Appendix 2

1[1] S. Barrett, “The Incredible Economics of Geoengineering,” Environmental & Resource Economics, vol. 39, 2008, pp. 45-54.

2According to Barrett, climate engineering (and SRM, in particular) is a serious alternative or rather serious additional option for counteracting climate change. Barrett emphasizes that low direct costs make deployment of SRM (and notably of stratospheric aerosol injection) relatively probable and believes the major potential risk to be the ensuing political challenges. It is important to find answers to the following questions:

• Who is supposed to decide on the deployment of CE measures?
• Which temperature target are we supposed to agree upon?
• How is the international community supposed to react to the attempt at a unilateral deployment?
• Should there be compensations for disadvantaged countries? If yes, how are these supposed to be fixed and who will pay?

3[2] L. Bengtsson, “Geo-Engineering to Confine Climate Change: Is it at all Feasible?,” Climatic Change, vol. 77, 2006, pp. 229-234.

4Considering arguments against the deployment of SRM (and against stratospheric aerosol injection, in particular), Bengtsson arrives at the conclusion that the world’s energy problem would be better solved without deploying CE technologies. Bengtsson notably (i) puts doubt on the reliability of detailed climate forecasts, (ii) points out that SRM measures would have to be continued for centuries, and (iii) outlines the problems that cannot be solved by deploying SRM (e. g. acidification and the hazards involved for ocean ecosystems).

5[3] J. J. Blackstock, D. S. Battisti, K. Caldeira, D. M. Eardley, J. I. Katz, D. W. Keith, A. A. N. Patrinos, D. P. Schrag, R. H. Socolow, and S. E. Koonin, “Climate Engineering Responses to Climate Emergencies,” http://arxiv.org/pdf/0907.5140, 2009.

6The Novim report roughly introduces a programme for R&D into SRM methods (and into stratospheric aerosol injection, in particular) that would minimise the risks of deploying related measures. The authors neither explicitly argue in favour of nor against the deployment of or R&D into such measures but emphasise that the political, sociological, and ecological dimensions of CE must not be ignored during R&D and must play a significant role in R&D and deployment decision-making.

7[4] J. J. Blackstock and J. C. S. Long, “The Politics of Geoengineering,” Science, vol. 327, 2010, p. 527.

8The authors spell out that SRM measures ought not to be understood as alternatives to mitigation policies and argue for responsible and internationally coordinated R&D into SRM. They suggest that both R&D and the relevant field tests be controlled by generally accepted, international standards and be transparent for the public. Since R&D field tests may have negative impacts across borders, unilateral research might lead to international tensions.

9[5] D. Bodansky, “May We Engineer the Climate?,” Climatic Change, vol. 33, July 1996, pp. 309-321.

10This article provides an overview of existing international agreements and general principles (precautionary principle, intergenerational equity) that may be of relevance to CE measures. Bodansky argues that these agreements and principles are absolutely insufficient for controlling CE adequately. International control presents a major challenge because the consequences of CE may differ globally and regionally. Three conceivable scenarios are sketched out by the author:

1. CE deployment is decided unilaterally by the different nations.
2. An international decision-making mechanism will be established to decide on CE deployment.
3. The international community basically prohibits deployment of CE.

11According to Bodansky, the great difficulties affiliated with option (2) make it most likely that option (3) will be realised.

12[6] R. Bodle and R. A. Kraemer, “Wer darf am Thermostat drehen? Der rechtliche Rahmen von Geo-Engineering,” Politische Ökologie, vol. 120, 2010, pp. 44-47.

13Bodle and Kraemer state that CE R&D and deployment cannot be regulated by existing international law. The great potential for conflict of unilateral deployment and field tests makes the authors advocate the creation of novel international agreements for regulating both CE R&D and deployment.

14[7] P. G. Brewer, “Evaluating a Technological Fix for Climate,” Proceedings of the National Academy of Sciences, vol. 104, 2007, pp. 9915-9916.

15Brewer points out negative consequences of SRM deployment:

• Severe climate changes in the case of abrupt termination.
• Unknown long-term impacts.
• Widely differing regional consequences.
• Decrease in precipitation.

