by Aaron Ray‡ Abstract References to geoengineering, loosely defined as the use of advanced technology to mitigate or adapt to the effects of climate change, have recently emerged in the popular press and academic literature. Governments, international organizations, and the scientific community are beginning to regard geoengineering seriously as a tool against global climate change. This paper examines the ways in which geoengineering has been defined, evaluates a number of leading proposals, considers some scientific critiques of geoengineering, and highlights some of the ethical, philosophical, and political implications of these proposals.
Introduction Human alteration of the environment is not new. Although human transformation of the natural environment predates the Industrial Revolution, the potential of human behavior to alter the climate on a global scale has accelerated with the development of industrial civilization. Within the debate about the veracity and implications of climate change and the costs and benefits of potential responses, a new line of argument has gained prominence. Journalist Graeme Wood articulated the potential of geoengineering: “What is new is the idea that we might want to deform the Earth intentionally, as a way to engineer the planet either back into its pre¬-industrial state, or into some improved third state.” An examination of the implications of these proposals is necessary.
Defining geoengineering Before evaluating various geoengineering proposals, it is essential to establish an understanding of what is meant by “geoengineering.” Writing more than a decade ago, Thomas Schelling observed that geoengineering was such a new concept that it was lacking a definition. He defined geoengineering as having three characteristics: “global, intentional, and unnatural.” This means that human activities such as building dams and clearing land for agricultural use, while having potentially profound local or regional impacts on humans and the environment, should not be considered geoengineering because they are not global in impact. The second requirement, intentionality, limits what is included as geoengineering by excluding the burning of fossil fuels and other activities whose effects are not intended to alter the natural global environment. David Keith, director of the Energy and Environmental Systems group at the University of Calgary, agrees, that because it is not intentional, pollution itself does not constitute geoengineering. The final requirement that an activity must meet to be labeled geoengineering is that it must be unnatural. For instance, adding metallic reflectors to the atmosphere, as some suggest, is an unnatural act and therefore a form of geoengineering.
For the purposes of this paper, I will use Schelling’s primary definition of geoengineering as something global, intentional, and unnatural.
Evaluating geoengineering proposals Geoengineering proposals can be divided into two major classes: those that manipulate the amount of carbon in the atmosphere and those that manipulate insolation, the amount of solar radiation reaching the earth. Proposals in both classes merit evaluation under Schelling’s definition.
Manipulating carbon Carbon capture and sequestration has become part of the mainstream conversation about mitigating climate change. This technique involves capturing carbon dioxide (CO2) at the point of combustion and preventing it from entering the atmosphere, possibly by injecting it into underground geologic formations. A related proposal is to directly remove CO2 from the air via carbon scrubbers. Such a proposal differs from traditional carbon capture and sequestration because it captures CO2 out of the ambient air, not at the point of combustion. Schelling has expressed support for research into carbon capture and sequestration, finding that, despite its high costs, this technique could prove valuable to mitigating the negative effects of climate change. He further stated that carbon capture “probably has no adverse effects, [and] will probably not scare anybody or provoke religious objections. If it works it may be exceptionally valuable.”
Physicist Freeman Dyson of the Institute for Advanced Study at Princeton has suggests that one way to remove CO2 from the atmosphere is to plant fast growing trees on large amounts of marginal land. He qualifies his proposal as a temporary way to reduce CO2 levels, explaining that planting trees will simply buy time for scientists and policymakers to create a more permanent solution to shift from fossil to renewable fuels.
Another method of manipulating CO2 levels is ocean fertilization, which involves the application of iron particles or other substances to the ocean’s surface to encourage phytoplankton growth. During their growth cycle, the phytoplankton capture atmospheric CO2. When they die, these phytoplankton then carry that CO2 to the ocean floor. This proposal could increase the absorption of carbon by the ocean. Ocean fertilization is already being tested and commercialized. In addition to a research expedition Bruce Frost describes in Nature, Kirsten Jerch reports in the Bulletin of the Atomic Scientists that two technology companies in California are planning to perform ocean iron fertilization to sell as carbon offsets., Alternately, an Australian company, Ocean Nourishment Corporation, is planning to use nitrogen rather than iron to increase phytoplankton photosynthesis.
