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The Future of Atmospheric Oxygen [1st ed. 2020]
 9783030436643

Table of contents :
Contents
Abbreviations
1 Introduction
2 Oxygen in the Past
3 Oxygen at Present
When Does ``Present'' Start?
When Does ``Present'' Start?
Current Observations of Atmospheric Oxygen
Current Observations of the Atmospheric Oxygen and Estimation of Global Oxygen Reservoirs and Fluxes
Impact of Oceans on Atmospheric Oxygen
Impact of Oceans on Atmospheric Oxygen
Industrial Use of Oxygen
Industrial Use of Oxygen
Air Separation Units
Air Separation Units
Updated Oxygen Budget
Updated Oxygen Budget
4 Oxygen in Future
5 Solutions?
6 Questions
Afterword
Bibliography

Citation preview

SPRINGER BRIEFS IN ENVIRONMENTAL SCIENCE

V. N. Livina T. M. Vaz Martins

The Future of Atmospheric Oxygen

123

SpringerBriefs in Environmental Science

SpringerBriefs in Environmental Science present concise summaries of cuttingedge research and practical applications across a wide spectrum of environmental fields, with fast turnaround time to publication. Featuring compact volumes of 50 to 125 pages, the series covers a range of content from professional to academic. Monographs of new material are considered for the SpringerBriefs in Environmental Science series. Typical topics might include: a timely report of state-of-the-art analytical techniques, a bridge between new research results, as published in journal articles and a contextual literature review, a snapshot of a hot or emerging topic, an in-depth case study or technical example, a presentation of core concepts that students must understand in order to make independent contributions, best practices or protocols to be followed, a series of short case studies/debates highlighting a specific angle. SpringerBriefs in Environmental Science allow authors to present their ideas and readers to absorb them with minimal time investment. Both solicited and unsolicited manuscripts are considered for publication.

More information about this series at http://www.springer.com/series/8868

V. N. Livina • T. M. Vaz Martins

The Future of Atmospheric Oxygen

V. N. Livina Data Science Group National Physical Laboratory Teddington, Middlesex, UK

T. M. Vaz Martins Computational and Systems Biology John Innes Centre Norwich, UK

ISSN 2191-5547 ISSN 2191-5555 (electronic) SpringerBriefs in Environmental Science ISBN 978-3-030-43664-3 ISBN 978-3-030-43665-0 (eBook) https://doi.org/10.1007/978-3-030-43665-0 © The Author(s), under exclusive license to Springer Nature Switzerland AG 2020 This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

Contents

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1

2

Oxygen in the Past . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3

3

Oxygen at Present . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Oxygen in Future . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

5

Solutions? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

6

Questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Afterword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

vii

Abbreviations

AR5 ASU AWG CMIP COD DEFRA GO2NE IAMC ICS IoT IPCC kgCO2 eq/kWh MIT Nm3 /hr ppm RCP SI SQS SRCCL SRES sTPD TAR tpd UN WRAP

Assessment Report 5 of IPCC Air separation unit Anthropocene Working Group Coupled Model Intercomparison Project Chemical oxygen demand Department for Environment, Food and Rural Affairs, UK The Global Ocean Oxygen Network Integrated Assessment Modeling Consortium International Commission on Stratigraphy Internet of Things Intergovernmental Panel on Climate Change kg of CO2 equivalent per unit of energy Massachusetts Institute of Technology Normal metre cubed per hour Parts per million, 10−6 , a dimensionless unit of concentration Representative Concentration Pathways Système international d’unités Subcommission on Quaternary Stratigraphy Special Report on Climate Change and Land Special Report on Emissions Scenarios Short ton per day (US unit, 0.907 metric tonne) Third Assessment Report of IPCC Tonnes per day United Nations Waste & Resources Action Programme

We use various units for oxygen (kg, mole) because industrial procedures can operate different phases (liquid O2 vs gas): gas is easier to quantify using the amount of matter (mole), whereas production of liquid in industry is commonly reported in kg or tonnes. Knowing the physical state of O2 , one can convert mass and matter using the O2 density (liquid or gas) and molar mass (0.032 kg/mol). Both mole and kg are the base SI units.

ix

Chapter 1

Introduction

Futurologists are almost always wrong B. Appleyard

What new can be learnt about oxygen, given the amount of knowledge accumulated since the works of scientists of the eighteenth century, who discovered and separated it chemically? Swede Carl Scheele, Englishman Joseph Priestly, Frenchman Antoine Lavoisier conducted various experiments to study the gas in oxidising and combustion conditions (Lavoisier 1790), and this knowledge constitutes the modern understanding of oxygen’s chemical role in the geochemical processes. Oxygen is highly reactive as one of the several oxidising agents (those that capture electrons). It forms oxidised compounds with many elements, in the form of oxides and other inorganic compounds (e.g., rock minerals within the Earth’s crust) and organic compounds (oxygenates, such as alcohols, ethers, ketones, amongst others). In fact, oxygen’s chemical signatures can be found everywhere in the organic and inorganic matter of our planet. Not to mention water, without which there would be no life, and atmospheric oxygen, without which there would be none of us. Oxygen is essential and abundant in our planet but is rarely considered in the context of climate change or environmental threats. The first aspect of the anthropogenic environmental impact that comes to mind is, generally, global warming, which has been widely discussed in the specialised literature and mass media in recent years (IPCC 2014). Oxygen is not a major concern of the community of environmental researchers, although some changes have occurred, and this is the topic of our book. We analyse the present dynamics of global atmospheric oxygen to identify major sinks, their scale and possible further evolution. Uncertainties are large, global data is approximate and often incomplete, which means that our analysis can be a lower or upper estimate of the ongoing changes. We hope that atmospheric oxygen will become a topic of debate for researchers and policymakers, to ensure, early

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2020 V. N. Livina, T. M. Vaz Martins, The Future of Atmospheric Oxygen, SpringerBriefs in Environmental Science, https://doi.org/10.1007/978-3-030-43665-0_1

1

2

1 Introduction

enough, that we do not cause irreversible damage to our planet. Similar processes have started in the community of ocean scientists who forge networks to increase awareness of ocean deoxygenation (OCIP 2020). We would like to thank Prof. Alistair Forbes, for suggesting to look at atmospheric oxygen data back in 2014; Ron Doering, for proposing to write a book after the first article (Livina et al. 2015); Kyril Calsoyas, for his enthusiastic support during the project; various invited researchers, who advised to work on this topic ourselves, and we have learnt a lot on the way; Louise Wright and Emma Richardson, for detailed comments on the manuscript; and the publishers, for their infinite patience during this project, despite multiple delays.

Chapter 2

Oxygen in the Past

Atmospheric chemistry is a slave to the dynamics of the mantle. D. Canfield Lovelock believed that the gases in the atmosphere were biological. L. Margulis

During the twentieth century, the works of leading geochemists opened a new chapter in our understanding of the historic processes and variability of the oxygen in the past. The Earth was not an oxidised entity in its beginning. Most of the information about previous oxygen concentrations (paleo, as well as more recent) are based on the so-called proxy data, i.e., not on direct measurements of air samples but on derivations of the atmospheric oxygen content using measurable oxidised compounds, such as geological materials. These materials are analysed using contemporary understanding of geochemical processes, which may change further with the development of scientific knowledge. Holland (2006) provided a description of the increase of atmospheric oxygen, as shown in Fig. 2.1. It is likely that atmospheric oxygen appeared first due to cyanobacteria, and as soon as burial of organic matter became effective, about 2.5 billion years ago, the atmospheric oxygen content started growing, reaching 30% about 300 million years ago. The Great oxidation event is described in detail in the book (Lenton and Watson 2011): the first oxygen-producing cyanobacteria appeared about 2.7 billion years ago, Huronian glaciation started with oxidation, and further indications, such as oxidised soils, started developing. This was the first global oxygen increase, which was followed by a second oxygen rise around 800 million years ago, reaching a maximum 300 million years ago and then reducing to the current level about 100 million years ago due to interplay of geophysical and biophysical conditions developing at geological scales.

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2020 V. N. Livina, T. M. Vaz Martins, The Future of Atmospheric Oxygen, SpringerBriefs in Environmental Science, https://doi.org/10.1007/978-3-030-43665-0_2

3

4

2 Oxygen in the Past

Fig. 2.1 Schematic of the oxygen atmospheric concentration during the history of the Earth, following (Holland 2006). Several major oxidising events can be seen, such as the Great Oxidation event around 2.5 billion years ago; further variability due to various reservoir processes of oxygen absorption, according to the current understanding of geo- and biochemistry of the Earth

In the book “Oxygen” (Lane 2016), the period of high oxygen is discussed. Nick Lane describes, in particular, gigantic insects of that time and discusses the further oxygen decrease to the modern levels of 20%, and this decrease is stated as largely beneficial for mammals, including humans (Graham et al. 1995). Lane argues that too high levels of oxygen may be toxic and lead to faster oxygenation and early death of animals. The reason for high levels of 30% would likely be due to the expanding biota of a warmer climate state, before large animals started appearing about 540 Ma ago (Cambrian explosion, see Dahl et al. 2019). One can hypothesise that the beginning of the Phanerozoic aeon provided negative feedback to rising oxygen by competing activities of the Plantae eukaryotic kingdom (cells with chlorophyll for photosynthesis) and the Animalia eukaryotic kingdom (multi-cellular organisms that require oxygen for breathing). Eventually their co-evolution, together with geochemical weathering (complex decomposition of rock minerals, often with formation of oxides and oxidised compounds), led to atmospheric process stabilisation at the modern level of 20% oxygen. This dynamic is reflected in various proxy datasets, describing the content of oxidised rocks, subject to the interpretation based on our knowledge of long-term geological processes. This shows that the planet’s bio- and geosphere can be in steady state at various levels of oxygen: the excess is being utilised by chemical weathering of rocks, while the lower content of oxygen, in the presence of life and photosynthesis, balances back to the equilibrium that allows the biota to function and flourish. At geological time scale, this happens by means of the organic burial, whose rate regulates the atmospheric pO2 level, and other stabilising negative feedbacks, which are provided, in particular, by the volcanic gases H2 , CO, SO2 , H2 S (Canfield 2014). In his book “Oxygen”, Donald Canfield provides the state-of-the-art understanding of paleo-oxygen formation. Oxygen is consumed by the planet because of