16[8] M. Bunzl, “An Ethical Assessment of Geoengineering,” Bulletin of the Atomic Scientists, vol. 64, 2008, p. 18.

17Bunzl asks the reader to consider that the various objections to CE are not per se a reason to reject CE options. Decisions on whether or not CE measures should be deployed cannot be taken before the impacts and related unequal distributions of risks and benefits can be assessed.

18[9] M. Bunzl, “Researching Geoengineering: Should not or Could not?,” Environmental Research Letters, vol. 4, 2009, p. 045104.

19Bunzl rejects the moral-hazard argument as being an exaggerated fear and says that the risk of CE R&D leading more or less inevitably to the deployment of the respective CE options is more significant. According to him, however, a burden of proof is imposed on proponents of R&D into CE through one crucial argument of methodological nature: Limited field tests and modelling cannot tell us anything about the side-effects that may occur during large-scale deployment. It seems that uncertainties are irreducible. And Bunzl ends up posing the question whether R&D into CE, hence, becomes unacceptable.

20[10] R. Cicerone, “Geoengineering: Encouraging Research and Overseeing Implementation,” Climatic Change, vol. 77, 2006, pp. 221-226.

21Cicerone argues in favour of R&D into CE while suggesting that research and deployment be treated separately. According to him, immediate research is necessary (but not sufficient) for possible future deployment because only research can reveal the different approaches’ potential risks and weaknesses. Moreover, Cicerone advocates a preliminary moratorium on large-scale field tests until agreements have been obtained as to further conditions for research, development, and deployment.

22[11] A. Corner and N. Pidgeon, “Geoengineering the Climate: The Social and Ethical Implications,” Environment, vol. 52, 2010, pp. 24-37.

23This article provides an overview of CE measures while expounding their ethical and social aspects. In particular, Corner and Pidgeon argue that issues of social and ethical relevance ought to be discussed in the general public and on an international level. Different possibilities of engaging the public at an early stage (“upstream public engagement”) are introduced based on experience gained in the debate on nanotechnology.

24[12] P. Crutzen, “Albedo Enhancement by Stratospheric Sulfur Injections: A Contribution to Resolve a Policy Dilemma?,” Climatic Change, vol. 77, 2006, pp. 211-220.

25Crutzen argues for R&D into SRM measures and for stratospheric aerosol injection, in particular, but points out that ambitious mitigation policies are the more appropriate reaction to climate change.

26[13] P. Crutzen, “Erdabkühlung durch stratosphärische Schwefel-Injektionen,” Jahrbuch Ökologie 2011, Stuttgart: S. Hirzel, 2010.

27Crutzen emphasizes that the “best strategy for solving the climate problem” would be to reduce greenhouse gas emissions. Since no such efforts are being made, Crutzen recommends R&D into SRM.

28[14] L. David, “Climate Change - A Geoengineering Fix?,” Aerospace America, vol. 45, 2007, pp. 32-37.

29David introduces CE measures placing emphasis on space-related solutions. Besides, he presents ideas and arguments of different critics and sceptics (such as Al Gore, Brad Edwards, and Dennis Bushell).

30[15] K. C. Elliott, “Geoengineering and the Precautionary Principle.” International Journal of Applied Philosophy, vol. 24, 2010, pp. 237-253.

31This article points out that there are rather different variants of the precautionary principle and that these variants, in part, imply contrary normative assessments of R&D into, deployment of, and, what is more, the public discussion of CE measures. Moreover, Elliott explains that the precautionary principle may possibly not lead to clear instructions on how to act, since both carrying out R&D into (deploying) CE as well as not doing so may have unforeseen negative effects. If that should be the case, Elliot suggests to consider further ethical principles, i.e.:

• The asymmetry between active and passive action is morally relevant and might be crucial.
• Acts that may have negative consequences for lots of individuals must be accepted by these very individuals.
• A cost-benefit analysis of all conceivable consequences decides on the moral status of relevant action alternatives.

32[16] ETC, “Retooling the Planet: Climate Chaos in a Geoengineering Age,” ETC Group, 2009.

