Why research on geoengineering?

It is currently strongly debated to which extent geoengineering options should be considered to limit climate change. A frequently used argument for studying geoengineering is that efforts to limit the emission of greenhouse gases may fail in preventing catastrophic climate change, and for this situation a backup option is needed. But it is also argued that even the consideration (or research) of geoengineering techniques may distract from efforts to limit climate change by emission control and thereby indirectly contribute to it.

The subsequent text describes some background on geoengineering and our motivation to  start scientific research in this field. The text was originally written as a statement to answer the request of the UK Royal Society for views on the topic of geoengineering. It can also be accessed as pdf.


Statement on geoengineering, its potential uses, costs and side effects

By the IMPLICC steering committee:
Hauke Schmidt1, Asbjorn Aaheim2, Jon-Egill Kristjansson3, Mark Lawrence4, Michael Schulz5, and Claudia Timmreck1

17 December, 2008

1: Max Planck Institute for Meteorology, Hamburg, Germany
2: Center for International Climate and Environmental Research (CICERO), Oslo, Norway
3: University of Oslo, Norway
4: Max Planck Institute for Chemistry, Mainz, Germany
5: Laboratoire des Sciences du Climat et de l’Environnement, CEA-CNRS-UVSQ, Paris, France

IMPLICC: Implications and risks of engineering solar radiation to limit climate change
IMPLICC is a small collaborative project that will be funded by the European Commission within the Framework Programme 7 (FP7) to study implications and risks associated with engineering solar radiation to limit climate change. The project is likely to start early in 2009. This text is intended to answer the request of the UK Royal Society for views on the topic of geoengineering (also known as “novel options” for climate change mitigation).
In the following, we will
·    provide a short introduction to the topic,
·    discuss reasons why we think it is necessary to study the physical aspects of geoengineering with respect to effectiveness and side effects of different proposed methods,
·    argue that for the proper understanding of effects and side effects of geoengineering, basic research on feedbacks in the climate system has to be continued,
·    give a short overview on the status of research on three proposed methods to manipulate the Earth albedo, and
·    make the point that a broad international discussion is necessary to address legal, ethical and economical aspects of geoengineering.