2 Oxygen in the Past

5

complex geological processes: burial of sediments, compactification of sediments into rocks, and their later chemical weathering and erosion, whose products end up in sediments again. Thus, oxygen is circulated in multiple oxidation processes that help shape and modify our planet. If the atmospheric content of oxygen decreases, which causes the ocean oxygen content to decrease, this increases the burial rates of organic carbon and pyrite sulphur, which will generate a greater oxygen source to the atmosphere at geological time scales. Oxygen reacts with organic matter and rock pyrite exposed to atmospheric contact—this is the oxygen sink from the atmosphere. On the other hand, this organic matter and pyrite, when they were buried and formed as rocks, are an indirect source of oxygen by means of locking carbon dioxide in shells and other carbonaceous compounds: during photosynthesis oxygen is released and carbon dioxide is locked in the organic materials that sediment (Hamingway et al. 2019). Another type of weathering, in addition to oxygenation, is hydrolysis, which may occur at low temperature, as well as at high temperature and pressure (during volcanic activity, for example). The geological evidence of oxygen development and its biomarkers are explained in detail in Canfield (2014). Husson and Peters (2017) too support the idea of mainly geologically driven oxygen dynamics. After a period of high level of oxygen (above 30%), about 300 million years ago the oxygen atmospheric content reduced to the present level, which may be due to a combination of events, such as the expanding fauna and the breakup of the supercontinent Rodinia. Canfield (2014) notes that geochemistry and crust dynamics are tightly interlinked, and we can only understand the planet development by taking into account the heterogeneous processes of various Earth components. In summary, production of oxygen was initiated by cyanobacteria (early prokaryotes), replenished by the photosynthetic activity of plants, counter-balanced by geological processes, such as weathering, with further impact of oxygen-consuming animals.

Chapter 3

Oxygen at Present

Oxygen enrichment can help the plant achieve operational excellence by reducing costs, increasing capacity, reducing emissions, providing operational flexibility to handle product demand or environmental load, all with minimal capital expenditures. R. Hendershot et al.

When Does “Present” Start? When humans appeared, they started influencing the environment by active interventions, which have led to the rise of the so-called Anthropocene—the epoch in the Earth’s development significantly impacted by the human activities. When did the Anthropocene start? Was it when humans started controlling fire roughly 1 million years ago to introduce the first basic technologies? Or was it with the beginning of the Holocene about 11,000 years ago (Fig. 3.1), when temperature stabilised at a warmer level and allowed people to concentrate on development instead of survival? Or was it the moment of the Agricultural Revolution of the eighteenth century, when Jethro Tull invented a seed drill and helped intensify agricultural practices, with broad consequences for land use and productivity, resolving the long-lasting threat of hunger? Or was it the invention in the eighteenth century of the commercial steam engine, which made coal the major source of energy? The date that marks the start of the Anthropocene is debated by the Anthropocene Working Group (AWG) of the Subcommission on Quaternary Stratigraphy (SQS) of the International Commission on Stratigraphy (ICS). Suggestions range from 12,000 years ago to the 1960s. In terms of climate, the beginning of the Holocene was an improvement favourable for humans. Prior to that, according to ice core records, there were large oscillations between warmer and much colder glacial periods; humans at that time were occupied with basic survival. Hodgson (2010) mentions climate as “a determining feature of civilisation”. The Holocene conditions allowed people, in a climate similar to today, to start living more comfortably, releasing them from © The Author(s), under exclusive license to Springer Nature Switzerland AG 2020 V. N. Livina, T. M. Vaz Martins, The Future of Atmospheric Oxygen, SpringerBriefs in Environmental Science, https://doi.org/10.1007/978-3-030-43665-0_3

7

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3 Oxygen at Present -32

-34

-38

18

O

-36

-40

-42

-44 -60000

-40000

-20000

0

time before present [years] Fig. 3.1 The oxygen isotope (proxy of temperature) of the Greenland GRIP ice-core data that indicates temperature variability. Eleven thousand years ago climate stabilised at warm temperatures that allowed development of agriculture and technologies; this gave rise to the Anthropocene

a struggle for survival in small pockets with bearable conditions. This boosted agriculture and technological development, eventually leading to modern society that has learnt to harvest planetary resources with ruthless efficiency. On 21st May 2019, AWG voted that the primary guide to mark the start of the Anthropocene should be given by the stratigraphic signals around the mid-twentieth century of the Common Era. They define Anthropocene as “the present geological time interval, in which many conditions and processes on Earth are profoundly altered by human impact. This impact has intensified significantly since the onset of industrialisation, taking us out of the Earth System state typical of the Holocene Epoch that post-dates the last glaciation”. Thus, the Anthropocene is classified as distinct from Holocene (Water et al. 2016). Humans influence atmosphere, hydrosphere, geosphere and biosphere, thus forming anthroposphere (the sphere that is created and shaped by human impact). Current research mainly focuses on the human contribution to increasing temperature in this context (Steffen et al. 2018). The concept of Gaia 2.0 (Lenton and Latour 2018) [which is an extension of the original Gaia theory of Earth’s selfregulation (Lovelock 1979)] discusses human environmental self-awareness as a possible addition to the planetary self-regulation. This awareness has to be wellinformed by evidence-based unbiased research.

Current Observations of the Atmospheric Oxygen and Estimation of Global. . .

9

Current Observations of the Atmospheric Oxygen and Estimation of Global Oxygen Reservoirs and Fluxes The present amount of atmospheric oxygen is estimated between 3.4 and 3.7 × 1019 mol (Canfield 2014; Petsch 2014), and more than half of this amount is generated by oceanic bacteria (Harris 1986). The mole is one of the seven base SI units (the International System of Units is the modern metric system). Mole expresses the amount of substance: one mole contains the number of particles (atoms or molecules) equal to the Avogadro number (6.022 × 1023 ). This unit is very convenient for estimation of molecular oxygen, because in the atmosphere it is gaseous, whereas in industry it is often used in liquid form, and the mole accounts for the amount of matter accurately regardless of phase transitions. The balance of geochemical processes of generation and consumption of oxygen in atmospheric and oceanic reservoirs with established fluxes, according to the current knowledge, are described in detail in Keeling et al. (1993), Petsch (2014) and shown schematically in Fig. 3.2. The main reservoirs of oxygen are atmosphere, terrestrial biosphere, marine biosphere and lithosphere. Fluxes between atmosphere and biosphere are expected to be in balance, lithosphere represents a minor sink of oxygen because of

ATMOSPHERE (3.5 x 1019 mol)

weathering 1 x 1013 mol/yr

photosynthesis respiration 9.2 x 1015 mol/yr

outgassing sedimentation 1.4 x 1017 mol/yr

FOSSIL FUEL RESERVES Fossil-fuel O2 consumption in 1982: 5.8 x 1014 mol

Fig. 3.2 Global oxygen budget with approximate reservoirs and annual fluxes (exchanges between reservoirs shown by arrows), following (Keeling et al. 1993; Petsch 2014)

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3 Oxygen at Present

weathering, and recently added anthropogenic use of oxygen is another, accelerating sink of atmospheric oxygen. In Keeling (1988), for the year 1982, it was estimated that consumption of oxygen due to the use of fossil fuels (i.e. combustion, see Eq. 3.1) was 1.87 × 1013 kg, while the related production of CO2 was 4.98 × 1012 kg. Here, the reported amount of oxygen is expressed in kilograms (another base SI unit), because of the conventions of the research community that monitors carbon dioxide emissions. Keeling et al. (1993) stated that the sink of oxygen due to fossil fuel use was 5.8 × 1014 mol per year that time, and the CO2 atmospheric content of that year (GGGRS 2020) was about 350 ppm (here, parts per million, ppm, denotes the number of particles of carbon dioxide in one million particles of air). The current level of CO2 is 430 ppm, therefore by linking the increase of carbon dioxide with oxygen depletion would account, at present, for a reduction of about 8 × 1014 mol of oxygen per year. The atmospheric oxygen content is large. It is less discussed, even in research communities, that oxygen is declining—by small quantities, but systematically, as can be seen in the data of Scripps O2 Program (2020), Fig. 3.4. These measurements have been taken by the research group of Prof. Ralph Keeling in the Scripps Oxygen Program at the University of California at San Diego. The group monitors atmospheric oxygen and continues the earlier established Scripps Carbon Dioxide Program by Prof. Charles Keeling, who started the Mauna Loa carbon dioxide observations and created “The Keeling Curve” depicting the increasing carbon dioxide in the atmosphere (see Fig. 3.5). The current decline of oxygen is about 1 × 1015 mol/yr (Petsch 2014), which is attributed mainly to oxidation of fossil fuels (Manning and Keeling 2006), assuming at that time that the sink was caused purely by combustion. However, this is not the only anthropogenic use of oxygen, as we will show later. The observational records encompass almost 30 years of direct measurement in several stations around the globe, from Antarctica to Alaska, as shown in Fig. 3.3. Samples of air are taken and stored in reliably sealed flasks (which are brought to sites for measurements and later returned to Scripps). The measured quantity is δ(O2 /N2 ), which is a convenient metric for small losses of oxygen (Scripps O2 Program 2020): δ = ((O2 /N2 )sample − (O2 /N2 )reference )/(O2 /N2 )reference ), where (O2 /N2 )sample is the mole ratio of an air sample, and (O2 /N2 )reference is the mole ratio of the stored reference (mid-1980s samples stored at Scripps). Because the atmospheric N2 has low chemical activity and is considered to be in steady state, δ reflects the variation of atmospheric oxygen with high precision. Already in Keeling (1988) it was noted that O2 is declining, but this decline was expected to be linear (based on the then available short observations), and Keeling estimated the possible time horizon of this decline towards critical levels as about 60,000 years. However, with longer observations, it became more apparent that the decline is actually nonlinear, as shown in Fig. 3.4, which means it may

Current Observations of the Atmospheric Oxygen and Estimation of Global. . .

