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Geoengineering of the Climate System: RSC

Geoengineering of the Climate System: RSC

by R M Harrison (Editor), John Thornes (Contribution by), R E Hester (Editor), Stuart Haszeldine (Contribution by), Tim Lenton (Contribution by)

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It is generally accepted within the scientific community that anthropogenic emissions of greenhouse gases are primarily responsible for a recent warming in global climate and that current trajectories of emissions may lead to potentially catastrophic changes in climate. While reduction in emissions of greenhouse gases, and particularly carbon dioxide, could lead to


It is generally accepted within the scientific community that anthropogenic emissions of greenhouse gases are primarily responsible for a recent warming in global climate and that current trajectories of emissions may lead to potentially catastrophic changes in climate. While reduction in emissions of greenhouse gases, and particularly carbon dioxide, could lead to a stabilisation of global temperatures, this requires international agreements which have yet to be achieved. A possible alternative, which has been widely mooted is to use methods known as geoengineering as an alternative way of limiting increases in global temperature. Geoengineering techniques fall into two main categories of carbon dioxide removal and solar radiation management; within each of these there are a number of options.

Following on from “Carbon Capture” (volume 29 in this series), Geoengineering of the Climate System presents an overview of the technologies currently being considered as large scale solutions to climate change, and considers some of the possible benefits and disadvantages of each. Invited contributions have been received by many of the leading experts on these technologies, and the volume provides a comprehensive overview of both carbon dioxide reduction and solar radiation management methods. These give rise to important ethical and governance issues which are also explored.

Written with active researchers, postgraduate students and policy-makers in mind, the latest addition to the Issues in Environmental Science & Technology series presents a balanced and informed view of this important field of research and is an essential addition to any environmental science library.

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Royal Society of Chemistry, The
Publication date:
Issues in Environmental Science and Technology Series , #38
Product dimensions:
6.14(w) x 9.21(h) x (d)

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Geoengineering of the Climate System

Issues in Environmental Science and Technology

By R.E. Hester, R.M. Harrison

The Royal Society of Chemistry

Copyright © 2014 The Royal Society of Chemistry
All rights reserved.
ISBN: 978-1-84973-953-5


Why do we need Solutions to Global Warming?



The atmosphere is the most valuable resource on the planet and as such every effort needs to be made to protect and manage it. Unfortunately the rise in greenhouse gases since the industrial revolution, and the intimately linked change in climate, is proving to be a most difficult environmental problem. Even though the strongest scientific evidence tells us that the anthropogenic release of greenhouse gases is responsible for climate change, there has been little success in emissions reduction. The reasons behind this failure are complex but the outcome is not; the regions of the Earth inhabited by humans are on average getting hotter and extreme weather is becoming more frequent. Since mitigation efforts against climate change are failing, the arguments for the possibility of geoengineering become louder. Geoengineering is a contentious issue which evokes strong reactions within all levels of society. Solar Radiation Management (SRM) technologies are more controversial than Carbon Dioxide Removal (CDR) technologies, since they do not solve the root cause of the problem, they do, however, potentially offer a more rapidly deployed solution. At present no geoengineering technology is fit for purpose or ready for deployment. However, geoengineering research is rapidly increasing with hundreds if not thousands of scientists and engineers working on the topic worldwide. As such, geoengineering research has now likely passed through its infancy, and conclusions are being reached about the efficacy, benefits and disadvantages of the different proposals. It seems increasingly likely that geoengineering technologies could be developed that will reduce climate change. These benefits need to be carefully weighed against the negative aspects. A true assessment of geoengineering cannot be achieved until we better understand the environmental, technological, economic and governance issues associated through its use.

On May 9, 2013 the daily mean concentration of atmospheric carbon dioxide levels passed 400 ppm at Mauna Loa according to independent measurements taken by both the National Oceanic and Atmospheric Administration (NOAA) and the Scripps Institution of Oceanography. NOAA had announced last year that its global cooperative air sampling network had detected 400 ppm for the first time over all its Arctic sites, just a prelude to what is now being detected over Mauna Loa. According to NOAA, locations throughout the Southern Hemisphere will follow over the next few years, as the increase in Northern Hemisphere levels is always a little ahead of the Southern Hemisphere, due to the fact that the majority of carbon dioxide producing behemoths are found in the Northern Hemisphere.