33This report outlines several CE approaches, introduces their proponents, points out the risks and side-effects of potential deployment, and quotes general arguments against the use of CE measures (moral-hazard argument, commercialisation, possible unilateral deployment, unforeseeable side-effects, etc.). The authors, in addition, argue for (i) a moratorium on field tests and (ii) an obligation to perform R&D solely under participation of a broad public, under the consideration of human rights, and with the informed consent of all persons concerned. Moreover, the report demands the creation of institutions that can bring about a global balance of interests between CE deployment beneficiaries and losers.

34[17] ETC, “Geopiracy: The Case Against Geoengineering,” ETC Group; 2010.

35This ETC report is a revised version of [16].

36[18] J. R. Fleming, “Fixing the Sky: Checkered History of Weather and Climate Control,” New York: Columbia University Press, 2010.

37In this critical book, Fleming proves that there are numerous historical forerunners to today’s proposals of controlling the climate system through technical options. Given the failure of these previous attempts, which had all been characterised by overestimation and hubris, Fleming advises extreme caution and asks the reader to consider that also currently discussed CE measures might be based on excessive confidence and technical overestimation.

38[19] S. M. Gardiner, “Is ‘Arming the Future’ with Geoengineering Really the Lesser Evil? Some Doubts about the Ethics of Intentionally Manipulating the Climate System,” Climate Ethics: Essential Readings, S. M. Gardiner, D. Jamieson, and S. Caney, eds., Oxford: Oxford University Press, 2010.

39Gardiner gives a comprehensive overview of the ethical aspects of CE measures. He critically analyses, in particular, the armthe-future argument which argues for research into CE and, among other things, considers the moral-hazard argument, the unstoppable-development argument, and aspects of intra-and intergenerational justice.

40[20] S. M. Gardiner, “Is Geoengineering the ‘Lesser Evil’?,” http://environmentalresearchweb.org/cws/article/opinion/27600, 2007.

41Gardiner takes up Crutzen’s lesser-evil argument for CE R&D and hints at some problematic points of the underlying argumentation:

• It is not necessarily clear whether CE is the lesser evil in the case of unsuccessful mitigation.
• Investments in CE R&D may undermine efforts into mitigation.
• Further alternatives ought to be considered.
• CE research alone does not suffice to fulfil our moral obligations. In fact, we rather have to think about our compensation obligations towards future generations.

42[21] J. Goodell, “How to Cool the Planet: Geoengineering and the Audacious Quest to Fix Earth's Climate,” New York: Houghton Mifflin, 2010.

43In this popular-science book, Goodell not only introduces readers to the main CE technologies but also discusses some ethical aspects of CE R&D and deployment, e. g. the dual-use problem, the moral-hazard argument, the problematic absence of an exit option, the priority of mitigation, and the ethical asymmetry between SRM and CDR. In spite of numerous concerns and doubts, the author ultimately advocates comprehensive R&D into CE. Besides, Goodell draws detailed and revealing portraits of the main actors in the CE controversy, e. g. of David Keith, Ken Caldeira, and James Lovelock, but also of Lowell Wood, Bill Gates, and Russ George (the founder of the Planktos company which offers ocean fertilization services).

44[22] C. Greene, B. Monger, and M. Huntley, “Geoengineering: The Inescapable Truth of Getting to 350,” Solutions, vol. 1, pp. 57 – 66, 2010.

45The authors argue for reaching the 350 ppm target by the end of the 21st century. They conclude that that target cannot be achieved by classical mitigation measures alone and that, thus, CDR measures are inevitable. Combined with bioenergy technologies, CDR methods removing CO₂ from the atmosphere are supposed to be particularly suited for reaching such a stabilization target at reasonable costs. The authors, moreover, advocate R&D into SRM measures which, although not being long-term solutions, may prevent a possible dangerous or catastrophic climate change.

46[23] A. Grunwald, “Der Einsatz steigt - Globale Risiken,” Politische Ökologie, vol. 120, 2010, pp. 37-39.

47This article critically appraises CE deployment while considering possible risks and impacts of (i) preparatory experiments, (ii) political decision-making, (iii) deployment, and (iv) sudden termination of CE measures. Besides drawing attention to the moral-hazard argument, Grunwald advises to take CE seriously and says that the potentials, risks, and possible side-effects of CE measures ought to be assessed through thorough and transparent research.

