Climate change : the science, impacts and solutions [2 ed.] 9781315870359, 1315870355, 9781844077861, 1844077861, 9780643094840

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e SECOND

EDITION

The Science, Impacts and Solutions

A. BARRIE PITTOCK

SECOND

EDI TI ON

CLIMATE

CHANGE The Science, Impacts and Solutions

A. BARRIE PITTOCK n p u b l is h in g fo r a s u s t a i n a b le fu t u r e

First published 2009 by Earthscan © C SIR O 2009 All rights reserved. Except under the conditions described in the Australian Copyright Act 1968 and subsequent amendments, no part o f this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, duplicating or otherwise, without the prior permission o f the copyright owner. National Library o f Australia Cataloguing-in-Publication entry Pittock, A. Barrie, 1938Climate change : the science, impacts and solutions / A. Barrie Pittock. 2nd ed. 9780643094840 (pbk.) Includes index. Bibliography. Climatic changes - Government policy. Climatic changcs - Risk assessment. Global environmental change. Greenhouse effect. Atmospheric. Global wanning. 551.6

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Front cover photos by (left to right): iStockphoto, N A SA , N A SA , the Australian National University Set in 10.5/14 Palatino Edited by Susannah Burgess Cover and text design by Jam es Kelly Typeset by Planman Technologies Index by Wordsharpcr Publishing Services

CONTENTS

Forew ord

ix

A ck n ow led gem en ts

xi

Introduction 1

2

3

xiii

C lim ate ch an ge m atters

1

Turning up the heat

2

W hy is the presen t rap id w arm in g h ap p en in g ?

7

The im portance of d elayed clim ate resp o n ses

10

O bserved im pacts

12

Trends in hum an vulnerability

15

Projections of future clim ate ch ange

16

Facing the challenge

17

C on clu sion

18

En dn otes

19

L e a rn in g from the p a st

23

Proxy data: clues from the p a st

24

The record of the ice a g e s

26

The cau se s of p a st clim ate ch ange

27

V ariations in the E arth 's orbit

28

Role o f green h ou se g a se s in am p lify in g clim ate ch an ges

29

V ariations in so lar ou tp u t

30

V olcanoes, cosm ic co llision s an d aero so ls

31

R ap id clim ate ch an ges in the p a st

32

The last 10000 y ears

35

C on clu sion s from the p ast record

37

En dn otes

39

P rojectin g the fu tu re

43

The n eed for, and n ature of, foresigh t

43

Predictions, scen arios and projections

44

iv

4

5

6

CLIMATE CHANCE: THE SCIENCE, IMPACTS A N D SO LUTIO NS

The em issio n s scen ario s u sed by the IPCC

45

Projections of socio-econom ic futu res

49

F orecasting the w eath er

51

W hy clim ate projections are different

52

H ow go o d are clim ate m o d els?

53

The state of clim ate projections

56

E n dn otes

57

U n certain ty is in e v ita b le , b u t risk is certain

59

D espite uncertainties, decision s have to be m ad e

59

U ncertainty in clim ate ch ange projections

60

From p olarisation to p robability and risk

63

E stim atin g risk

67

U ncertainty and the role o f scep tics

69

A pp lication of the 'p recau tion ary p rin ciple'

73

E n dn otes

74

W hat clim ate ch an g e s are lik e ly ?

77

Projected clim ate ch an ges

78

Su rface w arm in g

80

R egional w arm in gs

82

Precipitation and evaporation

82

Extrem e even ts

84

Sea-level rise

87

T h resh o ld s and ab ru p t or irreversible ch an ges

93

Scen arios in a nutshell

97

E n dn otes

99

Im p acts: w hy b e co n cern ed ?

107

C lim ate ch ange im pacts - reaso n s for concern

109

T h resh o ld s and ab ru p t ch an ges

110

R isks to u nique and threatened sy stem s

111

R isks from extrem e clim ate even ts

115

D istribution of im pacts

118

A g gre gate im pacts

121

CONTENTS

W aking the sleep in g gian ts

7

8

v

122

Effects of a b reakd ow n in the ocean circulation

122

R apid sea-level rise from m elting ice sh eets

124

R u n aw ay carbon dy n am ics

125

Security im plications

126

Stabilisation of green h ou se g a s concentrations

126

G row ing reason s for concern

128

E n dn otes

129

A d a p ta tio n : liv in g w ith clim ate ch ange

133

A daptation concepts and strategies

133

C o sts and benefits of ad ap tation

136

Im plem entation

137

Effects of different rates of clim atic change

140

Equity issu e s in ad ap tation

141

Enhancing a d ap tiv e capacity

144

E n dn otes

145

M itig a tio n : lim itin g clim ate ch an ge

149

W hy m itigation is n ecessary

149

Targets: how m uch m itigation is n eed ed ?

150

W here w e are now

157

H ow difficult is m itigation ?

159

The loom in g p eak in oil production

165

M itigation op tion s

167

Increased energy efficiency

167

C h an ge s in infrastructure and beh avio u r

170

Fuel su bstitution

172

N u clear p ow er

174

H y d ro p o w er

176

Solar energy

177

Wind p ow er

180

B iom ass energy

182

Tidal and w av e energy

186

vi

9

CLIMATE CHANCE: THE SCIENCE, IMPACTS A N D SO LUTIO NS

G eotherm al p o w er

187

The h yd rogen econom y

188

C arbon capture and sequ estration

190

L an d-based carbon sin ks

194

G eoen gin eerin g p o ssib ilities

197

T echnological innovation: attitude is vital

201

The road to effective m itigation

202

E n dn otes

206

C lim ate ch an ge in context

223

Su rface air pollu tion and clim ate ch ange

225

Stratosph eric ozon e depletion

225

L an d -u se ch ange, biodiversity, agricu ltu re and forestry

226

Lan d d e grad atio n and desertification

227

F reshw ater su p p ly

227

P opu lation grow th

229

Sy n ergies an d trade-offs

231

Integration, su stain ab le develo p m en t and equity

232

P ostscript: connections betw een econom ic and clim ate crises

234

E n dn otes

236

10 T h e p o litics o f g re en h o u se

239

Is the science credible?

239

W hat abou t the uncertainty?

241

H ow realistic are the scen ario s?

242

C h oosin g global and local em issio n s targets

243

H ow urgen tly do w e need to act?

246

H ow m uch w ill redu cin g em issio n s cost?

247

M eeting targets m o st efficiently

249

International equity: w h at is fair?

254

The im portance of equity within coun tries

260

E quity betw een gen eration s

261

The role of gov ern m en ts and N G O s

262

W hat role sh o u ld b u sin e ss take?

264

CO N T EN TS

vii

The role o f state an d local go v e rn m e n ts

268

So w h at are the p o litics o f g re en h o u se ?

270

E n d n o tes

271

11 In te rn a tio n a l co n cern a n d n a tio n a l in te r e sts

277

A b rief h istory

277

The K y oto P rotocol

280

N a tio n a l in terests an d clim ate ch an ge

282

A frican n atio n s

283

A u stra lia a n d N e w Z e a la n d

284

C h in a

289

E u ro p ean U nion

291

In d ia, P ak istan an d B a n g la d e sh

293

Latin A m erica

295

Th e R u ssia n F ed eratio n

296

Sm all Islan d S tate s

298

U n ited Sta te s o f A m erica

300

The co m m o n interest in g lo b a l so lu tio n s

306

E n d n o tes

307

12 A c c e p tin g the c h a lle n g e

317

L o o k in g b ey o n d the K y oto Protocol

321

A d d re ssin g the key issu e s

324

E n d n o tes

326

G lo s s a r y (w ith acro n y m s)

329

In d e x

337

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FOREW ORD

B arrie Pittock h a s been a le a d in g research er of co n sid e ra b le sta n d in g w o rld w id e on v a r io u s a sp ec ts of clim ate ch ange. The qu ality and content of research carried ou t by him h as estab lish ed a ben ch m ark that sets the stan d ard for several of his peers and p ro v id e s a m o d el for y o u n g researchers. In this book he h as p ro v id e d a com preh en sive an aly sis of v ario u s asp ects of clim ate change, which he begin s by exam in in g the p h ysical and biological asp ects of clim ate change and a detailed an aly sis of the science of the clim ate system . The book a ssu m es great topical interest for the reader because of several qu estion s that the auth or h as p osed and attem pted to answ er, su ch a s the recent h eatw ave that took place in Paris in the su m m er o f 2003, the frequency of closure of the T h am es barrier, and the m elting of

A n extrem ely eloquent statem en t is conveyed in the title of C h ap ter 4, w hich states 'U ncertainty is inevitable, b u t risk is certain'. This really is the key m e ssa g e in this book p articu larly a s it g o e s on to d e sc rib e the im p a c ts o f clim ate c h a n g e , the se rio u sn ess with w hich these sh ou ld be considered and the im perative need for adaptation . In C h apter 8 a co m p re h e n siv e a n d d e ta ile d a ss e s sm e n t is p ro v id e d on several m itigation actions. The volu m e en d s by m ak in g a logical tran sition into p olitical issu e s that h ave n ation al a s w ell a s international dim en sion s. For sh eer b read th and c o m p reh e n siv en ess of co verage, Barrie P ittock's b ook fills a un iqu e void in the literature in this field. C om in g a s it d o es from an au th or w h o k n o w s the scientific an d technical co m plexities of the w hole subject, this book sh ou ld

glaciers w hich affects not only p arts of Europe but even the high m ountain glaciers in the H im alay as. A stu d y o f p a le o c lim a te is an im p o rta n t com ponent of p resen t-day clim ate ch ange research,

be seen a s a v a lu a b le reference for scien tists and p olicym ak ers alike. In m y view , w hich is sh ared by a gro w in g b od y

an d the b o o k g o e s th ro u gh a lu cid an d u se fu l asse ssm e n t of the evid en ce that is av ailab le to us tod ay in u n d erstan d in g and qu an tifyin g the nature

of concerned citizens w o rld w id e, clim ate ch ange is a challenge faced by the glob al com m unity that w ill req u ire u n p re c e d e n te d re so lv e an d in c re a sin g

and extent of clim ate ch an ge in the p ast. A lso presen ted in co n sid erab le detail are projections of

ingenuity to tackle in the y ears ah ead . Efforts to be m a d e w o u ld need to be b a se d on k n o w led ge and inform ed a sse ssm e n t of the future. Barrie Pittock's

clim ate ch ange in the future in clu din g a d iscu ssio n of the e m issio n s scen ario s d e v e lo p e d and u sed by the IPCC an d projections obtained from it a s w ell as from other sources.

b ook p ro v id e s in form ation an d a n a ly sis that w ill greatly a ssist an d g u id e decision m ak ers on w h at n eed s to be done.

D R R A JE N D R A K P A C H A U R I Director-G eneral, The Energy and R esources Institute, India and C h airm an , Intergovernm ental Panel on C lim ate C h an ge 2005

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ACKNOW LEDGEMENTS

This book is the resu lt of m an y y ears w ork in g on clim ate ch a n g e , n early all b a se d in C SIR O A tm ospheric Research (now p art of CSIRO M arine a n d A tm o sp h e ric R esearch ) in A u stra lia an d e sp ecially with the In tergovern m en tal Panel on

T h ese are: F ig u re s 1, 7, 10, 15, 16, 17, an d 28 (all u n c h a n g e d ) from IP C C ; F ig u re 4 from U K

C lim ate C h an ge (IPCC). I therefore thank m any

U S N A S A ; F igu re 19, 20, an d 21 from the U S N ational Snow and Ice D ata C enter; Figure 23 from T. C olem an , In su ran ce G rou p A u stralia; F igu re 28 from the W ater C o rp o ra tio n , W estern A u stra lia ;

colleagues in CSIRO and m any others from n um erous countries w hom I m et through IPCC or other forum s. M y view s have been influenced by their collective research and argum ents, a s well as m y ow n research, and I ow e them all a debt of gratitude. A book such a s this inevitably d ra w s from and b u ild s on the w ork that h as gon e before it. Since su b tle ch a n g e s in w o rd in g can ea sily lead to m isin terpretation in this field, som e content in this bo o k h a s been carefu lly p a r a p h r a se d from , or clo sely fo llo w s the o rig in a l so u rc e s to en su re accuracy. Som e sectio n s in the p resen t b ook are draw n from the follow ing: p arts of the IPCC Reports, especially the Fourth A sse ssm en t R eport in 2007; a book that I ed ited for the A u stralian G reen h o use Office (A G O ) in 2003 Climate Change: An Australian Guide to the Science and Potential Impacts; and a p ap er I w rote for the journ al Climatic Change in 2002 'W hat w e know an d d o n 't know ab ou t clim ate change: reflections on the IPCC TA R' (Climatic Change vol. 53, p p. 393-411). This a p p lie s particu larly to p arts of C h ap ter 3 on p rojectin g the future, C h ap ter 5 on p rojected clim ate ch an ges, C h ap ter 6 on im p acts and C h ap ter 7 on ad ap tation concepts. I thank the A G O , the IPCC and Sprin ger (p ublish ers of Climatic Change) for p e rm issio n to u se so m e co m m on w o rdin g. I h ave en d e av o u red to ack n ow led ge all sources in the text, caption s or endnotes, how ever, if any have been overlooked I a p o lo gise to the original auth ors and / or p ublishers. The follow ing F igu res com e from other sources, w h o gran ted p erm issio n to u se them , for w hich I am gratefu l. Som e h ave been m o d ified , and the original sources are not resp on sib le for any changes.

Environm ent A gen cy; F igu re 5 from IN VS, France; F igu re 9 from D avid E th eridge, C SIRO ; F igu res 13, 14, and 26 from R oger Jon es, C SIRO ; F igu re 18 from

F igu re 30 from Dr. Jim H an sen , N A S A G o d d a rd Institute for Sp ace Science; F igu re 31 from M artin D ix of CSIRO and courtesy of the m o dellin g gro u p s, the P rogram m e for C lim ate M odel D ia g n o sis and In tercom p arison Project p h a se 3 (C M IP3) o f the W orld C lim ate R esearch P ro g ram m e; F igu re 33 fro m C S IR O C lim a te Im p a c ts G r o u p a n d G overn m en t of N ew Sou th W ales; F igu re 34 from G reg B ourn e, now at WWF A u stra lia ; F igu re 35 from the M u rray -D arlin g Basin C o m m issio n ; and F ig u re 36 from K ath y M c ln n e s, C SIR O and C h alap an K alu w in, A M SAT, Fiji. Particular p eop le I w ant to thank are: From C SIRO : Tom Beer, W illem B oum a, Peter K C am p b e ll, Joh n C h u rch , K ev in H en n essy , P au l H olper, R oger Jon es, K athy M clnn es, Sim on Torok, Penny W hetton, an d Joh n W right. A lso R achel A nning (U K Environm ent A gency), M artin Beniston (U niversité de Fribourg, S w itzerlan d), A ndre Berger (U n iversité C ath oliq ue de L o u vain , B elgium ), G reg B o u rn e (W W F, A u s tr a lia ), M ark D ie se n d o rf (U n iv ersity of N SW ), P ascal E m pereu r-B isson n et (IN V S, France), A n d rew G lik so n (A N U ), Ja m e s H an sen (N A SA G ISS), D ale H ess (BoM and CSIRO , A u stralia), W illiam H ow ard (U. T asm an ia), M urari L ai (C lim ate, Energy an d S u stain ab le D ev elop m en t A n a ly is C en tre, In d ia), K eith L o v eg ro v e (A N U ); M a rk M a s lin (U . C o lle g e L o n d o n , U K ), M ike M acC racken (C lim ate Institute, W ashington), Tony M cM ichael (A N U , A u stralia), Bettina M enne

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CLIMATE CHANCE: THE SCIENCE, IMPACTS A N D SO LUTIO NS

(W HO , Italy), N e v ille N ich o lls (BoM , A u stralia), M artin Parry (Jackson Institute, U K ), Jam ie Pittock (WWF an d A N U , A u stra lia ), T h o m as W. P o gge (C olum bia U niversity, U SA ), A lan Robock (R utgers U n iversity ), Brian S a d le r (IOCI, A u stralia), D avid S p ra tt (C arb on Equity, A u stra lia ), Ph ilip Su tton (G ree n le ap S tra te g ic In situ te , A u s tr a lia ), an d C h ristop h er T h om as (NSW G H O ffice, A u stralia). Probably I h ave om itted so m e p eo p le w ho helped, and ap o lo g ise to them for m y oversigh t. Sp e cial th an ks g o e s to G raem e P earm an an d G reg A yers, su cc e ssiv e C h iefs of C SIR O A tm o s­ pheric R esearch an d C M A R , for m y p ositio n a s a

Post-R etirem en t Fellow , an d m ore recently a s an H on orary Fellow. Special thanks also to Paul D urack and R oger Jon es for help with F igu res, and to John M anger, A nn C rab b (first ed ition ), Tracey M illen and co lleagues at CSIRO Publishing. Their insightful and helpful editin g com m ents and d iscu ssio n s have greatly im proved the book. The v iew s ex p re ssed in this w ork are m y ow n an d d o n ot n e ce ssarily re p re se n t the v ie w s of C SIRO , the A G O , the IPCC or other p arties. Finally, I w ant to thank m y partner D iana Pittock, for her su p p o rt and forbearance du rin g the w riting and extensive revision of this book.

IN TRO D U CTIO N

H u m an -in d u ced clim ate ch an ge is a h u ge, highly topical and rap id ly ch an gin g subject. N ew b ook s,

Back in 1972 I w rote a p a p e r en titled 'H ow im po rtan t are clim atic ch an ge s?' It con clu ded that

rep o rts and scientific p a p e r s on the su b ject are a p p e arin g w ith am az in g frequency. It is tem pting to say that if they w ere all piled in a heap and b u ried u n d ergrou n d the am ou n t of carbon so sequ estered w o u ld so lv e the problem . But seriously, there is a need to ju stify yet another book on the subject.

h u m an d e p e n d en ce on a stab le clim ate m igh t be m ore critical than w a s ge n e rally b eliev ed . T his d e p e n d e n c e , I a rg u e d , is re a d ily seen in the relation ship betw een rainfall p attern s and pattern s of land and w ater u se, including u se for in dustrial

This book is a su b stan tial u p d ate of m y Climate Change: Turning Up the Heat (2005). T h at b ook

severity of the econom ic ad ju stm en ts required by a ch an ge in clim ate d e p e n d on the relation betw een the existin g econom y and its clim atic environm ent, and the rap id ity of clim ate change.

w a s m ean t a s a se rio u s d isc u ssio n of the science, im plications and policy qu estion s arising, ad d resse d to an ed u cated n on-specialist audience. It presen ted both sid e s of m any argu m en ts, rather than ad o p tin g

a n d u rb an p u rp o se s. The p a p e r a rg u e d that the

M y first projections of p o ssib le future pattern s of clim ate ch an ge w ere p u b lish e d in 1980, b a se d on

a racy and sim p lified ad v ocacy p osition. It w as, in the w o rd s o f so m e frien ds, a 'solid read'. It fou nd a n iche a s a tertiary tex tb o o k in m an y m u lti­

the early fin d in g s of relatively cru d e co m p u ter m o d e ls o f clim ate, co m b in ed w ith a look at the contrasts betw een in d iv id u al w arm and cold y ears,

d isc ip lin a ry c o u rse s, w h ere its ob jectivity an d co m preh en siv en ess w ere app reciated.

p ale o -c lim atic reco n stru ctio n s o f earlier w arm epoch s, and so m e theoretical argu m en ts. In 1988 I fou nded the C lim ate Im pact G roup in CSIRO in A ustralia. This gro u p so u gh t to b rid ge the

D ev elop m en ts since 2005, in the science, the observations and the politics of clim ate change are so su bstan tial that they w arrant m ajor ch anges to both the content and tone of the book. Hence the new title Climate Change: The Science, Impacts and Solutions. The urgen cy of the clim ate ch ange ch allenge is now far m ore a p p a re n t than in 2005, w ith new o b serv atio n s sh ow in g that on m any fronts clim ate ch an ge and its im p a c ts are occu rrin g faster than expected. There is a gro w in g probability that we are a p p ro ac h in g or h ave alread y p a s se d one or m ore 'tip p in g p oin ts' that m ay lead to irreversible trends. This is now w ell docu m en ted , but there is a need for a concise and accurate su m m a ry o f the evid en ce and its im plication s for in d iv id u al and joint action. The m e ssa g e is n ot new, b u t a gro w in g se n se of u rgen cy is n eed ed , an d clarity ab o u t the choices an d op p o rtu n ities is essential. It is also essential to convey the n eed for continual u p d a tin g , an d to p ro v id e the m e an s to d o so via relevan t regu lar p ublication s, learned jo u rn als and w ebsites.

g ap betw een clim ate m odellers, with their projections o f clim ate ch an ge and sea-level rise, and p eo p le interested in the p oten tial effects on crops, w ater re so u rces, co asta l z o n es an d other p a rts of the natural and social sy stem s and environm ent. D espite re se rv atio n s from so m e co lle ag u e s w ho w an ted greater certainty before g o in g p u b lic on scientific fin din gs that identify risk, the C lim ate Im pact G roup a p p ro ach of p u b licly q u an tify in g risk w on w id e respect. This culm inated in the aw ard in 1999 of an A ustralian Public Service M edal, and in 2003 of the Sherm an Eureka Prize for Environm ental Research, one of A u stralia's m ost p restigio u s n ational a w ard s for environm ental science. The object of the CSIRO C lim ate Im pact G ro u p 's e n d e av o u rs w as n ever to m ake exact p red iction s of w h at w ill h ap pen , b ecau se w e recogn ised that there are inevitable u ncertain ties ab ou t both the science a n d so cio -eco n o m ic c o n d itio n s re su ltin g from

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CLIMATE C H A N C E: THE SCIENCE, IMPACTS A N D SO L U T IO N S

h u m an b eh av io u r. Rather, w e so u g h t to p ro v id e the

F u rth er p o in te rs to w a r d s u rg en cy h a v e a rise n

b e st p o ssib le ad v ic e a s to w h a t m ig h t h a p p e n , its

fro m the w e ll- d o c u m e n te d o b s e r v a tio n s in the

im p a c ts on society, a n d on the c o n se q u e n c e s o f

la st tw o y e a rs o f m ore ra p id clim ate ch an ge , an d o f

v a r io u s p o lic y c h o ices, so th at d e c isio n -m a k e rs

the k ic k in g in o f p o sitiv e fe e d b a c k (a m p lify in g )

co u ld m ak e in fo rm ed risk a sse ssm e n ts an d ch oices

p r o c e ss e s th at le a d to an a c c elera tio n o f g lo b a l

that w o u ld in fluence fu tu re ou tco m es.

w a r m in g

and

se a -le v e l

rise . C a r b o n

d io x id e

T h ese d a y s, w ritin g, or ev en u p d a tin g a b o o k on

co n cen tratio n s, g lo b a l w a rm in g an d se a-le v el rise

a 'h ot to p ic ' like clim ate ch an g e is a bit o f a w ild

are all track in g n ear the u p p e r en d o f the ra n g e of

rid e . L o ts o f th in g s k eep h a p p e n in g d u rin g the

un certain ty in the 2007 IP C C report.

p ro ce ss. T h is in c lu d e s the U S P resid en tial election

A rctic se a ice is m e ltin g m o re r a p id ly than

o f N o v e m b e r 2008, the in te rn a tio n a l ec o n o m ic

p ro je c te d in the IP C C re p o r t, a n d re a c h e d a

crisis, a n d the w ild flu c tu a tio n s in the p rice o f oil.

startlin gly low m in im u m exten t in S ep tem b e r 2007.

The im p licatio n s of su ch ev en ts rem ain to be p la y ed

M oreover, p e rm afro st is m eltin g, floatin g ice sh elv e s

ou t, a n d are m erely tou ch ed on in this b ook . S ev eral

h ave

oth er m ajo r d e v e lo p m e n ts h a v e sto o d o u t in the

p re v io u sly c o n sid e re d , fo re sts are b u rn in g m o re

case o f this b o o k an d are d e a lt w ith m ore fully.

frequ en tly , d r o u g h ts in m id - la titu d e s are g e ttin g

The In tergovern m en tal Panel on C lim ate C h an ge

r a p id ly

d is in te g r a t e d

by

p ro ce sses

n ot

w o rse , a n d so it go e s.

(IP C C ) re p o rt in 2007 stro n g ly co n firm e d th at

A ll th is le a d s to the p o ssib ility o f a p o c a ly p tic

clim ate ch an ge d u e to h u m an activities is h a p p e n in g

ou tco m es, w ith a sso c ia te d glo o m an d d o o m : m u lti­

an d th at its c o n se q u e n c e s are lik ely to b e se rio u s.

m etre se a -le v el rise d isp la c in g m illio n s o f p e o p le ,

Further, it b ro ad ly co n firm ed the fin d in g s o f the U K

re g io n a l w a te r sh o r t a g e s a n d m a s s sta rv a tio n ,

Stern R ev iew th at the c o n se q u e n c e s o f clim ate

con flict a n d ec o n o m ic d isa ste r. F ac ed w ith su ch

ch an ge u n d e r b u sin e ss-a s-u su a l sc en a rio s are likely

p o ssib ilitie s, three b ro a d p sy c h o lo g ic a l re a ctio n s

to be far m ore ex p e n siv e than efforts to lim it clim ate

are likely: n ih ilism (it's all h o p e le ss so let's enjoy

ch an g e b y re d u c in g g re e n h o u se g a s e m issio n s. It

o u rse lv e s w h ile w e can), fu n d a m e n ta lism (fa llin g

a lso p o in te d o u t th at sta b ilisin g co n ce n tratio n s of carbo n d io x id e eq u iv a le n t (treatin g all g re en h o u se

b ack on so m e rig id set o f b e lie fs su ch a s that G o d , or the free m ark et, w ill sa v e u s), or activ ism in the

g a s e s a s if they w ere carb o n d io x id e ) at 450 p p m

b e lie f that w e can still d e a l w ith the p ro b lem if w e

still le a v e s a m o re than 50% ch a n ce o f g lo b a l

a p p ly o u rse lv e s w ith a su fficien t se n se o f urgency.

w a rm in g s g re ater than 2 °C relative to p re in d u strial

1 tend to fa v o u r the third ap p ro a c h , in the b elief that h u m an b ein gs are intelligen t creatu res and that

co n d itio n s, an d p o ssib ly a s h igh a s 3°C . We are th u s forced to co n sid e r w h eth er in ord er

w ith in gen u ity an d co m m itm en t w e can ach ieve the

to a v o id d a n g e r o u s clim ate ch an g e w e m u st k eep

se em in gly u n ach ievab le, a s h a p p e n e d in the Secon d

g re en h o u se g a s co n cen tration s w ell below 450 p p m

W orld War an d the S p a c e Race. There is a lso still a

carb o n d io x id e e q u iv a le n t. T h is is a 'b ig a sk ', a s

lot o f uncertainty, an d the situ atio n m a y n ot be quite

co n cen tration s o f carb o n d io x id e alo n e are a lre ad y

as b a d a s w e m a y fear, so let's g iv e it a g o o d try.

in 2008 a b o u t 380 p p m an d risin g at an in creasin g

A few c o n tra ria n s co n tin u e to ra ise the sa m e

rate, recently a b o u t 2 p p m each year. Th is h igh ligh ts

tired o b je ctio n s th at so m e p a rtic u la r o b se rv a tio n s

the u rgen cy o f red u cin g g re e n h o u se g a s e m issio n s

or d e ta ils are in d o u b t. T h ey co n tin u e to a cc u se

far b elow p resen t lev e ls in the n ext d e c a d e , rather

clim ate m o d e lle r s o f n e g le c tin g w e ll-re c o g n ise d

than se v e ra l d e c a d e s d o w n the track. In d eed , IPCC

m e c h a n ism s like so la r v a ria b ility or w a ter v a p o u r

su g g e sts

gas

effects, w h ich h a v e lo n g b een in c lu d e d in clim ate

co n cen tration s at le ss than 450 p p m m a y requ ire u s

m o d e llin g . T h ey re fu se to look at the b a lan ce o f

to take carbo n d io x id e ou t of the atm o sp h ere after it

e v id e n c e a s p re se n te d in the IP C C re p o rts, an d

h as o v ersh o t this target.

p refe r to se iz e on the o d d o b se rv a tio n that m igh t

th a t

to

s t a b i li s e

gre en h o u se

IN T R O D U C T IO N

xv

not fit, or so m e altern ative theory, w ith o u t a p p ly in g

a n d a ct n o w to re a lly p u s h fo r a re d u c tio n in

the sa m e sc e p tic ism to th eir fa v o u r e d 'fa c t' or

g re e n h o u se e m issio n s th is d e c a d e . C lim a te ch an ge,

theory. O th ers se t o u t a fa lse d ich o to m y b etw een

a b ru p t or n ot, is a real risk . It is a lso a c h a lle n g e

c o m b a tin g

g lo b a l

a n d an o p p o rtu n ity for in n o v a tiv e th in k in g an d

p ro b lem s, or p ro p a g a te scare sto rie s a b o u t the co st

action . With a bit o f luck an d a lot o f sk ill, w e can

o f re d u cin g em issio n s.

tra n sfo rm the ch a lle n g e o f clim ate ch a n g e into a

c lim a te

ch an ge

and

o th e r

R e sp o n sib le d e cisio n -m ak e rs m u st follow a risk

p o sitiv e o p p o rtu n ity . R e d u c in g g re e n h o u se g a s

m a n a g e m e n t strategy , a n d look at the b alan ce o f

e m issio n s w ill a lso h elp a v o id oth er en v iro n m e n tal

e v id en ce , the full ra n g e o f u n certain ty, a n d p u t

d a m a g e s a n d p ro m o te su sta in a b le d e v e lo p m e n t

clim a te c h a n g e in the co n tex t o f oth er g lo b a l

a n d g re a ter eq u ity b etw een p e o p le s an d co u n tries.

p ro b lem s, w h ich in ge n e ral exacerb ate each other.

P u b lic o p in io n a n d g o v e rn m e n t a ttitu d e s are

I fa v o u r the a d v ic e an d e x a m p le s o f the so cial an d

c h a n g in g

te c h n o lo g ica l o p tim is ts a n d e n tre p re n e u rs w h o

g o v e rn m e n ts h a v e b een slo w to co m m it to u rgen t

r a p id ly ,

a rg u e an d d e m o n strate that w e can ra p id ly d e v e lo p

action on clim ate ch a n g e . O n e o f the sta n d -o u t

a p r o sp e r o u s fu tu re w ith low g re e n h o u se g a s

re lu ctan t c o u n trie s, m y v e ry o w n A u str a lia , h a s

e m issio n s if w e p u t ou r m in d s to it. That w ay w e can

re c e n tly

im p ro v e liv in g sta n d a rd s both in the in d u strialised

g o v e rn m e n t, to the K y o to P rotoco l a n d the new

a n d d e v e lo p in g co u n trie s, w h ile m in im isin g the

n e g o tia tio n p ro c e ss for m o re strin g e n t e m issio n s

risk s an d co sts o f clim ate ch an ge d a m a g e . N ecessity,

re d u ctio n s in the futu re. N ew in form ation is b ein g

a s the say in g g o e s, is the m oth er o f invention. We are

a b so r b e d a n d stro n g e r a d v o c a c y is c o n v in c in g

not sh o rt o f in ven tion s that m igh t co n serv e en ergy

p e o p le it is tim e to act. Th e 'fo rm e r n ext P resid en t

a n d re d u ce g re e n h o u se g a s e m issio n s. W hat is

o f the U n ited S ta te s', A1 G o re, h a s been in flu en tial

n eed ed is a co m m itm en t to d e v e lo p in g these into

w ith h is film a n d b o o k An Inconvenient Truth.

la rg e -sca le p ro d u c tio n a n d a p p lic a tio n , w ith the

H u rrican e K atrin a in A u g u st 2005 co n vin ced p eo p le

c o m m itte d

even

in

c o u n tr ie s

w h o se

itse lf, a fte r a c h a n g e

of

im plicit o p p o rtu n ity for n ew m ore en ergy-efficient

th at even rich co u n trie s like the U n ited S ta te s are

a n d su sta in a b le te c h n o lo g ie s. Efficiency, th at is, u sin g less energy, can be p rofitab le, an d the large-

v u ln e ra b le to clim a te d is a s t e r s , a n d n u m e ro u s b o o k s a d v o c a tin g action , su ch a s th ose b y G e o rg e

scale ap p lic atio n o f ren ew ab le en ergy tech n o lo gies

M o n b io t, M a rk L y n a s a n d Tim F la n n e ry h a v e

can redu ce their co st until they are com petitive.

a p p e a re d a n d so ld w ell.

W hile a c k n o w le d g e d u n certain ties m ean w e are

A b o v e all, IP C C h a s been fo rth rig h t, if still

d e a lin g w ith risk s rath er than certain ties, the risk s

g u a rd e d , in its statem en ts. A lo n g w ith A1 G ore and

w ill in crease o v er co m in g d e c a d e s if w e d o n ot act.

m a n y oth er a c tiv ists, the IP C C 2007 re p o rt h a s

If w e sit b ack a n d sa y to o u rse lv e s that the risk s are

stirred the w o rld to action, a s w a s re co gn ised b y the

too sm a ll to w o rry a b o u t, or too co stly to p rev en t,

a w a rd in g o f the N o b e l P eace P rize to A1 G o re an d

they are likely to catch u p w ith u s all too so on . We,

the IP C C in 2007.

a s c o n su m e rs, b u sin e ss p e o p le an d m e m b e rs o f the

H ow ever, even the IP C C is in evitab ly b eh in d the

p u b lic can turn th in g s a ro u n d b y o u r ch oices an d

tim es, a s its 2007 report only a ss e s se d new m aterial

esp e c ia lly by m a k in g o u r o p in io n s k n o w n . We d o

u p to a b o u t M ay 2006. M u ch n ew in fo rm atio n h a s

not h a v e to w a it for n atio n al go v ern m e n ts to act, or

b ecom e a v a ila b le sin ce then, a n d I h av e atte m p ted

for la w s an d ta x es to c o m p e l u s. In d iv id u a l an d g ro u p ch oices, in itiatives, ingenuity, in n ovation and

to su m m a rise it in w h at follow s. T h is b o o k is m eant

action can ach ieve w o n d ers.

an intelligen t a p p ro a c h to m eetin g the ch allen ge of

to con tin u e the p ro ce ss o f d e v e lo p in g an d in form in g

H o w ev e r, o u r in d iv id u a l a n d c o rp o ra te actio n s

clim ate ch an ge an d se iz in g the o p p o rtu n ity to help

w o u ld b e fa r m o re m o re e ffe c tiv e if w e co u ld

create a b etter an d m o re su sta in a b le w o rld w h ere

p e r s u a d e g o v e rn m e n ts to re c o g n ise the u rg e n cy

oth er g lo b a l p ro b le m s can a lso b e a d d r e s se d . It is

xvi

CLIMATE CHANCE: THE SCIENCE, IMPACTS A N D SO LUTIO NS

inten ded to answ er, in read ily u n d ersto o d term s, frequ en tly ask ed q u estio n s ab ou t clim ate ch ange, such as:

H o p e lies not on ly in scien ce, b u t in g o in g b ey o n d the scien ce to g ra p p le w ith the p olicy q u e stio n s an d the m o ral im p e ra tiv e s that the

•

scientific projections throw into stark relief. In this book I go so m e w ay dow n this ro ad , m ak in g direct

W hat is the relation ship betw een n atu ral clim ate variatio n s and h u m an -in d uced clim ate ch ange?

•

W hat are the m ajor concerns re gard in g clim ate ch ange?

•

W hy are there argu m en ts ab ou t the reality of clim ate ch ange, and its policy im plications?

•

H ow d o e sclim ate ch a n g e re la te to o th e rp ro b le m s like p o p u latio n grow th, poverty, pollution and land degrad atio n ?

•

H ow urgen t is the prob lem ? W hat can w e do abou t it, an d how m uch w ill it cost? T h is

book

is

m e a n t,

in

a

co n c ise

an d

u n d ersta n d a b le manner, to sort fact from fiction. It recognises that uncertainties are inevitable, and sets clim ate change in a fram ew ork of a sse ssin g clim ate risk alon gsid e all the other hum an p roblem s abou t which w e have im perfect know ledge. It sh ou ld help read ers to ch oose a sen sib le co u rse betw een the head-in-the-sand reaction of so m e contrarians and the d o om -an d -g lo om view of so m e alarm ists. It b u ild s on the scientific b ase of the w ell-tested and accepted reports of the Intergovernm ental Panel on C lim ate C hange, putting the findings in the context of other hum an concerns. We m u st look b ey o n d the do om an d gloom . P rojections o f ra p id clim ate ch an ge w ith severe con sequ en ces are a prophecy, not in the sen se that they are b ou n d to com e true, b u t in the sen se of a p ro p h etic w a rn in g that if w e co n tin u e on ou r p resen t co u rse these are the logical con sequ en ces. M odern scientific 'p rop h ets of d o o m ' follow in the tradition of the O ld Testam ent p rophets. The Biblical p ro p h e ts w ere n ot p re a c h in g d a m n a tio n , b u t a p p e a lin g for a ch a n g e o f d ire ctio n , so th at d am n atio n co u ld be a v o id e d . Sim ilarly, clim ate scien tists w ho w arn ab ou t poten tially d a n g e ro u s clim ate ch an ge h o p e that su ch fo re b o d in g s w ill m otivate p eop le to act to avoid the danger.

lin ks b etw een the science an d the co n seq u en ces, w hich are im po rtan t for policy. If this en co u rages y ou to a d d r e s s the issu e s , to m ak e y o u r ow n a sse ssm e n t o f the risk, and to act accordingly, this book w ill have ach ieved its p u rp o se. N ow a few w o rd s to the se rio u s stu d e n t of clim ate ch ange on how to u se this book. First, it co v ers a h u g e ran ge of su b je cts and d iscip lin es from p h y sics, ch em istry an d the other 'h ard ' and social sciences, to p olitics and policy. M y o rig in a l ex p ertise w a s in p h y sic s (w ith a sid e interest in an th rop ology ), so 1 h ave been forced to learn ab o u t the other sub jects from b ook s, p ap e rs and especially from w eb sites and talking to people. C lim ate ch an ge is an o v erarch in g topic, an d the reality is that everythin g is connected to everything else (for exam ple see C h apter 9), so policy-relevance requires an en qu irin g and open m ind. Secon d, there is a set o f en d n otes at the end of each chapter. These not only docu m en t w h at is said (o ften in c lu d in g o p p o s in g p o in ts o f v ie w ), b u t su p p ly p o in ters to m ore in fo rm atio n , an d esp e c ia lly to w e b site s or o n g o in g p u b lic a tio n s w here you can u p d ate w h at is in the book. Frankly, n ob ody can be expected to keep up to date in detail on ev ery a sp e c t of clim ate ch an ge scien ce and policy. The n u m b er o f scientific p a p e r s on the su b je ct h a s gro w n e x p o n e n tia lly o v er the la st decade. One of m y co lleagu es estim ates that if every relevan t scientific p ub lication since the IPCC 2007 report is referenced in the next edition in three or four y ears' tim e, it w ould require ab ou t a thousan d p a g e s ju st to list all the references. I h ave selected w eb sites an d learn ed jou rn als in m y en dn otes that w ill enable you to keep u p w here you can, b u t even that is not com plete - I h ave o b v io u sly m isse d or selected from a larger n um ber of relevant references. But w eb search es these d a y s are am azin gly efficient at fin din g w h at y ou n eed to know. U se them w ell

IN T RO D U C TIO N

and w ith go o d ju d ge m e n t a s to the reliability and p o ssib le b ia se s of the source. Finally, I w an t to d e d ica te this b ook to m y gran dch ild ren , Jenny, Ella, K yan and G em , w h ose futu re is at stak e, alo n g w ith that of all futu re gen eration s. It is for them that w e m u st m eet the

xvii

ch allenge of clim ate ch ange. If the u rgen cy is as great a s I fear it is, it is u s an d ou r children, alive today, w ho will have to deal with the consequences. We can have a positiv e influence on our ch ildren 's future.

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1 Climate change matters

Today, global climate change is a fact. The climate has changed visibly, tangibly, measurably. An additional increase in average temperatures is not only possible, but very probable, while human intervention in the natural climate system plays an important, if not decisive role. B r u n o P o r r o , C h ie f R is k O f f ic e r , S w is s R e i n s u r a n c e , 2 0 0 2 . '

Climate change is a major concern in relation to the minerals sector and sustainable development. It is, potentially, one of the greatest o f all threats to the environment, to biodiversity and ultimately to our quality o f life. F a c i n g t h e F u t u r e , M i n i n g M i n e r a l s a n d S u s ta in a b le D e v e lo p m e n t A u s t r a l ia , 2 0 0 2 . 2

We, the human species, are confronting a planetary emergency - a threat to the survival of our civilization that is gathering ominous and destructive potential even as we gather here. But there is hopeful news as well: we have the ability to solve this crisis and avoid the ivorst - though not all - o f its consequences, if we act boldly, decisively and quickly. A l G o r e , N o b e l P e a c e P r iz e L e c t u r e , 1 0 Decem ber 2 0 0 7 . 3

C lim ate is critical to the w o rld a s w e k now it. The

h u g e in v e stm e n ts o f tim e a n d m on ey. T ra d e,

la n d sc a p e , an d the p la n ts an d a n im a ls in it, are all

p a rtic u la rly o f fo o d a n d fibre for m a n u fa c tu re d

d e term in ed to a larg e extent by clim ate actin g ov er

g o o d s, h a s a lso been stro n gly in fluen ced b y clim ate.

lon g in terv als o f tim e. O v er g e o lo g ica l tim e, clim ate

R o a d s, b u ild in g s an d to w n s are d e sig n e d tak in g

h a s h e lp e d to sh a p e m o u n ta in s, b u ild u p the so il,

local clim ate into co n sid eratio n . D e sig n ru les, both

d e term in e the n atu re o f the riv e rs, an d b u ild flood

fo rm a l a n d in fo rm al, z o n in g a n d sa fe ty sta n d a rd s

p la in s a n d d e lta s. A t le a st u n til the a d v e n t of

are d e v e lo p e d to co p e not ju st w ith a v e ra g e clim ate

irrigation an d in d u stria lisa tio n , clim ate d eterm in ed

b u t a lso w ith clim atic ex trem e s su ch a s flo o d s an d

food su p p lie s an d w h ere h u m an b e in g s co u ld live.

d r o u g h ts. If the clim ate c h a n g e s, h u m a n so ciety

Today, w ith m o d ern technology, h u m a n s can live

m u st a d a p t b y c h a n g in g its d e s ig n s , ru le s an d

in p la c e s w h ere it w a s im p o ssib le b efo re. T h is is

in fra stru c tu re - often at g re a t e x p e n se , e sp e cia lly

ach iev ed by the p ro v isio n o f b u ild in g s an d co m p lex

for retrofitting ex istin g in frastru ctu re.

in frastru ctu re tu n ed to the ex istin g clim ate, su ch a s

In b ro ad term s, 'clim ate' is the typical ran ge of

u rb an an d ru ral w ater su p p lie s, d ra in a g e , b rid g e s,

w eather, in clu d in g its variability, exp erien ced at a

ro a d s an d oth er co m m u n ic a tio n s. T h ese in v o lv e

particu lar place. It is often exp ressed statistically, in

CLIMATE C H A N C E: THE SCIENCE, IMPACTS A N D SO L U T IO N S

2

term s o f av e ra g es over a seaso n or n um b er of y ears,

T h e W orld M e teo ro lo g ical O rg a n iz a tio n , w h ich

of tem perature or rainfall an d so m etim es in term s of

c o o rd in a te s w eath er se rv ice s a ro u n d the glo b e, h a s

other v ariab les su ch a s w in d, hum idity, and so on.

d e clare d that 2005 an d 1998 w ere the tw o w a rm est

Variability is an im portant factor. 'C lim ate variability'

y e a r s on re co rd , sin ce re lia b le w e a th e r re c o rd s

is variability in the av e ra g e w eath er b eh av io u r at a

b e g a n in 1861, a n d ju st w a rm e r th an 2003. The

p articu lar location from one year to another, or one

d e c a d e o f 1998-2007 w a s the w a rm e st on record.

d e cad e to another. C h a n g e s in the b eh av io u r o f the

T w elve o f the la st 13 y e a rs (1995-2007), w ith the

w eath er over longer tim e scales, such a s one century

ex cep tio n o f 1996, ran k a m o n g s t the 12 w a rm e st

to another, are u su ally referred to a s 'clim ate change'.

y e a rs sin ce reliab le record s b eg an in 1850. Since the

C o n v e n tio n a lly , 3 0 -y ea r in te r v a ls h a v e b een

sta rt o f the tw en tieth cen tu ry the g lo b a l a v e ra g e

u sed

fo r c a lc u la tin g a v e r a g e s a n d e s tim a tin g

su rfa ce tem p e ratu re h a s risen b y 0.74 ± 0.1 8 °C , and

w eath er variability. H ow ever, n atu ra l clim ate v a ries

the lin ear w a rm in g trend o v e r the la st 50 y e a rs,

on tim e sc a le s from year-to-year, th ro u gh d e cad e-

aro u n d 0.13 ± 0 .3°C p er d e c a d e , is n early tw ice that

to-d ecad e to lon ger-term flu ctu atio n s ov er cen tu ries

for the last 100 y e a rs.4

a n d m illen nia.

N o te th at w h en sc ie n tists g iv e su ch e stim a te s

E x trem e w e a th e r e v e n ts are p a r t o f clim ate.

they u su a lly in c lu d e a ra n g e o f uncertain ty, w hich

T h eir im p a c t is reflected in the d e sig n o f h u m an

in the fo rm e r c a se a b o v e is ± 0 .1 8 °C . T h u s the

se ttle m en ts an d activities (such a s farm in g ) so a s to

in c rease c o u ld b e a s low a s 0 .5 6 °C or a s h igh a s

b e ab le to su rv iv e flo o d s, d ro u g h ts, se v e re sto rm s

0 .9 2 °C . In th is c a se the u n c e rta in tie s a llo w for

a n d other w eath er-related stre sse s or cata stro p h e s.

p o ssib le in a cc u rac ie s in in d iv id u a l m e a su re m e n ts,

B e c a u se clim ate can v a ry from d e c a d e to d e c a d e ,

an d how w ell the a v e ra g e from the lim ited n u m b er

reliable a v e ra g e s o f the frequ en cy a n d m a g n itu d e s

o f in d iv id u a l m e a su re m e n t sta tio n s re p re se n ts the

o f e x trem e e v e n ts re q u ire w e a th e r o b se rv a tio n s

a v e ra g e from all location s.

o v er lo n g er p e rio d s than the co n ven tion al 30 y ears.

In d ire ct e v id e n c e fro m tree rin g s, ice co res,

E n gin e ers d e sig n in frastru ctu re (b u ild in g s, b rid g e s,

b o re h o le s, a n d oth er clim a te -se n sitiv e in d ic a to rs

d a m s, d r a in s, etc.) to co p e w ith extrem e w eath er

(see C h a p te r 2) in d ic ate s that, d e sp ite a lesse r w arm

ev en ts that occur on a v e ra g e only once in ev ery 50,

in terv al ro u n d 1000 A D (the so -c alle d 'M e d ie v a l

100 or 1000 years. The m ore se rio u s the co n sequ en ce

W arm P erio d ') the w arm th o f the last h alf century is

o f d e sig n failu re u n d e r extrem e w eath er co n d ition s,

u n u s u a l in at le a st the p r e v io u s

the lo n ger the tim e in terval co n sid ere d , for ex am p le

M o reo v er, the la st tim e the p o la r re g io n s w ere

for a large d a m a s o p p o se d to a street drain .

sig n ific a n tly w a rm e r th an the p r e s e n t fo r an e x te n d e d

p e r io d

(s o m e

125 000

1300 y e a rs.

y ears

a g o ),

re d u c tio n s in p o la r ice v o lu m e led to g lo b a l se a

Turning up the heat C lim a te

h as ch anged

levels 4 to 6 m a b o v e the p resen t. V ariation s o f the g re a tly

o v e r g e o lo g ic a l

E a rth 's su rfa ce tem p e ratu re sin ce 1850, a lo n g w ith

tim escales, a s w e sh a ll see in C h a p te r 2. But w h at is

g lo b a l a v e ra g e se a level from 1870 an d n orth ern

o f im m e d ia te concern is that clim ate h a s sh o w n an

h e m isp h ere sn o w co ver sin ce the 1920s, are sh ow n

a lm o st u n p rec ed en te d ra p id g lo b a l w a rm in g trend

in F ig u re 1.

in the last few d e c a d e s.

B a se d on su c h o b s e r v a tio n s, the In te r g o v e ­

Sin ce the sta rt o f re liab le o b se rv a tio n s in the

rn m en tal Pan el on C lim ate C h a n g e (IP C C ) in 2007

n in eteenth century, scien tists from w e ath er se rv ice s

co n clu d e d that 'w a rm in g o f the clim ate sy ste m is

a n d re se arch la b o ra to rie s in m a n y co u n trie s h a v e

u n e q u iv o c a l, a s is n ow e v id e n t from o b se rv a tio n s

ex am in ed local, re gio n al an d g lo b al a v e ra g e su rface

o f in c r e a se s in g lo b a l a v e r a g e a ir a n d o c ea n

a ir a n d w a te r te m p e ra tu re s, on la n d , fro m sh ip s

tem p e ra tu re s, w id e sp re a d m eltin g o f sn o w an d ice,

a n d m ore recently from orb itin g satellites.

an d risin g g lo b a l a v e ra g e se a level'.

CLIMATE C H A N C E

MATTERS

3

(a) Global average temperature 14.5

-0 .5 -

13.5

(c) Northern Hemisphere snow cover

sr £ 3

1850

1900

©IPCC 2007: WG1-AR4

2000

1950 Ypar

Figure 1: Observed changes in (a) global average surface temperature, (b) global average sea level and (c) northern hemisphere snow cover, from the start of good measurements. This is Figure SPM-3 from the IPCC 2007 Working Group I report (used with permission from IPCC).

T h re e th in g s a re n o ta b le a b o u t th e se IP C C

M o st im portan tly , the a v e ra g e rate o f w a rm in g

co n clu sio n s. F irst, it sh o w s that a w a rm in g o f at

at the en d o f the la st g la cia tio n w a s a b o u t 5 °C in

lea st 0.56°C a lm o st certain ly o ccu rred . S ec o n d , the

so m e 10 000 y e a rs, or 0.05°C p er century, w h ile the

m o st lik ely v a lu e o f 0.74°C , w h ile it m a y a p p e a r to

o b serv ed rate o f w a rm in g in the last 50 y e a rs is 1.3°C

be sm a ll, is a lre a d y a siz ea b le fraction o f the g lo b a l

p er cen tu ry a n d the e stim ate d rate o v er the n ext

w a rm in g o f a b o u t 5 °C th at took p la c e fro m the

100 y e a rs co u ld b e m ore than 5 °C p e r century, w hich

la st g la c ia tio n a ro u n d 20 000 y e a rs a g o to the

is 100 tim es a s fa st a s d u rin g the last d e glaciatio n .

p re se n t in te rg la c ia l p e rio d (w h ich c o m m e n c e d

Such ra p id rates o f w arm in g w o u ld m ak e ad ap tatio n

so m e 10000 y e a rs a go ). P rehistoric g lo b al w a rm in g

by n atu ral an d h u m an sy ste m s extrem ely d ifficu lt

led to a c o m p le te tra n sfo rm a tio n o f the E a r th 's

or im p o ssib le (see C h a p ters 2 an d 7).

su rfa c e , w ith the d is a p p e a r a n c e o f m a s s iv e ice

Som e

c r itic s

have

q u e s tio n e d

the

IP C C 's

sh e e ts, an d co n tin en t-w id e c h a n g e s in v e g eta tio n

e stim ate d w a rm in g fig u re s on the fo llo w in g m ain

cover, re g io n al ex tin ctio n s an d a se a -le v el rise of

g ro u n d s. First, there are q u e stio n s o f u n certain ties

ab o u t 120 m etres.

d u e to c h an ge s in in strum en ts. In strum ental ch an ges

4

CLIMATE C H A N C E: THE SCIENCE, IMPACTS A N D SO L U T IO N S

in c lu d e c h a n g e s in the h o u sin g o f th e rm o m eters

a n d s a te llite o r b ita l v a r ia t io n s . M o re o v e r, th ey

('m eteo rological screen s') w hich affect the ventilation

re co rd a v e r a g e a ir te m p e r a tu r e s o v e r the lo w e st

a n d ra d ia n t h eat re ach in g the th e rm o m eters, an d

se v e r a l k ilo m e tre s o f the a tm o s p h e r e (in c lu d in g

ch a n g e s in sh ip s' o b se rv atio n s from m e a su rin g the

the lo w e r s tr a to s p h e r e at m id - to h ig h - la titu d e s )

t e m p e r a tu r e o f w a te r o b ta in e d

fro m

b u c k e ts

ra th e r th an su r fa c e a ir te m p e r a tu r e s, so th ey d o

d r o p p e d ov er the sid e o f sh ip s to m e a su re m e n ts of

not

the tem p eratu re o f se a w ater p u m p e d in to cool the

o b s e r v a t io n s . R e ce n t c o rre c tio n s to the sa te llite

sh ip s' en gin es. T h ese ch a n g e s are w ell re co g n ised

a n d r a d io s o n d e e s t im a t e s to ta k e a c c o u n t o f

by sc ie n tists a n d h a v e been a llo w e d for. T h ey

th e se p r o b le m s h a v e re m o v e d the d is c r e p a n c ie s

contribute to the estim ate o f uncertainty.

a n d co n firm th at su r fa c e a n d tro p o s p h e ric (lo w er

S e c o n d , there are co n ce rn s th at e stim a te s are

m e asu re

th e

sam e

th in g

as

su rfa c e

a tm o sp h e ric ) w a rm in g are o c c u rrin g .

b ia se d b y o b se rv a tio n s fro m sta tio n s w h ere local

A ll the a b o v e c r itic ism s o f the te m p e ra tu re

w a rm in g is c a u se d b y the gro w th o f cities (an effect

record s h a v e been a d d re sse d exp licitly in su cc essiv e

k n o w n a s 'u rb an h eat isla n d s').

