Climate engineering: The way forward?

Environmental Development 2 (2012) 57–72 Contents lists available at SciVerse ScienceDirect Environmental Development journal homepage: www.elsevier.com/locate/envdev Climate engineering: The way forward? Aaron Welch, Sarah Gaines n, Tony Marjoram 1, Luciano Fonseca 2 UNESCO, Natural Sciences Sector, 1, rue Miollis, 75732 Paris Cedex 15, France a r t i c l e in f o Keywords: Geoengineering Climate engineering Climate change Earth system Solar radiation management Carbon dioxide removal Governance a b s t r a c t The deliberate large-scale manipulation of the climate is increasingly being discussed as a potential tool to ensure the basic condition for a sustainable future: a habitable climate. While far from the ideal solution, the rate of climate change continues to outpace our attempts at a response, prompting some scientists and politicians to call for the consideration of climate engineering or geoengineering to avoid catastrophic climate change, while political processes to reduce greenhouse gases catch up. A November 2010 expert meeting was held at UNESCO to raise awareness of geoengineering, its potential to counteract climate change and its risks, and to broaden the discussion within the international community. Potential geoengineering methods include solar radiation management and carbon dioxide removal techniques that are largely theoretical and remain untested, despite a long history. Responsible research can only proceed, and informed decisions be made, once governance structures have been developed beyond mere principles insufficient to guide researchers and policy makers. At the same time, realistic communication on these activities must increase and improve so that civil society can play a role in determining acceptable levels and types of human intervention. Appropriate geoengineering research should be considered for solar geoengineering methods that promise to quickly and affordably decrease global mean temperature, and for carbon geoengineering methods that target the core problem of climate change by directly removing carbon dioxide from the atmosphere. A small cadre of scientists and policy makers has advanced the discussion of geoengineering and its likely impacts, but the path to a sustainable future cannot n Corresponding author. Tel.: þ33 1 45 68 40 71; fax: þ 33 1 45 68 58 04. E-mail addresses: [email protected] (A. Welch), [email protected] (S. Gaines), [email protected] (T. Marjoram), [email protected] (L. Fonseca). 1 Formerly responsible for the engineering sciences programme at UNESCO, presently based in Melbourne, Australia, with interests in engineering, technology and development. 2 Present address: University of Brasilia, Brazil. 2211-4645/$ - see front matter & 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.envdev.2012.02.001 58 A. Welch et al. / Environmental Development 2 (2012) 57–72 be charted until the wider international community asks some fundamental questions about what kind of regulation is appropriate, how it should be implemented and by whom and at what cost. This task is urgent, and only by raising awareness of geoengineering can we secure the participation of the international community in developing governance structures and ensuring that responsible research on geoengineering proceeds in a timely and consensual manner. & 2012 Elsevier B.V. All rights reserved. 1. Introduction Previously the stuff of science fiction, man-made techniques to engineer climate are increasingly being discussed as a necessary tool in the pathway to a sustainable future. In most cases, climate engineering is proposed as an additional technique to cool the climate in a climate emergency, not as a replacement to the necessary reduction in greenhouse gases. While these debates carry on in the halls of Parliament and at academic meetings in the West, the majority of the world’s population remains unaware of the emerging subject although they are just as dependent on the climate system and more vulnerable to any engineered perturbations. This paper focuses attention on this trend in order to engage a wider international community and suggest a participative way forward. This paper is an extension of UNESCO’s involvement in the geoengineering discussion that began when the first UNESCO expert meeting on the subject was hosted in November 2010. To further raise international awareness, a UNESCO–SCOPE–UNEP Policy Brief explaining the state of research questions and policy implications of climate engineering was published in November 2011. In the organization’s role as an ‘honest broker’, UNESCO recognizes that geoengineering is a field with global impacts that demands an informed and engaged international scientific, policy, and civil society community. In this spirit, UNESCO has initiated a critical discussion of the efficacy of geoengineering, its possible benefits and potential for harm, and the status of both the science and governance of this rapidly evolving field. The organization’s involvement does not represent an endorsement of any geoengineering activity and the authors of this paper write in their personal capacities in order to contribute to this debate. 1.1. Definitions Geoengineering is the deliberate large-scale manipulation of environmental processes that affect the Earth’s climate with the intent to counteract the effects of global warming. The term ‘geoengineering’ was originally coined to describe a theoretical mechanism utilizing ocean currents to remove CO2 from the atmosphere (Marchetti, 1977). Since its first use a generation ago, the term has been expanded to apply to a suite of proposals that intentionally manipulate the Earth’s climate in an attempt to counter human-induced change, but does not include activities for which the climatic impact is a side-effect or unintended consequence. By design, geoengineering proposals have the potential for international impact. Similar alternative terms such as ‘climate engineering’ are also sometimes used for clarity’s sake, but in accordance with the dominant usage, the term geoengineering is predominantly used in this paper. The suite of proposed interventions range from ocean fertilization to extensive tree planting to favoring lighter more reflective crops to large-scale cloud seeding, exist at various degrees of modeling and experimental testing and carry uncertain consequences. Geoengineering is being considered alongside adaptation and mitigation in response to the threat of climate change. Increasingly, geoengineering is taken seriously as a reaction to concerns that the Earth’s climate is changing more rapidly than previously observed or estimated, and since there has neither been enough progress towards reducing greenhouse gas emissions nor evidence that A. Welch et al. / Environmental Development 2 (2012) 57–72 59 mitigation and adaptation measures now proposed are sufficient to avoid unfavorable, even catastrophic, climate change in the future. Often, geoengineering is proposed as an emergency stopgap to prevent the climate from passing critical tipping points of change, while adaptation and mitigation policies take effect. 1.2. History The modern conceptualization of geoengineering derives from more than a century of the application of technology to the weather, and predates the current focus on climate change (Fleming, 2010). Keith (2000) presents a twentieth-century history of geoengineering that more fully describes this arc, but for the purposes of this paper, geoengineering is understood to have passed through three important phases beginning after World War II. Geoengineering was shaped by (1) the Cold War race to control weather, (2) the rise of environmentalism and the focus on climate change, and (3) a twenty-first century renaissance spurred by the apparent failure of mitigation efforts. This controversial field of research has grabbed recent headlines over some of its more outlandish proposals, but is a legitimate scientific concern with a long history and is worthy of further inquiry. 