48[24] B. Hale, “You Say ‘Solution,’ I Say ‘Pollution’ Ocean Fertilization is a Fishy Solution to a Whale of a Problem,” Science Progress, Aug. 2009. (http://www.scienceprogress.org/2009/08/ocean-fertilization-ethics/)

49Hale holds the thesis that the positive consequences of an action do not suffice to legitimate that very action ethically. It is important instead to ascertain whether the relevant action is being taken while ensuring that the persons concerned by its consequences are respected and will be giving their consent. Against that background, the deployment of ocean fertilization which, in spite of the technical feasibility of the measures involved, is assumed to be very problematic. Hale advocates increased reduction efforts, the use of non-polluting energy sources, and the reduction of CO₂ in the atmosphere by means of reversible and local methods such as air capture and CCS.

50[25] B. Hale, “Getting the Bad Out: Remediation Technologies and Respect for Others,” The Environment: Philosophy, Science, and Ethics, W. P. Kabasenche, M. O'Rourke, and Slater, M., eds., MIT Press, forthcoming, 2012.

51Based on considerations introduced in [26] und [27], Hale argues for the use of general criteria for evaluation of the ethical permissibility of the deployment of different CE technologies. In the light of these criteria, neither SRM nor ocean fertilization are permissible. Only under extraordinary and disastrous circumstances should the permissibility of the related measures be evaluated once again. If anything, only methods which, like air capture, are aimed at establishing a former “unpolluted” state of the world are permissible.

52[26] B. Hale and L. Dilling., “Geoengineering, Ocean Fertilization, and the Problem of Permissible Pollution,” Science, Technology & Human Values, vol. 36, 2011, pp. 190-212.

53Hale and Dilling hold that measures which are meant to compensate or reverse pollution (of the environment) should not only be assessed regarding their effectiveness. They draw up fundamental ethical principles (in the sense of Jamieson, see [28]) to be considered in ethical assessment:

• The ethical assessment of such measures cannot be detached from the actions that have brought about that measures such as these have been considered.
• The measures concerned are not permissible unless all parties that may be affected by their consequences consent to implementing them. This includes, in particular, consideration of the interests of non-human parties.
• The respective measures, if possible, convert the world into a state that had existed prior to pollution.

54[27] B. Hale and W. Grundy, “Remediation and Respect: Do Remediation Technologies Alter Our Responsibility?,” Environmental Values, vol. 18, 2009, pp. 397-415.

55According to Hale and Grundy, environmental pollution, even with adequate reversing technologies at hand, forbids itself for ethical reasons. Technological solutions such as CE measures, thus, do not legitimate any further pollution of the environment.

56[28] G. C. Hegerl and S. Solomon, “Risks of Climate Engineering,” Science, vol. 325, 2009, pp. 955-956.

57Hegerl and Solomon point out that it is lopsided to focus the CE controversy on temperature change or stabilisation and stress that changes in precipitation, which are caused by SRM, are equally significant. The risks and side-effects of precipitation changes (e. g. droughts) may cause water resources conflicts, migration, and political instability. Current models even underestimate precipitation changes. Further research into the related side-effects is necessary.

58[29] M. Hulme, „ Why We Disagree About Climate Change: Understanding Controversy, Inaction and Opportunity “, Cambridge: Cambridge University Press, 2009.

59In his above book, Hulme militates against CE technology development by holding that if such technologies are available and are being deployed it may, in a global context, indeed become rather difficult to agree on a desired temperature. According to Hulme, it cannot be excluded that even wars may be caused by the conflicts that may be arising from such situation.

60[30] D. Jamieson, “Ethics and Intentional Climate Change,” Climatic Change, vol. 33, 1996, pp. 323-336.

61Jamieson discusses necessary conditions for CE deployment (technical feasibility, reliable forecasts of the related consequences, socio-economic preference over other alternatives, and non-violation of fundamental ethical principles) and argues that, at present, these are not fulfilled. In addition, he advocates R&D into CE under the condition that such R&D takes into account the relevant associated ethical and social aspects. Jamieson points out that R&D into CE may bring about that

• the money to be invested will not be available anymore for other areas of research,
• the respective measures will be deployed even in spite of massive uncertainties regarding effectiveness and side-effects.