IPCC rep o rts an d can n ow be d ism isse d .6 L egitim ate

The h eat isla n d effect is d u e to the h eat ab so rb ed or giv en o u t by b u ild in g s a n d ro a d s (e sp ecia lly at

e stim a te s o f u n ce rta in ty are g iv e n in the IP C C a sse ssm e n ts.

n igh t). H o w ev e r, th is effect w o rk s b oth w a y s on

S u p p o rtin g ev id en ce for recent g lo b a l w a rm in g

o b se rv e d tre n d s. In m a n y la rg e cities, o b se rv in g

c o m e s from m a n y d iffere n t re g io n s an d ty p e s of

site s, w h ich w ere o rig in a lly n ear city cen tres (an d

p h e n o m e n a . F o r e x a m p le , there is n ow a m p le

th u s su b je ct to w a rm in g a s the cities g re w ) w ere

ev id en ce o f retreat o f alp in e a n d continental glaciers

re p lace d by o b se rv in g site s at a irp o rts o u tsid e the

in re sp o n se to the tw entieth century w a rm in g (there

cities. T h is led to a te m p o ra ry o b se rv e d c o o lin g

are ex c ep tio n s in so m e m id- to h igh -latitu d e co astal

u ntil u rb a n isa tio n reach ed a s far a s the a irp o rts.

lo c a tio n s w h ere sn o w fa ll h a s in c re a se d ).7 T h is

O b se rv a tio n s from site s affe cte d b y u rb a n h eat

retreat h a s accelerated in the la st co u p le o f d e c a d e s

isla n d s h a v e , in g e n e ra l, b een either co rrected for

a s the rate o f glo b al w a rm in g h a s in creased. F ig u re 2

th is effect or e x c lu d e d from the a v e ra g e s. A recent

s h o w s d r a m a tic e v id e n c e o f th is fo r the Trient

stu d y o f tem p eratu re tren d s on w in d y n igh ts v e rsu s

G lacier in the V alais region o f so u th ern Sw itzerlan d .

all n ig h ts sh o w s sim ila r w a rm in g tre n d s, ev en

T h e su r v iv in g g la c ie r is in the u p p e r cen tre,

th o u gh w in d d is p e r se s locally g e n e ra te d h eat an d

ex te n d in g righ t to the sk y lin e. M e a su re d retreat o f

g reatly re d u ce s an y h eat isla n d effect.5

the term in u s o f the glacier sin ce 1986-87 is ro u gh ly

O ne o f the stren gth s of the su rface o b serv atio n s is

500 m etres b y 2000 an d an o th er 200 m etres b y 2003.

that those from lan d su rface m eteorological station s

E a r ly

tend to a gre e w ell w ith n earb y sh ip o b serv atio n s,

m o ra in e s (w here rock an d earth are d u m p e d at the

tw e n tie th -c e n tu r y

te r m in a l

and

la te ra l

d e sp ite different so u rces o f p o ssib le errors. A verage

en d or s id e s o f the g la c ie r b y the flo w in g an d

se a su rfa ce te m p e ra tu re s sh o w sim ila r tre n d s to

re ced in g ice) are ev id e n t, free o f trees, in d ic atin g

la n d -b a se d o b se rv a tio n s fo r the sa m e re g io n s.

recent ice retreat, a n d the p resen t term in u s o f the

A ir b o r n e

b a llo o n - b o r n e

g la c ie r is s lu m p e d , in d ic a tin g r a p id m e ltin g .8

ra d io -so n d e s at n ea r-g ro u n d le v e ls a lso ten d to

o b s e r v a t io n s

fro m

S im ilar p ictu re s, often p aire d w ith earlier o n es, are

su p p o rt the lan d -b ased ob serv ation al trends.

a v a ila b le for m an y g la ciers w o rld w id e .9

A n o th e r i s s u e o fte n r a is e d is th e a p p a r e n t

C h a n g e s in o th e r a sp e c ts o f clim a te, b ro a d ly

d iffe re n c e b e tw e e n the tr e n d s in t e m p e r a tu r e

co n sisten t w ith g lo b a l w a rm in g , h a v e a lso occurred

fo u n d in s u r fa c e o b s e r v a t io n s a n d th o se fro m

o v er the la st century. T h ese in c lu d e d e c re a se s of

s a t e llit e s , w h ic h b e g a n in 1979. T h e s a t e llit e

a b o u t 10% in sn o w co v er a s o b se rv e d b y sate llites

o b se rv a tio n s

as

sin ce the 1960s (see F ig u re lc ), a n d a larg e d e cre ase

c o rre c tio n s a re n e e d e d fo r in str u m e n ta l c h a n g e s

in sp rin g an d su m m e r sea-ice sin ce the 1950s in the

are

not

stra ig h tfo r w a rd ,

CLIMATE C H A N C E MATTERS

5

n orth ern h e m isp h ere. Th e latter reach ed a record

M e a su re m e n ts o f the S o u th ern P a ta g o n ia n ice

low in 2007, a n d the m elt rate is m u ch fa ste r than

sh eet in S o u th A m erica in d icate ra p id m eltin g, w ith

p ro je cted in the 2007 IP C C rep ort. W arm in g h a s

the

a lso been ra p id n e a r the A n ta rctic P e n in su la ,

m e a su re m e n ts by satellite a s 27.9 + 11 cu bic km p er

alth o u gh n ot a ro u n d m o st o f m a in la n d A ntarctica.

y ea r from 2002 to 2006. T h is is e q u iv a len t to n early

O b serv ed m eltin g of p erm afro st is do cu m en ted ,

ra te

o f m e ltin g

e s t im a t e d

fro m

g r a v it y

1 m m p e r d e c a d e rise in g lo b a l a v e ra g e se a le v e l.13

e sp e cia lly for A la sk a , b y the U S A rctic R esearch

G lo b al w a rm in g h a s led to th erm al e x p a n sio n of

C o m m issio n in its Permafrost Task Force Report in 2003,

the o cean w a te r s a s w ell a s m e ltin g o f m o u n tain

an d arou n d the Arctic by the Arctic C lim ate Im pact

g la c ie rs. Joh n C h u rch , from C SIR O in A u str a lia ,

A sse ssm e n t (A C IA ) in 2004 an d k ep t u p to d ate by

an d

the

c a lc u la tio n s

an n u al

N a t io n a l

O c e a n ic

A tm o sp h e r ic

c o ll e a g u e s of

r e c e n tly r e g io n a l

co m pared s e a - le v e l

r ise

m odel w ith

A dm in istration (N O A A ) 'R eport C ard ' on the state of

o b se rv atio n s from tid e g a u g e a n d satellite altim eter

the Arctic. O b served ch an ges in the A rctic an d their

re co rd s. T h ey c o n c lu d e d that the b e st e stim ate of

im plications are su m m a rised in Box 1 from A C IA .10

a v e ra g e sea-lev el rise g lo b a lly for the p erio d 1950 to

A cco rd in g to the N O A A A rctic 'R ep o rt C a r d ', a

2000 is a b o u t 1.8 to 1.9 ± 0.2 m m p er y ea r (that is

d e cre a se in sea-ice exten t in the A rctic su m m e r of

ju st u n d e r 10 cm ), an d that sea-level rise is gre atest

40% sin ce the 1980s is co n sisten t w ith an in crease in

(ab o u t 3 m m p er y e a r or 30 cm p er cen tu ry ) in the

sp rin g an d , to a lesse r extent, su m m e r tem p e ratu re s

eastern e q u a to r ia l P acific a n d w e stern e q u a to ria l

at h ig h n o rth e rn la titu d e s . T re n d s in su m m e r

In d ian O cean . O b se rv e d ra tes o f rise are sm a lle st

(Sep tem b er) a n d w in ter (M arch) se a ice exten t from

(a b o u t 1 m m p er y ea r) in the w e stern e q u a to ria l

1979 to 2007 a re

2.8% p e r d e c a d e ,

P acific a n d eastern In dian O cean , p articu la rly the

resp ectively .11 A ntarctic sea-ice extent h as fluctu ated

n orth -w est c o a st o f A u stra lia . R e gio n al v a ria tio n s

in recent d e c a d e s b u t re m ain ed fairly sta b le, a p a rt

are w e a k e r for m u ch o f the rest o f the g lo b al ocean s,

from the area a ro u n d the A ntarctic P en in su la w h ere

an d are d u e to differen t rates o f w a rm in g in different

r a p id re g io n al w a rm in g h a s led to sea-ice retreat

p a r ts o f the o cean s, a n d ch a n g e s in w in d s, cu rren ts

and

an d a tm o sp h eric p re ssu re .14

th e

11.3 a n d

d i s in t e g r a t i o n

s e m i- p e r m a n e n t

ice

of

s h e lv e s

sev eral a tta c h e d

la r g e to

the

Recent o b se rv atio n s in d icate that the g lo b a l rate o f sea-level rise in creased to a b o u t 3 m m p er y ear in

m ain lan d (see C h a p te r 5, F ig u re 21 below ). O ther ch a n g e s in clu d e ra p id recessio n o f the ice

the p e rio d 1993 to 2008. T h is co u ld b e in p a rt a

cap on M t K ilim an jaro in K en y a a n d other trop ical

n a tu ra l flu c tu a tio n , in c lu d in g e ffe c ts o f m a jo r

g la c ie rs in A frica, N e w G u in ea an d S ou th A m erica,

v o lcan ic d u st c lo u d s re d u cin g su rfa ce w a rm in g in

a s w ell as g la c ie rs in C a n a d a , the U n ited S tate s an d

so m e y ears. H ow ever, it co u ld a lso b e a re su lt o f an

C h in a. P e rm a fro st is m e ltin g in S ib eria (w h ere it

in c re a sin g co n trib u tio n from the m e ltin g o f the

h a s c a u se d p ro b le m s w ith r o a d s, p ip e lin e s an d

G re e n la n d an d A n tarctic ice sh e e ts, a s h a s been

b u ild in g s) an d in the E u ro p e a n A lp s (w here it h a s

o b se rv e d locally. The total tw entieth-century rise is

th reaten ed the sta b ility o f so m e m o u n tain p e a k s

e stim a te d to b e 17 ± 5 cm . T h is h a s n o d o u b t

a n d cable car sta tio n s d u e to re p e a te d m eltin g an d

co n trib u ted to co asta l erosion in m an y re gio n s, b u t

fre ez in g o f w a ter in crev ice s in the ro ck s, forcin g

in m o st c a s e s the se a -le v e l rise im p a c t w a s n ot

them a p art). C ata stro p h ic release o f w ater d a m m e d

en o u gh to be iden tified a s su ch , d u e to other m ore

beh in d the term in al m o ra in es o f retreatin g g la ciers

lo ca lised facto rs su ch a s v a ria tio n s in sto r m in e ss

in high v a lle y s is o f in c rea sin g concern in p a r ts of

and

the

N e p a l,

stru ctu res. Ja m e s H an sen a rg u e s that the acceleration

E n v iro n m e n t

w ill in crease ra p id ly d u e to in creasin g co n trib u tion s

H im a la y a s ,

a c c o r d in g

n o ta b ly

to a U n ite d

B h u ta n N a t io n s

and

the c o n str u c tio n o f se a w a lls a n d

o th e r

P ro g ra m re p o rt. A ll o f th e se p h e n o m e n a h a v e

from the m ajo r ice sh ee ts, le a d in g to u p to se v e ra l

accelerated in recent d e c a d e s.7,12

m etres sea-level rise by 2100.15

6

CLIMATE CHANCE: THE SCIENCE, IMPACTS A N D SO LUTIO NS

B O X 1: KEY F IN D IN G S OF THE A R C T IC C LIM A T E IM P A C T A SSE SSM E N T 1. The Arctic climate is now warming rapidly and much larger changes are expected. 2. Arctic warming and its consequences have worldwide implications. 3. Arctic vegetation zones are projected to shift, bringing wide-ranging impacts. 4. Animal species' diversity, ranges and distribution will change. 5. Many coastal communities and facilities face increasing exposure to storms. 6. Reduced sea ice is very likely to increase marine transport and access to resources. 7. Thawing ground will disrupt transportation, buildings, and other infrastructure. 8. Indigenous communities are facing major econom ic and cultural impacts. 9. Elevated ultraviolet radiation levels [a combined effect of global warming and stratospheric ozone depletion] will affect people, plants, and animals. 10. Multiple influences interact to cause impacts to people and ecosystems.

Figure 2:TheTrient Glacier near Forclaz in the Valais region of southern Switzerland in 2000. Rapid retreat has occurred during the latter part of the twentieth century. (Photograph by AB Pittock.)

CLIMATE C H A N C E MATTERS

7

E v id e n c e fo r a stre n g th e n in g o f the g lo b a l

g a s e s a n d act like a thick b la n k e t s u r r o u n d in g the

h y d ro lo gical cycle, in w h ich m ore ra p id ev ap o ratio n

E arth . In effe ct, the E a r th 's su r fa c e h a s to w a rm

ta k e s p la c e in low la titu d e s, a n d m o re rain an d

u p to g iv e o ff a s m u ch e n e rg y a s h e at ra d ia tio n a s

sn o w fa ll o c c u r s at h igh la titu d e s , c o m e s from

is b e in g a b s o r b e d fro m the in c id e n t s u n lig h t

o b serv atio n s o f salin ity in crease s in the trop ical an d

(w h ich in c lu d e s v isib le , u ltra v io le t a n d in fra-red

su b -tro p ic a l su rfa c e w a te rs o f the A tlan tic O cean

r a d ia tio n ). S o o t p a r tic le s from fires can a lso le a d

o v er the la st 50 y e a rs. T h is is a c c o m p a n ie d b y a

to lo c a l s u r fa c e w a r m in g b y a b so r b in g su n lig h t,

fresh en in g o f su rfa ce w a te rs in the h igh la titu d e s of

b u t reflectiv e p a r tic le s, su ch a s th o se fo rm e d from

the N o rth an d S o u th A tlan tic. E stim a te s in d icate

su lfu r o u s fu m e s (su lfa te a e r o so ls) can le a d to local

that n et ev a p o ratio n rates ov er the tropical A tlan tic

c o o lin g b y p r e v e n t in g s u n lig h t re a c h in g

m u st h a v e in c re a se d b y 5 -10% o v er the p a s t fo u r

E a r th 's su rfa c e . N a tu ra l

d e c a d e s, w ith an accelerated trend sin ce 1990.16

g r e e n h o u se

g ase s

in c lu d e

the

c a rb o n

O th er re g io n a l c h a n g e s are a lso e v id e n t in

d io x id e , m eth an e a n d w a ter v ap o u r. T h ese h elp to

r a in fa ll, c lo u d co v e r a n d e x trem e te m p e ra tu re

k eep Earth so m e 3 3 °C w a rm e r than if there w ere no

ev en ts, b u t d u e to large n atu ral v a ria b ility these are

g re en h o u se g a s e s an d c lo u d s in the atm o sp h ere .

n o t y e t q u ite so

w e ll e s t a b lis h e d . M ig r a tio n

H um an

a c tiv itie s h a v e in c re a se d

the c o n ­

o f the m id - la titu d e s t o r m s tra c k s

c e n tra tio n s o f se v e ra l g re e n h o u se g a s e s in the

a ss o c ia te d w ith the so -c a lle d 'a n n u la r m o d e s ' is

a tm o sp h ere, lea d in g to w h at is term ed the 'en h an ced

le a d in g to g re a te r a rid ity in so m e m id -la titu d e

g re e n h o u se effe ct'. T h e se g a s e s in c lu d e carb o n

r e g io n s

d io x id e , m e th a n e a n d

p o le w a r d s

and

in c r e a se d

p r e c ip ita tio n

at

h ig h

se v e r a l o th e r a rtific ia l

la titu d e s .17 H o w ev e r, re g io n a l clim ate p ro p e rtie s

ch em icals. Th e K y oto P rotocol, se t u p to b egin the

often v ary on tim e sca le s o f se v e ra l d e c a d e s. T h ese

ta sk o f re d u c in g g re e n h o u se g a s e m is sio n s (see

are difficult to d istin g u ish from longer-term ch an ge s

C h a p te r 11), in c lu d e s a p a c k a g e or 'b a sk e t' o f six

w ith o u t re c o r d s lo n g e r th a n

m ain g a s e s to b e re g u la te d . B e sid e s carb o n d io x id e

th o se

p re s e n tly

(C O ,) a n d m eth an e (C H 4), th ese are n itro u s o x id e

a v a ila b le in so m e regio n s.

(N zO ), h yd ro flu orocarb o n s (H F C s), p erflu o rocarb on s (P F C s) an d su lfu r h e x a flu o rid e (SF 6).

W h y is the present rapid w arm ing happening?

carb o n d io x id e , co m e m ain ly from the b u rn in g of

S c ie n tis ts b e lie v e the r a p id w a r m in g in the la st

fo s sil fu e ls su ch a s co al, oil a n d n a tu ra l g a s, the

se v e ra l d e c a d e s is d u e m o stly to h u m a n -in d u c e d

d e stru c tio n o f fo re sts a n d carb o n -rich so il a n d

c h a n g e s to the a tm o sp h e re , on top o f s o m e n a tu ra l

the m a n u fa c tu re o f ce m e n t from lim esto n e . The

v a r ia t io n s . C lim a te c h a n g e in d u c e d by h u m a n

co n cen tration o f carb on d io x id e before m ajo r lan d

A n th ro p o g e n ic , or h u m a n -c au se d in c re a se s in

the

c le a rin g an d in d u str ia lisa tio n in the eigh te en th

c o m p o sitio n o f the E a r th 's a tm o sp h e re from w a ste

ce n tu ry w a s a b o u t 265 p a r ts p er m illio n (p p m ).

g a s e s d u e to in d u s tr y , fa rm a n im a ls a n d la n d

M eth an e co m es from d e ca y in g v e g e ta b le m atter in

a c t iv ity

m ay

occur

due

to

ch anges

in

cle a rin g , or c h a n g e s in the la n d su rfa c e reflectivity

rice p a d d ie s, d ig e stiv e p ro c e sse s in sh eep an d cattle,

c a u se d b y la n d c le a rin g , c r o p p in g a n d irrig a tio n .

b u rn in g a n d d e c a y o f b io lo g ic a l m atter a n d from

T h e se g a s e s in c lu d e s e v e r a l, su c h a s c a rb o n

fo s sil fu el p ro d u c tio n . H F C s a re m a n u fa c tu re d

d io x id e , m e th a n e an d o x id e s o f n itro g e n , th at can

g a s e s on ce w id e ly u se d in re frig e ra n ts an d other

a b so r b h e a t r a d ia t io n (lo n g - w a v e o r in fra -re d

in d u strie s, b u t w hich are largely b ein g p h a se d ou t

r a d ia t io n ) fro m

o f u se b e c a u s e

the S u n o r the E a rth . W hen

o f th e ir p o te n tia l to d e stro y

w a rm e d b y the S u n or the E arth th ey g iv e o ff h e at

a tm o sp h e ric o z o n e. P F C s a n d S F 6 are in d u str ia l

ra d ia tio n b o th u p w a r d s into s p a c e a n d d o w n w a rd s

g a s e s u se d in the electronic a n d electrical in d u strie s,

to the E arth . T h e se g a s e s a re c a lle d g re e n h o u se

fire figh tin g, so lv e n ts an d other in d u strie s.

8

CLIMATE C H A N C E: THE SCIENCE, IMPACTS A N D SO L U T IO N S

W ater v a p o u r co n cen tration s in the a tm o sp h ere are clo sely co n tro lled by the su rfa c e tem p e ratu re .

ch an ge h u m a n b e h a v io u r an d red u ce ou r e m issio n s o f g re en h o u se g a s e s .18 Th e IP C C F ourth A sse ss m e n t R e p o rt in 2007

T h ese can act a s an a m p lifie r o f w a rm in g d u e to in c re a se s in o th e r g re e n h o u se g a s e s or in d e e d

co n clu d ed :

w arm in g d u e to E a rth 's o rbital v aria tio n s. S im ilarly c lo u d s can act a s an a m p lifie r b y a b so rb in g h eat

•

d io x id e , m eth an e a n d n itro u s o x id e h a v e

rad ia tio n , or a s a red u cer o f w a rm in g b y reflecting

in creased m a rk e d ly a s a re su lt o f h u m an

in co m in g su n ligh t. The n et re su lt o f c lo u d s on the

activities sin ce 1750 ... Th e g lo b a l in creases in

E a r th 's te m p e ra tu re d e p e n d s on th eir h e ig h t,

carb on d io x id e concentration are d u e p rim a rily

latitu d e and d ro p le t size.

to fo ssil fuel u se an d lan d u se ch an ge, w h ile

A m p lify in g effects are called p o sitiv e fe e d b a ck s

th ose o f m eth an e an d n itro u s o x id e are

(as in electron ic circuitry ). L o ss o f sn o w co v er d u e

p rim a rily d u e to agricu ltu re.

to w a rm in g is an o th er p o sitiv e fee d b a ck , a s it le a d s to g re a te r a b so r p tio n o f su n lig h t a t the E a r th 's

G lo b al a tm o sp h eric co n cen tration s o f carb o n

•

The u n d e rsta n d in g o f a n th ro p o gen ic w arm in g

su rfa c e a n d th u s m o re w a rm in g . O n the tim e-scale

an d co o lin g in flu en ces on clim ate h a s im p ro v e d

o f the g la c ia l-in te rg la c ia l cy c le s o f th o u sa n d s of

sin ce the [Third A sse ssm e n t R ep o rt in 2001],

y ears,

the

lead in g to very high confidence [at least 90%] that

a tm o sp h e re a lso act a s a p o sitiv e fe e d b a c k , w ith

the g lo b a l a v e ra g e n et effect o f h u m a n activities

the in itial w a rm in g effect co m in g from v a ria tio n s

sin ce 1750 h a s been one o f w a rm in g w ith a

in

th e

c a rb o n

E a r th 's

d io x id e

o r b it

c o n c e n tr a tio n s

aro u n d

th e

in

Sun.

The

a m p lific a tio n c o m e s from w a rm e r o c e a n s g iv in g

ra d ia tiv e forcin g o f +1.6 [+0.6 to +2.4] W m~2.

o ff d is so lv e d carb o n d io x id e , an d th u s in c re a sin g

A n im p o rtan t verification o f ex p ected im p a c ts of

the n atu ra l w a rm in g via the g re e n h o u se effect (see

in crease d g re en h o u se g a s e s on clim ate co m es from

C h a p te r 2).

a stu d y b y Ja m e s H a n se n a n d c o lle a g u e s. T h ey

A s early a s the nineteenth century so m e scien tists

ca lc u la te d the e n e rg y im b a la n c e at the su rfa c e

n oted th at in c rea se d e m issio n s o f carb o n d io x id e

d u e to in crease d g re e n h o u se g a s co n cen tratio n s in

m ig h t lea d to g lo b a l w a rm in g (see C h a p te r 11).

the a tm o sp h e re an d c o m p a re d this w ith p re c ise

P resent estim ate s o f futu re clim ate ch an ge are b a se d

m e a su re m e n ts o f in c re a sin g h e at co n ten t o f the

on p ro je ctio n s o f fu tu re e m issio n s o f g re e n h o u se

o cean s o v er the p a st d e ca d e. T h is stu d y h igh ligh ted

g a s e s an d re su ltin g co n cen tration s o f th ese g a s e s in

the im p o rta n c e o f the d e la y in o cean w a rm in g ,

the a tm o sp h e re . T h ese e stim a te s a lso d e p e n d on

w h ich im p lie s fu tu re w a rm in g , se a -le v el rise an d

fa cto rs su ch a s the se n sitiv ity o f g lo b a l clim ate to

ice sh eet d isin te g ra tio n .18

in c re a se s in g re e n h o u se g a s co n c e n tra tio n s; the

A p a p e r by W illiam R u d d im a n o f the U n iversity

sim u ltan e o u s w a rm in g or co o lin g effects o f n atu ral

o f V irginia, in 2003, ra ise s the p o ssib ility that h u m an

clim ate flu ctu atio n s; an d ch a n g e s in d u st an d other

influen ce on the clim ate h a s been sig n ifica n t sin ce

p a rtic le s in the a tm o sp h e re from v o lc a n o e s, d u st

w ell b efo re the In d u stria l R e v o lu tio n d u e to the

sto rm s an d industry. Su ch p rojectio n s are d isc u sse d

cu ttin g d o w n o f p rim e v a l fo re sts to m a k e w a y for

in m ore d e tail in C h a p ter 3 an d C h a p ter 5.

a g ric u ltu re , a n d irrig a te d rice fa rm in g in A sia .

G iv e n th a t clim a te h a s c h a n g e d d u r in g the

R u d d im a n cla im s that the E a rth 's o rbital ch a n g e s

tw entieth century, the key q u estio n is how m u ch of

sh o u ld h a v e led to a declin e in carbon d io x id e an d

this is d u e to h u m an -in d u ced in creased gre en h o u se

m e th a n e co n ce n tratio n s in the a tm o sp h e re from

g a s e m issio n s, an d how m u ch to other m ore n atu ral

8000 y e a rs ago . In ste ad there w a s a rise o f 100 p arts

c a u se s. T h is h a s gre at relevan ce to p o licy b e c a u se , if

p er b illion in m eth an e co n cen tration s, a n d o f 20 to

the c h a n g e s are d u e to h u m a n activity, they are

25 p p m in ca rb o n d io x id e by the sta rt o f the

lik ely to co n tin u e a n d ev en acc elera te u n le s s w e

in d u stria l era. H e ca lcu la te s that this h as led to the

CLIMATE C H A N C E MATTERS

9

E arth b ein g 0.8 °C w a rm e r than if h u m a n s h ad not

its d y n a m ic e ffe cts on a tm o sp h e ric circ u la tio n .

been active, an effect h id d en b e c a u se it h a s can celled

A n o th er stu d y sh o w s a ten d e n cy fo r m o re se v e re

o u t a n atu ral co o lin g d u e to orbital v a ria tio n s.19

d ro u g h ts in A u stra lia , related to higher tem p eratu res

S im u la tio n s o f the re sp o n se to n atu ra l forcin gs

an d in creased su rfa ce e v a p o ratio n . Both stu d ie s see

alo n e (that is, n atu ra l ch a n g e s c a u sin g the clim ate

te n ta tiv e a ttr ib u tio n

to ch a n g e ), su ch a s v a ria b ility in en ergy from the

en h a n ced g re e n h o u se effect, a n d are p o in te rs to

Su n an d the effects o f v o lcan ic d u st, d o not exp lain

fu tu re re gio n al clim ate c h a n g e s.21

o f d r y in g

tre n d s to the

the w a rm in g e x p e rie n c e d in the se c o n d h a lf o f

A d e e p e n in g an d p o le w a rd s sh ift o f the b elts of

the tw en tieth century. H o w ev e r, they m a y h a v e

low a tm o sp h e ric p re ssu re su rro u n d in g each p o le,

contributed to the o b serv ed w arm in g in the p re v io u s

k n o w n tech n ically a s an in c rease in the n orth ern

50 y e a rs (see C h a p te r 2). Th e su lfa te a e ro so l effect

a n d so u th e rn 'a n n u la r m o d e s ' o f the a tm o sp h e ric

w o u ld h a v e c a u se d c o o lin g o v e r the la st h a lf century, a lth o u g h b y h ow m u ch is u ncertain . T h is

circu latio n , h a s b een o b se rv e d in the la st se v e ra l

c o o lin g effect h a s b ec o m e le ss sin ce the 1980s a s

clim ate w ith in creasin g g re e n h o u se g a s co n cen tra­

su lfu r e m is s io n s h a v e been re d u c e d in N o rth

tions. H ow ever, the o b se rv e d sh ift is g re a te r than

d e c a d e s. It is a lso fo u n d in m o d e l sim u la tio n s of

A m eric a an d E u ro p e in o rd e r to re d u c e u rb an

the sim u la te d p rojectio n s. M o d el sim u la tio n s h a v e

p o llu tio n an d acid rain.

n ow at le a st p a r tia lly re so lv e d th is d iffere n ce b y

Th e b e st agre em e n t b etw een m o d el sim u la tio n s

in c lu d in g the effect o f re d u c tio n s in o zo n e in the

o f clim ate an d o b se rv atio n s o v er the la st 140 y e a rs

u p p e r atm o sp h ere , w h ich h a v e o ccu rred esp e cia lly

h a s been fou n d w h en all the a b o v e h u m an -in d u ced

in the h igh la titu d e w in ter, sin ce the 1970s (see

a n d n atu ra l fo rcin g fa cto rs are co m b in e d . T h ese

C h a p te r 9). Both e n h an ced g re e n h o u se g a s e s an d

resu lts sh ow that the factors in clu d ed are su fficien t

ozon e re d u ctio n s in the u p p e r a tm o sp h e re in crease

to exp lain the o b serv ed ch an ges, b u t d o n ot exclu d e

the eq u ator-to-p o le tem p e ratu re d ifferen ce, lea d in g

the p o ssib ility o f other m in or factors co n trib utin g.20

to a stre n g th e n in g o f the w e sterly w in d s at h igh

F u rth erm ore, it is v ery likely that the tw entieth

la titu d e s. T h ese c h a n g e s h elp e x p la in d e c re a sin g

cen tu ry w a rm in g h a s co n trib u te d sig n ifica n tly to

rain fall in so u th e rn A u stra lia , an d a stro n ge r N orth

the o b se rv e d se a -le v e l rise o f so m e 10 to 20 cm ,

A tlan tic O scillation , w h ich affects storm track s an d

th ro u g h the e x p a n s io n o f se a w a te r a s it g e ts

clim ate in E u ro p e .17

w arm er, an d w id e sp re a d m eltin g o f la n d -b a se d ice.

C lim ate m o d e ls s u g g e st a p o ssib le slo w d o w n of

O b se rv e d sea-lev el rise a n d m o d e l e stim ate s are in

the o v ertu rn in g circu latio n in the N o rth A tlan tic

a g re em e n t, w ithin the u n certain ties, w ith a lack of

that is d riv en b y vertical d ifferen ces in tem p e ratu re

sig n ific a n t acc elera tio n o f se a -le v e l rise d e tecte d

and

d u rin g m o st o f the tw entieth century. The lack o f an

c irc u la tio n '). S u ch a c h a n g e c o u ld re su lt from

o b serv ed acceleration u p to the 1990s is d u e to long

su rfa c e w a rm in g , in c rea se d rain fall an d ru n o ff at

tim e la g s in w a rm in g the d e ep o cean s, b u t there is

h ig h la titu d e s , a n d re d u c e d se a -ice fo rm a tio n .22

e v id e n c e o f an a c c e le ra tio n in the la st d e c a d e

T h e re ality o f a slo w d o w n o f the th erm o -h alin e

p ro b a b ly d u e to ra p id ly in c re a sin g co n trib u tio n s

circulation is su p p o rte d b y so m e recent ob serv atio n s

sa lin it y

(k n o w n

as

th e

'th e rm o - h a lin e

from m eltin g o f la n d -b a se d ice in A la sk a , P a ta g o n ia

fro m

an d G re e n la n d .14

ev id en ce that it h a s occurred before (see C h ap ter 2).23

se v e r a l a r e a s , a s w e ll a s p a le o -c lim a tic

S tu d ie s by U S sc ie n tists o f tw en tieth cen tu ry

T h is co u ld lead to ra p id clim ate c h a n g e s in the

d ry in g tre n d s in the M e d ite rra n e a n a n d A fric an

N o rth A tlan tic regio n , a n d h a s p ro m p te d the settin g

m o n soo n

o b serv ed

u p o f a m o n ito rin g a n d research p ro g ra m called the

w a rm in g trend in the In dian O cean, w hich is related

R a p id C lim a te C h a n g e P r o g ra m m e (R A P ID ) by

to the e n h a n c e d g re e n h o u se effect, is the m o st

the U K N a tu ra l E n viron m en t R esearch C o u n cil an d

im p o rta n t fea tu re d riv in g th ese d r y in g s, th ro u gh

the U S N a tio n a l Scien ce F o u n d a tio n . The aim is to

r e g io n s

su g g e st

th at the

10

CLIMATE C H A N C E: THE SCIENCE, IMPACTS A N D SO L U T IO N S

im p ro v e the ab ility to q u a n tify the ch a n ce s an d

a large a m o u n t o f w ater into three con n ected b o w ls,

m a g n itu d e o f fu tu re r a p id c lim a te c h a n g e .24 Its

from w hich there is only on e sm a ll o u tlet drain .

m ain fo c u s is the A tla n tic O c e a n 's c irc u la tio n , in c lu d in g the p o ssib ility o f a slo w -d o w n in the G u lf

relative m a g n itu d e a n d ra p id ity o f carb o n d io x id e

S trea m , re lativ e co o lin g in W estern E u ro p e a n d a

flo w s are in d ic ate d a p p ro x im a te ly b y the w id th of

re d u ctio n in the A tlan tic O c e a n 's ab ility to ab so rb

the arro w s. F o ssil fu el e m issio n s o f carb o n d io x id e

carbo n d io x id e from the atm o sp h ere.

into the a tm o sp h e re (large u p w a r d s arro w ) reach

T h is is illu strated sch em atically in F ig u re 3. The

eq u ilib riu m w ith carb o n in the lan d an d so il biota an d in the sh allo w o cean s ( 'C 0 2 ex c h a n g e' arro w s)

The importance of delayed climate responses

in only on e to ten y e a rs. C arb o n d io x id e is only

D e la y e d clim a te r e sp o n s e s to g re e n h o u se g a s

h u n d r e d s to t h o u s a n d s o f y e a r s ('n a tu r a l C 0 2

e m issio n s requ ire early action. A t p resen t there is a

rem ov al').

slo w ly re m o v e d

R a p id

large im balan ce b etw een p resen t a n d p a st e m issio n s

in to th e d e e p

exchan ges

ta k e

p la c e

o c e a n , ta k in g

b e tw e e n

the

so il) a n d

the

o f carb o n d io x id e into the a tm o sp h e re a n d their

b io sp h e r e (p la n ts, a n im a ls a n d

slo w re m o v al into the d e e p o cean . E v en if w e

a tm o sp h e re , b u t d u e to lim itatio n s o f clim ate and

sto p p e d em ittin g g re en h o u se g a s e s tom o rrow , the

so il fertility, the b io sp h e re can n o t ex p a n d en o u gh to

in c rease in a tm o sp h e ric co n cen tratio n o f carb o n

take u p the h u g e in crease in carb o n d io x id e from

d io x id e a s a re su lt o f the b u rn in g o f fo ssil fu e ls an d

fo ssil carb on . M o st o f the form er fo ssil carb o n sta y s

d estru ctio n o f fo re sts sin ce the in d u stria l revolu tion

a s ca rb o n d io x id e in the a tm o sp h e re , w h ere it

w o u ld p e rsist for cen tu ries. T h is is d u e to the slow

c h a n g e s the clim ate, or is a b so rb e d into the su rfa ce

rate at w h ich carb o n

d io x id e a lre a d y

in

la y ers o f the o cean s, w h ere it c h a n g e s the ch em istry

the

atm o sp h ere , su rfa ce o cean w a ters an d the b io sp h ere

o f the o c e a n s. T h e p o rtio n

(p la n ts, a n im a ls an d so il b io ta) can be re a b so rb e d

a tm o sp h e re is k n o w n a s the 'airb o rn e fraction ' an d

th at s t a y s in the

into the larg e re se rv o irs (called 'sin k s') on the ocean

is currently a b o u t 50% o f all em itted carbo n d ioxid e.

floor an d in the so lid earth. It is a s if w e are p o u rin g

The fraction d isso lv e d in the ocean is lim ited b y the

Atmosphere

è

C 0 2 exchange

C 02 exchange

Land/soil biota

Shallow oceans

C 02 emissions Natural C 02 removal *

Fossil fuels Deep oceans Geological formations Figure 3: Flows between carbon reservoirs. This schematic diagram illustrates the present imbalance between emissions of carbon dioxide into the atmosphere, soil and land biota and shallow oceans, and its eventual removal into the deep oceans.

CLIMATE C H A N C E MATTERS

11

so lu b ility o f carb o n d io x id e in the su rfa ce w a ters of

n o t u n til the left-h an d e m is sio n s arro w a n d the

the o cean s an d the rate o f d o w n w a rd p en etratio n of

low er-righ t re m o v al arro w b eco m e the sa m e size).

the carbo n d io x id e . T h u s, the airb orn e fraction w ill

A ltern atively , there is the p o ssib ility o f artificially

in crease, a s the u p p e r o c ea n s get w arm er, b e c a u se

in c re a sin g the rate o f se q u e stra tio n o f carb o n or

w a rm e r w a te r can h o ld le s s d is s o lv e d carb o n

c a rb o n

d io x id e , a n d there w ill a lso b e le s s m ix in g o f the

su b te rra n e a n s t o r a g e s (a rtific ia lly w id e n in g the

w arm e r w a ter into the relatively cold d e ep o cean s.

d o w n w a rd s arro w ) or ev en o f lo n g -lastin g ch arcoal

The

r e s u lt in g

a t m o s p h e r ic

carb o n

d io x id e

in to

the d e e p

ocean

or in to

d io x id e

('b io c h a r') into the soil. A rtificial se q u e stra tio n into

co n ce n tratio n w ill re m ain fo r c e n tu rie s n e a r the

the o c e a n s is c o n tro v e rsia l, w h ile su b te rr a n e a n

h igh e st lev els reach ed , sin ce n atu ral p ro c e sse s can

se q u e stra tio n is le ss c o n tro v e rsia l a n d is a lre a d y

on ly return carb o n to its n atu ra l sin k s in the d e ep

h a p p e n in g in so m e c a se s (C h ap te r 8). B alan cin g the

o c ea n s o v er m a n y cen tu ries.

in flo w s a n d o u tflo w s o f carb o n d io x id e into the

M ore or less p erm an en t n atu ral sin k s for carbon include carbon-rich d etritu s from m arin e o rgan ism s,

a tm o s p h e r e w ill ta k e m a n y d e c a d e s or e v en centu ries.

m ain ly m icro sc o p ic a lg a e a n d p lan k to n , b u t a lso

F u rth erm o re , b e c a u se o f the slo w m ix in g an d

from larger creatures, w hich fall to the ocean floor.

o v e rtu rn in g o f the o c e a n s, su rfa c e te m p e ra tu re s

C arb on is a lso tran sp o rted to the o cean s by riv ers

w ill con tin u e to rise slo w ly for cen tu ries, even after

a n d w in d -b o rn e o rg a n ic p a rtic le s, a n d so m e of

co n cen tration s o f carb o n d io x id e in the a tm o sp h ere

this a lso e n d s u p on the ocean floor in se d im e n t

h a v e sta b ilise d , an d the d e ep o c ea n s w ill con tin u e

layers. C arbon is also stored in p lan ts an d the soil on

to w a rm . T h is w ill le a d to co n tin u in g th e rm al

lan d , b u t this can be retu rn ed to the atm o sp h ere

ex p a n sio n , an d th u s risin g se a lev els, for cen tu ries

rap id ly by fire or d e co m p o sitio n . The p o ssib ility of

after sta b ilisatio n o f gre en h o u se g a s con cen tration s.

in creasin g sin k s artificially is d isc u sse d in C h ap ter 8,

O u r ch ild ren a n d g ra n d c h ild ren w ill be se e in g the

w hich d e a ls w ith m itigation .

in evitab le re su lts o f o u r co n tin u in g g re en h o u se g a s

E m issio n s o f carb o n d io x id e from the b u rn in g of

em issio n s lo n g after w e h a v e gon e.

and

Recent d e v e lo p m e n ts su g g e stin g that G reen lan d

d e fo re sta tio n w ill h a v e to be re d u ced ev en tu ally by

a n d e v en the W est A n tarctic Ice S h e e t m a y be

m ore than 80% glo b ally relative to p resen t e m issio n s

d e s ta b ilis e d b y ev en 2 °C g lo b a l w a rm in g (see

to sto p co n cen tration s in creasin g in the atm o sp h ere

C h a p te r 3) m a k e s m a tte r s e v e n w o r se , w ith

(C h a p te r 8). T h is w ill ta k e se v e ra l d e c a d e s to

m u ltim etre rise s in se a level p o ssib le . T h is su g g e sts

f o s s il

fu e ls

(o il, c o a l

and

n a tu r a l

g a s)

a ch ie v e w ith o u t d is r u p tin g h u m a n society. Th e

that sta b ilise d co n ce n tratio n s o f g re e n h o u se g a se s

m ore w e d e lay red u cin g g reen h o u se g a s em issio n s,

m ay in fact h a v e to b e re d u ced , that is, that w e m ay

the larger the inevitable m agn itu d e o f clim ate ch ange

g o th ro u g h a p e a k co n ce n tratio n o f g re e n h o u se

w ill be, an d the m ore drastic w ill be the redu ctio n s in

g a s e s in the a tm o sp h e re a n d then h a v e to red u ce

em issio n s n eed ed later to avoid d a n g e ro u s levels of

them . T h is is term ed an 'o v e rsh o o t sc e n a rio ' a n d

clim ate ch ange. To u se the w ater-in to-bow ls an alo g y

w o u ld requ ire that e m issio n s be re d u ced to zero or

a g a in , it is a s if w e w an ted to sto p the w ater risin g

ev en b ec o m e n e g a tiv e later th is century. T h at is,

ab o v e a certain level, b u t w ere slo w to red u ce the

carb o n d io x id e a n d oth er g re e n h o u se g a s e s m ay

rate at w hich w e k ep t a d d in g w ater - the slo w er w e

h av e to be rem o v ed from the a tm o sp h e re .25

are to redu ce the input, the m ore d rastically w e will need to redu ce it later.

The 2007 IPCC report d is c u s se s the p o ssib ility of su ch o v e rsh o o t e m issio n s sc e n a rio s. T h ey w o u ld

C arb o n d io x id e con cen tration s in the a tm o sp h ere

req u ire th at carb o n d io x id e b e re m o v e d th ro u gh

w ill sta b ilise on ly w h en the rate o f e m is sio n s is

so m e p r o c e ss th at n a tu ra lly or a rtificia lly ta k e s

re d u ce d to the rate o f d e p o sitio n or se q u e stra tio n

carb o n d io x id e o u t o f the a tm o sp h e re , m o st likely

into the d e ep o cean s (or, a s rep resen ted in F ig u re 3,

via g ro w in g p la n ts or a lg a e , w h ich m ay or m ay not

12

CLIMATE CHANCE: THE SCIENCE, IMPACTS A N D SO LUTIO NS

B O X 2: D ELA YED C LIM A T E SYSTEM R ESPO N SES M ATTER Slow or delayed responses are widespread (but not universal) characteristics of the interacting climate, ecological, and socio-economic systems. This means that some impacts of human-induced climate change may be slow to become apparent, and some could be irreversible if climate change is not limited in both rate and magnitude before crossing thresholds at which critical changes may occur. The positions of such thresholds are poorly known. Several important policy-relevant considerations follow from these delayed response effects: • Stabilisation of the climate and climate-impacted systems will only be achieved long after human-induced emissions of greenhouse gases have been reduced. • Stabilisation at any level of greenhouse gas concentrations requires ultimate reduction of global net emissions to a small fraction of current emissions. It will likely take centuries to reduce carbon dioxide concentrations much below the highest levels reached unless active steps are taken to remove carbon dioxide from the atmosphere (see Chapter 8). • Social and economic time scales for change are not fixed. They can be changed by policies, and by choices made by individuals, or by reaching critical thresholds where change may becom e rapid and traumatic (for example, emergency programs, policy revolutions, technological breakthroughs, famine or war). • Higher rates of warming and multiple stresses increase the likelihood of crossing critical thresholds of change in climatic, ecological, and socio-econom ic systems (see Chapter 6). • Delays and uncertainty in the climate, ecological, and socio-economic systems mean that safety margins should be considered in setting strategies, targets and timetables for avoiding dangerous levels of climate change. • Inevitable delays in slowing down climate change make some adaptation essential, and affect the optimal mix of adaptation and mitigation strategies. • Slow responses in the climate system, and the possibility of reaching critical thresholds in the interacting climate, ecological and socio-econom ic systems, make anticipatory adaptation and mitigation actions desirable. Delayed reductions in emissions in the near-term will likely lead to an 'overshoot' scenario, with a need for faster reductions and removal of greenhouse gases from the atmosphere at a later time, probably at greater cost. Source: M a in ly updated from IP C C 2001 Synthesis Report, pp. 8 7 -9 6 .

be u sed for fuel an d the carbon or carbon d ioxide

Observed impacts27

so m eh o w rem o v ed from the clim ate sy stem by sto rag e or sequ estration . P y rolysis of b io m a ss and the se q u estratio n of the re su ltin g b ioch ar is one

W hile the 0.74°C increase in glob al av erage su rface

p o ssib ility .26 T h ese p o ssib ilitie s are d isc u sse d in C h apter 8.

tem peratu re since the begin n in g of the tw entieth century m ay seem sm all, o b serv atio n al evid en ce indicates that clim ate ch an ges have alread y affected a variety of ph y sical and biological sy stem s. A s w ell

CLIMATE C H A N C E MATTERS

13

a s sh rin k a g e o f g la c ie rs an d th aw in g o f p e rm afro st

S a h e lia n a n d so u th e rn A frica. S ea -lev e l rise an d

m e n tio n ed ab o v e , e x a m p le s o f o b se rv e d ch a n g e s

h u m a n d e v e lo p m e n t are a lso a ffe c tin g c o a s ta l

lin k ed to clim ate in clu d e : sh ifts in ice freeze an d

w e tla n d s an d m a n g ro v es.

b re a k -u p d a te s on riv e rs an d la k e s; in c re a se s in

IP C C W orking G ro u p I h a s a lso re p o rte d that

rain fall an d rain fall inten sity in m o st m id- an d high

in c re a sin g carb o n d io x id e c o n c e n tratio n s in the

la titu d e s o f the n orthern h e m isp h ere; len gth e n in g

a tm o sp h e re h a s led the o c e a n s to b e c o m e m o re

o f g ro w in g se a so n s; an d earlier d a te s o f flo w erin g

acid ic, w ith an a v e ra g e d e cre a se in p H o f 0.1 u nits

o f trees, em erg en ce o f in sects, a n d e g g -la y in g in

sin ce 1750.2S C o n tin u atio n o f this trend is exp ected

b ird s. S tatistically sig n ifica n t a sso c ia tio n s b etw een

to a d v e rse ly affect m an y ocean ic sp e c ie s that gro w

c h a n g e s in re gio n al clim ate an d o b se rv e d ch a n g e s

sh ells in c lu d in g coral an d m an y sh ellfish .28

in p h y sic a l a n d b io lo g ic a l s y s te m s h a v e b ee n

S atellite o b se rv a tio n s p o in t to lo n g e r g ro w in g

d o cu m e n te d in fresh w ater, terrestrial a n d m arin e

se a s o n s , w ith e a rlie r 'g r e e n in g ' o f v e g e ta tio n in

en v iro n m en ts on all continents.

sp rin g . T h is m a y in crease total gro w th if w ater an d

The 2007 IP C C re p o rt from W orking G ro u p II

n u trien ts are n ot lim itin g , b u t co u ld a lso le a d to

fo u n d that o f m ore than 29 000 se ts o f o b se rv atio n s

p r o b le m s w ith d iffe re n c e s in se a s o n a l tim in g

o f p h y sic a l an d b io lo g ic a l sy ste m s, re p o rted in 75

b etw een so m e sp e c ie s an d o th e rs on w h ich they

stu d ie s, m o re than 89% sh o w e d sig n ifica n t ch an ge

rely fo r fo o d or oth er se rv ic e s lik e p o llin a tio n .

co n siste n t w ith the direction o f ch an ge ex p ected a s

H otter an d d rier su m m e rs m a y a lso c a u se lo sse s of

a re sp o n se to w a rm in g . Furth er, it fo u n d th at the

v eg etatio n d u e to h eat stre ss an d fire.29

sp a tia l a g re e m e n t b etw een re g io n s o f sig n ifica n t

A ttrib u tio n o f c h a n g e s in crop p ro d u c tio n is

w a rm in g a c r o ss the g lo b e a n d the lo ca tio n o f

co m p le x , w ith clim ate ch an ge b ein g only one factor

o b se rv e d c h a n g e s in sy ste m s w a s c o n siste n t w ith

a lo n g w ith ch a n g e s in crop v arieties, a p p lic atio n o f

g lo b al w arm in g rath er than local variability.

fertilisers, effects o f p o llu ta n ts su ch a s o z o n e an d

In ge n eral, w a rm in g effects on b io lo gical sy ste m s

n itro g e n fa llo u t, a n d d ire ct effe cts o f in c re a sin g

in c lu d e a v e ra g e ra n g e sh ifts p o le w a rd s o f a ro u n d

carb o n d io x id e co n ce n tratio n s a ffectin g w ater u se

5 to 10 km p e r d e c a d e , a n d e v e n ts in sp r in g

efficiency an d p h o to sy n th e sis. N e v erth eless, at least

o c c u rrin g tw o or three d a y s e a rlie r p e r d e c a d e .

tw o p a p e r s claim to h av e d etected yield tren d s d u e

P la n ts a n d a n im a ls w ill a lso m o v e to h ig h e r

to c lim a te c h a n g e in A u s tr a lia an d the U n ited

e le v a tio n s. Su ch m o v e m e n ts are lim ited in m an y

S ta te s.30

p la c e s by co astlin es, lim ited h eigh t o f m o u n tain s or

A t t r ib u t in g

ob serv ed

ch anges

alie n atio n o f la n d d u e to cle arin g or oth er h u m an

ch ange

in te r fe re n c e .

c a u s e s . T h is is s t r ik in g ly

T h is

p a r tic u la r ly

a ffe c ts

m any

is c o m p lic a t e d

to

b y p o s s ib l e ill u s t r a t e d

c lim a te m u ltip le b y the

b io lo g ic a l r e se r v e s se t u p to p ro te c t ra re a n d

in c re a sin g u se o f the T h a m e s B arrie r in the U K , a

e n d an g e re d sp ecie s.

m o v e a b le g a te -lik e stru c tu re d e sig n e d to co n trol

S ev eral m o d ellin g stu d ie s that linked re sp o n se s

f lo o d in g in th e lo w e r T h a m e s R iv e r, w h ic h

in so m e p h y sic a l a n d b io lo g ic a l s y s te m s w ith

b e c a m e o p e r a tio n a l in 1983. T h e n u m b e r o f tim e s

clim ate c h a n g e s fo u n d th at the b e st fit w ith the

th e T h a m e s B a rr ie r h a s b e e n c lo s e d e a c h y e a r

o b s e r v a tio n s o c c u rre d w h en b o th n a tu ra l a n d

sin c e 1983 is sh o w n in F ig u r e 4 b y th e b la c k

en h an ced g re en h o u se fo rcin gs w ere in clu d ed .

c o lu m n s; th e o re tica l c lo s u r e s fro m 1930 b a se d on

T h e IP C C a lso re p o r te d th at w a r m in g h a s a lr e a d y

a ffe c te d

a g ric u ltu ra l

and

tid a l a n d riv e r flow d a ta are d e n o te d b y the gre y

fo r e s t r y

c o lu m n s. T h e in c re a se in the fre q u e n c y o f c lo su r e

m a n a g e m e n t (earlier sp rin g p la n tin g s a n d ch a n g e s

sin c e 1983 c o u ld r e a d ily b e tak e n a s e v id e n c e o f

to fo re st fire an d p e st o ccu rren ces). T h ere are a lso

r is in g se a le v e l or sto r m in e s s . H o w e v e r, th e se

early in d icatio n s of im p ac ts on m o u n tain settlem en ts

c lo s u r e s c o u ld b e o c c u r rin g d u e to a co m b in a tio n

from m e ltin g g la c ie rs, an d on d rie r c o n d itio n s in

o f se v e r a l e ffe c ts, in c lu d in g re la tiv e se a -le v e l rise

14

CLIMATE C H A N C E: THE SCIENCE, IMPACTS A N D SO L U T IO N S

Year Figure 4: Has climate change increased the frequency of closure of the Thames Barrier? (Figure courtesy of Environment Agency, UK.)

(p a rt o f w h ich m a y b e d u e to la n d su b sid e n c e ),

S e r v ic e in Z u ric h re p o r te d an a v e r a g e lo s s o f

in c r e a se d s t o r m in e s s a n d c h a n g in g o p e r a tio n a l

ice in A lp in e g la c ie rs in E u ro p e e q u iv a le n t to a

p r o c e d u r e s .31

5 to 10% re d u ctio n o f the total v o lu m e o f all A lp in e

A cco rd in g to a review o f th is d a ta in 2003, the

g la c ie rs.32

b arrier is n ow so m e tim e s u se d to retain w ater in the

D aily m a x im u m an d m in im u m tem p e ra tu re s in

T h am es R iver at low tid e d u rin g d ro u g h t, a s w ell a s

P a ris at the h e ig h t o f the h e a tw a v e , w ith the

to re d u ce the risk o f flo o d in g from the se a at high

c o rre sp o n d in g d e a th s re co rd ed in m ajo r P a risia n

tide. In creased relative sea-level rise an d in creased

h o sp ita ls are sh o w n in F ig u r e 5. Th e line w ith

sto rm in e ss are both likely, at least in p art, to b e d u e

tria n g les sh o w s d aily m a x im u m tem p e ra tu re s, an d

to the en h an ced g re e n h o u se effect, a n d in c rea se d

the lin e w ith s q u a r e s sh o w s d a ily m in im u m

d ro u g h t m ay a lso be related to clim ate ch an ge, b u t

te m p e ra tu re s (scale on right). V ertical b a r s are the

so rtin g ou t the relative im p o rtan ce o f these p o ssib le

d a ily n u m b e r o f d e a th s reco rd ed in P aris (scale on

c a u se s req u ires a m ore d e ta iled a n a ly sis. A n oth er recent e x a m p le o f a clim ate im p a c t that

left). M a x im u m d e a th s o ccu r n ear the en d o f the h e a tw a v e on 13 A u g u st. Th e ex c e ss death rate w a s

is at le a st a fo re ru n n er o f w h a t m a y b e ex p e c te d

due

w'ith co n tin u e d g lo b a l w a rm in g is the se rie s of

airco n d itio n ed ap a rtm en ts. A lon ger-term w a rm in g

la r g e ly

to the a g e d

and

in firm

in n on

extrem e h igh te m p e ra tu re s ex p erie n c ed in E u ro p e

m igh t lead to a d a p ta tio n s su ch a s the in stallatio n of

d u rin g the n o rth ern su m m e r o f 2003. M a x im u m

a ir c o n d itio n e rs, b u t th is w o u ld b e c o stly a n d

tem p e ra tu re s w ere u p to 5 °C a b o v e the lon g-term

e n e rg y -in te n siv e . T h is E u ro p e a n h e a tw a v e w a s

a v e ra g e s for the sa m e d a te s b etw een 1961 an d 1990,

ch osen a s a c a se stu d y b y the 2007 IP C C in its

a n d the French H ealth M in istry re p o rte d 14 802

W orking G ro u p II report.

m o re d e a th s in A u g u st than w o u ld b e ex p ected on

M artin B en iston a n d H en ry D ia z cite the 2003

the b a s is o f re cen t s u m m e r s . T h o u s a n d s m o re

h e atw av e in E u ro p e a s an ex am p le o f w h at to expect

e x c e ss d e a th s w e re re p o rte d in G e rm a n y , S p a in

in fu tu re w a rm e r su m m e rs, w h ile G erry M eeh l of

a n d the U K . D ro u g h t co n d itio n s, low riv er flo w s

N C A R (U SA ) a n d co lleag u e sh ow that m ore frequent

a n d w ild fires w e re w id e s p r e a d a c r o ss E u ro p e

an d intense h e a tw a v es are to be ex p ected , esp ecially

d u rin g this p e rio d . Th e W orld M o n ito rin g G la cie rs

in E u ro p e and N orth A m erica, in the secon d h alf of

CLIMATE C H A N C E MATTERS

15

u

k.

3

•w

(Z k.