With the Kyoto protocol the United Nations took a first step to limit the anthropogenic increase of the atmospheric content of green house gases (GHGs) and thereby the projected climate change. Despite these attempts, carbon dioxide concentrations in the atmosphere have continued to rise. In order to prepare for possible failure of emission reduction measures put in place through international agreements, or other unexpected consequences such as an acceleration of climate change, the public and scientific communities begun more earnestly discussing the possibility of “geoengineering”, meaning the deliberate manipulation of the Earth system to manage the climatic consequences of human population and economic expansion (Schneider, 2001).  This discussion has been further intensified following an article by Crutzen (2006), in which he suggested considering and investigating methods of geoengineering Earth’s climate in order to provide, if the need arises, sound scientific support to policy makers.
As pointed out by the UK Royal Society, geoengineering schemes may be grouped broadly into two categories: a) greenhouse gas reduction schemes, and b) albedo modification schemes. As the IMPLICC consortium has proposed to study only the latter category of schemes, we will also focus our discussion here on them. This does not imply we prefer these schemes over greenhouse gas reduction schemes.
Suggestions to modify the albedo have been criticized heavily because they try to cure some symptoms of global climate change and not its cause. By engineering incoming radiation it might be possible to limit global temperature increase; however, the acidification of oceans as a consequence of increasing CO2 levels would not be stopped. Another problem is the long lifetime of atmospheric CO2 that would make it necessary to sustain geoengineering for periods of hundreds to thousands of years if no other technical way to remove CO2 from the atmosphere were to be found.
On the positive side, part of the long-term perturbation of the carbon cycle might be suppressed by geoengineering if positive feedbacks between global warming and the carbon cycle are as important as suggested in the recent IPCC report. Through such feedback mechanisms, the CO2 concentration might actually be reduced by geoengineering.  However, it is also possible that other, as yet unknown feedbacks could result in an increase in CO2 as a result of geoengineering.  Substantial scientific research is needed to better understand such possibilities.
Political and psychological concern exists that the discussion of geoengineering options might distract or prevent societies from investing in technological developments, or behavioral changes, that will reduce the emission of GHGs in the first. We acknowledge this concern, and strongly support that priority is given to emission reduction. However, we should not limit the scope of research addressing itself to these critical issues, because we can not exclude that a geoengineering option may be required at some point; for instance to buy time in the phase of unforeseen but catastrophic changes to the climate system. As pointed out by Lawrence (2006): “if we do not conduct careful research now, we will not be prepared to advise politicians on how to best approach large-scale geoengineering applications  including providing sound information on the various risks involved.“ Scientific advice on a new technology with broad consequences such as geo-engeneering can not be expected to be available on short notice. The research should try to determine the efficacy and costs, but in particular the range and magnitude of anticipated side effects connected with different geoengineering schemes.
The IMPLICC consortium plans to perform numerical studies of the effectiveness, side effects and economical implications of three geoengineering schemes:
a)    space borne reflectors (placed at the Lagrangian point between the Earth and sun);
b)    sulphur injections into the stratosphere; and
c)    engineering of low level marine clouds through sea salt injections;
which we discuss in turn below.
Over the last few years, a small number of groups have started to study the impact of geoengineering solar irradiance to limit climate change, using numerical simulations of the response of the atmosphere or the climate system to albedo modification schemes. However, numerical studies have mostly been performed with models that may be too simplified to fully assess important possible risks. Several studies have been performed by simply reducing the incoming solar radiation (e.g. Matthews and Caldeira, 2007). This would be the effect of space borne reflectors.
Crutzen (2006) suggested studying the injection of large amounts of sulphur dioxide in Earth’s stratosphere. Sulphate aerosol would build up, subsequently reflecting part of the solar radiation, thus changing the atmospheric energy budget and decreasing the temperature at the Earth’s surface.  This is analogous to the climate effect associated with big volcanic eruptions. The advantage of this scheme is that big volcanic eruptions may have similar climate effects, and in particular the relatively well observed Mt. Pinatubo eruption in 1991 may be considered as a test case. Studies have shown that an increased stratospheric sulphate aerosol loading leads to an enhanced loss of polar ozone (e.g. Tilmes at al., 2008) and impacts the hydrological cycle (e.g Robock et al., 2008). While the radiative and chemical effects of volcanic (or geoengineered) stratospheric sulphate aerosols seem to be quite well understood, possible dynamical effects, are less clear.  
Another suggestion is the modification of low level marine cloudiness via the injection of additional condensation nuclei (e.g. Latham, 2002; Bower et al., 2006) that should lead to a brightening of the clouds. It is debated whether an enhancement of cloud albedo can be deliberately introduced that is sufficient to counteract current and future global warming. Cloud-climate feedbacks belong to the most uncertain processes in our current understanding of climate change and introduce therefore a large source of uncertainty in numerical climate models.
These examples show that research on geoengineering requires a deep understanding of the functioning of the climate system. Therefore, not only studies specifically designed with respect to geoengineering are needed but also a continuation of the efforts to improve the basic understanding of the climate system. The other side of this coin is that research on the effects of geoengineering, if properly conducted, can advance our understanding of the climate system as a whole.
Numerical climate models are presently the only tools available for studying the climate evolution of the future under different emission and geoengineering scenarios.  They will thus play an important role in future geoengineering research.  They can, however, at best reflect the current state of knowledge on the climate system. Bengtsson (2006) has raised concern about inaccuracies of current numerical models that limit our capability to predict climate and to adequately study the consequences of geoengineering. Some of these deficiencies (different models show for instance different climate sensitivities), can be ameliorated by using a coordinated multi-model approach by a larger community as it is currently already being done in the case of future climate projections for which the IPCC provides the framework. Nevertheless, we should be aware that even the most thorough numerical study does not guarantee an error-free climate projection. In plain terms, history has examples of the physical system responding to imposed perturbations in ways that are not anticipated by any of our models; the rapid and unanticipated decline of arctic sea-ice being a recent and familiar one.
The possible application of geoengineering schemes raises not only questions concerning the physical climate system, but also carries economical, legal, political and ethical implications.
The current basis for economic evaluations of geoengineering schemes is thin. A report from the National Academy of Sciences (1992) is one of very few references with suggestions about the costs of some alternative geoengineering options. Furthermore, implications for the costs and benefits have been discussed with reference to certain properties of geoengineering, but we have found no attempts to actually estimate the benefits in terms of climate change impacts. An apparently common view among economists that actually have dealt with geoengineering is that costs are low. This statement is based primarily on the abovementioned report from the National Academy of Sciences from 1992 but has been echoed in more recent publications (e.g. Nordhaus and Boyer, 2000). Barrett (2008) emphasizes that the perception of low costs gives countries a strong incentive to start experiments with geoengineering on their own; hence there is some urgency to the task of more fully considering the costs, including those attributable to the response of the physical system, associated with various geoengineering proposals.
Although it is not our field of expertise we think it should be mentioned that the issue of geoengineering raises vital questions about global governance, like the following: Is any nation or group of nations allowed to intentionally modify climate on a global scale, since these modifications may be beneficial for some and detrimental for others, and since many of the side effects of such modifications cannot be predicted with any degree of certainty? Is there a political entity legitimated to decide on the application of the proposed novel options? These questions can only be discussed in an international framework that is as comprehensive as possible. Of course, similar questions relate to the unintended global effects of increased greenhouse gas concentrations to which different nations have contributed to a very different degree.
In the end, the question as to what to do cannot be separated from the broader international debate on climate; as many of the questions raised echo those that have long been considered in this broader context.  And as is the case for the climate change discussion more broadly, our task as scientists is to ensure that such a discussion is based on the most complete understanding of the system that we are able to master. It is in this sense that we hope IMPLICC can make a contribution.

