893 1894 1895 1896 1897 1898 1899 1900 1901 1902 1903 1904 1905 1906 1907 1908 1909

15.3 16.4

Sum 15.1 14.7 13.9

Ann

1 0 .8

14.4 15.2 10.4 22.4 15.5

1 1 .6

1 0 .8

14.1

13.6 13.9 15.5 19.0

2 0 .0

1 0 .1

19.1 15.7 15.1

1 2 .2

2 0 .6

1 2 .6

10.5 10.4

15.3 8.7 14.1

1 2 .1

10.7 16.2 16.0

11.0 1 1 .2

9.9 14.8

18.2 18.4 18.1 13.0 15.6 10.7 10.3 18.6

30.8

17.6

2 0 .0

2 1 .0

8 .1

15.0

19.3 14.0 35.9 4.7 20.3 23.2 28.8 16.9

1 1 .6

1 0 .8

9.4 17.1 12.3 13.8

13.5 19.0 9.8 17.1 15.3 17.3 11.4

1 2 .6

28.8 28.6 2 2 .0

30.8 28.0 28.7 27.5

11.0 14.3 11.7 19.1 1 0 .1

1 0 .8

12.3 13.7 11.5 16.7 4.6 9.1 9.3 13.4 1 2 .1

10.4 13.0 16.4

14.8 13.5 1 0 .6

17.7 17.5 16.4 18.1 18.2 18.4 13.3

Year

W in

1910 1911 1912 1913 1914 1915 1916 1917 1918 1919

30.6 24.0 16.3 28.3 24.6 28.3 25.3 4.1

1920 1921 1922 1923 1924 1925 1926 1927 1928 1929

1 1 .6

14.9 33.5 2 2 .1

35.3 28.4 2 1 .6

35.3 16.1 23.5 26.1

Sum

1 0 .6 1 0 .0 10 .1

13.8 14.9 7.5 9.8 10.4 12.9 15.0 14.3 11.4 19.0 16.1 15.7 17.3 13.3 12.7 1 0 .0

1 0 .6

11.9

1930 1931 1932 1933 1934 1935 1936 1937 1938 1939

30.1 28.1 14.0 20.7 23.9 24.2 3.1 27.2 21.5 23.4

16.3 10.7 14.3 18.7 13.3 19.2 16.0 14.9 17.0 12.7

1940 1941 1942 1943 1944 1945 1946 1947 1948 1949

5.4 9.9 18.5 27.3 24.4

15.2 14.7 13.6

2 2 .8

14.6 19.3 13.9 11.3 9.1

19.8 1 2 .6

17.5 27.8

1 1 .8 1 1 .6

Ann

16.9 16.2 14.9 19.6 18.7 10 .1

13.6 1 0 .0

15.3 12.5 19.9 18.5 18.0 18.5 15.1 15.0 14.6 13.8 17.3 14.1 17.2 14.0 13.4 14.1 17.9 17.3 13.0 14.3 2 1 .1

13.3 1 1 .8

10.9 13.7 19.8 15.7 12.3 17.1 10.4 16.1 17.1

LISTINGS OF CLIMATE DATASETS Table D.3 (cont.)

Year

Win

1950 1951 1952 1953 1954 1955 1956 1957 1958 1959

26.1 23.4 27.3 17.0 27.0 13.3 11.0 26.7 16.0 14.7

15.1 12.0 12.3 17.7 15.7 15.3 10.7 8.3 7.7 15.7

16.7 15.6 11.8 17.5 19.4 10.1 15.1 13.8 11.0 17.9

1960 1961 1962 1963 1964 1965 1966 1967 1968 1969

12.0 29.3 17.7 0.7 7.0 8.7 9.3 23.3 13.7 2.0

11.0 19.8 13.0 11.0 13.0 15.3 13.3 16.7 10.3 16.3

11.6 16.9 12.9 12.3 13.8 12.3 12.1 17.9 10.8 12.0

1970 1971 1972 1973 1974 1975 1976 1977 1978 1979

19.0 16.8 24.6 31.0 30.1 26.9 22.8 7.8 13.7 5.5

15.0 12.2 17.8 18.0 15.6 13.1 11.0 12.3 11.3 15.3

14.2 15.4 19.3 15.3 19.7 15.5 16.6 12.7 14.7 15.0

Sum

Ann

Year

Win

Sum

Ann

1980 1981 1982 1983 1984 1985 1986 1987 1988 1989

19.7 27.0 17.0 28.1 32.6 12.1 14.2 15.6 18.4 36.2

11.6 14.0 12.1 16.5 13.4 13.0 12.9 9.6 17.4 16.0

12.2 13.3 19.4 15.6 18.8 9.6 20.9 11.1 15.0 20.3

1990 1991 1992 1993 1994 1995

31.4 26.3 25.4 30.2 28.0 34.7

16.2 14.9 17.0 11.6 17.2 9.7

22.4 17.4 20.6 17.5 20.3 13.2

413

414

A P PEN D IX D

Table D.4 Northern Hemisphere (land areas only) surface air temperature anomaly ("C) Year