11

Fig. 3.3 Locations of the stations where atmospheric oxygen has been measured since the 1990s

oxygen concentration ratio (O2/N 2)

0

Alert, Canada Barrow, Alaska Cold Bay, Alaska Cape Kumukahi, Hawaii La Jolla Pier, California Mauna Loa, Hawaii American Samoa Cape Grim, Australia Palmer Station, Antarctica South Pole

-500

1992

1995

1998

2001

2004

2007

2010

2013

2016

2019

time [years] Fig. 3.4 The observed oxygen data from multiple stations around the globe (black curves) and the line of linear fit of the station Mauna Loa (red curve) applied only to first 10 years (1991–2000), with further extrapolation of the same linear fit. Clear deviation of the data from the fit in the later period illustrates nonlinear decline of the atmospheric oxygen

reach critical values much faster (Livina et al. 2015) (assuming the rate of decline does not change). This will be discussed later, when laying out the future of oxygen concentration and what additional processes may accelerate this dynamic.

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3 Oxygen at Present

Randerson et al. (2006) hypothesised that the global terrestrial biosphere became “more oxidised”, in an attempt to explain the decrease of O2 that seems to be faster than the increase of CO2 . Indeed, there are many uncertainties in the terrestrial O2 exchange with atmosphere, given complex processes, such as global deforestation, forest fires and possible release of methane due to global warming. However, neither reducing forest area nor increasing methane content in the atmosphere can explain the increasing consumption of oxygen. The additional sink of oxygen is somewhere else. What could be the origin of this sink? Vernadsky (1989) and Lovelock (1979) described the interactions between the biota and geochemical processes that maintain stable levels of atmospheric composition for long geological periods. Lovelock called this system “Gaia” from the Greek goddess that personified Earth, whereas Vernadsky, in his works in the 1920–30s named it “noosphere” (from the Greek “nous”, or mind/reason) to highlight the emergence of human intelligence as a part of biota capable of transforming geochemical processes. Canfield (2014) notes that this equilibrium changes with time, depending on the geochemical reorganisations, and suggests that the ocean anoxia drives a continuous cycle of balancing oxygen by causing increasing burial of organic carbon (by means of dying animals in an anoxic atmosphere) and hence release of oxygen into the atmosphere. However, the time scale of such natural processes is much longer than the processes of the anthroposphere, and the rate of organic carbon burial may soon be insufficient to balance the atmospheric oxygen: previously geochemical processes were dominated by the plate tectonics, but modern industrial processes occur at much faster time scale.

Impact of Oceans on Atmospheric Oxygen The oxygen circulation at present involves respiration and outgassing, and exchange between the atmosphere and the oceans, which is described in Petsch (2014). In particular, the world ocean outgasses about 5 × 1013 O2 mol/year (Manning and Keeling 2006). The ongoing deoxygenation of the global oceans raises concerns about the balance of gases within the atmosphere. The Kiel Declaration on ocean deoxygenation (Kiel Declaration 2018) and the UN Global Ocean Oxygen Network (GO2NE 2020) discuss various threats of the ocean deoxygenation: how the increasing temperatures will reduce the capacity of the ocean to hold oxygen and the capacity to produce oxygen; oxygen deficiency will alter biogeochemical cycles and food webs; reduced ocean oxygen concentrations will lead to an increase in greenhouse gas emissions, with new feedback to climate change. While oceanic bacteria generate a lot of oxygen to maintain atmospheric content (between 50 and 70%), recent observations are accurate enough to conclude that oxygen content of the coastal waters is declining (see Breitburg et al. 2018 and references therein for multiple regional studies). This may further accelerate decline

Industrial Use of Oxygen

13

of the atmospheric oxygen. The surface layer of the world’s oceans is rich in oxygen because of gas exchanges between ocean and atmosphere; deep waters are rich in oxygen due to sinking of the cold water in polar regions that is rich in oxygen from the surface; the intermediate level, between few 100 m and 1500 m depth, is an oxygen minimum zone (Canfield 2014). Along the shores, deoxygenation zones are created by rising temperature and anthropogenic impact on shallow waters (plastic pollution, sewage, salt brine after desalination processing in the areas with shortage of fresh water, agricultural runoff with residues of nitrogen and phosphorus fertilisers). Changes in the oceanic circulation further affect the outgassing into the atmosphere, i.e., the exchange of oxygen between ocean and atmosphere may become unbalanced, thus contributing to further reduction of atmospheric oxygen. Bender et al. (2005) explain how global warming leads to ocean deoxygenation in two ways: first, due to degassing because of rising temperature and decreasing solubilities; second, because of changes of the ocean carbon cycle (increased utilisation of nutrients in the upper ocean), with transfer of oxygen to the atmosphere. An excellent review of observations of ocean deoxygenation for the past 50 years, as well as its projection until 2100, is provided in Levin (2018). Decline of the ocean oxygen is expected to be global, up to −50 μmol L−1 . As both atmospheric and oceanic oxygen contents decline, it is unlikely that under the present stresses a new source of oxygen would appear to counteract these processes. We discuss this further in the chapter on the future of the atmospheric oxygen.

Industrial Use of Oxygen There are two main types of oxygen usage in industry: when oxygen participates in various chemical reactions, which often require supply of oxygen in purified form, and when atmospheric oxygen is consumed during combustion of fossil fuels that are used, for example, for energy generation, see Eq. (3.1). In the past few decades, the carbon emissions recorded globally (World Bank 2020) have a similar dynamics to the observed CO2 concentration in Mauna Loa (Fig. 3.5), and this is related to oxygen loss due to combustion. A number of World Development Indicators of the World Bank (2020) illustrate the ongoing nonlinear use of resources and the growth of the world economy, and some of these indicators do not show any slowing or reverse dynamics to mitigate these processes. Figure 3.6 shows that a majority of the natural resources are being depleted, while energy-demanding anthropogenic processes are being accelerated. Panels (a, d) indicate nonlinearly growing air and marine transport for the growing population (panel (i)); transport is mainly powered by fossil fuels, such as kerosene and petrol. Panel (i) shows the population statistics, the thicker curve is to the present day, whilst the thinner curve is the projection up to 2050. The latter anticipates some stabilisation, but this is still a matter of research debate depending on various statistical approaches in parameter estimation (Raftery et al. 2012; Murdoch et al.

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3 Oxygen at Present 4.0×107

420 global emissions Mauna Loa measurements

CO2 [ppm]

3.0×107

380

2.5×107 360 2.0×107

global CO2 [kt]

3.5×107

400

340 1.5×107 320 1950

1960

1970

1980

1990

2000

2010

1.0×107 2020

time [years] Fig. 3.5 Measured atmospheric content of CO2 at Mauna Loa station (the Keeling Curve, Scripps O2 Program 2020) and global carbon emissions (World Bank 2020) with more noticeable fluctuations (not smoothed by the atmospheric chemical processes). The more volatile pattern of emissions is due to the variability of industrial use following economic cycles

2018)). Panel (h) shows the rapid increase in global migration, which is often caused by a shortage of local resources, such as the drought of 2014 in Syria, which initiated migration of rural population into cities, and later is thought to have contributed to the unrest and civil war (Gleick 2014). Panels (c, f) show an increase of cereal production per hectare, which in turn is provided by a large increase in the use of fertilisers (this require lots of energy for production: for example, ammonia is generated from air with steaming of natural gas at high temperature and pressure). Panel (e) shows the energy use per capita, with increases when domestic electric appliances became mass-produced. Accordingly, electricity consumption per capita (which is a part of energy sources) tripled in the past 40 years (Panel (j)), and CO2 emissions per capita (Panel (b)) increased significantly. It is necessary to note that it is still common even in urban areas of wealthy countries to power a large house using oil (Watson Fuels 2020). This means that energy needs, including electricity, are often powered entirely by oil. Panel (l) shows the percentage of fossil fuels in the total energy consumption: despite technological advances with increasing penetration of renewables, it has remained at about the same level of 80% for the past 30 years, with only small fluctuations. This indicates that fossil fuels still play the major role in the energy requirements of main sectors of economy, and it is not clear what further steps could change this. Forest areas (panel (k)) continue to decline, which contributes to climate change and reduces wood resources. Fishing yield (panel (g)) was increasing rapidly in 1960s–1980s but then stalled at the same level in the past 30 years, despite the growing demand, primarily due to heavily depleted stock, with more than 75% of the global stock

Industrial Use of Oxygen

15

Fig. 3.6 World Development Indicators (World Bank 2020), which illustrate continuing nonlinear growth of the world economy fuelled by non-green technologies and the increasing stress on major resources. Panels: (a) air transport, freight (million ton-km); (b) CO2 emissions (metric tons per capita); (c) cereal yield (kg per hectare); (d) container port traffic (TEU: 20-foot equivalent units); (e) energy use (kg of oil equivalent per capita); (f) fertiliser consumption (kilograms per hectare of arable land); (g) capture fisheries production (metric tons); (h) international migrant stock, total; (i) population, total; (j) electric power consumption (kWh per capita); (k) forest area (sq. km); (l) fossil fuel energy consumption (% of total)

being overexploited (FS 2020). These World Indicators show the past 30–50 years of growing demand for energy and resources with intensifying production for the growing population. The structure of the sources of the anthropogenic emissions has changed with time, as one can see in Figs. 3.7, 3.8, and 3.9. It is interesting that in the context of nonlinearly growing carbon emissions, despite the attempts to make various industrial processes greener, the proportion of carbon emissions from the solid fuel (coal) remains the same, around 45% of the total fuel consumption (Fig. 3.7). This means that there is no positive tendency for reducing carbon emissions in this area yet. When considering electricity generation (which is one of the major sectors using fossil fuels), the proportion of fossil fuels has actually not decreased in the past 45 years (see the three blue sectors in Fig. 3.8). Similarly, despite attempts to decarbonise electricity production, its carbon emissions have been increasing with respect to other sectors, as shown in Fig. 3.9.