V

CL

E

T m in

-T m ax

5: Deaths during the heatwave in Paris, july-August 2003. (Figure courtesy of Institut de Veille Sanitaire, InVS, France, per Pascal Empereur-Bissonnet.) Figure

the tw e n ty -first century. P eter S to tt o f the U K

su ch d isa ste rs are greater in m an y richer d e v e lo p e d

M e te o ro lo g ic a l O ffice a n d o th e rs e stim a te th at

coun tries, an d that, irresp ective of clim ate ch an ge,

h u m an in fluence h a s at least d o u b le d the risk o f a

there is a risin g trend in su ch d a m a g e s.

h e a tw a v e in E u ro p e e x c e e d in g the m a g n itu d e o f

Even in rich co u n tries, there are tren d s to w a rd s

that in 2003 an d that the lik elih o od o f su ch ev en ts

g re a ter e x p o su re to w e ath er a n d clim atic h a z a rd s,

m a y in crease 100-fold ov er the n ext 40 y e a rs.33

su ch a s flo o d in g b y riv e rs a n d a lo n g lo w -ly in g

Su ch c h a n g e s w ill a lso lik ely affect the g lo b a l

c o a sts, d r o u g h t, h ail a n d w in d sto r m s. E x a m p le s

carbo n b alan ce, w ith m o re frequ en t h eat stre ss an d

in clu d e the in creasin g p o p u la tio n a n d in v e stm e n ts

fires re d u cin g carb o n u p ta k e in fo re sts, an d even

a lo n g the h u rrica n e -p ro n e A tlan tic C o a st o f the

le a d in g to n et in p u ts o f carb o n d io x id e into the

U n ite d S ta te s, a n d the cy c lo n e -p ro n e c o a s ts o f

a tm o sp h e re , a s h a s b een o b se rv e d d u rin g the hot

n orth ern A u str a lia . T h ese d e v e lo p m e n ts le a d to

su m m e r o f 2003 in E u ro p e .29

g re a te r p o te n tia l ec o n o m ic lo ss e s . R e d u c tio n s in lo s s o f life are o n ly a c h ie v e d

th ro u g h

e x p e n d it u r e s ,

c y c lo n e - p r o o f

fo r

e x a m p le

on

la rg e

Trends in human vulnerability

b u ild in g s, early w a rn in g sy ste m s, ev a cu a tio n , and

It is often a rg u e d that a s h u m an so cieties b ecom e

re scu e se rv ice s.

rich er an d m ore tech n o lo gically a d v a n c e d , they

E v id e n c e th at h u m an so c ie tie s are b e c o m in g

beco m e less d e p e n d en t on n atu re an d m ore ab le to

m ore v u ln e ra b le to clim ate-related d isa ste rs co m es

a d a p t to clim atic ch an ge. Poorer so cieties are likely

from the o b se rv e d ra p id in crease in d a m a g e s from

to be m o re a d v e rse ly affected by clim ate ch an ge

clim atic h a z a rd s in the la st se v e ra l d e c a d e s o f the

than richer on es, so the cap acity of a society to a d a p t,

tw entieth century.34

it is sa id , w ill in ev itab ly in crease w ith econ om ic

S o m e v u ln e r a b le citie s, e v en in d e v e lo p e d

develo p m en t. In term s of the n um b er o f d e ath s from

co u n trie s su ch a s the U n ited S ta te s an d A u stra lia ,

w eath er an d clim atic d isasters, su ch a s sto rm s, flood s

are at p re se n t u n p re p a re d for d irect h its b y m ajo r

a n d d ro u g h ts, this a p p e a r s to b e b orn e o u t by

tro p ical sto rm s, ev en w ith o u t clim ate ch an ge. T h is

co m m on o b serv atio n s an d statistics. H ow ever, the

is d e sp ite w a rn in g s o f p o ssib le d isaste r, a s in the

sa m e statistics sh ow that m o n etary d a m a g e s from

c a se o f N ew O rle a n s w ith h u rrica n e K a trin a in

16

CLIMATE C H A N C E: THE SCIENCE, IMPACTS A N D SO L U T IO N S

A u g u st 2005. S e v e ra l stu d ie s h a d w a rn e d o f N ew

o f the in crease is attrib u tab le to better re p o rtin g of

O rle a n s' v u ln erab ility, b u t re c o m m e n d a tio n s w ere

s m a lle r

n ot acted on, larg e ly d u e to their cost. T h e New7

p o p u la tio n s an d in v e stm e n ts in locatio n s su b ject to

O rlean s lo sse s illu strate the p articu la r v u ln erab ility

clim atic h a z a r d s, su ch a s lo w -ly in g co a sta l z o n es,

o f the p oor, even in rich co u n tries.35

d is a s t e r s

and

in c r e a se d

exp o su re

of

riverin e flo o d p la in s, a n d a re a s su b je ct to tro p ical

T re n d s th at m a k e m a tte r s w o r se ('c o u n ter-

cy c lo n e s an d sto rm su rg e s. Th e m u ch m ore ra p id

a d a p t iv e ' tre n d s) are w id e ly in e v id e n ce . T h ese

in crease in the n u m b e r o f re p o rted w eath er-related

in clu d e p o p u la tio n g ro w th in g e n e ra l, in c rea se s in

d is a s t e r s

p e r c a p ita c o n s u m p tio n o f w a te r a n d en ergy ,

d isa ste rs, su ch a s ea rth q u a k e s an d tsu n a m is, h in ts

as

o p p o se d

to n o n - w e a th e r- re la te d

preferen tial gro w th in clim atically h a z a rd o u s are as,

at an in crease in w eath er-related d isa ste r occurrence,

in c re a se d b a r r ie r s to m ig ra tio n o f p e o p le a n d

b u t th is co u ld b e in p art d u e to the sm a lle r sp a tia l

n atu ra l e c o sy ste m s, the sp re a d o f new m o n ocu ltu re

sc a le o f so m e w e ath er-re late d d is a s te rs . Th e 2007

crop c u ltiv a rs, a n d in c rea sin g relian ce on lim ited

IP C C report s u g g e s ts that the a ctu al in crease d u e to

te c h n o lo g ica l fix es. T h e la st in c lu d e flo o d levee

clim ate ch an ge is a ro u n d 2% p er y ear (som e 22% p er

b a n k s an d se a w a lls, w hich e n c o u ra g e in v e stm e n t

d e cad e), b u t that the greater p art o f the total in crease

in h a z a rd z o n e s a s they p ro v id e p rotection from

is d u e to in creasin g vu lnerability.

sm a ll h a z a rd s, b u t fail w h en la rg e r h a z a rd s occur.

The M ississip p i flood ex a m p le s u g g e sts societal

T h is w a s ev id en t in the ca se o f the m ajo r flo o d s in

ch a n g e s m a y in so m e c a se s h a v e m ore in fluence on

the u p p e r M ississip p i V alley in the U n ited S ta te s in

v u ln e ra b ility a n d resilien ce to clim atic v a ria b ility

1993, w h en m a jo r le v e e s w ere b re a ch e d c a u sin g

an d ex trem e s than clim ate ch a n g e , a n d th at they

m illion s o f d o lla rs d a m a g e . R e v e rsin g su ch counter-

eith er c o m p o u n d or re d u ce the effects o f clim ate

a d a p tiv e tren d s is not easy .36

ch an ge . M u ch m o re atten tion n e e d s to be p a id to

E v id en ce o f in creasin g vu ln e rab ility co m es from

such q u estions, which h ave strong policy im plications

the o b s e r v e d r a p id in c re a se in d a m a g e s from

th ro u gh the identification o f d e v e lo p m e n ta l tre n d s

clim atic h a z a rd s in the la st se v e ra l d e c a d e s o f the

th at m a y m a k e e x p o su re , a d a p tiv e c a p a c ity an d

tw en tieth cen tu ry .34 T a b le 1 s u m m a r is e s so m e o f

m itig atio n p o ten tial b etter or w o rse . C lim a te ch a n g e a d d s to the im p a c t o f th ese

the ev id en ce u p to the late 1990s. D ata u p to 2006, from the World D isasters Report 2007, sh o w s that the

co u n ter-a d a p tiv e so cietal tren d s.

n u m b e r o f rep orted d isa ste rs in creased b y a furth er 60% from 1987-96 to 1997-2006. W hile p a r t o f th is in c rea se in the n u m b e r of

Projections of future climate change

w eath er-re late d d is a s te rs a n d d a m a g e s m a y h a v e

In 2001 the IP C C d e v e lo p e d a se t of clim ate ch an ge

been d u e to an in crease in the frequ en cy o f clim atic

p rojectio n s, b a se d on p la u sib le sc en ario s for future

h a z a rd s, this h a s n ot been clearly esta b lish ed . M o st

g re e n h o u se g a s e m is sio n s (the so -c a lle d S R E S

Increase in disasters since 1960. Comparison, decade by decade, of the number and costs (US$ billion) of catastrophic weather-related and non-wcather-related events since the 1960s. Note the marked increase in weather-related disasters and their costs, but only a small increase in non-weather related disasters. Data comes from the International Federation of Red Cross and Red Crescent Societies annual World Disasters Report 2004.

T A B L E 1:

1 9 8 0 -8 9

1 9 9 0 -9 9

Ratio 90s/60s

N um b er of weather-related disasters

1 9 6 0 -6 9 16

29

44

72

4.5

N um b er of non weather-related disasters

11

18

19

17

1.5

Econom ic losses

50.8

74.5

118.4

399.0

7.9

6.7

10.8

21.6

91.9

13.6

Insured losses

1 9 7 0 -7 9

CLIMATE C H A N C E MATTERS

17

sc en a rio s d e v e lo p e d in 2000). T h ese w ere b a se d on

fe e d b a c k s a n d in 'the fu ll effects o f ch a n g e s in ice

'sto ry lin e s' a b o u t fu tu re d e v e lo p m e n t a ffectin g

sh eet flo w '. The rep o rt s u g g e s ts that an a d d itio n a l

g re en h o u se g a s em issio n s, a s an u p d a te on earlier

1 0 -2 0 cm o f se a -le v e l rise c o u ld o c cu r d u e to

sc e n a rio s u se d in 1992 an d 1996 (see C h a p te r 3

in c re a se s in ice sh eet flow , an d th at 'la rg e r v a lu e s

for d e tails). U sin g m o d e ls o f the carb o n cycle, that

can n o t be e x c lu d e d '. A cceleratio n s in ou tflo w from

is, o f h o w carb o n is m o v e d a ro u n d b etw een the

G reen lan d an d p a r ts o f A n tarctica sin ce the IPCC

atm o sp h ere , the b io sp h e re, the so il an d the ocean s,

re p o rt w a s d ra fte d s u g g e s t th at in d e e d se a -le v el

the IPCC estim ated th atb y the y ear 2100, atm osph eric

rise co u ld b e w ell a b o v e the u p p e r estim ate s in the

carbon d io x id e con cen tration s w o u ld ran g e in total

IP C C report b y 2100.

anyw h ere from 490 to 1260 p p m . Such concentrations

T h e p ro je c te d w a r m in g in the tw e n ty -first

are 75 to 350% high er than the p re-in du strial estim ate o f 280 p p m in 1750. C arb o n d io x id e con cen tration s

centu ry is lik ely to b e betw een tw o an d 10 tim es a s la rg e a s the o b se rv e d w a rm in g in the tw entieth

in late 2007 w ere a lre a d y a b o u t 382 p p m , or 36%

century, a n d la rg e r than an y sin ce the la rg e an d

a b o v e the p re - in d u str ia l v a lu e a n d co n tin u e to

a b ru p t Y ou n g er D ry a s ev en t 11 000 y e a rs a g o (see C h a p ter 2). P rojected te m p e ra tu re s w o u ld b e m u ch

increase at 2 to 3% p er an n u m . T h ese projected co n cen tration s o f carbon d io x id e

w a rm e r than d u rin g the so -called M e d ie v a l W arm

in the 2001 IP C C report led to estim ate s that by 2100

P e rio d , w h ich w a s m o st e v id e n t in the N o rth

a v e ra g e g lo b a l su rfa ce te m p e ra tu re s are likely to be

A tlan tic region a ro u n d 800 to 1300 A D . W arm ing a s

b etw een 1.4 a n d 5 .8 °C w a rm e r than in the IP C C

large an d ra p id a s that p rojected for the tw enty-first

b ase lin e y ear o f 1990 (see C h a p ter 5). The IPCC d id

century m igh t b e exp ected to create severe p ro b lem s

n o t sa y w h a t the p r o b a b ilitie s o f the v a r io u s

for n atu ra l e c o sy ste m s an d h u m a n so cieties. In deed

in crease s w ere w ithin this ra n g e b e c a u se estim ate s

e v id e n c e fro m p a s t clim a te c h a n g e s o f sim ila r

o f p ro b a b ility are d iffic u lt an d d e p e n d on how

m a g n itu d e p oin t to m ajo r im p a c ts, w hich, if h u m a n s

so ciety c h a n g e s its u se o f fo ssil fu e ls in the futu re.

h a d b een p re se n t in n u m b e rs like tod ay , w o u ld

The IP C C a lso e stim ate d sea-lev el rise b y 2100 to be

h av e been d isa stro u s.

in the ra n g e o f 9 to 88 cm , m o stly from th erm al

P o te n tia l in c re a se s in se a level re m ain v ery

e x p a n sio n o f the o c e a n s a s th ey w a rm u p an d

u ncertain , b u t co u ld w ell be a b o v e the u p p e r en d of the 2007 IP C C e stim ate s. A n in creasin g n u m b e r of

m eltin g o f m o u n tain glaciers. For the 2007 report IPCC ch ose not to u se the

scie n tists n ow a gre e w ith Ja m e s H a n se n in a rg u in g

w h o le se t o f SR E S sc e n a rio s in d e ta ile d m o d e l

th at sea-lev el rise co u ld be w ell in ex c e ss o f a m etre

ca lcu latio n s, d u e to the d e m a n d on co m p u tin g

b y 2100 (see C h a p te r 5), w ith p o ten tially d isa stro u s

resou rces, b u t in stead u se d three o f the five m ain

co n se q u e n c e s for m a n y c o a sta l c o m m u n itie s an d

sc e n a rio s, n o t in c lu d in g the A 1FI or fo ssil fuel

re so u rc e s.15

intensive scenario. This w as om itted argu ab ly b ecause o f criticism that the A 1FI scen ario w a s too high. In fact, em issio n s h av e since 1990 been follow in g at or

Facing the challenge

ab o v e the A 1FI levels. F ortu n ately IP C C d id also

Scientific research in the latter h a lf o f the tw entieth

calculate, u sin g sim p lified m o dels, the clim atic effect

c e n tu ry

of this higher scen ario (see C h ap ter 5).

g o v e rn m e n ts to the issu e o f clim ate ch an ge. T h is

le d

m any

c lim a te s c ie n tis ts

to a le rt

Th e 2007 IP C C rep o rt fo u n d , for the full ran g e of

w a s d o n e in d iv id u a lly an d th ro u gh co n feren ces

SR E S e m issio n s sc e n a rio s, th at g lo b a l w a rm in g by

an d p o licy statem en ts. T h is led to the settin g u p of

2100 w o u ld be in the ran g e 1.1 to 6 .4 °C , relative to

the In tergo v e rn m en tal P an el on C lim ate C h a n g e to

1980-99 a v e ra g e s. E stim ate s o f se a -le v el rise w ere

p ro v id e p o licy -relevan t scientific a d v ic e, an d it led

g iv en a s 18 to 59 cm , b u t w ith the ca v e a t that this

to d is c u s s io n

o m itte d

A sse m b ly (see ch ap ter 11).

u n c e rta in tie s in c lim a te - c a rb o n

cy cle

in the U n ite d N a t io n s G e n e ra l

CLIMATE C H A N C E: THE SCIENCE, IMPACTS A N D SO L U T IO N S

18

T h e G e n e ra l A s s e m b ly c a lle d fo r a U n ite d

T h ese p ro v isio n s, an d n ego tiatio n s to w a rd s their

C lim a te

im p le m e n ta tio n , h a v e led to m u ch a r g u m e n t

C h a n g e (U N F C C C ) in 1990. Th e C o n v e n tio n w a s

b e tw e e n the c o u n trie s th at are p a r tie s to the

fin ally a d o p te d in N e w York in M ay 1992, an d w a s

C o n v en tio n (an d w h o m e et a s the 'C o n fe ren ce of

o p e n e d fo r s ig n a tu r e s a t the In te rg o v e rn m e n ta l

P a rtie s', or C O P ), e sp e cia lly o v er the co n ten ts an d

C o n fe ren ce on S u sta in a b le D e v e lo p m e n t, h eld in

im p le m en ta tio n o f the K y o to P rotoco l a d o p te d in

Rio d e Jan e iro in 1992. F ra m e w o rk co n v e n tio n s are

1997. The K y oto P rotocol is a first agre em e n t to start

N a t io n s

F ram ew ork

C o n v e n tio n

on

g e n e r a l a g r e e m e n ts th a t le a v e the d e t a ils o f

the p ro c e ss o f re d u cin g g re e n h o u se g a s em issio n s,

im p le m en tatio n to be w o rk ed o u t later via a se ries

w ith v ery m o d e s t ta rg e ts se t fo r re d u c tio n s in

o f p ro to c o ls, le g a l d e v ic e s or a g re e m e n ts to be

A n n ex I co u n trie s a v e ra g in g 5.2% re lativ e to 1990

a d o p te d

the

e m is s io n s , to b e a c h ie v e d b y 2 0 0 8 -1 2 . T h e se

C o n v e n tio n . U p to late 2007, 193 co u n trie s h a v e

arg u m e n ts h av e been co m p o u n d e d b y un certain ties

by

th e

c o u n t r ie s

th a t

s ig n e d

ratified the U N F C C C . The objective o f the U N F C C C is sta ted in A rticle 2 to be:

a s to the a ctu a l risk from clim ate ch an ge , a n d the c o sts o f im p a c ts an d ab atem e n t m e a su re s. There h as a lso been a clash o f v a rio u s n atio n al an d co rp o rate in te r e sts, id e o lo g ic a l p o s it io n s , a n d

e c o n o m ic

... the stabilisation o f greenhouse g a s

a d v a n ta g e s. A s at 12 D ecem b er 2007, 176 co u n tries

concentrations in the atm osphere at a level that

h a d ratified the P rotocol, w ith th ose a g re ein g to an

w ould prevent dangerous anthropogenic

e m is sio n s re d u ctio n ta rg e t a c c o u n tin g for so m e

interference with the clim ate system . Such a level

63.7% o f w o rld e m issio n s. A u stra lia a g re ed to ratify

should be achieved within a tim efram e sufficient

the P rotocol fo llo w in g a ch an ge o f g o v e rn m e n t in

to allow ecosystem s to adapt n atu rally to clim ate

N o v e m b e r 2007. Th e on e m ajo r coun try re fu sin g to

change, to ensure that food production is not

ra tify the P rotoco l a s o f late 2008 is the U n ited

threatened, an d to enable economic development

S ta te s.38 T h ese p o litical m atters are d is c u s se d m ore

to proceed in a su stain ab le m anner.*7

fully in C h a p te rs 10 an d 11.

The U N F C C C co n tain s no b in d in g co m m itm en ts on e m issio n s le v e ls, b u t it d o e s lay d o w n so m e g e n e ral p rin c ip le s a n d o b je ctiv es to sh a p e fu tu re n eg o tia tio n s on these co m m itm en ts. T h ese in clu de that: •

•

D ev elo p ed co u n tries (m o st m e m b e rs o f the O rgan isatio n for E con om ic C o o p era tio n and

c h a n g e is h a p p e n in g , a n d is p ro je cted to in crease d u e to the o n g o in g a n d in c re a sin g re le a se o f gre e n h o u se g a s e s into the a tm o sp h e re . The m ain gre en h o u se g a s (other than w ater v a p o u r) is carbon

D e v elo p m en t (O E C D )) p lu s fo rm er c o m m u n ist

d io x id e , an d its co n cen tration in the a tm o sp h e re

sta te s u n d e rg o in g tran sition to a m ark et

h a s in creased from the p re-in d u strial v a lu e of a b o u t

econom y, collectively k n o w n a s 'A n n ex I'

280 p p m to so m e 382 p p m in 2008. It w ill tak e

co u n tries, sh o u ld take the lea d w ith ab atem e n t

cen tu ries to red u ce this con cen tration , an d p o ssib ly

m e a su re s.

m o re th an a ce n tu ry ev en to sto p it in c re a sin g .

The clim atic an d econ om ic v u ln e rab ilitie s of d e v e lo p in g co u n trie s sh o u ld b e re co gn ised .

•

C onclusion T h is d is c u s s io n stro n g ly s u g g e s t s th at c lim a te

M e an w h ile th is in c rease in g re e n h o u se g a s e s h a s alre a d y h ad im p a c ts on the clim ate, an d on n atu ral e c o sy ste m s a n d h u m an societies, an d h a s co m m itted

A batem en t, or e m issio n s red u ctio n s, sh o u ld be

u s to furth er clim ate ch an g e d u e to the la g s in the

co n sisten t w ith su sta in a b le d e v e lo p m e n t an d

clim ate sy stem .

n ot in fringe the g o a ls o f an o p en an d su p p o rtiv e international econom y.

The im p ac ts o f clim ate ch an ge w ill b ecom e m ore serio u s a s g lo b al w arm in g continues over the com ing

C L IM A T E C H A N C E M A TTERS

decades, with an increasing risk of drastic changes to the climate system . W hether this is d isastrou s will depend on how rapidly greenhouse g as em issions can be reduced and at w hat level greenhouse gas concentrations can be stabilised. A s w e shall see in Ch apters 6 and 8, greenhouse g as concentrations m ay in fact need to be reduced below' som e potentially d an gerou s level reached in the next decade or tw’O if we are to avoid highly dam agin g im pacts. O ur capacity to a d ap t is lim ited and adaptation is costly, so it is im perative that hum ans reduce their em issions of greenhouse gases as soon as possible to limit the rate and m agnitude of climate change. G lobally, p ractically all countries have

19

already agreed that there is a problem and, despite differences, through the U N FCCC and other channels they are trying to work tow ards a solution. In the follow ing chapters we look in more detail at the co m p lex ities of clim ate ch an ge and its potential im pacts. We will also exam ine potential policy responses, nam ely adaptation and m itigation, in the con text o f oth er e n v iro n m en tal and developm ental problem s and the varying interests of different countries. My ow n position is that, despite som e costs, there are realistic and m utually beneficial solu tion s, which can be reached with som e effort and cooperation. O ur task is to see that this h appen s, and that it starts now'.

ENDNOTES 1. Preface to Opportunities and Risks of Climate Change (2002) Sw iss Reinsurance, p. 4, available at h ttp://w w w .sw issre.com . 2. From 'F acing the future' (2002), a report to the International Institute for Environm ent and D evelopm en t, p. 52, available at h ttp ://w w w .iie d .o rg /m m sd . 3. Full texts of the speech es at the 2007 N obel Peace Prize cerem ony aw ard ed to A1 G ore and the IPCC for w ork related to clim ate change can be found at h ttp ://w w w .n o b elp riz e.o rg. 4. Latest inform ation on recent global tem peratures is available from the World M eteorological O rganization at h t t p :/ / w w w .w m o .in t/p a g e s/m e d ia c e n tre /p re ss_ re le a se s/. See for exam ple p ress release no. 805 re 2007. See also h t t p :/ / w w w .n a s a .g o v /to p ic s/e a rth /fc a tu r e s/c a rth _ te m p _ p rt.h tm , an d h t t p :/ /w w w .n c d c .n o a a .g o v /g c a g /in d e x .jsp , w here data can be accessed and plotted. A full d iscu ssion of o bservation al evidence is in the IPCC C lim ate C hange 2007, W orking G roup I report, Su m m ary for Policym akers and C h apter 3, at h ttp ://w w w .ip cc .ch . 5. See 'L arge-scale w arm in g is not u rb an ', by D avid Parker, Nature, 432, p p . 290 (18 N ov em b er 2004). A detailed d iscu ssio n of m an y of the scep tics' argu m en ts is found in the IPCC report a s above. For corrections to satellite observation s see Fu and colleagues, Nature, 429, p p. 55-8 (2004), and Science, 304, p p. 805-6 (2004). See also h ttp :// w w w .realclim ate.com / and h ttp ://ro y a lso c ie ty .o rg /p a g e .a sp ?id = 4 7 6 1 . 6. See IPCC 2007 report, W orking G roup I, C hapter 3. 7. See h ttp ://w w w .g e o .u n iz h .c h /w g m s/. R ecession of m ountain glaciers is d iscu sse d in C h apter 4.5 of the IPCC 2007 report, WGI. M ap s of decreasin g glacier extent on M t K ilim anjaro can be found in H astenrath and G reischar,/o«nifl/ of Glaciology, 43, pp. 455-9 (1997). See also G eorge W oodwell in Ambio Special Report 13, (N ovem ber 2004), pp. 35-8. Further docum en tation of glacier and ice sh eet retreat is fou nd in p ap e rs such a s M ark an d Seltzer in Journal of Glaciology, 49, p. 271 (2003) for Peru; Shiyini and colleagues, sam e journal, p .117 (2003) for north-w est China. H e and colleagues, Journal of Geophysical Research, 108 (D17), doi:10.1029/2002JD 003365, p. 4530 (2003) for south-w est China; and C huca and colleagues in Journal of Glaciology, 49, p p. 449-55 for Spain. See also the report by M ark D yurgerov 'G lacier m a ss balance and regim e: data of m easu rem en ts and an aly sis', O ccasional P ap er no. 55 (2002), Institute of Arctic and A lpine R esearch, U niversity of C o lo rad o ; and 'The statu s of research on glaciers and glob al glacier recession: a review ', by RG Barry, Progress in Physical Geography 30, p p. 285-306 (2006).

20

C L IM A T E C H A N C E : TH E SC IEN C E, IM P A C T S A N D S O L U T IO N S

8. O ther pictures of the Trient G lacier can be found at h ttp ://w w w .d p e c k .in fo /m ts/trie n t2 .h tm and relevant data at h ttp ://co m m o n s.w ik im e d ia .o rg /w ik i/Im a g e :T rie n t_ g la cie r_ stats.sv g . 9. See for exam ple h ttp ://w w w .w o rld v ie w o fg lo b a l w a rm in g .o rg /. 10. Earlier sp rin g sn ow m elt in A lask a is reported in Stone and others, Journal of Geophysical Research, 107, no. DIO, 10.1029/2000JD 000286 (2002). M elting of p erm afro st in the high A rctic is d escrib ed in G o ld m an , Science, 297, pp. 1493-4 (2002). O ther articles on recent ch anges in the Arctic are also in this issu e of Science. See also Sturm and others in Scientific American, 289 (4) pp. 42-9 (O ctober 2003) and further reading listed there, and 'C lim ate change, p erm afrost, and im pacts on civil infrastructure', U S Arctic Research C om m ission , P erm afrost Task Force Report, (D ecem ber 2003), Special R eport 01-03. The Arctic C lim ate Im pact A ssessm en t (A CIA ) report (2004) can be found at h ttp ://w w w .a c ia .u a f.e d u /. 11. The N O A A 'R eport C ard ' (2007) is at h ttp ://w w w .a rc tic .n o a a .g o v /re p o rtc a rd /. See also: Thierry Fichefet and colleagues, EOS, 85, p. 39 (20 A pril 2004); W Meier, J Stroeve, F Fetterer, K Know les, 'Reductions in arctic sea ice cover no longer lim ited to su m m er', EO S 86, p. 326 (2005); Serreze and others, in Geophysical Research Letters, 30 (3), doi:10.1029/2002GL016406 (2002); and Stroeve and others, 'Arctic sea ice decline: faster than forecast', in Geophysical Research Letters, 34, L09501, doi:10.1029/2007GL029703 (2007). A Sea Ice Index is available at h ttp ://n s id c .o r g /d a ta / s e a ic e jn d e x /. See also Vanishing ¡ce, N A SA Earth O bservatory (M ay 2003) at h ttp ://ea rth o b serv a to ry .n asa .g o v / F eatu res/v an ish in g; h ttp ://c ire s.c o lo ra d o .e d u /ste ffe n /m e lt/in d e x .h tm l, and C om iso and Parkinson, 'Satelliteobserved changes in the Arctic', in Physics Today (A ugust 2004), pp. 38-44. Regular u pdates are available at the U S National Snow and Ice Data Center, for exam ple, h ttp ://n sid c.org/n ew s/p ress/2 0 0 7 _ seaicem in im u m /2 0 0 7 0 8 1 0 _ in d ex.h tm l. See also N A SA w ebsite at h ttp ://n a s a .g o v /c e n te r s /g o d d a r d /n e w s and h ttp ://ea rth o b serv a to ry .n asa .g o v /. 12. Problem s arisin g from the thaw ing of perm afrost in the Eu ropean A lp s are d iscu sse d in Nature, 14, p. 712 (A u gu st 2003). The problem of glacier lake ou tb ursts is dealt w ith in a sp ecial report from the U nited N atio n s Environm ent P rogram m e, an d in K attelm ann, N atural Hazards, 28, p p. 145-54 (2003), w ho recom m en ds drain in g the lakes. A n um ber of stu d ies docum en t an increase in the n um ber of d a y s o f ice-free flow in rivers, including a recent p ap er by H od gk in s, D ud ley and H untington in Climatic Change, 71, p p. 319-40 (2005). 13. Satellite data on the m elting of the P atagon ian Ice Sheet is by JL Chen and others, in Geophysical Research Letters, 34, L22501 doi:10.1029/2007G L 031871 (2007). See a lso Eric R ign ot and co llab o rato rs in Science, 302, p p . 434-7 (17 O ctober 2003), and S H arrison, and others, The Holocene 16, pp. 611-20 (2006). 14. Relevant p ap ers include: Church and White, 'A 20th century acceleration in global sea-level rise, Geophysical Research Letters, 33, do i:10.1029/2005G L 024826 (2006); Sheph erd and W ingham , 'R ecent sea-level con tribution s of the Antarctic and Greenland ice sh eets', Science, 315, p p. 1529-32 (2007); G ehrels and others, 'A 20th century acceleration of sea-level rise in N ew Z ealan d ', Geophysical Research Letters, 35, doi:10.1029/2007G L032632 (2008); and D om in gues an d others, 'Im p ro v ed estim ates of u pp er-ocean w arm in g and m u lti-dim en sion al sea-level rise', Nature, 453, p p. 1090-93 (19 Jun e 2008). See also a region al m ap of local sea-level rise, 1993-2008 from N A SA at h t t p :/ / photojournal.jpl. n a sa .g o v /c a talog/P IA 11002. 15. H an sen 's argu m en t w a s first p u t in Climatic Change, 68, pp. 269-79 (2005), and again in 'Scientific reticence and sea level rise', Environmental Research Letters, 2, doi: 1 0 .1 0 8 8 /1 7 4 8 -9 3 2 6 /2 /2 /0 2 4 0 0 2 (2007). 16. See C urry and others, Nature, 426, pp. 826-9 (2003) and Bulletin of the American Meteorological Society (M arch 2004) p p. 328-30. 17. A recent p ap er on the w ell-know n p olew ard m ovem ent of the atm osph eric circulation sy stem s is by DJ Seidel and others in Nature Geoscience, 1, p p. 21-4 (2008). See also C h apter 5. O b served ch anges in the ann u lar m ode, and their sim u lation in clim ate m o d els, are d iscu sse d in p ap e rs by H artm an n and others, Proceedings National Academy of Sciences of the US, 97, pp. 1312-417 (2000); Th om pson and W allace, Journal of Climate, 13, pp. 1000-16 (2000); Gillett and others, Nature, 422, p p. 292-4 (2003); M arshall, Journal of Climate, 16, pp. 4134-43 (2003); and O sterm eier and W allace, Journal of Climate, 16, pp. 336-41 (2003).

C L IM A T E C H A N C E M A TTER S

21

18. Jam es H ansen and colleagues, 'E arth 's energy im balance: confirm ation and im plications', Science, 308, p p. 1431-5 (2005). 19. W illiam R u d d im an , 'The anth rop ogen ic green h ou se era b eg an th o u sa n d s of y ears a g o ', Climatic Change, 61, pp. 261-93 (D ecem ber 2003). 20. A ttribution stu d ie s are com preh en sively review ed in C h ap ter 9 o f IPCC 2007 report, WGI. A nother review of attribution is 'D etecting and attributing external influences on the clim ate system : A review of recent ad v an ces', by The International A d H oc Detection and A ttribution G roup , in Journal of Climate, 18, p p. 1291-314 (2005). 21. The stu d y of M editerran ean an d A frican m on soon dry in g is by H oerlin g and co lleag u es, p ap e r p resen ted at C L 1V A R /P A G E S/IP C C D rought W orkshop, N ovem b er 16-21 (2003). The A ustralian stu dy is by N icholls, in Climatic Change, 63, p p. 323-36 (2004). 22. M odelling of the slow d o w n in the therm o-haline circulation is review ed in Stocker, International Journal of Earth Sciences, 88, pp. 365-74 (2000) and Lockw ood, International Journal of Climatology, 21, p p. 1153-79 (2001). O bservational evidence su gge stin g a p ossib le slow do w n in the therm o-haline circulation com es from D elw orth and Dixon, Journal of Climate, 13, pp. 3721-7 (2000); M atear and others, Geochemistry, Geophysics, Geosystems, 1, Paper no. 20000GC000086 (21 N ov em b er 2000); Kim and others, Geophysical Research Letters, 28, p p. 3293-6 (2001); D ickson and others, Nature, 416, p p. 832-7 (2002); G ille, Science, 295, pp. 1275-7 (2002); F u k asaw a and others, Nature, 427, pp. 825-7 (2004), and Peterson and co lleagu es in Science, 298, pp. 2171-3 (2002). The RAPID project h as a w ebsite h ttp ://w w w .so c .so to n . a c .u k /r a p id /r a p id .p h p . See also Vellinga and W ood, Climatic Change, 91, pp. 43-63 (2008). 23. O bservational eviden ce, su p p o rtin g the p ossibility that a slow do w n of the therm o-haline circulation in the oceans is alread y u nder way, includes D elw orth and D ixon, Journal of Climate, 13, p p. 3721-7 (2000); D ickson and others, Nature, 416, pp. 832-7 (2002); G ille, Science, 295, pp. 1275-7 (2002); H ansen and others, Nature, 411, pp. 927-30 (2001); Kim and co lle ag u e s, Geophysical Research Letters, 28, p p . 3293-6 (2001); M atear and co lle ag u e s, Geochemistry, Geophysics, Geosystems, 1 (11), 1050, do i:10.1029/2000G C 000086 (2000), and F u k a sa w a and others, Nature, 427, p p. 825-7 (2004). See also Baehr and others, Climatic Change, 91, p p. 11-27 (2008). 24. The RAPID project is reported briefly in Nature, 427, p. 769 (26 February 2004) and m ore fully by M Srokosz in EOS (Transactions of the A m erican G eoph ysical Society) (24 February 2004), p p. 78, 83. See also h ttp ://w w w .n o c .so to n . a c .u k /r a p id /. 25. See IPCC 2007 report, WGII1, Fig. SPM-6 and related text. 26. See h ttp ://w w w .b io ch ar-in tern ation al.org. 27. The IPCC 2007 report, W GII, h as tw o ch apters on ob serv ation s, C h apter 3 on atm osph eric and su rface clim ate change, and C h apter 4 on ob served ch anges in snow , ice and frozen groun d. Projected ecological im pacts are found in the WGII report, in ch apters by sector and region. See also the p ap er 'A ttributing physical and biological im pacts to an th ropogen ic clim ate ch an ge', Nature, 453, p p. 353-7 (15 M ay 2008). A n d see Pew Centre, Observed Impacts of Global Climate Change in the U.S. (2004); and Reale and others, Proceedings of the Royal Society of London, B270, pp. 586-91 (2003); and an A ustralian review by H u gh es, A ustral Ecology, 28, pp. 423-43 (2003). 28. See the IPCC 2007 report, W GI, C h ap ter 5.4 an d Box 7.3. Projections of future ch an ges and their im pacts are in C h apter 10.4. See also W GII, C hapter 4 for m ore on im pacts. 29. For effects of heat stress on the carbon balan ce see A A ngert and others in Proceedings National Academy of Sciences (U S), 102, p p. 10 823-7 (2005). For effects of the 2003 su m m er in E u rope see P C ia is and others, Nature, 437, p p. 529-33 (2005). 30. The A ustralian crop yield stu d y is N icholls, Nature, 387, p p. 484-5 (1997). The U S stu d y is Lobell and A sner, Science, 299, p. 1032 (2003), with a com m ent in the sam e issu e, p. 997. A critical view is presen ted by G o dden and others, Nature, 391, pp. 447-8 (1998).

22

C L IM A T E C H A N C E : TH E SC IEN C E, IM P A C T S A N D S O L U T IO N S

31. The frequency of closures of the T h am es Barrier w a s u sed a s an indicator of clim ate ch ange in Science, 303, p. 176 (2004). For ch an ges in the operatin g rules for closure see Review of UK Climate Change Indicators (June 2003, revised Jan u ary 2004) at h ttp ://w w w .n b u .a c .u k /ic c u k /. 32. See ECM W F Newsletter, no. 99 (A u tu m n /w in te r 2003) p p. 2-8. See a lso Weatherwise (M a rc h /A p ril 2004), pp. 24, 27. 33. See Beniston and D iaz in Global and Planetary Change, 44, p p. 73-81 (2004); M eehl and Tebaldi in Science, 305, pp. 994-7 (2004), and Stott and others in Nature, 432, pp. 610-13 (2004). See also IPCC 2007 WGII report, cross-chapter case study, availab le at h ttp ://w w w .ip c c .c h . 34. C hangn on and C h angn on , Natural Hazards, 18, p p. 287-300 (1999); Pielke and L an d sea, Weather and Forecasting, 13, pp. 351-61 (1998); C hangn on and others, Bulletin American Meteorological Society, 81, p p. 437-42 (2000); and Vellinger and M ills, in M cCarthy and others, C h apter 8. The d e cad al av erage data in Table 1 is from World Disasters Report 2004. U p d ate d data, alth ough not strictly com parable, can be found in World Disasters Report 2007 (at h t t p ://w w w . ifrc.org) and in Natural and human-induced environmental hazards (2005) on the IC SU w ebsite at h ttp ://w w w .ic su .o r. See also the Report of the Workshop on Climate Change and Disaster Losses (2006) at h ttp ://scie n ce p o licy .c o lo ra d o .ed u / sp a re/re se a rch /p ro je cts/ex tre m e _ ev e n ts/m u n ic h _ w o rk sh o p /in d e x .h tm l, and Annual Review: Natural Catastrophes 2004 from M unich R einsurance at h ttp ://w w w .m u n ich re.c o m . 35. For a rem arkably accurate forecast of w h at w ould h ap pen if a m ajor hurrican e struck N ew O rlean s see M ark Fischetti, 'D row nin g N ew O rlean s', Scientific American (O ctober 2001) p p. 68-77. See also, 'W ashing A w ay', Special rep ort, New Orleans Times-Picayune, (23-27 Ju n e 2002) at h t t p ://w w w .n o la .c o m /h u r r ic a n e /c o n te n t.s s f? / w ash in g aw ay /in d ex .h tm l. A lso see: SB G old en berg and others, Science, 293, p p. 474-9 (20 July 2001), 'The recent increase in A tlantic hurricane activity: cau ses and im plications'; and JB Eisner and others, 'E stim ated return p eriod s for H urricane K atrin a' in Geophysical Research Letters, 33, L08704 (2006). 36. See accoun ts by N an W alker and others in EO S, 75, p. 409 (6 Sep tem b er 1994); an d the article by Lee Larson at h ttp ://w w w .n w r fc .n o a a .g o v /flo o d s/p a p e r s /o h _ 2 /g r e a t.h tm ; and Sheaffer, M ullan and Hinch in Environment, 44 (1), p p. 33-43 (2002). 37. The text of the U N F C C C can be found at h ttp ://u n fc c c .in t/2 8 6 0 .p h p . 38. Several histories exist of the clim ate ch ange n egotiation s and exp osition s of the U N F C C C and the K yoto Protocol: G rubb, Vrolijk and Brack (1999), The Kyoto Protocol: A Guide and Assessment, Royal Institute of International A ffairs and Earthscan Publications, London; and O berthur and Ott (1999), The Kyoto Protocol: International Climate Policy for the 21st Century, Springer-V erlag, Berlin. See also C hapter 11 and related en dn otes, and h t t p ://w w w .iis d .c a /.

2 Learning from the past1

Time present and time past Are both perhaps present in time future. And time future contained in time past. T S E lio t ( 1 8 8 8 - 1 9 6 5 ) , F o u r Q u a r t e t s .

We recommend that scientists from many disciplines be encouraged to undertake systematic studies of past climates, particularly of climates in epochs when the Arctic Ocean was free of ice ... R e p o r t o f t h e S t u d y o f M a n ' s I m p a c t o n C l im a t e , M a s s a c h u s e t t s In stitu te o f T e c h n o lo g y , 1 9 7 1 .

G iven all the fuss about clim ate change, it is im por­ tant that we u n derstan d the Earth's clim ate and how it w orks. We b ase this know ledge on tw o things: •

k n o w led ge of how the clim ate h as beh aved in the p ast, and

•

ou r ability to explain p a st clim ate ch anges. If w e can e x p la in the p a s t, w e can b u ild

co n cep tu al an d then d e tailed co m p u ter m o d els. T h ese w ill en able u s to m ak e p red ic tio n s ab o u t fu tu re clim ate ch an g e s, giv en the lik elih o od of futu re ch an ges in those factors w hich d riv e the clim ate sy stem . A s a ge n e ral ru le, if so m eth in g h a p p e n e d once, the sy stem is su ch that it could h a p p e n a g a in , giv en sim ila r p reco n d itio n s. But w e on ly truly u n d e rsta n d the sy stem if w e can exp lain w h at h a p p e n e d before. If w e h ave that u n d e rsta n d in g , w e h ave so m e ability to pred ict w h at m ay h ap p en from now on, especially if w e see sim ilar precon d ition s occurring.

Life h as existed on the Earth for 3.5 th ou san d m illion y ears, so p oten tially w e h ave a very long record to exam ine for clim atic behaviour, alth ough it is only since the start of the C enozoic p eriod, about 65 m illion years ago, that w e have a u sefu l clim atic record. This record p lu s theories b ase d on the law s of p h y sics, chem istry and m ath em atics can tell u s w h at so rt of things influence clim ate. Id eally this h elps u s to develop a 'm o d el' of the clim ate system , that is, how the so lid earth, w ater, atm osph ere and b iosp h ere interact w ith the en ergy from the Su n to p ro d u ce clim ate. Such a m o d el m ay be m erely a set of qu alitativ e id e as, or a set of qu an titative m athem atical representations of those id eas, which can be u sed to m ake calculations on a com puter. O nce w e h ave su ch a m o d e l o f the clim ate sy stem , detailed k n o w led ge of p ast conditions and clim atic b eh avio u r en ab les u s to test how w ell the m o d el w ork s. Such testing can be done by looking at ep iso d e s o f clim atic ch ange in the distan t p ast, or

24

CLIMATE C H A N C E: THE SCIENCE, IMPACTS A N D SO L U T IO N S

b y lo o k in g at w h a t h a s h a p p e n e d o v e r the la st

g e o lo g ic a l fo rm a tio n s su ch a s g la c ia l m o ra in e s

ce n tu ry or so , fo r w h ich w e h a v e m u ch m o re

(soil a n d ro ck s left b eh in d b y re treatin g

d e tailed o b serv atio n s.

g la c ie rs), the a n n u a l g ro w th rin g s in trees,

A cco rd in g ly , w e can u se tw o m ain ty p e s of clim atic d a ta for a n a ly sin g p a s t clim atic v a ria tio n s: •

D irect or in stru m e n ta l m e a su re m e n ts. T h ese g e n e ra lly sta rte d u p to a b o u t 200 y e a rs a g o w ith the a d v e n t o f m o d e rn in stru m e n ts su ch a s th e rm o m e te rs, rain g a u g e s a n d a n em om eters, an d w ere d isc u sse d in C h ap ter 1.

la y e rs o f se d im e n t d e p o site d on the b e d s o f la k e s or o c e a n s, or the ra d io a c tiv e iso to p e s o f v a r io u s ch em ical e le m e n ts d e p o site d in ice c o res, tree rin g s or se d im e n ts. P rox y d a ta is v ita lly im p o rta n t to o u r u n d e rsta n d in g o f p a s t clim atic v a ria tio n s an d c h a n g e s, so it m e rits fu rth er e x p la n a tio n .

T h ey p ro v id e a fairly a cc u ra te reco rd , b u t the record is too sh o rt to sa m p le the w h o le ra n g e o f clim ate c h a n g e s th at h a v e o ccu rred b efo re a n d m a y o ccu r a g a in . •

Proxy data: clues from the past D ra m a tic ev id e n ce o f p a s t clim a te s c o m e s from la n d sc a p e fea tu res su ch a s U -sh a p ed v a lle y s (see

'P ro x y ' or in d irect d a ta . Su ch d a ta can p ro v id e

F ig u re 6) and large and sm all lak es d a m m e d behind

a m u ch lo n g e r tim e p e rsp e c tiv e , a n d are

g la cia l m o ra in es. T h ese are ev id en ce that g la c ie rs

o b ta in e d from n atu ra l or h u m a n a rch iv e s that

a n d ice c a p s once co v ered far m o re o f the E a rth 's

in so m e w a y record p a s t clim ate v a ria tio n s.

su rfa c e than today. Th e G re a t L a k e s in N o rth

P roxy d a ta in c lu d e s w ritten re c o rd s of

A m erica are a strik in g e x a m p le: they w ere fo rm ed

h a rv e sts, or p ro p e rtie s o f a rte fa c ts or

at the so u th e rn e d g e o f h u g e ice c a p s c o v erin g

s u b sta n c e s th at h a v e been in flu en ced by

C a n a d a an d the northern p a r ts o f w h at is n ow the

clim ate in the p a st. N o ta b le e x a m p le s are

U n ited S ta te s. W hen w e m a p su ch fe a tu re s a n d

Figure 6: The glacial valley above Lautenbrunnen, Switzerland, in 1999. This characteristically U-shaped valley was carved out by a large glacier during the last glacial period some 20000 years ago. The glacier, visible in the distance, has now receded many kilometres up the valley in response to a global average warming of only some 4 or 5°C in the last 20000 to 10000 years. The glacier is retreating further now due to warming in the twentieth century. This is dramatic evidence of past natural climatic change and of the potential impacts of future climate changes that may be due to human influence. (Photograph by AB Pittock.)

L E A R N IN G F R O M THE PAST

25

m a k e in fe re n ce s a b o u t clim a te from th em , w e are

b o tto m frictio n , e la stic ity o f the ice, a n d so on . T h is

u s in g 'p r o x y ' e v id e n c e or d a ta to m a k e sc ie n tific

can a ll b e p u t in a m a th e m a tic a l m o d e l a n d the

d e d u c tio n s a b o u t p a s t o r p a le o -c lim a te s ('p a le o - '

c h a n g e s w ith tim e c a lc u la te d on a co m p u ter.

m e a n s old or an cien t).

P roxy

T h ere a re m a n y ty p e s o f p r o x y d a t a u s e d b y

d a ta

in s t r u m e n t a l

m u st

d a ta

fo r

be

c a lib r a te d

a g a in st

a

m e a n in g f u l

c lim a t e

c lim a to lo g ists (T a b le 2), a n d th ey are o ften u se d in

in terpretation to b e m a d e , a n d they va ry in u se fu ln e ss

c o m b in a tio n to b u ild u p a re lia b le p ic tu re o f the

a cc o rd in g to h o w clo sely re late d they are to clim ate,

p a s t .2 E a c h h a s its m e r its a n d lim ita tio n s . T h e

a n d h o w w e ll the d a t e s c a n b e d e te rm in e d . Th e

in t e r p r e t a t io n s

on

d a tin g a n d tim e re so lu tio n (the a b ility to s e p a r a te

so m e tim e s c o m p le x m o d e ls o r u n d e r s ta n d in g s o f

a d ja c e n t tim e in te r v a ls) is e s p e c ia lly im p o r ta n t

w h at

m ade

fro m

th e m

depend

under

w h ere a tte m p ts are m a d e to lo o k a t sp a tia l p a tte r n s

w h a t c o n d itio n s. F o r e x a m p le , g la c ie r s re su lt fro m

o f c h a n g e , or to se e w h e th e r o n e e v e n t p re c e d e d

sn o w th a t h a s a c c u m u la te d in h ig h e r e le v a tio n s

an o th er, a s m a y b e n e c e ssa r y to h e lp e sta b lish c a u se

c o m p a c t in g

a n d effect.

ca u se d

th e

in to

p ro xy

ice

and

d a ta

and

g ra d u a lly

f lo w in g

D a tin g o f g la c ie rs can b e d o n e fro m fra g m e n ts o f

d o w n w a r d s a lo n g v a lle y s , u n til it re a c h e s lo w e r e v a p o rate s.

p la n t m a te r ia l in the te rm in a l m o r a in e s , or fo u n d

R e la tio n sh ip s b e tw e e n the le n g th o f a g la c ie r a n d

u n d e r w h e re the g la c ie r w a s a fte r it h a s re c e d e d

the te m p e ra tu re a n d sn o w fa ll ca n b e d e d u c e d fro m

a g a in . S u ch d a te s can c o m e fro m ra d io a c tiv e ca rb o n

o b s e r v a t io n s , o r fro m first p r in c ip le s fro m

c o n c e n tr a tio n s, sin ce sh o rt-liv e d is o t o p e s su c h a s

e le v a tio n s

w h ere

it

m e lts

m a t h e m a t ic a l r e la t io n s h ip s

or

b e tw e e n

the

s n o w fa ll,

14C (fo r m e d in th e a t m o s p h e r e b y c o sm ic r a y s

d e p th o f ice or sn o w , v o lu m e , e v a p o r a tio n , m e ltin g ,

str ik in g a ir m o le c u le s) g r a d u a lly d is a p p e a r a fte r

TABLE 2: Proxy indicators of climate-related variables2 Ind ica tor

Property m easured

Tim e resolution

Tim e span

Clim ate-related inform ation obtained

Tree rings

W idth, density, isotopic ratios, trace elements

A nn ua l

Centuries to m illennia

Temperature, rainfall, fire

Lake and b o g sedim ents

D ep osition rates, species assem blages from shells and pollen, m acrofossils, charcoal

Annual

M ille n n ia

Rainfall, atm ospheric water balance, vegetation type, fire

Coral grow th rings

Density, isotope ratios, fluorescence

Annual

Centuries

Temperature, salinity, river outflows

Ice cores

Isotopes, fractional melting, annual layer thickness, dust grain size, gas bubbles

A nn ua l

M ille n n ia

Temperature, sno w a ccum ulation rate, w indiness, gas concentrations

O c e a n sedim ent cores

Species assem blages from shells and pollens, deposition rates, isotopic ratios, air-borne dust, pollen

U su a lly m ulti-decadal or centuries

M ille n n ia

Sea temperatures, salinity, acidity, ice volum es and sea level, river outflows, aridity, land vegetation

Boreholes

Temperature profile

D eca d e s

Centuries

Surface air temperature

O ld groundw ater

Isotopes, n ob le gases

Centuries

M ille n n ia

Temperature

G lacial m oraines

M a x im u m glacier length

D eca de s

Centuries to m illennia

Temperature and precipitation

Sand dunes

Orientation, grain size

Centuries

M ille n n ia

W in d direction and speed, aridity

Coastal landform s

Ledges, form er beach lines, debris lines

D eca d e s to centuries

D eca d e s to m illennia

Former sea-level, tropical cyclones

D ocu m e n tary evidence

Reports o f extremes, harvests, dates of break-up of river or lake ice

A nn ua l

Centuries to m illennia

Temperature, precipitation

CLIMATE C H A N C E: THE SCIENCE, IMPACTS A N D SO L U T IO N S

26

the p lan t m aterial d ies. D a tes from ra d io c a rb o n are

or 'g la c ia l p e r io d s', w h en h u g e ice sh e e ts co v ered

u se fu l for m aterial u p to a b o u t 50 000 y e a rs old , b u t

la rg e a r e a s th at are n o w ice-free, to p e r io d s like

on ly acc u ra te to w ithin a few p er cent o f the a g e

n ow

from the p resen t. D atin g for m u ch o ld e r m aterial

A n ta rctica , G re e n la n d a n d the flo a tin g A rctic se a

w h en ice sh e e ts are la rg e ly c o n fin e d

to

c o m es from other iso to p e s w ith lo n g er d e ca y tim es.

ice. R e c o rd s in d ic ate th at clim ate c h a n g e s occu rred

A n e x a m p le is U ran iu m iso to p e 238, w h ich d e c a y s

o v er the la st tw o m illio n y e a rs in a rath er re g u la r

to U ra n iu m 234, a n d w h ich in turn d e c a y s to

cyclic m an n er, w ith g la c ia l p e r io d s la stin g ro u g h ly

T h oriu m 230. R atio s o f 230Th to ^ U can be u se d for

10 0 0 0 0 y e a r s , a n d w a rm e r in te r g la c ia l p e r io d s

d a tin g back m illion s o f y ears. Tim e resolu tion w ith

o c c u r rin g in b e tw e e n . T h e la tte r la ste d m u ch

th ese m e th o d s is co arse.

sh o rte r tim e in te r v a ls o f a ro u n d 10 000 y e a r s

E stim ate s o f sp a tia l p atte rn s o f d e c a d a l, a n n u al

(see F ig u r e 7). T h e se clim a tic flu c tu a tio n s w e re

o r se a so n a l clim ate v a ria tio n s in p a s t ce n tu rie s,

a c c o m p a n ie d b y la rg e v a ria tio n s in g lo b a l a v e ra g e

h o w ev er, m u st rely on p ro x y ev id en ce h a v in g finer

se a level, o f u p to a b o u t 120 m e tre s, a n d re su lte d

tim e reso lu tio n . T h at is, it n e e d s to re so lv e an n u al

in d r a m a tic c h a n g e s in v e g e ta tio n co ver, la k e s,

o r se a so n a l v a ria tio n s. T h is e v id en ce in c lu d e s the

riv e rs a n d w e tla n d s, a n d the d istrib u tio n o f p la n ts

w idth or d e n sity o f a n n u al gro w th rin g s in trees;

an d a n im a ls.

la y e r th ick n e ss a n d p article siz e in a n n u a l la y e rs

H u g e a re a s o f the co n tin en tal sh e lv e s w ere

in se d im e n t c o re s fro m the b o tto m o f la k e s or

ex p o sed d u rin g the glacial p erio d s, joining A la sk a to

o c e a n s; the iso to p ic c o m p o sitio n , c h e m istry an d

Siberia, the A u stralian m ain lan d to N ew G u in ea and

th ick n e ss o f a n n u a l la y e rs in ice co res; iso to p e s

T asm an ia, Britain and Ireland to W estern Europe, and

from co ral gro w th la y ers; an d sc a tte red h istorical

m any South-East A sian islan d s to the A sian m ainland.

in form ation from h u m an d o cu m en ta tio n o f th in gs

A t the en d of the la st glaciation so m e 18000 y ears

like crop y ie ld s, flo o d s, fro sts an d the b re ak -u p o f

ag o , the ice sh eets m elted ov er C a n a d a , northern

frozen rivers.

E u ro p e a n d elsew h ere , a n d the G reen la n d an d

A n n u al gro w th rin g s in trees are a g o o d exam p le.

A ntarctic ice sh eets contracted. T h is a gain flood ed

T h ese can often be co u n ted b ack from the p resen t

the ab o v e a re as o f the continental sh elv e s, takin g

u s in g

th o u san d s o f y ears to d o so.

s a m p le s

fro m

m any

d iffe re n t tre e s o f

o v e rla p p in g ag e. In so m e c a se s, for e x a m p le , w ith

S m a lle r c h a n g e s in re la tiv e se a le v e ls are still

O ak in W estern E u ro p e, K au ri in N ew Z e a la n d , and

o c cu rrin g re g io n a lly d u e to the co n tin e n tal p la te s

B ristlecon e Pine in the w e stern U n ited S ta te s, this

slo w ly r e b o u n d in g a n d fle x in g . T h is h a p p e n s

record can be taken b ack th o u sa n d s o f y ears. S im ilar

b e c a u s e o f the re m o v a l o f the w e ig h t o f the ice

d a tin g is p o ssib le from a n n u al lay ers o f silt in lak es,

sh e e ts fro m the c o n tin e n ta l in te r io rs a n d the

alth o u gh in lo n ger tim e se rie s from the floor o f the

in c re a se d w e ig h t o f se a w a ter a lo n g the co n tin en tal

ocean w h ere se d im e n t la y ers m ay be d istu rb e d by

m a rg in s. T h u s m u ch o f S c a n d in a v ia is still risin g

b u rro w in g creatures, rad io ac tiv e d a tin g is necessary.

re la tiv e to the se a , w h ile p a r ts o f the e a st c o a st of

S ed im en t record s m ay go b ack m an y th o u sa n d s or

the U n ite d S ta te s are g r a d u a lly s u b s id in g . S ea-

m illio n s o f y e a rs u sin g m u ch lon ger-liv ed iso to p e s

level c h a n g e s are th u s n ot u n ifo rm , a n d e stim a te s

than 14C.

o f a c tu a l g lo b a l a v e r a g e se a -le v e l rise m u st co m e from c o m b in in g m e a su re m e n ts from m a n y p a r ts o f the w o rld .