Manipulating insolation The second class of proposals involves manipulating insolation, which is the amount of solar radiation reaching the earth. Schelling encourages us to consider that, if climate change “is defined as radiation balance, people may think the problem is not just too much CO2 but also too little sulfur aerosols, too little reflective cloud cover, too little albedo.” Thus defined, climate change could be “fixed,” not only by reducing the amount of CO2 released into or present in the atmosphere, but also by reducing the amount of solar radiation reaching lower levels of the atmosphere. Two potential methods for manipulating insolation include aerosol injection and the use of solar reflectors.
The idea for manipulating insolation derives from natural environmental mechanisms. For example, the 1991 eruption of Mount Pinatubo in the Philippines resulted in a reduction in global temperatures by half a degree Celsius in subsequent years. In theory, it is possible to mimic this effect by releasing particles into the atmosphere that would reflect solar radiation back into space rather than allowing it to warm the planet. Tom Wigley of the National Center for Atmospheric Research claims that adding aerosols to the stratosphere, similar to the Mount Pinatubo eruption, will likely present only minimal climate risks.
Aerosol injection is not the only strategy for reducing incoming solar radiation. An array of mirrors or solar shades could be placed into orbit around the earth to reflect solar radiation back into space. Edward Teller of the Lawrence Livermore National Laboratory reviewed a variety of methods for reducing insolation, including sulfur molecules and metallic reflectors. He concluded that modulating insolation is technically feasible and cost effective. Soviet planners have also considered this proposal and found it to have the advantage of being adjustable. If mirrors could be controlled, the amount of radiation could be adjusted over time and even directed toward specific regions. This element of control might then be used to modulate the differential effects of reduced insolation on disparate regions.
Table 1 evaluates the preceding proposals using Schelling’s definition of geoengineering as global, intentional, and unnatural.
Table 1: Evaluating Geoengineering (GE) Proposals[21(a-f)]
Scientific critiques of geoengineering Geoengineering’s skeptics warn of the dangers of these proposals. These skeptics have two main concerns. First, critics warn that we cannot foresee geoengineering’s consequences and therefore should not risk the unintended negative outcomes. Second, critics argue that there are known negative consequences of implementing geoengineering proposals.
Unintended consequences A primary critique of geoengineering is that it carries the risk of serious unintended consequences. Jeff Kiehl, senior scientist at the National Center for Atmospheric Research, writes, “a basic assumption to this approach is that we, humans, understand the Earth system sufficiently to modify it and ‘know’ how the system will respond.” The complex nature of the environmental systems being altered makes them difficult to effectively manage; even without considering possible human mistakes that could occur. Robock goes on to question the ability of scientists to model and evaluate the potential impacts of geoengineering proposals. He warns that scientists cannot understand the complex interactions or predict the impacts of geoengineering proposals. An editorial in Scientific American acknowledges that aerosol injection was “the best–studied proposal,” but also identified the significant expected dangers of this method. These included that: “sulfates would slow or reverse the recovery of the ozone layer; they might also reduce global rainfall, and the rain that did fall would be more acidic,” in addition to other potential unforeseeable risks. Fears over unintended consequences of geoengineering are also being raised for proposals aimed at reducing incoming solar radiation.
Despite these concerns, some scientists argue that the risk of unintended consequences must be evaluated relative to the risks of doing nothing. Michael MacCracken, chief scientist at the Climate Institute, insists that “geoengineering is far less risky than proceeding ahead to a 4-6 C global warming as we seem to be likely to experience if negotiations keep going as they are.” In short, any consideration of geoengineering proposals must occur within a wider context that includes the potential costs and benefits of multiple alternatives.