W in

Spr

Sum

1851 1852 1853 1854 1855 1856 1857 1858 1859

-0.28 0.44 -1.05 -0.60 -0.92 -0.48 -0.44 0.27

-0.83 -1.07 -0.99 -0 .2 1 -0.28 -0.83 -0.91 -0.56 0.23

0.09 0.14 0.29 0.16 0.18

1860 1861 1862 1863 1864 1865 1866 1867 1868 1869

-0.69 -1.51 -1.26 0.57 -0.64 -0.94 0.24 0.14 -1.05 0.75

-0 . 8 8 -0.64 -0.13 0.16 -0.47 -0.46 -0.59 -1.07 -0.04 -0.47

-0.13 0.39 -0.38 -0.05 0.04 0.09 0.04 -0.33 0.58

1870 1871 1872 1873 1874 1875 1876 1877 1878 1879

-0.75 -1.91 -0.75 -0 . 1 2 0.32 -1.35 -0.24 -0.48 0.46 -0.44

1880 1881 1882 1883 1884 1885 1886 1887 1888 1889

-0.37 -0.96 0 .6 8

-1.06 -0.24 -0.92 -0.80 -0.72 -1.18 -0.52

Aut

Ann

Year

W in

Spr

Sum

-0.09 -0.54 -0.31 -0.23 -0.46 -1.17 -0.51 -0.55 -0.30

-0.23 -0.29 -0.40 -0.13 -0.57 -0.51 -0.39 -0.42 0.07

1890 1891 1892 1893 1894 1895 1896 1897 1898 1899

-0 . 0 2 -0.81 -0 . 1 0 -1.98 -0.44 - 1 .2 2 -0.33 -0.35 -0.23 -0.25

-0.34 -0 . 6 8 -0.78 -0.64 -0.08 -0.43 -0.50 -0.26 -0.74 -0.44

-0.33 -0.39 -0.23 -0 . 2 0 -0 . 2 0 -0.36 -0 . 0 2 0.04 -0.08 -0.16

-0.50 -0.49 -0.42 -0.34 -0.41 -0.23 -0.50 -0 . 2 0 -0.25 0.29

-0.35 -0.49 -0.56 -0.69 -0.28 -0.58 -0.31 -0.25 -0.27 -0 . 2 0

-0.73 -0.30 -0.73 -0.04 - 1 .2 2 0.13 -0.52 -0.45 -0.54 -0.47

-0 . 6 8 -0.37 -0.73 0.30 -0.72 -0.18 -0.17 -0.55 -0 . 1 1 -0 . 1 0

1900 1901 1902 1903 1904 1905 1906 1907 1908 1909

-0.56 -0.18 -0.13 -0 . 2 2 -0.72 -0 . 8 6 -0 . 2 0 -0.49 -0.33 -0.61

-0.27

0 .0 2

0 .0 0

0 .2 2

-0.43 -0.35 -0.65 -0.50 -0.15 -0 . 8 6 -0.55 -0.82

-0.40 -0.52 -0.46 -0 . 1 2 -0.09 -0.59 -0.37 -0.31

0.08 -0.31 -0.55 -0.47 -0.32 -0.08 -0.24 -0.36 -0.55 0 .0 2

-0.07 -0.15 -0.42 -0.37 -0.49 -0.37 -0.16 -0.62 -0.45 -0.45

0.32 -0.28 -0.16 0.05 0.24 0.24 -0 . 6 8 0.26 -0.64 0.08 0 .0 2 -1.06 -0.56 0.31 -0.85 0.28 0.29 0.50 -0.27 -0.23

-0.41 -0.92 -0.13 -0.62 -0.25 -1.05 -0.73 -0.23 0.15 -0.50

-0.46 -0.67 -0.24 -0.16 -0.90 -0.38 -0.13 0.23 -0.41

1910 1911 1912 1913 1914 1915 1916 1917 1918 1919

-0.40 -0.70 -0.23 -0.42 0.43 -0 . 0 2 0.06 -1.07 -0.95 -0.25

-0.13 -0.57 -0.46 -0.49 -0 . 2 0 -0.36 -0.51 - 1 .1 1 -0.52 -0.49

-0.30 -0.13 -0.51 -0.45 -0.18 -0 . 2 0 -0.28 -0.15 -0.33 -0 . 1 2

-0.43 -0 . 2 1 -0.90 -0.15 -0.25 -0.11 -0.37 -0.30 -0 . 1 0 -0.39

-0.31 -0.35 -0.55 -0.32 -0 . 1 2 -0.13 -0.38 -0.70 -0.36 -0.35

-0.09 -0.37 -0.14 -0.83 -0.83 -0.70 -0.53 -0.31 -0.85 -0.03

-0 . 8 8 -0.55 -0.60 -0.51 -0.69 -0.63 -0.35 -0.59 -0.53 -0.76

-0.31 -0.40 -0 . 2 0 -0.58 -0.62 -0.60 -0.53 -0.51 -0.71 -0.35

1920 1921 1922 1923 1924 1925 1926 1927 1928 1929

-0.41 0.09 -0.39 -0 . 2 0 -0.14 -0.23 0.57 -0.19 -0.14 -0.90

-0.09 0.24 -0.07 -0.53 -0.37 -0.08 -0.18 -0.36 -0.44 -0.39

-0.09 0.07 -0.03 -0.16 -0.07 -0.04 -0.09 0.05 -0.15 -0.11

-0.36 -0.32 -0.19 0.25 -0.04 -0.08

0 .0 2

0.04 0.27 0.36

0 .1 2

-0.15 -0.07 -0.34 -0.18 -0.59 -0.40 -0.29 -0.25 -0.43 -0 . 2 2

0 .0 1

Aut

Ann

-0 . 2 2 0.07 -0.18 -0 . 1 2 -0.24 -0.03 0 .1 0 0.04 0 .2 2 -0 . 1 2 0.07 -0.07 0.06 -0.40

LISTINGS OF CLIMATE DATASETS

Table D.4 (cont.)