1 Introduction – Life and the Evolution of the Earth's Atmosphere

Life and the Earth's current atmosphere are intimately linked. You can't have one without the other. Imagine what would happen to the atmosphere if life was wiped out by the gamma rays of a supernova or by a supervirus that killed every living cell on the planet. The Earth would slowly convert, over 100 million years or so, to a planet much like Venus. It would be hotter than the Earth's atmosphere before life, as the sun was about 30% fainter then, than it is now. Thus the atmosphere, weather and climate that we enjoy today are completely dependent on the abundance of life. Lovelock powerfully shows us, through the metaphor of Gaia, that the Earth carefully self-regulates the thin layers of land, ocean and atmosphere to provide a flourishing environment for life. However to achieve a lasting symbiosis of mutual benefit to both the host (Earth) and the invader (life) can we prevent an eventual 'Tragedy of the Commons'? The human population continues to exploit and pollute the atmosphere and 'foul its own nest', for the pursuit of energy and growth, supposedly for the benefit of today's 7 billion citizens and the 9 billion citizens expected by 2050. As a result, the Earth's climate is changing and we have already seen a rise in the planet's surface temperature of 0.8 °C due to radiative forcing caused by greenhouse gas emissions and land-use changes. This global warming is predicted to raise global mean surface temperatures by up to 5 °C by the end of this century if emissions of greenhouse gases continue to rise in a 'business as usual' fashion. Global warming is set to double even if we cease to emit any further pollution, due to the slow release of energy already stored in the oceans. This additional energy available to the atmosphere has already led to an increase in extreme weather around the globe and agreement that a realistic limit of 2 °C could well be surpassed.

The Intergovernmental Panel on Climate Change (IPCC) was set up in 1988 by two United Nations organisations: the World Meteorological Organisation (WMO) and the United Nations Environment Programme (UNEP) to critically assess the scientific, technical and socio-economic consequences of climate change and to examine options for society to mitigate greenhouse gas emissions and adapt to changing weather and climate. The IPCC is in the process of submitting its fifth set of Assessment Reports (AR1 in 1990, AR2 in 1995, AR3 in 2001, AR4 in 2007 and AR5 in 2014, http://www.ipcc.ch/) to support the United Nations Framework Convention on Climate Change (UNFCCC, https://unfccc.int/kyoto_protocol/items/2830.php), an international treaty that set up the Kyoto Protocol which became effective in 2005. In the first commitment period (2008–2012), the Kyoto Protocol sought to set binding targets for 37 industrial countries and 15 European Union (EU-15) countries, on four greenhouse gases: carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), sulphur hexafluoride (SF6) and two groups of ozone depleting gases: hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs).

The binding targets were modest and even so the results have been disappointing. Progress towards a new agreement (2012–2020) has been unsatisfactory because of the impasse in limiting the growth of greenhouse gas emissions. Alternative approaches (Plan B) such as geoengineering and the United Nations initiative Sustainable Energy for All (SE4ALL) are therefore being seriously considered.

The focus of this chapter is on the options to sustainably manage this problem to prevent the atmosphere being polluted to such an extent that changes to the climate will be irreversible and damaging. Time is running out for solutions to be found that can be implemented in a sustainable way.

Firstly, we will scrutinize the value of the services that the atmosphere provides for society and their sensitivity to change. Secondly, we will look at how the climate is changing due to anthropogenic activity and the impacts that it is having on examples such as extreme weather, sea level rise, melting glaciers and ice caps. Thirdly, we will define geoengineering, and fourthly, we will examine the broad arguments for and against geoengineering, and the likely success of geoengineering as an instrument to manage the atmosphere should the mitigation of greenhouse gases fail to deliver.