Known risks The known risks of geoengineering are numerous, according to its critics. For example, “the Pinatubo eruption played an important role in the record decline in land precipitation and discharge, and the associated drought conditions in 1992.” Hydrological effects and reduced precipitation are not the only risks. According to Alan Robock, “aerosol particles in the stratosphere serve as surfaces for chemical reactions that destroy ozone;” and therefore, adding aerosol to the atmosphere could exacerbate the ozone depletion caused by the release of chlorofluorocarbons. Concerns about the risks of geoengineering led the American Geophysical Union to release a position statement on geoengineering that recommends caution because any manipulation of the Earth’s environment could result in unpredictable and potentially damaging outcomes.
Critics also worry that a single-minded focus on temperature obscures other negative environmental effects of fossil fuel combustion. Climate change is only one environmental consequence of current patterns of energy production and consumption. For example, the ocean is currently “30 percent more acidic than it was before the Industrial Revolution.” If this acidification continues, it will endanger the entire oceanic biological chain, from coral reefs to humans. Supporters for emissions reductions instead of geoengineering conclude that changing production and consumption choices can address many environmental challenges, while geoengineering proposals are limited solely to manipulating temperature.
Ethical and philosophical dimensions of implementing geoengineering solutions In addition to the scientific and political questions surrounding geoengineering, there are ethical and philosophical issues that require some contemplation to inform decisions about whether and how to utilize technology to alter the environment globally. In this section I explore concerns about distributive and procedural justice, human attitudes toward technology, and the relationship between humans and nature. Each of these issues has impacts on the implementation of geoengineering as policy.
Ethical considerations One ethical dimension of this debate is the asymmetrical impact of climate change and geoengineering on nations and individuals. Martin Bunzl, a climate change policy expert at Rutgers University, notes that like climate change itself, geoengineering projects could cause shifts in climate that would be distributed unevenly across the globe. He warns “roughly 10% of the World’s population might be worse off even if the other 90% was better off.” This asymmetry raises questions of both distributive and procedural justice. The distributive question concerns who should bear the costs and benefits of geoengineering. Addressing this question requires a procedural mechanism through which the nations of the world can decide how to apportion benefits and harms. However, at the moment, we lack a credible means of deciding global questions of distributive justice. Dean suggests that scientists and engineers may be able to predict some of the consequences of geoengineering proposals, but do not have the authority to decide whether those risks are acceptable. Identifying who does have this authority is exceedingly difficult. Dean thus concludes that it would be better to preempt these problems by reducing emissions caused by heat-trapping gasses and thereby avoid having to utilize geoengineering techniques. While that may indeed be the best approach, it has thus far proved to be all but politically infeasible at the pace and scale that may be necessary. The lack of a binding international agreement to reduce GHG emissions calls into question the willingness or ability of national governments to achieve the reductions Dean proposes.
Philosophical considerations One of the philosophical elements of the debate over geoengineering is the way in which the debate reveals human attitudes toward technology. The editors of Scientific American frame the issue as one of a fundamental belief in the promise of technology: “If technology got us into this mess, maybe technology can get us out of it.” This argument posits that GHG emissions are the consequence of a progression of technological developments involving the utilization of the energy stored in fossil fuels to drive economic development and improvements in standards of living. Surely, continued technological advancement can allow for continued economic development even while mitigating the negative consequences of growth. Keith suggests “geoengineering implies a countervailing measure or a ‘technical fix’; an expedient solution that uses additional technology to counteract unwanted effects without eliminating their root cause.”
