Geoengineering Research

Published: September 16, 2013

Updated: October 2013

This is a writeup of a medium investigation, a brief look at an area that we use to decide how to prioritize further research.

In a nutshell

  • What is the problem? Geoengineering – i.e., large-scale interventions in the climate to attempt to reduce global warming or its impacts – could conceptually mitigate some of the most catastrophic impacts of climate change, but major questions remain regarding the feasibility, likely costs and benefits, and optimal governance of the various possible geoengineering approaches.
  • What are possible interventions? A philanthropist could directly fund research on these issues, lobby a government to fund research, or fund the development of governance mechanisms to enable research.
  • Who else is working on it? Although there appears to be significant academic interest in geoengineering as a research area, funding appears to be limited. There appears to be much more funding on carbon dioxide removal than on solar radiation management; carbon dioxide removal is likely less risky than solar radiation management, but also likely more expensive and less fast-acting.

1. What is the problem?

Unmitigated climate change is likely to have large negative humanitarian impacts across a range of outcomes, and may have disastrous impacts. We have written about the likely impacts of unmitigated climate change here, summarizing the findings of the Intergovernmental Panel on Climate Change’s 2007 Fourth Assessment Report. We have also written about less likely but potentially extremely harmful impacts of more extreme climate changes on a separate page.

Once emitted, carbon continues to warm the planet for decades and a portion remains in the atmosphere (keeping temperatures warmer) for many centuries.1 In the event that existing efforts to limit carbon emissions fail to adequately reduce emissions, technology to rapidly limit temperature increases could be quite valuable, particularly in the event of worse-than-anticipated outcomes.

Geoengineering refers to large-scale interventions in the climate to attempt to reduce global warming or its impacts.2 We have seen two broad types of geoengineering discussed:

  • Solar radiation management (SRM): reflecting back more sunlight to cool the earth without directly affecting carbon dioxide concentrations. The particular strategy we’ve seen discussed most frequently is injecting sulfate aerosols into the stratosphere to reflect back some sunlight, but other proposals include using saltwater spray to brighten clouds or using large mirrors in space to reflect back more sunlight.3
  • Carbon dioxide removal (CDR): there are a number of technical proposals for attempts to remove carbon dioxide from the atmosphere that we have seen discussed, including direct air capture with chemical processes, biochar, ocean iron fertilization, and bio-energy with carbon capture and storage.4

Most of our research to date on geoengineering has focused on stratospheric injection of sulfate aerosols. Our understanding is that, relative to other geoengineering approaches, stratospheric injection is likely to be faster-acting and cheaper (in simple financial terms, not necessarily in terms of risks or costs and benefits), making it a plausible candidate for use in response to a climate emergency.5 On the other hand, our understanding is also that SRM has a greater potential for causing harm than CDR6 and that research into SRM is not as well-funded as research into CDR.7 We believe there to be many open questions about the potential effectiveness and side-effects of SRM, the answers to which could inform the behavior of policymakers facing climate emergencies.8

We have not done any systematic comparison of the case for funding further research on SRM compared to further research on CDR, and we have looked at only a subset of all possible SRM approaches, for instance, not thoroughly investigating albedo modification or marine cloud brightening. We regard these as important questions for further investigation should we proceed further with this research.

1.1 Background on stratospheric aerosol injection

Volcanic eruptions naturally produce aerosol that cools the planet by reflecting back sunlight. For example, the eruption of Mount Pinatubo in the Philippines in 1991 decreased the 1992 global mean temperature of the Earth by about 0.5ºC.9

These “natural experiments” raise the possibility of intentionally injecting sulfate aerosols into the stratosphere to offset the warming effects of climate change. Our understanding is that scientists believe it to be likely, though not certain, that such an effort would be feasible and would result in lower average global temperatures.10

Unlike many other approaches to climate change, such as emissions reductions or carbon dioxide removal, stratospheric injection of sulfate aerosols does not address the fundamental issue of elevated greenhouse gas concentrations. This means it would perform worse than other climate response strategies in many ways, including:

  • Since it does not reduce carbon dioxide concentrations, sulfate aerosol injection would not address all of the results of high carbon emissions, such as ocean acidification.11
  • Once started, rapidly halting aerosol injection would lead to far faster warming than climate change itself, with potentially more disruptive results.12

In addition, stratospheric aerosol also carries a variety of risks. For instance, some models have suggested that solar geoengineering could negatively affect precipitation, leading to droughts in some places.13 Some scholars have also pointed to the risk of conflict over control of geoengineering efforts as another potential negative outcome,14 and “unknown unknowns” are a central cause for concern.15

1.2 Open questions

Despite its potential benefit as a form of insurance against catastrophic climate emergencies, we believe that there remain many unanswered questions about whether and how stratospheric injection could or should be deployed, and what the likely positive and negative effects of deployment would be.