62[31] D. W. Keith, “Geoengineering the Climate: History and Prospect,” Annual Review of Energy and the Environment, vol. 25, 2000, pp. 245-284.

63This article gives an overview of the history and terminology of climate engineering, discusses some of its risks and points out the following aspects:

• Potential undesirable side-effects (ozone depletion, ocean acidification),
• undermining mitigation efforts (moral-hazard argument),
• creation of political tensions,
• problems arising from setting a precedent (if CE were justifiably deployed, it would be admissible to reshape nature, using technical means, in virtually unlimited ways),
• the problem of merely fighting symptoms.

64[32] D. W. Keith, E. Parson, and M. G. Morgan, “Research on Global Sun Block Needed now,” Nature, vol. 463, 2010, pp. 426-427.

65Keith et al. advocate starting SRM R&D (inclusive of field tests) without delay. Moreover, they advise against immediate multilateral agreements and recommend instead cooperating internationally in terms of transparent, loosely coordinated programs that support R&D and risk assessment and are coordinated by independent institutions. The authors emphasise that SRM is to be understood exclusively as a supplement to mitigation policies.

66[33] J. Kiehl, “Geoengineering Climate Change: Treating the Symptom over the Cause?,” Climatic Change, vol. 77, 2006, pp. 227-228.

67Kiehl criticises CE measures as fighting symptoms only and advocates R&D into these measures while stressing the limited reach and scope of model calculations.

68[34] E. Kintisch, “Hack the Planet: Science's Best Hope – or Worst Nightmare – for Averting Climate Catastrophe,” Hoboken, New Jersey: John Wiley & Sons, 2010.

69In this popular-science publication on the CE controversy, Kintisch also touches upon ethical aspects. He describes the controversy as being extremely polarized. His book sheds light on the motivations of numerous CE proponents. In chapter 10, which is of particular interest regarding the ethical assessment of CE, Kintisch explains how conservatives and climate sceptics politically capitalize on the CE option and backs up a variant of the moral-hazard argument, which is central to the debate.

70[35] M. Lawrence, “The Geoengineering Dilemma: To Speak or not to Speak,” Climatic Change, vol. 77, 2006, pp. 245-248.

71Lawrence advocates open, cautious, and scientific R&D into CE.

72[36] T. Leisner and S. Müller-Klieser, “Aerosolbasierte Methoden des Climate Engineering. Eine Bewertung,” Technikfolgenabschätzung - Theorie und Praxis, vol. 19, 2010, pp. 25-32.

73This article gives an overview of aerosol-based CE methods, points out their socio-economic uncertainties and risks, and recommends to research into them in order to be able in the future to make a founded decision in favour of or against their deployment.

74[37] U. Lohmann, “Der Sonne entgegen - Sonneneinstrahlungsmanagement,” Politische Ökologie, vol. 120, 2010, pp. 23-26.

75Lohmann introduces the reader to different SRM approaches and advises against deploying the respective measures because such interventions in a complex system may have unknown impacts. According to Lohmann, we rather ought to opt for a rapid and significant reduction of greenhouse gas emissions.

76[38] M. MacCracken, “Geoengineering: Worthy of Cautious Evaluation?,” Climatic Change, vol. 77, 2006, pp. 235-243.

77MacCracken introduces different CE measures, placing emphasis on difficulties arising from stratospheric aerosol injection. Considering the facts that such a measure must be continued for centuries and entails serious consequences if suddenly terminated, it cannot be but an emergency solution and mitigation efforts ought to be increased. MacCracken, in addition, advocates R&D into SRM to better understand the long-term impacts of aerosol injection into the atmosphere.

78[39] M. MacCracken, “Impact Intervention: Regional Geoengineering as a Complementary Step to Aggressive Mitigation,” IOP Conference Series: Earth and Environmental Science, vol. 6, 2009, p. 452003.

79The author advocates immediate R&D into CE. He stresses that he does not understand CE measures as being an alternative to mitigation policies.

80[40] D. R. Morrow, R. E. Kopp, and M. Oppenheimer, “Toward Ethical Norms and Institutions for Climate Engineering Research,” Environmental Research Letters, vol. 4, 2009, p. 045106.