1.2.1. Cold War weather makers Measures to control rainfall were advanced in the early years of the Cold War by competition between the USSR and US to establish a strategic supremacy in weather modification. Despite focusing on some of the same techniques – namely cloud seeding – the two nations arrived at a concern for climate change from separate corners. The USSR began cloud seeding field experiments before the war and expressed, in the 1950s and 1960s, an overt desire to control climate (Zikeev and Doumani, 1967). The Soviets were first to conceive of solar radiation management by injecting aerosols into the upper atmosphere (Budyko, 1977). Soviet investigations of climate modification would persist throughout the Cold War, while in the US, a burgeoning weather modification industry dominated any concern for climate until CO2-induced climate change was first identified as a threat in a seminal 1965 climate assessment by President Johnson’s Science Advisory Committee (Keith, 2000). The report assessed the impact of global fossil fuel combustion on atmospheric CO2 concentration in order to estimate rises in the planet’s temperature (President’s Science Advisory Committee (PSAC), 1965)). Although dismissed by the President, the only response to a warming climate presented in the assessment was a geoengineering scheme to increase the albedo of the sea surface. 1.2.2. Rise of environmentalism and the focus on the climate problem The 1970s and 1980s witnessed a marked shift away from the type of thinking that allowed geoengineering to be the sole proposed response to climate change. Despite a growing number of climate policy assessments that considered geoengineering, two developments caused the intentional manipulation of climate to be seen in a different light: attempts to wield weather as a weapon and an expanding ecological awareness. Attempts by the US to modify the weather in Vietnam had a lasting negative impact on the perception of geoengineering. Whether or not cloud seeding over the Ho Chi Minh trail dampened the progress of the Viet Cong, it did diminish the public’s appetite for weather modification and provoked a 1973 resolution by the US Senate urging the outright ban of environmental weapons (Harper, 2008). The United Nations followed suit in 1976 with an international convention prohibiting the hostile use of environmental modification techniques (United Nations, 1976). These events were part of a larger transition to an environmental understanding of humanity’s relationship with nature. An ecological awareness that saw the potential danger in applying technology to the climate was reflected in climate reports of the period that did not consider geoengineering as a countervailing measure to CO2-induced climate change (Study of Critical Environmental Problems (SCEP), 1970; Study of Man’s Impact Climate (SMIC), 1971). Other reports that did mention the intentional manipulation of climate did so with less optimism and always considered geoengineering to be less 60 A. Welch et al. / Environmental Development 2 (2012) 57–72 practical than mitigation (Geophysics Study Committee (GSC), 1977). Despite this departure from technological fixes to the climate problem, when geoengineering methods were considered, they were found to be a relatively low-cost option worthy of further investigation (Committee on Science Engineering and Public Policy (COSEPUP), 1992). The methods considered included reforestation, ocean fertilization, albedo modification and removal of atmospheric chlorofluorocarbons. 1.2.3. Renaissance of geoengineering Geoengineering as a countervailing measure to CO2-induced climate change commanded renewed interest in the first decade of the twenty-first century when the prospects for greenhouse gas mitigation sufficient to stabilize the climate began to wane, observed rates of temperature change emerged to be faster than those predicted by the early US climate assessments of the 1960s and 1970s, and climate model studies increasingly confirmed the feasibility of stratospheric aerosol geoengineering techniques. These three factors have encouraged a re-examination of the intentional manipulation of climate and have marshaled a geoengineering renaissance that is the focus of this analysis. The suite of currently proposed geoengineering activities, as shown in Table 1, fall into two main categories: ‘solar geoengineering’ or solar radiation management (SRM) interventions that aim to reduce the amount of solar radiation – or insolation – absorbed by the Earth, to engineer lower global average temperatures; and ‘carbon geoengineering’ or carbon dioxide removal (CDR) interventions that would actively remove carbon dioxide from the atmosphere by using artificial structures or by the enhancement of ecosystem processes. Both types of intervention intend to reduce the detrimental impacts caused by the accumulation of greenhouse gases in the atmosphere. These concepts were revitalized when Paul Crutzen, the Nobel Prize winning atmospheric scientist, proposed to use solar geoengineering to resolve the dilemma posed by policies that mandate cleaner skies but carry the unintended consequence of enhanced global warming (Crutzen, 2006). In this scenario, the climate cooling lost by the necessary removal of sulfate particles in the lower atmosphere, where they damage human health, could be compensated for by sulfate particles intentionally injected in the upper atmosphere. The scientific feasibility of such schemes that would diminish insolation to stabilize climate – albeit while leaving the atmospheric concentration of carbon dioxide unaddressed – has been affirmed by climate model studies (Caldeira and Wood, 2008). Considerations of side-effects have shown that an insolation reduction of not quite 2%, considered sufficient for climate stabilization under the current warming scenario, would not necessarily limit terrestrial primary productivity (Govindasamy et al., 2002). In fact, according to models, crop yields are likely to improve in most regions as the spraying of stratospheric aerosols would dampen climate change impacts harmful to plants, like heat, but leave untouched the higher concentrations of carbon dioxide (Pongratz et al., 2012). This approach, however, brings with it the risks of regional drought, ozone depletion, diminished sunlight and a lesser blue in the sky, all of which need further quantification to allow for informed decision making (Robock et al., 2009). Even if insolation can be appropriately manipulated, these methods treat only the symptoms of a warming climate and leave the underlying problem of greenhouse gas emissions unaddressed. This is to say that geoengineering methods should not replace carbon-dioxide mitigation efforts but could buy time while we shift away from fossil fuels. We can conceivably push back the clock as far as Table 1 Range of geoengineering interventions proposed. Solar geoengineering Carbon geoengineering Injecting sulfate aerosols into the stratosphere Bio-engineering crops to be a lighter color, thus more reflective Suppressing high-altitude cirrus clouds Installing space mirrors Spraying seawater into low-altitude clouds to brighten or increase them Painting streets and roofs white Fertilizing the ocean with iron Enhancing natural rock weathering Encouraging intensive large-scale forestry Building carbon dioxide scrubbers Injecting carbon dioxide underground or into the ocean Fast, inexpensive, uncertain Slow, expensive, effective Large scale Bio-char A. Welch et al. / Environmental Development 2 (2012) 57–72 61 we require by taking carbon dioxide out of the atmosphere. In one category of proposals, engineered ‘‘carbon banks’’ of fast growing trees or peat that trap carbon in the topsoil could exploit the natural ability of plants to absorb carbon dioxide from the atmosphere (Dyson, 1977). Similarly, carbon dioxide could be captured from the air by engineered structures that would use vented grids to chemically remove carbon dioxide, readying it for permanent storage underground in a process that accelerates the natural carbon cycle (Keith et al., 2005). So too, the oceans could lock up excess carbon dioxide, according to the iron hypothesis that posits phytoplankton productivity to be limited by iron deficiency and suggests that fertilization of the ocean with iron could seed a massive phytoplankton bloom that would sequester carbon once the phytoplankton die and settle to the deep ocean (Martin, 1990; Martin et al., 1994). Perhaps together these CDR methods could stabilize the climate if deployed at sufficiently large scale. The most significant recent assessment to consider the full spectrum of geoengineering methods was conducted by the UK’s Royal Society in 2009. The report deems that the global effort to reduce