The record of the ice ages

L ife su r v iv e d , an d in d e e d flo u r ish e d , d e sp ite

By st u d y in g m a n y d iffe re n t p ro x y d a ta re c o rd s

th e se h u g e c lim a tic a lly fo rc ed v a r ia tio n s in the

from p la c e s a ro u n d the g lo b e sc ie n tists h a v e fo u n d

e n v iro n m e n t, b u t m a n y in d iv id u a l s p e c ie s o f

e v id e n ce o f g lo b a l-sc a le clim ate c h a n g e s. C lim a te

p la n ts a n d a n im a ls b e c a m e extin ct, a n d o th e rs h a d

h a s v a rie d from tim es k n o w n lo o se ly a s 'ice a g e s '

to m ig r a te la rg e d is ta n c e s to m o re c o n g e n ia l

L E A R N IN G F R O M THE PAST

27

S ' 100 -

15 400

300

200

100

0

T h o u sa n d s of years before present (Ky BP) Figure 7: Climate variations over the last 400 thousand years. The top graph shows percentage variations in tree pollen amount, excluding pine tree species. High percentages correspond to warm climates. The lower three curves show estimated sea surface temperatures in the North Atlantic, equatorial Indian Ocean and the South Atlantic, based on deep-sea cores. Variations between glacial and interglacial periods were large in high latitude regions, but much less in low latitudes. Variability was much greater in the North Atlantic region. (Graphs are from Figure 2.23 in the IPCC 2001 WGI report.)

re g io n s . T h e la tte r in c lu d e d o u r h u m a n a n c e s to r s,

rig id n a tio n a l b o u n d a r ie s , th an a t th e en d o f the

w h o s k ir t e d a r o u n d ice s h e e ts to m ig r a t e fro m

la s t ice a g e w h e n th e E a r th w a s o n ly s p a r s e l y

A sia to N o r th A m e r ic a , a n d c r o ss e d s m a ll str a its to

p o p u la t e d b y h u m a n s .3

m ig r a te fro m S o u th - E a st A sia to A u s tr a lia . R is in g s e a le v e ls b e tw e e n 20 00 0 a n d 10 000 y e a r s a g o fo rc ed p e o p le to m o v e fro m la n d th at is n o w u n d e r

The causes of past climate change

th e B la c k S e a , a n d m a n y to m o v e in la n d from

T h ere are m a n y co n trib u to ry c a u s e s o f p a s t clim a te

c o a s t a l p la i n s in N o r th A m e r ic a , E u r o p e a n d

c h a n g e , in c lu d in g c o n tin e n ta l d rift, v a r ia tio n s in

A u s tr a la s ia . S u c h m a s s m ig r a t io n s w o u ld b e m u ch

the E a r th 's o rb it a ro u n d the S u n , c h a n g e s in so la r

m o re d iffic u lt n o w , w ith six b illio n p e o p le a n d

o u tp u t, v o lc a n ic e m is s io n s , c o sm ic c o llisio n s a n d

28

CLIMATE C H A N C E: THE SCIENCE, IMPACTS A N D SO L U T IO N S

p artic u la te m atter in the a tm o sp h e re , co m m o n ly

But the lon g a x is (A -P in F igu re 8) o f the elliptical

referred to a s 'a e ro so ls'. N a tu ra l g re en h o u se g a se s,

o rb it a lso re v o lv e s slo w ly a ro u n d the S u n . It

w hich a b so rb h eat rad ia tio n , a lso p la y e d a p art.

c o m p le te s on e revolu tion after an irre g u la r interval that a v e ra g e s 96600 y e a rs a n d so the tim e o f y ea r at w h ich the E arth is clo sest to the Su n ch a n g e s v ery

Variations in the Earth's orbit4

g r a d u a lly

Th e re m ark a b le h isto ry o f m o re or le ss re g u la r

m atters, the eccentricity o f the orbit (the d e g re e to

flu ctu atio n s in the E a rth 's clim ate, a s ev id en ce d by

w h ich it d e p a r ts from b ein g circular) v a rie s a s the

the sea-level an d tem p e ratu re re co rd s o v er the last

o rb it re v o lv e s in sp a c e , w ith the sa m e p e rio d of

tw o m illio n y e a rs, s u g g e s t s a stro n g p e rio d ic

a b o u t 96000 y ears.

w ith th at tim e sc a le . To c o m p lic a te

influen ce on the clim ate. The se ries o f p erio d icities,

A lso , the E a rth 's a x is o f ro tation is n o t u p rig h t

o r re g u la r v a ria tio n s, a sso c ia te d w ith the E a rth 's

('n o rm a l') w ith re sp e c t to the p la n e o f its o rb it

orbit a ro u n d the Su n is the o b v io u s ca n d id a te for

(called the 'e clip tic '). T h is sp in a x is w o b b le s like

this, sin ce the p e rio d s in v o lv e d are sim ilar. T h ese

that o f a sp in n in g top , so that it m a rk s o u t a cone in

o rbital ch a racteristics are sh o w n sch e m a tica lly in

sp a c e c o m p le tin g on e re v o lu tio n in a b o u t 2 6 0 0 0

F ig u re 8.

y e a rs, a p h en o m e n o n k n ow n a s the p re c e ssio n of

D u rin g the co u rse o f a year, the E arth m o v e s in

the e q u in o x e s. B e c a u se the p re c e ssio n is in the

a slig h tly e llip tical o rbit a ro u n d the S u n , w h ich is

o p p o site direction to the rotation o f the E arth in its

at p resen t at a d istan ce o f a b o u t 147.1 m illion km at

o rbit, the p erih elio n recu rs at the sa m e tim e o f the

its p o in t o f c lo se st a p p ro a c h ('p e rih e lio n ', P), an d

y e a r after a p e rio d o f le ss than 26 0 0 0 y e a rs, a b o u t

152.1 m illion km at its fu rth est d istan ce ('a p h e lio n ',

2 0 6 0 0 y ears. The tilt o f the E a rth 's a x is o f rotation,

A ). T h is c a u se s the so la r ra d ia tio n re a ch in g the

an d the E a rth 's a n n u a l jo u rn e y a ro u n d the S u n ,

Earth to v a ry b y a b o u t 3.5% a b o v e or b elo w the

m e a n s that first the n orth ern h e m isp h ere, an d six

a v e ra g e 'so la r co n stan t' d u rin g each year. A t p resen t

m o n th s later the so u th e rn h e m isp h ere, is m o re full-

the stro n g e st ra d ia tio n reach es the earth in Jan u ary , d u rin g the so u th ern h e m isp h ere su m m er.

c a u sin g the p ro g re ssio n of the se a so n s.

on to the S u n a n d re c e iv e s m o re so la r en ergy ,

N orm al to plane of the ecliptic ^ Equinox

Solstice

N' ^

\ / " Y ”\

Equinox

^

E a rth 's , axis of rotation _

\ ^art^

Figure 8: Geometry of the Sun-Earth system. This figure illustrates the origin of changes in solar radiation reaching the Earth at particular latitudes and seasons associated with variations in the Earth's orbit around the Sun. (P = perihelion, A = aphelion.)

LEARNIN G FR O M THE PAST

Finally, the tilt o f the E a rth 's a x is o f rotation from

29

con tain ed in the p eriod icity d u e to eccentricity, w ith

the n o rm al to the ecliptic (k n ow n a s the o b liq u ity of

so m e 25% d u e to the o b liqu ity cycle (ab ou t 40000

the e c lip tic ) its e lf v a r ie s , u n d e r g o in g a slo w

y ears) an d 10% d u e to p recessio n .

o sc illa tio n , w ith a p e rio d o f a b o u t 4 0 0 0 0 y e a rs, betw een 2 4 °3 6 ' a n d 2 1 °5 9 '. A t p re se n t the a n g le is 2 3 °2 7' a n d d e c re a sin g . T h is is w h y the T rop ics of

Role of greenhouse gases in am plifying

C an ce r an d C ap rico rn (w here the Su n is o v erh ead

climate changes

in m id - su m m e r) are at a b o u t 2 3 °2 7' n orth a n d

C o m p u te r m o d e ls o f clim ate can n ow b e u se d to

so u th , respectively.

c a lc u la te q u a n tita tiv e ly the effe cts o f the v a rio u s

H ow d o these astro n om ical p erio d icities help to

d r iv e rs o f clim atic ch a n g e . U se o f clim ate m o d e ls

exp lain the glacial-in terglacial record? That qu estion

sh o w s th at v a ria tio n s in so la r en erg y at the E arth

o c c u rre d

to the S e rb ia n c lim a to lo g ist M ilu tin

a ss o c ia te d w ith the a stro n o m ic a l cy cle s ca n n o t b y

M ilan k ovitch in the 1930s. M ilan k ovitch th eorised

th e m se lv e s e x p la in the re la tiv e stre n g th o f the

that v a ria tio n s in so la r en ergy received o v er the

ob serv ed

n orthern co n tin en ts at a b o u t 6 5 °N d u e to these

A c c o rd in g to th ese m o d e ls the effe cts o f the o rb ital

p e r io d ic itie s in the c lim a tic re co rd .

o rb ital v a ria tio n s , p a r tic u la rly in the n orth ern

e c ce n tricity cy cle m u st h a v e been a m p lifie d or

su m m er, w o u ld h av e driven the grow th and decay

e n h a n c e d b y so m e o th e r factor. T h a t a d d itio n a l

of the continental ice sheets. H e a rg u ed that a sp a n of

fa cto r h a s n ow b een id e n tified a s v a ria tio n s in the

cool su m m ers, ca u se d b y relatively large E arth -Su n

g r e e n h o u se g a s c o n c e n tr a tio n s p re se n t in the

distan ces, w o u ld resu lt in w inter sn ow accu m u latin g

a tm o sp h e re . M o st n o tab le are the co n ce n tratio n s

from y ear to y ea r a s it failed to co m p letely m elt,

o f carb o n d io x id e a n d m e th an e , b oth o f w h ich are

w h ereas w arm su m m e rs w o u ld ca u se w in ter sn ow

sto red in larg e q u a n titie s in p e a t, tu n d ra a n d ocean

to m elt and glaciers and ice sh eets to recede. In 1938

se d im e n ts d u rin g co ld e r clim a te s, an d are re le ase d

M ilankovitch p u b lish ed tables of how so lar radiation

in to the a tm o s p h e r e in w a rm e r c lim a te s. A n y

v a rie d w ith tim e at k ey la titu d e s, n o tab ly 6 5 °N .

w a rm in g d u e to o rb ita l c h a n g e s re su lts in m o re

T hese tables h av e been recalcu lated m ore accurately

carb o n d io x id e a n d m e th a n e b e in g re le a se d into

since, an d the origin al theory se e m s to hold true.

the a tm o sp h e re , le a d in g to g re a te r w a rm in g .

O n the m u ch lo n g e r tim e sc a le s (h u n d re d s of

T h is ex p lan atio n is su p p o r te d b y p aleo -ev id en ce

m illio n s o f y e a rs) a ss o c ia te d w ith la rg e tectonic

for v a ry in g co n ce n tratio n s o f th ese g a s e s in the

c h a n g e s like co n tin en tal d rift a n d u p lift, c h a n g e s

atm o sp h ere , n otab ly from m e a su re d con cen tration s

in the d istrib u tio n o f lan d an d se a a n d in elevation

in g a s b u b b le s sto re d in ice co res from A n tarctica

of the continents p lay a large p art in clim ate, an d vary

a n d G re e n la n d (see F ig u r e 9). R ecen t w o rk by

the effect of the astro n om ical cycles. M ilan k ovitch 's

W illiam R u d d im a n at the U n iv e rsity o f V irgin ia

focu s on 65°N w a s reaso n ab le b ecau se d u rin g the

co n firm s the M ilan k o v itch th eory a n d the cru cial

P leisto cen e a n d H o lo cen e ep o c h s (the la st tw o

role o f am p lification by m eth an e a n d carbon d io x id e

m illion y ears) large continental are as w h ere sn ow

v a ria tio n s.5

could accu m u late existed at these latitudes.

C o m p a r in g

m o d e lle d

ch anges

over

th e

With the a d v en t o f m ore p ow e rfu l c o m p u ters and

a stro n o m ic a l c y c le s w ith o b s e r v e d p a le o -c lim a tic

m ath e m atical tech n iq u es, the a sso cia tio n b etw een

ch a n g e s e n a b les an in d e p e n d e n t e stim ate to be

the astro n o m ical cycles an d the clim atic record h as

m a d e o f the sen sitivity o f the clim ate to ch an ge s

been refined. H a y s and others in 1976 d em on strated

in green h ou se g a s concentration s. T h is su g g e sts a

excellent tim e co rre sp o n d en ce betw een the cycle of

clim ate sen sitivity (glo b al w arm in g for a stab ilised

the eccentricity of the orbit at ab o u t 96000 y ears an d

d o u b lin g o f carb o n d io x id e co n ce n tratio n s) in

the m ain o b se rv e d g la cia l-in terg la cia l cycle. A b o u t

the u p p e r p a r t o f the ra n g e a d o p te d b y the

h a lf the total v ariatio n in the clim atic record is

Intergovernm ental Panel on C lim ate C h an ge (IPCC)

30

CLIMATE C H A N C E: THE SCIENCE, IMPACTS A N D SO L U T IO N S

Ice core drilled from Antarctica. This core from Law Dome in East Antarctica is shallow and only about 50 years old. Ice layers formed from refrozen melt water during summer months alternate with winter snow layers. Water isotopes are measured and used as proxies of temperature. Incorporated impurities from marine emissions, volcanic eruptions, atmospheric chemistry and so on provide information on conditions in the past. When the ice becomes deeper and denser, the air inclusions are sealed off and represent samples of the past atmosphere from which past concentrations of carbon dioxide and methane can be measured. (Photo courtesy of David Etheridge, CSIRO Atmospheric Research.) Figure 9:

in its 2007 report, w hich rem ain s 1.5 to 4 .5°C (with so m e qualifications).6

30 y e a rs a g o ). It is on ly in recen t d e c a d e s th at acc u ra te m e a su re m e n ts o f so la r v a ria tio n s h a v e

T h e re su lts re latin g to the M ilan k o v itch cy cles

b een m a d e . T h ese h a v e been u se d to e x trap o la te

p ro v id e stro n g su p p o r t for the role o f g re en h o u se

estim a te s o f v a ria tio n s in so la r ra d ia tio n b ack in

g a s e s in c h a n g in g p a s t clim ate, an d confirm that

tim e u sin g c o rre la tio n s w ith su n s p o t n u m b e rs,

a n y c h a n g e s to g re e n h o u se g a s co n ce n tratio n s in

w hich h a v e been o b se rv e d sin ce the 1700s.7

this cen tu ry are very likely to affect futu re clim ate.

The IP C C in its Fourth Assessm ent Report in 2007

H ow ever, so m e sceptics have claim ed that because

d is c u s se s recent e stim a te s o f the in crease in so la r

in p arts of so m e paleo-clim atic records tem perature

ra d ia tio n sin ce the 'M a u n d e r M in im u m ' in the

v a ria tio n s p re c e d e c h a n g e s in g re e n h o u se g a s

sixteen th centu ry o f a b o u t 1 Watt p er sq u a re m etre,

co n cen tration s, this m e a n s that g re en h o u se g a se s

or a p p ro x im a te ly 0.1% o f the total irra d ia n c e (or

m erely re sp o n d to clim ate ch an ge. In fact, orbital

so la r c o n sta n t). V a rio u s s u g g e s t io n s h a v e been

v aria tio n s initiated so m e p a st g lo b al w a rm in g an d

m a d e a s to h o w su ch a sm a ll c h a n g e m a y b e

this led to the release o f m o re g re en h o u se g a se s,

a m p lifie d in the atm o sp h ere , for ex a m p le b y effects

w hich ca u se d m ore g lo b al w arm in g.

on o zo n e or c lo u d s. Th e effect on o zo n e h a s been m o d elled , an d is taken into accoun t, w h ile the other m e ch a n ism s rem ain h igh ly sp e c u la tiv e .8

Variations in solar output

C lim a te m o d e ls h a v e b een ru n w ith v a r io u s

The b a sic so u rce o f all e n ergy for d riv in g the clim ate

ty p e s o f fo rcin g in c lu d in g ch a n g e s in g re e n h o u se

sy stem on Earth is rad iatio n from the Su n . T h u s any

g a s e s , v o lc an ic p a r tic le s, o z o n e , so la r v a ria tio n s

v a ria tio n s in so la r o u tp u t w o u ld d riv e c h a n g e s in

an d the effects o f air p o llu tio n p article s. W hen u se d

the clim ate. There is a lon g h istory o f claim s to h ave

to sim u la te the o b se rv e d te m p e ra tu re v a ria tio n s

d e te cte d effe cts o f so la r v a ria tio n s on su rfa c e

o v er the tw entieth century, the clim ate m o d e ls tend

w eath er an d clim ate, b u t m an y o f these claim s have

to g iv e a b etter rep ro d u ctio n o f the o b se rv a tio n s if

b een b a se d on p o o r sta tistic s (a s I d e m o n stra te d

they d o in c lu d e so la r v a ria tio n s. T h is is e sp e cia lly

in critical re v ie w s o f the scientific literatu re so m e

so for the first h a lf o f the tw en tieth century, w h en

LEARNIN G FR O M THE PAST

31

so la r ra d ia tio n w a s in c re a sin g a n d in c re a se s in

stra to sp h e re , w h ich is free from w a ter c lo u d s an d

g re e n h o u se g a s e s w ere re lativ ely sm all. H ow ever,

p re c ip ita tio n , the d u s t a n d g a s e s can re m ain for

so la r ra d ia tio n d id n ot in c rease m u ch d u rin g the

lo n g er p e rio d s. The h e a v ie r large p article s still fall

se c o n d h alf o f the tw en tieth cen tu ry , b u t b oth

o u t d u e to g ra v ity , b u t fin er p a r tic le s, m o stly

tem p e ratu re an d g re e n h o u se g a se s d id .

fo rm e d in the a tm o sp h e re b y ch em ical re a ctio n s

A ll re c o n stru c tio n s o f so la r ra d ia tio n c h a n g e s o v e r the tw en tieth cen tu ry d u e to so la r v a ria b ility

b e tw e e n g a s e s , m a y sta y in the stra to sp h e re fo r m a n y y ears.

in d ic a te th at it w a s o n ly a b o u t 20 to 25% o f the

Th e m o st lo n g -la stin g effects co m e from sm a ll

total ch a n g e in ra d ia tio n at the E a rth 's su rfa ce . The

su lfate p article s that form in the stra to sp h ere d u e to

b u lk o f the c h a n g e s in r a d ia tio n w e re d u e to

re a ctio n s b etw een the su lfu r o u s g a s e s a n d ozon e.

in c re a se d g r e e n h o u se g a s e s . C h a n g e s in s o la r

T h ese g e n e rally rem ain in the stra to sp h ere until the

ra d ia tio n can n o t e x p la in the r a p id g lo b a l w a rm in g

lo w e r str a to s p h e r ic a ir is e x c h a n g e d w ith the

in the 1980s a n d 19 9 0 s, a n d fu tu re w a r m in g is

tro p o sp h e re , w h en they can b e w a sh e d ou t. T h is

lik ely to b e in c re a sin g ly d o m in a te d b y in c re a se s in

can take se v e ra l y e a rs for the la rg e r o n es, an d the

g re e n h o u se g a s e s , u n le s s su b sta n tia l g re e n h o u se

fin est p article s can rem ain in the m id d le an d u p p e r

g a s e m issio n re d u c tio n s are a c h ie v e d in the n ext

stra to sp h e re for d e ca d e s. O b se rv a tio n s s u g g e s t th at fo r the few y e a rs

few d e c a d e s.

fo llo w in g a m a jo r e x p lo siv e v o lc a n ic e ru p tio n re gio n al effects on clim ate occur, w ith w a rm in g in Volcanoes, cosm ic collisions and aerosols

the stra to sp h e re a n d co o lin g at the su rfa c e , d u e to

A fter M t T am b ora in In d o n e sia e x p lo d e d in 1815,

the p article s a b so rb in g so m e su n lig h t a n d reflecting

the northern h e m isp h ere exp erien ced w h at b ecam e

m o re b ack into sp a c e . R e gio n al su rfa c e co o lin g of

k n ow n a s the 'y e a r w ith ou t a su m m e r ' in 1816. T h is

a b o u t 1°C h a s been o b se rv e d , a lo n g w ith w a rm in g

in sp ire d L o rd B yron to w rite h is p o e m D arkness,

in the stra to sp h e re b y a few d e g re e s. B oth th ese

w h ich in clu d ed the lines:

e ffe c ts a re w e ll r e p ro d u c e d b y recen t c lim a te

I had a dream, which was not all a dream. The bright sun was extinguish'd, and the stars Did wander darkling in the eternal space, Rayless, and pathless, and the icy earth Swung blind and blackening in the moonless air ... W hile B y ro n 's p o e m ra th e r e x a g g e r a te d the situ a tio n , there w ere m a n y cro p fa ilu re s in the

m o d e ls. E ffects are g re a tly re d u c e d b y the se co n d y ea r after su ch eru p tio n s, an d are q u ite m in or after se v e ra l y ears. So u n le ss there are a se rie s o f m ajo r e r u p tio n s in q u ick su c c e ssio n , n o m a jo r clim atic effe cts are to b e e x p e c te d . P ro je ctio n s o f fu tu re clim ate ch a n g e s u su ally h a v e an im plicit reservatio n th at v o lcan ic eru p tio n s m a y p ro v id e a tem p o ra ry in terru p tio n to an y w a rm in g trend. C ollisions of Earth with a m ajor m eteor or asteroid

su m m e r o f 1816. A recent m ajo r e x p lo siv e v o lcan ic e ru p tio n w a s

could be far m ore disastrou s, and there is geological

M t P in a tu b o in the P h ilip p in e s in 1991. S u ch

eviden ce for such ev en ts in the p ast. N on e havin g

e r u p tio n s inject la rg e q u a n titie s o f d u s t p a r tic le s

m ajor effects h as been recorded in h u m an history.

a n d re a c tiv e g a s e s (m a in ly s u lfu r d io x id e a n d

H o w ev e r in the 1980s, they d id p ro v id e so m e

upper

inspiration and an an alogy in considerations of the

a tm o sp h e re . If the p a r tic le s an d s u lfu r o u s g a s e s

p ossible climatic effects of a nuclear w ar (via the release

rem ain in the tro p o sp h e re (the w e ll-m ix ed lo w e r

o f large clou d s o f sm ok e from burnin g cities) - an

a tm o sp h e re w h ere c lo u d s a n d rain occu r), they can

effect k n ow n a s 'n u c le a r w in te r'.9 M ajo r co sm ic

b e w a sh e d o u t in a m atter o f d a y s to w e e k s, an d so

c o llisio n s are far le ss lik ely than m ajo r v o lcan ic

h av e little clim atic effect. H o w ev er, if the d u st an d

eru p tio n s in the next few centuries, an d are ign o red

reactiv e g a s e s en ter the m o re sta b le re gio n o f the

in current clim atic projections.

h y d ro g e n

s u lfid e ) in to the lo w e r a n d

32

CLIMATE C H A N C E: THE SCIENCE, IMPACTS A N D SO L U T IO N S

M ore re le v an t to cu rre n t p ro je ctio n s are the p resen ce o f large qu an tities o f sm a ll p articles in the

R ecen t

ex c ite m e n t

abou t

so -c a lle d

'g lo b a l

d im m in g ' (for e x a m p le a p a p e r b y G Stanh ill in

low er atm osph ere com m on ly referred to a s 'aeroso ls'.

Weather, Jan u ary 2005, and v ario u s m ed ia reports) is

T h ese arise m ain ly from the em issio n of su lfu ro u s

in fact a rediscovery and m easu rem en t o f these effects

g a se s an d so o t p articles, from the b u rn in g o f fo ssil

o f aerosols, w hich h av e lon g been held resp on sib le in

fuels, a s w ell a s m ore n atu ral d u st p articles from arid

p art for the co olin g exp erien ced in the northern

w in d y su rfaces. A ll of these particles h av e only sh ort

hem isphere in the 1950s an d 1960s.12 The direct effects

lifetim es in the low er a tm osp h ere before they fall ou t

o f aero so ls h ave been in clu ded in m o st recent glob al

o r are w a sh e d ou t. H o w ev e r, they are q u ick ly

clim ate m o d el sim u la tio n s, an d so m e sim u la tio n s

replaced a s m ore fossil fuels are b u rnt, or by w ind

have also included estim ates of the indirect effects.

erosion in arid a re a s.10

A e ro so l a m o u n ts d u e to in d u stria l activ ity are

M e a su re m e n ts from the g r o u n d a n d sa te llite s

n o w d e c r e a sin g in so m e re g io n s, e s p e c ia lly in

in d ic a te th e la r g e p r e s e n c e o f su c h p a r tic le s

E u ro p e an d N o rth A m erica, d u e to effo rts to clean

regio n ally , a n d th at th ey h a v e sig n ifica n t effects on

up e m issio n s o f su lfu r o u s g a s e s b e c a u se o f a cid

re g io n a l clim ate. A e ro so ls d irectly a b so rb or reflect

rain a n d u rb a n p o llu tio n effe cts. T h u s, w h ile

in c o m in g s o la r e n erg y , a n d a ls o a b so r b so m e

g re en h o u se g a s em issio n s con tin u e to in crease, the

o u t g o in g h e a t r a d ia t io n . A b s o r p t io n

o f s o la r

p a r tic le s th at w e re h a v in g a co o lin g effect are

e n e r g y w ill c a u s e lo c a l h e a tin g in the lo w e r

d e c r e a sin g , le a d in g to a g re a te r d o m in a n c e o f

a tm o sp h e re , w h ich m a y in turn h e at the su rfa c e .

in c re a se d g re e n h o u se w a rm in g on the o b se rv e d

T h u s s o o t p a r tic le s a d d

to g lo b a l w a r m in g .

clim a te. T h is is p a r t o f the e x p la n a tio n fo r the

A b so r p tio n by p a r tic le s o f h e at ra d ia tio n from the

in creased rate o f glo b a l a v e ra g e w a rm in g in the last

s u rfa c e a lso te n d s to h e a t the su rfa c e . H o w e v e r,

tw o d e c a d e s. W hen a e ro so l effects are a d d e d to

reflection o f in c o m in g so la r ra d ia tio n h a s a co o lin g

g lo b a l c lim a te m o d e l sim u la tio n s, they b etter

e ffe c t a t the su r fa c e . T h is is th o u g h t to h a v e

acc o u n t for the te m p e ra tu re v a ria tio n s o b se rv e d

d o m in a te d in re cen t d e c a d e s , le a d in g to so m e

o v er the tw entieth century. T h ey a lso se em to h a v e

p o llu te d re g io n s d o w n w in d o f m a jo r in d u s tr ia l

h ad effects on a tm o sp h eric circulation an d rain fall,

a re a s e x p e rie n c in g le ss w a rm in g than w o u ld h a v e

largely d u e to their effects on the m o n so o n s.13 P ast records from sed im en tary lay ers offsh ore of

o th e rw ise occu rred . A recen t d r a m a tic e x a m p le o f h o w a e r o so ls

the co n tin en ts (n otab ly C h in a, north A frica an d

a ffect the d a ily te m p e ra tu re cy cle w a s o b se rv e d

A u stra lia ), an d in ice co res from G reen lan d an d

in the U n ite d S ta te s w h en c o m m e rc ia l a ircra ft

A n tarctica, in d icate that in crease s in w in d-b lo w n

w ere g ro u n d e d fo llo w in g the terro rist attac k on

d u st h av e occurred in p re v io u s m ore arid clim ates.

11 S e p te m b e r 2001. A s re p o r te d in N atu re on

D e p en d in g on the siz e an d ra d ia tio n a b so rp tiv e

8 A u g u st 2002, this led to few er v a p o u r trails from

q u alities of these p articles, they m ay h av e locally

a ircraft, w ith a sta tistic a lly sig n ifica n t in crease in

contributed to w a rm in g or coolin g. Th ey certainly

the d iffe re n c e

testify to the ability of clim ate ch an ge to alter the

b e tw e e n

d a ily

m a x im u m

and

m in im u m tem p e ra tu re s. T h ere are a lso in d irect effe cts o f a e r o so ls on

frequency an d severity of d u st storm s and soil erosion through ch an ges in land cover an d w in din ess.

c lo u d s , first s u g g e s t e d b y S e a n T w o m ey o f the U n iversity o f A riz o n a in 1977, that is, a red u ctio n in c lo u d d ro p le t siz e d u e to the p a rtic le s a ctin g a s

Rapid climate changes in the past14

co n d e n sa tio n n uclei. T h is in c rea se s the reflectivity

D e s p ite

o f the clo u d s, an d d e cre a se s p recip itatio n efficiency,

a stro n o m ic a l v a ria tio n s, the p ale o -c lim atic record

the

slo w ly

v a r y in g

n a tu re

of

the

w h ich in c re a se s c lo u d w a te r co n ten t a n d c lo u d

is re p lete w ith e x a m p le s o f s u r p r isin g ly ra p id

lifetim e, le a d in g to furth er su rfa ce co o lin g .11

clim atic ch a n g e s. Th e extrem e ra p id ity o f so m e of

LEARNIN G FR O M THE PAST

33

these c h a n g e s h a s on ly b eco m e a p p a re n t in recent

clim ate la ste d for 1200 y e a rs, a n d w a s fo llo w e d

d e c a d e s a s im p ro v e d a n a ly sis, sa m p lin g a n d d a tin g

b y a v e ry r a p id w a r m in g o f a b o u t 8 °C in 10

tech n iq u es h a v e en ab led ch a n g e s to be o b se rv e d on tim e sc a le s o f y e a rs to d e c a d e s rath er than cen tu ries

y e a rs, tak in g the clim ate to in terglacial co n d itio n s n o t m u ch d iffe re n t from tod ay . P rox y d a ta for

a n d m illen n ia. O ld e r a n a ly se s h a d sm o o th e d ou t

the Y ou n ger D ry a s ev en t is esp e cia lly p ro m in en t in

v ery ra p id ch a n g e s that can n ow b e seen clearly.

the ice core re co rd s from G re e n la n d (top cu rv e),

R ich ard Alley, C h air o f the C om m ittee on A b ru p t

w h ere there is e v id e n ce o f co o lin g , re d u ced sn o w

C lim ate C h an ge of the U S N atio n al R esearch C ouncil

a cc u m u la tio n , a n d ch a n g e s in w in d in e ss a n d d u st

(N R C ), w rote in the p reface to its 2002 report:

a c c u m u la tio n . W ithin a b o u t 30 y e a rs o f the final

Large, abru pt clim ate changes have repeatedly affected much or all o f the earth, locally reaching a s much as 1 0 °C change in 10 years. A vailable evidence su g g e sts that abrupt clim ate changes are not only possible but likely in the fu tu re, potentially with large im pacts on ecosystem s and societies.

w a rm in g , a tm o sp h eric m eth an e concentration rose a b o u t 50% , reflecting c h a n g e s in w e tla n d s in b oth the tro p ics a n d h igh latitu d es. E v id en ce for a sim ila r late-glacial re v ersa l co m es fro m ice co re s on B affin Isla n d in C a n a d a , an d g la c ie rs in Peru a n d B o liv ia, an d th is is p ro b a b ly a lso the Y ou nger D ry as. H o w e v e r in A n tarctica the ev id en ce is m ix ed , w ith re co rd s from Byrd sh o w in g

A lley is not talk in g a b o u t ab ru p t ex tern al c a u se s o f ch an g e su ch a s la rg e m eteo r im p a c ts or n u clear

relative w arm th at the tim e o f the cold co n d itio n s in G reen lan d .

w ar, b u t rath er a b ru p t clim ate c h a n g e s th at can

P o lle n e v id e n c e fo r c h a n g e s in v e g e ta tio n ,

o ccu r w h en v a ria b le s th at are g ra d u a lly c h a n g in g

h ow ever, p ro v id e s a w id e r g e o g ra p h ic a l co v erag e.

p u sh the Earth sy ste m a c ro ss so m e th resh o ld of

D u r in g

in sta b ility . H e lik e n s th is to h o w

the slo w ly

th ro u g h o u t E u ro p e , from N o r w a y to S p a in an d

in creasin g p re ssu re o f a fin ger can flip a light sw itch

Italy, w ith the stro n g e st effe cts n e a r the w estern

from o ff to on. G r a d u a l ch a n g e s in the E a rth 's orbit,

co ast. A v erag e Ju ly tem p e ra tu re s in N o r w a y w ere

or d riftin g o f the con tin en ts, can sw itch the E arth to

7 - 9 °C lo w e r than today, a n d a s m u ch a s 8 °C low er

a new an d very differen t clim atic state. W hen orbital

th an to d a y in S p a in . E v id e n ce a lso c o m e s from

the Y o u n g e r D r y a s c o o lin g

o c c u r re d

c h a n g e s an d risin g g re e n h o u se g a s co n cen tratio n s

N o r th A m e r ic a

w a rm e d the E arth after the la st g la c ia tio n , p ale o -

sig n ifica n t effects there. F o ssil p o lle n s sh o w that in

th a t the Y o u n g e r D r y a s h a d

th at the sm o o th c h a n g e s w e re

the so u th e rn N ew E n g la n d regio n o f the U n ited

p u n c tu a te d b y a b ru p t g lo b a l or re g io n a l c o o lin g s

S ta te s Ju ly te m p e ra tu re s w ere 3 -4 °C co oler an d in

r e c o r d s sh o w

a n d w a rm in g s, w e ttin g s an d d ry in g s.

the eastern m aritim e p ro v in c es o f C a n a d a they w ere

It sh o u ld be a d d e d th at su ch a sw itch can n o t

6 -7 °C cooler. E v id en ce o f so m e w h a t w e a k e r effects

re ad ily be tu rn ed o ff a g a in , d u e to larg e d e la y s or

is a lso fo u n d in the U S M id w e st, c o a sta l B ritish

inertia in the clim ate sy stem : it is m o re like on e of

C o lu m b ia an d A la sk a , C o sta Rica an d G u a te m a la .

th ose se n so r sw itc h es u se d for lig h tin g, w h ich can

In the so u th e rn h e m isp h e r e e v id e n c e is m o re

b e tu rn ed on b y so m e su d d e n m o v em en t b u t only

co n fu sin g, w ith so m e coolin g, b u t so m e a re as w here

turn th e m se lv es o ff in their ow n g o o d tim e.

w a rm in g m a y h a v e occu rred , an d oth ers w h ere no

Th e b est k n ow n o f th ese larg e an d a b ru p t p a st

effects are fo u n d in the reco rd s. G laciers a d v a n c e d

c h a n g e s w a s the Y o u n g er D ry a s ev en t, in d ic ate d ,

d u r in g the Y o u n g er D ry a s in m a n y E u ro p e a n

a lo n g w ith tw o other le sse r ev en ts, b y the sh a d in g

re gio n s, n o tab ly in N o rw ay , F in lan d an d Sco tlan d ,

in F ig u re 10. T h e Y o u n g er D ry a s w a s a su d d e n

a n d a lso in C a n a d a , W y o m in g in the U S an d

in terru p tio n o f a g r a d u a l g lo b a l w a rm in g after the

E c u a d o r. Ice retreated in P eru , p ro b a b ly d u e to

en d o f the la st g la cia tio n , an d b e g a n a b o u t 12800

re d u ced p recip itatio n , b u t the F ran z Jo se p h G lacier

y e a rs a g o . T h is s u d d e n retu rn to a co ld g lo b a l

a d v a n c e d in N e w Z ea la n d .

34

CLIMATE C H A N C E: THE SCIENCE, IMPACTS A N D SO L U T IO N S

-3.4 -

Central Greenland ----- C h a n g e in Isotope ----- Tem perature

8.2 Ky BP Event

Western Europe

200 >, a> U_ U

Tropical N orth Atlantic

160

20

15

10

5

0

T h o usa n d s of years before present (Ky BP)

Records of climatic variations from the height of the last glaciation until the present. This includes three rapid climate change events (shaded), namely the Younger Dryas, the Antarctic Cold Reversal and the 8.2 thousand years before present event. (Source: IPCC 2001a, Figure 2.24, used with permission.) Figure 10:

M arin e se d im e n t co res from the N o rth A tlan tic

C arib b e a n , the N o rth Pacific, the In dian O cean an d

d u r in g the Y o u n g e r D ry a s sh o w an in c re a se d

the A ra b ia n S ea p o in t to a g lo b a l scale p h en om en o n ,

a b u n d a n c e o f p o l a r p la n k t o n ic s p e c ie s , w h ic h

alth o u gh so m e re g io n s sh ow little effect.

su g g e s t s that the fo rm atio n o f d e ep w ater, by the

D e sp ite the n eed for m o re d a ta , the p ictu re

sin k in g o f su rfa ce w ater, w a s re d u ce d in the region .

e m e rg e s o f the Y ou n g er D ry a s a s co ld , d ry an d

O ther ocean ic ev id en ce su p p o r ts this an d p ro v id e s

w in d y in m a n y re g io n s at le a st o f the n orth ern

ev id en ce for the origin o f the Y ou n ger D ry a s ev en t

h e m isp h e re . H o w e v e r, there are lo ca lly w e tte r

in the w a ters o f the N o rth A tlan tic. M arin e record s

re g io n s, p o ss ib ly a sso c ia te d w ith ch a n g e s in the

from m an y other p a rts o f the w o rld , in c lu d in g the

track s o f sto rm s. A t the sa m e tim e, the far S ou th

LEARNIN G FR O M THE PAST

35

A tlan tic, the so u th ern In dian O cean an d A ntarctica

freq u en cy a n d se v e rity o f extrem e ev en ts su ch a s

w ere relatively w arm . C h a n g e s w ere la rg e st a ro u n d

d r o u g h ts a n d flo o d s. E ven th ese re lativ ely sm a ll

the N o rth A tla n tic , a n d a p p e a r to h a v e b ee n

ch a n g e s ev id en tly h ad larg e im p a c ts on e c o sy ste m s

a sso cia ted w ith red u ced d e ep w ater form ation and

an d h u m an so cieties, a lth o u g h u su a lly at a re gio n al

related ch a n g e s in ocean circu lation . D eep w ater

rath er than g lo b a l scale.

fo rm a tio n re su lts from the sin k in g o f co ld , h igh

In relation to h u m a n im p a c ts, it is so m e tim e s

salinity an d thus m ore d en se su rface w aters. S low in g

d ifficu lt to p in d o w n ex actly w h at w a s c a u se an d

or c e ssatio n o f d e e p w a ter fo rm a tio n w a s d u e to

w h at w a s effect, d u e to v a ria tio n s in facto rs other

w arm in g or fresh en in g o f the su rfa ce w aters. E v en ts sim ila r in siz e, rate an d exten t to the

than clim ate. P o p u latio n p re ssu re s, d is e a se s, w a rs, e c o n o m ic

fo r c e s ,

t e c h n o lo g ic a l

ch anges

and

Y ounger D ry as even t occurred so m e 24 tim es d u rin g

resource su b stitu tio n s can all affect h u m an societies

the 110000 y ear record d e riv ed from the ice cores of

in w a y s that m ay or m ay not be related to clim ate.

central G reen lan d . T h ey all sh ow g ra d u a l co olin g

H ow ever, in so m e ca ses the clim atic influence is clear

from a w arm in terval, then m ore ab ru p t co olin g, a

and w ell docu m en ted . A case in poin t is the settlem ent

cold in terval, an d finally an a b ru p t w a rm in g . The

o f G reen lan d by the V ikin gs in the tw elfth century

w arm tim es h ave been term ed D a n sg a a rd /O e sc h g e r

d u rin g w h at is know n a s the M ed iev al W arm Period,

ev e n ts, an d the se q u e n c e s D a n s g a a r d /O e s c h g e r

an d the a b a n d o n m en t o f these settlem en ts d u rin g

o scillatio n s. Th e co ld e r p h a se s w ere m a rk e d by

the fifteen th cen tu ry a s co n d itio n s in the N o rth

in creased raftin g b y iceb ergs of glacial d eb ris (rocks

A tlan tic regio n b ecam e cooler, a gricu ltu re b ecam e

an d dirt scrap e d u p b y glaciers) into colder, fresher

m ore m argin al, se a ice ex ten d ed an d the settlem en ts

su rface w ater, an d by a redu ction in the strength of

b ecam e m ore isolated.

N orth A tlan tic d e ep w ater form ation . C h a n g e s in

Th e exten t to w h ich h u m a n h isto ry h a s been

m aterial su ch a s d u st an d m eth an e from o u tsid e

in flu en ced b y clim ate h a s been lo n g d e b a te d by

G reen land, trap p ed in the ice cores, d em on strate that

h isto ria n s an d c l i m a t o l o g i s t s .T h e U S h istorian -

th ese e v e n ts affe cte d la rg e a r e a s o f the E arth

g e o g ra p h e r H u n tin gton in 1915 fam o u sly ad v o cated

sim u ltan eously.

a form o f clim atic d eterm in ism , that is, that clim ate

D esp ite only g ra d u a l ch an ge s in d riv in g forces,

d eterm in ed h u m an racial differen ces an d levels of

these o b serv ed rap id clim ate ch an ges a p p e a r to have

civilisation .16 C arp en ter and L am b in the 1960s argu e

occurred b e c a u se the d riv e rs reached so m e so rt of

for the influence o f clim ate on G reek civilisation , an d

tip pin g poin t or thresh old at w hich clim ate flip s into

Le R oy L a d u rie, in h is se m in al b o o k in 1971, for a

a new state. Such m e ch an ism s su g g e st that sim ilar

w id e r influen ce e sp e cia lly on E u ro p e a n h istory .17

ra p id clim ate ch a n g e s co u ld h a p p e n a g a in , even

D a n sg a a rd an d co lleag u es in 1975 a rg u ed for a strong

w hen driv en by only g ra d u a l increases in green h ou se

in fluence on N o rse culture, esp e cially in re gard to

g ase s. We w ill return to the sign ifican ce o f these p a st

the settlem en t of Iceland and G reen lan d , and Singh

ev en ts for clim ate ch an ge risk in the tw enty-first

in 1971 for a d e term in in g clim atic im p ac t on the

century an d b ey o n d in C h ap ter 5, w hich d e a ls w ith

civilisation o f the In d u s valley in n orth -w est In dia,

w h at clim ate ch an ge s are likely, an d in C h ap ter 6, on

w hich co llap sed follow in g d ro u gh ts in the eighteenth

clim ate ch an ge im pacts.

century B C .18 C lim atic flu ctu ation s are also a rg u ed to h a v e in fluen ced the m ig ra tio n s o f p e o p le s in the S o u th P acific, in c lu d in g the se ttle m en t o f N ew

The last 10 000 years

Z ealan d b y the M aori p eo p les aro u n d 800 A D .19 The

C lim a tic c h a n g e s sin ce the Y ou n g er D ry a s ev en t

Z h ou D y n asty in C h in a w a s affected b y in creasin g

m o re than 100 0 0 y e a rs a g o h a v e g e n e ra lly been

aridity arou n d 1150 A D .20

sm a lle r in a m p litu d e , b u t n e v e rth e le ss

C lim atic flu c tu a tio n s su ch a s ex te n d ed d ro u g h t

so m e tim e s ra p id , w ith s u d d e n in c re a se s in the

are th o u g h t to h a v e p la y e d a m a jo r p a r t in the

m u ch

36

CLIMATE C H A N C E: THE SCIENCE, IMPACTS A N D SO L U T IO N S

a b a n d o n m e n t o f A m eric an In d ian se ttle m e n ts in

relatively w et (c o rre sp o n d in g at lea st in p a rt to the

the so u th -w e stern U n ited S ta te s a ro u n d 1090 A D ,

cool p e rio d in E u ro p e k n o w n a s the Little Ice A ge).

a n d a g a in in the thirteenth cen tu ry A D ,21 a n d the

M o reo v er, three sh o rte r p e r io d s o f d r o u g h t, in

fall o f the M a y a n civ ilisa tio n in C en tral A m erica

13 9 0 -1 4 2 0 ,1 5 6 0 -1 6 2 5 an d 1760-1840 co rre sp o n d to

a ro u n d 850 A D .22 E x te n siv e a n a ly sis o f tree rin g

p e rio d s o f political u n rest a n d large-scale m igration ,

d a ta , la k e le v e ls a n d sa n d d u n e s in the G re a t

a c c o r d in g

P lain s o f the U n ited S ta te s in d ic ate s that o v er the

p ro sp e rity in betw een .

to o r a l t r a d itio n s , w ith p e r io d s o f

d r o u g h t c o n d itio n s

E v id e n ce for a L ittle Ice A g e a n d a M e d ie v a l

c o m p a r a b le w ith , o r m o re se v e re th an , th at o f

W arm P e rio d is fa irly w id e sp r e a d a c ro ss E u ro p e

la s t 2000 y e a r s e x te n d e d

the 1930s d u st b o w l o ccu rred on se v e ra l o ccasio n s.

an d p a r ts o f N o rth A m e ric a , to a le s se r exten t

It w a s co n clu d e d th at if su ch la rg e -sca le d ro u g h ts

elsew h ere in the n orth ern h e m isp h e re , a n d m u ch

h ave a

le ss e v id en t in the so u th ern h em isp h ere. Pollen and

sign ifican t im p a c t on N o rth A m erican society, with

ch arco al a n a ly se s from se d im e n ts in p a r ts o f the

a redu ctio n in w ater su p p ly , crop failu re, ra n g ela n d

n orth-w estern U n ited S ta te s, an d from Y ellow ston e

stre ss, su sp e n sio n of recreation al a n d to u rist activity

N a tio n a l P ark a n d cen tral Id a h o p o in t to g re a te r

a n d heat-related d e a th s.23

fire fre q u en cy d u rin g the M e d ie v a l W arm P erio d ,

w e re to o c c u r in fu tu re th ey w o u ld

L a rg e

a r e a s o f the A fric a n

and

E u ro p e a n

a n d le sse r fire freq u en cy d u rin g the Little Ice A ge.

co n tin en ts u n d e rw e n t m a s siv e c h a n g e s in their

H o w e v e r, in A lb e rta , C a n a d a , the sa m e so rt of

v e getatio n co ver an d e c o sy ste m s in the early an d

a n a ly se s p o in t to the o p p o site tendency. T h is local

m id -H o lo cen e p e rio d s, so m e ten to five th o u san d

effect h a s b ee n related to d e clin in g g ro u n d w a te r

y ears ago. Th is m u st h ave h a d en o rm o u s im p acts on

le v e ls at on e site in A lb e rta , le a d in g to a ch an g e

the lives of the scattered h u m an in h abitants at those

from fire-prone sh ru b Birch trees to le ss fire-prone

tim es, forcin g large-scale p o p u latio n m o v em en ts or

A sp e n .25 R e co rd s o f p reh isto ric trop ical cy clo n es occur in

p o p u latio n losses. In A frica, the S a h a ra w en t from a largely g r a s sy

the form o f r id g e s o f co ral ru b b le, sa n d , sh ell an d

area, p o p u la te d by h u n te r-g a th e rin g p e o p le s w h o

p u m ice ; ero sio n a l terraces in ra ise d g ra v e l b each es; b a rrie r w a s h o v e r d e p o s it s ; a n d v a r io u s o th e r

left a rtefacts an d record s o f the a n im a ls they hu n ted in rock p ain tin g s, to d e se rt rather su d d e n ly a ro u n d

se d im e n ts. S u ch re c o rd s fo r a n u m b e r o f site s

6000 y e a rs a g o . E v id en ce for th is is fo u n d in lake

a ro u n d the w o rld s u g g e s t that the freq u en cy an d

se d im e n ts a n d estim ate d lev els, a n d in m arin e an d

p o ss ib ly the in ten sity o f tro p ic a l c y c lo n e s h a v e

lan d p o lle n re co rd s. T h is ch an g e is th o u g h t to be

v a ried in the p a st. H ow ever, the n u m b e r o f ev en ts

re la te d to the E a r th 's o rb ital v a ria tio n s an d an

a n a ly se d is sm a ll an d sta tistic a l sig n ific a n c e is

a m p lific a tio n

therefore not great.

o f the effe ct o f c h a n g in g

so la r

rad iatio n b y the interaction o f the v e g eta tio n w ith

C h a n g e s in se a level since the end of the last

clim ate, p o ss ib ly p a s s in g so m e critical th resh old .

glaciation are dom in ated by the slow b u t m assiv e rise

T h is s u d d e n d ry in g m a y h a v e sp u rre d m ig ra tio n

o f so m e 120 m etres d u e to the m eltin g o f the h u ge

into the N ile V alley a n d the sta rt o f the E g y p tia n

continental ice sh eets in the northern h em isp h ere

civ ilisatio n . C lim a te m o d e ls h a v e p artly sim u la te d

betw een ab ou t 20000 and 8000 y ears ago. Th is w a s

these ra p id clim ate ch a n g e s, alth o u gh re su lts differ

n ot entirely regular, b u t w a s p u n ctu a ted b y p a u se s

from one m o d el to anoth er.24

an d su d d e n rises of a few m etres d u e to tem p orary

A n d in E a st A fric a , la k e le v e ls a n d sa lin ity

glacial re -ad v an ces an d su d d e n o u tb u rsts o f m elt-

flu ctu atio n s in L ak e N a iv a sh a (K en y a) in d icate that

w ater stored by h u ge glacial d a m s or su rg e s in glacial

the era from 1000 to 1270 A D (d u rin g the M e d iev al

m otion an d iceberg form ation.

W arm P erio d in E u ro p e ) w a s sig n ific a n tly d rie r

S ea-lev e l c h a n g e s in the la st 8000 y e a rs26 or so

than to d ay , w h ile the era 1 2 7 0 -1 8 5 0 A D w a s

h a s ten d e d to b e sm a ll an d re gio n al, w ith rise s in

LEARNIN G FR O M THE PAST

37

so m e re g io n s an d re lativ e fa lls in o th e rs, m ain ly

a n o m a lie s can o ccu r for m a n y re a so n s, a n d often

d u e to ea rth m o v e m e n ts a n d re b o u n d o f the

can cel o u t a c ro ss la rg e r re g io n s, so the n u m b e r o f

co n tin e n ta l p la te s . T h e m a jo rity o f the E a r th 's

o ccu rren ces o f sh o rt w arm p e rio d s in lo n g re co rd s

co astlin es are at p resen t su b ject to relative sea-level

from m an y d ifferen t re g io n s is n ot c o m p a ra b le to

rise a n d erosion . L o cal c o n so lid a tio n o f se d im e n ts,

h em isp h eric a v e ra g e w a rm in g su ch a s h a s occurred

either d u e to slo w n atu ral a d ju stm en ts, earth q u ak es,

in the tw entieth century.29

or w ith d r a w a l o f g ro u n d w a te r, oil or n a tu ra l

M o re recen t re -a n a ly se s o f the te m p e ra tu re

g a s, h a s con trib uted to co asta l p ro b le m s.27 N o tab le

record sh o w m o re v a ria b ility o v e r the la st 1300

is the lo ss o f so m e a n cie n t citie s a ro u n d the

y e a rs, b u t co n tin u e d to fin d an u n p re c e d e n te d

M e d iterran e an co ast, su ch a s an cien t A le x a n d ria,

w arm in g in the secon d h alf of the tw entieth century.

M e n o u th is a n d H e ra k lio n in E g y p t, a n d o th ers

T h is w a rm in g h a s co n tin u ed into the tw en ty -first

a ro u n d G reece, Italy a n d Turkey. G ro w in g s u b ­

century, w ith the la st d e ca d e b ein g the w a rm e st on

sid en ce p ro b lem s a lso exist in other cities su ch a s

record. M o reo ver, a s p o in te d o u t b y Tim O sb o rn

B an gk ok , L o n d on an d Venice, an d in the C h esap e ak e

a n d K eith Briffa o f the C lim atic R esearch U n it in the

Bay regio n in the U n ited S tates. T h ese p ro b le m s

U K , the larger estim ate d tem p e ratu re v a ria tio n s in

w o u ld be accen tu ated by any sy stem a tic sea-level

the 10 0 0 -y ear record s u g g e s t a g re a te r c lim a te

rise d u e to the en han ced green h ou se effect, especially

se n sitiv ity to sm a ll c h a n g e s in forcin g fa cto rs an d

if sea-level rise accelerates, a s n ow se em s likely.

this w o u ld a lso a p p ly to g re en h o u se g a se s.30 T h is is

T h ere is a lso cle ar e v id en ce that m eltin g o f ice

co n siste n t w ith the c la im s for h u m a n in flu en ces

c a p s h a s led to the u n d e rly in g la n d slo w ly risin g a s

o v er this p e rio d , v ia ch a n g e s in lan d cover, m a d e b y

the w e ig h t o f ice w a s re m o v ed . T h is is called 'glacial

W illiam R u d d im a n .5

re b o u n d ', an d a s w ell a s c a u sin g local sea-level falls

R u d d im a n s u g g e s t s that the cool p erio d before

(w ith c o m p e n sa tin g rise s elsew h ere a s the w ater is

the M e d ie v a l W arm P e rio d , a n d the Little Ice A g e

d is p la c e d ), it a d d s s tr e ss to tecto n ic fa u ltlin e s,

after it, m a y both h a v e been d u e to b u b o n ic p la g u e -

le a d in g to local in c rease s in ea rth q u a k e activity.28 A s r e g a r d s p ro x y e v id e n c e fo r te m p e ra tu re

in d u c ed d e p o p u la tio n in w estern A sia an d E u ro p e, w h ich le d to re g ro w th o f fo re st on a b a n d o n e d

v a ria tio n s, w e sa w in C h a p te r 1 th at the p ro x y

fa rm la n d s. T h is theory h a s ca u se d w id e d isc u ssio n

record o v e r the la st 1300 y e a rs s u g g e s t s that the

in the scientific com m unity. If true, it s u g g e s ts high

tw entieth cen tu ry sa w the la rg e st tem p e ratu re rise,

clim ate se n sitiv ity to re la tiv ely sm a ll c h a n g e s in

at le a st in the n o rth e rn h e m isp h e r e , w ith the

g re e n h o u se g a s co n ce n tratio n s a n d that h u m a n s

sh a rp e st rise occu rrin g sin ce the 1970s. The o rigin al

are c a p a b le o f ach ie v in g these ch an ge s. M o reover, it

claim for a 'h o ck ey stick ' like te m p e ra tu re record

m e a n s th at w h ile p a s t h u m a n activ ity m a y h a v e

o v er the la st 1000 y e a rs, im p licit in the re su lts of

h elp ed to a v o id p ro lo n g e d co n d itio n s like the Little

M ich ael M an n an d oth ers w a s ch allen ged b y Soon

Ice A g e b y w id e sp r e a d lan d cle a rin g , p ro je cted

a n d B a liu n a s in a p a p e r in 2003 c la im in g that:

in crease s in g re en h o u se g a s co n cen tration s at a rate

'A c ro ss the w o rld , m a n y re co rd s re v e a l th at the

at least ten tim es faster than ou r an c esto rs ach iev ed

tw entieth centu ry is p ro b a b ly n ot the w a rm e st nor

m e a n s th at w e w ill see m u ch la rg e r w a rm in g s in

a u n iq u e ly e x trem e clim a tic p e rio d o f the la st

the tw en ty-first cen tu ry an d b ey o n d .

m ille n n iu m .' H o w e v e r, th is is v e ry m isle a d in g , sin ce the p a p e r d o e s not co m p a re e stim ate s o f p a st global or hemispheric a v e r a g e te m p e ra tu re s w ith

Conclusions from the past record

th o se o f the tw en tieth century, b u t m erely non-

P ast clim atic ch a n g e s are relevan t b e c a u se they

synchronous (that is, n ot occu rrin g regio n b y regio n

d em o n strate w h at is p o ssib le in the n atu ral clim ate

at the sa m e tim e) a n d u n q u a n tifie d te m p e ra tu re

sy stem w h en forces occur su ch a s volcanic eru p tion s

(an d rain fall) 'a n o m a lie s' in each local record. L o cal

or v ariatio n s in the E arth 's orbit aro u n d the Sun.