2 The Atmosphere – The Most Valuable Resource on the Planet

Today's atmosphere has evolved slowly over more than 4 billion years. Changes in the composition of the atmosphere to what it is today are directly attributable to the development of living micro-organisms. Deliberate and inadvertent interventions, by forms of life, into the composition and behaviour of the atmosphere are consequently not new. Animal life (including humans) has evolved to become totally dependent on the atmosphere. The word 'animal' comes from the Latin word animalis, meaning 'having breath'. Typically on average we humans breathe about 15 m3 of air per day. Without the air that we breathe we would die within minutes. Yet we take the atmosphere totally for granted. It is not just the air that we breathe that is vital. The atmosphere provides us with a whole range of 'atmospheric services' that are more valuable than any other resource on the planet. Table 1 lists 12 of these services that are key to all life on Earth.

Typically the atmosphere is portrayed in the media as a hazard with almost daily tragedies caused by floods, droughts, gales, tornadoes, typhoons/hurricanes, heat waves, snow and ice storms. The insurance group, Munich Re, compiles the best database of the worldwide number and costs of such hazards. During the period 1980–2012 they have estimated that there have been 18 200 weather catastrophes costing US$ 2.8 trillion (at 2012 prices) with the loss of 1 405 000 lives. They identify an upward trend that has seen a doubling in the annual number and cost of weather catastrophes since 1990 (see Figure 1). In 2012 there were more than 800 weather catastrophes logged at an estimated cost of US$ 150 billion.

Poor air quality is another vital issue that adds to the annual cost of breathing a polluted atmosphere. The World Health Organisation (WHO) considers clean air to be a basic requirement of human health and well-being. The European Commission has declared 2013 to be the 'Year of Air' and will take the opportunity to review current European air quality legislation. A recent estimate suggests that poor air quality is responsible for more than two million deaths worldwide each year:

We estimate that in the present-day, anthropogenic changes to air pollutant concentrations since the preindustrial era are associated annually with 470 000 (95% confidence interval, 140 000 to 900 000) premature respiratory deaths related to ozone, and 2.1 (1.3 to 3.0) million CPD (cardiopulmonary disease) and LC (lung cancer) deaths related to PM2.5 ... We estimate here that 1500 premature respiratory deaths related to ozone and 2200 CPD and LC deaths related to PM2.5 occur each year due to past climate change.

The number of weather catastrophes is undoubtedly increasing due to climate change whereas the impact of climate change on air pollution is relatively small. Overall the impact of the atmosphere as a hazard to human life would be much worse if the atmosphere did not disperse air pollutants. In total, however, the atmosphere is worth orders of magnitude more as a resource than it costs as a hazard.

The well mixed atmosphere is approximately 100 km deep, which is very thin in comparison to the size of the Earth. Indeed the troposphere, the lowest part of the earth's atmosphere is only about 8–12 km over the poles and 15–18 km deep over the equator and most of the life on the planet survives within the lowest 5 km which comprises half the atmosphere by weight. The effective atmosphere is therefore extremely thin, vulnerable and fragile and has been compared in size to the varnish on a globe. Hence the atmosphere is always taken for granted as it is effectively invisible and free.

3 The Greenhouse Effect and Global Warming

The natural greenhouse effect is responsible for keeping the global mean surface temperature 33 °C warmer than it would otherwise be. Without the atmosphere the mean temperature of the Earth would be -18 °C but with the atmosphere the mean global surface temperature is +15 °C. This natural greenhouse effect is caused by greenhouse gases in the atmosphere that are basically transparent to incoming solar radiation but trap and re-emit the Earth's thermal infrared radiation at certain wavelengths. This warms the atmosphere and the analogy of the workings of a greenhouse has been adopted for simplicity by policy makers (in reality the warming effect of a greenhouse depends on other factors too such as sheltering the air inside from the wind). Water vapour in the atmosphere is the most important natural greenhouse gas accounting for approximately 29.4 °C (89%) of the 33 °C. Carbon dioxide is only responsible for about 7.5% of the remaining 11% of natural warming.