greenhouse gas emissions has not yet been sufficiently successful to avoid dangerous climate change and sees no credible scenario in which global mean temperature will decline in this century. Actions beyond mitigation then, like geoengineering, may therefore be essential should it become necessary to cool the climate in this century (Royal Society, 2009). A major conference to guide such actions and minimize the risks of climate geoengineering was held in March 2010 at the Asilomar Conference Center near Monterey, California, where, a generation before, guidelines for genetic engineering were established. Five tenets promoting the safe, responsible and effective pursuit of research on climate engineering, shown in Table 2, were adopted and, after much discussion, the conference’s scientific organization committee upheld geoengineering as a feasible way to avoid catastrophic climate change and expressed the hope that the open and collegial ‘spirit of Asilomar’ ‘‘will help the international community to better understand potential responses to the increasingly serious climate change issue’’ (Asilomar Scientific Organizing Committee (ASOC), 2010). Far from clarifying the debate, some members of the press were dissatisfied by the closed nature of the proceedings and some scientists were distressed by what some perceived as the commercial orientation of the conference in general, and by the positioning of a private ocean fertilization enterprise in particular. The Intergovernmental Panel on Climate Change (IPCC) made its first overt inquiry into geoengineering by convening an expert working group in June 2011 tasked with the scientific assessment of geoengineering. The first four reports of the IPCC, beginning in the early 1990s, focus on mitigation and give only peripheral consideration to geoengineering. Although the outcomes of the working group will not be published until the release of the Fifth IPCC Assessment Report in 2014, they will include a scientific accounting of geoengineering methods and their likely impacts, but will not contain policy recommendations. We anticipate that the IPCC’s accounting will perhaps support research on geoengineering as a potential response to catastrophic climate change, but only for those solar geoengineering methods already known to be feasible and relatively low cost. Table 2 Five tenets to guide geoengineering research. Oxford principles (Rayner et al., 2009)      Geoengineering to be regulated as a public good Public participation in geoengineering decision-making Disclosure of geoengineering research and open publication of results Independent assessment of impacts Governance before deployment Principles for responsible conduct of climate engineering research (ASOC, 2010)      Promoting collective benefit Establishing responsibility and liability Open and cooperative research Iterative evaluation and assessment Public involvement and consent 62 A. Welch et al. / Environmental Development 2 (2012) 57–72 A 2011 report of the German Federal Environment Agency asked the question looming over all of these activities in its title: Geoengineering: effective climate protection or megalomania? (Umweltbundesamt, 2011). 2. Outstanding issues Against this backdrop of debate, modeling, and some experimental testing as described above, there are numerous outstanding issues in the geoengineering discussion. These issues start from the sheer possibility of altering the climate system and understanding unintended consequences (science), range to the practicability of these large-scale interventions (engineering and technology development) and hinge on a decision of desirability to implement these proposals (governance and public communication). 2.1. Science of understanding the Earth system Humans are a sufficiently dominant force in the Earth system to warrant a proposal that the current geological epoch is now the ‘Anthropocene’ (Crutzen, 2002; Zalasiewicz et al., 2010). It therefore should be no surprise that we are discussing the intentional alteration of the Earth system. Advancing the science that underlies geoengineering is an opportunity to better understand the interlinked system of feedbacks and buffering capacities that maintain a climate suitable for human life. Mankind has posited how to build a habitable planet for years, but the contemporary question has become how to maintain one. Geoengineering methods will advance in step with our capacity to answer this question. Our search for answers necessarily begins in nature, and although all proposed techniques do not necessarily mimic natural phenomena, there is precedence in the Earth system for geoengineering. For example, the eruption of Mount Pinatubo in the Philippines in 1991 injected 20 megatons of SO2 into the stratosphere which absorbed and reflected enough sunlight to lower the global average temperature a half degree Celsius for nearly two years (Robock, 2002). Similarly, iron-rich dust acts as a fertilizer when it is blown from African deserts to the Atlantic Ocean where it triggers phytoplankton blooms that in turn sequester carbon. Table 1 lists a range of various proposals, from amplified natural systems to science fiction-inspired engineering. In order to be considered climate engineering, these interventions must be deployed at a sufficiently large scale to impact the global climate system. Geoengineering the Earth’s climate by one of the techniques described in Table 1 is very likely to be technically possible, however the technology is at various degrees of development. Moreover, serious uncertainties about effectiveness, cost and environmental impact persist. Much more research is needed on the potential social and environmental impacts of any intervention, especially the unintended consequences which, depending on the scale of the trial, could have major impacts on global weather, geochemical cycles and resulting negative effects on human health, biodiversity and food production. The degree of uncertainty in our current state of science related to geoengineering carries serious risks for the human and natural environment, should it not be addressed through careful modeling and research. A consideration of the degree of uncertainty in predicting unintended consequences of geoengineering interventions quickly reveals that our understanding of the climate system is still insufficient to quantify the risks inherent in tinkering with this system. Research may well determine that geoengineering techniques are neither effective practical nor desirable although without further research, uncertainties will continue to predominate. Most research has focused on modeling studies and small-scale laboratory tests. Table 3, from the UNESCO–SCOPE–UNEP policy brief on this topic, describes the status of research. It is useful to note that research and development is not a linear process—it is also cyclical, in that results of testing feed back into theory and modeling, design and development. Two large-scale field tests that have been conducted were presented at the UNESCO workshop, one on ocean fertilization and the other on sulfate aerosol injections. These field tests clearly show results that open further questions which must feedback into a cyclical development process. 