81The authors argue for a detailed analysis of the ethical and institutional aspects of R&D into SRM. Based on ethical norms that regulate experiments on humans and animals, they discuss three elementary principles and point out the difficulties arising when they are applied to SRM research. These difficulties are particularly relevant to field tests within SRM:

1. Respect towards humans: The autonomy of humans ought to be respected by letting them decide themselves whether and in what way they would participate in an experiment. Since SRM field tests would involve humans of many nations, one must ask whether it would suffice to have the consent of the representatives of the respective nations.
2. Justice and charity: The risks associated with experiments must not be unreasonable. Moreover, the risks and benefits of the experiments must be fairly balanced.
3. Minimalisation: Experiments must not last longer, nor be extended over a larger area, nor have a greater impact on the global climate than is necessary for achieving the experiment’s objectives.

82[41] Nationales Komitee für Global Change Forschung, „The Debate on Geoengineering: Arguments, Risks and Consequences,“ Nationales Komitee für Global Change Forschung, 2010.

83After giving an overview of the advantages and disadvantages of CE in general, the report points out the pros and cons of specific SRM and CDR methods.

84[42] NERC, “Experiment Earth? Report on a Public Dialogue on Geoengineering.” Natural Environment Research Council (NERC), Sciencewise Expert Resource Center, 2010.

85“Experiment Earth?” is a participative procedure, a “public dialog” that has been carried out on the subject of CE in Great Britain in spring 2010, involving a total of 85 laypersons, plus further experts. The report gives a qualitative summary of the laypersons’ assessments of nine different CE technologies. It finds that:

• In principle, CDR technologies are preferred over SRM technologies.
• CE measures have not been rejected or excluded categorically. The participants agreed that (i) mitigation measures alone may not suffice or may take effect too late to avoid a dangerous climate change, (ii) mitigation measures must not be replaced by CE measures, and (iii) mitigation efforts must not be weakened through CE.
• The question of how strongly CE technologies interfere in and change natural processes has been an essential criterion for CE technology evaluation. The environment has been understood as a self-regulating system whose natural equilibrium should not to be modified, if possible.
• The participants gave the following further key criteria: Controllability, reversibility, effectiveness, governability, and a fair balance between costs and benefits.

86The authors of the report conclude that it is essential to keep on considering the public opinion about climate engineering and to inform and actively involve the public.

87[43] K. Ott, “Die letzte Versuchung: Geo-Engineering als Ausweg aus der Klimapolitik?,” Internationale Politik, vol. 66, 2010, pp. 58-65.

88Ott criticises the lacking or insufficient consideration of the ethical aspects of stratospheric sulphate injection in the corresponding report by the Royal Society, points out diverse arguments against using the sulphate option (e. g. the moralhazard argument, the exit problem, and the hubris argument), and emphasises that a permanent sulphate solution must be rejected from the point of view of ethics.

89[44] K. Ott, “Die letzte Versuchung – Eine ethische Betrachtung von Geo-Engineering,” Politische Ökologie, vol. 120, 2010, pp. 40-43.

90Ott introduces the reader to the major pro and con arguments of the CE controversy and discusses their weaknesses and strengths. (cf. also [43].)

91[45] K. Ott, “Kritische Kartierung der Argumente der Klimamanipulation,” Jahrbuch Ökologie 2011, Stuttgart: S. Hirzel, 2010.

92Ott gives a systematic overview of the major arguments in favour of (the arming-the-future, lesser-evil, efficiency, easiness, innovation, and do-it-alone arguments) and against (the risk transfer, termination problem, informed-consent, moral-hazard, undermining-better-options, political-economy, loss-of-intangible, and hubris arguments) CE measures. He evaluates each of these arguments and draws the tentative conclusion that the cons outweigh the pros.

93[46] K. Ott, “Argumente für und wider „Climate Engineering“. Versuch einer Kartierung,” Technikfolgenabschätzung - Theorie und Praxis, vol. 19, 2010, pp. 32-41.

94This article is a slightly revised version of [45].