16

3 Oxygen at Present 1960

1988

9%

2014

gaseous fuel

20% solid fuel 45%

34%

57% 35%

liquid fuel

Fig. 3.7 Carbon emissions from consumption of different fuels (% of total). Coal and oil remain the most polluting fuels. Data from the World Bank Portal 1993 renewables

1971 < 1%

2015 7%

hydro

24%

17% coal

40%

41%

2%

8%

nuclear 12% oil

21%

3%

gas

24%

Fig. 3.8 Electricity generation based on different fuel sources (% of total). The three blue sectors corresponding to fossil fuels remain almost unchanged for the past 40 years. Data from the World Bank Portal 1960 3% 29%

1987 other 20%

2014 2% 9%

buildings and services

electricity and heat

20% 49% transport

19% 29%

manufacturing and construcion

20%

Fig. 3.9 Carbon emissions in different industrial sectors (% of total). Data from the World Bank Portal

In modern industry oxygen is used in a vast number of applications. Some oxygen sinks are indirect: for example, when electric energy is used, somewhere off-site a power station is burning fossil fuels and thus depletes oxygen. The renewable electricity stations, which constitute about 20% of the world energy, have their production emissions embodied and indirect, due to the energy use during manufacturing of solar panels or wind turbine blades. On the other hand, there are industrial processes that require direct oxygen input for their successful

Industrial Use of Oxygen

17

Table 3.1 While indirect use of oxygen is usually related to combustion of fossil fuels in electricity generation, direct use of oxygen often involves operation of air separation units Indirect use of oxygen (energy-demanding production) Metallurgy (power supply) Transport (electricity-based) Fossil-fuel electricity supply Fossil-fuel heat supply Fertilisers production Petrochemical production Cement production Seawater desalination Hydrogen production

Direct use of oxygen (oxygen-demanding production) Metallurgy (combustion and coal gasification) Transport (petrol-based) Oxyfuels in glass manufacturing Pharmaceutical ammoxidation Food and farm industry (oxygenation) Aeration in wastewater treatment Construction industry (welding) Medical supply of oxygen Bleaching of fibres (delignification)

operations, such as aluminium production, where oxygen-enriched air is blown into a production cell for intensification of the process. Many of these uses are difficult to account for, so the impact of industry on atmospheric oxygen presented in this section is likely to be an underestimation (Table 3.1). Indirect oxygen use is mainly related to energy consumption, i.e., burning offsite fossil fuels of different origin and carbon intensity. Direct oxygen use implies supply of the gas obtained by air separation, either cryogenic or non-cryogenic (see the review of air separation technologies in Smith and Klosek 2001, Marquez and Tian 2017). This process, in turn, requires energy—either electrical obtained from the grid, or from on-site fossil fuels if an air separation unit (ASU) is installed in a refinery, which is often the case in the largest industrial installations. Many industrial processes also require high pressure and temperature (such as the Haber-Bosch process for fertiliser manufacturing), which demand additional supply of electric energy or fossil fuel combustion. The life cycle of different sinks of oxygen may vary: oxygen that is used in the food industry may be stored in food products until they are consumed, and the waste products are released for further recycling. On the other hand, oxygen used in metallurgy and construction industries may be locked in various waste oxides for long periods, whose time scale may be too great to balance the oxygen loss. Steelmaking requires two tonnes of oxygen per one tonne of product (Flank et al. 2009), and in 2017 the world crude steel production was 1.6 billion tonnes (World Bank 2020), see Fig. 3.10. Because steel production includes high-energy processes (indirect carbon emissions in power generation) and combustion (direct use of oxygen), this industry represents one of the major anthropogenic oxygen sinks in the contemporary economy. It is necessary to mention that many steel and aluminium manufacturers recognise the need to address the environmental impact of their activities: for example, the company (Alcoa Corporation 2020) construct their aluminium

3 Oxygen at Present

production [thousand tonnes]

18

6×104

aluminium

3×104 0 2.0×106

1980

1990

2000

1980

1990

2000

2010

steel 1.5×106 1.0×106 2010

time [years] Fig. 3.10 Aluminium and steel production. While the amount of aluminium is much smaller than of steel, the energy demand for aluminium is about ten times higher than for steel, which makes them comparable in terms of emissions and resources consumption. Data from the World Bank Portal

production installations with renewable energy supplies, such as hydropower in Brazil. Currently 70% of their power generation is reported to be renewable. An example of a direct oxygen sink is generation of oxides for removal of impurities. Sulphur removal is a common stage in production of steel and petrol products, and one of the side products is sulphur dioxide (Schrama et al. 2017). Some of these products are further used in industrial chemical processes, such as bleaching. A direct sink of oxygen occurs in a multitude of production processes that can be divided into the following reactions: combustion (in industry, usually of carbohydrates), oxidation, gasification and fermentation. Combustion

  Cx Hy + x + 14 y O2 → xCO2 + 12 yH2 O,

Oxidation

2xA + yO2 → 2Ax Oy ,

Coal gasification

3C + O2 + H2 O → H2 + 3CO,

Fermentation

C6 H12 O6 → 2C2 H5 OH + 2CO2 , no direct chemical interaction with oxygen but its presence intensifies the process significantly.

(3.1)

Industrial Use of Oxygen

19

Methane (CH4 ) is the least emitting among carbohydrates (Eq. 3.1), and many regions with large gas reserves consider this fuel as a long-term energy solution (including Europe and the Middle East). In glass production, during furnace melting with oxyfuels, methane undergoes combustion, not with air (3.2), CH4 + 2(O2 + 3.76N2 ) → CO2 + 2H2 O + 7.52N2 ,

(3.2)

but with oxygen (3.3), and the equation of such glass-production combustion with oxyfuels yields CH4 + 2O2 → CO2 + 2H2 O.

(3.3)

Adding oxygen in manufacturing increases the efficiency of furnaces by an order of magnitude, and is currently promoted by industry as a solution to environmental problems (i.e., reduction of carbon emissions, leaving other aspects aside), and to reduce costs (Levine 2001). In fermentation of yeast, Eq. (3.1) summarises how glucose transforms into alcohol and carbon monoxide. The intermediate processes in living cells include aerobic oxidation of glucose, which allows cells to accumulate large amounts of energy in the form of ATP (adenosine triphosphates). Here oxygen provides the means for sterol synthesis for membrane growth with aerobic oxidation of glucose: 3− C6 H12 O6 + 6O2 + 36P2− + 36H+ i + 36ADP

→ 6CO2 + 36ATP4− + 42H2 O,

(3.4)

where Pi is inorganic phosphate unit based on PO− 4 that participates in transformations between ADP and ATP, such as ATP + H2 O → ADP + Pi . For more details on glucose oxidation, see Lodish et al. (2007). We note that unlike regular respiration, this fermentation is an intense process in the food industry, with supply of molasses derived in sugar production. Therefore these carbon emissions are not naturally balanced by photosynthesis, due to its intensive industry-based origin and growing scale. In the context of the current work, the main outcome of this organic chemistry process is that large-scale fermentation in food production requires a lot of industrially produced oxygen for aeration, similarly to industrial combustion and oxidation. Small fermentation installations run air pumps to extract the necessary oxygen from air on-site, whereas large-scale industrial installations operate with a continuous supply of pure oxygen. Nitrogen fertiliser production increased from 13 to 113 million tonnes from 1961 to 2014, according to the UN Food and Agriculture Organisation (FAO WI 2020). This production uses the Haber–Bosch process of the reaction of nitrogen and hydrogen at high pressure and temperature, hydrogen being obtained by steam

20

3 Oxygen at Present

reforming of natural gas. Each stage of the process is of high energy demand, with combustion of fossil fuels. Oxygen delignification (removal of biopolymer lignin) is the process of bleaching fibres under alkaline conditions at raised temperature (Asgari and Argyropoulos 1998). There is a growing demand for this process, which is required in textile and paper industries. Large amounts of oxygen are used for coal gasification (a mix of gases with pulverised coal and air/oxygen): there are plants producing above 3000 tpd (tonnes per day) for that purpose (Higman and van der Burgt 2008). This process is still widely used in coal-based economies for electricity generation; in industry it is used for chemical compound generation. The electric energy required for the production of metals (besides the oxygen directly involved in burning) has been rising steadily (Fig. 3.10). The average carbon intensity of electricity grids around the world, according to (USDE 2020), is currently around 0.5 kg CO2 eq/kWh. This means that the global warming potential of a kWh electricity would be equivalent to 0.5 kg CO2 , which results from production of carbon and other gases with warming potential. To produce electricity, fossil fuels are burnt, such as natural gas in a turbine of a power station. For example, in 2017 steel manufacturing produced 1.7 × 1012 kg CO2 eq of carbon emissions. In 2018, global electricity reached 900 TWh, with increasing use of coal and gas to meet energy demand (IEA 2018), which illustrates the conflicting needs for environmental improvement and energy supply. In addition, the direct emissions due to various stages of metal production (when burning, steaming and other operations are performed) lead to further direct carbon emissions, up to four tonnes of carbon emissions per one tonne of metal (Fraunhofer Institute 2009). Rao and Muller (2007) analysed the contemporary technologies of oxygen production and stressed the importance of its use in glass furnaces, coal gasification, biomass and municipal solid waste gasification, gas-to-liquid technologies and metal oxidation. The Saline Water Conversion Corporation of Saudi Arabia has installed capacity for more than 4.6 million of cubic metres of desalinated water, where production of 1 L of water requires 3–10 kWh of electric energy for reverse osmosis (Voutchkov 2014; Dashtpour and Al-Zubaidy 2012). For example, Carlsbad desalination plant in California produces 230 million litres of water per day (Carlsbad Plant 2020). Similarly, freshwater supply in Israel and in the Thames tidal estuary in the UK is based on the same desalination technology (reverse osmosis), with power provided by electric stations (in Israel they are running on the recently discovered natural gas deposits in the Mediterranean sea). Estimation of the world’s production of glass and plastic is problematic, because of the multitude of small-to-medium enterprises working in this area, especially in developing countries. Just to give one example, production of the so-called float glass that is manufactured at large scale in industrial lines can be estimated approximately as 500 lines of output with more than one million tonnes of glass a week (Devlin and Dick 2019). Chemical oxygen demand (COD) reported in

Industrial Use of Oxygen

21

ATMOSPHERE (3.5 x 1019 mol)

weathering 1 x 1013 mol/yr

photosynthesis respiration 9.2 x 1015 mol/yr

Industrial and medical needs [2..3] x 1013 mol in 2017

ASU

outgassing sedimentation 1.4 x 1017 mol/yr

FOSSIL FUEL RESERVES Fossil-fuel O2 consumption in 2017: 3.3 x 1015 mol

Fig. 3.11 Updated global oxygen budget, with added use of atmospheric oxygen by ASUs, compare with Fig. 3.2. The updated budget includes the previously unaccounted sink of atmospheric oxygen

documentation on glass manufacturing (MIGA 2020) is 150 mg/L. Given the average density of glass about 4000 kg/m3 , annual oxygen consumption for glass manufacturing is about 6 × 107 mol (in Fig. 3.11, this amount is included in the module with industrial air separation). Glass production has accelerated since A. Pilkington modernised the technology in the 1950s (Bricknell 2009). The majority of modern glass production is located in Asia (China and India), where only large enterprises can be estimated accurately, and they are estimated to produce less than half of the total glass amount (Devlin and Dick 2019). Yet another industrial process that requires oxygen is ammoxidation, which produces nitriles using ammonia and oxygen. Nitriles are extremely important in pharmaceutical industry, in drugs applications ranging from diabetes to breast cancer. Nitriles are produced in millions of tonnes a year, and one of the typical compounds in this family is acrylonitrile produced from a hydrocarbon by ammoxidation (in presence of ammonia and oxygen): 3 CH3 CH=CH2 + O2 + NH3 → NCCH=CH2 + 3H2 O. 2 Acrylonitrile is also used for production of acrylic textiles and synthetic rubber.