63 A. Welch et al. / Environmental Development 2 (2012) 57–72 Table 3 Status of geoengineering research (Blackstock et al., 2011). Geoengineering research stages Research stage Description Research challenges Research status Environmental impacts 1. Theory and modeling Publications and computational models studying the anticipated climatic impacts of geoengineering techniques International cooperation, research funding, and development of more comprehensive models Studies began more than 20 years ago and continue for both Carbon and Solar technologies None 2. Technology development Design and laboratory development of geoengineering deployment technologies Emergence of governance issues when technologies are patented or classified. Who has access to and control over new technologies? Many carbon geoengineering technologies are currently under development None 3. Sub-scale field testing Feasibility testing of geoengineering deployment technologies at levels posing ‘demonstrably negligible’ environmental and transboundary risks Evaluating risks and modeling uncertainties related to the environmental impacts of field testing Limited recent tests of atmospheric aerosol injection and ocean iron fertilization have taken place By design, these tests must take place at a scale which does not carry significant environmental or transboundary impact The boundary between stages 3 and 4 can be very difficult to define. Due to the current uncertainties surrounding geoengineering science, demonstrating that a proposed field test of moderate scale poses negligible risk to humans and ecosystems can be very difficult. As a result, the limits below which a test would be considered ‘‘sub-scale’’ could be politically contentious 4. Large-scale field testing Testing the climatic impacts of geoengineering deployment, nominally at scales below actual deployment, but with notable transboundary environmental impacts Environmental and governance challenges of experiments spread unevenly at local, national and regional levels. Definition of large-scale No serious calls for this kind of testing to begin soon Global effects In 2009, Yuri Izrael at the Institute of Global Change in Moscow and a team of Russian scientists conducted the first published field tests of aerosols as a geoengineering technique. Although conducted in the troposphere, the approach has applications to the understanding of stratospheric aerosols. Most importantly, fine aerosols close in size to natural stratospheric aerosols of volcanic origin have been shown to yield a solar radiation attenuation of about 1% (Izrael et al., 2009). Before conducting field tests, model experiments were conducted and calculations were made to determine the ecological safety of tests. The experimental measurements of optical parameters of aerosol formations were performed with groundbased and airborne equipment. The paper posits that the light absorption observed meets the required levels to limit the warming climate. The paper further asserts that research of this kind does not violate international laws, as the 1976 Convention on the Prohibition of Military or Hostile Use of Environmental Modification Techniques does not refer to peace-time use of environmental modifications. The authors of this study would like to see organized international experiments on stratospheric aerosols. Proposals for large-scale ocean fertilization have been around since the late 1980s, and a number of small-scale field trials have shown that iron addition in high nutrient regions greatly increases the 64 A. Welch et al. / Environmental Development 2 (2012) 57–72 drawdown of CO2 in surface water through phytoplankton and bacteria blooms (Wallace et al., 2010). Most recently, LOHAFEX, an Indo-German iron fertilization experiment conducted by researchers from the National Institute of Oceanography and the Alfred Wegener Institute, was confined to the low silica waters of the sub-Antarctic Southern Ocean, on account of the regulatory framework on ocean fertilization. A 300 square kilometer area in the core of an eddy was fertilized with six tons of dissolved iron after which plankton communities and ocean chemistry were observed for 39 day (Alfred Wegener Institute, 2011). The LOHAFEX experiment showed that while chlorophyll biomass does build up after fertilization, grazing pressure by zooplankton also increases and there is no conclusive evidence that the carbon then sinks and becomes effectively sequestered. There are also a variety of environmental and ecological impacts of ocean fertilization. These include changes in the food web, algal blooms, nutrient redistributions, further acidification of seawater, the expansion of hypoxic/anoxic zones, and the enhanced productivity of greenhouse gases like nitric oxide. The main summary of the LOHAFEX research is that the potential of ocean iron fertilization as a means of CO2 sequestration is substantially smaller than previously considered (Alfred Wegener Institute, 2011). These two field trials give insight on the feasibility of geoengineering techniques, but also raise many additional questions. The Royal Society highlighted the primary research priorities needed to understand the Earth system sufficiently to seriously consider employing geoengineering techniques in their 2009 report, as summarized in Table 4. These priorities, necessarily, include interdisciplinary research in the social sciences and technology development. 2.2. Engineering and technology development Technological innovation is the main driver of economic and social change and transition. Innovations change history – from the Stone and Iron to the Information Ages. Innovation occurs at Table 4 Priorities for geoengineering research. Adapted from Royal Society Report, 2009. Research priorities Cross-cutting priorities include:  Extensive climate and Earth system modeling studies including pilot-scale laboratory and field trials focused on understanding costs, effectiveness and impacts  Comprehensive evaluation of environmental, ecological and socio-economic impacts relative to those expected with no intervention  Analysis of ethical and social issues associated with research and deployment Research priorities for CDR methods include:       Estimates of effectiveness for achieving reduced CO2 concentrations Evaluation of time between deployment and achievement of intended affect Investigation of material consumption and waste Life cycle analysis of carbon and economic costs Potential side-effects of the processes and their products Critical research areas: land-use management in critical ecosystems (i.e. boreal forests and peat lands), effectiveness and residence time of various weathering and fertilization processes in land and ocean-based environments Research priorities for SRM methods include:         Estimates of effectiveness for achieving the desired climate state Evaluation of time between deployment and achievement of intended affect Life cycle analysis of financial and carbon costs Assessment of the full range of climate effects including properties other than global mean temperature, including extent and spatial variation of impacts Investigation into the effects on atmospheric chemical composition and on ocean and atmosphere circulation Detailed modeling studies to resolve seasonal and regional effects, global and annual averages Modeling, theoretical studies, long-term empirical research into the impacts of persistent high CO2 concentrations in a low temperature world for ecosystem processes and ecological communities Critical research areas: albedo of the Earth’s surface, clouds, stratosphere, and space A. Welch et al. / Environmental Development 2 (2012) 57–72 65 all levels – from lower to higher technologies, from smaller to higher size and scales of technology, and may be radical or incremental in application. The types of technology required for geoengineering solar radiation management and carbon dioxide removal are not new, but are theoretical and untested at the scale of application, and indeed radical. To make a meaningful impact on solar insolation and CO2 levels, such technologies would be at the truly mega engineering level, orders of magnitude larger than existing mega engineering activity, for example, in the oil and gas industry, with mega capital and operating costs. Research relating to technologies, costs and benefits at the levels of scale, impact and risk in terms of economic, social and environmental change and transition will be essential to inform engineering, technology and wider policy perspectives, to enable informed decisions to be made and governance structures developed. No geoengineering method will prove effective unless it can be applied at sufficient scale and at affordable cost. The paucity of field experiments leaves us with only rough estimates. Questions about engineering and technology development have focused primarily on the scale and costs of interventions that would be necessary to carry a real climatic impact. Cost estimates can be made based on the knowledge that approximately 5 g of sulfur in the stratosphere roughly offsets the climate forcing of 1 t of carbon in the atmosphere (Pierce et al., 2010). There is growing recognition that this ratio makes solar geoengineering considerably cheaper than emissions cuts, with a total cost estimated in the billions of dollars per year—much less than the likely cost of retooling the global economy (Keith et al., 2010; McClellan et al., 2010; Robock et al., 2009). On the other hand, in order for carbon geoengineering to take affect at sufficient scale to alter climate, such massive volumes of iron filings or tree plantings would be required that many critics consider these techniques to be too prohibitively scaled and priced for practical application. Let it be understood that the scale required for meaningful field testing, while perhaps less than the massive scale required for full deployment, will necessarily approach full-scale implementation (Robock et al., 2010). The testing and deployment of carbon and solar geoengineering technologies at such a level – call it mega-engineering – is an enormous challenge that exists at the limits of human experience and expertise. Such mega-engineering will involve investment, expenditure and economic challenges on par with the planetary scale of the problem. Due diligence in technology development is required to address environmental impacts and to demonstrate that public safety is a central concern of the governance regime. It is critical that environmental, social and economic impact assessments investigate potential direct and indirect effects and be carried out by a responsible entity not directly involved in geoengineering research. Only in this way can we ensure a standard of care for the global ecosystem. 