Barret, S. (2008), “The Incredible Economics of Geoengineering”, Environmental Resource Economics [39] 45-54.
Bengtsson, L., (2006), Geo-engineering to confine climate change: Is it at all feasible? Climatic change, 77, 229-234.
Bower, K., T. Choularton, J. Latham, J. Sahraei, S. Salter (2006), Computational assessment of a proposed technique for global warming mitigation via albedo-enhancement of marine stratocumulus clouds. Atm. Res., 82, 328-336.
Crutzen, P. J. (2006), Albedo enhancement by stratospheric sulfur injections: A contribution to resolve a policy dilemma? Climatic Change, 77, 211-220.
Latham, J. (2002), Amelioration of global warming by controlled enhancement of the albedo and longevity of low-level maritime clouds. Atm. Sci. Lett., doi:10.1006/asle.2002.0048.
Lawrence, M. (2006), The geoengineering dilemma: to speak or not to speak, Climatic change, 77, 245-248.
Matthews, H. D., Caldeira, K. (2007), Transient climate-carbon simulations of planetary geoengineering, PNAS, 104, 9949-9954
National Academy of Science (1992), Policy Implications of Greenhouse Warming: Mitigation, Adaptation and the Science Base, Committee Science, Engineering, and Public Policy, The National Academies Press. Washington D.C.
Nordhaus, W.D. and J. Boyer (2000), Warming the World. Economic Models of Global Warming, The MIT Press, Cambridge, Mass.
Robock, A., L. Oman, and G. Stenchikov (2008),  Regional climate responses to geoengineering with tropical and Arctic SO2 injections. J. Geophys. Res., 113, D16101, doi:10.1029/2008JD010050.
Schneider, S. H. (2001), Earth systems engineering and management, Nature, 417421.
Tilmes, S., R. Müller, R. Salawitch (2008), The Sensitivity of Polar Ozone Depletion to Proposed Geoengineering Schemes, Science, 320, 1201  1204.


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