Year

Win

Spr

Sum

-0.02 -0.28 -0.24 -0.42 -0.10 -0.30 -0.20 -0.26 0.36 0.00 -0.12

Aut

Ann

Year

Win

Spr

Sum

0.20 -0.27 -0.63 0.23 -0.26

-0.11 -0.37 -0.19 0.28 -0.10 0.19 -0.39 0.46 0.07 -0.05

0.03 -0.18 -0.09 0.14 -0.09 0.02 -0.30 0.07 -0.21 0.04

1930 1931 1932 1933 1934 1935 1936 1937 1938 1939

-0.34 -0.03 0.28 -0.45 -0.19 0.39 -0.48 0.19 0.14

0.16 0.29 0.12 0.06 0.10 0.09 0.32 0.33 0.25 0.24

0.05 0.02 0.32 0.09 0.06 0.03 -0.02 -0.28 0.26 0.13 -0.04 -0.02 0.14 0.01 0.42 0.10 0.54 0.31 0.04 0.19

1970 1971 1972 1973 1974 1975 1976 1977 1978 1979

1940 1941 1942 1943 1944 1945 1946 1947 1948 1949

0.04 0.00 0.10 0.29 -0.08 0.17 -0.33 - 0.11 0.05 -0.06 -0.01 0.03 0.70 0.08 0.12 -0.55 -0.09 0.02 -0.02 0.09 0.01 -0.53 0.14 0.08 0.24 0.02 0.12 0.00 -0.07 -0.03

0.17 0.01 -0.02 0.04 0.20 -0.03 0.27 0.10 0.22 0.18 0.07 -0.15 0.07 0.06 0.39 0.07 0.21 0.13 0.20 0.01

1980 0.36 -0.01 0.13 1981 0.74 0.52 0.27 1982 0.13 -0.05 -0.06 1983 0.83 0.25 0.32 1984 0.08 0.06 0.13 1985 -0.61 0.02 -0.07 1986 0.24 0.28 0.07 1987 0.41 -0.04 0.24 1988 0.54 0.39 0.49 1989 0.67 0.45 0.31

1950 1951 1952 1953 1954 1955 1956 1957 1958 1959

-0.58 -0.56 0.33 0.18 -0.21 0.07 -0.55 -0.36 0.56 0.20

-0.10 -0.17 -0.12 0.10 -0.13 0.20 0.27 0.28 -0.33 0.00 -0.42 0.04 -0.49 -0.28 -0.30 0.03 0.04 -0.01 0.17 0.10

-0.27 0.16 -0.17 0.12 0.25 -0.06 -0.43

-0.27 -0.04

1990 1991 1992 1993 1994 1995 1996

1960 1961 1962 1963 1964 1965 1966 1967 1968 1969

0.29 0.38 0.18 0.24 -0.19 -0.33 -0.03 -0.46 -0.33 -0.92

-0.43 0.21 0.07 -0.16 -0.33 -0.29 -0.15 0.04 0.17 -0.15

0.11 0.11

0.01 -0.09 0.08 0.48 -0.26 -0.17 -0.03 0.09 -0.15 0.01

0.03 0.10

-0.06 0.05 -0.17 -0.27 0.13 -0.06 -0.22 -0.06

0.00

0.25 -0.12 -0.10 -0.45 0.11 -0.04 0.08 0.14 -0.18 0.05

* Parentheses indicate provisional values.

0.11 0.13 -0.26 -0.23 -0.07 -0.05 -0.16 -0.22

0.11 -0.07 -0.44 -0.03 -0.31

0.69 0.62 0.74 0.56 0.21 1.17 0.38

Aut -0.14 0.07 -0.32 -0.05 -0.21 -0.06 -0.66 0.20 0.07 0.20

Ann -0.07 -0.15 -0.33 0.18 -0.21 0.06 -0.37 0.12 -0.03 0.07

0.20 0.09 0.15 0.47 0.01 0.00 0.54 0.44 -0.19 -0.06 -0.10 -0.13 -0.06 0.15 0.15 0.25 0.26 0.42 0.25 0.39

0.90 0.46 0.63 0.67 0.36 0.46 0.42 0.50 0.24 -0.13 -0.20 0.17 -0.21 0.21 0.33 0.11 0.61 0.48 0.57 0.50 0.54 0.62 0.57 0.70 0.06 (0.25)* (0.05) (0.18)

415

416

APPENDIX D Table D.5 Globol average (land and marine areas) surface air temperature anomaly (‘C) Year