2.3. Governance In 2010, the US Congress and UK Parliament launched coordinated joint inquiries in their respective Committees on Science and Technology on the research and development and governance issues, respectively, of geoengineering (Gordon, 2010; UK Government, 2010). A series of expert hearings, based on statements made by many experts cited elsewhere in this paper, aimed to form the foundation for an informed and open dialog on the science and engineering of geoengineering and to provide a US Congressional record to underpin the formation of future legislation authorizing the United States to engage in geoengineering research at the federal and the international level. The report did conclude that no country should proceed to conduct research without a rigorous governance structure in place and that certain techniques, such as space mirrors and desert-based reflectors, were too costly and environmentally and socially dangerous to be pursued to the research stage. In addition, a number of european reports have recently emerged (Kiel Earth Institute, 2011; ETC Group, 2011b). Global government awareness and involvement in this issue drops off steeply from there. Customary international law does not allow activities under national control to damage the territories of other states. For example, the 1972 London Dumping Convention requires members to prohibit certain types of dumping by nationals of certain substances loaded at their ports. Dumping is defined to mean ‘‘deliberate disposal’’ and does not include the ‘‘placement of matter for purposes 66 A. Welch et al. / Environmental Development 2 (2012) 57–72 other than disposal’’ (UNESCO, 2010). Upholding the precautionary principle, the Convention on Biological Diversity decided in 2008 that ocean fertilization activities should be carried out in only coastal waters until a stronger scientific justification exists with a global regulatory mechanism (Wallace 2010). This mechanism is now being developed through the London Convention and the London Protocol. Further, the 2010 Assessment Framework for Scientific Research that defines Legitimate Scientific Research includes research that: is designed to answer questions that will add to scientific knowledge; is not for financial gain; must be subject to peer review; includes a commitment to publish and make data available. The Solar Radiation Management Governance Initiative (SRMGI), a joint project of the Royal Society, the Academy of Sciences for the Developing World and the Environmental Defense Fund, has produced the first major report considering governance of solar geoengineering in late 2011. Solar geoengineering was prioritized on account of the potential for imminent deployment to global effect. With a goal of facilitating dialog, the initiative does not consider geoengineering as an alternative to mitigation and takes the human dimension to be critical. Four primary issues for the governance of solar geoengineering have been identified:  What are the goals and concerns regarding SRM geoengineering? The Initiative is not endorsing    SRM geoengineering, but recognizes the need to better understand the range of reasons for and against SRM geoengineering. What are the different categories of research that might benefit from differentiated governance arrangements? How are the options within SRM geoengineering differentiated? How can they be defined? What are the mechanics of governance? Who approves and funds projects? How is public opinion incorporated into decision making? Which are the appropriate international/policy institutions to address SRM geoengineering? At the 10th Conference of the Parties to the Convention on Biological Diversity (CBD) which took place in October 2010, a decision was made that geoengineering activities which may affect biodiversity should not take place ‘in the absence of science based, global, transparent and effective control and regulatory mechanisms’ (CBD, 2010). However, an exception was made for ‘small scale scientific research studies that would be conducted in a controlled setting’ and as justified by a need ‘to gather specific scientific dataysubject to a thorough prior assessment of the potential impacts on the environment’ (CBD, 2010). Although considered by some to be a de facto moratorium, the UNESCO expert meeting took note of the exception for small-scale geoengineering activities and agreed that the statement does not necessarily forbid all research, but rather advocates responsible research at appropriate scale. It was recognized that the CBD statement declares that geoengineering should not be deployed without environmental safeguards which is welcomed by the research community. 2.4. Global communication While geoengineering becomes more complicated as researchers devise new ways to manipulate the climate – encompassing disparate techniques from painting roofs white and launching trillions of space mirrors – the conversation about climate engineering is just beginning. In fact, the most pressing outstanding issue may be the geographically balanced communication of geoengineering representing all sides of the geoengineering debate. To date, the few attempts to assess public perception of the issue suggest that geoengineering is poorly understood and that the current conversation shaping the issue is insufficiently broad to engage the public in a meaningful way. It may not come as a surprise that, outside expert meetings, geoengineering is poorly understood. The Yale Project on Climate Change, the longest running social survey on the perceptions of climate change, found that 74 percent of respondents have heard ‘nothing’ about geoengineering as a possible response to climate change (Leiserowitz et al., 2010). To make matters worse, many of those that had heard of the issue incorrectly conflate it with geothermal energy. Other groups confuse it A. Welch et al. / Environmental Development 2 (2012) 57–72 67 with engineering geology. A poll in Japan produced similar results (UNESCO, 2010). Together, these polls indicate that there is but a tiny understanding of geoengineering across the globe. Where geoengineering is discussed, it is often discussed by the same people in the same places in a conversation that is too narrow to bring an awareness of geoengineering to the people that stand to be most impacted. In fact, the vast majority of news items about intentional climate modification originate in North America, the UK, Europe and Australia, with only a tiny fraction emerging from other parts of the globe (Buck, 2010, 2012). This comes despite the fact that geoengineering is poised to have global impacts. Perhaps the media treatment of the issue is narrow because the geoengineering debate is driven by a relatively small number of experts, mostly natural scientists. These individuals command the authority, whether or not they want it, and tend to frame the subject as a reluctant response to a looming catastrophe (Buck, 2010, 2012). This may be the most appropriate way to approach the subject, but if the current trend is not met with a concerted effort to communicate and engage with all nations, the geoengineering debate is likely to become