38

CLIMATE C H A N C E: THE SCIENCE, IMPACTS A N D SO L U T IO N S

O rbital v a ria tio n s act slow ly, on tim e sc a le s of

cen tu ry w e can e x p ec t clim ate to ch a n g e so ra p id ly

th o u sa n d s o f y ears, w h ile volcanic eru p tion s act in a

th at fo r e sts w o u ld n e e d to m ig ra te a t ra te s o f

m atter o f d a y s or w eeks. N ow w e are forcing ch anges

h u n d r e d s o f k ilo m e tre s p e r ce n tu ry to rem ain in

on the clim ate sy stem d u e to large green h o u se g a s

their o p tim al clim atic zo n es. T h is is clearly unlikely.

e m issio n s on a tim e scale of d e c a d e s to a century.

W hat is far m o re likely is th at fo re sts that no lo n ger

T h ese are eq u iv alen t to ch a n g e s w h ich occurred

are lo cated in their correct clim atic z o n e s w ill d ie

p rev io u sly ov er th o u sa n d s of y ears. T herefore w e

fro m

m igh t w ell expect sim ilar im p acts on n atu ral sy stem s

S im ilarly , m a n y c ro p s w ill n o lo n g e r y ield w e ll in

h eat stre ss, d ro u g h t, d ise a se

and

fire.

to those which occurred in the p a st over th o u san d s of

th eir p re se n t lo c a tio n s, a n d w ill h a v e to b e re­

y ears, b u t telescoped into a m uch faster tim e fram e,

lo c a te d h u n d re d s o f k ilo m e tre s a w a y to p ro v id e

lead in g to ra p id an d p o ssib ly catastroph ic ch anges.

e q u iv a le n t clim ate co n d itio n s. But m o st often the

C lim a te ch a n g e h a s o c cu rred n a tu ra lly in the

c ro p s w ill be on d iffere n t so ils, on lan d o w n e d by

p a s t d u e to in tern al flu c tu a tio n s in the clim ate

o th e r p e o p le , a n d ev en in d iffe re n t c o u n trie s.

s y ste m c o n sistin g o f the a tm o sp h e re (air, w a te r

D islo c a tio n s to so ciety w ill th erefore b e la rg e , far

v ap o u r, co n stitu en t g a se s, c lo u d s a n d p article s), the

la rg e r than w a s the c a se fo r the sm a ll n u m b e rs of

h ydrosphere (oceans, lakes, rivers and groun dw ater),

h u n te r-g a th e re rs w h o e x iste d ten s o f th o u sa n d s of

and the c ryo sp h ere (continental ice sh eets, m oun tain

y e a rs ago .

g la c ie rs, se a ice a n d su rfa c e sn o w cover). E xtern al

P a le o - c lim a tic

a n a lo g ie s

to

our

p resen t

c h a n g e s su ch a s v o lc an ic e ru p tio n s, v a ria tio n s in

p red ic am en t co n fu se m an y p eo p le. T h ey a rg u e that

the S u n 's o u tp u t an d the E a rth 's orbital v a ria tio n s,

if la rg e c lim a te c h a n g e s o c c u rre d b e fo re , a n d

a n d c h a n g e s in the so lid Earth (con tin en tal drift,

h u m a n s a n d oth er sp e c ie s su rv iv e d , then life, an d

m o u n tain b u ild in g , erosion an d siltation ) h a v e also

ev en h u m a n s, can su rv iv e to d ay , so there is n ot

d riv en ch a n g e s in clim ate.

m u ch to be co n cern ed ab ou t. T h is fa ils to co n sid er

A t the en d o f the la st gla cia tio n , a v e ra g e g lo b al

the differen t tim e sc a le s, the very differen t p lace of

w a rm in g o ccu rred at a rate o f a b o u t 1°C or le ss p er

h u m a n ity in the e c o sy ste m s then co m p ared to now ,

th o u sa n d y e a rs, alth o u gh there w ere sh o rt p e rio d s

an d the m an y re strictio n s that e x ist to d a y w h ich

d u rin g w h ich w a rm in g w a s m u ch faster. Th e la st of

lim it o u r ab ility to a d a p t to su ch larg e an d ra p id

these w a s at the en d o f the so -called Y ou n ger D ry as

ch a n g e s. T h ese in c lu d e n atio n al b o u n d a rie s, m a s s

re v e rsa l, a b o u t 11 500 y e a rs a g o . Sin ce then, an d

relian ce on relativ ely few cro p s for fo o d , an d other

c e rta in ly sin ce the d a w n o f civ ilisa tio n , ra te s o f

e n v iro n m e n tal stre sse s c a u se d b y so m e six b illion

w a rm in g h a v e n e v e r e x c e e d e d a b o u t 0 .5 °C p er

p eo p le. H u m an b e in g s an d their so cieties m ay w ell

cen tu ry (0 .05°C p er d e c a d e ) for p e r io d s o f m o re

b e th reaten ed , n ot w ith extinction , b u t w ith severe d isru p tio n , an d p o ssib ly catastro p h ic econ om ic an d

than a few d e c a d e s. O u r interest in the p a s t is n ot only in w h at so rts

so cial effects. T h is is esp e c ia lly so if w e h a p p e n to

o f clim ate c h a n g e s can h a p p e n , b u t a lso in w h at

c r o ss a th re sh o ld w h ich le a d s to ra p id clim ate

so rt o f im p a c ts they h a d on n atu ra l sy ste m s su ch a s

ch a n g e o f a m a g n itu d e a n d s p e e d u n p a r a lle le d

p la n t s , a n im a ls a n d

sin ce the Y o u n g er D ry a s ev e n t, a n d on e w h ich

la n d s c a p e s . H o w e v e r, in

in te rp re tin g p a le o -c lim a te in d u c e d c h a n g e s w e

can n o t b e q u ick ly re v ersed .

m u st think carefu lly a b o u t rates o f ch an ge ra tes o f

T h e u p sh o t o f all th ese stu d ie s is th at clim ate

a d a p ta tio n , an d ch a n g e d circ u m sta n ce s a s re g a rd s

c h a n g e o f the m a g n itu d e w e are e x p e c tin g in the

h u m an p o p u la tio n s an d so cieties.

next 100 y e a rs an d b e y o n d h a s h a p p e n e d b efo re,

P ollen re co rd s sh o w that in re sp o n se to w a rm in g

alth o u gh u su a lly at a m u ch slo w e r rate a n d from a

a fter the en d o f the la st g la cia tio n a ro u n d 15000 to

co o ler sta rtin g poin t. P rojected ch a n g e s in clim ate

1 0 0 0 0 y e a rs a g o , fo re sts m ig ra te d at ra te s of, at

b y 2100 a re c o m p a r a b le to th o se from the la st

m o st, ten s o f m e tre s p e r cen tu ry . O v e r the n ext

gla cia tio n (20000 y e a rs a g o ) to the p resen t, w h ich

L E A R N IN G F R O M THE PAST

led to large rises in sea level, m assive changes in plan t and anim al num bers and distribution, and ch an ges in the lan d -se a bord ers. Som e p laces changed from tundra to tem perate forests, and

39

others from forests to desert. Today we face sim ilar change, but m uch faster, and from a base clim ate which is already as w arm as any experienced since hum an societies began.

ENDNOTES 1. M uch of the inform ation on p ast clim atic variations in this chapter is draw n from IPCC 2001 report, W G I, C h apter 2 'O bserved C lim ate Variability and C h an ge' and IPCC 2007, W G I, C h apters 2, 4, 6 and 9. R ecom m ended references on p aleo-clim atolog y include RS Bradley, Paleoclimatology: Reconstructing Climate of the Quaternary, 2nd ed n , In ternational G e o p h y sics S eries, vol. 68, H arcourt A cadem ic P ress, San D iego (1999) and T h om as C row ley, Paleoclimatology, O xford U niversity Press, N ew York (1991). See also Fritts, Tree Rings and Climate, Blackburn Press, C ald w ell, N ew Jersey (reprint 1991) regardin g the u se of tree rings, and the Tree Ring Newsletter at h t t p ://w w w . treeringsociety.org. The text Quaternary Environments by M A J W illiam s and others, E d w ard A rnold, London, 2nd edn, (1998), is another excellent resource, with a detailed A p p en d ix describin g v ariou s m ethods for datin g paleoclim atic records. 2. A m ore extensive table and d iscu ssio n of p roxy clim ate in d icato rs is fou n d in the N R C (2002) book on Abrupt Climate Change (see endnote 14). 3. M igration of ancient p eop les across land bridges, and their subsequen t isolation by sea-level rise, is discussed for the A ustralian region in M ulvaney and K am m inga, Prehistory of Australia, Allen & U nw in, Sydney (1999) and M ulvaney and G olson, Aboriginal Man and Environment in Australia, A ustralian N ational University Press, C anberra (1971). See also Bird and others, Quaternary International, 118-119, pp. 145-63 (2004). M igration across the Bering Strait land bridge w as once the favoured theory for N orth A m erica, but it m ay have been by sm all b oats along the then coast, see Scientific American (Septem ber 2000) pp. 62-7. The d ispersal of people from the flooding of the Black Sea is discussed in Ryan and Pitman, Marine Geology, 138, pp. 119-26 (1997), and in Nature, 430, pp. 718-19 (12 A u gu st 2004). 4. The astronom ical theory of the glacial-in terglacial cycles is d iscu ssed in Frakes, Climates Throughout Geological Time, Elsevier, A m sterdam (1979), with key p ap ers by H ay s and others, Science, 194, p p. 1121-32 (1976), Im brie and others, Paleoceanography, 7, p p. 701-38 (1992) and 8, p p . 699-735 (1993), Shackleton, Science, 289, p p . 1897-902 (2000), R u dd im an , Quaternary Science Reviews, 22, pp. 1597-629 (2003) and EO S, 85 (6 Janu ary 2004). See also M A J W illiam s and others, Quaternary Environments, E d w ard A rnold, London (1993). 5. R u d d im an 's w ork on the role of green h ou se g a se s in the M ilankovitch theory is reported in EOS (6 Jan u ary 2004) and references therein. See also WE R u dd im an , Plows, Plagues and Petroleum, Princeton U niversity Press, Princeton (2006). 6. The IPCC 2007 estim ates of clim ate sensitivity to doub lin g of carbon dioxide concentrations arc slightly higher than in the 2001 report. Instead of the bald statem ent that the range is likely betw een 1.5 and 4.5°C , it now qu alifies this by say in g that it is very unlikely to be less than 1.5°C but could be sub stan tially higher than 4.5°C. 7. See Pittock in Revieius of Geophysics and Space Physics, 16, pp. 400-20 (1978) and in Quarterly Journal of the Royal Meteorological Society, 109, pp. 23-55 (1983). M ore recent stu dies include Th om as Crow ley in Science, 289, pp. 270-77 (2000); Judith Lean in Geophysical Research Letters, 19, p. 1591 (1992); and M eehl and others, in Journal of Climate, 16, pp. 426-44 (2003). Solar and volcanic influences are d iscu ssed in the 1PCC 2007 report, WGI, C hapters 1.4.3 and 2.7.1. 8. The role of solar variability in clim ate is also d iscu ssed in Lean and Rind, Science, 292, pp. 234-6 (2001), Philipona and Durr, Geophysical Research Letters, doi: 10.1029/2004G L020937,2004) and Lockw ood and Frohlich, 'Recent oppositely directed trends in so lar clim ate forcing and the glob al m ean su rface tem perature', Proceedings Royal Society A,

40

C L IM A T E C H A N C E : THE SC IEN C E, IM P A C T S A N D S O L U T IO N S

doi:10.1098/rspa.2007.1880 (2007). See also D am on and Lault in EOS, 85, p. 370, (28 Septem ber 2004) for a discussion of how errors have been repeated in a series of p ap ers claim ing a strong role for solar forcing. 9. P ossible clim atic effects of a m ajor nuclear w ar ('n uclear w in ter') are described in a special issu e of Ambio (Royal Sw edish A cadem y of Science), 18 (7) (1989), and in the SCO PE R eport no. 28, Environmental Consequences of Nuclear War, John Wiley and Son s, C hichester (1986). A lvarez and others in Science, 208, pp. 1095-108 (1980) d iscu ss clim atic effects of cosm ic collision s with the Earth. 10. P ossible effects of hum an em ission s lead in g to increased p articu lates in the atm osph ere and su rface cooling were d isc u ssc d by Reid Bryson and W ayne W endland in Global Effects of Environmental Pollution, Fred Sin ger (ed.), pp. 130-38, D R eidel Publishers, D ordrecht (1970) and in the Report of the Study of M an's Impact on Climate (SM IC), MIT Press, C am b rid ge, M assach u setts (1971). 11. Indirect aerosol effects w ere first d iscu sse d by Sean Tw om ey in 1977 in the Journal of Atmospheric Sciences, 34, p p. 1149-52. Effects of volcanic em issio n s are d iscu sse d in a ch apter by A lan Robock in The State of the Planet: Frontiers and Challenges in Geophysics, G eoph ysical M o n ograph 150, A m erican G eoph y sical U nion, W ashington DC, p p. 125-34 (2004). See also: R obock and O pp en h eim er (eds), Volcanism and the Earth's Atmosphere, G eoph y sical M on ograph 139, A m erican G eoph ysical U nion, W ashington DC (2003). 12. 'G lobal d im m in g' is in fact regional, not glob al, a s docu m en ted by Pinhas A lpert and co lleag u es in Geophysical Research Letters, 32, L17802 (2005). 13. A erosol effects on clim ate are d iscu sse d extensively in the IPCC 2007 report, W GI, C h apters 2.4 and 7.5. M ore recently, p o ssib le effects of aerosols, prim arily in the northern h em isph ere, on the southern hem isphere clim ate h ave been do cu m en ted in a se ries o f p a p e r s by: C ai an d oth ers, Geophysical Research Letters, 33, L21707, d o i:1 0 .1 0 2 9 /2 0 0 6 G L 0 2 7 5 1 3 (2006); R o tstay n an d o th e rs, Journal of Geophysical Research, 112, D 09202, d o i:1 0 .1 0 2 9 /2 0 0 6 JD 0 0 7 7 1 2 (2007); an d C a i an d C o w a n , Geophysical Research Letters, 34, L23709, doi:10.1029/2007G L031706 (2007). 14. R apid clim ate change even ts, including the Y ounger D ry as event, are d iscu ssed m ore fully in sections 6.4.2 and 6.5.2 of the IPCC 2007 report; a review by R Alley and others in Science, 299, p p. 2005-10 (2003); and in the U S N ational Research C ouncil report Abrupt Climate Change: Inevitable Surprises (2002). See also M C M acC racken, F M oore and JC T oppin g Jr, Sudden and Disruptive Climate Change, Earth scan , Lon d on (2008). See also 'The p h y sics of clim ate m odellin g', by G A Schm idt, in Physics Today (January 2007) p p. 72-3. 15. A d iscu ssion on the effect of clim ate change on hum an history, w ith n um erous references, is found in C h apter 7 of Pittock and others (eds), Climatic Change and Variability: A Southern Perspective, C am b rid ge U niversity Press (1978). See also: Reid Bryson and T h om as M urray, Climates of Hunger, U niversity of W isconsin Press (1977); Wigley, Ingram and Farm er (eds), Climate and History, C am b rid ge U niversity P ress (1981); L am b, Climate, History and the Modern World, M ethuen (1982); and Jon es, O gilvie, D avies and Briffa, History and Climate: Memories of the Future?, K luw er A cad e m ic/P len u m Publishing (2001). 16. H un tin gton 's book is Civilization and Climate, Yale U niversity P ress (1915). 17. See C arpenter, Discontinuity in Greek Civilization C am b rid ge U niversity P ress (1966), and L am b , 'C lim atic ch anges du rin g the course of early Greek history', in Antiquity, 42, p p. 231-3 (1968). Le Roy L ad u rie's book is Times of Feast, Times of Famine, G eorge Allen & U nw in (1971), and D ou b leday (1972). 18. D an sgaard and co lleagu es 'C lim atic ch anges, N orsem en and m odern m an ', Nature, 255, pp. 24-8 (1975). S in gh 's p ap er is in Archaeology and Physical Anthropology in Oceania, 6, p p. 177-89 (1971). 19. Pacific Islan d er and M aori m igration s are d iscu sse d by Finney in Science, 196, p p. 1277-85 (1977); W ilson and H en dy in Nature, 234, pp. 344-5 (1971); B rid gm an in Palaeogeography, Palaeoclimatology, Paleoecology, 41, pp. 193-206 (1983); and Patrick N u n n in Geoarchaeology: An International Journal, 15, p p. 714-40 (2000), Geografiska Annaler, 85B, pp. 219-29 (2003) and Asia Pacific Viewpoint, 44, p p. 63-72 (2003).

L E A R N IN G F R O M TH E PAST

41

20. See C h un C h a n g H u a n g an d c o lle ag u e s in Climatic Change, 61, p p . 361-78 (2003). 21. The A n a sa z i, a n c e sto rs o f the m o d ern P u eb lo In d ia n s o f the A m erican S o u th -w est, w ere forced to m ig ra te by d ro u gh t. See A nasazi America: Seventeen Centuries on the Road from Center Place b y D a v id S tu art, U n iv ersity of N ew M exico P ress (2000), an d review in Science, 290, pp. 941-3 (3 N o v e m b e r 2000). 22. See H a u g an d co lle ag u e s, Science, 299, p p . 1731-5 (2003). 23. See d e M e n o cal's review 'C u ltu ral re sp o n se s to clim ate ch an ge d u rin g the late H olocen e' in Science, 292, p p . 667-73 (2001); R o se n m e ier an d o th ers, Q uaternary Reviews, 57, p p . 183-90 (2002), an d referen ces therein; an d F o rem an , O glesb y and W ebb in Global and Planetary Change, 29, p p . 1-29 (2001). W ood h ou se an d O verpeck , in Bulletin American Meteorological Society, 79, p p . 2693-714 (1998), review d ro u g h t in the sa m e regio n ov er the last 2000 y ears. See a lso Trenberth an d oth ers, EO S, 85, p. 20 (Jan u ary 2004), an d references therein. 24. C a u se s of the S a h a ra n d ry in g are ex am in ed in C la u sse n an d co lle ag u e s, 'S im u latio n o f an a b ru p t ch an ge in Sa h a ra n vegetatio n in the m id -H o lo cen e', Geophysical Research Letters, 26, p p . 2037-40 (1999) an d N o b let-D u co u d re, C la u sse n an d Prentice, in Climate Dynamics, 16, p p . 643-59 (2000). 25. See W hitlock an d c o lle a g u e s in Forest Ecology and M anagem ent, 178, p p . 5-21 (2003); M ey er a n d Pierce in Forest Ecology and Managem ent, 178, p p . 89-104 (2003); an d C am p b e ll a n d C am p b e ll in Palaeogeography, Palaeoclimatology, Palaeoecology, 164, p p . 263-80 (2003). 26. Sea-level ch an ge d u rin g the p resen t in terglacial is w ell co vered in the IPCC 2007 report, W GI, C h a p ter 5.5. For m ore recent in form ation see en d n ote 14 in C h a p ter 1. 27. For v ariatio n s in regio n al se a level an d its p oten tial im p acts on ty p e s o f c o asts see IP C C 2007 report, W GI, C h a p ters 5.5.4 an d W GII, C h a p te r 6.4.1.1 a n d references therein. 28. A n u m b e r of p a p e r s h a v e co n n ected d e g la c ia tio n w ith the o n se t o f e a rth q u a k e s in clo se p ro x im ity to form er ice m a s se s . S e e R A r v id s so n , 'F e n n o sc a n d ia n e a r th q u a k e s: w h o le c ru sta l ru p tu rin g re la te d to p o stg la c ia l re b o u n d ', Science, 274, p p . 744-6 (1996); M uir-W 'ood, 'D e g la c ia tio n se ism o te cto n ic s: a p rin c ip a l in flu en ce on in trap late se ism o g e n e sis at h igh la titu d e s', Quaternary Science Reviews, 19, p p . 1399-411 (2000); S tew art an d oth ers 'G lacio-seism otecton ics: ice sh eets, cru stal d e fo rm atio n a n d se ism icity ', Q uarternary Science Reviews, 19, p p . 1367-91 (2000); a n d P W u, P Joh n ston an d K Lam b eck , 'P o stg lacial reb oun d an d fau lt instab ility in F en n o scan d ia', Geophysical Journal International, 139, p p . 657-70 (1999). 29. See S o o n an d B aliu n as, Climate Research, 23, p p . 89-110 (2003), an d reb u ttal by M ann an d o th ers in E O S, 84 (27) p p . 256-57. There is a furth er attack on the tem p eratu re recon stru ction s in F igu re 1 by M cIntyre an d M cK itrick in Energy and Environment, 14, p p . 751-71 (2003). T h is centres on the differen t selection an d correction of d ata. M an n an d co -au th ors are the re co gn ised ex p erts in this field, an d thus b e st q u a lified to m ak e the ex p ert ju d g e m e n ts on d ata q u ality an d re p re se n tativ en ess n eed ed . M an n an d Jo n e s in Geophysical Research Letters, 30 (15) p p . 1820-3 (2003) h av e exten d ed the tem p eratu re recon stru ction b ack to 2000 y ears. See other d isc u ssio n s in IP C C 2007 report, W GI, C h a p te r s 3.2 an d 6.6, an d on v a rio u s co m m e n ta ry w e b site s su ch a s th at o f the U K R o y al S o ciety at h t t p : / / ro y a lso c ie ty .o r g /p a g e .a sp ?id = 6 2 2 9 , R eal C lim a te at h ttp ://w w w .r e a lc lim a t e .o r g / an d the A u stra lia n C lim ate C h a n g e D e p a rtm e n t's 'F req u e n tly A sk e d Q u e stio n s' at h t t p ://w w w .c lim a t e c h a n g e .g o v .a u /s c ie n c e /f a q /in d e x . htm l. 30. See H a n s von Storch a n d others, Science, 306, p p . 679-82 an d co m m en t p p . 621-2 (22 O ctob er 2004); an d O sb o rn and Briffa, Science, 306, p p . 621-2 (2004). See also the d isc u ssio n in IPCC 2007 report, W GI, C h a p ter 6.6.

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3 Projecting the future

Foresight provides the ability to influence the future rather than to predict it. R ic h a r d F r e e m a n .

As we know, there are known knowns. There are things we know we know. We also know there are known unknowns. That is to say we know there are some things we do not know. But there are also unknown unknowns, the ones we don't know we don't know. D o n a l d R u m s f e l d , U S S ec r e t a r y o f D efe n se , n e w s b r ie f in g 1 2 F e b r u a r y 2 0 0 2 .

The scenarios point to both risks and opportunities in the future. O f particular significance are the risks of crossing thresholds, the potential of reaching turning points in the relationship between people and the environment, and the need to account for interlinkages in pursuing a more sustainable path. G l o b a l E n v ir o n m e n t a l O u t l o o k 4 , U N E P 2 0 0 7 .

The need for, and nature of, foresight W hile I am not a fan o f D on ald R u m sfeld , I think the quote above from one of his n ew s b riefings drew som e rather unfair lam bastin g. It su m m arises, if one concentrates on its m eaning and ap p lie s it to clim ate ch ange, so m e im po rtan t a sp e c ts o f the science of clim ate change a s well as defence policy questions. That is, there is a w hole ran ge of asp ects of clim ate ch ange, w ith som e m uch m ore certain than others. There are also uncertainties and p ossib ilities w e are aw are of, and m ay even be able to quantify in term s of risk. But, there is also a p ossib ility that there are things ab ou t clim ate that w e sim p ly do not know, and which m ay totally su rp rise us. The Intergovernm ental Panel on C lim ate C hange (IPCC) w a s form ed to p rovid e foresight in relation to the p o ssib le h u m an im pacts on clim ate, with a

view to h elping govern m ents form ulate w iser policy op tion s and decision s in relation to clim ate change. Foresight is the act or p ow er of seeing into the future, a perception gained by looking forw ard, and care or provision for the future. It is an everyd ay occurrence. Prudent p eop le use foresight to decide or p lan their actions so a s to im prove their future p rosp ects. In this sp irit g o v ern m e n ts arou n d the w o rld have recogn ised that hum an societies, through their use o f reso u rces an d w a ste p ro d u cts are cap a b le of ch anging the environm ent, including the clim ate. F o re sig h t re q u ires so m e estim ate o f fu tu re conditions. In the case of clim ate change this includes projections of future em ission s of green h ou se g ase s and p articu lates into the atm osph ere, con sequ en t concentrations of these p ollu tants in the atm osphere, and their effects on the clim ate. In addition , so a s to

44

CLIMATE CHANCE: THE SCIENCE, IMPACTS A N D SO LUTIO NS

u n d erstan d how seriou s this m ight be, estim ates are also n eed ed of the consequen ces for society in term s of poten tial im p acts on are as such as agriculture, w ater su p p ly , health and b u ild in g safety and com fort. This is com plicated by the fact that im pacts d ep en d not ju st on the stresses a p p lied by clim ate, bu t also on the strength and adap tab ility of society. This requires an u n d erstan d in g of how ch an ges in society w ill affect its capacity to absorb or a d a p t to

p red ictio n is m a d e, an d a ssu m p tio n s a s to the p h y sical or other p ro ce sses that w ill lead to change. Such p rediction s are seldom certain b ecau se present

clim atic stress. There are other co m p lica tin g facto rs in any

u n ce rta in tie s d u e to in ex act o b se rv a tio n s an d w e a th er m o d e ls. Th ey are often e x p re sse d in p robabilistic term s, such a s 'There is a 60% chance of rain tom orrow '. A scen ario is a p la u sib le d e scrip tio n o f so m e future state, with no statem en t of probability. It is

attem pt to project the future, n am ely non-linearities an d th resh olds. N on -lin earities are w hen ste ad y in p u ts to a sy stem cau se u n ste a d y o u tp u ts. For exam ple, stead y effort to p u sh a bicycle up a stead y hill g iv es easily predictable p rogress, b u t if the slope ch an g e s, and e sp e cia lly if the top of the hill is reached, rap id ch an ges in the b icycle's p ro gre ss can occur. Sim ilarly , if a flood is risin g re su lts are pred ictable until it reaches the top of a levee bank, w hen o v e rto p p in g m ay ero d e the levee, ca u sin g it to co llap se, an d a co n seq u en t d isaster. Sim p le extrap olatio n is n ot go o d en ou gh . P red iction s of w hat w ill h ap pen m u st take such irregularities and th re sh o ld s in the sy stem into accoun t. We w ill d isc u ss this further in the context of clim ate change in C h apter 5. There are, as view ed from the p resen t, m any

co n d ition s are often not know n precisely, and the p ro c e sse s affectin g the fu tu re are n ot p erfectly u n d ersto o d . P red iction s are th u s b est e x p re sse d with p robabilities attached. D aily w eath er forecasts are 'p red iction s' in this sen se - they are p rediction s o f w h at the w e a th er w ill be lik e, b u t h av e

u se d to enable p eo p le to explore the qu estion 'W hat if su ch an d such w ere to h a p p e n ?' Scen ario s are often u sed in literature to stretch the im agin atio n , an d in creasin gly in b u sin e sse s an d gov ern m en t to help to d evelo p a ran ge of strategies or contingency p lan s to cope with p o ssib le ch an ges in b u sin e ss or other conditions. Scen arios are altern ative p ictu res of how the future m igh t develo p. They are u sed to a sse ss con sequ en ces, and thus to p ro v id e a b a sis for policies that m igh t influence future develo pm en ts, or en able b u sin e sse s or gov ern m en ts to cope w ith

w e fo re se e the fu tu re

the future situation if an d w hen it occurs. E xam ples m igh t in clu d e b u sin e sse s p la n n in g for v a rio u s p o ssib le future d evelo pm en ts like a new com petitor,

p o ssib ilitie s, an d the c o n scio u s or u n co n scio u s choices w e m ake that w ill influence develo pm en t of society, w ill help determ in e w hich of the p o ssib le fu tu res w ill actu ally occur. The p u rp o se , from a

a fire, or a failu re of the electricity su p ply . N o one kn ow s w hen or if these contingencies or scen ario s m ay h ap pen , bu t the b u sin e ss n eed s p la n s in place to en sure su rv iv a l if they do happen.

p o ss ib le fu tu res. H ow

policy p ersp ectiv e, is not to p red ict w hich of the p o ssib le futu res will occur, but rather to inform u s so that w e m igh t choose which one w e w o u ld prefer and attem pt to brin g to reality.

Predictions, scenarios and projections P eop le are often co n fu sed by v a rio u s term s u sed to ch aracterise fu tu re clim ate ch a n g e s, n am ely 'predictions', 'scenarios' and 'projections'. A prediction is a statem ent that som eth in g will h ap pen in the future, b ase d on know n con d ition s at the tim e the

P rojectio n s are se ts o f fu tu re co n d itio n s, or con sequ en ces, b a se d on explicit a ssu m p tio n s, such a s scen arios. For exam ple, in the case of a b u sin e ss faced w ith lo ss o f p ro d u ctio n d u e to a fire, how m uch p rodu ction w o u ld be lost, how soon can it be recovered, and how w ill it affect contracts and the solven cy of the co m p an y ? Even for a given scenario or set o f a ssu m p tio n s, projections introduce further u n certain ties d u e to the u se of in exact ru les or 'm o d e ls' connecting the scen ario conditions to the p rojected o u tco m es. T h u s, a clim ate m o d el can project the future clim ate b a se d on a given scenario

PROJECTING THE FUTURE

45

for fu tu re g re e n h o u se g a s e m issio n s, a n d a crop

p ro p h ec ie s: if h igh em issio n s d e m o n strab ly lea d to

m o d e l m a y p ro je ct h o w th is w o u ld affect y ield .

d is a s t r o u s im p a c ts, th ey m a y w ell be a v o id e d

Su ch projectio n s are co n d ition al on the scen ario an d

th rough policy se ttin g s aim ed a t low erin g em issio n s.

the m o d e ls u sed .

T h is w o u ld b e the lo g ica l o u tco m e o f a p ro p e r an d

A key issu e in p rojectin g the fu tu re on the b a sis

w ell-in form ed risk -m a n a g e m e n t strategy.

o f a scen ario is the p la u sib ility o f the scen ario . If a sc en ario is not p la u sib le it is n ot w o rth w o rry in g a b o u t in settin g policy, b u t if it is p la u sib le w e m ay

The emissions scenarios used by the IPC C

n eed to take its p o ssib ility into accou n t. Sce n ario

In o rd e r to p ro v id e p o lic y -re le v a n t a d v ic e on the

p lau sib ility h a s se v e ra l elem en ts: that the scen ario

co n se q u e n ce s o f h u m a n -in d u c ed clim ate ch an g e in

m u st b e lo g ic a lly , p h y sic a lly , b io lo g ic a lly , a n d

the tw en ty -first century, the IP C C c o m m issio n e d a

h isto rically p o ss ib le .1

ra n g e o f sc e n a rio s o f g re e n h o u se g a s a n d su lfa te

P la u sib le sc e n a rio s are u se fu l for a sk in g 'W hat

a e r o so l e m is s io n s u p to the y e a r 2100. T h e se

if ...' q u e stio n s, a n d th u s for h e lp in g to m ak e p o licy

e m issio n sc e n a rio s w ere d e v e lo p e d b y a p a n e l of

ch o ices th at m ay in flu en ce w h ich o f the 'w h a t ifs'

a u th o r s, w ith w id e c o n su lta tio n , a n d an o p en

a c tu a lly c o m e s to p a s s . In the c lim a te c h a n g e

p r o c e ss o f re v iew an d c o m m e n t b y e x p e r ts an d

co n te x t th ey a re u se fu l fo r in flu e n c in g p o lic y

g o v e rn m e n ts, fo llo w e d b y s u b se q u e n t re v isio n s.

r e g a r d in g the n e e d to re d u c e g r e e n h o u se g a s

Th e sc e n a rio s w ere re p o rte d in the 'S p e c ia l re p o rt

em issio n s. If re d u cin g g re e n h o u se g a s e m issio n s is

on e m issio n s sc e n a rio s' (SR E S), p u b lish e d in 2000.

costly, the u rg e n c y a n d exten t o f su ch re d u c tio n s

T h ey w e re in te n d e d to fe e d in to p ro je c tio n s o f

d e p e n d s n ot ju st on the p o ssib ility o f a sc e n a rio ,

c lim a te c h a n g e in the Third A ssessm ent Report in

b u t a lso on its p ro b a b ility . T h e p ro b a b ility o f

2001, an d to en a b le a d is c u s sio n o f the p o ten tia l

p ro jectio n s b a se d on g iv e n sc e n a rio s is th erefore a

im p a c ts, a d a p ta tio n s an d v u ln e ra b ility o f se cto rs,

le g itim a te is s u e .2

re g io n s a n d co u n trie s.3

E ven in the a b se n c e o f e stim ate d p ro b a b ilitie s,

F u tu re e m is sio n s are the p ro d u c t o f co m p le x

sc e n ario s are a lso o f u se in relation to a d a p ta tio n

in teractin g sy ste m s d riv e n b y p o p u la tio n ch an ge,

policy (that is, how to co pe w ith u n a v o id ab le clim ate

so cio -e co n o m ic d e v e lo p m e n t, a n d te c h n o lo g ica l

ch an ge) in that they su g g e s t w h at co n d itio n s w e

ch an ge. All o f w hich are h igh ly u ncertain , esp e cially

m igh t n eed to a d a p t to in futu re. Scen ario s h elp u s

w h en ex te n d ed a s far a s the y e a r 2100.

to a n ticip a te w h a t so rt o f a d a p ta tio n s m ig h t be

T h e o r ig in a l 40 S R E S s c e n a r io s w e re b a s e d on

n e e d e d , a n d to id e n tify the n eed fo r in c re a se d

fo u r d iffe re n t 's to r y lin e s ' o f in te r n a lly c o n siste n t

resilien ce (c a p a city to b o u n c e b ack ) a n d a d a p tiv e

d e v e lo p m e n t s a c r o s s d if f e r e n t d r iv in g fo r c e s

cap acity (cap acity to a d a p t to ch an ge). H ow ever, in

(se e B o x 3), a n d m u ltip le m o d e llin g a p p r o a c h e s .

o rd e r to a n sw e r sp e c ific p la n n in g q u e stio n s like

T h is led to a red u ced total o f 35 sc en a rio s co n tain in g

'H o w la rg e sh o u ld the sp illw a y o f a n ew d a m at

d a ta on all g a s e s re q u ired to force clim ate m o d els.

lo catio n x be in o rd e r to co p e w ith the m a x im u m

R esu ltin g acc u m u la te d e m issio n s by 2100, ex p re sse d

p o ssib le flood at that location in 2070?' it is n ecessary

in u nits o f th o u sa n d s o f m illion s o f ton n es of carbon

to know m ore than th at a g iv en ch an ge in rain fall is

e q u iv a le n t (G tc) ra n g e from a low o f 770 G tc to

possible. R ath er, the probability o f su ch a ch a n g e

a p p ro x im a te ly 2540 Gtc. T h is ra n g e co m p a re s w ith

n e e d s to be k n o w n , sin ce e x p e n siv e en g in e e rin g

p r e v io u s IP C C p ro je c tio n s from 1992 a n d 1995

d e sig n n e e d s to b e b a se d on co st-e ffe ctiv e risk

(b a se d on w h a t is k n o w n a s the IS92 sc e n a rio s),

m in im isation .

w hich ran g e from 770 to 2140 G tc, so the u p p e r end

C lim a te c h a n g e p ro je c tio n s b a s e d on h igh -

o f the S R E S p rojected ran ge w a s greater than b efore.

e m is sio n sc e n a r io s fo r g r e e n h o u se g a s e s m ay,

A ccu m u la te d e m issio n s are an im p o rtan t in d icato r

h o p e fu lly, b e seen in re tro sp e c t a s se lf-d e n y in g

o f e v e n tu a l clim atic effe cts b e c a u se the effectiv e

46

CLIMATE CHANCE: THE SCIENCE, IMPACTS A N D SO LUTIO NS

BO X 3: THE SRES E M IS S IO N S S C E N A R IO S A1. The A1 storyline and group of related scenarios describe a future world of very rapid econom ic growth, global population that peaks in mid-century and declines thereafter, and the rapid introduction of new and more efficient technologies. Major underlying themes are convergence am ong regions, capacity building and increased cultural and social interactions, with a substantial reduction in regional differences in per capita income. The A1 group scenario is split into three groups that describe alternative directions of technological change in the energy system. The three A1 groups are distinguished by their technological emphasis: fossil intensive (AT FI), non-fossil energy sources (A1T), or a balance across all sources (A1 B) (where balanced is defined as not relying too heavily on one particular energy source, on the assumption that similar improvement rates apply to all energy supply and end-use technologies).

A2. The A2 storyline and group of scenarios describe a very heterogeneous world. The underlying theme is selfreliance and preservation of local identities. Fertility patterns across regions converge very slowly, which results in continuously increasing population. Economic development is primarily oriented to particular regions and per capita econom ic growth and technological change more fragmented and slower than other storylines.

B1. The B1 storyline and group of scenarios describe a convergent world with the same global population that peaks in mid-century and declines thereafter, as in the A1 storyline but with rapid change in econom ic structures toward a service and information economy, with reductions in material intensity and the introduction of clean and resource-efficient technologies. The emphasis is on global solutions to economic, social and environmental sustainability, including improved equity, but without additional climate initiatives.

B2. The B2 storyline and group of scenarios describe a world in which the emphasis is on local solutions to economic, social and environmental sustainability. It is a world with continuously increasing global population, at a rate lower than A2, intermediate levels of econom ic development, and less rapid and more diverse technological change than in the A1 and B1 storylines. W hile the scenario is also oriented toward environmental protection and social equity, it focuses on local and regional levels. Source: IP C C 2001 W o rk in g G ro u p I, B o x 4 of Technical Summary.

lifetim e of carbon d io x id e in the atm osp h ere is so lon g that this figure largely determ in es ev en tu al carbon d io x id e co n cen tration s an d the resu ltin g global w arm in g. C o r r e s p o n d in g

p ro je c te d

c a rb o n

d io x id e

concentration s for the illu strative scen ario s in the y ear 2100 ran ge from 540 to 970 p p m , that is, rough ly 2 to 3.5 tim es pre-in du strial levels. A s the scen ario s only w ent to 2100 and concentrations had not stabilised by then, stab ilised concentrations are likely to be w ell in excess of these n um bers.

The SR E S scen ario s in clu de estim ated e m issio n s o f carb o n d io x id e , m eth an e, n itro u s o x id e an d su lfu r d io x id e . G e n e rally , the S R E S e m issio n sc e n a rio s contain h igh er u p p e r lim its on carbon d io x id e e m issio n s, b u t low er e m issio n s o f su lfu r d io x id e than the p re v io u s IS92 sc e n a rio s. The h ig h e r u p p e r lim it carb o n d io x id e e m is sio n s w o u ld in crease the u p p e r lim its of g lo b a l w arm in g d u e to in creased in fra-red a b so rp tio n , but a large p art of the in crease in w arm in g relative to earlier sc e n a rio s co m es from the lo w er su lfu r d io x id e

PROJECTING THE FUTURE

e m issio n s, w h ich le a d to re d u c e d re g io n a l c o o lin g

47

ch an ge ov er the next 100 y ears, bu t are m o st unlikely

b y su lfa te a e r o so ls in h ig h ly in d u s tr ia lise d re g io n s

to alter the m ain co n clu sio n s that sign ifican t clim ate

su ch a s E u ro p e , the U n ited S ta te s a n d so u th e rn

ch an g e is likely to occur, w ith sig n ifica n t im p a c ts.

an d eastern A sia. E x p lic it p o lic y o p tio n s to re d u c e g re e n h o u se

Th e S R E S e m issio n s p ro jectio n s w ere d ra w n from the p u b lish e d lite ra tu re , a n d co n siste n t w ith it,

e m issio n s, su ch a s m ig h t b e a d o p te d u n d e r the

in c lu d in g se v e ra l m o re recen t s tu d ie s th at u se d

U n ited N a tio n s F ram e w o rk C o n v en tio n on C lim ate

m o re so p h istic a te d m o d e ls than w ere a v a ila b le at

C h a n g e (U N F C C C ), w ere e x c lu d e d from the SR E S

the tim e the S R E S sc e n a rio s w ere d e v e lo p e d .

sc e n a rio s. H o w e v e r, o th e r so c io -e c o n o m ic an d

The IPCC 2007 report a d o p ts the SR E S sc en a rio s

tech n ological tren d s co n sid ere d by the SR E S lead in

(see C h a p te r 10.2 o f W GI) b u t d o e s n ot m o d e l in

so m e c a se s to co n sid erab le re d u ctio n s in g reen h o u se

d e ta il the o u tc o m e s o f the A 1 F I or fo s sil fu el

g a s a n d / o r su lfu r e m issio n s. T h ese sc en a rio s w ere

in te n siv e sc e n a rio s. A lth o u g h n o e x p la n a tio n is

all ch aracterised by the S R E S a s 'p la u sib le ', b u t no

g iv e n fo r th is o m issio n , it is ev id e n tly in p a r t a

furth er e stim ate s o f p ro b ab ility w ere a ttach ed , an d

re sp o n se to the criticism o f A 1FI a s an 'ex trem e' or

in d ee d e stim a te s o f p ro b a b ility w o u ld b e d ifficu lt

u n realistic scen ario .

to d e riv e w ith an y con fiden ce. Th ey are clearly not p re d ic tio n s, an d d o n ot h a v e e q u a l p ro b a b ility of occurren ce in the real w o rld .

H o w e v e r, e s t im a t e s

and

m e a s u r e m e n ts

of

g re e n h o u se g a s e m is sio n s a n d ca rb o n d io x id e co n ce n tratio n s in the a tm o sp h e re , d o cu m e n te d by

Som e critics, m ain ly statistical econ om ists, argu ed

S tefa n R a h m sto rf a n d o th e rs in 2007, sh o w that

on tech n ical g ro u n d s , re late d to how cu rren cy

sin ce 1990 (the sta rtin g d a te for the S R E S scen ario s)

exchan ge rates betw een countries are calculated, that

em issio n s an d co n cen tration s h a v e been at or a b o v e

the h igh e m issio n s sc e n a rio s w ere u n re alistic.

the h igh est o f the SR E S sc en a rio s, the A 1FI or fossil

H ow ever, carbon dioxide em ission s are related, in the

fu e l in te n siv e sc e n a rio . In d e e d , g lo b a l a v e r a g e

final an aly sis, sim p ly to p o p u latio n , en ergy u se p er

te m p e ra tu re s a n d se a -le v e l rise h a v e a lso rise n

capita an d carbon d ioxide em issio n s p er unit energy.

faster sin ce 1990 than that calcu late d on the b a sis of

T h us the u se of different exchan ge rates in m easu rin g

all b u t the h ig h e st o f the S R E S s e n a r io s .5 M ik e

g r o ss d o m e stic p ro d u c t m a k e s no d ifferen ce to

R a u p a c h o f C S IR O , A u s tr a lia , n o te s (p e r so n a l

calcu late d e m issio n s in each in d iv id u a l country.

co m m u n ica tio n ) that the 50-y ear a v e ra g e gro w th

W hether or n ot it m a k e s any differen ce g lo b ally

rate for carb o n d io x id e e m issio n s to 2050 u n d er the

d e p e n d s on how the nation al figu res are com bined to

A 1 F I sc e n a rio is 2.4% p e r a n n u m , w h e re a s the

get global on es, that is, w hether the add ition is don e

o b se rv e d g ro w th rate from 2000 to 2006 w a s 3.3%

before or after em issio n s are calcu lated . N atio n al

p er an n u m .

e m issio n s d e p e n d on n ation al en ergy u se an d the

A s a n u m b e r o f p a p e r s h av e sh o w n , the re a so n s

carbo n p er u nit energy, not on how the n ation al

for th is are se v e ra l. T h ey in c lu d e fa ste r ra te s of

econom y is m e asu red .4

g ro w th o f the e c o n o m ies o f d e v e lo p in g co u n trie s,

In an y case, the critics m iss the real poin t, w hich

e sp e cia lly C h in a a n d In d ia, than m an y e c o n o m ists

is that the S R E S sc e n a rio s are n ot p re d ic tio n s, b u t

th o u gh t p o ssib le . T here h a s a lso been a re v ersa l in

m e rely a p la u sib le ra n g e o f e m is sio n s, u se d to

the d o w n w a rd trend in e m issio n s p er u nit econ om ic

bound

g ro w th ('c a rb o n in te n sity ') sin ce 2000, a n d an

d is c u s s io n

o f c lim a te c h a n g e im p a c ts.

M o reover, the clim ate m o d e ls u se d to p ro d u c e the

in crease in the fraction o f em issio n s that sta y in the

p rojection s o f clim ate ch an ge that u n d erlie the IPC C a sse ssm e n t are d e v e lo p e d a n d v a lid a te d se p a ra te ly

atm o sp h ere (the 'airb orn e fraction ') d u e to d e cre ase s

from the e m issio n s scen ario s. A n y re -a sse ssm e n t of

V icto ria

the ra n g e o f the SR E S sc en ario s m ay affect the u p p e r

e stim ate s that, w ith u n ch a n g e d p o lic ie s, g lo b a l coal

a n d / o r lo w e r b o u n d s o f the p ro je c te d clim a te

u se w ill rise by n early 60% o v er the d e ca d e to 2010

in the n a tu ra l ca rb o n sin k s. P eter S h e e h a n o f U n iv e r sity

in

M e lb o u r n e , A u s tr a lia ,

48

CLIMATE C H A N C E: THE SCIENCE, IMPACTS A N D SO L U T IO N S

a n d th at g lo b a l e m issio n s o f carb o n d io x id e from

lan d clearin g an d b u rn in g o f stu b b le. Su ch em issio n s

fo ssil fu el co m b u stio n are lik ely to n early d o u b le

h ave

their 2000 lev el by 2020. T h is e x c e e d s the IP C C

se a s o n a lly

fossil fuel in ten sive sc en a rio .5 Th e g lo b al econ om ic

sig n ifica n t re g io n a l su rfa c e w a rm in g effects. A ny

crisis o f 2008 m a y ch an ge this picture.

in crease in w ild fires m ay in crease this effect.

sh o rt

life tim e s

in th e a tm o s p h e r e , b u t

th ey ca n b e la rg e a n d

m ay h ave

E m is sio n s o f ch e m ic a ls, m a in ly su lfu r d io x id e

A n o th er facto r is the effect o f lan d cle a rin g ,

a n d h y d ro g e n su lfid e from the b u rn in g o f fo ssil

fa rm in g a n d irrigatio n on a b so rp tio n or reflection

fu e ls, le a d to the fo rm a tio n o f su lfa te a e r o so ls ,

o f su n lig h t at the la n d su rfa c e . A g a in , th is v a rie s

w h ich h a v e a lo c a lise d c o o lin g e ffe ct a n d a lso

re g io n a lly , b u t is in g e n e ra l o n ly im p o rta n t in

c a u se u rb an air p o llu tio n an d acid rain. H istorically,

lim ite d a re a s o f the co n tin en ts. Its m ain effect is

su ch e m issio n s h a v e b een co n cen trated in the larg e

on local su rfa c e h e atin g a n d the effect o f this on

in d u str ia l re g io n s o f the U n ited S ta te s, E u ro p e an d

c u m u lu s c o n v e c tio n , a lth o u g h

so u th e rn a n d ea ste rn A sia . Th e re su ltin g lo c a lise d

d o w n w in d e ffe cts on the w e a th e r if the area

c o o lin g h a s c o u n te ra c te d or m a s k e d so m e o f the

con cern ed is large. C lim ate m o d e l calcu latio n s h av e

w a r m in g

gas

fo u n d that this effect m a y b e im p o rta n t w h ere large

c o n c e n tr a tio n s in an d im m e d ia te ly d o w n w in d

forest are as are b ein g cleared , su ch a s in the A m a z o n

due

to

in c r e a s in g

g re en h o u se

th is can

h ave

o f th ese re g io n s. H o w e v e r, it h a s b ee n re la tiv e ly

B asin , an d id e ally it sh o u ld be in c lu d e d in clim ate

e a s y to re d u c e th e se a e r o so l- fo rm in g e m is sio n s

ch an ge sim u la tio n s. L an d clearin g can in g e n e ral be

b y the u se o f lo w - su lfu r fu e ls a n d sc ru b b in g o f

rev ersed in m o st a re as, an d in d ee d so m e fa rm la n d s

the c o m b u stio n fu m e s. T h is is w e ll u n d e r w a y in

in d e v e lo p e d co u n trie s h a v e recen tly re v erte d to

the U n ited S ta te s a n d E u ro p e, b u t n o t to the sa m e

fo re sts. S c e n a rio s o f la n d -u se c h a n g e are b e in g

exten t in so u th e rn a n d eastern A sia . SR E S sc e n a rio s

d e v e lo p e d in co n su ltatio n w ith the IP C C .

p roject co n tin u in g re d u c tio n s in a e r o so ls in N orth

Irrig a tio n a lso a ffe c ts su rfa c e clim ate v ia the

A m e ric a a n d E u ro p e , a n d a lso in A sia in co m in g

co o lin g effect o f e v a p o ratio n , an d a lso by injecting

d e c a d e s.

m o istu re into the atm o sp h ere . But a g a in , the a re as

The re su lt o f th ese c h a n g e s in su lfu r e m issio n s

are relatively sm a ll, e sp e cia lly in c o m p a riso n w ith

a n d a e r o so l le v e ls is th at the m a s k in g effe ct

the area o f the o c ea n s, so they h a v e little effect on

on e n h a n c e d

g r e e n h o u se w a r m in g is r a p id ly

large area an d g lo b a l w ater b u d g e ts. C lim atic effects

d is a p p e a r in g o v er N orth A m erica an d E u ro p e, a s

o f irrigatio n are e sse n tia lly local. M oreo ver, w h ile

seen in recent record w arm th in th ese re g io n s. A

e v a p o ra tio n h a s a local co o lin g effect, it re su lts in

sim ila r effect is ex p e c te d to o ccu r later o v e r A sia ,

laten t h eat b e in g tra n sp o rte d e lse w h e re in the

a n d is on e re aso n for a p rojected in crease in the rate

a tm o sp h ere , an d it is re le a se d a s se n sib le h eat (that

o f g lo b a l w a rm in g . T h is is on e re a so n w h y the

is, h e a t felt a s a h ig h e r te m p e r a tu r e ) w h ere

re su ltin g p ro je cted g lo b a l w a rm in g in the IP C C

c o n d en satio n occu rs.

2001 an d 2007 re p o rts are larger than in the Second

T h e IP C C 2007 re p o rt c o n sid e rs the effe cts o f

A ssessm en t Report in 1995, w h en a le s s ra p id

clim ate ch an ge on the g lo b a l carb on cycle that lead

red u ctio n in su lfu r e m issio n s w a s exp ected .

to the lan d b io sp h e re an d the o cean s both tak in g u p

im p a c t on

le ss carb o n d io x id e than if th ese effects are ign o red .

p ro jectio n s h av e n ot been taken into acco u n t in the

F or the A 2 e m issio n s sc en a rio in the m id d le o f the

SR E S sc e n a rio s, a s is e v id e n t from the d isc u ssio n

S R E S ra n g e the fe e d b a ck o f clim ate ch an g e on the

S e v e r a l o th e r f a c to r s th at m a y

a b o v e re g a rd in g the A 1FI sc e n a rio , w h ich m u st

carb o n cycle le a d s to an a d d itio n a l 20 to 220 p a r ts

n ow be c o n sid e re d m o d e ra te rath er than extrem e

p er m illion o f carb o n d io x id e in the atm o sp h ere by

u n le ss e m issio n s reduction policies are im p le m e n te d .

2100 d e p e n d in g on the m o d e l. T h is m e a n s that

O ther facto rs in clu d e the e m issio n o f carb o n b lack

g lo b a l w a rm in g w ill be g re a te r than w ith the

p article s, larg e ly from o p en fires su ch a s w ild fires,

sta n d a rd sim u la tio n s for a giv en em issio n s scen ario ,

PROJECTING THE FUTURE

49

an d that gre ater e m issio n s redu ctio n are requ ired to

p ro g re ss. L o cal v u ln e ra b ility m ay be lin k ed w ith

a c h ie v e the sa m e sta b ilis a tio n le v e l o f ca rb o n

in tern atio n al co m p e titio n a n d co m m o d ity p rices,

d io x id e in the atm o sp h ere .

w h ich

It a lso d is c u s se s the effect o f acid ification of the o c e a n s by in c re a sin g carb o n d io x id e a n d that this

in

turn

m ay

be

a ffe c te d

by

ch an ges

elsew h ere. Id e a lly ,

so c io - e c o n o m ic

s c e n a r io s

u se d

to

w ill p ro b a b ly re d u ce the ca p a city o f the o c ea n s to

e stim a te fu tu re e m is sio n s o f g re e n h o u se g a s e s

a b so rb ca rb o n d io x id e , a s w ill a slo w d o w n in

sh o u ld b e u se d at the local or re g io n a l sc a le a s the

vertical m ix in g in the o c ea n s a s the su rfa ce w a rm s

b a s is fo r c o n siste n t e s tim a te s o f e x p o s u r e an d

faster than the d e ep w ater. T h ese latter effects h av e

a d a p tiv e capacity. Th e SR E S sc e n a rio s con tain su ch

not yet been fully q u a n tifie d .6

d a ta at a b ro a d re g io n a l lev e l, fo r e x a m p le in 13 w o rld re g io n s for sc e n a rio s A l , B1 a n d A 2 an d 11 re g io n s for scen ario B2, a lth o u g h these d a ta h av e

Projections of socio-econom ic futures

n o t b ee n w id e ly u s e d in im p a c t st u d ie s . It is

A n im p o rta n t c o n sid e ra tio n in e stim atin g p o ten tia l

c o m p lic a te d , h o w ev er, b y the fact th at d iffere n t

im p a c ts o f clim ate ch a n g e is the fu tu re e x p o su re of

g lo b a l so c io - e c o n o m ic sc e n a r io s m a y

p o p u la tio n s, h u m a n s y s te m s an d e c o sy s te m s to

sim ila r m a g n itu d e s o f clim ate ch an ge g lo b a lly an d

clim a tic a lly in d u c e d str e ss e s , a n d the c a p a c ity o f

re g io n a lly b u t w ith d iffere n t re g io n a l e x p o s u r e s

th ose so e x p o s e d to a d a p t to the stre sse s. W ith the

a n d a d a p tiv e cap acities.

le a d

to

n o tab le ex c ep tio n o f the U K F a st Track p roject, this

The g lo b a l S R E S so cio-eco n om ic sc e n a rio s h av e

h a s b ee n la rg e ly n e g le c te d , w ith o n ly the m o st

b een re d u ced to a n atio n al scale b y S tu a rt G affin for

g e n e ra l c o m m e n ts on lik e ly c h a n g e s in e x p o su re

the U n ited S ta te s an d W olfgan g L u tz for A u stria .

an d the ca p a c ity o f so c ie tie s to a b so rb or a d a p t to

A d d itio n ally , the U K F ast Track p roject w ent on to

clim ate c h a n g e s.7 F o r e x a m p le , se a -le v e l rise a n d

p ro d u ce finer resolu tion d a ta at a su b -n atio n al scale

sto rm s u r g e s are lik e ly to c a u se m o re d a m a g e

in o rd e r to e stim a te a n d m a p g lo b a l im p a c ts of

in

p a r tic u la r

p o p u la t io n s

lo w - ly in g and

c o a s ta l

in v e stm e n ts

zon es

are

w h ere

te n d in g

to

c lim a te ch a n g e on a n u m b e r o f in d u s tr ia l an d so cie ta l se cto rs. H o w ev e r, d o w n sc a lin g w a s often

in c rease m o st rap id ly . W ealth v e r s u s p o v e rty a lso

b a se d on a ss u m e d u n ifo rm b e h a v io u r a c ro ss each

a ffects a d a p tiv e cap acity , for e x a m p le , the c a p a city

n ation . G enerally, the so cio-eco n om ic d a ta h a v e not

to p a y for a d e q u a te p ro te c tiv e se a w a lls or le v e e s

b een p ro v id e d at the sp a c e sc a le s a p p ro p ria te to

fo r p ro tec tio n a g a in st flo o d s, a s in N e w O rle a n s in

sp ecific re g io n s that m a y b e at risk , fo r e x a m p le ,

2005.

e s tim a te s o f v u ln e ra b ility a n d a d a p t a b ilit y to

A s sta te d by E d w a rd P a rso n s a n d co lle a g u e s in

sea-level rise on ra p id ly d e v e lo p in g co asta l strip s in

referen ce to the 2001 U S N a tio n a l A sse ss m e n t of

the so u th -eastern U S, so u th -eastern C h in a or n orth ­

P oten tial C o n se q u e n c e s o f C lim a te V ariability an d

eastern A u stra lia .