95[47] C. L. Parkinson, “Coming Climate Crisis?: Consider the Past, Beware the Big Fix,” Lanham, Maryland: Rowman & Littlefield, 2010.

96In his above book, Parkinson comments on and interprets the climate controversy. Three chapters are dedicated to the subject of climate engineering. Parkinson brings back into mind the precedents set by a number of well-intentioned technical interventions in complex systems whose unforeseen negative side-effects have by far been exceeding the intended consequences. Pointing out several massive and presumably irreducible uncertainties, Parkinson militates against CE deployment but at the same time advocates further R&D into CE technologies.

97[48] Parliamentary Office of Science and Technology, “POSTnote: Geo-Engineering Research,” Parliamentary Office of Science and Technology, 2009.

98Based on the judgment that all previous forecasts have been underestimating future greenhouse gas emissions, different CE measures (SRM, CDR) are explained and their respective pros and cons are discussed. The POSTnote implicitly advocates immediate R&D into CE technologies which, if necessary, should be available as emergency options.

99[49] U. Potzel, “Rechnung mit vielen Unbekannten - Geo-Engineering-Forschung,” Politische Ökologie, vol. 120, 2010, pp. 34-36.

100According to Potzel, R&D into CE is imperative to be able to prepare for climate crises. Such R&D is to be financed exclusively by the governments and should preferably be carried out through international cooperation. Potzel points out that since CE is associated with possible negative side-effects, it must not be understood as an alternative to mitigation policies.

101[50] S. Rayner, “Geoengineering Governance. Regulierung der Klimamanipulation,” Jahrbuch Ökologie 2011, Stuttgart: S. Hirzel, 2010.

102Rayner introduces different CE options, argues for research into these options and points out difficulties in reaching international agreement on the regulation of research and potential deployment. In that context, he discusses possible relationships to existing international agreements and points to the Oxford Principles as a conceivable framework for CE technology research, development, and deployment:

• CE ought to be treated like a public good.
• Decision-making ought to involve the broad public.
• Any research ought to be published and be made publicly accessible.
• There should be independent assessments and evaluations of the consequences of CE measures.
• CE regulation and governance ought to be clarified prior to the deployment of the corresponding measures.

103[51] A. Robock, “20 Reasons Why Geoengineering May Be a Bad Idea,” Bulletin of the Atomic Scientists, vol. 64, 2008, pp. 14-18.

104According to Robock, we do not need any climate engineering options to solve the problem posed by potential climate change. Robock lists several reasons against CE: Regionally different consequences (e. g. droughts), ocean acidification, ozone depletion, negative impacts on vegetation, acid rain, changes in cloud formation, white sky, reduced efficiency of solar plants, environmental impacts due to transport of aerosols into the stratosphere, severe climate change in the case of abrupt termination, risks of human errors, undermining of emission reduction, underestimation of long-term costs, problems of commercial control, possibility of military abuse, conflicts with existing agreements (ENMOD), international conflicts of interests when trying to agree on a target temperature, issues of moral responsibility, and unforeseen side-effects.

105[52] A. Robock, “Atmospheric Science: Whither Geoengineering?” Science, vol. 320, 2008, pp. 1166-1167.

106Robock critically points out the disadvantages of SRM measures (stratospheric aerosol injection). SRM deployment

• decreases the political pressure to reduce greenhouse gas emissions;
• triggers food-supply-threatening droughts in Asia and Africa;
• does not solve the problem of ocean acidification;
• causes a sudden and severe climate change if terminated prematurely;
• reduces the efficiency of solar energy production;
• depletes the ozone layer or retards its recovery.

107[53] A. Robock, M. Bunzl, B. Kravitz, and G. L. Stenchikov, “A Test for Geoengineering?” Science, vol. 327, 2010, pp. 530-531.

108Robock et al. postulate that a field test for SRM measures based on stratospheric aerosol injection amounts to a full-scale implementation of such measures. Only through such largescale field tests (approximately 5 Tg SO₂) can the measured climate effects be distinguished from the climate system’s natural variability and be clearly attributed to the experimental intervention. In addition, any field test of that kind creates commercial interests and, hence, cannot be stopped immediately.

109[54] Royal Society, “Geoengineering the Climate: Science, Governance and Uncertainty,” London: The Royal Society, 2009.