On May 9, 2013 the daily mean concentration of atmospheric carbon dioxide levels passed 400 ppm at Mauna Loa, a background site in the middle of the Pacific Ocean, well away from industrial sources. Figures 2 and 3 show the steady upward rise of atmospheric CO2 at Mauna Loa. There is no sign of a levelling off despite Kyoto, the global recession and other global attempts at mitigation. Annual CO2 emissions from fossil fuel combustion and cement production were about 9.5 GtC (giga tons of carbon) in 2011, an increase of 54% over 1990 levels. From 1750 to 2011, cumulative global anthropogenic CO2 emissions amount to approximately 545 GtC, of which 240 GtC have accumulated in the atmosphere, 155 GtC have been taken up by the ocean and 150 GtC have accumulated in natural terrestrial ecosystems.

Global warming is the increase (0.8 °C so far) in the mean global surface temperature, above the 33 °C caused by the natural greenhouse effect, due to the human emitted greenhouse gases and also aerosol particles that directly absorb solar radiation. Carbon dioxide is responsible for nearly half of this increase. Figure 4 shows the latest estimate (for 2011) of radiative forcing caused by emissions of greenhouse gases and other drivers of change such as aerosols and black carbon. Radiative forcing of the climate drives climate change across the planet due to the uptake of additional energy into the climate system. The solar constant is on average 1365 Wm-2 and the additional total anthropogenic radiative forcing relative to 1750 is estimated by the IPCC (AR5) to be 2.29 (1.13 to 3.33) Wm-2. This estimate is 43% higher than the estimate in AR4 (2005) due to the continued increase in greenhouse gases and an adjustment to give a weaker negative forcing caused by aerosols. There is not a simple linear relationship between radiative forcing and the global mean surface temperature increase as shown in Figure 5. Natural variability of the climate means that the global warming signal is superimposed on the noise of the natural greenhouse effect. However the IPCC (2013) state:

Warming of the climate system is unequivocal and since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, sea level has risen, and the concentrations of greenhouse gases have increased. (p.2)

What are the measurable impacts of global warming so far on the climate and the Earth's surface environment? Although the mean surface temperature rises have been observed across most of planet there is less certainty about precipitation. There is some evidence for increased precipitation since 1901 over land areas in the northern hemisphere with greater intensities of precipitation also in North America and Europe. Over the oceans, however, more evidence is needed. Since 1950 more extreme weather and climate events have been observed. On the global scale the number of warm days and nights has increased, as have the number of heat waves. The number of cold days and nights has decreased despite a number of recent cold winters in the northern hemisphere.

Ocean warming dominates the increase in energy stored in the climate system, accounting for more than 90% of the energy accumulated between 1971 and 2010. (p.6)

The warming of the upper oceans is especially important and it has been estimated that of this 90%, it is likely that 60% is in the upper oceans (0–700 m) and 30% below 700 m. This energy will eventually be released into the atmosphere and add significantly to global warming this century.

Over the last two decades, the Greenland Antarctic ice sheets have been losing mass, glaciers have continued to shrink almost worldwide, and Arctic sea ice and Northern Hemisphere spring snow cover have continued to decrease in extent. (p.7)

This has been most noticeable in the Arctic where annual sea ice extent has shrunk considerably, especially in summer. The picture is less clear in Antarctica where some areas are seeing growth of ice extent where other areas are seeing a retreat. Permafrost temperatures have increased and in parts of the Russian European North reductions in permafrost thickness and extent have been observed since the 1970s.

The rate of sea level rise since the mid-nineteenth century has been larger than the mean rate during the previous two millennia. Over the period 1901–2010 global sea level rose by 0.19 (0.17–0.21) m. (p.9)

Ocean thermal expansion and glacier mass loss together explain about 75% of the observed global sea level rise since 1970. In the last interglacial, 129 000 to 116 000 BP (before present years), sea level was between 5 and 10 m above present levels.


Excerpted from Geoengineering of the Climate System by R.E. Hester, R.M. Harrison. Copyright © 2014 The Royal Society of Chemistry. Excerpted by permission of The Royal Society of Chemistry.
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