22

3 Oxygen at Present

Cement production similarly requires large amounts of energy for the hightemperature decomposition of carbonate minerals into calcium oxide and carbon dioxide CaCO3 → CaO + CO2 .

(3.5)

Recent studies allocate most of those emissions to Chinese industries (Andrew 2018; Marland et al. 2008), because of large-scale construction, rapidly growing across the country. In the context of declining atmospheric oxygen, most oxygen consumption takes place when high-temperature processes are used; the source of heat in different enterprises may vary widely (large governmental industries may use natural gas, whereas small factories may use oil burners, depending on fuel costs and availability). The cement-related oxygen sink is highly uncertain, although it is obviously large. The UK government has been developing Industrial Decarbonisation and Energy Efficiency Roadmaps 2050 (IDEE 2017), with focus on eight main industries: cement, ceramics, chemicals, food and drink, glass, iron and steel, oil refining, pulp and paper. This national strategy addresses well global industrial processes. If solutions for industrial decarbonisation are applied globally, rather than shifted between regions, that will be an efficient solution for reducing carbon emissions. It would be highly desirable to add estimates of oxygen sinks to these roadmaps in future.

Air Separation Units One candidate for the unaccounted O2 sink is the lesser known anthropogenic utilisation of air, in which oxygen is extracted and further used for industrial purposes, both with and without combustion. This process is performed by largescale air separation units (ASU) that are being rapidly constructed and deployed across the globe. Industrial players, who have realised the economic potential of oxygen use in various applications, make large efforts in promoting an increase of oxygen extraction because of the cost effectiveness and reduction of carbon emissions (Hendershot et al. 2010). The areas include metallurgy, petrochemical production, glass making, sulphur removal in refineries (Claus process), and many other large-scale industrial operations, where combustion and other chemical processing can be intensified with increasing oxygen content, from low (25–28%) to high levels (90–99%) of oxygen purity (Baukal 2013). Therefore, it is important to estimate the oxygen sinks caused both by fossil fuel burning and by the direct extraction of atmospheric oxygen. For obtaining pure oxygen, installation of ASUs has been steadily growing in the past few decades. Just recently, in 2017, the world’s largest oxygen production plant was opened in South Africa, with total production capacity of 5000 tonnes of O2 per day (GasWorld 2018) and in 2018 Linde group installed an ASU in India,

Air Separation Units

23

producing 5250 tonnes per day (tpd) of O2 (Linde Group 2017). This corporation owns more than 400 ASUs, and has built more than 3000 ASUs for other companies. With expansive corporate ambitions, the companies aim to build larger and larger installations (Smith and Klosek 2001; Linde Group 2017), reaching many thousands tpd of oxygen and entering new markets, where oxygen can be utilised for low-cost mass production of goods. There are four major players in the industrial gas market: Air Liquide (including Airgas), Air Products (including Yingde Gases Group), Praxair and Linde, with estimated total revenue in 2017 of about 65 billion US dollars (Reaction Magazine 2017). The merger of Praxair and Linde covers about half of the international industrial gas market. Praxair and Linde currently own 1200 gas plants (GasWorld 2017). Air Liquide has built more than 6000 ASUs of various sizes (Air Liquide 2016). From 1996 to 2006, the global industrial oxygen production has risen from 0.75 to 1.2 million tpd (Hurskainen 2017; OGMR 2007). Taking into account the molar mass of molecular oxygen 0.032 kg/mol, this means that the 2006 oxygen sink from the atmosphere was 438 million tonnes of oxygen, or 1.37×1013 mol. Meanwhile, a recent report (FMI 2019) estimates global sales of industrial oxygen as 380 million tons in 2018 (revenues worth US$ 45 Mn) which is more than 1 × 1013 mol of oxygen. Thus, nowadays the effect of ASUs exceeds the weathering oxygen sink effect (Fig. 3.2). The same report (FMI 2019) predicts that in 2019–2029 the global industrial oxygen market will continue to grow. Still, smaller-scale production of oxygen from air is likely to be under-reported and under-estimated. For a crude estimate of world oxygen production, based on the number of ASUs reported by separate companies in industrial documentation, such as (Air Liquide 2016), we assume their current approximate number as 20,000 units, and their average capacity about 100 tpd of O2 , although the capacity of such units and fullscale installations may vary between 10 and 6000 tpd (Manenti et al. 2013). Then air separation technology, besides the conventional combustion and fermentation, may drain atmospheric oxygen content by about [2 . . . 3] × 1013 mol of O2 per year. The associated uncertainties are difficult to quantify, because the reported industrial numbers are few and based on incomplete data. With high probability, they still under-estimate the actual global oxygen production, due to a large number of underreported smaller scale plants. Therefore, our value of [2 . . . 3] × 1013 mol of O2 per year is likely to be a lower estimate of the actual oxygen sink. As shown in Fig. 3.2, the total atmospheric content of oxygen is of the order of 1019 mol, so the impact of ASU on the atmospheric oxygen remains small—but it exceeds natural weathering and approaches percent points of land photosynthesis and respiration (see Fig. 3.11). Moreover, the growth of the air separation industry is currently likely to be nonlinear, as their first installation appeared in 1902, and recently grew significantly in both number of installations and in their capacity.

24

3 Oxygen at Present

Updated Oxygen Budget As explained in previous sections, the declining trend of the atmospheric oxygen is likely to be caused by multiple anthropogenic processes. This complex oxygen sink is composed of the two main nonlinearly growing, non-reversible (at least at shorter time scales than geological) processes: combustion of fossil fuels and consumption of the gases constituting air, using industrial air separation. Both of them represent a unbalancing nonlinear impact on the the atmosphere; only one of them (fossil fuels and consequent carbon emissions) has been discussed extensively in the research literature and mass media so far. The other seems less well known and should be taken into account in global policymaking. Given the above, at present the updated oxygen budget should include a new, largely irreversible sink of oxygen due to massive increase of industrial air separation, whose effect on atmospheric oxygen is neither monitored nor regulated, and it is even encouraged because of the optimisation of industrial processes, cost reduction, and often carbon emission reduction: less air is used, less fuel is burned— yet, atmospheric oxygen is drained and embodied in long-lasting materials, such as glass, plastic and aluminium (as the surface oxidised layer). The updated oxygen budget (Fig. 3.11) is based on the reported global carbon emissions (GCB) and oxygen consumption factors (Keeling 1988), with added ASU oxygen sink. Broecker (1970) stated that each square metre of the Earth’s surface is covered by 6 × 104 mol of oxygen (given the planet’s area of about 5 × 1014 m2 and atmospheric content of 3.5×1019 mol). Following the large forest fires in Amazonia in 2019, atmospheric oxygen became a topic of discussion in mass media, and in the article (Denning 2019) it was mentioned that “there is enough oxygen in the air to last for millions of years”. Can oxygen be taken for granted because of its abundance? “Millions of years” may be an overestimation, as already in 1988 Keeling in his PhD thesis estimated that with simple linear decline (as was assumed then) atmospheric oxygen would last several tens of millennia. Given what we know now, with the oxygen decline more likely to be nonlinear, “millions of years” seem optimistic. Broecker in his Science paper of 1970 states that the main loss of oxygen is caused by the burning of fossil fuels, and because their reserves are limited, the oxygen decline would never exceed a few percent of the atmospheric content during the next several centuries, and therefore is not a major environmental concern. From his point of view, a threat at the scale of several thousand years can be dismissed because man “will succumb to some other fate long before his oxygen supply is seriously depleted”. Broecker bases his estimates on several assumptions, including the finiteness of fossil fuels and linear dependencies in the geosystem. We now know that depletion is nonlinear, hence time scales are faster than those linear estimates. We now know that combustion is not the only reason for oxygen depletion. Moreover, are we certain that fossil fuels are limited? New deposits keep

Updated Oxygen Budget

25

appearing (the recent discoveries of the natural gas deposits in the Mediterranean sea illustrate this). Given the growing demands and still available supply, can we be certain that the carbon emissions, globally, can be circumvented? Are we certain that the life-cycle emissions of the renewable solutions, such as fibre blades of wind farms, are smaller than the direct emissions of low-polluting fossil fuels, such as methane?