110The report introduces the distinction between SRM (solar radiation management) and CDR (carbon dioxide removal) measures. CDR measures, which bear fewer uncertainties and risks, ought to be preferred over SRM measures although they unfold their effect on the climate system in the long term only and are not cost-effective at present. Since SRM measures, on the other hand, can bring about a rapid temperature decrease or stabilisation and are less costly, in addition, they can be deployed in the case of unexpectedly short temperature increases. SRM, however, must not be used as an alternative to but only together with increased conventional mitigation policies, which can be combined with CDR. Due to the high risks and uncertainties, the report advocates immediate R&D (within an annual budget of approximately ten million pounds in Great Britain) that is to be coordinated internationally.

111[55] G. Sardemann and A. Grunwald, “Einführung in den Schwerpunkt,” Technikfolgenabschätzung - Theorie und Praxis, vol. 19, 2010, pp. 4-7.

112Sardemann and Grunwald argue for R&D into CE, inclusive of a scientific reflection of ethical, legal, and socio-economic aspects. They give an overview of the main arguments of the CE controversy and differentiate between the following types of risks:

• Risks of preparatory experiments: SRM field tests may already have undesirable and global consequences.
• Risks within the political process: Heterogeneous CE consequences may bring about conflicts and decision blockades.
• Legal uncertainties: It is not yet clear how CE measures can be implemented under international law.
• Operational risks: Once being deployed, CE may trigger unforeseen interactions with the atmosphere and ecological systems.
• Risks of long-term continuation: CE measures must be upheld over centuries or millennia without the occurrence of political instabilities.
• Risks of CE termination: Premature termination may cause a rapid increase in the mean global temperature.
• Risks due to abuse.
• Climate policy uncertainties: It is not yet clear which effects CE may have on the international climate regime.

113[56] D. Scheer and O. Renn, “Klar ist nur die Unklarheit – Die sozio-ökonomischen Dimensionen des Geo-Engineering,” Politische Ökologie, vol. 120, 2010, pp. 27-29.

114This article sketches the socio-economic dimensions of climate engineering and points out that the CE controversy so far has neither been held systematically nor been evaluated. The authors demand that technological risks be assessed and that ethical aspects be analysed. They stipulate, moreover, that the development and deployment of CE measures be coordinated internationally and be regulated by governments.

115[57] S. Schneider, “Geoengineering: Could or Should We Do It?,” Climatic Change, vol. 33, 1996, pp. 291-302.

116Schneider raises strong objections against the deployment of CE methods and argues for increased mitigation efforts while, under reserve, advocating R&D into CE.

117[58] S. Schneider, “Geoengineering: Could We or Should We Make It Work?,” Philosophical Transactions of The Royal Society A-Mathematical Physical, vol. 366, 2008, pp. 3843-3862.

118Schneider introduces different CE measures and argues explicitly for increased mitigation efforts. He points out that SRM measures would have to be upheld for more than one to two centuries and doubts that international cooperation would be stable enough to render this possible. Schneider eventually advocates R&D into CE.

119[59] J. Virgoe, “International Governance of a Possible Geoengineering Intervention to Combat Climate Change,” Climatic Change, vol. 95, 2009, pp. 103-119.

120Virgoe discusses the socio-political characteristics of CE measures (for example the moral-hazard problem, potential unilateral deployment, possible risks and side-effects, and the necessity of continuing SRM measures for a long time). He shows that existing international law only insufficiently captures CE and he introduces readers to three possibilities of future control of research and deployment:

1. control through the United Nations,
2. unilateral control,
3. control through a consortium of nations.

121Virgoe argues for early R&D into the technological, political, environmental, and regulatory aspects of CE to enable an informed and, if possible, multilaterally legitimated decision in favour of or against the deployment of CE.

122[60] T. M. L. Wigley, “A Combined Mitigation/Geoengineering Approach to Climate Stabilization,” Science, vol. 314, 2006, pp. 452-454.

123Wigley advocates a combined mitigation/climate engineering (SRM) strategy with CE making available additional time for solving the economic and technological difficulties of mitigation. Moreover, he presents simulation results of several mitigation/CE scenarios.