the exclusive domain of scientists and policy wonks from the developed world. This imbalance will leave geoengineering without the broad support necessary to deliver a significant, equitable and desirable response to climate change. The beginnings of a broader discussion can be found outside the scientific literature and geoengineering news items that these papers instigate. Recently, a number of groups expressed dissent in an open letter to the IPCC written in the lead-up to the recent convening of the IPCC geoengineering working group. These environmental and social justice groups, perhaps unknowingly, echo the prevailing opinion amongst geoengineering researchers when they assert that geoengineering is teeming with complicated legal and ethical questions and is mired in uncertainty. They urged the IPCC not to ‘‘squander its credibility on geoengineering’’ and called for a broader global conversation that would better represent developing nations (ETC Group, 2011a). These environmental and social justice groups, and the interests they represent, need to be incorporated into the discussion so that it is better understood that their concerns about geoengineering are, in fact, shared by the scientific community. In early 2012, at the request of the CBD and in accordance with its ‘honest-broker’ role, UNESCO became involved in a consultative process, with a strong focus on sharing balanced information, to understand the opinions and concerns of local and indigenous people on geoengineering through an interactive webportal (www.climatefrontlines.org) which serves as a global forum for indigenous peoples, small islands and vulnerable communities. Geoengineering was previously mentioned in the Anchorage Declaration, from the 2009 Indigenous Peoples Global Summit on Climate Change, as one of the ‘false solutions to climate change that negatively impact Indigenous Peoples’ rights, lands, air, oceans, forests, territories and waters’ (Anchorage Declaration, 2009). One concern voiced during the consultation is that supporting further research is supporting a trajectory towards implementation; once that path is started, it will become increasingly difficult to stop. This message that science and research is itself a separate culture, is an important element in how we make decisions and who is included in this decision making process about questions on this scale. Engaging the public on an issue with which it is not even aware is difficult but not impossible. The recent UNESCO–UNEP–SCOPE policy brief on geoengineering is one attempt to raise awareness amongst policy makers globally. However it is one small step and needs to be taken up by the popular media and matched by researchers globally. The nonexistent public perception of geoengineering means that attempts at assessing public opinion are complicated by the necessity to inform, and thereby help to create, those same opinions. This leaves prospective geoengineers in a difficult position, which could easily slide towards manipulation. The more diverse the media informing the public perception of geoengineering, the better. It is encouraging that the issue is an increasingly popular topic for web blogs, magazines and popular science books and has even been the subject of a recent alternative reality drama in Australia called the Bluebird Project. Despite the beginnings of a broader discourse, it remains to be seen how the public will ultimately respond to geoengineering. One possible outcome, supported by the increased attention given the subject in the published literature, is a greater commitment to reduce greenhouse gas emissions in the first place. This would come in spite of a long-held concern by some scientists of ‘moral hazard’, a term derived from the insurance industry that encapsulates the notion that 68 A. Welch et al. / Environmental Development 2 (2012) 57–72 knowledge of geoengineering reduces incentives for carbon dioxide reductions (Royal Society, 2009). This is a valid concern, however the mere fact that geoengineering is emerging as a serious consideration demands an increase in public awareness. We must have confidence in the ultimate benefit on an informed scientific community, political community and public alike. 3. Outcome from the UNESCO meeting The goal of the UNESCO geoengineering meeting was to begin an international discussion to create awareness of the science and governance issues in this controversial field. Experts from academia, civil society and government in a dozen countries were asked their opinion regarding the role of UNESCO in the geoengineering debate. Although we make no claim that the participants’ diverse views can be represented by a single voice, there are three central outcomes that support better communication and controlled, small-scale geoengineering field experiments. First, geoengineering methods were categorized into two broad categories of solar geoengineering and carbon geoengineering. These categories are directly analogous to SRM and CDR. The participants recommended this simpler language to aid in global communication. UNESCO was requested to work to improve global awareness of the status of geoengineering research, governance and debates. The categories were also distinguished because of the grossly different technical, governance and side-effect challenges of the two types of geoengineering. Treating carbon and solar proposals separately in the governance debate will be critical for the progress of research in either field. The meeting made no attempt to prioritize the various methods but recognized that certain methods are more viable than others given their respective technological feasibility, estimated cost and level of uncertainty, all of which can be improved through controlled field experiments. Second, it was recommended that the statement by the Secretariat of the Convention on Biological Diversity (CBD) made at its October 2010 meeting in Nagoya should not be interpreted as a blanket moratorium on all geoengineering research. Rather, the CBD statement recognizes that small-scale geoengineering field experiments should be allowed as long as a number of controls are put in place. Third, a geoengineering research program could address the technological and scientific challenges of geoengineering and ensure that legitimate scientific research may proceed. An appropriate research program would necessarily have broad participation and transparent administration. Such a program would help guarantee that the experimental controls called for by the CBD are indeed put in place. For this purpose, the creation of an international research program in geoengineering similar to the World Climate Research Programme was proposed. Such a program would be comprised of a joint scientific committee selected by the mutual agreement of multiple international sponsoring organizations and would thereby subject geoengineering research to international approval. These outcomes help inform and disseminate the geoengineering debate and UNESCO will continue to seek consultation from all stakeholders about the organization’s most appropriate role as the discussion moves ahead. Based on the interdisciplinary mandate of UNESCO, including expertise in oceans (the Intergovernmental Oceanographic Commission), ecology (Man and the Biosphere Programme), Earth sciences (International Geoscience Programme), engineering, ethics and social sciences, UNESCO is uniquely positioned to assist in the development of an international research program with a strong focus on balanced communication. 