Chapter 4

Oxygen in Future

There is enough oxygen in the air to last for millions of years S. Denning

One of the first attempts of scientific forecasts of global development was the report “The Limits to Growth” (1972), in which early computer simulations were used, and the conclusions of the report (Meadows et al. 1972) summarised projections of population growth, development of industry and agriculture, and pollution. The forecasts were based on the MIT World3 model and were criticised for pessimism and simplified assumptions, but after several decades reviewers started reconsidering the report in a positive light, because its projections were confirmed by observations. The update of the report in the beginning of the twenty-first century (Meadows et al. 2005) repeated the main assumptions of the first version: the inherently exponential growth of population and economy; physical limits of the planetary resources; delayed human response to ecological and economic threats; the state of resources being not only limited but already largely exhausted. Similarly, in the World Watch Institute (Vital Signs report 2002), key indicators of industry and environment were analysed, in an attempt to identify their critical connections. The UK Future of Food Report (FFR, 2040) considered the trends of food production in the UK, which is representative of the European food markets. However, while the UK has a trend of decreasing agricultural emissions (GGE 2019; ASCC 2019) and aims at zero-emission agriculture within the next few decades, this is currently unachievable for most non-European countries due to limited resources, population growth and low wealth, as well as outsourced industries (in particular, in Asia and Africa). Moreover, use of fertilisers increases globally, as shown in the World Bank data in Fig. 3.6. Future dynamics of oxygen depends on a combination of drivers related to global environmental change and land use, global warming, growing human population and extensive agricultural practices, which, in turn, act together to affect ecosystems— thus a multi-stressor approach is important. At the same time, there may exist and manifest in future as yet unknown feedbacks between the subsystems. The complexity of the system may produce effects that are faster and more severe than © The Author(s), under exclusive license to Springer Nature Switzerland AG 2020 V. N. Livina, T. M. Vaz Martins, The Future of Atmospheric Oxygen, SpringerBriefs in Environmental Science, https://doi.org/10.1007/978-3-030-43665-0_4

27

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4 Oxygen in Future

what linear anticipations project; therefore it is important to monitor such changes and be ready to react early enough using policymaking and public awareness with active response. To forecast the atmospheric oxygen at the time scale of interest (tens of thousands of years if we assume nonlinear decline), paleo-studies of glacial-interglacial climate variability can be used for comparison, where oxygen isotopes were used as tracers of biosphere productivity. In particular, Luz et al. (1999), Blunier et al. (2002) used oxygen isotopes to analyse and model oxygen fluxes (land and ocean photosynthesis and respiration, and the exchange flux between the troposphere and the stratosphere). However, one of the possible consequences of the anthropogenic consumption of oxygen is that the time scale of interest may be shorter than that (possibly a few thousand years). Moreover, the models used for paleo simulations rely upon a number of parameters (such as mean fractinations and isotope ratios), which may not remain constant at long-time scales. In addition, current models may underestimate the ocean deoxygenation because of unresolved transport processes, unaccounted variations in respiratory oxygen demand and missing biogeochemical feedbacks (Oschlies et al. 2019). Furthermore, stresses such as increasing temperature and changes in the atmospheric chemistry may lead to unexpected geochemical effects, which at the current stage are not possible to outline. An unexpected feedback can arise from the warming atmosphere in relation to oceanic photosynthesis by phytoplankton. Secerci and Petrovskii (2015) used a coupled model of oxygen and phytoplankton to demonstrate that increasing temperature may halt oxygen production in the ocean, and induce a major disruption in the oceanic processes and oxygen outgassing into atmosphere. This is a potential feedback loop that may further accelerate the decrease of oxygen in the atmosphere as well as in the ocean. In this case, the time scale of the oxygen decline may be much shorter than what linear assumptions indicate. In the previous section, it was shown that the industrial consumption of oxygen has already exceeded the scale of the natural loss of oxygen by means of weathering, as industrial air separation units deplete the global atmospheric content by a larger amount than the natural geochemical processes involving the surface erosion with oxygenation. This may indicate that the optimistic view of Don Canfield in his book (Canfield 2014), that the planet is capable of balancing anthropogenic processes by means of its bio- and geochemistry may no longer be valid. The accelerating growth of industrial demand for oxygen in various sectors of the economy, without any means of monitoring its scale and operational volumes, may lead in the future to faster loss of atmospheric oxygen. The time scale of the changes may be fast enough to cause ocean anoxia (alongside the effects of raising temperature), with further positive feedback due to phosphate fertiliser washed down the global ocean from agricultural lands. This may lead to an impact on the biota similar to the Permian–Triassic event of mass extinction of species about 250 million years ago. In the long-term perspective, however, even such an extreme event did not prevent further evolution

4 Oxygen in Future

29

CO2 emissions [million tonnes]

30000

20000

10000

0 1800

1900

2000

time [years] Fig. 4.1 Historic carbon emissions, data from Boden et al. (2010)

and planetary development. This is something that makes futurology optimistic, if not pacifying. To understand the meaning of nonlinear growth, it is sufficient to look at the historic anthropogenic carbon emissions due to the use of fossil fuels: they started from almost zero approximately two centuries ago, and accelerated growth (as shown in Fig. 4.1) has led to the current climate change. Currently, atmospheric oxygen decline does not look concerning, given the abundance of oxygen in the atmosphere. But the presence of nonlinearity implies that it would be wise to start accounting for all oxygen sinks, and monitor their feedback effects on the environmental system. The first experiment of air separation was conducted by Carl von Linde in 1895 (Linde Group 2017), the first ASU was created in 1902—and in just one century the technology has grown to the scale of installations like the recently built Jamnagar refinery that produces 26,000 tpd of oxygen per day (Linde Group 2017). The appearance of such installations, as well as multiple small generators of oxygen supply in medium hospitals, is reported with technological pride; this is understandable, but given their nonlinearly growing capacity, sinking of atmospheric oxygen should be monitored. On the scale of decades and centuries, in the context of our impressively advanced civilisation, we can and must monitor and mitigate potentially dangerous processes at early stages. Huang et al. (2018) and Liu et al. (2019) attempted to investigate the anthropogenic impact on oxygen consumption, even taking into account respiration of livestock (such as chickens and ducks). Their estimate of the amount of respiring oxygen per chicken multiplied by the hypothetical number

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4 Oxygen in Future

of the world population of chickens may still provide an estimate of how growing livestock may influence atmospheric oxygen. Life-cycle emissions from agricultural production may reach hundreds of kg CO2 eq per kilogram of protein (FAO GHG 2020), and that involves consumption of oxygen in various forms, including combustion and fermentation. At geological time scales, the planet is capable of balancing its geochemical processes, as described by Canfield (2014). The question is whether the geological time scale is the right one when the accelerated dynamics of anthropogenic processes reduce the horizon of the dynamics to a few thousand years? It is important to remember that many sectors of the economy are linked, and their growth influences other sectors and resources, directly or indirectly. The socalled Water-Energy-Food Nexus (WEF Nexus 2020) describes the interconnections between major areas, such as freshwater, which requires more and more energy for its retrieval and purification, and food production, with increasing demand for supply of energy and water as well. Water use can be direct and indirect, and an average water consumption of an USA citizen is about 10,000 litres per day. This includes indirect water use due to eating, driving and shopping; for example, production of cotton goods requires hundreds of litres of water per item. Middle Eastern countries, with abundant fossil fuel resources and limited water supply, expand their water desalination facilities. Qatar (QNV 2009) exploits dozens of desalination units, which operate under high pressure (hence, large carbon emissions and oxygen sink), and discharge the salt brine into the ocean at high temperature. Some of such plants are powered by natural gas and some even by oil. Oil and gas are extremely cheap in the region; this water desalination technology is unlikely to become more sustainable or greener in the future, as fossil fuels are the major pillar of the countries’ economy and are considered as a basis of future prosperity. Moreover, the supply of fresh water is not a matter of simple distilling of readily available ocean water. Processed water misses the ions that are present in mineral water due to its filtering through soil. Through the blood– brain barrier (connection between blood stream and neurons) only plasma and electrolytes can pass. These ions are key for electric conductivity in neurons, without which brain activity is impossible. Currently, distilled water has to be processed with remineralisation; drinking only distilled water leads to problems in the neural system. What could be the alternative to such a water supply? Imported water with transport emissions? Keeling et al. (1993) estimated the fossil global fuel reserves as 7.6×1017 moles. However, there are theories of oil formation, such as abiogenic origin, for which one of the major arguments is the presence of methane on the other planets, where there is no life. Some studies (Wang et al. 2017), however, argue that even a century-long projection of coal use may be limited by supply. If fossil fuels remain abundant, and in future more deposits of fossil fuels will be uncovered and available for use (such as in the Arctic), then depletion of oxygen will continue its nonlinear trend, with possible critical consequences. New large deposits of fossil fuels are being discovered (for example, “Tamar” and “Leviathan” in the

4 Oxygen in Future

31

1000 Manua Loa observed data A1B A1T A1F1 A2 B1 B2 A1p

900

700

A2p B1p

2

CO [ppm]

800

B2p

600

IS92a IS92a/SAR

500

400

300 1960

1980

2000

2020

2040

2060

2080

2100

time [years] Fig. 4.2 Mauna Loa observed CO2 data and projections of carbon dioxide emissions in various SRES IPCC-TAR scenarios until 2100

Mediterranean Sea), and it is not certain at present that ecological considerations would prevent their use by the countries with access. The currently dominant economic model is expansive rather than conservative, yet claiming to achieve sustainability in the future; larger and larger natural resources are utilised for an increasing population with growing consumer demands. Less developed countries that aim to achieve prosperity are currently unlikely to prioritise climate change over their fight with poverty. Even in Europe, some countries continue to produce electricity using heavily polluting fossil fuels, such as lignite; it has a carbon content between 60 and 70%, compared to the 92–98% of carbon content in anthracite, which is the coal with the highest fixed-carbon content—yet countries like Serbia use lignite for energy production, despite climate change awareness and EU legislation on carbon emissions. The Special Report on Emissions Scenarios (SRES) was used in the Third Assessment Report of the Intergovernmental Panel on Climate Change (IPCCTAR), and global circulation models (GCMs) were used to generate projections in various scenarios (Fig. 4.2). These forecasts start with contemporary high emissions and assume better or worse economic and political pathways of development. The IPCC scenarios take into account expected changes in population, economy, energy and land use, and constitute four groups: globalised (groups 1) or regionalised (groups 2) and economically focused (groups A) or environmentally focused (groups B). It is easy to see that more regionalised (hence less legislated) and more economically oriented scenarios (group A2) will impact the environment more adversely. Indeed, the highest carbon emissions are forecast by the Coupled Model

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Fig. 4.3 Representative Concentration Pathways of industrial carbon dioxide emissions until 2100, four curves correspond to the radiative forcings of 3, 4.5, 6 or 8.5 W/m2

Intercomparison Project (CMIP) models under the IPCC-TAR “A2p” scenario. Later in 2011, these scenarios were replaced by the Representative Concentration Pathways (RCPs) (Meinshausen et al. 2011). While the previous scenarios were operating the units of ppm of carbon dioxide, the new pathways report the carbon emissions in terms of GtCO2 (aiming at making one think about the future mass balance of the atmosphere as well). Figure 4.3 shows the carbon emissions in these four scenarios, which assume a continuing rise of emissions at least until 2040. It is not clear whether the following decline of carbon emissions would be supported by the development of the world industries and would comply with these expectations: panels (j) and (l) of Fig. 3.6 indicate continuously growing electricity demand, while the content of the fossil fuels in energy production remains almost constant at 80%. This happens because the currently available renewable technologies are intermittent and require balancing, for reliable supply, using conventional fuels. Countries like Norway and Iceland may utilise their unusually generous supplies of unconventional energy (thermal in Iceland and hydro in Norway), but for many other countries the future non-fossil energy is likely to be nuclear (Hodgson 2010)— which requires a very large supply of concrete for construction. This, in turn, means large amounts of energy generated again (in the current conditions) by fossil fuels. The Representative Concentration Pathways (IPCC RCP 2020) replaced SRES scenario in the 5th Assessment Report (AR5). They assume socioeconomic scenarios of the Integrated Assessment Modelling Consortium (IAMC), which lead to four trajectories with 3, 4.5, 6 or 8.5 W/m2 radiative forcings (Fig. 4.3).