Some of the open questions we see as most important are:

  • Could stratospheric aerosol injection offset several degrees of warming on an ongoing basis? Although volcanic eruptions serve as precedent for small levels of short-term cooling, some have argued that there are limits on how much cooling sulfate aerosols could produce,16 and, in any case, there is the possibility of other limitations on the viability of sulfate aerosols.
  • What are the likely humanitarian costs of conducting such an effort, and are there technical strategies that could be used to mitigate them? One example that has been cited is the possibility that sulfur aerosol injection would reduce the strength of the Asian monsoon.17 Another possibility we’ve seen discussed is that sulfate aerosols would harm the ozone layer.18
  • How should a global geoengineering scheme be governed? What would the political implications of the availability of sulfate aerosol injection technology be? International violence arising from disputes over the appropriate amount of aerosol injection to employ could conceivably be much more harmful than aerosol injection itself.19

Researching this topic could be very valuable no matter the findings. In the event that large-scale stratospheric aerosol injection could not feasibly reduce temperature, or that deploying it would cause more harm than benefit, having that knowledge prior to attempts to deploy the technology in an emergency situation could be enormously valuable. If large-scale stratospheric aerosol injection could feasibly reduce temperature, and would be net-beneficial under some future set of adverse climate conditions, that also seems to be quite valuable knowledge for policymakers to have. In either case, effective and informed governance could be invaluable.

2. What are possible interventions?

The two main strategies we see for using philanthropic funding to help address these questions are:

  • directly funding further research
  • advocating for governmental funding of further research.

In practice, either overarching approach could involve a focus on governance discussions and research, as opposed to a focus on directly attempting to answer the kinds of questions mentioned above. Governance of geoengineering research itself appears to be an active area of research.20

We are not aware of any non-profit organizations currently raising money to systematically pursue any of these aims, and we do not have a strong sense of what the likely costs or returns to these approaches would be.

3. Who else is working on this?

Our understanding is that there is a significant amount of academic interest in stratospheric aerosol injection, but that government and philanthropic funding for research is limited:

  • A September 2010 report by the United States Government Accountability Office assessed U.S. federal funding for geoengineering research in fiscal years 2009 and 2010, reporting $949,000 of research on solar radiation management and about $101 million on geoengineering research overall, the vast majority of which was on conventional mitigation approaches that could be relevant to geoengineering.21
  • During a May 2013 conversation, Andrew Parker estimated that the total sum of global government research spending on ongoing solar geoengineering research projects was roughly $20-25 million; since many of the projects span multiple years, the figure does not represent an annual estimate.22
  • Bill Gates has personally funded $4.6 million worth of geoengineering research, including but not exclusively focused on stratospheric aerosol injection.23

Building on a list compiled by Andrew Parker and David Keith (PDF), we have tried to identify funded projects and funding sources around the world that explicitly include a significant solar geoengineering component (XLS).24 Our total tally of funding for such projects (for which we have funding information) amounts to about $11 million/year. This may be an overestimate of total resources directed to solar geoengineering, as it incorporates non-solar-geoengineering aspects of grants that are only partially devoted to solar geoengineering, but we believe it is more likely to be an underestimate of total resources because:

  • research that is supported by general institutional resources (such as unrestricted funding to a university, graduate students stipends, or computing resources) is not accounted for
  • some funded research that might be classified as solar goengineering may not be explicitly portrayed as such by the researchers or grant agencies
  • our search strategy of explicitly enumerating all the grants that we know of and taking the sum of their funding means than any missed funding sources would entail an underestimate, and we believe that we missed at least some funding.25

For details of the projects included in our tally, see our spreadsheet on geoengineering research funding.

4. Questions for further investigation

Our research in this area has been relatively limited, and many important questions remain unanswered by our investigation. (These are meant to be distinct from the questions above, for which we believe further academic research is necessary. These questions are for our further research.)

Amongst other topics, further Open Philanthropy Project work on this cause might address:

  • How would further research on sulfate aerosol injections compare with other research related to climate change, such as further monitoring of feedbacks, or with other types of geoengineering research, such as carbon dioxide removal or marine cloud brightening?
  • How likely is it that funding research on geoengineering would cause harm (e.g. by undermining public support for optimal emissions reductions or by starting down a “slippery slope” towards deployment)? To what extent are policymakers considering geoengineering likely to respond to improved evidence?
  • What type of research is likely to be most helpful for policymakers, and what is the best way to facilitate its creation? Should a philanthropist focus on directly supporting scientific research or on improving the governance of research, or both?
  • How long is it likely to take to obtain the main benefits from a geoengineering research program? How likely are major funders to enter the field over that time horizon?
  • What would the appropriate level of investment in a research program be, and how does this vary based on strategy (e.g. by whether a philanthropist directly funds research versus governance versus lobbying for more research)?