Win

Spr

Sum

Aut

Ann

Year

Win

Spr

Sum

-0.25 -0.46 -0.20 -0.83 -0.34 -0.51 -0.25 -0.13 -0.26 -0.30

-0.35 -0.34 -0.42 -0.48 -0.37 -0.42 -0.28 -0.07 -0.52 -0.33

-0.36 -0.28 -0.41 -0.31 -0.35 -0.31 -0.08 -0.10 -0.24 -0.20

-0.50 -0.34 -0.40 -0.33 -0.41 -0.22 -0.11 -0.22 -0.35 -0.04

-0.38 -0.33 -0.41 -0.45 -0.37 -0.36 -0.16 -0.15 -0.34 -0.23

Aut

Ann

1856 -0.42 -0.26 1857 -0.32 -0.52 -0.38 1858 -0.61 -0.46 -0.26 1859 -0.23 -0.17 -0.22

-0.47 -0.62 -0.34 -0.30

-0.36 -0.46 -0.42 -0.23

1890 1891 1892 1893 1894 1895 1896 1897 1898 1899

1860 1861 1862 1863 1864 1865 1866 1867 1868 1869

-0.31 -0.75 -0.63 -0.25 -0.53 -0.38 -0.07 -0.19 -0.55 -0.02

-0.47 -0.54 -0.27 -0.28 -0.46 -0.30 -0.39 -0.38 -0.12 -0.31

-0.17 -0.12 -0.45 -0.39 -0.20 -0.20 -0.06 -0.28 -0.04 -0.30

-0.45 -0.39 -0.56 -0.31 -0.50 -0.19 -0.29 -0.24 -0.31 -0.37

-0.39 -0.41 -0.53 -0.25 -0.45 -0.24 -0.21 -0.30 -0.20 -0.29

1900 1901 1902 1903 1904 1905 1906 1907 1908 1909

-0.27 -0.16 -0.28 -0.27 -0.60 -0.49 -0.23 -0.45 -0.46 -0.56

-0.17 -0.15 -0.40 -0.39 -0.56 -0.43 -0.23 -0.51 -0.55 -0.62

-0.09 -0.15 -0.34 -0.48 -0.48 -0.30 -0.30 -0.49 -0.48 -0.45

-0. Í4 -0.35 -0.42 -0.56 -0.40 -0.31 -0.42 -0.47 -0.57 -0.34

-0.14 -0.23 -0.37 -0.44 -0.48 -0.37 -0.30 -0.49 -0.52 -0.50

1870 1871 1872 1873 1874 1875 1876 1877 1878 1879

-0.36 -0.65 -0.39 -0.24 -0.19 -0.59 -0.37 -0.34 0.16 -0.23

-0.32 -0.18 -0.19 -0.35 -0.58 -0.39 -0.42 -0.38 0.15 -0.24

-0.20 -0.19 -0.09 -0.20 -0.31 -0.27 -0.26 -0.05 -0.04 -0.26

-0.30 -0.48 -0.21 -0.38 -0.40 -0.46 -0.51 -0.03 -0.13 -0.32

-0.32 -0.36 -0.20 -0.29 -0.39 -0.42 -0.41 -0.13 -0.00 -0.29

1910 1911 1912 1913 1914 1915 1916 1917 1918 1919

-0.48 -0.60 -0.27 -0.42 -0.12 -0.13 -0.26 -0.64 -0.57 -0.17

-0.42 -0.60 -0.34 -0.52 -0.27 -0.15 -0.37 -0.68 -0.51 -0.21

-0.43 -0.45 -0.42 -0.43 -0.26 -0.13 -0.38 -0.26 -0.41 -0.28

-0.49 -0.40 -0.53 -0.37 -0.27 -0.17 -0.38 -0.31 -0.23 -0.39

-0.46 -0.48 -0.40 -0.41 -0.24 -0.15 -0.37 -0.49 -0.38 -0.28

1880 1881 1882 1883 1884 1885 1886 1887 1888 1889

-0.33 -0.34 -0.06 -0.43 -0.30 -0.47 -0.28 -0.41 -0.55 -0.14

-0.22 -0.17 -0.20 -0.34 -0.40 -0.40 -0.22 -0.34 -0.37 -0.05

-0.26 -0.14 -0.25 -0.17 -0.33 -0.33 -0.19 -0.31 -0.25 -0.18

-0.40 -0.36 -0.31 -0.35 -0.39 -0.23 -0.29 -0.36 -0.15 -0.33

-0.27 -0.24 -0.23 -0.31 -0.36 -0.33 -0.26 -0.37 -0.31 -0.17

1920 1921 1922 1923 1924 1925 1926 1927 1928 1929

-0.36 -0.28 -0.27 -0.28 -0.20 -0.44 0.05 -0.17 -0.26 -0.47

-0.13 -0.21 -0.33 -0.34 -0.33 -0.26 -0.12 -0.26 -0.33 -0.42

-0.19 -0.18 -0.28 -0.34 -0.27 -0.22 -0.14 -0.14 -0.23 -0.32

-0.25 -0.26 -0.32 -0.22 -0.38 -0.23 -0.12 -0.12 -0.18 -0.19

-0.23 -0.21 -0.31 -0.28 -0.34 -0.24 -0.09 -0.20 -0.23 -0.38

LISTINGS OF CLIMATE DATASETS

Table D .5 (cont.)