The view that continued technological advancement will allow for unchecked energy consumption is found not only among proponents of geoengineering, but also among those who favor the use of renewable energy technologies that permit continued energy consumption with fewer known environmental costs. The hope is that the right technology can enable us to continue to consume in our current fashion—or even increase aggregate energy consumption as developing nations modernize—without incurring the negative environmental consequences of the past. A similar argument was made at the dawn of the nuclear age. Looking back on his attitude toward nuclear energy, Alvin Weinberg, former head of the Oak Ridge National Laboratory, recalled that “…you had uranium in the rocks, in principle, an inexhaustible source of energy—enough to keep you going for hundreds of millions of years. I got very, very excited about that, because here was an embodiment of a way to save mankind.” Nuclear energy turned out to have monetary costs and concerns about safety and waste that have since tarnished its promise. That nuclear energy does not provide clean and free energy might be a warning to those who believe that any technological innovation can deliver humans from the fundamental economic condition of scarcity.
We often find hope in the promise of technological innovation to release us from the limits of scarcity or mitigate the effects of previous technological developments. Reliance on this transformational power of technology may have much in common with systems of religious belief. Writer David Noble argues that technological development is a religious endeavor involving the merging of technology and faith. Noble summarizes the historical arc of faith in technology from steam power to geoengineering with this observation: “We demand deliverance. This is apparent in our virtual obsession with technological development, in our extravagant anticipations of every new technical advance – however much each fails to deliver on its promise.” It may be that geoengineering represents only the latest technological development that we have adopted due to faith in its promise, without a guarantee to deliver.
A final philosophical implication of geoengineering relates to the relationship between humans and the planet we inhabit. Keith debates one of the fundamental questions of philosophy: should we maximize the benefits to mankind by exploiting all the tools at our disposal or should we preserve nature by minimizing our interference with it? The first position is one of active management, the drive to extract the most utility from a set of finite resources. The second position is that of minimal impact, to use as few of those resources as necessary to satisfy our basic needs.
The promise of technological development is integral to the active management position, that we can use technological innovations to extract more utility from the finite resources available to us while minimizing the environmental costs. Geoengineering proposals clearly tend toward the active management position. We have tools to manipulate the environment so as to maintain or create the optimal conditions for human growth and development. Active management is a fundamentally human-centric proposition: the value of any natural resource stems from its capacity to provide for human welfare. Keith addresses this point by asking: “Is human welfare the sole consideration, or do we have a duty to protect natural systems independent of their utility to us?” It is not at all clear whether in fact we have such a duty or, even from where such a duty might emanate.
Some of the opposition to both continued GHG emissions and geoengineering proposals is rooted in the minimal impact position. This view argues not for new technology that allows for continued energy consumption, but rather for changes in behavior to reduce consumption. Burning fossil fuels alters the natural state of the planet, as do aerosol injection and ocean fertilization. Schelling’s inclusion of the dimension of naturalness in his definition of geoengineering comes into play here. Opponents of geoengineering see active management as inherently unnatural. Lest the critics of geoengineering get too comfortable, Keith reminds us that “the Earth is already so transformed by human actions that it is, in effect, a human artifact.” How can one distinguish now between what is natural and unnatural? This challenge rises often in relation to environmental issues, including questions of habitat management and invasive species. We are unlikely to come to a resolution regarding this issue, but being aware of the question serves to inform this and other debates involving human choices that impact the environment.
Political implications of geoengineering There are important political questions that arise when considering whether and how geoengineering proposals should be implemented. First, from where does the authority to experiment with or implement geoengineering proposals emanate? Second, what is the relationship between geoengineering projects and emissions reduction efforts? Third, what are the costs of geoengineering proposals relative to emissions reduction? And fourth, how and by whom would the application of geoengineering technology be controlled? I will examine each of these questions in the hope of identifying the political implications of developing this capability.