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These pathways forecast that eventually carbon emissions will cease. However, the base assumption of evolving expansion is not guaranteed, whereas the available polluting technologies are too easy to use to be abandoned. To achieve globally low-carbon conditions, with growing demand for energy, the world economy may either shift to purely nuclear energy supply or to purely renewable supply backed by large-scale storage infrastructure. How to reach a storage capacity that will be large enough to serve industry, remains an unresolved technological challenge. In order to compare dynamics of future carbon emissions and atmospheric oxygen on the scale of a thousand years, it is easier to use the earlier published IPCC projections of carbon emissions in ppm than absolute emissions in Gt. These projections of carbon emissions under various scenarios are provided only for the twenty-first century, but if we consider them as the basis for projections of O2 consumption (only those scenarios that do not expect significant reduction of CO2 , which is currently unlikely), we can convert CO2 ppm content into percentage of atmospheric O2 . This can be further compared with a nonlinear extrapolation of the currently observed oxygen decline, similarly to Livina et al. (2015). It is necessary to stress that such a long-term projection would not only be highly hypothetical, but also unfeasible in terms of the state of the atmosphere with high CO2 content: normally exhaled air contains 4–5% of CO2 , and this is not the air that would sustain life for long. Similar arguments were discussed in Broecker (1970). The purpose of this exercise is to show how the current sink of oxygen differs from the one expected due to only fossil fuels combustion (because of additional, previously unaccounted sink of oxygen due to air separation), and what is the time scale of such decline in the case of “business-as-usual” scenario. The resulting Fig. 4.4, remarkably shows that the current trend (assuming a moderate parabolic nonlinear decline of O2 ) is more extreme than the scenario “A2p”. Scenario “A2p” is the worst of the IPCC scenarios, which is usually assumed as the upper boundary for climate estimates; the nonlinear extrapolation of atmospheric oxygen decline, however, shows the current trend being worse than the upper boundary, which, too, indicates an additional oxygen sink that was not taken into account by the IPCC scenarios. Long-term climate projections are highly uncertain; some of the uncertainties are very complex, while others may be unmeasurable. Usually we have a better grasp of what is simple and easy to measure, whereas the key processes may be hardest to estimate. Hydrogen is being considered as the fuel of the future (indeed, very clean energy is produced by this fuel: it oxidises to produce water), but again, the current technologies of hydrogen generation are far from being clean or renewable. Its production is based either on hydrolysis (extremely energy-demanding, about 10 kWh of electricity is required to generate 1 m3 of hydrogen in this way), or on steam methane reforming—this means fossil fuels and high temperature processing (energy-intensive). Most worryingly, current production and use of hydrogen means a double sink of oxygen: it is consumed at the stage of hydrogen generation due to energy fuel combustion, and consumed again when hydrogen is used as the fuel.

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atmospheric O2 content [percent]

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20

19

18

2000

B2 A1p A2p B1p B2p IS92a IS92a/SAR extrapolation of observed O2 data

4000

6000

8000

10000

12000

time [years] Fig. 4.4 Estimation of O2 decline under the extrapolated IPCC scenarios and the extrapolation (thick curve) of the currently observed decline of O2 . The level of physiological asphyxiation at 19% of oxygen is marked by the dashed line, and would be reached at about 9000 AD

Ideally, hydrogen should be generated only by renewable power stations; whether it is feasible and sustainable is a question for further research. There is ongoing research on photo-electrolytic cells, which essentially create artificial photosynthesis, and there is hope that this approach will evolve into an industrial-scale solution. The main challenges of this approach are efficiency and resistance: the materials are exposed to oxygen and water, and this leads to fast degradation. An observation from fundamental thermodynamic principles: what produces a lot of energy, first must be created using a lot of energy. Stars like our Sun were created by Big Bang; similarly, hydrogen has large power as a fuel, yet it needs a lot of energy to be generated. Attempts to split carbon dioxide by high-energy laser (Suits and Parker 2014) only confirm this observation. The natural canopy of trees that maintains photosynthesis decays within months, which only biosystems can afford to replenish; attempts to make batteries based on the same principles may remain unsustainable. The presence of plants on the planet may return it to a highly oxygenated state soon enough (on the geological scale), provided the anthropogenic impact ceases. In any case, it is unlikely that on a scale of thousands of years the global economic model and technologies would remain the same, with similar emissions and consumption demands. The anthropogenic impact on all subsystems of the climate system is unquestionable. The question is rather what are the priorities to be addressed, and what are the time scales of the upcoming changes and their impact on the environment?

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Emerging technologies should be tested in terms of their life-cycle performance not only for costs and resources but also for their environmental impact. Imagine a future without hydrocarbon-based polymers (fibres, dyes, resins, oils—all the achievements of the technological development over the past centuries). The problems of energy supply and transport power can be resolved with new technologies (nuclear power, renewable generators, high-capacity power storage). However, no plastic, no industrial polymers, no artificial textiles. Is it feasible? Previously, human civilisation existed without them, but as they are now an essential part of our lives, are we prepared to abandon these convenient items without a ready substitute?

Chapter 5

Solutions?

Making humans a multi-planetary species E. Musk

Possible solutions to the problem of increasing carbon emissions (and decreasing oxygen) are imply various scenarios with higher or lower use of oil and its products. In the short term (over the scale of decades), stopping the use of fossil fuels altogether is unlikely, and therefore various alternative measures are proposed, with different currently feasible levels of implementation. While an increasing amount of renewable energy will be generated, the base load of electric grids will still require power stations with inertia. This is currently provided mainly by conventional fuels such as nuclear and gas. Carbon sequestration is proposed as one of the major solutions, with technologies ranging from carbon burial to reverse conversion (which, according to thermodynamic principles, requires additional energy). Can this be a global solution? Such industrial complexes already operate as pilot installations in the UK (Drax Power Station 2019). The results are promising, and this may be a future pathway for solving the carbon emission problem. However, it may take decades before the scale of this solution will grow sufficiently large to compensate for accelerating emissions. The much-discussed carbon sequestration (Lal 2008), as it is currently being implemented (prior- or post-combustion in the industrial processes), requires additional measures: infrastructural, chemical, material, all of which mean additional supply of life-cycle energy. This demonstrates that carbon sequestration is a resource-heavy and energy-demanding temporary solution to constrain carbon emissions. Altogether, carbon sequestration may mitigate carbon emissions but will not stop combustion or the oxygen sink. The recently initiated project for aerosol injection over California (SCoPEx 2020), in order to reduce regional air temperature, will attempt a geoengineering intervention in the climate system. It will soon (as at the time of writing in 2019) be testing the influence of an anthropogenic injection of stratospheric aerosols in the context of solar geoengineering (reduction of the incoming solar radiation © The Author(s), under exclusive license to Springer Nature Switzerland AG 2020 V. N. Livina, T. M. Vaz Martins, The Future of Atmospheric Oxygen, SpringerBriefs in Environmental Science, https://doi.org/10.1007/978-3-030-43665-0_5

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to improve the regional climate). The project has organised an Advisory Board, with involvement of the Union of Concerned Scientists (UCS 2020). The initiative, however, has already caused concern, with the international community opposing geoengineering interventions (Open Letter to SCOPEX 2019). The project is privately funded (Bill Gates Foundation) but it will affect the lives of people in California and beyond. Is this a future framework for resolving global issues? Geoengineering continues to be discussed in the research literature (Heutel et al. 2015), and private investors are likely to continue to intervene with similar enterprises. Such interventions look like concerning attempts of opening the Overton windows (the range of ideas of different levels of tolerance in public discourse) and should be governmentally regulated. Currently, it seems unlikely that the global solution would be a self-controlling reduction of consumption, even if it will be promoted by some governments (potentially easier in China than in the USA). Because the levels of development greatly differ around the globe, and there is no global government that would be prepared to rule all nations in an orchestrated manner while maintaining a laissezfaire economy, the global reduction of consumption of the nonlinearly growing population is unlikely on a scale of decades and greater. The intergovernmental agreements and organisations, so far, proved well in research and discussions but not in constraining regulations. Emerging ideas of a circular economy have started to develop at national level in the UK: the Waste and Resources Action Programme (WRAP 2020) attempts to reduce waste in the construction, retail and clothing industries. To address global carbon emissions and oxygen sinks, with distributed supply of goods and materials, multiple challenges of modelling and logistics have to be resolved. The feasibility of the global circular economy, as well as its time scale, is a matter of further research. The key point is to ensure that the measures maintaining the resource circulations do not introduce unaccountable carbon emissions or energy demands. New methods are needed to meet the requirements of complex heterogeneous modelling and forecasting, without which circular economy would be difficult to implement. This will require big data processing and modelling, where machine learning and artificial intelligence techniques will be of great importance. Meanwhile, governments continue to introduce measures that will likely remain regional, such as the UK decision to outlaw wood burners by 2022 (Clean Air Strategy 2019). At the same time the industry produces soap dispensers powered by lithium batteries (most likely, shipped from overseas); IoT innovations install multiple sensors, again powered by lithium batteries that will require regular replacement—such innovations are unsustainable. Isn’t it contradictory to condemn one technology as polluting, and promote another, no less polluting with indirect carbon emissions? It may be the right time to start reconsidering previously developed and since abandoned mechanical technologies, such as those Victorian wonders of engineering that were previously powered by steam and may return as new electrically powered innovations (Barber 2013).