Year

Year

Win

0.05 0.08 0.09

-0.06 -0.16 - 0.11 -0.08 -0.09 -0.12 -0.24 -0.24 -0.07 -0.12 -0.17 -0.17 -0.08 -0.12 0.05 -0.04 0.12 0.06 -0.17 -0.02

1970 1971 1972 1973 1974 1975 1976 1977 1978 1979

0.15 -0.22 -0.28 0.21 -0.24 -0.13 -0.26 -0.05

-0.03 0.01 0.06 -0.05 0.12 0.01 -0.09 -0.07 -0.12 -0.13

0.05 0.04 0.03 0.03 0.27 0.13 -0.22 -0.09 -0.06 -0.12

-0.04 -0.02 0.11 0.06 0.00 0.04 0.13 0.04 0.19 0.19 0.15 0.06 -0.10 -0.12 -0.07 - 0.11 -0.12 - 0.11 -0.09 - 0.11

1980 0.24 1981 0.20 1982 0.12 1983 0.39 1984 0.13 1985 -0.11 1986 0.12 1987 0.20 1988 0.36 1989 0.18

-0.32 -0.38 0.12 0.05 -0.11 -0.12 -0.31 -0.15 0.25 0.09

-0.18 -0.14 -0.01 0.13 -0.23 -0.30 -0.31 -0.02 0.09 0.06

-0.12 0.05 0.05 0.07 -0.18 -0.13 -0.21

-0.23 -0.21 0.02 -0.08 -0.06 0.01 - 0.00 0.07 -0.08 -0.18 -0.17 -0.18 -0.25 -0.26 0.08 0.04 0.03 0.10 -0.03 0.03

1990 1991 1992 1993 1994 1995 1996

0.03 0.12 0.01 0.05 -0.08 -0.27 -0.09 -0.22 -0.20 -0.15

-0.17 0.09 0.01 -0.05 -0.24 -0.22 -0.10 -0.04 -0.11 0.09

0.03 0.05 -0.00 0.05 -0.19 -0.13 0.02 -0.07 -0.06 0.05

Win

Spr

Sum

1930 1931 1932 1933 1934 1935 1936 1937 1938 1939

-0.38 -0.20 -0.12 - 0.11 -0.06 -0.17 -0.25 -0.24 -0.31 -0.23 -0.07 -0.28 -0.26 -0.20 -0.05 -0.14 -0.04 0.10 -0.07 -0.09

-0.14 0.02 -0.13 -0.14 -0.03 -0.14

1940 1941 1942 1943 1944 1945 1946 1947 1948 1949

-0.03 0.07 0.16 -0.06 0.23 -0.01 0.03 -0.28 -0.13 -0.09

1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969

-

0.00

0.11 0.06 0.05

Aut

-0.00 -0.04 0.04 0.15 -0.30 -0.10 -0.06 -0.02 -0.03 0.06

* Parentheses indicate provisional values.

Ann

-0.01 0.03 0.02 0.05 -0.24 -0.16 -0.07 -0.08 -0.10 0.03

Spr

0.01 -0.25 -0.07 0.16 -0.16 -0.05 -0.28 0.12 0.00 -0.01 -0.06 -0.03

0.30 0.34 0.29 0.28 0.11 0.53 0.26

Sum

Aut

Ann

-0.05 -0.18 0.03 0.10 -0.08 -0.10 -0.16 0.07 -0.10 0.06

-0.08 -0.13 0.02 -0.03 -0.14 -0.17 -0.20 0.08 -0.02 0.14

-0.03 -0.19 -0.04 0.09 -0.17 -0.12 -0.21 0.06 -0.03 0.06

0.13 0.15 0.04 0.22 0.08 0.03 0.12 0.14 0.30 0.15

0.10 0.08 0.01 0.21 0.05

0.08 0.03 0.07 0.21 -0.02 0.01 0.07 0.26 0.17 0.19

0.11 0.13 0.06 0.24 0.03 0.01 0.10 0.24 0.25 0.18

0.41 0.32 0.21 0.26 0.27 0.33 0.21

0.30 0.34 0.34 0.21 0.29 0.34 0.07 0.00 0.14 0.14 0.08 0.19 0.34 0.26 0.24 0.37 0.39 0.39 (0.25)* (0.15) (0.22)

0.00 0.09 0.26 0.24 0.19

417

G L O SSA R Y

8,80 record: the* past record of the oxygen isotope rario (l80 / l60 ) found in carbonate and carbon dioxide samples expressed as a departure from the current rario found in Standard Mean Ocean Water (SMOW). A 5 ,80 value o f—10, for example, indi­ cates a sample with an l80 / ,60 ratio 1 per cent (or ten parts in a thousand) less than SMOW. 500 hPa level (or geopotential height): a surface of constant pressure in the atmosphere, where the pressure equals 500 hectopascals (or millibars). Commonly used as a measure of the state of the total tropospheric column of air, the 500 hPa level is usually at around 5,500 to 6,000 metres above sea level at mid-latitudes, acid rain: a colloquial term used to describe precip­ itation in a polluted environment, where the rain­ drops become acidified by either sulphur dioxide or by a combination of sulphur dioxide and nitrogen oxides emitted from e.g. motor vehicle exhausts, advection: the process by which the property of a mass of air is transferred by movement, usually in the horizontal direction, aerosols: suspended minute particles (solid or liquid) of dust, sea salt, sulphates and, in urban environ­ ments, carbon, lead and aluminium compounds, produced by combustion of fuels, air mass: a body of air in which the horizontal gradi­ ents of temperature and humidity are relatively slight and which is separated from an adjacent body of air by a transition zone (front) in which these gradients are relatively large, albedo: the proportion of solar radiation which is diffusely reflected from a nonluminous body.