Authority to experiment and/or implement One of the questions raised by the prospect of geoengineering is that of authority: Who has the authority to manipulate the climate and from where is that authority derived? Current international negotiations leave control for regulating emissions with individual nations. As a result, no international body currently exists that has the authority to govern and control geoengineering. However, since geoengineering is, by definition, global in impact, it does not fit in the present nation-centric framework. Schelling argues it is essential to identify or create an authority to approve the experimentation needed to explore the potential consequences of these proposals. He finds the creation of this body to be even more important than actually conducting geoengineering experiments, because having an international body is critical for establishing parameters by which any future geoengineering program be judged and implemented. Whether or not one supports continued research into geoengineering projects, there is a clear need for some authorizing body to be responsible for regulating both experimentation and possible implementation. Keith concurs with the other experts in seeing the need for an international body to provide a forum for democratic debate on the potential global impacts of geoengineering projects. Implicit in Keith’s analysis is the view that, for decisions that have global consequences, there should be a global, democratic process of adjudication.
Geoengineering and emissions reductions The second political element at issue is the relationship between geoengineering projects and emissions reductions efforts. One of the primary arguments for geoengineering is its simplicity relative to the political complexity of negotiating and enforcing GHG emissions reductions. Schelling writes that pursuing geoengineering has the potential to transform GHG policy from its current complicated state, replete with regulations, to a simpler approach based on balancing costs among nations. Because geoengineering schemes do not require nations to reduce emissions or economic output, they would allow the debate to focus only on how to pay for the technology. This process may be further simplified if the proposals turn out to be as cost effective as their proponents suggest.
Schelling argues that one of the virtues of geoengineering is its ability to mitigate climate change while “not depending on the behavior of populations, not requiring national regulations or incentives, [and] not [being] dependent on universal participation.” This is in contrast to reducing CO2 emissions, which involves a decentralized regulatory approach that requires changing behavior in many realms, including personal energy consumption, transportation, and energy production. He also suggests that emissions reduction depends upon the implementation of policies that governments are incapable of due to a lack of expertise, resources, or political will. Geoengineering would alleviate the need for national governments to undertake the interventions necessary to achieve emissions reductions.
Teller agrees that, despite concerns about finding an acceptable means of authorizing their use, geoengineering proposals present a much simpler solution to the threat of global warming than the current practice of developing international consensus on how to quickly and dramatically reduce usage of fossil fuels. Given the lack of progress thus far toward a binding international agreement to cut emissions, and the difficulty of adopting national programs that change personal behavior, a simple solution is attractive.
However, the ease of implementation of geoengineering projects presents a concern with regard to the relationship between geoengineering and emissions reductions. Critics of geoengineering have argued that just having geoengineering as an option could weaken the commitment to limit emissions in time to avert the most serious warming. Kerr reminds us that, if “serious efforts to cut back greenhouse gas emissions were failing, a stopgap approach would become more attractive.” If emissions reductions fail to materialize, the prospect of having an alternative method to prevent the worst effects of climate change seems prudent. Yet, geoengineering represents exactly the type of stopgap measure that would likely deflate political will to change international consumption patterns or make the energy infrastructure more sustainable.
Schelling advocates for further research to determine the feasibility and effectiveness of geoengineering proposals. At the same time, he acknowledges the risk of undermining mitigation efforts when he warns that geoengineering proposals may be so attractive that they steal the focus away from emissions reductions, and that this change in focus could have serious negative repercussions. It is this prospect that critics of geoengineering are concerned about when they warn of the harmful environmental consequences of continuing GHG emissions that could occur even if geoengineering projects control global temperature change. MacCracken also supports research into geoengineering proposals, but cautions scientists and policymakers to never view geoengineering as a replacement for actual efforts to mitigate the negative impacts of climate change, particularly because no nation has the appropriate information to change its entire focus to implementation of geoengineering proposals.