C h a n g e , co n stru ctin g so cio-eco n om ic sc en a rio s for

In the c a se o f co asta l e x p o su re to se a-le v el rise

im p act a sse ssm e n t is m ore c o m p lex an d ch allen gin g

an d storm su rg e s, e x istin g tren d s m ak e it reaso n ab le

than co n stru c tin g sc e n a rio s o f fu tu re e m is sio n s.8

to a ss u m e g re a te r g ro w th ra tes in p o p u la tio n an d

E m issio n s sc e n a rio s req u ire on ly a few n ation al-

in v e stm e n t in c o a s ta l a r e a s th a n

level ch a ra cteristics su ch a s p o p u la tio n , econ om ic

a v e ra g e s . T h is a ffe cts n ot o n ly the e x p o su re , b u t

gro w th , total en ergy u se , an d carbon em issio n s p er

a lso the rate o f lo ca lised sea-lev el rise, sin ce gre ater

u n it e co n o m ic o u tp u t. H o w ev e r, so cio -eco n o m ic

co asta l p o p u la tio n s tend to w ith d raw m ore g ro u n d

d e te rm in a n ts o f v u ln e ra b ility a n d a d a p ta tio n to

w ater, le a d in g to g re ater local su b sid e n c e.

in n a tio n a l

clim ate ch an g e can b e v ery lo c a lise d , m a y n ot be

Scen ario s o f futu re p o p u latio n ch an ge s are w ell

o b v io u s, a n d in teract stro n g ly w ith oth er facto rs

d o cu m en ted b y b oth the U n ited N a tio n s a n d the

su c h a s s o c ia l o r g a n isa tio n a n d te c h n o lo g ic a l

In ternational In stitute o f A p p lie d S y ste m s A n a ly sis

50

CLIMATE C H A N C E: THE SCIENCE, IMPACTS A N D SO L U T IO N S

(IIA SA ), alth o u gh the U N stu d ie s tend to be b ro ad

in other a re as w ill also clearly affect so cietal cap acity

scale. They w ere d o w n sca led to the n ation al level b y

to a d a p t. B u t in all fo u r sc e n a rio s a tm o sp h e ric

IIA SA . There is a convenient d iscu ssio n entitled 'The

carb o n d io x id e co n ce n tratio n s are still in c re a sin g

end of w orld p o p u latio n gro w th ' by W olfgang Lu tz

an d se a-le v el rise is still acceleratin g in 2050. T h u s

of IIA SA , w hich su g g e sts that g lo b al p o p u latio n is

one of the m o st sign ifican t le sso n s d ra w n from the

likely to p e a k in the tw enty-first century, w ith early

scen ario exercise b y the a u th o rs is that m u ch o f the

declines in m an y d e v e lo p e d coun tries, b u t continued

en v iro n m en tal ch an ge th at w ill occur o v er the n ext

gro w th m ain ly in the p o o re st coun tries o f A frica and

se v e ra l d e c a d e s h a s a lre a d y been se t in m o tion by

south ern A sia until later in the century. Joel C ohen of

p a st an d cu rren t action s. N e v e rth e le ss, the a u th o rs

R o ck efe lle r U n iv e rsity a lso p ro je cts p o p u la tio n

c o n clu d e that: 'the sc e n a rio s clearly illu stra te that

trends until 2050, an d e m p h asise s the im portan ce of

the fu tu re that w ill u n fo ld in the lon g-term w ill be

m igratio n from the p o o rer to the richer co u n tries.9

v e ry d e p e n d e n t on the d e c isio n s in d iv id u a ls a n d

M igration is d isc u sse d a g a in in C h a p ters 6 an d 10,

so ciety m ak e to d ay '.

w h ere w e co n sid er the p oten tial im p a c ts o f clim ate

S o m e id e a o f fu tu re e x p o s u r e a n d a d a p tiv e

ch an ge, an d esp e cia lly sea-level rise, on m igratio n

c a p a c ity co u ld b e b a se d on v a rio u s sc e n a rio s of

for econ om ic and en viron m ental reason s. T h e U n ited N a tio n s E n v iro n m e n t P ro g ra m m e

re g io n a l p o p u la tio n g ro w th a n d so cio -eco n o m ic co n d itio n s con tain ed in v a rio u s fore sigh tin g stu d ie s

h a s p u b lis h e d a se rie s o f G lo b a l E n v iro n m e n t

a lr e a d y

O u tlo o k s. Th e late st, p u b lish e d in 2007, lo o k s at

sto ry lin e s o f the g lo b a l SR E S sc e n a rio s n eed to be

e n v iro n m e n ta l c h a n g e a n d re la te d p o lic ie s a n d

b orn e in m in d w hen a ss e s sin g likely e x p o su re and

p r o v id e s an o u tlo o k u p to 2050. It ta k e s fo u r

a d a p tiv e cap acity at the local level.

c o n trastin g so cio-eco n om ic scen ario s: •

m a rk e ts first, in w hich m o st o f the w orld a d o p ts the v a lu e s an d ex p ec tatio n s p rev a ilin g in to d a y 's in d u stria lise d co u n tries,

•

p o licy first, w h ere d e cisiv e in itiativ es are taken

the b r o a d

It m a y b e m o re re le v a n t for m a n y local or e con om ic d e v e lo p m e n t in that country. T h ese m ay c a p tu re so m e o f the relev an t d e ta il a b o u t in tern al sh ift s

in

g r o w th

p a tte rn s,

an d

c o m m u n ity

d e p e n d e n c e on local in d u s tr ie s, w h ich m a y be

b y go v e rn m e n ts try in g to reach sp ecific so cial

a ffe c te d

a n d en v iro n m en tal g o a ls,

c o m m o d ity p ric e s. S o m e o f th ese lo cal sc e n a rio s

se cu rity first, in w h ich there is a w o rld of

c o n siste n c y w ith g lo b a l sc e n a rio s is p ro b lem atic.

strik in g d isp a ritie s, w h ere in eq u ality an d

T h is m ay n ot be critical, h ow ever, sin ce an y g lo b a l

conflict p rev ail, an d •

N e v e r th e le s s ,

n atio n a l stu d ie s , to u se lo cal sc e n a rio s fo r so c io ­

a ls o •

u n d e rta k e n .

su sta in a b ility first, in w h ich a n ew en viron m en t a n d d e v e lo p m e n t p a r a d ig m e m e rg e s in re sp o n se to the ch allen ge o f su sta in a b ility .10

by

have

te c h n o lo g ic a l p o lic y

ch ange

r e le v a n c e ,

or

a lth o u g h

g lo b a l th e ir

scen ario , su ch a s the SR E S sc en a rio s, w ill n ot a p p ly u n ifo rm ly in re gard to so cio -eco n o m ic c h a n g e s, so that local d e p a rtu re s from the b ro a d -sca le sc en ario s m ay n ot greatly affect g lo b al em issio n s a n d resu ltin g clim ate ch an ge s.

A s m ig h t be e x p e c te d , the effect in relation to

For e x a m p le , tw o clo sely related re p o rts for the

g re en h o u se g a s e m issio n s is that the first an d third

A u stra lia n B u sin e ss F o u n d a tio n a im ed 'to iden tify

sc en a rio s, lack in g effective en v iron m en tal p o licie s,

a lte rn a tiv e , p la u sib le sc e n a rio s fo r the fu tu re of

lead to sig n ifica n t in crease s in g re en h o u se g a se s b y

b u sin e ss in A u str a lia ' an d ex p lo re d fo u r altern ative

2050. T h e p o lic y first sc e n a rio le a d s to a c tu a l

sc e n a rio s sty le d 'S o u n d the R e trea t', 'B ra v e O ld

red u ctio n s in e m issio n s sta rtin g a ro u n d 2030, w h ile

W orld', 'F irst G lo b a l N a tio n ' an d 'G reen is G o ld '.

the su sta in a b ility first scen ario le a d s to a declin e b y

The la st d e a lt exp licitly w ith g lo b a l en v iron m en tal

the m id-2020s. D ifferen t en v iro n m e n tal o u tco m e s

c o n ce rn s.11

PROJECTING THE FUTURE

51

A n oth er stu dy , co m m issio n e d b y the B u sin e ss

To d a te v e ry few in tern atio n al clim ate im p a c ts

C oun cil o f A u stralia, w a s called 'P o pu lation F utures',

stu d ie s h av e taken different p o ssib le socio-econ om ic

A u stralian A ca d e m y o f Tech nological Scien ces and

fu tu re s into a c c o u n t a lth o u g h a lte rn a tiv e so c io ­

E n g in e e rin g (2001). T h is a im e d

to a s s e s s the

e co n o m ic sc e n a rio s are cen tral to the IP C C SR E S

en viron m en tal co n strain ts to p o p u latio n gro w th in

e m is sio n s sc e n a rio s. T h ese a n d oth er is s u e s are

A u stra lia , ou t to 2050, an d to a s s e s s tech n ological,

d is c u s se d in the 2007 IP C C report, W GII, C h a p te r

b e h a v io u r a l, p ric in g

2.4.6 an d are a key to realistic im p acts an d ad a p tatio n

and

se ttle m e n t p la n n in g

in te rv e n tio n s th at m ig h t b e u se d

to m a n a g e

stu d ies.

p o p u latio n -relate d en viron m en tal issu e s. Its focu s w a s m ore on w h at im p act an in creased p o p u latio n m igh t h av e on the en viron m ent, rather than on w h at

Forecasting the weather

influence en viron m en tal p ro b lem s, su ch a s clim ate

F o re sig h t is ro u tin ely u se d in re g a rd to the w eath er,

ch an ge, m igh t h av e on the h u m an p op u lation .

an d affects m an y o f o u r d a y -to -d a y d e cisio n s. It is

A n o n g o in g A u stra lia n stu d y b y the R eso u rces

th erefore u se fu l to c o m p a re the b a sis fo r w e ath er

F u tu res P rogram o f C SIR O S u stain ab le E co sy stem s

fo re c a stin g w ith th at fo r c lim a te p ro je ctio n s, in

h a s an in te g ra te d a p p ro a c h w h ere in tera ctio n s

o r d e r to u n d e r s ta n d b o th w h a t they h a v e in

b etw een

co m m o n an d w h a t the d ifferen ces are.

the e n v iro n m e n t an d

p o p u la tio n

are

sim u la te d . T h is stu d y a im s essen tially at p ro v id in g

W eath er f o r e c a stin g

u se d

to b e b a s e d

on

in sig h t into o p tio n s fo r A u s tr a lia 's p o p u la tio n ,

ex p erie n ce w ith p a s t situ a tio n s, w h ich d e v e lo p e d

technology, resou rces an d en viron m ent to 2050 w ith

into ch a n g e d w e a th er p a tte rn s that e x p e rts co u ld

an e m p h a s is on su sta in a b ility . It lo o k s at the

either re m em b er or look u p from p a s t record s. T h is

co n seq u en ces of low, m ed iu m an d high p o p u latio n

w a s called 'a n a lo g u e fo re ca stin g ', that is u sin g the

gro w th ra te s, an d e x p lo re s the co n se q u e n ce s for

p a s t a s an a n a lo g u e fo r the future. D u rin g a n d after

p eople, urban infrastructure, the n atural environm ent,

the S ec o n d W orld War, th in g s sta rte d to ch an g e

energy, w ater an d a ran ge o f other issu e s.12 A m o n g st

w ith the u se o f g ro w in g theoretical u n d e rsta n d in g

the con clu sion s o f their 2002 report 'Future d ilem m as'

o f h o w w e a th e r d is tu r b a n c e s gro w , m o v e an d

w a s a need to recogn ise that:

d e ca y .

•

A u s tr a lia 's so cial, econ om ic an d p h y sica l sy ste m s are lin ked o v er very lon g tim e sc a le s,

•

•

Q u a n tita tiv e

c a lc u la tio n s

of how

the

a tm o sp h e re ch a n g e s w ere p io n ee re d b y L e w is Fry R ich ard so n , an E n glish Q u ak e r sc h o o lte ac h e r and sc ie n tist w h o, b y h a n d , ca lcu la te d so lu tio n s to the

sh ort-term d e cisio n s h a v e lon g-term

g o v e rn in g e q u a tio n s o f m o tion a n d co n tin u ity of

c o n seq u en ce s, an d

m a tte r to p r o d u c e the first n u m e ric a l w e a th e r

there is in bu ilt in ertia in o u r in stitu tion al sy ste m s, re q u irin g tim e for ch an ge to take effect.

fo re ca st. H is w o rk , d o n e in the tre n ch es a s an a m b u la n c e w o rk e r in the F irst W orld War, w a s p u b lish e d in 1922.13 H ow ever, R ic h a rd so n 's calcu lation w a s not v ery

T h ese co n clu sio n s a p p ly in m an y p la c e s b e sid e s

a c c u ra te , a n d a p p lic a tio n o f h is m e th o d s h a d to

A u str a lia , a n d are th e m es reflected in the v a rio u s

w a it fo r the d e v e lo p m e n t o f la rg e ele ctro n ic

IP C C A sse ss m e n t R e p o rts. T h ey s u g g e s t th at any

co m p u ters. John von N e u m an n an d Ju le s C h arn ey

realistic a sse ssm e n t o f the overall im p a c ts of clim ate

took u p the ch alle n ge at Prin ceton U n iv e rsity ju st

ch an ge on an y local or n atio n al co m m u n ity, an d of

after the Seco n d W orld War, u sin g on e o f the first

its cap a city to co p e w ith or a d a p t to clim ate ch an ge,

ele ctro n ic c o m p u te rs. Th e first c o m p u te r- b a se d

w ill n eed to in te g ra te stu d ie s o f so cio -eco n o m ic

w eath er fo re ca sts w ere issu e d in 1955.

fu tu re s w ith clim ate ch an g e stu d ie s. T h ey are all p art o f an intercon nected future.

It q u ic k ly b e c a m e a p p a r e n t th at the sk ill of n u m e rica l w e a th e r fo re c a stin g d e c re a se s ra p id ly

52

CLIMATE C H A N C E: THE SCIENCE, IMPACTS A N D SO L U T IO N S

w ith tim e into the fu tu re. M a th e m a tic a l theory,

P ro g re ss to w a rd s im p ro v e d w eath er fo re casts is

d e v e lo p e d by E d w a rd L o ren z o f M a s sa c h u s e tts

p artly d u e to better ob serv atio n s o f initial conditions,

In stitu te o f T e ch n o lo g y d e m o n str a te d th at the

an d m ore a ccu rate ca lcu la tio n s that m in im ise any

accu racy o f fo re casts d eclin e s d u e to the gro w th of

ro u n d in g-off errors. T h u s n um erical w eath er m o d els

e rro rs p re se n t in the in itial in p u t d a ta . K n o w n a s

c a lcu la te p ro p e rtie s o f the a tm o sp h e re to m an y

'ch a o s th eory ', th is sh o w s that sm a ll d ifferen ces in

d e cim a l p la c e s to slo w d o w n the p ro p a g a tio n of

in itial c o n d itio n s, su ch a s th o se th at a rise from

erro rs. R e p e a te d m o d e l ca lc u la tio n s o f the sa m e

im p e rfect o b se rv atio n s o f the p resen t w eath er, lead

situ a tio n

to la rg e r an d larg e r erro rs w ith tim e. L o ren z u se d

co n d itio n s can a lso p ro v id e m u ltip le forecasts, w ith

w ith

im p e r c e p tib ly

d iffe re n t

in itia l

the a n a lo g y o f a p in b a ll m ach in e to ex p la in w h at

the a v e ra g e u su ally b ein g m ore reliable than a sin gle

h a p p e n s .14 In a p in b a ll m ach in e, a ro llin g b a ll h its a p o st (or

forecast. T h is is know n a s 'e n se m b le forecastin g'.

pin ) a n d b o u n c e s o ff in a stra ig h t line until it strik es

h a v e co m e from the in c o rp o ra tio n o f h e at an d

a se c o n d p in , then a th ird a n d so on. L o ren z

m o istu re e x c h a n g e b etw een the a tm o sp h e re a n d

O th er im p r o v e m e n ts in w e a th e r fo re c a stin g

co n sid e re d that if the b all, in its initial m o tion , ran

the o cean s, a ssiste d b y satellite o b se rv atio n s o f sea-

o v e r a sm a ll p ie c e o f d u s t it w o u ld b e slig h tly

su rfa c e te m p e ra tu re s. T h e fact th at the sk ill of

d e fle c te d , strik in g the p in at a slig h tly d iffere n t

n u m e rica l w e ath er p red ic tio n h a s im p ro v e d o v er

an g le . A fter se v e ra l su ch strik e s the b a ll w o u ld be

the y e a rs is testim o n y to im p ro v e d o b se rv atio n s of

tra v e llin g in a su ffic ie n tly d iffe re n t d ire ctio n to

initial co n d itio n s (in clu d in g satellite o b se rv atio n s),

m iss a p in th at it w o u ld h a v e h it in the n o -d u st

the g ro w in g u n d e rsta n d in g o f h ow the atm o sp h ere

c a se , so th at the p re d ic ta b ility o f w h ich p in s it

a n d o c e a n s co m b in e to p ro d u c e w eath er, a n d to

w o u ld strik e later on w o u ld ra p id ly d e cre a se . The

h ow this is in c o rp o rated into co m p u ter m o d e ls.15

p re d ic ta b ility is critically d e p e n d e n t on k n o w in g exactly w h at p ath the b all tak e s in its first encounter, an d the m o re a c c u ra te ly th at is k n o w n the m ore strik e s co u ld be a cc u ra te ly p re d ic te d . H o w ev e r, if the e x p e r im e n t w e re re p e a te d m a n y tim e s, an a v e r a g e p a th c o u ld b e fo u n d , a n d it w o u ld be p o ss ib le to sa y h ow p ro b a b le it w a s th at the b all w o u ld strik e a p a rtic u la r p in . T h u s it w o u ld not b e p o ssib le to p red ic t w ith co m p le te co n fid en ce w h ich

W h y climate projections are different N u m e r ic a l p re d ic tio n o f c lim a te is a d iffe re n t p ro b le m , e v e n th o u g h it sta r ts w ith the sa m e e q u a tio n s g o v e r n in g a tm o s p h e r ic m o tio n a n d con tin u ity of m atter (the a m o u n t o f air an d w ater in the atm o sp h ere ). There are tw o m ain differen ces: •

First, clim ate projectio n s are n ot ab o u t

p in w o u ld be hit, b u t from re p e a te d o b se rv a tio n s

p red ictin g the exact w eath er at any tim e in the

the p ro b a b ilitie s o f strik in g v a rio u s p in s co u ld be

future, b u t rather a b o u t p rojectin g the statistics

d e term in ed .

(a v e ra g e b eh a v io u r a n d v ariab ility ) o f the future

W eather fo re castin g is a sim ila r ty p e o f initial

w eather. T h is re d u ces the relevan ce o f sh o rt­

v a lu e p ro b lem , that is, on e in w h ich the ev en tu al o u tco m e d e p e n d s on h o w a c c u ra te ly the in itial co n d itio n s are k n ow n . A n y error in sp e c ify in g the initial co n d itio n s is am p lified (that is, m a d e larger) an d ev en tu ally lead s to a b reak d ow n in p redictability o f the exact ou tcom e, alth o u gh it m ay resu lt in the ability to p red ict the p rob ab ility o f v a rio u s ou tcom es, that is, to pred ict the statistics o f the w eather. Loren z an d oth ers sh o w e d that the lim it o f p red ictab ility of p articu lar w eath er is ab o u t three w eek s.

term chaotic b eh a v io u r in the atm osph ere. •

S ec o n d , b e c a u se clim ate p ro jectio n s are a b o u t the sta tistic s o f w e ath er m an y m o n th s, y e a rs or even cen tu ries into the fu tu re, m u ch slo w er in flu en ces on the w eath er or clim ate m u st be taken into accoun t, an d in d eed tend to d o m in a te the p ictu re. T h u s the p r o p a g a t io n

c o n d itio n s

is

not

of erro rs

im p o r ta n t,

but

in

in itia l

ra th e r

the

PROJECTING THE FUTURE

53

k n o w le d g e o f slo w e r in tern al v a r ia tio n s in the

H ow good are climate m odels?

clim ate sy stem , a n d so -called 'b o u n d a ry co n d itio n s'

Tw o or three d e c a d e s a g o m o st clim ate m o d e ls

and

c h a n g e . S lo w e r in te rn a l

co n sid e re d the o c e a n s to b e ex te rn al a n d u se d

v a ria tio n s in c lu d e e x c h a n g e s o f h e at, sa lt an d

how

th ey

m ay

p rescrib ed se a -su rfa c e tem p e ra tu re s at the b ottom

ch e m ica ls su ch a s carb o n d io x id e w ith the d e ep

o f the atm o sp h ere . R e su lts w ere co n d itio n al on the

ocean , an d the g ro w th an d d e ca y o f ice sh ee ts an d

a ss u m e d se a -su rfa c e te m p e ra tu re s. T oday, fa ste r

gla ciers. F ig u re 11 sh o w s so m e o f the c o m p o n e n ts

co m p u ters en able n early all clim ate m o d e ls to have

that are in c lu d e d in the in tern al p a r t o f a clim ate

an interactive ocean, an d in d eed ocean currents and

m o d el. O th ers, n ot sh o w n , in clu d e in teractiv e so il

d e ep w ater tem p eratu res are calcu lated. H istorically,

an d v e g etatio n , a tm o sp h e ric ch em istry, an d clou d

the scientific literature is full o f p a p e r s d e sc rib in g

interactio n s w ith p article s (a e ro so ls).16

sim u la tio n s o f clim ate u sin g m o d e ls o f v a ry in g

E xtern al factors in clu de ch an ges in atm osph eric

co m plexity an d detail, an d it is im p o rtan t in re ad in g

and land su rface p roperties, variatio n s in the orbit of

these p a p e r s to u n d e rsta n d ju st w h at is calcu lated

the E arth a ro u n d the S u n , so la r v ariab ility an d

a n d w h a t is g iv e n a s a ss u m e d in p u t. It is a lso

volcanic eruption s (which p u t g a se s and particles into

im p o rtan t not to rely on o u td a ted a sse ssm e n ts o f the

the atm osph ere). Som e of these external factors can be

sk ill of clim ate m o d e ls, w hich ten d s to occur in the

sp ecified a s in p u ts or b o u n d a ry co n d ition s to the

critiqu es o f clim ate m o d ellin g b y so m e w h o qu estion

clim ate m o d els, rather than calculated. H ow ever, they

clim ate ch an ge. C itin g ou t-o f-d ate a sse ssm e n ts of

can be calcu lated internally in an en larged clim ate

clim ate m o d e ls ig n o re s recen t im p ro v e m e n ts in

system , if they can be p red icted an d the eq uation s can

m o d ellin g an d sh o w s a lack o f ap p reciation o f how

be a d d e d to the m odel. A s co m pu ters becom e bigger,

m uch w ork h as gon e into im p ro v in g their accuracy.

faster and cheaper, m ore and m ore that u sed to be

A ra n g e o f differen t ty p e s o f clim ate m o d e ls are

external to the clim ate m o d els can now be incorporated

a v a ila b le , a n d v a rio u s n a m e s or a b b re v ia tio n s are

into the m o d els an d thus predicted rather than given

u se d to in d icate d ifferen ces in their com plexity. For

a s external b o u n d ary conditions.

e x a m p le , there are v e ry sim p le 'e n e rg y b a lan ce

ATM OSPH ERE

O CEAN

Figure 11: Some internal components of a climate model. Some of these components can be changed by external forces (such as variations in the Earth's orbit around the Sun or in solar radiation) or changes in the composition and radiative properties of the atmosphere (such as the addition of more greenhouse gases or particles of dust). (After John Mitchell, UK Meteorological Office, 2003.)17

CLIMATE C H A N C E: THE SCIENCE, IMPACTS A N D SO L U T IO N S

54

m o d e ls ' w h ich c a lc u la te on ly the in c o m in g an d

sim u la te d o u tp u ts for m a n y m o re v a ria b le s, so m e

o u t g o in g

o f w h ich w ere n ot u se d to tun e the m o d e ls, n ow

en ergy

in to

the c lim a te

sy s te m

to

d e te rm in e the E a r th 's g lo b a l a v e r a g e su r fa c e

ch ecks this.

tem p e ratu re , or that in latitu d e b a n d s. T h ese ign ore

O th er te sts u se d in c lu d e h o w w ell the clim ate

lots of in tern al p ro c e sse s a n d d o n ot g iv e o u tp u ts

m o d e ls sim u la te v a ria tio n s in clim ate o v er the d aily

u se fu l at p articu la r lo catio n s on E arth , b u t they are

cycle, for e x a m p le d a ily m a x im u m an d m in im u m

q u ick an d ch eap to u se an d are often u se d to stu d y

te m p e ra tu re s, or d e p th o f the w e ll-m ix ed su rfa c e

a w id e ra n g e o f co n d ition s.

lay er o f the atm o sp h ere . C h a n g e s in a v e ra g e clo u d

N e x t there are 'a tm o sp h e ric ge n e ral circulation

co ver an d rain fall w ith tim e o f d a y are other m ore

m o d e ls' or A G C M s. T h ese calcu late w h at g o e s on

so p h istica te d v a ria b le s that are so m e tim e s tested.

in the atm o sp h ere , in clu d in g ch a n g e s to clo u d co ver a n d p ro p e rtie s, b u t h a v e p re scrib e d or g iv en sea-

R elated tests in v o lv e ca lcu la tin g in the m o d e ls v a r ia b le s th at can b e c o m p a r e d w ith sa te llite

su rfa c e te m p e ra tu re s. T h u s, they d o n ot allo w for

o b s e r v a tio n s, su ch a s c lo u d c o v e r a n d e n e rg y

c h a n g e s in the o c e a n

ra d ia t e d

c lim a te

(c u rr e n ts, a n d

back

to sp a c e

fro m

the to p

o f the

tem p e ratu re an d salin ity w ith location an d depth ).

a tm o sp h e re . U n til recen tly m a n y clim ate m o d e ls

T o d ay n early all clim ate m o d e ls u se d for clim ate

h a v e n ot d o n e v ery w ell on so m e o f th ese tests, b u t

p ro je c tio n s h a v e fu lly in tera ctiv e o c e a n s. T h ese

they are im p ro v in g .18

are c a lle d 'c o u p le d a tm o s p h e r e - o c e a n g e n e ra l

To test lo n g e r tim e-sc ale v a ria tio n s, te sts are

c irc u la tio n m o d e ls ' or A O G C M s, a n d u su a lly

m a d e o f h o w w e ll c lim a te m o d e ls sim u la te the

in clu d e ca lcu latio n s o f sea-ice cover. Even so , there

a n n u al cycle o f the se a so n s. D ifferen t test lo cation s

are still m an y extern al co m p o n e n ts o f the clim ate

from those the m o d el b u ild e rs m ay h a v e lo o k ed at

sy ste m that are on ly g ra d u a lly b ein g in tern a lised

w h en b u ild in g their m o d e ls are often u se d . For

into clim ate m o d e ls, even w h ere th ese co m p o n e n ts

e x a m p le , h ow w e ll d o e s an A u s tr a lia n c lim a te

a ct on a n d are c h a n g e d b y the c lim a te . T h ese

m o d e l p erfo rm o v e r E u ro p e, or a E u ro p ea n m o d e l

co m p o n e n ts in clu d e g laciers, continental ice sh eets,

p erform ov er A frica?

a n d su rfa c e p ro p e rtie s, su ch a s su rfa c e ro u g h n e ss a n d reflectivity that are d e term in ed b y vegetatio n .

A p o p u la r test is to u se a clim ate m o d e l w ith o b se rv e d b o u n d a ry lay er co n d itio n s, for e x a m p le

C lim ate m o d e ls h av e been tested an d im p ro v e d

se a -su rfa c e te m p e ra tu re s in an a tm o sp h e ric glo b al

q u ite sy ste m a tic a lly o v er tim e. T h ere are m an y

clim ate m o d e l, to sim u la te y ear-to-y ear v a ria tio n s

w a y s o f d o in g th is. O n e is to c lo se ly c o m p a re

su ch a s a y e a r w ith a stro n g m o n so o n o v er In dia

s im u la te d p re se n t c lim a te s w ith o b s e r v a tio n s.

v e rsu s a y ear w ith a w e ak m o n so o n . Sim ilarly, tests

C lim ate m o d e lle rs often ju d g e m o d e ls b y h o w w ell

are m a d e o f h ow w ell a clim ate m o d e l re p ro d u ce s

th ey d o in re p ro d u c in g o b s e r v a tio n s, b u t u n til

the n atu ra l v a ria tio n s in a co m p le x w eath er p attern

recen tly th is h a s m ain ly been by te stin g o u tp u ts

su ch a s the El N in o -S o u th e rn O scillation (E N S O ),

from

w h ich is im p o rta n t in y ear-to -y ear v a ria tio n s in

m o d e ls a g a in s t o b s e r v a tio n s fo r sim p le

v a ria b le s su ch a s su rfa c e tem p e ra tu re a n d rain fall.

c lim a te . E N S O

H ow ever, this p ro c e ss can be circular in that clim ate

a tm o sp h eric circu lation , m ain ly a c ro ss the trop ical

m o d e ls, w ith all their sim p lific a tio n s (for e x a m p le

Pacific O cean , b u t h a s effects in m an y other p a r ts of

is a v a ria tio n

in o c e a n ic an d

in h o w th ey re p re se n t c o m p le x p r o c e s s e s lik e

the w o rld . G ettin g E N S O righ t is an im p o rta n t test,

c u m u lu s co n vection , sea-ice d istrib u tio n or a ir -se a

a n d it is on ly recen tly th at so m e A O G C M s h a v e

e x ch an ge o f h eat an d m o istu re) can b e a d ju ste d , or

d o n e w ell w ith this test.

'tu n e d ', to g iv e the rig h t a n sw e rs, so m e tim e s b y

A t even lo n ger tim e sc a le s, tests can b e m a d e a s

m a k in g c o m p e n sa tin g erro rs. S u ch e rro rs m ig h t

to h o w w ell clim ate m o d e ls can re p ro d u c e p ale o -

then lea d to se rio u s d ifferen ces from reality in so m e

clim a tic v a ria tio n s. T h is is o n ly p o s s ib le w h ere

other v aria b le not in clu d e d in the tests. C o m p a rin g

ch an ge s in extern al co n d itio n s can be w ell sp ecified ,

PROJECTING THE FUTURE

such a s ch an ges in so lar en ergy input, atm osph eric c o m p o sitio n , la n d - s e a d istrib u tio n an d su rfa ce p roperties. It is also n ecessary to h ave lots of paleoev id en ce for clim ate p attern s at the tim e b ein g sim u lated to see if the clim ate m o d els reprodu ce it w ell. T h is is a tall order, bu t n ev erth eless paleom o dellin g is u sefu l a s a test of clim ate m o dels, and a lso h elp s u s to u n d e rsta n d an d test th eories of w h at c a u se s clim ate flu c tu a tio n s an d w h at is p ossib le. In ord er to p ro v id e clim ate ch an ge projections relevant to m an y local and region al clim ate ch ange im pacts, clim ate m o d els n eed to p ro v id e ou tp u t at finer an d finer sp a tia l scales. That is, w here glob al clim ate m o d e ls a d e ca d e b ack only g a v e o u tp u t d a ta on clim ate ch a n g e s at d ista n c e s se v e ra l h u ndred k ilom etres a p art, for m an y p u rp o se s the n eed is for d a ta at lo cation s only a few ten s of k ilo m etres a p art. The lim itatio n w a s esse n tially com pu ter capacity, since the n um ber o f calculation s in creases ro u gh ly by a factor o f eigh t for every h alvin g of the distan ce betw een data points. There are three w a y s in which this finer sp atial resolution can be achieved: •

running global clim ate m o d els at finer and finer sp atial scales,

•

statistical do w n scalin g, which u ses observed relation sh ips betw een large-scale w eather variab les and local w eather, and

•

running local or regional clim ate m o d els driven by ou tp u t from glob al m odels. R ap id im p ro v e m en ts in co m p u ter sp e e d and

capacity h ave en abled glob al clim ate m o d els to be run at finer and finer spatial resolutions. Som e m o d els now routinely p ro d u ce ou tp u t at sp a tia l scales as fine as 100 or even 50 kilom etres, alth ou gh this still cannot be done for m an y different scen arios. There h a s a lso been a technical d e v e lo p m e n t u sin g v a ria b le sp a tia l re so lu tio n in g lo b a l m o d e ls, w h ereby it is p o ssib le to run a glob al m o d el w ith co arse resolu tion ov er m o st of the glob e, b u t fine resolution over an area of interest. This latter option is fine if you only w an t detailed inform ation abou t

55

one region , for ex am p le if you are in a n ation al lab oratory m o d ellin g for in form ation relevan t to one regio n , su ch a s the U K or Ja p a n . H ow ever, w hile it is im portan t to get detailed inform ation for y ou r ow n region, m an y countries w ill also w an t to know w hat m ay h ap pen in detail in other p arts of the w o rld , at lea st for b ro a d policy re aso n s, and m aybe even for telling w h at the im p acts of clim ate ch ange m ay be on trade p artn ers and com petitors. The n eed for truly glo b al sim u la tio n s at fine sp a tia l sc a le s thus rem ain s im portan t. Ja p a n h as recogn ised this and h as b u ilt the Earth S im u lator su p erco m p u ter cap ab le of m o d ellin g the clim ate at fine sc a le s for the w h ole glob e. It co n tain s the e q u iv a le n t o f m a n y h u n d r e d s o f o r d in a ry s u p e rc o m p u te r s (circa 2004), an d cu rren tly is ru n n in g a clim ate m o d el w ith 100 lev e ls an d a horizontal resolution of 10 kilom etres, com pared to m o st A O G C M s that h ave a resolu tion of arou n d 100 or m ore kilom etres.19 The secon d w ay of getting finer sp atial detail for p articu lar locations is to u se statistical relation sh ips betw een the ob serv ed large-scale clim ate pattern s an d lo cal clim ate to d e riv e e stim a te s o f local ch an ges from m odel-sim u lated large-scale changes. This is called statistical downscaling, an d requ ires a lot of detailed clim ate ob serv ation s for the region of interest. It is a lso im p o rtan t that the statistical relation sh ips betw een the large-scale ch an ges and local ch an ge w ill be v a lid u n d er co n d itio n s of clim ate ch an ge a s o p p o se d to p resen t o b serv ed clim ate variability. T h at is n ot the case w ith all large-scale v ariab les an d m u st be tested. The third m ethod for ob tain in g d etailed local ou tp u t is to u se a local or regional fine-scale climate model d riv en b y the o u tp u t o f a g lo b a l co arseresolution m odel. The easy w ay to d o this is to use ou tp u t from the glob al m odel at the b o u n d a ries of the regional m odel do m ain to determ ine the m odel v a lu e s at the b o u n d aries of the regional m odel, and force the regional m odel to a d ju st its v a lu e s inside the b o u n d a rie s to be co n sisten t w ith this. T h is is term ed 'on e-w ay n estin g'. H ow ever, local ch an ges w ithin the region m ay in reality force ch anges at a larger scale, for exam ple

56

CLIMATE CHANCE: THE SCIENCE, IMPACTS A N D SO LUTIO NS

if the region in clu des a large lake from w hich the atm osp h ere m ay pick u p a d d itio n al m oistu re. To account for this possibility, ideally the ou tp u t from

scales from seasonal to decadal. The varying sets o f strengths and iveaknesses that models display lead us to conclude that no single model can be

the regio n al m o d el sh o u ld be fed back into the g lo b a l m o d el an d th u s m o d ify the large -scale clim ate. T h is is term ed 'tw o -w ay n estin g '. M an y clim ate-m odelling g ro u p s h ave perform ed one-w ay n estin g, bu t tw o-w ay n estin g is less com m on , and h as revealed so m etim es-sign ifican t differen ces in

considered 'best' and it is important to utilise results from a range o f coupled models. \Ne

resu lts for the sam e region. Th e p e rfo rm a n c e o f fine sp a tia l re so lu tio n m o d e llin g h a s a lso b een c a re fu lly te ste d by co m p arin g different m o d els over the sa m e regions, an d by try in g to re p ro d u ce p artic u la r h isto rical situ a tio n s u sin g re gio n al m o d e ls forced at their b o u n d a rie s by o b se rv a tio n s. R e su lts h av e been m ixed , and in gen eral it is conceded that regional d etail is not a s reliable a s the large-scale ou tpu t. T h is a p p lie s p a r tic u la rly to ra in fa ll p a tte rn s, a lth o u g h re gio n al d e tail is n e ce ssary e sp e cia lly for ra in fa ll b e c a u se it can v a ry gre atly ov er sm all distan ces d u e to to p o grap h y an d la n d -sea bou nd aries.20 O v e rall, m o d el p erfo rm an c e an d v erification is c o m p le x , b u t is b e in g a c tiv e ly te ste d a n d im p ro v e d . C lim a te m o d e ls p ro v id e p ro je ctio n s that are far m ore so p h istic a te d an d reliab le than sim p le e x tr a p o la tio n s from o b s e rv e d c lim a te trends. They are far m ore reliable than h a n d w av in g a rg u m e n ts a b o u t fu tu re clim ate m a d e b y so m e scep tics that are often m a d e on the b a sis of sim p le ex trap o la tio n s or co rrelation s. M oreover, the IPCC

consider coupled models, as a class, to be suitable tools to provide useful projections o f fu tu re climates. A w hole ch apter of the 2007 IPCC report (WGII, C h apter 8) is devoted to clim ate m o d els and their ev alu atio n and e x p o u n d s on their stren g th s and w eakn esses.

The state of climate projections Projecting the future is an ev ery d ay p roced u re for p ro v id in g insigh t into w hat m ay h ap p en . It form s the b a sis of m an y d e cisio n s ab o u t w h at to do. In relation to clim ate it is m ad e m ore difficult by the co m p lex ity o f the clim ate sy stem , the lon g tim e scales and the p o ssib le hum an influences on clim ate through future hum an behaviour. Projecting futu re clim ate is not ju st a m atter of ex tra p o la tin g from recent tren d s, b u t of u sin g com pu ter m o d els that take m any different p rocesses into accoun t. W hile clim ate m o d els are b a se d on w eath er p red iction m o d els, they in vo lv e lon ger tim e scales and include slow er p rocesses. They are n ot d e p e n d e n t on g e ttin g the d e ta ile d initial

an d oth er b o d ie s stu d y in g clim ate ch an g e h av e taken the u n c e rta in tie s in to a c c o u n t. T h e se

co n d itio n s correct. The p erfo rm an ce of m o d ern clim ate m o d els is tested in m any w a y s and they are rap id ly b ecom in g m ore reliable. Prediction of hum an b eh aviour, and thus of

u n ce rta in tie s are b e in g p ro g re ss iv e ly d e c re a se d to p r o v id e m o re re lia b le a n d p o lic y -re le v a n t in form ation .

future green h ou se g a s em ission s, is probably less reliable than p red ictin g clim ate on the b a sis of a p articu lar scenario of hum an behaviour. Therefore

The IPCC 2001 report su m m arises its conclusions re gard in g the state of co u p led a tm o sp h ere -o cean

any clim ate projections b ase d on clim ate m o dels is conditional on scen arios of hum an behaviour. The SRES scenarios for future greenhouse g a s em issions,

clim ate m o d els a s follow s: Coupled models have evolved and improved significantly since [1995], In general, they provide credible sim ulations o f climate, at least down to sub-continental scales and over temporal

u sed by the IPCC in its 2001 and 2007 reports, cover a w ide range of possibilities, which w as not influenced by clim ate policy. W hat is m ore relevant for climate policy are projections for a ran ge of policy-driven scenarios. These will be discu ssed later in this book.

P R O J E C T IN G TH E F U T U R E

57

ENDNOTES 1. I am in d eb ted to R o g er H B radbury, 'C an the F utu re b e K n o w n ?' Greenhouse Beyond Kyoto: Issues, Opportunities and Challenges, C on feren ce P ro ce ed in gs, B u reau of R u ral R eso u rces, C an b erra (1998) for id e a s on w h at is p la u sib le. See h t t p :/ / a ffa sh o p .g o v .a u /p r o d u c t.asp ?p ro d id = 1 3 2 3 1 2. W hether p ro b a b ilitie s are n eed ed for clim ate ch an ge sc e n a rio s is d e b ated in L e m p e rt an d S ch lesin g er, Climatic Change, 45, p p . 387-401 (2000); B arn ett, World Development, 29, p p . 977-93 (2001); Pittock and oth ers, Nature, 413, p. 249 (2001); an d Sch neider, Nature, 411, p p . 17-19 (2002). 3. The IP C C S R E S sc e n a rio s are fu lly d o cu m e n te d in N a k ic en o v ic, Technological Forecasting and Social Change, 63, p p. 105-385 (2000) and 65, p p . 149-66 (2000); an d N ak icen o v ic an d S w art, Special Report on Emissions Scenarios, IPCC (2000) a v a ila b le at h t t p ://w w w .ip c c .c h . The p o ssib ility that e m issio n s m ay follow either a low -carb o n or a highcarbo n d e v e lo p m e n t p ath w ay , rath er than an in term ed iate on e, is d isc u sse d in G ritse v sk y i an d N ak icen o v ic, Energy Policy, 28, p p . 907-21 (2000). 4. The a rg u m e n t ov er the u se o f differen t ex ch an ge rates (m ark et exch an ge rates, M ER, or p u rc h a sin g p o w e r parity, PPP) in calcu latin g futu re glo b a l carbon d io x id e e m issio n s is review ed in p art by M cK ib b en an d co lle ag u e s in Long Run Projections for Climate Change Scenarios, L o w ry Institute for In ternational Policy, W orking P a p ers in In ternational E con om ics, no. 1.04 (M ay 2004). K ey p a p e r s a p p e a re d in the jo u rn al Energy and Environment, 14, p p . 159-85 (2003) b y C astle s an d H en d erso n ; 14, p p . 187-214, b y N ak in o v ic an d others; 14, pp. 415-35, b y C a stle s an d H en d erso n ; and 15, p p . 11-24 (2004), b y G ru b ler an d oth ers. P an t an d Fisher, from the A u stra lia n B u re au o f A g ric u ltu ra l an d R eso urce E con om ics, co n clu d e in a 2004 p a p e r P PP versus M E R : Comparison of real incomes across nations that: 'The u se o f M E R by IP C C ... rem ain s v alid an d the critiqu e b y C astle s an d H en d e rso n can n ot be su sta in e d .' See h t t p :/ / w w w .ab are.g o v .au . 5. P a p e rs d o c u m e n tin g g lo b a l e m issio n s track in g at or a b o v e the A 1 FI sc e n a rio in clu d e : JG C a n a d e ll an d o th ers, 'C o n trib u tio n s to a cceleratin g a tm o sp h e ric C O , gro w th from eco n o m ic activity, carb o n intensity, an d efficien cy of n a tu ra l sin k s ', Proceedings o f the N ational Academy of Sciences (U S A ), 104, p p . 18 866-70 (2007). S R a h m sto rf an d o th ers, 'R ecen t clim ate ch an ge : O b se rv a tio n s c o m p a re d to p ro je ctio n s', Science, 316, p. 709 (2007). M R R au p ac h a n d o th ers, 'G lo b a l a n d re g io n a l d r iv e rs o f a cc e le ra tin g C 0 2 e m is sio n s', Proceedings of the National Academy of Sciences (U S A ), 104, p p . 10 2 8 8 -9 3 (2007). P S h e eh an a n d F S u n 'E n e rg y u se in C h in a: in terp re tin g c h a n g in g tre n d s a n d fu tu re d ire c tio n s', V ictoria U n iv ersity , C S E S C lim a te C h a n g e W orking P a p e r no. 13, a v a ila b le at h t t p ://w w w .c fs e s .c o m . (2007). P S h e eh an , 'T he n ew g ro w th p ath : im p lic a tio n s for clim ate ch an g e a n a ly sis an d p o lic y ', V ictoria U niversity, C SE S C lim ate C h an ge W orking P ap er no. 14 (2007), av ailab le at h ttp ://w w w .c fse s.c o m . 6. T h ese feed b ack effects are d isc u sse d in IPCC 2007 report, W GI, C h a p ter 10.4. 7. The u se of the SR E S so cio-econ om ic sc en a rio s in the U K F ast Tracks p roject is d escrib ed by N ig e l A rn ell and oth ers in Global Environmental Change, 14, p p . 3-20. See a lso the d isc u ssio n in the IPCC 2007 report, W GII, C h a p ter 2.4.6. 8. See E d w a rd P a rso n s an d oth ers, Climatic Change, 57, p p . 9 -4 2 (2004). 9. P o p u la tio n sc e n a rio s are d is c u s se d in A rn ell an d oth ers, op .cit., an d in Lu tz an d oth ers, Nature, 412, p p . 543-5 (2001). See a lso W L u tz (ed.) The Future Population of the World: What Can We A ssum e Today? 2nd ed n , E arth scan , L o n d on (1996). N ico K eilm an d isc u sse s p ro b ab ilistic p o p u latio n fo recasts in Nature, 412, p p . 490-1 (2001). See also lo e l C oh en in Science, 302, p p. 1172-5 (2003). 10. See Global Environment Outlook 4 (G E 0 4 ) re p o rt a v a ila b le at h t t p :/ / w w w .u n e p .o r g / G E O / . Th e sc e n a rio s are d isc u sse d in C h ap ter 9 of G E 0 4 . K ey co n clu sio n s can b e fo u n d on p. 451 of the report. 11. See Alternative Futures: Scenarios fo r Business in A ustralia to the Year 2015, G B N A u stra lia (1999), a n d Alternative Futures fo r Business in A ustralia to the Year 2015: Towards Strategies, G B N A u stra lia (2000).

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C L IM A T E C H A N C E : TH E SC IEN C E, IM P A C T S A N D S O L U T IO N S

12. See Future Dilemmas: Options to 2050 for Australia's Population, Technology, Resources and Environment, CSIRO (2002). It can be found at h ttp ://w w w .c se .c sir o .a u /re se a r c h /fu tu re d ile m m a s/. Later stu d ies focu s on particu lar sectors and regions. 13. There is a short account of R ich ardson 's w ork on num erical w eather forecasting in The Meteorological Magazine, 122, pp. 69-70 (M arch 1993) by Peter Lynch. See also: O liver M A shford, Prophet or Professor? The Life and Work of Lewis Fry Richardson. A d am H ilger, B ristol and Boston (1985); and L ew is F R ich ardson (1922) Weather Prediction by Numerical Process, C am b rid g e U niversity P ress reprin ted by D over P u blication s, N ew York (1965) w ith a new Introduction by Sydn ey C hapm an . 14. Sec E d w ard Lorenz, The Essence of Chaos, U niversity of W ashington P ress (1996) and Ja m es Gleick, Chaos: Making a New Science, Penguin, N ew York (1988). 15. Skill in w eath er forecasting is d iscu sse d in IT Jolliffe and DB Stephen son Forecast Verification. A Practitioner's Guide in Atmospheric Science, Wiley and Son s (2003) and RW K atz and A H M u rphy (eds), Economic Value of Weather and Climate Forecasts, C am b rid g e U n iversity P ress, C am b rid g e (1997). See also the jo u rn al Weather Forecasting for up-to-date inform ation. N atio n al W eather B ureaus u su ally d iscu ss p rogress in im provin g forecasting skill in their ann ual reports. 16. D etailed description s of global clim ate m o d els and their perform ance can be found in the IPCC Fourth A ssessm en t Report, W GI, C h apter 8, w hile that for Regional C lim ate M odels and dow n scalin g is in chapter 11.10. Standard texts on clim ate m o delling include K M cG uffie and A H en derson-Sellers, A Climate Modelling Primer, Wiley, N ew York (2005), and WM W ashington an d C L Parkinson , An Introduction to Three-Dimensional Climate Modelling, O xford U n iversity P ress, O xford, and U n iversity Science B ooks (2005). See also H altiner an d M artin, Climate System Modelling, C am b rid ge U niversity Press, C am b rid ge (1992). 17. Figure 11 is b ased on one by John Mitchell in Handbook of Weather, Climate, and Water: Dynamics, Climate, Physical Meteorology, Weather Systems, and Measurements, Thom as Potter and Bradley Colm an (eds), John Wiley and Sons (2003). 18. Im provem en ts in the skill of w eather prediction m o d els is docum en ted by H ollin gsw orth and others in Bulletin of the World Meteorological Organization, 52 (1), pp. 33-9 (2003). 19. The Earth Sim u lator C enter in Jap an is at h ttp ://w w w .e s.ja m ste c .g o .jp . Their co m pu ter in 2007 co n sisted of 640 p ro ce sso r n o d es running in parallel, w ith a total p eak perform an ce of 40 T eraflops (40 1012 floatin g-point operation s p er secon d) and a total m ain m em ory of 10 Terabytes. 20. The perform ance and techniques of regional clim ate m o d els and statistical do w n scalin g are review ed in C hapter 11.10 of the IPCC 2007 report, WGI, and in W ang and others, 'R egion al clim ate m odelling, p rogress: ch allenges and p rosp ects', Journal of the Meteorological Society of Japan, 82, p p. 1599-628 (2004). See also Climate Change Prediction: A Challenging Scientific Problem, by A lan Thorpe (UK Institute of Physics), at h ttp ://w w w .io p .o r g ; and Ronald Prinn, 'C om p lexities in the C lim ate System and U ncertainties in F orecasts' in The State of the Planet: Frontiers and Challenges in Geophysics, G eoph ysical M onograph 150, A m erican G eoph ysical U nion, W ashington, DC (2004).

4 Uncertainty is inevitable, but risk is certain

... it would be wrong to completely ignore possible developments simply because they are regarded as not very probable - or not sufficiently probable to justify an examination o f their possible consequences. Probability itself should not be the criterion fo r deciding whether or not to prepare ourselves for an event, but only for hoio we prepare ourselves. Swiss

R e in s u r a n c e C o m p a n y , O p p o r t u n it ie s a n d R isk s o f C lim a te C h a n g e ,

2002.

Where there are threats of serious or irrroersible damage, lack of full scientific certainty shall not be used as a reason fo r postponing cost-effective measures to prevent environmental degradation. T h e P r e c a u t i o n a r y P r in c ip l e , a s s t a t e d in t h e R io D e c l a r a t io n a t t h e E a r t h S u m m i t , J u n e 1 9 9 2 .

Despite uncertainties, decisions have to be made

m e a su re m e n ts ran g e from 52.8 to 53.5, the a v e ra g e

M an y y e a r s a g o , w h en I s u p e r v is e d first y ea r

d e v iatio n from the a v e ra g e ) is a b o u t 0.14. The exact

p h y sic s stu d e n ts at M elb o u rn e U niversity , w e u sed

n u m b e rs w ill d e p e n d on w h o did the m e asu rem en ts,

to g iv e them a ste e l b a ll a n d a m ic ro m e te r to

u n d e r w h at c o n d itio n s they d id them , an d on the

m e a su re its diam eter. We a sk e d them to m e a su re it

n u m b e r o f m e a su re m e n ts m ad e.

is 53.1, an d the 'sta n d a rd e rro r' (root m e an sq u a re

ten tim es an d se e w h a t v a lu e s they got. M a n y of

A s this e x a m p le illu strates, co n trary to a w id ely

them w ere su rp rise d to fin d that the a n sw e rs w ere

h e ld b e lie f, n o m e a su re m e n t o f a c o n tin u o u s

n ot all the sa m e , for e x a m p le , 53.1, 52.8, 53.2, 52.9, 53.1, 53.5, 53.0, 52.9, 53.2, a n d 53.3 m m . W hy d id

qu an tity is a b so lu te ly exact.

they g e t su ch a ra n g e o f a n s w e r s to a sim p le

science. It is co m m on in the p h y sica l scien ces to sa y

m e a su re m e n t o f a cle ar p h y sic a l q u a n tity ? A n d

that so m eth in g is 'tru e', 'certain ' or 'w ell-estab lish ed '

M o re o v e r, n o th in g is a b so lu te ly c e rta in in

w h a t then w a s the a c tu a l d ia m e te r? W ell there

if the e v id e n ce s u g g e s t s that there is le ss th an a

are se v e ra l re a so n s fo r a ra n g e o f a n s w e rs, for

5% ch ance (1 in 20) o f it b ein g w ron g. If y ou w an t to

e x a m p le , n o b all is e x a c tly sp h e ric a l, it ch a n g e s

b e even m ore c a u tio u s, y ou m igh t in sist on le ss than

its d ia m e te r a s it e x p a n d s o r co n tra c ts d u e to

a 1% ch ance (1 in 100), or ev en a 0.1% ch ance (1 in

c h a n g e s in te m p e ra tu re , an d the m e a su re m e n t

1000). Such a low p rob ab ility o f b ein g w ro n g a p p lie s

d e p e n d s on how h ard the m icrom eter is tigh ten ed .

to su ch co m m o n e x p e c ta tio n s a s the Su n risin g

The 'a ctu al d ia m e te r' can n o t b e k n o w n exactly: the

tom o rrow m o rn in g, so m eth in g that w o u ld on ly fail

CLIMATE C H A N C E: THE SCIENCE, IMPACTS A N D SO L U T IO N S

60

if so m eth in g extrem e like a co sm ic collision w ere to

is th at it w ill m is s u s, the e x a c t p re d ic tio n is

h ap p e n . It also a p p lie s to m an y p ractical en gin eerin g

u n certain . E ven a sm a ll ch ance o f a d isa ste r m a k e s

m atters, that is, m atters o f a p p lie d science, like the

it w o rth w h ile to take p rec au tio n s.

d e sig n o f a b rid g e or d am to en su re that it w ill not

In a m o re extrem e ca se , m o st o f u s p ru d e n tly

c o lla p se . H ere the d e sig n sta n d a rd is se t to en su re

in su re o u r h o u se a g a in st lo ss by fire, ev en th ou gh

th at there is on ly a v e ry sm a ll ch an ce o f fa ilu re,

w e b eliev e that it is very u n lik ely that o u r h o u se w ill b u rn d o w n . We k now that the total lo ss o f ou r

b e c a u se failu re w o u ld be catastro p h ic. H ow ever, even in the case o f en gin e erin g d e sig n

h o u se w o u ld be d is a s tr o u s, a n d the p re m iu m w e

there is a ch oice o f sa fe ty level or risk level, w hich

p a y the in su ra n ce co m p a n y is re lativ ely sm a ll, so

m a y d e p e n d on ex p ec ted freq u en cy an d d u ratio n

w e in su re a g a in st the low p ro b a b ility o f a fire.

o f u se , e x p e n se a n d u rg en cy - fo r e x a m p le le sse r

W hether w e in su re d e p e n d s on the relative siz e of

s a fe ty

le v e ls m a y b e le g itim a te ly

a p p lie d

to

a te m p o r a r y b rid g e b u ilt in w a rtim e than for a p e rm an e n t stru ctu re in p eacetim e. Su ch ch oices are a m atter o f circu m stan ce, p u rp o s e an d v a lu e s.

the p rem iu m v e rsu s the siz e o f the p o ten tial lo ss, as w ell a s on the p ro b ab ility o f a fire. W hen it c o m e s to so -c a lle d T a w s' a b o u t, or p red ic tio n s o f h u m a n b e h a v io u r (as o p p o se d to the

T h ere are m an y circ u m sta n ce s w h ere a le ss

b e h a v io u r o f the p h y sic a l w o rld ), u n ce rtain ty is

exactin g stan d ard of certainty is su fficient to find a

u su a lly m u ch greater. T h is a p p lie s in m an y o f the

p roposition, prediction or theory useful. For exam ple,

so cial sc ie n c es, for e x a m p le e co n o m ics. E con om ic

w e find w eath er forecasts u sefu l even if the chances

fo re ca sts are m a d e b a se d on v a rio u s th eories (often

of their bein g w ron g are ten p er cent (1 in 10) or even

ju st sim p le ex trap o la tio n s) of h u m an b e h a v io u r and

33% (1 in 3). T h is is b e c a u se , in m o st ca se s, the

v a rio u s a ssu m p tio n s. T h ese a ss u m p tio n s m a y n ot

co n sequ en ces of b ein g w ron g are not d isastro u s, for

h o ld in the fu tu re a s h u m a n b e h a v io u r m a y ch an ge

exam ple if w e w ould only get w et if w e did not take

or be in fluen ced by factors n ot co n sid ere d .

an u m b rella. G iven that w e k n o w that w eath er

As

th e

case

of

in s u r a n c e

d e m o n strate s,

forecasts are not entirely accurate, w e m igh t h e d ge

u n certain ty d o e s n ot p rev e n t d e c isio n s b ein g m ad e.

ou r bets an d take an um brella anyw ay.