allergens: a substance capable of provoking an allergy. ambient temperature: the temperature of the envi­ ronment surrounding a subject or object, anemograph trace: the record of wind speed by a pen on paper trace. Now largely superseded by electronic loggers, anemometer: an instrument that measures wind speed, usually by means of three rotating cups, angular momentum: the angular momentum of a particle rotating about a fixed axis is the product of the particle’s momentum (its mass X velocity) and its perpendicular distance from the axis of rotation. anthropogenic: of human origin, anticyclone: an area of high pressure and subsiding air, generally accompanied by dry, settled condi­ tions. anti-oxidant: a substance which ‘mops up’ oxidising (potentially harmful) compounds in the human body. Atlantic period: part of the Holocene according to the Blytt/Sernander climate sub-division, referring to a period of supposedly warm and moist condi­ tions in north-western Europe, roughly dated between about 7,500 and 5,200 b p . atmospheric sounder: a satellite-based multispectral radiometer used to make indirect measure­ ments of the vertical distribution of some atmos­ pheric property (e.g., temperature, humidity, etc.). atmospheric thickness: the vertical distance, expressed in metres, between two pressure surfaces in the atmosphere, often 1,000 hPa and 500 hPa.

GLOSSARY

barotropic: the state of a gas or fluid whereby surfaces of constant density lie parallel to or coin­ cide with surfaces of constant pressure, baroclinic: the state of a gas or fluid whereby surfaces of constant density intersect surfaces of constant pressure, implying major atmospheric instability, probable around the frontal zone, baroclinic wave: a wave depression which forms in a strongly baroclinic region of the atmosphere. Beaufort scale: a numerical wind force scale ranging from 0 (calm) to 12 (hurricane) devised by Admiral Beaufort in 1805. benthic foraminifera: unicellular microscopic organisms that live on or in the sediments of the sea-floor and which commonly, but not always, secrete a skeleton of calcium carbonate, blocking: the occurrence of a persistent anticyclone (or cyclone) at the surface, and pressure ridge (or trough) at height in the atmosphere, which disrupts the dominant zonal flow in mid­ latitudes. Over the British Isles, blocking is usually associated with weather extremes (heat or cold, drought or flood). Boreal: a climate zone characterised by long snowy winters and short summers. It is a term also applied specifically to the coniferous forests of the Northern Hemisphere (or more generally to refer to the Northern Hemisphere). The Boreal period may also refer to a part of the Holocene according to the Blytt/Sernander climate sub-division, refer­ ring to a period of cold winters, warm summers and dry conditions in north-western Europe, roughly dated between about 9,500 and 7,500 B P . It gave way to the Atlantic period, boundary layer: used in the sense of the planetar)' boundary layer (i.e., the layer of air from the surface to the level where the frictional influence is absent). Thus, the average wind speed within the boundary layer is lower than the free-stream value. A typical height of the boundary layer is 600 m, but this varies depending on atmospheric conditions, such as temperature and humidity, bubbler: a bottle containing a gas absorbent which can be analysed after a volume of air is bubbled through.

carbon dioxide equivalent: refers to the increase in the concentration of carbon dioxide which would give the same increase in radiative forcing as the combined effect of specified increases in the concentration of an ensemble of greenhouse gases, carcinogenic: capable of causing cancer, circulation types: a synoptic configuration of the atmospheric circulation which is similar to one of several pre-defined configurations. These types form the basis of synoptic weather classifications, circumpolar vortex: the circumpolar flow of winds circuiting from west to east around the Earth over each hemisphere, mainly over the middle lati­ tudes, and carrying most of the momentum of the atmosphere. The depth of this flow through the troposphere may vary from about 2 km to 15 to 20 km above the surface, climate analogue regions: regions which are climatically similar to a source region even though they may be geographically distant, climate response surface: a three-dimensional representation of the geographical distribution of, for example, some plant taxon graphically expressed in terms of different temperature and moisture axes (e.g., mean July temperature on one axis, annual temperature range on the second, and precipitation minus evaporation on the third), climate sensitivity: can be defined as the eventual change in global average surface air temperature which occurs following a doubling of the concen­ tration of carbon dioxide in the atmosphere, coccolithophores: planktonic (floating) microscopic algae, which live in ocean surface waters and which contribute their minute calcium carbonate skele­ tons to the ocean floor in vast quantities, cold front: the boundary line between advancing cold air and a mass of warmer air. The passage of a cold front is normally marked at the surface by a rise in pressure, a fall in temperature and dew |K )in t and a veer in wind, continental drift: the concept, originating in the nineteenth century, which suggests that continents have moved relative to one another and around the Earth’s surface, convection: a type of heat transfer which occurs in

419

420

G LOSSARY

a fluid by the vertical movement of large volumes of the heated material by differential heating (at the bottom of the atmosphere) thus creating, locally, a less dense, more buoyant fluid, convergence: negative divergence, cooling degree days: the number of degrees above a specific threshold temperature, accumulated over all days in the year or season on which the temper­ ature is above the same threshold value. This is a useful measure of energy use for space cooling applications. Coriolis parameter: the factor 2Cl sin(t>, where Q is the Earth’s angular velocity and d 229 Flitwick 280 Florence 139 Fort Augustus 272 Fort William 278 Fortrose 336—7 Foynos 268, 289 Fraserburgh 286, 289 Friar Waddon 276