4. Way forward The rising interest in geoengineering is evidence enough that our collective efforts to slow greenhouse gas emissions and reverse climate change have yet to succeed. So where do we go from here? Before geoengineering can provide real solutions to the problem of climate change and a sustainable future, a means of governing geoengineering research must be developed. The debate surrounding geoengineering has produced a set of principles for its open governance (Rayner et al., 2009). These principles, shown in Table 2, describe how geoengineering might be broadly governed, A. Welch et al. / Environmental Development 2 (2012) 57–72 69 but do not detail how to treat the various methods of geoengineering. In order for the geoengineering discussion to avoid following the frustrated path of the greenhouse gas mitigation deliberations, there must be a clear governance structure developed to guide further research. At the very least, separate treatments are necessary for carbon and solar geoengineering. In the first instance, the SRMGI seeks ‘‘to ensure that [SRM] research is conducted in a manner that is responsible, transparent and environmentally sound’’ (SRMGI, 2011). A major stride in this direction has been realized by the recent publication of the SRMGI’s governance of research report (SRMGI, 2011). The report summarizes the opinions of a wide variety of stakeholders from 22 countries and makes several key conclusions. Chief among the conclusions is that flexible governance and regulatory arrangements could be most effective and that more information is positive with regard to the assessment of SRM research, but unpredictable with regard to the likelihood of deployment (SRMGI, 2011). However, the report concedes that there are many difficulties yet to be overcome, not least of which, the fact that there exists no institution or international convention adequate to govern SRM research. Meanwhile, the way forward for carbon geoengineering is less clear. A similar governance initiative is needed that focuses on carbon geoengineering methods, incorporating the lessons learned by the recent attempts to regulate ocean fertilization experiments (CBD, 2010). Although CDR methods target the problem rather than the symptom, and are therefore alluring, these methods have yet to be proven technologically feasible, are costly at large scale with undocumented risks and are therefore much farther from implementation. On the other hand, CDR technologies are much more accessible to developing countries and could be linked through a scaling exercise with already established carbon sequestration activities, the larger carbon market and REDDþ activities. Although the majority of attention is now focused on solar geoengineering, carbon geoengineering merits more serious consideration. Even if researchers are provided with guidance sufficient to move geoengineering research forward on both fronts, we will still be faced with the task of how to prioritize the various technologies and decide which should be advanced first. There are any number of ways we might conceivably do this, but if we are to learn from the international effort to reach a consensus regarding mitigation, we would be wise to prioritize activities with the greatest chance of public acceptance. This is not a call to pander to the often incomplete media perceptions of geoengineering, but rather a recognition that social and political barriers rather than scientific or economic ones will ultimately determine the fate of geoengineering (Jackson and Salzman, 2010). The largest barriers stem from concerns over risk, ethics and justice and stand as a rubric for identifying those activities with the greatest likelihood of public acceptance. We share the view of Jackson and Salzman (2010) that ‘‘increasing R&D on its own will do nothing to ensure the successful implementation of geoengineering and may, in fact, prove counterproductive if it is not matched by comparable investment in strengthening the social and political understanding of geoengineering’’. The research agenda should therefore be interdisciplinary and serve to increase public awareness and engagement while supporting the creation of a geoengineering governance framework. More likely than not, there is no geoengineered silver bullet. A realistic climate solution may actually be a patchwork of adaptation, mitigation, and various publicly acceptable geoengineering interventions at a range of scales, including tree planting, aerosol injections, and a range of carbonsequestering land-uses and industrial processes. 5. Discussion The authors hope that this journal will provide a new venue for raising awareness about climate engineering and that this article will be followed by a series of focused regional perspectives that will help build toward a broadly supported geoengineering governance framework. It is critical that geoengineering become better understood so that unintended consequences may be estimated, relative risks be weighed, society engaged globally and short-sighted moratoria not hinder beneficial research. Appropriate governance mechanisms will ensure that where risks do occur, they are only entered under conditions of international legitimacy and consent, and with the correct safeguards. Raising public awareness of geoengineering is the first step in this process and requires that we ask what a more sustainable future would look like and how we might achieve it. When considering 70 A. Welch et al. / Environmental Development 2 (2012) 57–72 climate, a sustainable future will demand, first and foremost, a reduction in the amount of carbon dioxide that we put into the atmosphere, but may also require some engineering of the climate should we be unable or unwilling to achieve sustainability through mitigation alone. To be sure, addressing the many challenges involved in governing geoengineering research will require a new form of governance that can function at multiple levels and spatial scales and across multiple regions and actors. In pursuit of an appropriate geoengineering policy we must consider several fundamental questions:      How Who How How How much regulation is appropriate? At what scale? will create and carry out governance structures? can the conversation be expanded to the greatest number of nations? can transparency and fairness be ensured? do we prevent discussion of geoengineering from slowing mitigation efforts? Since humans are implicit in the currently changing climate, it will be imperative that we take an active role in a multi-faceted conscious response involving adaptation, mitigation, and a serious look at the possibility of geoengineering. The balance between mankind’s control and self-control will determine the story of our future climate and indeed the story of our own future. Acknowledgments The authors are grateful to the United Nations Educational, Scientific and Cultural Organization (UNESCO) according to their past or present affiliation and for providing a forum for a broad discussion of geoengineering. Special thanks are extended to Jason Blackstock (Centre for International Governance Innovation and International Institute for Applied Systems Analysis), Nigel Moore (Centre for International Governance Innovation) and Clarisse Siebert (Stockholm Environment Institute) who co-authored the UNESCO–SCOPE–UNEP policy brief on geoengineering. The authors of this article are also grateful to our many colleagues who attended the first UNESCO expert meeting on geoengineering: Jason Blackstock; David Freestone (IUCN and the George Washington University Law School, US); Steven Hamburg (Environmental Defense Fund, US); Debora Iglesias-Rodriguez (University of Southampton, UK); Yuri Izrael (Institute of Global Climate and Ecology, Russia); David Keith (University of Calgary, Canada); Peter McGrath (Academy of Sciences for the Developing World); Luiz Gylvan Meira-Filho University of Sao Paulo, Brazil); Wajih Naqvi (National Institute of Oceanography, India); Andrew Parker (UK Royal Society); Ulrike Potzel (Technical University Munich, Germany); Alexey Ryaboshapko (Institute of Global Climate and Ecology, Russia); Masahiro Sugiyama (Central Research Institute of Electric Power Industry Socioeconomic Research Center, Japan); Liz Thompson (former Minister of Energy and Environment of Barbados); Raoul Weiler (Technical University Munich, Germany); and the Member States of UNESCO. Finally, the authors are grateful to all those that provided feedback on this article. References Alfred Wegener Institute, 2011. LOHAFEX Project Website. Accessed 5 August 2011 at /http://www.awi.de/en/news/ selected_news/2009/lohafex/S. Anchorage Declaration, 2009. Accessed 1 February 2012 at /http://unfccc.int/resource/docs/2009/smsn/ngo/168.pdfS. Asilomar Scientific Organizing Committee (ASOC), 2010. The Asilomar Conference Recommendations on Principles for Research into Climate Engineering Techniques. Climate Institute, Washington, DC. Budyko, M.I., 1977. Climatic Changes. American Geophysical Union, Washington, DC. Blackstock, J.J., Moore, N., Siebert, C.K., 2011. Engineering the Climate: Motivations, Risks, and Research Directions. UNESCO– SCOPE–UNEP Policy Brief Series, vol. 14. Buck, H.J., 2010. What can geoengineering do for