In d e ed , in an y p ractical situ atio n p a s siv e or active

Even w here lo sse s m ay be incurred if a forecast is

d e c isio n s are in ev itab ly m a d e all the tim e, d e sp ite

w ron g, w e w ill gain on a v e ra g e b y actin g rep eated ly

u ncertainty. We either d e cid e to take o u t in su ran ce,

on im perfect forecasts, if they h av e so m e skill, than

or w e d e cid e (p e rh a p s u n co n scio u sly ) n ot to d o so.

b y ig n o rin g them . F or in sta n ce , if fo re c a sts are

In v e sto rs an d p o lic y -m a k ers m ak e d e cisio n s ev ery

w ro n g on e tim e in three, w e m a y still g a in on

d a y d e sp ite u n certain ties - they a s s e s s p ro b ab ilitie s

a v e ra g e by actin g m an y tim es on them , b e c a u se w e

an d risk s a n d then m ak e d e cisio n s, b e c a u se w ith ou t

w ill h a v e acted correctly tw o tim es in ev ery three.

these d e cisio n s n oth in g w o u ld b e done.

T h is m igh t app ly, for instan ce, to a farm er actin g on se a so n a l rain fall fo recasts a s he or sh e d e cid e s how m u ch to plan t: g o o d h a rv ests tw o y ears in three m ay

Uncertainty in climate change projections

w ell m ak e u p for a crop failu re one y ea r in three.

In an y estim ate s of futu re clim ate ch an ge there are a

H o w w e react to u n certain ty d e p e n d s on w h at is

n u m b e r o f so u rc e s o f uncertainty. S o m e o f these

h a n g in g on the re su lts. F or e x a m p le , fo re c a sts of

a rise

trop ical cyclone la n d in g s on the c o ast are se rio u s -

u n ce rta in ty

if w e are p ru d e n t w e take p re c a u tio n s ev en if w e

e sp e cially futu re e m issio n s o f green h o u se g a se s. A s

are only n ear the p o ssib le p ath o f a trop ical cyclone,

it h a p p e n s, these tw o m ajo r so u rces o f u ncertain ty

b e c a u se w e k now that there is a m arg in for error in

each accou n t for a b o u t h a lf the total uncertainty.

the p red ic tio n s. In su ch c a se s, w e take p re c au tio n s

T h is is fortu n ate, sin ce it m e a n s that, d e sp ite the

because w e k n o w that, ev en if the ex act p red ictio n

total uncertainty, different a ssu m p tio n s a b o u t future

from

the scie n ce itself, an d about

fu tu re

h u m an

so m e

from

b e h a v io u r -

U NCERTAINTY IS INEVITABLE, BUT RISK IS CERTAIN

h u m an b e h av io u r can be u se d to test the effect of

61

with the cau ses of clim ate change, w e need to know

su ch b e h a v io u r on clim ate. Th is can g iv e u s u sefu l

future greenhouse g a s em ission s, and any other effects

inform ation ab o u t w h at so rt o f h u m an b eh av io u r is

su ch a s em issio n s lead in g to m ore p articles in the

d esirab le to a void the w orst p o ssib le clim ate ch anges.

atm osphere, or natural climatic variability and change.

In other w o rd s, it is u sefu l for d e v e lo p in g policy.

H u m an em issio n s w ill d ep en d on w o rld p opu lation

In the case o f futu re clim ate im p ac ts, there are a

grow th, the rate of grow th in energy u se p er p erson,

n u m b er o f differen t a ssu m p tio n s, an d a n u m b er o f

the m ix o f en ergy so u rces (for exam p le coal an d oil

m o d e ls o f d iffere n t p a r ts o f the clim ate sy ste m .

v e rsu s su n and w in d) an d energy efficiency (that is,

T h ese ran ge from m o d e ls o f h u m an society lead in g

em issio n s p er unit en ergy p ro d u ce d , and econom ic

to future green h o u se g a s e m issio n s (socio-econom ic

production per unit energy used ), rates of deforestation

m o d els), through m o d els of how m u ch o f the em itted

or reforestation, an d ind ustrial em issio n s such a s the

g re e n h o u se g a s e s sta y in the a tm o sp h e re (carbon

m an ufacture o f steel or fertiliser. M ost of these factors

cycle m o d e ls), to their effects on g lo b a l clim ate

are a p rodu ct of h u m an behaviour, w hich m ay change

(clim ate m o d e ls), local or re gio n al clim atic ch an ge s

w ith attitu d es to qu ality o f life an d w ealth. M any

(d o w n scalin g m o d els), an d ev en tu ally to the effects

d e p e n d on rates o f technological ch ange, inclu ding

o f clim ate ch an ge on b io logical an d h u m an sy ste m s

research and developm ent, and rates o f penetration or

(secto ral im p ac t m o d e ls). S ectoral im p a c t m o d e ls

ad o p tio n o f new tech n ologies. N e arly all of these

m u st a lso co n sid er the a d a p tiv e cap acity o f society,

factors can be influenced b y policy, which m ay depen d

w h ich w ill c h a n g e w ith tim e a n d a lso le a d to

on the u n d e rsta n d in g p o licy -m ak ers h av e o f the

uncertainty. U ncertain ties at each sta g e in this chain

consequ en ces of alternative policies.

o f re aso n in g lead to w h at so m e au th o rs h ave called a 'c a sc a d e o f u n certain ty', a s sh ow n in Figure 12.1

O th er u n ce rta in tie s re la tin g to the c a u s e s o f clim ate ch an g e in clu d e n atu ra l clim ate flu ctu atio n s

There is a lon g list o f u ncertain ties relating to

d u e to internal p ro c e sse s in the clim ate sy stem (for

p ossible future clim ate change and its im pacts. To start

e x a m p le c h a n g e s in v e g e ta tio n or d e e p o cean

E S T IM A T E D V A R IA B L E

PRO CESS A P P L IE D

R A N C E OF U N C E R T A IN T Y

C H g a s e m issio n s C a rb o n cycle m o d e l

!

C lim a te m o d e l

I

D o w n s c a lin g m e th o d

I

Sectoral im p a ct m o d e ls

I

C H g a s co n c e n tra tio n s

G lo b a l clim ate c h a n g e

R e g io n a l clim ate c h a n g e

Sectoral im p a ct

Figure 12: The 'cascade of uncertainty'. Schematic representation of the growth of the range of uncertainties in the chain of reasoning associated with climate change and its potential impacts. New uncertainties at each step expand the total range of uncertainty at the previous step. However, the individual ranges are not additive since the extremes will become progressively less likely as different ranges of uncertainty are combined. (After Henderson-Sellers, 1993; Jones, 2000.)

CLIMATE C H A N C E: THE SCIENCE, IMPACTS A N D SO L U T IO N S

62

circulation ), or n atu ra l extern al forces o p e ra tin g on

T hen there are the u n ce rtain tie s in m o d e ls that

the clim ate sy ste m (in clu d in g p erio d ic v a ria tio n s in

calcu late the im p a c ts o f clim ate ch an ge, for ex a m p le

the E a rth 's orbit a ro u n d the Su n , v a ria tio n s in so la r

on crop p ro d u c tio n , riv er flow , flo o d in g , c o a sta l

en ergy o u tp u t, an d v o lcan ic e ru p tio n s). T h ere are

storm su rg e s, a n d d a m a g e co sts. H ow w ell d o crop

p o ss ib le fu rth er effects on clim ate d u e to h u m a n

m o d e ls tre at the e ffe c ts o f d iffe re n t so ils , o f

a c tiv itie s su c h a s la n d c le a rin g , irrig a tio n , a n d

in c re a sin g a tm o sp h e ric co n ce n tratio n s o f carb o n

a tm o sp h e ric p o llu tio n (for e x a m p le , carb o n b lack

d io x id e on p la n t gro w th , an d o f p e sts a n d d ise a se s?

from fires or in crease d d u st from d esertification ).

C o stin g is a v e x e d q u estio n (d isc u sse d in C h a p ters

There are also u ncertain ties a b o u t how m u ch of

6 ,7 an d 8), that in c lu d e s a sse ssm e n t o f the co sts an d

the e m issio n s into the atm o sp h ere stay there. T h is

b en efits o f v a r io u s a d a p ta tio n s to clim ate ch an g e

requ ires m o d ellin g o f the ch em ical p ro ce sse s in the a tm o sp h e re fo r m eth an e a n d n itro u s o x id e , an d

an d o f m e a su re s to red u ce e m issio n s. T h e first ru le in a s s e s s in g u n ce rtain ty , a n d

m o d ellin g o f rem ov al p ro ce sse s for p articu lates such

p a r tic u la r ly

a s w ash o u t or grav itatio n al settlin g ov er the ocean s

a ss e s sm e n ts , is th at w e sh o u ld u n d e rsta n d w h at

a rg u m e n ts

b ase d

on

r e s u lt s

of

an d land su rface s. R em ov al p ro ce sse s for the m ain

u n ce rta in tie s h a v e b ee n tak en into a c c o u n t a n d

g reen h o u se g a s, carbon d io x id e , largely d e p e n d on

w h a t a ss u m p tio n s h a v e b ee n m a d e . T h is a p p lie s

b iological in teraction s, the tem p e ratu re -d ep en d e n t

esp e cia lly in a re as w h ere ra n g e s o f u n certain ty are

so lu b ility o f carb o n d io x id e in w a ter (it is m ore

often n ot g iv e n , su ch a s e stim a te s o f the c o sts o f

so lu b le in co ld er w ater) an d rates o f o v ertu rn in g of

clim a te

the su rfa c e w a ters o f the ocean . G row th ra tes of

a d a p ta tio n m e a s u r e s . T oo o fte n r e s u lt s o f su c h

ch an ge

im p a c ts

or o f m itig a tio n

or

v egetatio n an d p lan k to n , the effects o f forest fires,

a s s e s s m e n t s se e m to b e b ia s e d , in ten tio n a lly or

an d interactions betw een clim ate itself an d the rates

n o t, to w a r d s the o u tc o m e s w a n te d b y sp e c ia l

of all these p ro ce sse s are all factors.

in terests that co m m issio n or fu n d the stu d ie s. T h is

G iven the e m issio n s an d how m u ch sta y s in the

often tak es the form of ch oices a s to w h at is in clu d ed ,

atm o sp h ere , clim ate m o d e ls are n e e d e d to calcu late

w h a t sc e n a rio s are u se d , w h at v a lu e s are a ssu m e d ,

w h at

an d w h at a lte rn ativ e s are co n sid ere d .

e ffe c t

th e

ch anged

c o n c e n tr a tio n s

of

gre e n h o u se g a s e s w ill h a v e on the clim ate. W hile

For e x a m p le , in co n sid e rin g the co st o f clim ate

th ese m o d e ls are b a se d on the w e ll-e sta b lish e d

ch ange im p acts, p o ssib le a d v e rse im p ac ts o f extrem e

la w s

e v e n ts or ec o n o m ic g a in s fro m

o f m o tio n ,

a tm o s p h e r ic

r a d ia tio n ,

and

th e rm o d y n a m ics (tran sfer o f h eat), there are m an y

re d u c e d fro st

frequ en cies m ay be ign o red . Sim ilarly, in estim atin g

u n certain ties. S o m e o f the m ain a re as o f concern are

the c o sts o f e m issio n s re d u ctio n s, a d v e rse im p a c ts

the b e h a v io u r o f c lo u d s th at a b so rb an d reflect b oth

on carb o n in ten sive in d u strie s m ay b e co n sid ere d

h eat an d ligh t rad iatio n , in teractio n s at the lan d an d

b u t not the econ om ic b en efits from en ergy efficiency

ocean su rfa c e s, an d the effect o f sm a ll sp a tia l scale

or the gro w th in ren ew ab le en ergy in d u stries.

a n d very ra p id p ro c e sse s in the a tm o sp h ere that are

The im p o rta n t thing w ith all these u n certain ties

n ot w ell m o d elled . T h ese in clu d e rain fall v a ria tio n s

is that w e sh o u ld be a w a re o f them an d take them

in re g io n s o f v a ry in g to p o g ra p h y (m o u n ta in s an d

into a cco u n t, both in o u r ow n e stim a te s an d in

c o astlin es), an d extrem e ev en ts su ch a s h e a v y rain,

a s s e s s in g th o se o f o th e rs. We sh o u ld e x a m in e

tro p ical cy clo n es, th u n d e rsto rm s, p e a k w in d s an d

a sse ssm e n ts to see how clearly (or 'tra n sp a re n tly ')

hail. C o n fid e n ce in the sim u la tio n o f these so rts of

they state a ss u m p tio n s an d u n certain ties. Further,

ev en ts in g lo b a l clim ate m o d e ls is low. It is higher,

w e sh o u ld n ot re g a rd re su lts a s o f no u se at all if

how ever, in m o d e ls that calcu late w h at is h a p p e n in g

they h a v e la rg e u n ce rta in tie s a tta c h ed to them -

on fin er s p a t ia l sc a le s, e s p e c ia lly in fin er sc a le

after all, a d m itte d u n certain ty im p lie s a d e g re e of

re gio n al m o d e ls, w h ich can be d riv en by the g lo b a l

u n d e rsta n d in g an d h onesty, and su ch re su lts still

m o d e ls at their b o u n d a rie s.

lim it the p o ssib ilitie s. M o reo v er, the m o st lik ely

UNCERTAINTY IS INEVITABLE, BUT RISK IS CERTAIN

resu lts are p rob ab ly som ew h ere near the m id d le of the ran ge of uncertainty, u n less the stu d y is b iased by its a ssu m p tio n s. Som e k n o w led ge is better than none, p rovid ed we u se it w isely in full aw aren ess of

63

(IPCC), h ave only recently started to com e to grip s w ith this com plex p rob lem , and there w a s a new e m p h asis on qu antifyin g uncertainty in the IP C C 's Third Assessment Report in 2001 and the Fourth report

its lim itations. O bviously, w here u ncertain ties are large w e sh o u ld try to reduce them , but in the m ean tim e w e n eed to m ake the b est of w h at w e h ave to gu id e both ad ap tatio n an d m itigation policy. W hen it co m es to estim atin g how uncertain

in 2007. T h us, m an y of the estim ates of uncertainty g iven in this b ook are prelim inary, an d m ay not cover the full ran ge of uncertainty in so m e cases. In particular, there m ay be u nexpected d evelo p m en ts

projections of future clim ate ch ange and clim ate ch an ge im p acts m ay be, w e n eed to d istin g u ish

sm aller, clim ate ch an ges and im pacts. In deed, new o b serv atio n s, esp ecially in the last few years, su g g e st that so m e key uncertainties m ay be larger than p rev io u sly thought, especially in the direction of m ore ra p id clim ate ch an ge and sealevel rise. These are d iscu sse d in C h apter 5. G e n u in e sc e p tic ism a b o u t o v e r-c o n fid e n t

betw een tw o ty p e s of uncertainty. O ne is the uncertainty abou t som eth in g that can be m easu red repeatedly. T h is can in p rin cip le be red u ced by takin g m ore m e asu rem en ts: the b est an sw e r is likely to be the a v e ra g e d e riv ed from the m o st m easu rem en ts and is in m ost cases the m ost frequent answ er. Statisticians call this a 'frequentist' problem . The exam ple at the start of this chapter, of m easu rin g the diam eter of a steel ball, illustrates this. The other sort of uncertainty arises w hen there cannot be repeated m easu rem en ts. This is u su ally becau se w e are dealin g with som e prediction of the futu re b a se d on a theory or m o d el, often w ith assu m p tio n s ab ou t future beh avio u r or influences. Future clim ate cannot be m easu red now, and there w ill only be one future clim ate. H ere uncertainty can be estim ated by calculating the effects of different assu m p tio n s in the in p ut d ata, the theory and the m o d els. In this case w e n eed to u se ad d itio n al know ledge abou t the assu m p tio n s and m o dels, such as how uncertain they are, and then exp lore the ran ge of resu lts arisin g from the ran ge of plau sib le assu m p tio n s or m odels. Estim ation of uncertainty of future clim ate or its im pacts requ ires u s to look at the re su lts o f all the p o ssib le co m b in atio n s of assu m p tio n s, which m ay n um ber in the th ou san ds. This sort of uncertainty estim ate requires com plex co m pu tation s. It is know n a s 'B ay esian statistics' after the eigh teen th centu ry R everen d T h o m as Bayes, w ho first su gge sted the m ethod, but did not have a com pu ter to carry out the calculation s.2 P eop le w o rk in g on clim ate im p acts, in clu din g the scien tists an d policy a d v iso rs a sso cia ted w ith the In tergovern m en tal Panel on C lim ate C h an ge

and 'su rp rise s', which m ay well lead to larger, or to

p red ic tio n s is to be a p p la u d e d . A g o o d e x a m p le is a b o o k that at first glan ce m igh t be th ou gh t to ru bb ish clim ate m o d els - Useless Arithmetic: Why Environmental Scientists Can't Predict the Future, (C olum bia U niversity Press, 2007). H ow ever, a s Fred Pearce notes in a review in New Scientist, the b ook in fact com m ends the authors of the IPCC for 'painfully lon g d isc u ssio n s ab o u t errors, u ncertain ties and m issin g d ata'. Pearce notes that the book trash es m ore m o d els for com placency than for predictin g disaster. In m y view, this book ad v ocates ju st w hat I am advocatin g: the u se of m o dels w ell-inform ed by observation s and u p d ated as new inform ation com es in - and with a full recognition of uncertainty.1

From polarisation to probability and risk P eople resp on d in different w ay s to uncertainty. Som etim es they get confused and see it as a reason for concluding that they know nothing u sefu l on the subject, and therefore see no reason to act. This is especially the case if action to deal with a potential risk w ould have up front costs. This is the position taken by m an y w ho ch allen ge the reality or seriou sn ess of hum an-induced climate change. These peop le in denial tend to focus on the uncertainties, particularly at the low end of the range of possibilities, rather than on w h at is know n. Som e (but not all) m ay have a vested interest (financial or ideological)

64

CLIMATE C H A N C E: THE SCIENCE, IMPACTS A N D SO L U T IO N S

in d o in g n oth in g, an d u se the u n certain ty a s an

su p e rfic ia l c o n c lu sio n , first the re al p ro b a b ility of

excu se for d e layin g m ean in g fu l action.

n e g a t iv e c h a n g e s in r a in fa ll, a n d s e c o n d the

In o th e r s it u a t io n s , h o w e v e r, p e o p le

m ay

co m b in e d effe cts o f ra in fa ll c h a n g e s an d w a rm in g

co n clu d e that a lth o u g h there is u n certain ty , it is

on w a te r s u p p ly a n d d e m a n d . In th is c a se the

w orth tak in g a g a m b le an d d o in g so m eth in g ev en if

p ro je cted ra in fa ll ch a n g e by 2070 in w in ter (w hich

the o d d s are on ly m a rg in a lly fa v o u ra b le . We all d o

is the w e tte st s e a so n , w ith m o st ru n o ff in to the

th is to a certain extent. F a rm e rs d o this a s p art of

riv e r s) r a n g e d fro m a d e c r e a s e o f 25% to an

their e v e ry d a y c o p in g w ith the u n certain ties o f the

in c rea se o f 8%. W hile th is still s p a n s zero , it m e a n s

w eather. S o m e p e o p le ev en g a m b le w h en the o d d s

th at the m o st lik ely ch a n g e is a d e c re a se o f a ro u n d

are stack ed a g a in st them , a s in g a m b lin g c a sin o s or

8% , w ith a b o u t a 50% ch an ce th at the d e c re a se w ill

lo tteries. In oth er c a se s, p e o p le m a y d e c id e that ev en a sm a ll ch ance of a d a m a g in g o u tco m e m a k e s

be m o re th an 8% (the m id d le o f the ra n g e o f u n certain ty ). M o reo ver, the w a rm in g w a s p ro jected

it w o rth w h ile to take so m e form o f in su ran ce , even

to b e b etw een 1.0 an d 6 .0 °C by 2070, w h ich w o u ld

at so m e exp en se.

in c r e a se e v a p o r a t iv e l o s s e s o f w a te r, th e reb y

H o w w e react to u n certain ty d e p e n d s in large

re d u cin g ru n o ff a n d in c rea sin g w a ter c o n su m p tio n

p art on h ow w ell w e u n d e rsta n d the o d d s, a n d on

b y c r o p s a n d to w n s in the v alley . U sin g ru n o ff

w h at is at stak e. C o n sid e r a w eath er fo recast o f a

m o d e ls , the p ro je c te d c h a n g e in ru n o ff into the

30% chance of rain in a rather large district (typically

m ain w a te r s to r a g e d a m w a s in fact b etw een no

100 km b y 100 km ). W hat that u su a lly m e a n s is a 30% chance that it w ill rain so m ew h ere in the district

ch an g e (zero) a n d a d e c re a se o f 35% b y 2070, w h ich m e a n s a 50% ch an ce o f w a te r s u p p ly d e c re a sin g

(but not n ecessarily at o u r p articu la r location) so m e

b y m o re than 17%. It is th is fig u re th at n e e d s to be

tim e in the n ext 24 h o u rs. If all that is at issu e is

c o n sid e re d in c a lc u la tin g w h a t is at sta k e in the

w h ether w e sh o u ld w alk the d o g w e m a y accep t the

M a c q u arie R iver b a sin for irrig a tio n fa rm e rs, tow n

risk an d go an y w ay . B u t if w e w ere th in k in g of

w a te r su p p ly , an d the e c o n o m y o f the re g io n . So

p o u rin g a large slab o f concrete that m igh t be ru in ed

an a p p a re n tly v e ry u n ce rtain p ro jectio n o f ra in fa ll

b y h e av y rain an d co st u s th o u sa n d s o f d o lla rs, w e

c h a n g e tra n sla te s, w h en all th in g s are co n sid e re d ,

m ay w ell hesitate to d o it. We w o u ld w a n t to know

into a re su lt th at h a s im p o rta n t im p lic a tio n s for

w h at so rt o f rain w a s ex p ec ted , an d certain ly look

p la n n in g a n d p o licy .4

into p ro v id in g co v ers to go ov er the slab.

To p u t this in m ore gen eral term s, w h at m atters

So w e n eed to u n d e rsta n d w h at the u n certain ty

is not the p ro b a b ility o f a p a r tic u la r n u m e rica l

m e a n s for o u r p articu la r situ atio n , an d to w eig h the

o u tco m e co m in g to p a s s , w h ich is u su a lly q u ite

p o ssib le c o n se q u e n c e s o f eith er ta k in g the risk or

sm a ll, b u t the c u m u lativ e p ro b a b ility o f g e ttin g a

a v o id in g it. It is n o t o n ly the p ro b a b ility th at

ran ge of o u tco m es that is o f p ractical im portan ce. It

m atters, b u t a lso the co n seq u en ce s.

is n o t a m a tte r o f the a c c u ra c y o f a p a r tic u la r

C o n s id e r a sim p le e x a m p le o f a clim ate ch a n g e

p re d ic tio n , b u t o f the p ro b a b ility o f a ra n g e of

p re d ic tio n , su ch a s th at w h ich a ro se fro m a stu d y

o u tco m es w ith se rio u s co n sequ en ces. T h is is u su ally

o f fu tu re clim ate ch a n g e im p a c ts on the M a c q u arie

e x p r e ss e d a s a risk a ss e s s m e n t , w h ere risk is

R iv e r in N e w S o u th W ales, A u s tr a lia . H ere the

u n d e r s to o d a s the p ro b a b ility o f an o u tco m e

p r o je c te d ra in fa ll c h a n g e s in a ll fo u r s e a s o n s

m u ltip lie d by its c o n se q u e n c e s. T h u s a lik ely

s p a n n e d a ra n g e from in c re a se to d e c re a se , w ith

o u tcom e h a v in g la rg e co n seq u en ce s is a larg e risk,

slig h tly m o re ch an ce o f an in c rease in su m m e r an d

w h ile a sm a ll p ro b a b ility o f a lo w -co n seq u en ce

a stro n g e r ch an ce o f a d e c re a se in w in ter. To the

ou tcom e is a sm a ll risk. A h igh p rob ab ility o f a sm a ll

u n in fo rm e d or the sc e p tic th is m ig h t w ell sig n a l

b u t n on-n egligible effect m ay also b e w orth w orry in g

th at the c h a n g e co u ld b e z ero , so there is n o th in g

a b o u t, a s w o u ld b e a low , b u t n o t-n e g lig ib le

to w o rry a b o u t. T w o th in g s a r g u e a g a in s t th is

prob ability o f a very se rio u s effect.

U NCERTAINTY IS INEVITABLE, BUT RISK IS CERTAIN

65

In the case of clim ate ch ange, n atu ral an d h u m an

or oth er p ro b le m s. E v en if w e ca n n o t sa y w h en

sy ste m s h av e been forced b y p a s t n atu ra l clim ate

e x a c tly the th re sh o ld w ill b e e x c e e d e d , w e can

variab ility to ev o lv e or a d a p t so that m o st o f the tim e

estim ate , from a lon g record o f o b se rv atio n s o f the

they o p erate w ithin a 'co m fo rtab le' ran g e in which

v a ria b le , how frequ en tly on a v e ra g e the th resh old

they o p erate w ell. S o m etim es sy ste m s exist o u tsid e

is ex cee d e d . T h is e n a b les u s to calcu late the risk to

that ra n g e in clim atic c o n d itio n s in w h ich they

o u r e n te rp rise a n d w h a t so rt o f p re c a u tio n s w e

su rv iv e , b u t not w ell. T h is is so m etim e s called the

n eed to take to su rv iv e that risk.

'c o p in g ' ran ge. O ccasion ally , n atu ra l a n d h u m a n

The case o f clim ate ch an ge is sh o w n in F ig u re 14.

sy ste m s exp erien ce extrem e clim atic even ts that are

H ere an u n c h a n g in g clim ate is sh o w n at the left,

d a m a g in g , so m etim es fatally. T h ese ev en ts are called

a n d a c h a n g in g clim a te at the righ t. A g a in , the

'n atu ra l d is a s te r s ' a n d in c lu d e d ro u g h ts, flo o d s,

c o p in g ra n g e an d th re sh o ld s for v u ln e rab ility are

storm su rg e s an d w ild fires. C lim ate ch an ge m o v es

sh o w n by the h o riz o n tal lin es. In the u p p e r g ra p h

the a v e ra g e clim ate so that co m fortab le co n d ition s

w e see h o w clim ate ch an g e can c a u se the v ariab le

beco m e le ss co m m on , an d extrem e ev en ts, w hich

(su ch a s rain fall) to ra p id ly in crease the frequ en cy

can be defin ed a s those fallin g o u tsid e the p rev io u s

w ith w h ich it e x c ee d s the th resh old for vulnerability,

co p in g ran ge, b ecom e m ore co m m on or o f greater

an d th u s the risk to the en terp rise. The low er g ra p h

severity. W hat is o f concern in clim ate ch an ge is

in c lu d e s an exte n sio n o f the c o p in g ra n g e d u e to

therefore the risk a sso cia te d w ith ch an ge s that take

im p ro v in g ou r ab ility to co p e (called 'a d a p ta tio n '),

u s m o re frequ en tly into m o re extrem e co n d itio n s

w h ich re d u c e s the v u ln e rab ility to clim ate ch an ge

th at are d a m a g in g or d is a s tr o u s. W hat w e are

a n d th u s the risk.

con cern ed ab o u t is the p rob ab ility o f ch a n g e s that p u sh u s ov er the threshold into these extrem es.

F o rtu n a te ly , the p ro b a b ility o f e x c e e d in g a p articu la r im p a c t th resh old of, say, tem p e ra tu re or

F ig u re 13 illu stra te s how n o rm al clim ate v a ria ­

rain fall a t so m e tim e in the future can be determ in ed

bility, w ith no clim ate ch an g e , c o v e rs a ra n g e of

m o re co n fid e n tly than the p ro b a b ility th at the

v a lu e s that m a y b e fa v o u ra b le for a g iv en activity,

tem p e ra tu re or rain fall w ill h a v e a p articu la r v a lu e

b u t so m e tim e s g o e s o u tsid e th at ran g e to c a u se lo ss

at that tim e.

Critical Thresho Id C o p in g Range

Vulnerable

^ Critical Threshold

Figure 13: The concept of exceeding a threshold. This schematic illustrates at lower left a coping range under an unchanging but variable climate for a variable such as rainfall (with time increasing towards the right), and an output such as profit from a crop (upper right). Vulnerability is assumed not to change over time. The upper time series and chart shows a relationship between climate and profit and loss. The lower time series and chart shows the same time series divided into a coping range using critical thresholds to separate the coping range from a state of vulnerability. The bell-shaped curve in the lower right-hand side is the probability distribution for the variable having a particular value. The upper critical threshold might represent the onset of dangerous flooding, while the lower threshold might represent the onset of drought. Darker shading represents more severe consequences. (Figure courtesy of RN Jones, CSIRO.)

66

CLIMATE C H A N C E: THE SCIENCE, IMPACTS A N D SO L U T IO N S

Stationary Climate & Coping Range

C han ging Climate Vulnerable

Stationary Climate Coping Range

&

i

\j i ( W

y |wy

v *

C han ging Climate l «Vulnerable

/U A ft /\ WW/V |\| V

Adaptation Coping Range

"

Vulnerable

Planning Horizon Figure 14: The effect of climate change on vulnerability. Illustrates the coping range for a variable such as rainfall, showing how climate change can rapidly lead to exceeding the threshold for vulnerability more frequently (upper curve), and how adaptation to change can reduce that vulnerability (lower curve). (Figure courtesy of RN Jones, CSIRO.)

To u n d e rsta n d w h y th is is so , w e n eed to know

c a u tio u s) a ssu m p tio n is to a ss u m e th at an y v a lu e

w h at a probability distribution is, a n d w h at it lo o k s

w ithin the ran g e h a s an eq u a l probability. A rg u ab ly

like. T h is is the w a y in w hich the p ro b ab ility o f a

that is w h at the IPCC report in 2001 d id b y failin g to

p articu lar v ariab le h av in g a p articu la r v a lu e v a ries

d isc u ss different p ro b ab ilities for different scen ario s

w ith the v a lu e o f the v a ria b le . F or in sta n ce , the

of future carbon d io x id e e m issio n s, an d o f resu ltin g

tem p eratu re at so m e p lace x at so m e tim e y co u ld be

glo b al w a rm in g estim ates. An a ssu m p tio n o f eq u al

an y w h ere b etw een 5 .0 °C a n d 1 0 .0 °C , w ith a v ery

p ro b ab ility g iv e s a m u ch gre ater p ro b ab ility to the

sm a ll ch an ce (sa y le ss than on e in 20) o f it b ein g

ex trem es o f the ran ge than in a n orm al distribu tion .

either le ss than 5 .0°C or gre ater than 10.0°C , b u t a

(A s it h a p p e n s , the m o st ex trem e o f the S R E S

large ch ance of it b ein g betw een those tw o v alu e s,

sc en a rio s, the A 1FI sc en ario , n ow lo o k s c lo se st to

an d p ro b a b ly g re a te st o f b ein g a b o u t 7 .5 °C . The

w h at h a s h a p p e n e d so far sin ce 1990 - the sta rt of

p rob ab ility is u su ally a ssu m e d to v ary acco rd in g to

the S R E S sc e n a rio s - b u t IP C C in its 2007 report

a 'n orm al distrib u tion ', in w hich case the distrib u tion

a c t u a lly

g ra p h is b ell-sh ap ed an d w e can a ssig n p rob ab ilities

p re su m a b ly b e c a u se it th ou gh t it least likely.)

d e - e m p h a s is e d

the

A 1FI

s c e n a r io ,

o f the v a ria b le ly in g in an y giv en ra n g e, w ith the

In the a b o v e e x a m p le , if w e a ssu m e the v ariab le

m o st likely b ein g the m id d le v alu e (see low er right

is n o rm ally d istrib u te d , an d the th resh old is 7 .5°C ,

o f F ig u re 13). But not all v a ria b le s follow a n o rm al

then w e find the p ro b a b ility o f e x c e e d in g th is

distribu tion (p articu larly on es like d a ily rain fall that

th resh o ld is 50% . If w e m a k e the v ery d iffere n t

can h av e p o sitiv e v a lu e s or b e zero, b u t n e v e r a

a ssu m p tio n o f a flat or eq u al p rob ab ility d istrib u tion

n e g ativ e v a lu e ). A n a ssu m p tio n that a v a ria b le is

o v er the ran ge, then, a lth o u g h the p ro b ab ility o f the

n o rm ally d istrib u ted is con ven ien t b e c a u se it allo w s

te m p e ra tu re b ein g ex actly 7 .5 °C is m u ch sm aller,

u s to a p p ly sim p le statistics to its b eh aviour, b u t it is

the p ro b a b ility o f the te m p e ra tu re e x c e e d in g this

not a lw a y s ap p ro p ria te .

v a lu e is still 50%. T h is is b ec a u se the p ro b ab ility of

A ssig n in g a normal distribution to a v ariab le is an a ssu m p tio n , an d if w e really h a v e no id e a w h at the

e x c ee d in g a thresh old in teg rates (or a d d s u p) all the v a lu e s b elow the th resh old.

p ro b a b ility d istrib u tio n lo o k s like, a p a rt from its

S u ch a re su lt is ev en m o re ro b u st w h en w e

lim itin g v a lu e s , a m o re c o n se rv a tiv e (th at is,

co n sid er the resu lt of co m b in in g tw o or m ore ran ges

U NCERTAINTY IS INEVITABLE, BUT RISK IS CERTAIN

67

o f uncertain ty. T h is is b e c a u se the p ro b a b ility of

w ith o u t lik e lih o o d s, if they h elp d e cisio n -m a k e rs

e x c e e d in g a p a rtic u la r th resh old is the re su lt o f a

ch oose betw een p o lic ie s that m ay lead to d e sira b le

n u m b er of different in d iv id u a l probability distributions

or u n d e sira b le ou tco m es.

for a n u m b e r o f d iffere n t v a ria b le s all o f w hich contribute to the uncertainty. W hile any one o f these

N e v e rth e le ss, the lack o f p ro b a b ility estim a te s p resen ts p ro b lem s in d e v e lo p in g p olicy for red u cin g

p robability d istrib u tio n s m ay be difficult to quantify,

g re e n h o u se g a s e m is sio n s a n d in p la n n in g for

the p ro b a b ility d istrib u tio n o f the co m b in atio n is

a d a p ta tio n to c lim a te c h a n g e s. D e c isio n -m a k e rs

often le ss u ncertain , an d in gen eral m ore likely to be

n eed to b a se d e c isio n s on so m e risk a ss e s sm e n t

p e a k e d , a n d for c o m b in a tio n s o f m o re v a ria b le s

b oth in m itig atio n a n d a d a p ta tio n p o lic ie s, sin ce

b e c o m e s in g e n e ra l c lo se r to b e in g n o rm a lly

su ch p o lic ie s in v o lv e co sts. C learly, a s the ra p id rise

d istrib u ted . This is b ec a u se w hen an y tw o probability

in carb on d io x id e e m issio n s sin ce 1990 h a s sh o w n ,

d is tr ib u tio n s are c o m b in e d , the p ro b a b ility o f

estim ate s n eed to b e re -a sse sse d a s n ew in form ation

co m b in in g extrem e v a lu e s o f the tw o v a ria b le s to

co m es to h an d . W hat w a s once co n sid ere d u n likely

p ro d u c e a n ew extrem e o f the co m b in atio n is le ss

m a y b e c o m e m o re lik ely a s e v e n ts or scien tific

than the p robab ility o f m u ltip le co m b in atio n s o f the

u n d e rsta n d in g p ro g re ss.

tw o v a ria b le s le a d in g to the sa m e in term ed iate v a lu e o f the p rod u ct.

The U nited N a tio n s F ram e w o rk C on v en tion on C lim a te C h a n g e (U N F C C C ) sta te s that the central

W hat this m e a n s in p ractice is that the p rob ab ility

o b je c tiv e m u s t b e to a v o id c o n c e n tr a tio n s o f

d istrib u tio n o f an y v a ria b le in flu en ced b y m u ltip le

g re e n h o u se g a s e s th at m a y lea d to 'd a n g e r o u s

u n ce rta in tie s is lik ely to b e b ell sh a p e d , w ith the

in terferen ce w ith the clim ate sy s te m '. T h erefore,

m o st likely v a lu e n ear the m id d le o f the co m b in ed

d e v e lo p in g a p p ro p ria te m itig atio n p o licy re q u ires

u n certain ty ran ge, an d the c u m u lativ e p ro b ab ility

an u n d e rsta n d in g n ot on ly o f the im p a c ts o f any

o f e x c e e d in g the m id -ra n g e v a lu e is lik ely to be

g iv e n co n ce n tratio n o f g re e n h o u se g a s e s in the

a ro u n d 50% . W hile th is is a g o o d ru le o f th u m b ,

a tm o sp h e re (w hich h a s a ran g e o f u n certain ty ), but

there are excep tio n s, esp e cia lly w h ere the com b in ed

a lso o f the likelihood o f re ach in g a critical level o f

v a ria b le (for e x a m p le , ru n o ff in a river) can n o t be

g r e e n h o u se

n e g a tiv e .

p ro b a b ility

th resh old) at so m e tim e in the futu re. The u rgen cy

d istrib u tio n is likely to be sk e w e d , w ith m ore sm all

an d se v e rity o f any m itig ation m e a su re s n eed ed to

v a lu e s an d a few larg e v a lu e s.

a v o id reach in g a critical th resh old d e p e n d s on the

In

th e

la tte r c a s e ,

th e

gas

c o n c e n tr a tio n s

(a

d an gerou s

risk (p ro b a b ility m u ltip lie d b y co n se q u e n c e ) of w h at m ay h a p p e n if su ch m e a su re s are n ot taken.

Estimating risk

S im ila rly , a p p r o p r ia te

a d a p t a t io n

p o lic y is

Th e IP C C , in its su c c e s siv e re p o r ts h a s b ee n

related to the rate an d m a g n itu d e o f clim ate ch an ge

re lu c ta n t

to p a r tic u la r

that affects d e sig n p ara m e te rs or critical th resh o ld s

m a g n itu d e s o f w a rm in g s w ithin the large ran g e of

fo r p a r tic u la r in fra s tr u c tu re (b u ild in g s , d a m s ,

to attach

p ro b a b ilitie s

1.4 to 5.8°C (in the 2001 report) an d 1.1 to 6.4 °C (in

d ra in s, sea w alls, etc.) an d activities (farm in g , w ater

the 2007 report) that it estim ate d for the y ea r 2100.

su p p ly , etc.). F or e x a m p le , e n g in e e rs d e sig n in g a

T h is w a s d u e to the g re a t d ifficu lty o f a ssig n in g

d a m re q u ire d to la st 100 y e a rs or m o re n e e d to

p ro b a b ilitie s to the re le v a n t p o p u la tio n , so c io ­

k now the lik ely m a x im u m flood flo w s for w h ich a

ec o n o m ic an d te c h n o lo g ica l fa c to rs th at w o u ld

sp illw a y w ill n eed to co p e to a v o id p o ssib le co llap se

decades

o f the d a m . E n gin e ers an d p la n n e rs requ ire sim ila r

a h e ad . T h is d ifficu lty w a s accen tu ated b y the likely

e stim ate s for the h eigh t o f b rid g e s, size o f d ra in s, or

in flu en ce o f fu tu re p o lic ie s on th ese fa cto rs that

se tb a ck s from riv ers or co astlin es su b ject to p o ssib le

d eterm in e e m issio n s. M o reover, m u ltip le sc en ario s

flo o d in g or c o a sta l sto rm s. It is re lativ ely e a sy to

o f the fu tu re are u se fu l to d e c isio n -m a k e rs, ev en

e s ta b lish the se n sitiv ity o f s y s t e m s to c lim a te

d e te rm in e

g re e n h o u se

gas

e m is sio n s

68

CLIMATE CHANCE: THE SCIENCE, IMPACTS A N D SO LUTIO NS

ch an ge, an d to su g g e st m e a su re s for in creasin g ad ap tab ility an d resilience, such a s higher b rid ges, larger sp illw a y s an d stro n ger b u ild in g s. But the extent and urgency of the m e asu res that sh ou ld be taken d e p e n d s on the p robability of a given ch ange and its consequ en ces. Such m e asu res incur costs, so a risk assessm e n t is n eeded. R isk can n ot be m a n a g e d or treated efficiently u n le ss it is p ro p erly a ss e s se d . T h is req u ires an e stim ate o f both the p ro b a b ility o f an ev en t occurring and an a sse ssm e n t of its con sequ en ces. The risk o f e x c e e d in g so m e critical lev e l of co n seq u en ces (defined by collective glo b al v alu e ju d g e m e n ts in the case of the U N F C C C ) is central to d e cid in g the u rgen cy an d extent o f redu ction in g lo b a l g re e n h o u se g a s e m issio n s (th at is, m itigation ) that is n eeded. Once a global em ission s reduction target is agreed , there w ill then be a need to d ecid e on n ation al or other local targets on an equitable b asis. That in vo lv es n egotiation , p o ssib le co m p rom ises and further uncertainty. Som e scientists have argu ed that it is too difficult to a ssig n p ro b ab ilities to futu re clim ate ch ange. H ow ever, Steve Sch neid er of Stanford U niversity h as a rg u e d that, in the ab sen ce o f better exp ert advice, decision -m akers w ill m ake their ow n form al or inform al estim ates of probability, and that this is w o rse than u sin g inform ed estim ates p rovid ed by relevan t exp erts.5 T h at su ch p robability estim ates for global w arm in g are p o ssib le is illu strated by a n u m b er of estim ate s in the scientific literature, alth o u gh they g e t v a ry in g a n sw e rs.6 M o st find sin gle-p eak ed prob ab ility distrib u tion s (that is, a sin gle m o st p ro b ab le ou tcom e), b u t a stu d y by G ritsev sk y i an d N ak icen ovik of the In ternational In stitute of A p p lie d S y ste m s A n a ly sis fo u n d a d o u b le -p e a k e d d istrib u tio n (th at is, tw o very different but m ore or less equally likely ou tcom es).7 Th ey attrib u ted this to a sp lit in tech n ological developm en t p ath w ay s tow ards either a low-carbon e m issio n s technology or a high-carbon em issio n s technology, rather than so m e m ixture of the two. This su g g e sts that an early and deliberate choice of em issio n s technology p ath w a y s m ay be crucial to future outcom es.

A lth ough probability estim ates are n eeded, and in p rin c ip le p o ss ib le , m e th o d s for d e riv in g probabilities require further developm ent and cannot be said to be w ell-establish ed at present. In fact, a risk m a n a g e m e n t a p p ro a c h re q u ire s n ot an assessm en t of the probability of a particular em ission am oun t or global w arm in g at som e future time, but rather, a s R oger Jo n es of C SIR O (A u stralia) h as pointed out, an estim ate of the likelihood of exceeding an identified critical im pact threshold. This integrates the p robabilities from the greatest or u p p e r lim it w arm in g dow n to som e critical level, and is m uch less dependen t on the underlying assu m p tion s.8 H ow ever, the relatively low b u t not n egligib le p ro b a b ility o f la rg e or c a ta stro p h ic c h a n g e s, so m e tim e s c a lle d 's u r p r i s e s ', m u st a ls o be co n sid ered , since these m ay contribute ap p reciab ly to the o v erall risk. In deed , even if su ch catastroph ic c h a n g e s occu r m an y d e c a d e s or even cen tu ries into the fu tu re , they m a y d o m in a te an y risk a sse ssm e n t b e c a u se of their very high co sts (see d iscu ssio n in C h ap ter 6). The im po rtan ce of these p o te n tia lly h ig h -risk e v e n ts m e a n s th at h igh p rio rity m u st be p la ce d on b etter u n d e rsta n d in g them , esp ecially their likelihood, p oten tial im pacts, an d any p re c u rso rs th at m ay en ab le them to be d e tecte d in a d v a n c e an d a v o id e d . T h o se w ho a rg u e that the risk from clim ate ch an ge is sm a ll often ignore these un certain ties on the h igh -im pact en d o f the ra n g e o f p o ssib ilitie s. H ig h im p a c t o u tc o m e s m a y n ot be sim p ly m a rg in a l, a s is a ssu m e d in m o st cost-benefit a n a ly se s, b u t co u ld re su lt in the fa ilu re o f the w h ole sy ste m , for ex am p le, not sim p ly h igh er food p rices, b u t m a ss starv atio n and co m m u n ity b reak d ow n . Instead of d iscou n tin g future co sts to negligible am ou n ts in to d ay 's term s, future costs m ay increase d u e to grow th in p o p u latio n s an d in vestm en ts at risk, and p o ssib le n egativ e inflation. Futu re co sts m ay also 'blow ou t' if catastroph ic ch ange occurs that ca u se s system failure rather than ju st m argin al lo sses.9 It is interesting to note that a joint U S -E u ro p e an project called 'R A P ID ' is now fo cu sin g on one p o ssib ly catastro p h ic possib ility , a slow -d ow n of

UNCERTAINTY IS INEVITABLE, BUT RISK IS CERTAIN

69

certain N orth A tlantic currents in clu din g the G u lf Stream , w hich could h ave large region al effects on clim ate in Europe and elsew here. Early detection of any ch ange is seen a s a high priority.10 If p ro b a b ilitie s are n ot a ttach ed to p o ssib le

3. accept that risk m an agem en t m ay require

clim ate ch ange im p acts, the p resen t w ide ran ge of IPCC projected w arm in gs su g g e sts that en gin eers and p lan n ers, a s they a d a p t d e sig n sta n d a rd s and

u n certain ties, one test of w h ether a scien tist, or scientific challenger, is open to all the eviden ce and therefore u n p reju d iced is w hether they sa y 'on the one hand this, and on the other hand that'. W hile su ch a d m issio n s o f uncertain ty are often u sed to

z on in g to clim ate ch an ge, w ill n eed, for the tim e b ein g, to foster resilience an d a d a p tiv e capacity. They w ill n eed to h e d g e their b e ts, an d d e lay in v e stm e n t d e c isio n s, or g a m b le on w h eth er h u m an ity w ill go d o w n high or low e m issio n s develo pm en t p ath w a y s.11 H ow ever, p robabilities w o u ld allow p ro p er risk a sse ssm e n ts and the co sts and ben efits of specific ad ap tatio n p olicies to be calcu lated. T his is a high p rio rity for fu rth er research to a ss is t in p olicy d e v e lo p m e n t.12 It im p lies a so m ew h a t differen t app roach , involvin g d ealin g w ith uncertainty by a strate gy that e m p h a sise s flexibility an d ch an ges with the circum stances.13 Probability estim ates need to be u p d ate d a s new ob serv ation s of ch an ges and p ro ce sses com e in, even if the p ro ce sses h ave not y et been in c lu d e d in clim ate m o d e ls. T h u s o b se rv a tio n s p o in tin g to p ro c e sse s le a d in g to accelerated outflow from or m elting of the G reenland and A ntarctic ice sh ee ts sh o u ld lead to revised estim ates of the probability of rapid sea-level rise.

ap p ro p riate policy re sp o n ses desp ite uncertainty. It is a safe gen eralisation that in a w orld of m any

p u t d o w n sc ie n tists, g e n u in e sc ie n tists se ld o m m ak e sta tem en ts w ith ou t so m e qu alificatio n or caveat b ecau se there are u su ally at least tw o sid e s to any co m p lex argu m en t. P eop le w h o a d m it to only one sid e are u su ally either b iased or takin g a 'd e v il's adv o cate' role. Som e genuine sceptics (often academ ic scientists) take the 'd e v il's a d v o ca te' positio n to stim u late debate and test p ropositions. This is b olstered by one tradition al acad em ic view of science a s a p rocess lead in g to a body of tested p rop osition s or theories that can be re gard e d a s 'tru th s' (at least until su b seq u en tly d isp ro v ed ). This view , in statistical term s, traditionally requ ires that a prop ositio n be establish ed at the 95 or 99% probability level (that is, 95 or 99 chances out of 100 that it is true, respectively) before it can be regarded as established. On this b asis one or tw o p ieces of contrary eviden ce is u su ally en ou gh to d iscred it a p ro p o sitio n . Such a view p rotects the lim ited b o d y of 'tru th ' from any

Uncertainty and the role of sceptics G enuine questioning and scepticism in science is good: it is one of the w ay s that science p rogresses, leading to the critical exam ination of assum ptions and conclusions, and eventually the substitution of newer and m ore reliable theories for older ones that are less robust. This is the scientific m ethod of hypothesis testing and developm ent of new p arad igm s. H ow ever challengers need to do three things: 1. a p p ly their critical facu lties to both sid e s of an argu m ent, 2. ad m it uncertainties that m ay w ork for or a g a in st any p articu lar p rop osition ,

falseh o o d , but m ay end up den yin g a s u nproven m an y p rop osition s that m ight be true. For exam ple, if a p rop ositio n h a s been sh ow n to h ave an 80% chance of bein g true, this view w o u ld reject it as unproven, when in fact it m ay well be true and could have seriou s consequences. This acad em ic view of science takes little account of the relative consequen ces of w hether a p roposition is true or fa lse , an d fa ils to ack n o w le d g e that d e cision s on p ractical m atters m ay require u s to act d e sp ite uncertainty. If this view w ere a d o p te d in d a ily life w e w o u ld se ld o m in su re a g a in st acciden ts b ecau se they are not certain to h ap pen to us. It ign o res the con cept of risk , that is, that in m ak in g practical decision s w e w eigh the probability

70

CLIMATE C H A N C E: THE SCIENCE, IMPACTS A N D SO L U T IO N S

o f an ev en t a g a in st its co n seq u en ces. Policy-relevant

p o ssib le a rg u m e n t a g a in st a p ro p o sitio n to w h ich

or a p p lie d scien tific a d v ic e m u st tak e acc o u n t of

they are o p p o se d for non-scientific re aso n s, in stead

risk even w h en it is less than 95% certain.

of look in g at the b alan ce o f evid en ce. In a d v e rsa ria l

A noth er problem with this view that 'it m u st be

politics, w h ere 'p o in t-sco rin g' is co m m on , an d often

p roven b ey o n d reason ab le d o u b t' is that in practical

accepted a s legitim ate, su ch selective u se o f eviden ce

m atters o u tsid e the lab oratory it is often difficult to

is often co n d o n e d , even if its so u rce is d u b io u s and

find cou n ter-ev id en ce o f a p ro p o sitio n that is any

its veracity in d o u b t. H ow ever, in a d eb ate affecting

m ore certain than each in d iv id u a l line o f ev id en ce

w o rld a ffa ir s , e c o n o m ie s a n d h u m a n w e lfa re ,

for the p ro p o sitio n . We can n o t then au to m atically

d e b a te sh o u ld be re sp o n sib ly d irected at fin d in g

u se a sin gle ap p aren tly inconsisten t 'o b serv atio n ' or

the

p u b lish ed p a p e r to 'd isp ro v e ' a p rop ositio n : w e need to test the co n trary line o f e v id e n ce at le a st a s

sta tem en ts, an d the free a d m itta n c e o f all d o u b ts an d un certain ties, w h ether they fa v o u r a p articu lar

rig o ro u sly a s the su p p o rtin g ev id en ce, an d d ecid e

p r o p o sitio n or n ot. In th is co n tex t, o n e -sid e d

on a b a lan c e o f e v id e n c e , c o n sid e rin g all the

c h a lle n g e rs sh o u ld m o re a c c u ra te ly b e la b elled

u n certain ties. For e x a m p le, if w e h a v e ten se ts of

'c o n tra ria n s' rath er than sc e p tic s, sin ce they are

b a la n c e

of

e v id e n c e ,

the

te s tin g

of

all

o b se rv a tio n s p o in tin g to g lo b a l w a rm in g (lan d

scep tical of one p ositio n b u t d o n ot a lso qu estio n the

tem p e ratu re s, ocean tem p eratu res, sea ice, glaciers,

contrary.14

sn ow cover, plan t flow ering d ates, bird distrib u tion s,

E x a m in in g the projectio n o f g lo b a l w a rm in g by

d ate s o f river ice b reak -u p , bore hole tem p eratu res,

2100 in the ran g e o f 1.1 to 6 .4 °C , m a d e b y the IPCC

m eltin g p erm afro st), an d one w hich d o e s not (som e

in its Fourth A ssessm ent Report in 2007, a ge n u in e

satellite d ata), d o w e sim p ly co n clu de that the 10 sets

scep tic m a y w ell sa y that the ra n g e o f u n certain ty

are w ron g, or d o w e look critically at the reliability of

h a s been u n d ere stim ated . But w h at so m e co n trarian s

all the evid en ce and decid e which is m ore likely?

arg u e is that the w a rm in g m ay b e (or is defin itely)

Th e d e v il's a d v o c a te p o sitio n is le g itim a te in a

le ss than 1.1°C b e c a u se o f so m e selected uncertainty.

p u re ly scien tific d e b a te , w h ere there is p le n ty of

H o w often d o y o u h e a r th ese sa m e co n tra ria n s

tim e for co n ten d in g a rg u m e n ts to b e p u t a n d an

arg u e that d u e to u n certain ty it m igh t e q u a lly w ell

e v e n tu a l

b e gre ater than 6 .4 °C ?

d e c isio n

re a c h e d

by

the

sc ie n tific

co m m u n ity a s a w h o le. H o w ev e r, w h ere critical

An A u stra lia n m a th e m a tic ia n , Ian E n tin g, h a s

p o lic y is s u e s or u rg e n t d e c isio n s are a t sta k e ,

d e sc rib e d the co m m o n sc e p tic s ' a rg u m e n ts in a

re sp o n sib le sc ie n tists w ill g iv e b a la n c e d a d v ic e ,

b o o k c a lled Tivisted: The D istorted M athem atics of

a d m ittin g an d tak in g into accou n t u n certain ties on

Greenhouse D enial.15 E n tin g a rg u e s that the sc e p tics'

both sid e s o f an y d eb ate.

a rg u m e n ts p re c lu d e them from b ein g taken a s a

In the current d eb ate ab o u t the reality, se rio u sn e ss

v a lid a lte rn a tiv e view o f the scie n ce b e c a u se of

a n d u rg e n c y o f c lim a te c h a n g e , g o v e rn m e n ts,

d isto rtio n o f the d a ta , in c o n siste n c ie s b etw een

th ro ugh the IP C C , re q u este d a p ro tem co n se n su s

a rg u m e n ts, an d

p o sitio n , b a se d on the b a la n c e o f e v id e n ce . Th e

in d iv id u a ls co m m o n ly tell the m e d ia an d w h at the

co n clu sio n s from the IPCC h av e a lw a y s been su bject

sa m e in d iv id u a ls s a y w h en su b je c t to g re a te r

to uncertainty, a lw a y s su b ject to revision , an d a s the

scru tin y. H e c h a ra c te rise s m u ch o f the sc e p tic s '

scien ce h a s p r o g r e ss e d the co n clu sio n s h a v e been

b e h a v io u r a s p u b lic re latio n s, a n d q u o te s R ich ard

d is c r e p a n c ie s

b e tw e e n

w h at

e x p re ss e d m o re a n d m o re e x p lic itly in te rm s of

F e y n m a n , the A m eric an N o b e l P rize w in ner, a s

estim ate d ra n g e s an d p ro b ab ilities.

sa y in g '... reality m u st take p reced en ce o v er p u b lic

A n u m b e r o f p e o p le h a v e e m e rg e d w h o d e n y

re latio n s, for n atu re can n o t b e fo o le d '. Reality, in

there is sign ifican t h u m an -in d u ced g lo b al w a rm in g

the form o f recent o b se rv atio n s, in d eed tells u s that

a n d treat scie n ce lik e a d e b a te in w h ich they

clim ate ch an g e is h a p p e n in g , a n d d o in g so fa ste r

ap p a re n tly see their job a s to se lectiv e ly u se an y

than even the IP C C h a s p red icted .