We believe that answering these questions would require a considerably deeper investigation than we have done to date.

5. Our process

We initially decided to investigate solar geoengineering as part of our more general shallow investigation of climate change as a potential philanthropic program area because we had heard about it in the popular press and because the Copenhagen Consensus report on climate change identifies geoengineering as a particularly promising mechanism for responding to the threat of climate change.26

Our initial investigation in mid-2012 consisted of reading a number of articles about geoengineering and speaking with several senior scholars who had written about the issue. We returned to have a few more conversations and to write up this review in the spring of 2013. Public notes are available from our conversations with:

We also attended a portion of the Fourth Interdisciplinary Summer School on Geoengineering at Harvard in August 2013, entitled “Solar Radiation Management: Exploring uncertainties and trade-offs.”

Our research has particularly but not exclusively focused on stratospheric injection of sulfate aerosols, one particular geoengineering approach, because we believe it may be worse-funded, relative to its potential importance, than other aspects of geoengineering research, but this is something we have not investigated deeply and regard as an important issue for further investigation.

6. Sources

Blackstock et al. 2009 Source Archive
Copenhagen Consensus on Climate: Findings of the Expert Panel Source Archive
GAO 2010 Source Archive
IPCC AR4 WGI Source Archive
Keller conversation Source –
Moreno-Cruz and Keith 2012 Source Archive
Parker conversation Source –
Rasch et al. 2008 Source Archive
Ricke, Morgan, and Allen 2010 Source Archive
Robock 2008 Source Archive
Robock, Oman, and Stenchikov 2008 Source Archive
Ross and Matthews 2009 Source Archive
Solar Radiation Management Governance Initiative 2011 Source Archive
Fund for Innovative Climate and Energy Research Source Archive
Expand Footnotes Collapse Footnotes

1.“For example, carbon dioxide (CO2) is exchanged between the atmosphere, the ocean and the land through processes such as atmosphere-ocean gas transfer and chemical (e.g., weathering) and biological (e.g., photosynthesis) processes. While more than half of the CO2 emitted is currently removed from the atmosphere within a century, some fraction (about 20%) of emitted CO2 remains in the atmosphere for many millennia. Because of slow removal processes, atmospheric CO2 will continue to increase in the long term even if its emission is substantially reduced from present levels…. Stabilisation of CO2emissions at current levels would result in a continuous increase of atmospheric CO2 over the 21st century and beyond, whereas for a gas with a lifetime on the order of a century (Figure 1b) or a decade (Figure 1c), stabilisation of emissions at current levels would lead to a stabilisation of its concentration at a level higher than today within a couple of centuries, or decades, respectively. In fact, only in the case of essentially complete elimination of emissions can the atmospheric concentration of CO2 ultimately be stabilised at a constant level. All other cases of moderate CO2 emission reductions show increasing concentrations because of the characteristic exchange processes associated with the cycling of carbon in the climate system.
More specifically, the rate of emission of CO2 currently greatly exceeds its rate of removal, and the slow and incomplete removal implies that small to moderate reductions in its emissions would not result in stabilisation of CO2 concentrations, but rather would only reduce the rate of its growth in coming decades. A 10% reduction in CO2 emissions would be expected to reduce the growth rate by 10%, while a 30% reduction in emissions would similarly reduce the growth rate of atmospheric CO2 concentrations by 30%. A 50% reduction would stabilise atmospheric CO2, but only for less than a decade. After that, atmospheric CO2 would be expected to rise again as the land and ocean sinks decline owing to well-known chemical and biological adjustments. Complete elimination of CO2 emissions is estimated to lead to a slow decrease in atmospheric CO2 of about 40 ppm over the 21st century.” IPCC AR4 WGI FAQ 10.3

2.“Recently, policymakers and scientific organizations have begun to raise questions about a third possible risk-management strategy for climate change—geoengineering. The Royal Society, the United Kingdom’s national academy of sciences, provided the definition of geoengineering that we use in this report: deliberate large-scale interventions in the earth’s climate system to diminish climate change or its impacts.” GAO 2010 pgs 2-3.