Us? Public participation and the new media landscape. Paper Presented at a Workshop on The Ethics of Geoengineering: Investigating the Moral Challenges of Solar Radiation Management. University of Montana, Missoula, Montana, October 18–20. /http://www.umt.edu/ethics/EthicsGeoengineering/Work shop/articles1/Holly%20Buck.pdfS (accessed 29.02.12). Buck, H.J., 2012. Geoengineering: re-making climate for profit or humanitarian intervention? Dev. Change 43, 253–270, doi:10.1111/j.1467-7660.2011.01744.x. A. Welch et al. / Environmental Development 2 (2012) 57–72 71 Caldeira, K., Wood, L., 2008. Global and Arctic climate engineering: numerical model studies. Philosophical Transactions of the Royal Society A, Series A 366, 4039–4056. Committee on Science Engineering and Public Policy (COSEPUP), 1992. Geoengineering options, Appendix Q. In: Policy Implications of Greenhouse Warming: Mitigation, Adaptation and the Science Base. National Academies Press, Washington, DC. Convention on Biological Diversity, 2010. COP 10 Decisions. Accessed 2 August 2011 at /http://www.cbd.int/decisions/cop/ ?m=cop-10S. Crutzen, P.J., 2002. The ‘‘anthropocene’’. Journal de Physique IV France 12, 1–5, doi:10.1051/jp4:20020447. Crutzen, P.J., 2006. Albedo enhancement by stratospheric sulphur injections: a contribution to resolve a policy dilemma? Climatic Change 77 211–220, doi:10.1007/s10584-006-9101-y. Dyson, F.J., 1977. Can we control the carbon dioxide in the atmosphere? Energy 2 287–291. ETC Group, 2011a. Open Letter to IPCC on Geoengineering. Accessed 5 August 2011 at /http://www.etcgroup.org/en/node/ 5267S. ETC Group, 2011b. Retooling the Planet?—Climate Chaos in the Geoengineering Age. Report Commissioned by the Swedish Society for Nature Conservation. Fleming, J.R., 2010. Fixing the Sky: The Checkered History of Weather and Climate Control. Columbia University Press, New York. Geophysics Study Committee (GSC), 1977. Energy and Climate. National Academy of Sciences, Washington, DC. Gordon, B., 2010. Engineering the Climate: Research Needs and Strategies for International Coordination. Committee on Science and Technology, U.S. House of Representatives, 111th Congress. Govindasamy, B.G., Thompson, S., Duffy, P., Caldeira, K., Delire, C., 2002. Impact of geoengineering schemes on the terrestrial biosphere. Geophysical Research Letters 29, 2061, doi:10.1029/2002GL015911. Harper, K.C., 2008. Climate control: United States weather modification in the Cold War and beyond. Endeavour 32, 20–26. Izrael, Y.A., Zakharov, V.M., Petrov, N.N., Ryaboshapko, A.G., Ivanov, V.N., Savchenko, A.V., Andreev, Y.V., Eran’kov, V.G., Puzov, Y.A., Danilyan, B.G., Kulyapin, V.P., Gulevskii, V.A., 2009. Field studies of a geo-engineering method of maintaining a modern climate with aerosol particles. Russian Meteorology and Hydrology 34 (10), 635–638. Kiel Earth Institute, 2011. Large-Scale Intentional Interventions into the Climate System? Assessing the Climate Engineering Debate. Report Commissioned by the Federal Ministry of Education and Research, Germany. Keith, D.W., 2000. Geoengineering the climate: history and prospect. Annual Review of Energy and the Environment 25, 245–284. Keith, D.W., Ha-Duong, K., Stolaroff, J., 2005. Climate strategy with CO2 capture from the air. Climatic Change 74, 17–45. Keith, D.W., Parson, E., Granger Morgan, M., 2010. Research on global sun block needed now. Nature 463, 426–427, doi:10.1038/463426a. Leiserowitz, A., Maibach, E., Roser-Renouf, C., Smith, N., 2010. Project on Climate Change Communication. Yale University and George Mason University, New Haven, CT. Lovejoy, T., 2011. Geo-Engineering Can Help Save the Planet. Op-Ed in the International Herald Tribute (published June 10, 2011). Marchetti, C., 1977. On geoengineering and the CO2 problem. Climatic Change 1, 59–68, doi:10.1007/BF00162777. Martin, J.H., 1990. Glacial–interglacial CO2 change: the iron hypothesis. Paleoceanography 5, 1–13. Martin, J.H., Coale, K.H., Johnson, K.S., Fitzwater, S.E., Gordon, R.M., Tanner, S.J., Hunter, C.N., Elrod, V.A., Norwick, J.L., Coley, T.L., Barber, R.T., Lindley, S., Watson, A.J., Vanscoy, K., Law, C.S., Liddicoat, M.I., Ling, R., Stanton, T., Stockel, J., Collins, C., Anderson, A., Bidigare, R., Ondruesk, M., Latasa, M., Millero, F.J., Lee, K., Yao, W., Zhang, J.Z., Friederich, G., Sakamoto, C., Chavez, F., Buck, K., Kolber, Z., Greene, R., Falkowski, P., Chisholm, S.W., Hoge, F., Swift, R., Yungel, J., Turner, S., Nightingale, P., Hatton, A., Liss, P., Tindale, N.W., 1994. Testing the iron hypothesis in ecosystems of the equatorial Pacific Ocean. Nature 371, 123–129. McClellan, J., Sisco, J., Suarez, B., Keogh, G., 2010. Geoengineering cost analysis. Prepared by Aurora Flight Sciences Corp. under contract to the University of Calgary. Accessed 9 November 2011 at /http://people.ucalgary.ca/  keith/Misc/ AuroraGeoReport.pdfS. Pongratz, J., Lobell, D.B., Cao, L., Caldeira, K., 2012. Crop yields in a geoengineered climate. Nature Climate Change, 2, doi:10.1038/nclimate/1373. Pierce, J.P., Weisenstein, D.K., Heckendorn, P., Peter, T., Keith, D.W., 2010. Efficient formation of stratospheric aerosol for climate engineering by emission of condensable vapor from aircraft. Geophysical Research Letters 36, L18805, doi:10.1029/2010GL043975. President’s Science Advisory Committee (PSAC), 1965. Restoring the Quality of our Environment. Executive Office of the President, Washington, DC. Rayner, S., Redgwell, C., Savulescu, J., Pidgeon, N., Kruger, T., 2009. Memorandum on Draft Principles for the Conduct of Geoengineering Research. House of Commons Science and Technology Committee Enquiry into the Regulation of Geoengineering. Accessed 29 July 2011 at /http://www.sbs.ox.ac.uk/centres/insis/Documents/regulation-of-geoengineer ing.pdfS. Robock, A., 2002. Pinatubo eruption: the climatic aftermath. Science 295, 1242–1244, doi:10.1126/science.1069903. Robock, A., Marquardt, A., Kravitz, B., Stenchikov, G., 2009. Benefits, risks, and costs of stratospheric geoengineering. Geophysical Research Letters 36, L19703, doi:10.1029/2009GL039209. Robock, A., Bunzl, M., Kravitz, B., Stenchikov, G., 2010. A test for geoengineering? Science 327 530–531, doi:10.1126/ science.1186237. Royal Society, 2009. Geoengineering the Climate: Science, Governance and Uncertainty. Royal Society Working Group on Geoengineering, London. Accessed 29 July 2011 at /http://royalsociety.org/geoengineering-the-climate/S. Solar Radiation Management Governance Initiative (SRMGI), 2011. Solar Radiation Management: The Governance of Research. Accessed January 18, 2012 at /www.srmgi.orgS. Study of Critical Environmental Problems (SCEP), 1970. Man’s Impact on the Global Environment: Assessment and Recommendations for Action. MIT Press, Cambridge. 72 A. Welch et al. / Environmental Development 2 (2012) 57–72 Study of Man’s Impact Climate (SMIC), 1971. Study of Man’s Impact on Climate: Inadvertant Climate Modification. MIT Press, Cambridge. United Nations, 1976. Convention on the Prohibition of Military or any Other Hostile Use of Environmental Modification Techniques. UN, Treaty Series 1108, p. 151. Accessed 29 July 2011 at /http://www.un-documents.net/enmod.htmS. UK Government Response to the House of Commons Science and Technology Committee 5th Report of Session 2009–10: The Regulation of Geoengineering, 2010. Accessed 2 August 2010 at /http://www.parliament.uk/business/committees/ committees-a-z/commons-select/science-and-technology-committee/inquiries/geoengineering-/S. Umweltbundesamt, 2011. Geoengineering: Effective Climate Protection or Megalomania? Report Prepared by the Federal Environmental Agency, Germany. UNESCO, 2010. UNESCO Expert Meeting on Geoengineering. Accessed 8 August 2011 at /http://www.unesco.org/new/en/ natural-sciences/environment/Earth-sciences/emerging-issues/geo-engineering/S. Wallace, D.W.R., Law, C.S., Boyd, P.W., Collos, Y., Croot, P., Denman, K., Lam, P.J., Riebesell, U., Takeda, S., Williamson, P., 2010. Ocean Fertilization: A Scientific Summary for Policy Makers. IOC/UNESCO, Paris (IOC/BRO/2010/2). Zalasiewicz, J., Williams, M., Steffen, W., Crutzen, P., 2010. The new world of the Anthropocene. Environmental Science & Technology 44 (7), 2228–2231, doi:10.1021/es903118. Zikeev, N.T., Doumani, G.A., 1967. Weather Modification in the Soviet Union, 1946–1966: A Selected Annotated Bibliography. Library of Congress, Science and Technology Division, Washington, DC.