Gatwick 34, 36-7, 41, 44, 48, 54, 59, 61 Geneva 149 Glanllynnau 89 Glasgow 147, 247-8, 291 Glasnevin 268 Glazebury 247-8 Glencoe 278 Glenquoich 278, 280 Gloucester 122 Gorleston 227, 229 Grantown-on-Spey 270 Gray’s Thurrock 273 Great Dun Fell 224, 227, 229, 247-8, 255 Greenwich 144, 228 Guernsey 277, 281 Gunnersbury tube station 287 Halstead 268 Hampstead 277, 283 Harwell 247-8 Hawarden Bridge 267 Herne Bay 280 Ilewenden Reservoir 277 High Brad field 221, 227, 229, 231-2 High Muffles 247-8 Hillsborough 336 Hindolveston 277 Hitchin 268 Holme Chase 279-80 Horsham 269 Hudson Bay 33 Hull 247-8 Hurn 34 Ilkley 277 Inverness 336 Isle of Portland 34, 37 Keith 270 Kew 147, 227-8, 229, 289, 293 Kew Gardens 223, 267—8 Kew Observatory 263, 292 Kilarney 268 Kilkenny 34, 37, 41, 44-5, 48, 53-4, 60-1, 268

Kilkenny Castle 268 Kincraig 272 Kingston-on-Soar 268 Kinlochquoich Lodge 273, 276 Kinnaird Head 286 Kirkwall 34, 37, 41, 44-5, 48, 53-4, 229, 289 Knockholt 277

432

I ND EX OF PLACE N A M E S

Lady bower 247—8 Lagganlia 272 Lairg 265 Lambeth 290 Langdon Bay 285 Langstamps 280 Leeds 247-8 Leicester 247-8 Lerwick 177-83, 229, 282, 285 Lewis 293 Leyden 139 Limerick 280 Linslade 287 Lisburn 271 Little Chalfont 280 Littleover 277 Liverpool 145, 247-8, 288, 291 Lizard 229 Llidiart y Waun 222 Llyn Idwal 95 Loch Sloy Main Adit 276 Logie Coldstone 270, 272 London 37, 74-5, 144-5, 201, 243-51, 255-7, 263, 268, 280, 285, 290-2 London Bridge 214 Long Ashton 34, 37, 41, 44, 48 Long Barrow 276 Longstone Barrow 274 Lossiemouth 227, 229 Lough Navar 247-8 Louth 277 Lowestoft 34, 37, 49, 51 Lowther Hill 286, 288 Lullington Heath 247—8, 255 Lyncmouth 229 Lynford 272 Lynmouth 273-6 Lyonshall 34, 37

Milford Haven 229 Moor House 229 Moscow 33, 149, 155, 315 Mostrim 271 Nettlecombe 282 Newcastle 247—8 Newmarket 282 Newport 267, 270 Newton Rigg 272 Norrh American Rockies 20 North Fleet 287 North Heath 268 Oak Park 268 Oakham 141 Okehampton 269 Oxford 34, 37, 4 ), 44-5, 48 9, 50, 53-4, 175, 228, 336-7 Paris 140, 147 Pate ham 280 Pegwell Bay 271 Pentlow 280 Peny-Gwrhyd Hotel 272 Pershore 277 Phoenix Park 268 Pitcombe Vicarage 276 Plymouth 34, .36-7, 41, 44, 48, 53-4, 56, 61, 229, 336-7 Ponta Delgada 183, 402 Poole 280 Port William 280 Portland Bill 229 Prestatyn 269 Preston 277 Quilcy 289

Maidenhead 277 Malin Head 289 Malvern 173 Manchester 173, 244, 247-8, 272, 291 Mannheim 140—1 March 268 Margate 280 Markree Castle 271 Marlow 193 Martinstown 275-7 Mayflower Park 268—9 Melbourne 145, 150, 315 Middlesbrough 247-8, 253 Mile End 278, 280 Milford 268

Radcliffe Observatory 175 Ramsgate 271 Rannoch 229 Rannoch Moor 101, 103 Raunds 267-8 Reading 268, 317 Regent's Park 268-9, 281 Revesby Reservoir 277 Rhayader 270-1 Rhondda 276 Rhoose 229 Rickmansworth 271 Ringway 34, 37, 41, 44, 48, 53-4, 173 Rio de Janeiro 2

INDEX OF PLACE NAMES Ronaldsway 229 Ross-on-Wye 280 Rothamsted 173, 263, 292 Royston 38-9, 40, 42-3 Santon Downham 31, 34, 37, 41, 44, 48, 57, 61, 269, 272, 336-7 Scaleby 271 Scarborough 36, 280 Sciily 229, 283, 289 Seathwaite 276 Seathwaite Farm 273 Selbourne 169 Sellafield 229, 340 Sexey’s School 276 Shalford 337 Shannon 268 Shawbury 34, 37, 41, 44-5, 48, 53-4, 269-70 Sheerness 273 Sheffield 247-8, 282, 286-8 Shoeburyness 229 Shoreham 285, 289 Sibton 247-8 Siichester House 277 Simonsbath 275 Southampton 161, 163, 247-8 Southport 228 Southwark 290 Speke 288 Squires Gate 173, 229 St Bees 89 St Harmon 272 St Helier 268 St Kilda 95 St Mawgan 227, 229 St Pancras 280 Stonyhurst 147 Stornoway 34-5, 37, 41, 44-5, 48, 52-4, 58, 61, 177-83, 289, 293 Straith Vaich 247-8 Stratton Strawless 152 Stykkisholmur 183, 402 Sumburgh 229 Sunderland 247-8 Svalbard 123 Swansea 247-8