Relative cost of geoengineering and emissions reduction Schelling contends that one advantage of geoengineering projects is that unlike mitigation, they only require us to decide what to do and how to pay for it. In fact, low cost is one positive aspect of geoengineering often cited by its proponents. Teller, in surveying solar reflection enhancement proposals, finds that the total cost would probably be no more than $1 billion per year—“an expenditure that is two orders of magnitude smaller in economic terms than those underlying currently proposed limitations on fossil-fired energy production.” This can be compared to the Stern Review’s conservative approximation of the costs of mitigation, which was estimated at 1% of global GDP. Skeptics, however, do not accept this analysis. Robock argues that the costs of geoengineering projects are much higher than what the international community currently spends on renewable energy. Robock also criticizes the multibillion–dollar subsidies given by the U.S. government to the coal, oil, gas, and nuclear industries, while providing little support to alternative energy producers. He implies that if funds planned for geoengineering were directed toward the development of renewable energy generation technology, we could reduce emissions and avoid global warming without the risks of geoengineering.
Schelling suggests that the low cost of geoengineering proposals means that we can dispense with national and international negotiations altogether because some geoengineering projects can be performed by “exo-national” programs—programs not confined to national borders. The idea is that wealthy individuals, corporations, or foundations have the resources to implement geoengineering proposals without the need for national or international agreement. Wood is more skeptical of the desirability of exo-national implementation of geoengineering proposals. He suggests that “the scariest thing about geo–engineering, as it happens, is also the thing that makes it such a game changer in the global warming debate: it’s incredibly cheap.” He is concerned by the number of multibillionaires in the world who could potentially take immediate action to singlehandedly reverse climate change. Geoengineering projects may in fact be easier and cheaper to implement than national and international emissions reductions. But the relative ease of implementation and the risk of adverse consequences of geoengineering lead to a greater concern for the need to regulate its use.
Regulating use of geoengineering technology The development of geoengineering technology means that nations and international organizations must now consider whether and how to restrict individuals and nations from implementing unauthorized projects. MacCracken suggests that the international community needs to establish a consensus on policy. One where individual countries are not allowed to implement solar management programs without authorization from an international body. Yet even an international agreement reached through democratic means is unlikely to produce unanimity. If a decision is made at the national or international level that geoengineering projects, particularly those with the greatest risk of adverse consequences, should not be implemented, how can rogue nations, corporations, or individuals be prevented from going ahead with programs on their own? One can imagine a low-lying nation facing inundation and frustrated with the lack of international progress on emissions reductions sponsoring a program of aerosol injection without international approval.
This scenario introduces the risk of global negative consequences that stem from the actions of a single individual, corporation, or nation. Wood argues that governments would need to step in to prevent a rogue entity from taking independent action, either by enforcing current regulations or developing new ones. The challenge though, is how to regulate this technology that is, according to its proponents, so economically and technologically feasible. Wood foresees some international effort to “monopolize the technology and prevent others from deploying it, through diplomatic and military means… Such a system might resemble the way the International Atomic Energy Agency (IAEA) now regulates nuclear technology.”
The example of the IAEA may be an unfortunate one, at least from the perspective of those concerned about the misuse of geoengineering technology. International attempts by this agency to regulate the spread of nuclear weapons technology have failed. The nuclear club has grown since its birth at the end of World War II. International efforts at arms control have been unable to prevent India, Pakistan, or North Korea from developing nuclear weapons technology. Wood explains that the challenge faced when attempting to regulate geoengineering technology may be even more difficult than that faced when regulating nuclear technology because it is much easier and cheaper to implement many geoengineering proposals than it is to develop nuclear weapons. Furthermore, one could argue that the global scale of geoengineering projects means that their potential adverse consequences are potentially greater than the threat of a single nuclear device.
Conclusion As the debate over whether, how, and how much to reduce GHG emissions develops, geoengineering proposals are likely to draw increasing interest due to their technical, political, and economic feasibility. The consideration of these proposals is a necessary part of the scientific and political process regarding global warming. Experimentation into various mechanisms for manipulating climate may enrich our understanding of the complex interactions driving global climate change. Much more needs to be known about the potential adverse environmental consequences of these proposals before they are implemented. The political challenges presented by geoengineering may outweigh the environmental risks. Some legitimate international means of authorizing implementation, adjudicating costs and risks, and regulating and controlling the use of this technology would have to be developed. The most immediate political risk for those advocating for emissions reductions, is the possibility that the existence of geoengineering alternatives could reduce the willingness of nations to agree to binding emissions targets. Finally, exploring our attitudes toward geoengineering can help elucidate our complicated relationship with technology and the environment.