U NCERTAINTY IS INEVITABLE, BUT RISK IS CERTAIN

71

It is in v id io u s to a sc rib e m o tiv e s to p a rtic u la r

n ot rule o u t the sim u ltan e o u s occurren ce o f h u m an -

in d iv id u a ls, a n d in m o st c a se s I w ill n o t d o th at

in d u c ed clim ate ch an ge. M oreover, h u m an -in d u ced

here. H ow ever, w e can think o f a n u m b e r o f p o ssib le

clim ate ch an ge m a y b e m o re im m e d ia te an d rap id

u n d e rly in g p o sitio n s or in terests, re late d to the

than p a s t c h a n g e s, an d it w o u ld h a p p e n at a tim e

en h an ced g re en h o u se effect an d its im p a c ts, w hich

w h en there are an u n p rec ed en te d six billion h u m an

m a y m o tiv a te or e x p la in the p o sitio n s h eld a n d

b e in g s aliv e on Earth. C o n sid e rin g the co n seq u en ces

arg u m e n ts u se d b y so m e co n trarian s.

to su ch a h u m a n p o p u la tio n if it h a d ex iste d d u rin g

O ne su ch p re ju d ic e c o m e s from p e o p le , often

the la st gla cia l cycle sh o u ld d isp e l an y eq u an im ity

scie n tists in d isc ip lin e s other than clim atology , w ho

a b o u t the co n seq u en ce s o f im m in en t ra p id clim ate

are n o t c o n v in c e d

ch an ge.

o f the v a lu e o f p re d ic tiv e m a th e m a tic a l

A n o th er c la s s o f co n tra ria n is th ose w h o are

scien ces. S o m etim es su ch p e o p le think o f a 'm o d e l'

d riv en by eco n o m ic a n d p o litic a l ju d g e m e n ts. A

as m erely a th eoretical fra m e w o rk to ex p la in a set

ca se in p o in t is the b e st-se llin g b o o k The Skeptical

m o d e llin g

in th e p h y s ic a l a n d

o f o b se rv a tio n s, rath er th an a se t o f w e ll-teste d

Environm entalist b y the D a n ish sta tistic ia n Bjorn

m ath em atical n on -lin ear eq u a tio n s that can be u se d

L o m b e r g , w h o se

to p ro je ct b e h a v io u r o f p h y sic a l an d ch e m ica l

L o m b erg tak es the p ositio n that m an y en viron m en tal have

b ee n

r e a so n in g

is

issu e s

d e e p ly su sp ic io u s o f an y claim to u se a 'm o d e l' to

s e le c tiv e ly

p red ict fu tu re b eh av io u r, ev en o f a p u re ly p h y sica l

e n v iro n m e n ta l im p r o v e m e n ts in recen t d e c a d e s

p h en o m e n o n , h o w ev er sim p le or co m p lex. The fact

(m an y the resu lt o f a gitatio n b y the en viron m en tal

is, o f co u rse, th at su ch p re d ic tiv e m o d e ls d o ex ist

m o vem en t). C o n sid e rin g the en h an ced gre en h o u se

a n d are u se d routin ely for m an y p ractical p u rp o s e s

effect, L o m b e rg , w h ile te n d in g to d o w n p la y the

su ch a s d a ily w e ath er fo re ca stin g , p re d ic tin g the

risk s from clim ate c h a n g e , c o n c e d e s th at it is a

tid e s, a n d p re d ic tin g the m o tio n s o f the p la n e ts.

reality. H is a rg u m e n t is n ot th at h u m a n -in d u c e d

C lim a te p ro je c tio n s are ju st m o re c o m p le x , an d

clim ate ch an g e is not h a p p e n in g , b u t rath er th at it

a d m itte d ly m o re u n ce rta in , th an so m e o f th ese

is m a n a g e a b le , an d that re d u cin g g re e n h o u se g a s

e x a m p le s. C lim a to lo g ists are w ell a w a re an d op en

em issio n s w o u ld b e p ro h ib itiv ely e x p e n siv e .16

p ro d u ce

and

e x p lic it.

s y s te m s fo rw a rd in tim e. Su ch p e o p le m a y b e

to

e x ag g e rate d

q u ite

s t a t is t ic s

p ro ceed s

p o in tin g

to

a b o u t the u n certain ties. If c lim a to lo g ists are d o in g

L o m b e rg in h is m o re recent b o o k Cool It, aim ed

their job w ell, they b u ild their m o d e ls carefully, test

sp ec ifica lly at con cern a b o u t clim ate ch an ge , a g a in

the m o d e l's co m p o n e n ts a n d o v era ll p erfo rm a n c e,

c la im s that the im p a c ts o f clim ate c h a n g e w ill be

a n d carefu lly estim ate their reliab ility an d p o ssib le

n e g lig ib le a n d e a sily d e a lt w ith, a n d that e m issio n s

e rro rs.

re d u c tio n s are n o t u rg e n t a n d w ill b e e n o rm o u sly

T h is

is

p art of a

c lim a t o lo g is t 's

job

d escrip tio n .

costly.17 Th ese c la im s are n ot true, a s is e v id en t later

A n o th er q u e stio n ra ise d b y so m e co n tra ria n s

in th is b o o k . H is c la im s are v a lu e - ju d g e m e n ts

co m e s from th ose fa m ilia r w ith the g e o lo g ic a l an d

b a s e d on d is c o u n tin g the m o re se v e re p o ss ib le

oth er p a le o -e v id e n c e o f p a s t n atu ra l c h a n g e s in

im p a c ts , te c h n o lo g ic a l o p tim ism r e g a r d in g o u r

clim ate, w h ich clearly w ere large, an d not the resu lt

a d a p t iv e ca p a city , a n d te c h n o lo g ic a l p e ss im is m

o f h u m an in fluen ce. T h ese co n tra ria n s sa y that if

r e g a r d in g o u r a b ility to re d u c e g re e n h o u se g a s

su ch ch a n g e s h a p p e n e d n atu ra lly in the p a st, w h y

e m is sio n s at low cost. H is a rg u m e n ts h a v e been

sh o u ld any ch an ge s occu rrin g n ow be d u e to h u m an

r o u n d ly d e b u n k e d

influence? O r else they a rg u e that, since life su rv iv e d

elsew h ere.

su ch c h a n g e s in the p a st, it w ill su r v iv e sim ila r

on the G r is t w e b site a n d

A n op en letter b y a large g ro u p of scep tics (m any

c h a n g e s in the fu tu re , so w h y w o rry a b o u t it?

w ith o u t re le v a n t e x p e r tise )

H o w e v e r, w h ile

has

Secretary-G en eral of the U n ited N a tio n s at the Bali

h a p p e n e d b efo re an d can h a p p e n a g a in , this d o e s

C lim a te C h a n g e C o n fe re n c e in D e c e m b e r 2007

n a t u r a l c lim a te

ch ange

a d d resse d

to the

72

CLIMATE C H A N C E: THE SCIENCE, IMPACTS A N D SO L U T IO N S

m a d e sw e e p in g a sse rtio n s th at recen t o b se rv e d

p r o c e d u r e s a d o p te d b y the IP C C to s a fe g u a r d

clim ate c h a n g e s are en tirely n atu ra l, can n o t be

a g a in st b ia s, a n d the fact th at its re p o rts h a v e to

sto p p e d , an d that the co st o f m e a su re s to redu ce

b e a p p r o v e d b y a w h o le ra n g e o f g o v e rn m e n ts

e m issio n s w o u ld be prohibitive. They ad v o cated that

with m an y differen t v ie w s an d interests. T h is view

m oney sh o u ld instead b e sp en t on b u ild in g resilience

a lso ig n o re s the e n d o rse m e n t o f the sc ie n c e b y

to clim ate ch ange. O nce a gain , they clearly either did

the in d e p e n d e n t a c a d e m ie s o f sc ie n c e o f a ll the

n ot re a d , or took little n otice o f a n d co m p le te ly

G 8 c o u n trie s (U K , F ran ce, R u ssia , G erm an y , U S ,

d ism isse d the d etailed stu d ie s reported in the 2007

Ja p a n , Italy an d C a n a d a ) a lo n g w ith th ose o f B razil,

IP C C report. M an y o f their claim s are co n fo u n d ed

C h in a an d In dia. In a statem en t p u b lish e d in Ju n e

later in this b o o k .18

2005

th e se

a c a d e m ie s

s a id

'T h e

s c ie n tific

S o m e o f the m o re e x tre m e c o n tr a r ia n s h a v e

u n d e rsta n d in g of clim ate ch an ge is n ow su fficien tly

c h a ra cterised 'e n v iro n m e n ta lism ' a s a n ew religio n

clear to ju stify n atio n s tak in g p ro m p t a ctio n ' (See

or id e o lo gy , or a s so m e n ew form o f to talitarian ism .

h ttp ://w w w .ro y a lso c ie ty .o rg ).

V ariou sly , su ch c o n tra ria n s m a y h o ld b e lie fs a b o u t

Beyond

a ll th e se p o s s ib le m o tiv a tio n s fo r

'e n v iro n m e n ta lists' w h o m they se e a s w ish in g to

c o n trarian p reju d ice are th ose w h o h a v e a real or

h alt 'p r o g r e s s ' or 'd e v e lo p m e n t' for id e o lo g ic a l

p erceiv ed econ om ic interest in d e n y in g that h u m an -

r e a so n s. T h ey ten d to a sc rib e u lte rio r m o tiv e s to

in d u c ed clim ate ch an g e is a reality. S o m e o f these

p ro p o n e n ts w ith a g e n u in e co n cern a b o u t h u m an -

gen u in ely believ e the en h an ced g re en h o u se effect is

in d u c e d c lim a te c h a n g e , a n d d o n o t a c c e p t the

n ot so , w h ile oth ers fail to see an y u rgen cy a n d seek

n eed to c o n s id e r the s u p p o r tin g e v id e n c e on its

to d e la y action for their ow n (an d p o ssib ly oth ers')

m erits. It is true that so m e en v iro n m e n ta l a la rm ists

e con om ic b en efit.19

d o h ig h lig h t a s fa ct e x tre m e d is a s t e r sc e n a r io s

O ccasio n ally in d iv id u a l co n trarian s are accu sed

th a t m a y b e u n ce rta in to o c cu r (a n d th u s th e se

o f a rg u in g the w a y they d o p u re ly for their ow n

a la r m ists su ffe r fro m so m e o f the sa m e se le ctiv e

econ om ic benefit, in o rd er to receive p ay m e n ts from

c h a ra c te ristic s a s c o n tra ria n s). H o w ev e r, th is d o e s

fo ssil fuel in d u strie s or oth er in terests an d lo b b ies

n o t e x c u se the se le c tiv e d e n ia l b y c o n tra ria n s o f

su ch a s p o litic a lly c o n se rv a tiv e th in k ta n k s. In

m o re lik ely p o ssib ilitie s. M o reo ver, recent e v id en ce

m an y in d iv id u a l c a se s I know , it se e m s to m e that

s u g g e s t s th at so m e o f the sc e n a r io s fo r clim a te

su ch co n trarian s d o n ot se ek ou t p a y m e n ts; rather,

c h a n g e o n ce th o u g h t 'e x tre m e ' (even b y m e) are

su ch eco n o m ic or p o litical lob b y g r o u p s se e k o u t

n o t a s u n lik e ly a s sc ie n tists th o u g h t ju st a few

c o n tra ria n s a n d p a y to p ro m o te th eir co n trarian

y e a r s a g o (se e C h a p te r 5). S o - c a lle d 'e x tr e m e '

v ie w s th ro u g h g r a n ts, p a id to u rs, p u b lic a tio n s,

e n v ir o n m e n ta lis m

te s tim o n ie s

is o fte n a m a tte r o f a lo w

and

so

fo rth .

T h e se

sp o n so red

to le r a n c e o f e v e n s m a ll p r o b a b ilit ie s o f la rg e

co n trarian s m a y in a se n se be hired g u n s, b u t they

a d v e r s e im p a c ts . It is in su c h c a s e s a v a lu e

w ere often c o n tra ria n s, or ev en g e n u in e sc e p tic s,

ju d g e m e n t a b o u t risk toleran ce.

first, a n d are u su a lly g e n u in e in their b eliefs. T h is

O th er co n tra ria n s are d e e p ly su sp ic io u s o f the m o tiv e s an d in teg rity o f clim ate sc ie n tists. A llied

m akes

th em

m o re

c o n v in c in g

th ro u g h

th eir

sincerity, b u t no m o re correct.

w ith th is is often a d e e p su sp ic io n o f in tern ation al

T h e e c o n o m ic se lf-in te re st a rg u m e n t is often

clim ate scien ce a s too m u ch in flu en ced b y fu n d in g

u se d a g a in st th ose scie n tists w h o b eliev e there is a

a n d go v e rn m e n t (d esp ite there b ein g no co n se n su s

real p ro b lem o f h u m a n -in d u c e d clim ate ch a n g e ,

a m o n g st g o v e rn m e n ts on m an y m atters related to

n am ely that sc ie n tists sa y th ese th in g s b e c a u se it

clim ate ch an ge). T h ey esp e c ia lly su sp e c t the IPCC

g e ts them g ra n ts or p a y s their sa la rie s. T h is is the

a s d e e p ly b ia s e d a n d fla w e d a n d a c c u se it of

ch arge o f lack o f in tegrity an d asc rib in g o f ulterior

c e n so rin g or d o c to rin g its re p o rts. T h is is q u ite

m o tiv e s to d o b a d scien ce th at m o st o ffe n d s the

c o n trary to the rig o r o u s o p e n re v ie w s a n d oth er

co n trarian s w h en a p p lie d to them . In the case o f the

UNCERTAINTY IS INEVITABLE, BUT RISK IS CERTAIN

clim atologists e n gage d in the science it is an ironic a rg u m e n t for scie n tists in co u n tries su ch a s the U nited States and A u stralia, w here gov ern m en ts in the recent p a st have not a lw a y s w elcom ed explicit p olicy-related co n clu sio n s an d re com m en d ation s that qu estion govern m ent inaction.20 The p ublic perception of the debate over clim ate ch an ge h as been sh a p e d by the m e d ia 's com m on

73

p ub lic and decision -m akers to d istin g u ish betw een a rg u m e n ts d e riv e d from w e ll-b a se d sc ie n tific ju d g e m e n ts an d those a risin g from u n-checked p erson al op in ion s.22

Application of the 'Precautionary Principle' In su m m ary, uncertainty in regard to the rate and

adh eren ce to a do ctrin e o f 'b alan ce d rep ortin g'. T his ten ds to giv e eq u al sp a ce to the co n sid ered

m agn itu d e of clim ate ch ange, and in relation to its effects, o p erates in both directions: it can m ean that

ju d g e m e n ts of the scientific com m unity, ex p ressed in p eer-review ed p u b lic a tio n s su ch a s the IPCC re p o rts, an d the often c o m p le te ly un-refereed o p in io n s or a d v o c a c y o f a co n trarian m inority.

effects m ay be less than the current b est estim ates, or m ore. This raises the problem , com m on to m ost h u m an en d e a v o u rs, o f how to m ak e d ecisio n s in the face of uncertainty. The p roblem is even m ore

A lth ough this is ch an gin g in so m e cases, there h as been a m ed ia tendency for giv in g eq u al sp a c e to

acu te, in the case o f clim ate ch an ge, b ecau se d e cision s m ad e now m ay determ ine con sequ en ces

u n e q u a l sc ie n tific a r g u m e n ts , w h ic h often m isrep resen ts the b alan ce of ev id en ce an d p la y s into the h a n d s of v ested interests o p p o se d to any real action to lim it clim ate ch an ge.21

m an y d e ca d es into the future. C learly there are a n u m b er of strategies, w hich are u sed co n sciously or u n con sciously in ev ery d ay life. E sse n tia lly th ese a m o u n t to w e ig h in g the poten tial con sequ en ces in term s of the probabilities and w h at is at stak e (that is, in form al term s, w e

Peer review is the p ro ce ss in w hich scien tists norm ally su bm it their research fin din gs to a journal, w hich se n d s the d raft p ap e r out to be a sse sse d for

do a risk a sse ssm e n t). If the co n seq u en ce s o f a

c o m p e te n c e , sig n ific a n c e a n d o r ig in a lity by in d ep en d en t ex p erts in the relevan t field. These e x p e r ts d o n o t n e c e ss a r ily a g re e w ith the co n clu sion s, but if they agree that the argu m e n ts and con clu sion s are w orthy of con sid eration , then the p a p e r is p u b lish e d . The p eer review sy stem

p articu lar co u rse of action m ay be d isa stro u s, w e tend to a v o id that ev en tu ality b y cau tio u s action, takin g ou t so m e form o f in suran ce, or w o rk in g to p rev e n t the w o rst p o ten tial co n seq u en ce s from occurring. A nd if w e believe that w e can reduce the

m ean s that statem en ts b a se d on such p ap e rs tend to be m ore reliable than other k in d s of statem en ts or claim s. C la im s m a d e b y p o litician s, n e w sp a p e r c o lu m n ists, sp e c ia l in te re st think ta n k s an d

to d elay the d e cision s or take a bet each w ay until w e becom e better inform ed. This is called h ed gin g ou r b ets.23 We m ay m ak e a ten tative or p ro tem decision , to av o id the w o rst h ap p e n in g , and then

cam p aign g ro u p s are not n orm ally subject to such in d ep en d en t qu ality review b efo reh an d , b u t are often given eq u al w eigh t in m edia reports.

review the decision in the light of d evelo p m en ts. T his is called ad a p tiv e decision -m aking. The w hole

Peer review is not perfect and d o es not gu aran tee correctness. It is ju st the first stage: a h y p oth esis or argu m en t that su rv iv e s this first test is still subject to further testing by other scientists. H ow ever, peerreview ed p ap e rs and reports can be con sid ered to be m ore than an opin ion, and sh ou ld not be lightly d ism isse d in fa v o u r of u n tested o p in io n s. A n a w a re n e ss o f the p eer-rev iew sy stem an d the so u rc e s o f in form ation can help the m e d ia, the

uncertainty by seek in g better inform ation we tend

pro cess is one of risk m an agem en t.12 The Precautionary Principle, a s in clu d ed in the Rio D eclaration at the Earth S u m m it in Jun e 1992, and a ssen ted to by rep resen tativ es of m o st of the n ation s of the w orld, states Where there are threats o f serious or irreversible dam age, lack o f fu ll scientific certainty shall not be used as a reason fo r postponing cost-effective measures to prevent environmental degradation.

74

CLIMATE C H A N C E: THE SCIENCE, IMPACTS A N D SO L U T IO N S

T h is p rin cip le h a s been in c o rp o rated into m an y

U n certain ty sh o u ld be seen , n o t a s a re a so n for

en v iro n m en tal ag re e m e n ts an d re g u la to ry re g im es,

in actio n on c lim a te c h a n g e , b u t a s a re a so n for

in c lu d in g A rticle 3 o f the U N F C C C , w h ere it is

p ro c e e d in g ca u tio u sly , w ith a re a d in e ss to a d a p t

ex p re sse d as: The p arties should take precautionary m easures to anticipate, prevent or m inim ize the causes o f clim ate change an d m itigate a g a in st its adverse affects. Where there are threats o f seriou s or irreversible dam age, lack o f f u ll certainty should not be used as a reason fo r p ostponing such m easures, taking into account that policies and m easures to deal ivith clim ate change should be cost-effective so a s to ensure global benefits at the lowest possible cost. T h is is the ty p e o f re a so n in g that, in a b ro a d e r

p o licie s to ch a n g in g in sig h ts a n d circ u m stan ce s, a s w e continu e to co n d u ct w h at the Toronto C onferen ce on clim ate ch an g e in 1988 called an u n co n tro lled g lo b a l exp erim en t. T h is le a d s to tw o key q u estio n s: w h at co u n ts as se r io u s e n v iro n m e n ta l d a m a g e th at sh o u ld be a v o id e d , a n d

w h a t m e a su r e s are ju stifie d

as

reason ab le an d cost-effective re sp o n ses? The an sw ers to these q u estio n s are really w h at su cc e ssiv e IPCC rep o rts, a n d the U N F C C C are all ab o u t: they are co m p le x an d m u lti-fac eted , co m b in in g scien tific in form ation an d h u m an v a lu e s.24 D ifferin g h u m an v a lu e s and different self-interests will inevitably lead

c o n text, h a s lo n g g o v e rn e d e n g in e e rin g d e sig n ,

to controversy, d e b ate, an d the exercise o f political

sa fe ty re g u la tio n s , the in su ra n c e in d u stry , a n d in d eed fo reig n p o lic y a n d m ilitary p la n n in g . It is

p o w e r in d e cid in g w h at action is actu ally taken by

n o rm a l to c o n sid e r w o rst c a se sc e n a rio s a n d to

In w h at fo llo w s, this b o o k w ill e xp lore the a b o v e

c o n sid er w h at action is a p p ro p ria te either to a v o id

q u estio n s, w ith a view to su g g e stin g w h at a creative

su ch sc e n a rio s co m in g to fru ition , or to d e al with

an d a d a p tiv e p olicy re sp o n se m igh t en tail, an d how

them if they d o occur.

w e m igh t help it alon g .

gov ern m en ts, b u sin e sse s an d ordin ary peop le.

ENDNOTES 1. See Henderson-Sellers, Climatic Change, 25, pp. 203-24 (1993); and Jones, Climatic Change, 45, pp. 403-19 (2000). 2. For frequentist versus Bayesian statistics see DR Cox, Frequentist and Bayesian Statistics: A Critique, Nuffield College, Oxford, UK, at http://w w w .physics.ox.ac.u k/phystat05/proceedings/files/papbayesrev.pdf, and standard texts, for example, VD Barnett, Comparative Statistical Inference, 3rd edn, Wiley, Chichester (1999); DR Cox, Principles of Statistical Inference, Cam bridge University Press (2006). 3. Sec OH Pilkey and L Pilkcy-Jarvis, Useless Arithmetic: Why Environmental Scientists Can't Predict the Future, Columbia University Press (2007), and a review in Nezv Scientist (17 March 2007). 4. The Macquarie River study is by RN Jones and CM Page (2001) in Modsim 2001, International Congress on Modelling and Simulation, Ghassemi and others (eds), pp. 673-8. 5. See Schneider, Nature, 411, pp. 17-19 (2001). 6. Estimates of the probability of various amounts of future global warming, based on various assum ptions, have been m ade by Shlyakter and others, in Chemosphere, 30, pp. 1585-618 (1995); Schneider, in Nature, 411, pp. 17-19 (2001); Webster and others in Atmospheric Environment, 36, pp. 3659-70 (2002); and Wigley and Raper in Science, 293, pp. 451-4 (2001). 7. Gritsevskyi and Nakicenovik 'M odelling uncertainty of induced technological change' in Energy Policy, 28, pp. 907-21 (2001).

U N C E R T A IN T Y IS INEVITABLE, BU T RISK IS CERTAIN

75

8. See Jon es, Climatic Change, 45, p p. 403-19 (2000) and 'M an agin g C lim ate C h an ge R isk s', C h apter 8 in The Benefits of Climate Change Policies, O rgan isatio n for E con om ic C o o p eratio n and D ev elo p m en t, p p . 249-97 (2004), at h ttp ://w w w .o e c d .o rg . 9. See for exam ple Richard Tol, Climatic Change, 56, pp. 265-89 (2003), and N ew ell and Pizer, Discounting the Benefits of Climate Change Mitigation: How Much Do Uncertain Rates Increase Valuations? Econom ics Technical Series, Pew Center on G lobal C h an ge (2001). See h ttp ://w w w .p e w clim a te .o rg . 10. For Project 'R A PID ' see Nature, 427, p. 769 (26 February 2004) and h ttp ://w w w .n o c .so to n .a c .u k /r a p id /ra p id .p h p . 11. Barnett, in World Development, 29, pp. 977-93 (2000); and Lem pert and Schlesinger, Climatic Change, 45, pp. 387-401 (2000) argue that, given uncertainty, increasing resilience is the best m eans of adaptin g to climate change. How ever, whatever information can be su pplied about the likelihood of particular climate changes can minim ise the cost of adaptation. 12. A recent su m m ary of risk m an agem en t app roach es is provided by the IPCC 2007 report, WGII, C h apter 2. See also: Beer and Foran, in Risk Management and the Future, T Beer (ed.), AM EEF, M elbourne, p p. 39-67 (2000); Jon es, Natural Hazards, 23, p p. 197-230 (2001); N ew and H u lm e, in Integrated Assessment, 1, p p . 203-13 (2000); and T Beer 'G eop h y sical Risk, Vulnerability, and Su stain ab ility ' in The State of the Planet: Frontiers and Challenges in Geophysics, G eoph ysical M on ograph 150, A m erican G eoph y sical U nion, W ashington D C , p p. 375-85 (2004). 13. This approach is adv ocated by Popper, Lem pert and Bankes, in Scientific American (A pril 2005) p p. 48-53. 14. A sem antic discu ssio n of the m eaning of the w ord 'sceptic' can be found in an article by M ichael Sherm er, publisher of Skeptic m agazin e, h t t p :/ /w w w .sk ep tic.com , in Scientific American (A pril 2002) p. 23. 15. Ian En tin g's book Twisted: The Distorted Mathematics of Greenhouse Denial is p u blished by the A ustralian M athem atical Sciences Institute (2007), see h ttp ://w w w .a m si.o r g .a u /tw iste d . 16. See: Bjorn Lom berg, The Skeptical Environmentalist: Measuring the Real State of the World, C am b rid ge U niversity Press (2001). Two critical review s are: Stuart Plim m and Jeff H arvey 'N o need to w orry abou t the future', Nature, 414, pp. 149-50 (2001), and M ichael G rubb, 'R elying on m anna from h eaven ?' Science, 294, p p. 1285-7 (2001). O ther b ook s sceptical of the enhanced green house effect include John L D aly The greenhouse trap: why the greenhouse effect will not end life on Earth, Bantam Books, Sydn ey (1989), Patrick J M ichaels and Robert C Balling Jr, The Satanic Gases: Clearing the Air about Global Warming, C ato Institute, W ashington DC (2000). 17. L o m b erg's m ore recent book is Cool It: The Skeptical Environmentalists's Guide to Global Warming, K n o pf (2007). See interview s in Scientific American (26 N ovem b er 2007) and New Scientist (27 O ctober 2007) and article in the Guardian (17 O ctober 2007) by Jessica A ldred. An extensive critique can be found on G ristm ill at: Part 1: h ttp ://g ristm ill.g rist. o r g .sto ry /2 0 0 7 /9 /1 3 /1 0 5 1 3 0 /6 7 2 ; Part 2: h t t p :/ / gristm ill.grist.o rg.sto r y /2 0 0 7 /9 /1 4 /1 4 2 5 1 4 /3 5 7 ; Part 3: h t t p :/ / gristm ill.grist.org.s t o r y /2 0 0 7 / 9 / 17/151133/245. See also h ttp ://g r istm ill.o r g .sto r y /2 0 0 7 /9 /1 7 /2 1 1 3 5 /7 7 0 1 for a review by Bill M cK ibben. O ther w eb sites for d iscu ssio n of glob al w arm in g scepticism include h ttp ://w w w .sk e p tic a lsc ie n c e .c o m /, h ttp ://w w w .g re e n h o u se . g o v .a u /sc ie n c e /h o tto p ic s and the w ebsite run by several clim ate scientists at h ttp ://w w w .re a lclim a te .o rg . The U K R oyal Society also h as a w eb site d e v o te d to clim ate ch an ge co n trov ersies, at h t t p ://r o y a ls o c ie t y .o r g /p a g e . asp ?id=622 9 . Fred Pearce presented a brief review of com m on contrarian argu m en ts in 'C lim ate change: m enace or m yth?' Nezv Scientist (12 February 2005) pp. 38-43. 18. The open letter to the U N Secretary-G eneral and the list of sign ato ries can be found at h ttp ://w w w .n a tio n a lp o st. com /story-prin ter.h tm l?id=164002. C om m ents on the in d iv id u al argu m en ts can be found on the w ebsites listed in endnote 17 above. 19. D ocum entation of the fact that so m e lead in g contrarians have been fun ded by fossil fuel g ro u p s such as the US Western F uels A ssociation , Exxon and M obil Oil w ill be found in R oss G elbspan , 'The heat is on', Harper Magazine (D ecem ber 1995) pp. 31-7; R oss G elb sp an , The Heat is On: The High Stakes Battle over Earth's Threatened Climate,

76

C L IM A T E C H A N C E : T H E S C IE N C E , IM P A C T S A N D S O L U T IO N S

R e a d in g , M a ssa c h u sse ts (1997); an d Smoke, M irrors and Hot A ir, U nion of C o n cern ed Scien tists (2007) at h t t p :/ / w w w .u c su sa .o r g /a s se ts /d o c u m e n ts /g lo b a l_ w a r m in g /e x x o n _ r e p o r t.p d f. See a lso en d n ote 15. 20. F or A u stra lia , se e for ex a m p le C liv e H am ilto n , Scorcher: the D irty Politics of Climate Change, Black Inc., M elb ou rn e (2007); G u y P earse, High and Dry, V iking (P en guin ), R in gw o o d (2007); C liv e H am ilto n an d S arah M a d d iso n (ed s), Silencing Dissent, A llen & U n w in , C ro w s N est, N SW (2007). For the U S A , se e U nion o f C on cern ed Scien tists, Agencies Control Scientists' Contacts zoith Media (2007), at h ttp :/ / w w w .u c su sa .o r g /; Ja m e s H an sen , Political interference ivith government climate change science, T estim on y to C o m m ittee on O v e rsig h t an d G o v ern m e n t R eform , U S H o u se of R e p resen tativ es (19 M arch 2007); 'U S scien tists figh t p olitical m e d d lin g ', Nature, 439, p p . 89 6 -7 (2.3 F eb ru ary 2006). 21. The cffect of m e d ia adh eren ce to 'b alan ce' in the U S, in lea d in g to b ias, is d o cu m en ted in B oykoff a n d Boykoff, in Global Environmental Change, 14, p p . 125-36 (2004). S ee a lso D em erritt in A nnals of the Association of American Geographers, 91, p p . 307-37 (2001); M T B oykroff in Climatic Change, 86, p p . 1-11 (2008); an d B W ard, Climatic Change, 86, p p . 13-17 (2008). 22. Th e sy stem of scien tific p e e r review is d is c u s se d in Peer Revieiv and the Acceptance of New Scientific Ideas, by the W orking Party of S en se A b o u t Scien ce, at h ttp ://w w w .se n se a b o u tsc ie n c e .o r g .u k / . 23. The n eed to h e d g e a g a in st an uncertain clim ate future is d isc u sse d in econ om ic term s b y G a ry Yohe an d co lle ag u e s in Science, 306, p p . 4 1 6 -1 7 (2002). They co n clu d e that u n certain ty is the reason for actin g in the n ear term , an d it can n ot be u sed a s a ju stification for d o in g n othing. 24. For a furth er d isc u ssio n see the IP C C W orksh op R e p o rt (M ay 2004), D escribing Scientific Uncertainties in Climate Change to Support A nalysis of Risk and of O ptions, at h t t p ://ip c c - w g l.u c a r .e d u /m e e t in g /U R W /p r o d u c t/U R W _ R e p o rt_ v 2 .p d f. See also a se rie s o f articles in Global Environmental Change, 17, p p . 1-85, w ith so m e e m p h a sis on u ncertain ty in relation to ad a p tatio n .

5 W hat climate changes are likely?

In terms of key environmental parameters, the Earth system has recently moved well outside the range of natural variability exhibited over at least the last half million years. The nature of changes now occurring simultaneously in the Earth System, their magnitude and rates of change are unprecedented and unsustainable. P a u l C r u t z e n ( N o b e l L a u r e a t e ) a n d W i n S t e ff en (I n t e r n a t io n a l C e o s p h e r e - B io s p h e r e P ro g ra m m e , Executive D ir e c t o r ) , 2 0 0 3 . '

The Earth's climate is now clearly out of balance and is warming ... Evidence from most oceans and all continents except Antarctica shows warming attributable to human activities. Recent changes in many physical and biological systems are linked with this regional climate change. A sustained effort, involving many A GU members and summarized in the 2007 assessments of the Intergovernmental Panel on Climate Change, continues to improve our scientific understanding of the climate. A m e r ic a n G e o p h y s ic a l U n i o n , r e v is e d P o s it i o n S t a t e m e n t , D e c e m b e r 2 0 0 7 . 2

Although the consequences of global climate change may seem to be the stuff of Hollywood - some imagined, dystopian future - the melting ice of the Arctic, the spreading deserts of Africa, and the swamping oflowlying lands are all too real. We already live in an 'age of consequences’, one that will increasingly be defined by the intersection of climate change and the security of nations. T h e A c e o f C o n s e q u e n c e s , C e n t e r f o r a N e w A m e r ic a n S e c u r it y , 2 0 0 7 . 3

H um an-induced clim ate change is only an issu e if it is large en ou gh and rap id en ou gh to create real p rob lem s for n atu ral eco sy stem s and for hum an societies. In this and the follow ing ch apter w e will look at the m agn itu d e and rate of clim ate change, in clu din g sea-level rise an d ch an ges in extrem e events, that are likely to result from hum an-induced e m issio n s of green h ou se g a se s, and at w h at the effects m ight be on nature and society. G iven the a c k n o w le d g e d u n certain ties, the Intergovernm ental Panel on Clim ate C hange (IPCC)

h as tried in su ccessive reports to state w hat it w as confident about, and w hat w as m ore or less likely or possible, but still rather uncertain. The statem ent from the A m erican G eoph ysical U nion - the professional association of Am erican geophysical scientists - does the sam e in a very su m m ary form. The IPCC, in its reports in 2001 and 2007 extended this process to a treatm ent of possible su d d en or irreversible changes in the clim ate system which m ight be catastrophic, b ut about which we know relatively little regarding likelihood, tim ing, m agnitude and im pacts.

78

CLIMATE C H A N C E: THE SCIENCE, IMPACTS A N D SO L U T IO N S

C o m p le te

s u r p r is e s a re p o s s ib le . A p rim e

Em issions Scenarios (S R E S )5 d is c u s se d in C h a p te r 3,

e x a m p le is the s u d d e n a p p e a ra n c e o f the 'o z o n e

the p ro je c te d a c c u m u la te d e m is s io n s b y 2100,

h o le ', w h ich first o ccu rred w ith o u t w a rn in g ov er

e x p r e ss e d in u n its o f th o u s a n d s o f m illio n s of

the 1 9 7 0 s in the so u th e rn

to n n e s o f carb o n e q u iv a le n t (G tc), ra n g e from a

h e m isp h e re 's sp rin g . Th e o zo n e hole a p p e a re d far

low o f 770 G tc w ith the B1 scen ario to a p p ro x im a te ly

m o re ra p id ly a n d is far m o re lo n g la stin g than

2540 G tc w ith the A 1 F I (or fo s sil fu e l in te n siv e )

a n y o n e an ticip ated in the early 1970s. A t that tim e

sc e n a rio . T h is ra n g e c o m p a r e s w ith the e a rlie r

sc ie n tists like m e w ere w o rry in g a b o u t p o ss ib le

IP C C IS92 p ro je c tio n s r a n g in g from 770 to 2140

grad u al

G tc, so the u p p e r en d o f the ra n g e is n ow g re a ter

A n ta rc tic a

d u r in g

d e str u c tio n

of

ozone

in

the

upper

a tm o sp h e re . We w ere taken by su r p r ise w h en it

than

h a p p e n e d in a few y e a rs o v er A n tarctica, far from

d io x id e co n ce n tratio n s b y 2100 ra n g e from 540 to

th e s o u r c e s o f the c h e m ic a ls th o u g h t to be th reaten in g the o zo n e layer. 'R e p a irin g ' the o zon e

970 p a r ts p er m illion (p p m ). W hile the A 2 em issio n s

h o le is lik e ly to tak e the b e st p a r t o f a century,

2100 a s the A 1FI (see F ig u re 16, left-h an d p an el), it

d e sp ite stro n g in tern atio n al a g re e m e n ts on d o in g

d o e s so m o re g r a d u a lly a n d th u s h a s lo w e r

so (see C h a p te r 9 for a m ore d e ta iled d isc u ssio n of

a c c u m u la te d e m is sio n s an d re su lts in le ss g lo b a l

the o z o n e p ro b le m ). A n d it co u ld h a v e been far

w a rm in g by 2100. T h is is im p o rta n t in term s o f the

w o rse . A s P au l C ru tz e n sta te d , on re ceip t o f the

im p re ssio n created b y the 2007 IP C C report b e c a u se

N o b e l Prize for h is w o rk on ozon e: ... if the chemical industry had developed organobromine compounds [which contain bromine] instead of the CFCs [which contain chlorine] ... then without any preparedness, we would have been faced with a catastrophic ozone hole everywhere and in all seasons during the 1970s ... Noting that nobody had given any thought to the atmospheric consequences of the release of Cl or Br [chlorine or bromine] before 1974,1 can only conclude that mankind has been extremely lucky.*

b e fo re . C o r r e s p o n d in g p ro je c te d

ca rb o n

sc en a rio re ach e s the sa m e h igh rate o f e m issio n s b y

the latter, in its F ig u re SPM -5 o f W G I (righ t-h an d p a n e l o f F ig u re 16) d o e s n ot sh o w a g ra p h o f the w a rm in g re su ltin g from the A 1FI scen ario , alth o u gh it w a s sh o w n in the c o rre sp o n d in g F ig u re in the IP C C 2001 re p o rt, w h ich is re p ro d u c e d h ere a s F ig u r e s 15. A s d is c u s s e d in C h a p te r 3, the A 1FI scen ario is the clo sest to w h at h a s actu ally h a p p e n e d sin ce 1990. N o te F ig u re 16 (righ t-h an d p an e l) sh o w s only three o f the SR E S sc e n a rio s, A 2, A 1B an d B l, a s w ell a s on e w h ere the co n cen tratio n s o f all g re e n h o u se g a s e s w ere h eld fix ed at 2000 lev e ls (to sh o w the

A s I w rite this in 2008 w e are in a m u ch stro n ger

c o m m itm e n t to w a rm in g from p a s t e m issio n s).

p o sitio n in re g ard to clim ate ch an g e in that it h as

A lth o u g h the ch o ice o f S R E S sc e n a r io s to b e

been a n tic ip a te d in ge n e ra l term s, w e h a v e been

m o d e lle d in d e tail w a s m a d e o ste n siv e ly m erely to

w a rn e d , an d w e a lre a d y h a v e an in tern a tio n a l

lim it the n u m b e r o f sim u la tio n s, it h ad the effect of

convention in p lace to d e a l w ith it. H ow ever, w e are

e lim in a tin g the on e w ith the g re a te st w a rm in g

still b ein g su r p r ise d b y the u n fo re se en ra p id ity of

im p a c t by 2100. H o w ev e r, ra n g e s o f w a rm in g s by

so m e d e v e lo p m e n ts, su ch a s the r a p id retreat of

2100 for all SR E S m a rk e r sc en a rio s are giv en in the

A rctic se a ice in the la st few y e a rs, an d the n ece ssary

s id e b a r s at the rig h t o f the F ig u re , a n d in the

se n se o f u rgen cy is still not u n iv ersa lly accep ted .

ta b u la te d re su lts w h ich are su m m a rise d b elo w in T a b le 3. T h is c h a p te r d e sc r ib e s p ro je c te d c h a n g e s in

Projected climate changes

c lim a te b a s e d

T h e m a g n itu d e o f e v en tu a l clim ate ch an ge d e p e n d s

sc e n a rio s' (w hich are not driv en b y clim ate p olicies)

to a fir st a p p r o x im a tio n on the a c c u m u la te d

a n d 'sta b ilisa tio n sc e n a rio s' th at a ss u m e p o lic ie s

e m is sio n s. O n the b a s is o f the Special Report on

le a d in g to a le v e llin g o ff o f g r e e n h o u se g a s

on b o th th e se S R E S 'tra n sie n t

W H A T C L IM A T E C H A N C E S ARE LIKELY?

Several m odels all SRES envelope

■ A1FI

■ A 1B 5-

“

M o d e l ensem ble all SRES e n v e lo p e .

U

79

I : I

'S92

ili : ii 1r Bars s h o w the ra n ge in 2 1 0 0 p ro d u c e d b y 2000

2020

2040

2060

2080

2 1 0 0 several m od els

Year Figure 15: Global average temperature projections for six illustrative SRES scenarios, as depicted in the 2001 IPCC report. The darker shading represents the envelope of the full set of 35 SRES scenarios used as input to the climate models, using the then accepted average climate sensitivity of 2.8°C. The lighter shading is the envelope based on a range of climate sensitivities in the range 1.7 to 4.2°C. The bars show, for each of the six illustrative SRES scenarios, the range of model results in 2100. For comparison, the IPCC IS92 range of warmings in 2100 is also shown. (Adapted with permission from the IPCC 2001 W G I report, Figure 5 (d) of Summary for Policymakers.)

Year

Year

Figure 16: Left Panel: Global greenhouse gas emissions (in C 0 2-equivalent) in the absence of climate policies for the six illustrative SRES marker scenarios (solid lines) and the 80th percentile range of recent scenarios published post-SRES (dark grey shaded area). Dashed lines show the full range of post-SRES scenarios. Right Panel: Solid lines are multi-model global averages of surface warming for scenarios A2, A 1B and B1, shown as continuations of the twentieth century simulations. These projections also take into account emissions of short-lived G H G s and aerosols. The lowest curve is not a scenario, but is for A O G C M simulations where atmospheric concentrations are held constant at year 2000 values. The bars at the right indicate the best estimate (solid line within each bar) and the likely range assessed for the six SRES marker scenarios at 2090-2099. All temperatures are relative to the period 1980-1999. This is Figure SPM -5 of the IPCC 2007 Synthesis Report (reproduced with permission from IPCC).

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CLIMATE C H A N C E: THE SCIENCE, IMPACTS A N D SO L U T IO N S

co n ce n tratio n s at v a r io u s v a lu e s. M a n y d iffere n t

e m issio n s in the h igh e m is sio n s sc e n a rio s a n d le ss

st a b ilis a t io n

su lfu r e m issio n s.

s c e n a r io s h a v e

ap p eared

in the

literature sin ce the 2001 IP C C report, an d these are

A b o u t h a lf the ran g e o f u n certain ty in projected

su m m a rise d in W orking G ro u p III, C h a p ter 3.3.5, o f

w a rm in g is d u e to the ch oice o f sc e n a rio s, w hich in

the 2007 IP C C re p o rt. L ik e ly c lim a te c h a n g e s

reality can b e in flu en ced b y p o licy d e v e lo p m e n ts,

p rojected on the b a sis o f all these sc e n a rio s in clu d e

an d h a lf to the u n ce rtain ty fo r a g iv e n sc e n a rio ,

su rfa c e w a rm in g , c h a n g e s to rain a n d sn o w fa ll,

w h ich is d u e to scien tific u n ce rtain tie s. The latter

in c re a se d e v a p o ra tio n , c h a n g e s to the m a g n itu d e

esse n tia lly co n cern s the se n sitiv ity o f clim ate to a

a n d frequ en cy o f extrem e ev en ts su ch a s d ro u g h ts

g iv e n in c rea se in carb o n d io x id e co n ce n tratio n s.

an d flo o d s, rise s in sea level, an d the p o ssib ilitie s of

T h is scien tific u n ce rta in ty is a h igh p rio rity for

a b r u p t c h a n g e s a n d la rg e -sc a le c h a n g e s o f the

fu rth er research a n d is g re atly affected b y v a rio u s

clim ate sy stem su ch a s ocean cu rren ts or the m eltin g

p o sitiv e (a m p lify in g ) or n e g a tiv e (sta b ilisin g or d a m p in g ) 'fe e d b a c k ' effects in c lu d in g clo u d cover,

o f ice sh eets. Th e p o lic y -re le v an t q u e stio n s are h ow ra p id ly

p o s s ib le r e d u c tio n s in o c e a n ic a n d b io sp h e ric

su ch effects w ill occur, their m a g n itu d e , an d how

u p ta k e o f carb on , an d ch a n g e s in su rfa ce p ro p e rtie s

w ell w e w o u ld be able to a d a p t to them . If w e cannot

su ch a s sn o w a n d ice cover, a n d v e g e ta tio n . Th e

a d a p t at reaso n ab le co st w e w ill need to a v o id such

rate an d m a g n itu d e o f su ch fee d b a ck s is the su b ject

sc en ario s by red u cin g green h o u se g a s em issio n s.

o f m u ch cu rrent research an d o b serv atio n , w ith the IP C C sta tin g in its 2007 re p o rt th at the clim ate se n sitiv ity is lik ely to b e in the ra n g e 1.5 to 4 .5 °C ,

Surface w arm ing

bu t that it co u ld be c o n sid e ra b ly higher.

T h e IP C C 's 2001 re p o rt p ro je c ts g lo b a l a v e r a g e fro m

Th e e stim ate d tran sien t w a rm in g s for the SR E S

1.4 to 5 .8 °C by 2100 (see F ig u re 15) for n on-clim ate-

sc e n a rio s in the 2007 IP C C re p o rt are su m m a rise d

p o lic y S R E S sc e n a r io s, c o m p a r e d to the e a rlie r

in T a b le 3. 'T ra n sie n t' w a rm in g s are reach ed at a

IP C C IS92 ra n g e o f 1.5 to 3 .5 °C . T h e c o rre sp o n d in g

certain d a te , w h ile the c lim a te sy s te m

su rfa c e

t e m p e r a tu r e

in c r e a s e s

r a n g in g

is still

r a n g e from the 2007 IP C C re p o rt is 1.1 to 6 .4 °C .

u n d e rg o in g c h a n g e , a s o p p o s e d to 'e q u ilib riu m '

T h is la te st p ro je c te d rate o f w a rm in g is ro u g h ly

w a rm in g s that are th ose reach ed at a tim e w h en the

tw o to 10 tim es that o b se rv e d d u rin g the tw entieth

clim ate sy ste m h a s sto p p e d c h a n g in g an d settled

century, w h ich w a s a b o u t 0 .6 °C . T h e rate is m u ch

do w n into a new , stab le state.

fa ste r than the a v e r a g e w a rm in g at the en d o f the

N o te th at in F ig u r e s 15 a n d 16 an d in T a b le 3,

la st g la c ia tio n . T h e g re a te r w a rm in g at the h igh

there is a large u n certain ty ran g e for each scen ario ,

en d o f the ra n g e , c o m p a r e d to th at in the IS92

d u e m ain ly to the u n certain ty in the se n sitiv ity of

r a n g e is d u e to b o th g r e a te r c a rb o n d io x id e

clim ate to sp ec ified in c re a se s in g re e n h o u se g a se s.

Projected global average surface warming at 2090-99 relative to 1 980-99 for various transient scenarios gas emissions. After IPCC 2007, W C I Table SPM-3

T A B L E 3:

Scenario

of

Best estimate (°C)

Likely range (°C)

0.6

0.3-0.9

SRES B1

1.8

1.1-2.9

SRESA1T

2.4

1.4-3.8

SRES B2

2.4

1.4-3.8

SRESA1B

2.8

1.7-4.4

SRES A2

3.4

2.0-5.4

SRES Al FI

4.0

2.4-6.4

Constant year 2000 concentrations

greenhouse

W H AT CLIMATE C H A N C E S ARE LIKELY?

81

E stim ate s are b a se d on the IP C C 2007 h ierarch y of

m u st be slo w in g the increase in sen sib le h eat (that

clim ate m o d e ls o f v a ry in g d e g re e s o f com plexity ,

reflected in tem perature rises). Surface tem perature is

with a ran g e o f differen t clim ate se n sitiv itie s.

thus likely to rise faster once the ice is m elted.7

It is sig n ific a n t that there is re la tiv e ly little

S ta b ilisa tio n

e m is s io n s sc e n a r io s an d

their

d iffere n c e in tra n sien t w a rm in g s b y 2050 for the

re su lta n t g lo b a l w a rm in g s are m o re re le v an t to

v a r io u s e m issio n s sc e n a rio s, w ith w a rm in g s only

p olicy than the SR E S tran sien t scen ario s, sin ce they

d iv e rg in g ra p id ly in the latter h a lf o f the century.

d e sc rib e o u tc o m e s b a se d on v a rio u s p re sc rib e d

T h is is d u e to the re la tiv e ly sm a ll d iffere n c e in

e m issio n s re d u ctio n p r o g r a m s, su ch a s m a y be

c u m u la tiv e e m is sio n s by 2050 im p lie d b y the

introdu ced to redu ce the m agn itu d e of future clim ate

differen t e m issio n s p a th w a y s an d the slow re sp o n se

ch an ge. C oncern ab o u t clim ate ch an ge h as alread y

o f the clim ate sy ste m , w h ich is still catch in g u p to

led to lim ited n ation al an d international p olicies that

the effects o f earlier em issio n s. The w a rm in g at 2050

h a v e re d u c e d e m issio n s sligh tly re lativ e to w h at

is la rg e ly d e te rm in e d b y c h a n g e s a lre a d y in the

they m igh t h a v e b een o th e rw ise . A n d g ro w in g

p ip e lin e d u e to p a s t e m is sio n s, b u t c h a n g e s in

concern a b o u t clim ate ch an g e w ill likely lea d to

e m issio n s in the n ext few d e c a d e s w ill m a k e a b ig

greater p o lic y -in d u c ed re d u ctio n s in e m issio n s in

differen ce to w a rm in g s by 2100. It is w orth a d d in g , for the sa k e o f th o se w h o

the n ear future, even though recent e m issio n s h ave in fact been at or a b o v e the rate in the SR E S fo ssil

m igh t b e in fluen ced b y the o c casio n al cooler y ea r to

fu e l-in te n siv e

d o u b t g lo b a l w a rm in g , th at in the n ex t d e c a d e

o u tc o m e s u n d e r v a r io u s e q u ilib riu m

in teran n u al v a ria b ility o f the clim ate sy ste m , su ch

scen ario s g iv e s so m e id ea o f the effect on clim ate of

a s that a sso c ia te d w ith El N iñ o , flu ctu atio n s in the

v a rio u s e m issio n s redu ction p ro g ra m s an d targets.

sc e n a rio

A 1 F I.

C o m p a r is o n

of

w a rm in g

o cean c irc u la tio n , a n d a n o m a lie s in o cean h e at

The ev en tu al sta b ilise d g lo b a l w a rm in g s from

content, can still lead to so m e y e a rs that are sligh tly

stab ilised em issio n s are reported in the 2007 IPCC

cooler than the recent a v e ra g e . In d e ed , so m e British

report an d are su m m a rise d in T a b le 4.8 Th ey are

clim a to lo g ists h av e d e v e lo p e d an im p ro v e d m eth od

given for v ario u s g ro u p in g s or categories o f scen arios,

o f p red ic tin g clim ate o v er the n ext d e c a d e that tak es

stab ilisin g at carbon d io x id e concentrations in ran ges

a cc o u n t o f the in tern al v a ria tio n s a s w ell a s the

from 350-400 p p m (category I) to 660-790 p p m in

lo n g-term tren d . T h ey s u g g e s t th at c lim a te w ill

category VI (colum n 2). T h ese co rresp o n d to larger

co n tin u e to w a rm , w ith at lea st h a lf o f the y e a rs

ra n g e s o f carb o n d io x id e -e q u iv a le n t (colu m n 3),

a fter 2009 p re d ic te d to ex cee d the w a rm e st y ea r

w h ere oth er g re e n h o u se g a s e s a n d a e r o so ls are

cu rren tly on record.6

in c lu d e d a s the e q u iv a le n t a m o u n t o f carb o n

N a tu r a l in teran n u al v a ria b ility o f g lo b a l se a

d io x id e . C o lu m n 4 sh o w s the y e a r at w h ich C 0 2

su rface tem peratu re is largely d u e to v a ry in g heat

e m issio n s m u st p e a k , or reach a m a x im u m , if the

exch an ge betw een the atm o sp h ere an d the ocean.

sc en a rio is to sta b ilise at the d e sire d v a lu e , w h ile

This is m ainly d u e to the El N iñ o -L a N iñ a cycle, w ith

co lu m n 5 sh o w s the p erc en ta g e ch an g e in carb o n

El N iñ o y ears ten din g to be w arm er d u e to redu ced

d io x id e em issio n s n ece ssary b y 2050 if this is to be

u pw ellin g of cold w ater in the eastern tropical Pacific.

a c h ie v e d . C o lu m n 6 sh o w s the e v e n tu a l g lo b a l

A tm osp h eric an d oceanic circulation ch an ges d u e to

a v e ra g e w arm in g ab o v e p re-in d u strial tem p eratu res

global w arm in g a lso affect the heat exch an ge with

for each categ o ry o f e m issio n scen ario . I h av e left

the d e ep ocean, esp e cially in the Sou th ern O cean

o u t the ev en tu al sea-level rise e stim ate s, sin ce those

arou n d 50-60 d e g re es south. In ad d itio n , in creased

in the IPCC rep o rt leav e o u t the effects o f ice sh eet

h eat e n e rg y at the su rfa c e d u e to in c re a sin g

m e ltin g a n d d is in te g ra tio n , w h ich w ill cle arly

green h ou se g a se s is b ein g partially ab so rb ed a s latent

d o m in ate o v er therm al e x p a n sio n of the o cean s on a

heat, lead in g to the rap id m eltin g o f A rctic sea ice,

tim e scale o f cen tu ries. (We w ill return to sea-level

m oun tain glaciers and p arts of m ajor ice sheets. This

rise below , see T ab le 6.)

82

CLIMATE C H A N C E: THE SCIENCE, IMPACTS A N D SO L U T IO N S

TABLE 4: Characteristics and results of various categories of greenhouse gas concentration stabilisation scenarios

Emissions scenario category

CO, concentration at stabilisation (ppm)

COj-equivalent concentration at stabilisation (ppm)

Peak year for emissions

Change in emissions needed by 2050 (% )

Eventual warming above pre-industrial

5? 5002 5 % increase in peak gust causes 5 5 0 % increase in b uild in g dam ages

£