Tewkesbury 38-9, 42-3 Thorshavn 35, 178 Threadbare Hall 280 Timberscombe 276 Tiree 289 Tiverton 283 Tottenham 268 Tredegar 282 Tummel Bridge 270 Tunbridge Wells 269 Twickenham 278 Upton Warren 77 Upwey 276 Valentia 38-9, 42-3, 147, 177-83, 267 Valley 34, 37, 41, 44, 48, 53-4 Veil 138 Ventnor 280 Verkhoyansk 35 Wakefield 268 Walsall 247-8 Walshaw Dean 277 Warrington 280 Warsop 280 Washington DC 149, 315 Wellingborough 280 West Freugh 229 West Linton 271, 283 Westminster 290 Wharley Croft 247-8 Whipsnade 272 Wick 229 Wilton 268 Winterbourne St Marlin 275 Wisbech 277 Wisley 277 Witney 280 Wittering 288 Wootton Courtenay 274 Worthing 292 Wynford House 276 Yarner Wood 247-8 York 281

433

G E N E R A L INDEX

ablation 84, 95 abnormal weather events 265 absolute severity time-series 240 absolute vorticity 20 absolute vorticity, conservation of 302 acceleration due to gravity 307 account roll evidence 115 account rolls 115, 118-19, 122 accounts 115, 119 accumulated mean temperature 337 acid pollution 165 acid rain 246, 329 adiabatic changes 303 adiabatic cooling 301 adiabatic energy 307 adiabatic equation 301 adiabatic processes, dry and saturated 302 advection 13; of the humidity field 307; of tropical air 272; of warm air 265 aerodynamic radius 259 aerosol forcing uncertainties 331 aerosol(s) 107; anthropogenic emissions of 329; effects 333, 335; forcing 329, 331, 333-4 agricultural production 335 agricultural yields 197 agriculture 54, 335-7 air, malodorous 243; saturated 48 air flow 29, 34, 154, 161, 287, 303 air frost 40, 337; average annual frequencies of 337 air mass 29-30, 41, 98, 147, 155, 165, 265, 305; characteristics 165; concept 155; trajectory 165 air pollutants 24-8, 257-258 air pollution 6, 243-6, 253, 257-9; exposure to 257; legislation 6; monitoring equipment 245; monitoring network 246; policy 259; records 246; traffic-related 258 air quality 243-4, 246, 258, 335; ambient 259; change 251; standard 253

air temperature 40, 335; average annual 80 air trajectory analysis 302 airborne lead 255 airborne parriculate matter 253 AIRMET 320 albedo 27, 31, 331 aldehydes 253 alert thresholds 246, 259 alkenes 253 All Ireland series 202-3, 206-7 allergens 255, 258 almanacs 139 amateur observations 150 amateur observer 137, 150-2 ambient temperature 53 analogue region 347 analogue techniques 319 ancient Egyptian civilisations 299 ancient Greeks 300 anemograph 225 anemograph trace 225 anemometer 223, 225, 227, 289; network 223; record 225; sires 223, 227; wind speed 227; wind speed, monthly 227 Anglian glacial deposits 74 Anglian Glaciation 66, 74 angular momentum 17-18; conservation 16; transport 17-18 annals 123; Icelandic 130 annual correlations 203 annual cycle 41, 166, 198 annual growth rings 103, 112 annual mean wind speeds, reconstructed 227, 231—2 annual range in temperature 15 annual series 202 annual standard deviation 198 annual temperature 129, 179, 183, 193; cycle 341; indices 120, 129; range in 175

G EN ER AL INDEX

annual time-series 178, 180, 184-5 Antarctic ice core 355; ice-sheet 69 anthropogenic carbon dioxide 350 anthropogenic climate change 334 anthropogenic effects 354 anthropogenic forcing 341 anthropogenic gas emissions 11 anthropogenic global warming 347, 351 anthropogenic greenhouse effect 329, 331 anthropogenic warming 350 anti-oxidant status 258 anticyclone 11, 19, 23, 29, 143, 153-7, 222, 302; cold 265, 269 anticyclonic blocking conditions 171 anticyclonic conditions 160. 166-9, 171, 243—4, 265, 271, 293 anticyclonic curvature 20-1 anticyclonic days 160—3, 171, 253 anticyclonic frequencies 166 anticyclonic type 156, 158, 160-1, 164, 166-7, 171 anticyclonic vorticity 22—3 anticyclonic weather 183, 288, 290 anticyclonic westerly (AW) type 156, 166 anticyclonicity 165, 169, 171, 364 aquatic snails 85 Arctic air 45, 153, 280 Arctic seaway 70 Arctic species 70 arsenic 246, 260 artificial hygroscopic nuclei 290 asteroid impact 68 asthma 243, 255, 257—8; incidence of 258 astrological hypothes