Endnotes  David Keith, “Engineering the Planet. Forthcoming,” in Climate Change Science and Policy, ed. S. Schneider and M. Mastrandrea, (Washington, D.C.: Island Press, 2009).  Graeme Wood, “Re-Engineering the Earth,” The Atlantic Online, http://www.theatlantic.com/doc/200907/climate-engineering.  Thomas Schelling, “The Economic Diplomacy of Geoengineering,” Climatic Change, 33(1996): 303.  Ibid., 303.  Ibid., 304.  David Keith, 1.  David Keith, Minh Ha-Duong, and Joshuah K. Stolaroff, “Climate Strategy with CO2 Capture from the Air,” Climatic Change, 74(2005): 17-45.  Thomas Schelling, email message to author, November 12, 2009.  Freeman J. Dyson, “Can We Control the Carbon Dioxide in the Atomsphere?,” http://adamant.typepad.com/seitz/files/Dyson_Energy_1977.pdf.  Bruce W. Frost, “Phytoplankton Bloom on Iron Rations,” Nature, 383(1996): 475.  Ibid., 475.  Kirsten Jerch, “Capitalizing on Carbon,” Bulletin of the Atomic Scientists, 64(2008): 16.  Ibid., 16.  Thomas Schelling, “The Economic Diplomacy of Geogengineering,” 305.  Ibid., 305.  Alan Robock, “20 Reasons Why Geoengineering May Be a Bad Idea,” Bulletin of the Atomic Scientists, 64(2008):14-18.  Graeme Wood, “Re-Engineering the Earth,” 2.  T.M.L. Wigley, “A Combined Mitigation/Geoengineering Approach to Climate Stabilization,” Science, 314(2006): 452.  Edward Teller, Lowell Wood, and Roderick Hyde, “Global Warming and Ice Ages: I. Prospects for Physics-Based Modulation of Global Change,” Lawrence Livermore National Laboratory (presented at 22nd International Seminar on Planetary Emergencies, Erice, Italy), 16.  Richard A. Kerr, “Pollute the Planet for Climate’s Sake?,” Science, 314(2006): 401-403.  (a) Alan Robock, “20 Reasons Why Geoengineering May Be a Bad Idea,” Bulletin of the Atomic Scientists, 64(2008):14-18; (b) Graeme Wood, email message to author, November 6, 2009; (c) Freeman J. Dyson, “Can We Control the Carbon Dioxide in the Atomsphere?,” http://adamant.typepad.com/seitz/files/Dyson_Energy_1977.pdf; (d) T.M.L. Wigley, “A Combined Mitigation/Geoengineering Approach to Climate Stabilization,” Science, 314(2006): 452-474; (e) Bruce W. Frost, “Phytoplankton Bloom on Iron Rations,” Nature, 383(1996): 475; (f) Edward Teller, Lowell Wood, and Roderick Hyde, “Global Warming and Ice Ages: I. Prospects for Physics-Based Modulation of Global Change.”  Jeffrey T. Kiehl, “Geoengineering Climate Change: Treating the Symptom Over the Cause?,” Climatic Change, 77(2006): 227.  Alan Robock, “20 Reasons Why Geoengineering May Be a Bad Idea,” 17.  Ibid., 17.  “Overshadowing Difficulties,” Scientific American, November 2008, 38.  Richard A. Kerr, “Pollute the Planet for Climate’s Sake?,” 403.  Michael C. MacCracken, email message to author, November 6, 2009.  Keven E. Trenberth, and Aiguo Dai,“Effects of Mount Pinatubo Volcanic Eruption on the Hydrological Cycle as an Analog of Geoengineering,” Geophysical Research Letters, 34(2007): L15702, doi:10.1029/2007GL030524, 4.  Alan Robock, “20 Reasons Why Geoengineering May Be a Bad Idea,” 15  American Geophysical Union, “Position Statement on Geoengineering the Climate System,” http://www.agu.org/sci_pol/positions/geoengineering.shtml.  