Chapter 6

Questions

I will breathe. I will think of solutions S. McClendon

The uncertainty in the future of atmospheric oxygen increases with the length of the horizon of the attempted forecast. The complexity of planetary feedback may influence nonlinearly the dynamics of interactions and gas exchange between the atmosphere, the world oceans and the Earth’s crust. Which of the currently known factors may reduce or increase the decline of atmospheric oxygen? Which yet unknown factors may contribute further? • Can geothermal energy replace other renewables, being less intermittent and potentially low-emitting? • Sustainable farming practices with integration of animals and biosystems may be a long-term solution for food production and the preservation of ecosystems. Such attempts already exist (Foros de Vale Figueira 2019) and should be upscaled. Can global agriculture change in this way soon enough? • If hydrocarbons have abiogenic origin, as was suggested by Humboldt, Mendeleev (1877), and later Kudryavstev (1959) and Gold (1993) (with one of the supportive arguments being the presence of methane in other planets of the Solar system), or if yet undiscovered deposits are as large as the Israeli Leviathan in the Mediterranean Sea, the supply of fossil fuels will remain abundant in the longterm perspective. Will the combustion industries and industries using air for oxygen extraction continue to accelerate growth, according to the growing demand of society? What will be the bounds of oxygen consumption? • The popular idea of using biofuels as an alternative to fossil fuels faces a serious challenge: rapeseed plants attract a very large number of pests (Gu et al. 2007). This requires either large amounts of pesticides (most of which are banned in the EU as they affect bees and have to be used sparingly and only at night), or cumbersome use of cultivars and crop rotations (which many farmers cannot afford despite the high prices on rapeseed). How sustainable is the trend for biofuel production, given also the rising problem of soil quality?

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2020 V. N. Livina, T. M. Vaz Martins, The Future of Atmospheric Oxygen, SpringerBriefs in Environmental Science, https://doi.org/10.1007/978-3-030-43665-0_6

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• Global warming is the most publicised environmental threat, which is considered to be impactful on the scale of the next 100 years. Is this the most urgent challenge? Or do we have to first focus on the challenges of the globally diminishing supply of fresh water and declining water horizons in previously self-sustainable regions? There are already conflicts because of water between Israel and Syria and between Egypt and Sudan. Supply of fresh water is tightly linked to rising temperatures in areas such as Alpine valleys: diminishing glaciers reduce supply of water to large European rivers, for example, the Rhône; if the level of the Rhône decreases, that will affect a large agricultural area in France, with reduced food supply. Is global warming the next most urgent challenge, or will it be the global depletion of soils, which is happening due to continuously growing use of artificial fertilisers currently required to sustain crop yield (Amundson et al. 2015)? Those fertilisers require energy for their production, and some, such as phosphates, are being lost to the global ocean irreversibly (at the current level of development of marine exploitation). In addition, the heavy use of fertilisers depletes soils of micro-elements and reduces the quality of food at the pace of decades (Maltas et al. 2018; Thomas 2003, 2007). Additionally, excessive use of fertilizers has created ocean’s dead zones, areas without sufficient oxygen to sustain marine life. This happens through fertiliser runoff, when chemical nutrients find their way into waters and stimulate an overgrowth of algae that deplete oxygen levels. Land degradation is the subject of the recent IPCC Special Report on Climate Change and Land (SRCCL 2019), which discusses multiple factors affecting land use, such as population growth, agricultural technologies, inequality and others. It may happen soon that one would see a land plot that would appear suitable for agriculture, but nothing planted there would germinate; and what has grown would not flourish. This may cause mass-migration and unrest. In its turn, it may cause more conflicts and decrease of population with possible loss of technologies and damaged infrastructure. Do we want that kind of negative feedback of unsustainable growth? Attempts of land restoration, such as the Great Green Wall Project in Africa (GGW 2020), which will stretch across 8000 km in 11 countries as a 16 km-wide stripe of trees, are yet to prove their feasibility and efficiency under the current trends of growing population and constrained resources in the region. Currently, the most pressing environmental challenges seem to be ordered as: Challenge Diminishing fresh water Depleting soils Increasing temperature Decreasing atmospheric oxygen

Timescale Decades Decades Centuries Millennia

6 Questions











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It is unclear when or if the dynamics of these environmental challenges may become irreversible. While decline of atmospheric oxygen currently seems a less urgent environment issue than others, the nonlinearity and complexity of the Earth system interconnection may (or may not) lead to faster changes, or tipping points. For example, can the ongoing minor ocean deoxygenation lead to sudden collapse of the ocean phytoplankton that would eventually shut down supply of oxygen to the atmosphere? Because society and the environment are interlinked, the imbalance in supply of water and food may be so detrimental for population that the demand for resources falls drastically. As such, further forecasts of anthropogenic environmental impact may potentially become irrelevant. In recent decades, the amount of the energy supply based on fossil fuels has stabilised at about 80%, despite the growing fleets of renewable generators (see panel (l) of Fig. 3.6 and Fig. 3.8). Currently, a major technological challenge is to develop a battery storage with a qualitatively larger capacity and a longer life expectancy than what is currently available. Only in the presence of such storage can renewable generators be used efficiently within the national grid. Such storage would resolve the current issues with the intermittency of renewable supply. If the storage problem is not resolved, renewables penetration, despite the growing energy demand, will remain proportionally low. This means further burning of fossil fuels for electricity production (if not for transport) and further loss of atmospheric oxygen due to combustion. If power supply for transport, electricity and heating has been replaced by renewable and non-emitting technologies, will we fully decarbonise industry by removing any combustion-based processes? Is it possible to abandon the achievement of the chemical industry of the past 150 years in terms of the materials used in our environment on a daily basis? Societies may not be prepared to change their consumer behaviour: richer countries consume energy and produce emissions in ever greater amounts (whilst trying to talk each other into more frugal or sustainable lifestyles), whereas poor countries have only started accelerating their consumerism, having observed others’ prosperity. Will these two trends converge into something sustainable, soon enough and without intervention? In the context of policymaking, what should be the global regulatory body for observing the local implementation of measures for environmental control? Is it feasible to establish such a body? In industry, due to the continual renewal of model ranges, there is a lot of over-production with unnecessary waste of materials. The automobile industry is an example: whereas the manufacturing of one car may produce more than 17 tonnes of CO2 emissions, there are large numbers of unsold cars that later find their way into automobile “graveyards”. Industrial corporations often operate beyond national regulations, which makes it challenging to reduce their harmful environmental practices. What could be a regulatory solution in such circumstances?

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• What are the alternatives to hydrocarbons for the production of materials? How green is green, if energy is needed at every step of manufacturing renewables and the current energy supply is primarily based on fossil fuels? • In the past, there were large eruptions of thousands of square kilometres of magma and gases, which dwarf the recent (1991) Pinatubo eruption which ejected roughly 10 km3 of magma. If volcanic activity intensifies, carbon dioxide content of the atmosphere will increase drastically; this will also affect the Earth’s climate. How quickly can societies respond to global hazards, which may accelerate all the environmental threats? • A rise in sea level caused by the warming climate may reduce the area of exposed land, and therefore reduce the weathering processes (loss of rocks due to winds and oxidation). On the other hand, sedimentation may increase. How will this affect the atmospheric geochemistry? • The Earth’s thin crust is floating on the viscous upper mantle underneath and there are ridges in the ocean where the junctions between the crust plates vent thermal energy in continuous volcanic activity. The average surface heat due to the internal planetary energy is about 80 mW/m2 (Pollack et al. 1993), reaching 120 mW/m2 in the tectonic plate junctions (Vieira and Hamza 2018). Is this thermal energy varying with time? How can it affect weathering processes and other gas exchanges? • The paleodynamics of the continents—in particular, the rift pulse at ∼150 million years ago that opened the Atlantic and forced the subduction of the oceanic lithosphere—possibly caused a drop of the sea level of up to 130 m (Karlsen et al. 2019). Can this exposure of large landmass be linked to the intensified weathering and contribute to the stabilisation of the atmospheric oxygen at the modern concentration (Fig. 2.1)? • Broader implementation of renewables may create new threats caused by the large-scale production of equipment, which is often energy-demanding (e.g., carbon fibres, aluminium) or environmentally dirty (e.g., dangerous chemicals and solutions). Utilisation of these substances and materials may need to be addressed soon.

Afterword

We obviously do not suggest that technological development should be stopped or that the achievements of civilisation should be abandoned. On the contrary, a more scientific and optimised approach is necessary for sustainable development: markets should be investigated, and production should be planned, especially in energydemanding technologies such as automobile manufacturing. Economy should be circular, with assessment of demand for resources. Consumerism should not be encouraged, as it is often vain and destroys resources. An accelerating economy has to be assessed for potential environmental impact in early stages of innovation; launching new technologies without assessing their life-cycle environmental impact may lead to quick wealth, yet in the long-term it may create global threats that would later cost dear to many countries. Taxing populations for their environmental impact when earlier somebody else profited from the same technologies is arguably unfair. Technologies should be used for the common good. There is no need to change gadgets every few years—these often end up in landfill with all rare-earth metals, plastics, resin and glass. Excessive consumerism pumps the Earth’s resources. It often entertains masses with momentary pleasures to make a few richer. The result is catastrophic for everybody.

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2020 V. N. Livina, T. M. Vaz Martins, The Future of Atmospheric Oxygen, SpringerBriefs in Environmental Science, https://doi.org/10.1007/978-3-030-43665-0

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Afterword

The public interest in climate change Is most commendable in its intentions, In giving us a slim survival chance, And certain hopes for future generations. Yet, people do not think of dying soils, Of drinking water that is getting sparser. That’ll trouble us long before the planet boils, Before we find a living place on Marses. The only way to face the coming age Is to reduce and circumvent consumption: For waste and carelessness, the nature will revenge Much worse than the UN with any sanctions. Consume what’s really needed, no excess, Avoid the false directions to progress.

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