Alan Robock, “20 Reasons Why Geoengineering May Be a Bad Idea,” 15.  Martin Bunzl, comment on “Geoengineering and Equity,” Bunzl’s Blog, comment posted May 12, 2008, http://ccspp.blogspot.com/2008/05/geoengineering-and-equity.html, comment posted May 12, 2008.  Cornelia Dean, “Engineering a Climate Solution,” The New York Times, September 1, 2009, from http://greeninc.blogs.nytimes.com/2009/09/01/engineering-a-climate-solution/  Ibid.  “Overshadowing Difficulties,” 38.  David Keith, 1.  Arjun Makhijani and Scott Saleska, “The Nuclear Power Deception,” Institute for Energy and Environmental Research, http://www.ieer.org/reports/npd.html.  David F. Noble, The Religion of Technology: The Divinity of Man and the Spirit of Invention (New York: Penguin, 1999), 4.  Ibid., 6.  David Keith, Minh Ha-Duong, and Joshuah K. Stolaroff, “Climate Strategy with CO2 Capture from the Air,” 6.  David Keith, 6.  Ibid., 7.  Alan Robock, “20 Reasons Why Geoengineering May Be a Bad Idea,” 17.  Thomas Schelling, email message to author, November 12, 2009.  David Keith, 8.  Thomas Schelling, “The Economic Diplomacy of Geogengineering,” 303.  Ibid., 303.  Ibid., 306.  Edward Teller, Lowell Wood, and Roderick Hyde, “Global Warming and Ice Ages: I. Prospects for Physics-Based Modulation of Global Change,” 17.  Richard A. Kerr, “Pollute the Planet for Climate’s Sake?,” 403.  Alan Robock, “20 Reasons Why Geoengineering May Be a Bad Idea,” 17.  Thomas Schelling, email message to author, November 12, 2009.  Michael C. MacCracken, email message to author, November 6, 2009.  Thomas Schelling,“The Economic Diplomacy of Geogengineering,” 303.  Edward Teller, Lowell Wood, and Roderick Hyde, “Global Warming and Ice Ages: I. Prospects for Physics-Based Modulation of Global Change,” 2-3.  Nicholas Stern, “The Stern Review on the Economics of Climate Change,” Office of Climate Change. http://www.hm-treasury.gov.uk/sternreview_index.htm, xvi  Alan Robock, “20 Reasons Why Geoengineering May Be a Bad Idea,” 17.  Ibid., 18.  Thomas Schelling, “The Economic Diplomacy of Geogengineering,” 303.  Graeme Wood, “Re-Engineering the Earth,” 4.  Michael C. MacCracken, email message to author, November 6, 2009.  Graeme Wood, email message to author, November 6, 2009.  Graeme Wood, “Re-Engineering the Earth,” 4-5.  Graeme Wood, email message to author, November 6, 2009.
‡ Aaron Ray is studying Environmental and Regulatory Policy at the Georgetown Public Policy Institute. He earned a Master of Arts in Secondary Education from the University of New Mexico and a Bachelor of Arts in Philosophy, Political Science, and Religion from Linfield College. He taught Philosophy at Dine College, the tribally-controlled college of the Navajo Nation. He also taught history, government, and economics at Crownpoint High School in New Mexico and the César Chávez Schools for Public Policy in Washington, D.C. His interests include sustainable development, land and resource management, and the ethics and philosophy of public affairs.