3.“The Royal Society identified several SRM approaches that would reflect a small percentage of incoming sunlight back to space, as shown in figure 2. SRM approaches are generally discussed in terms of which sphere they would act upon—space, the atmosphere, or the earth’s surface. Examples of SRM approaches include:

  • Space-based methods. Reflecting or deflecting incoming solar radiation using space-based shielding materials, such as mirrors.
  • Atmosphere-based methods.
    • Stratospheric aerosol injection—injecting reflective aerosol particles into the stratosphere to scatter sunlight back into space. Although it is possible that a wide range of particles could serve this purpose, most attention has been on sulfur particles—partly because temporary global cooling has been produced in the past by volcanic eruptions.
    • Cloud-brightening—adding sea salt or other cloud condensation surfaces to low-level marine clouds to increase their ability to reflect sunlight before it reaches the earth’s surface.
  • Surface-based methods. Increasing the reflectivity of the earth’s land or ocean surfaces through activities such as painting roofs white, planting more reflective crops or other vegetation, or covering desert or ocean surfaces with reflective materials.”

GAO 2010, pg 10.

4.“Examples of ocean-based CDR approaches include:

  • Enhanced removal by physical processes. Enhanced upwelling/downwelling—altering ocean circulation patterns to bring deep, nutrient rich water to the ocean’s surface (upwelling), to promote phytoplankton growth—which removes CO2 from the atmosphere, as described below—and accelerating the transfer of CO2-rich water from the surface of the ocean to the deep-sea (downwelling).
  • Enhanced removal by biological processes. Ocean fertilization— introducing nutrients such as iron, phosphorus, or nitrogen to the ocean surface to promote phytoplankton growth. The phytoplankton removeCO2 from the atmosphere during photosynthesis, and some of the CO2 is transported to the deep ocean as detritus.
  • Enhanced removal by chemical processes. Ocean-based enhanced weathering— accelerating chemical reactions between certain minerals and CO2, which convert the CO2 to a nongaseous state. Methods include adding chemically reactive alkaline minerals, such as limestone or silicates, to the ocean to increase the ocean’s natural ability to absorb and store CO2. (Not shown in figure 1.)

Examples of land-based CDR approaches include:

  • Physical removal by industrial processes. Direct air capture— technology-based processing of ambient air to remove CO2 from the atmosphere. The resulting stream of pure CO2 can either be used or injected into geological formations for storage (geological sequestration).
  • Enhanced removal by biological processes.
    • Biomass energy with CO2 capture and geological sequestration— harvesting vegetation and using it as a fuel source with capture and storage of the resulting emissions in geological formations (geological sequestration).
    • Biomass for sequestration—harvesting of vegetation and sequestering it as organic material by burying trees or crop wastes, or as charcoal (biochar).
    • Afforestation and land-use management—the planting of trees on lands that historically have not been forested, or otherwise managing vegetation cover to maximize CO2 sequestration in soil or biomass.
  • Enhanced removal by chemical processes. Land-based enhanced weathering—accelerating chemical reactions between certain minerals and CO2, which convert the CO2 to a nongaseous state. Methods include mining reactive minerals such as silicates, and then exposing them to the air by spreading them on agricultural fields, or injecting a stream of CO2 into a geological formation of reactive minerals.”

GAO 2010 pgs 7-8.

5.“SWCE with stratospheric aerosols minimally requires: (1) the ability to produce bulk quantities of aerosol particles with appropriate radiative properties; and (2) the ability to disperse and maintain a concentration of those aerosol particles in the stratosphere, ideally with spatial and temporal control of their distribution.
The 1992 National Academy of Science (NAS) review estimated that a basic stratospheric aerosol delivery system: ‘appear[ed] feasible, economical, and capable of [offsetting] as much CO2 equivalent per year as we care to pay for… [and] could probably be put into full effect within a year or two of a decision to do so.’83
Although we did not explore deployment costs in any detail, our order-of-magnitude cost estimates for utilizing aircraft, guns or rockets for aerosol lofting (between ~$10B and ~$30B per year to loft 109 kg per year,84 as calculated in Appendix I) agrees roughly with the NAS and other previous cost estimates.85 Our technical review of aerosol deployment options (see Box 3.1.1.1 and Appendix I) confirms the feasibility of a rapid deployment of sulfate aerosol SWCE intervention. Interventions with more highly engineered particles are also likely feasible, but would need to be evaluated on a case-by-case basis. However, we emphasize that rapid deployment of SWCE prior to comprehensive CS [Climate Science: “concentrating on understanding the response of the climate system to a stratospheric aerosol SWCE intervention”, p. 30] and CM [Climate Monitoring: “focuses on the development of broad climate monitoring capabilities to detect the impact of an SWCE intervention for both evaluation and control purposes”, p. 30] research would induce a climate response laden with uncertainty and risk. These uncertainties and risks would be even greater for engineered particles that are significantly different from those in the volcanic ‘natural experiments’ described above in Box 2.1.2.3.” Blackstock et al. 2009, pg 31.

“Solar Radiation Management (SRM) has two characteristics that make it useful for managing climate risk: it is quick and it is cheap. SRM cannot, however, perfectly offset CO2-driven climate change, and its use introduces novel climate and environmental risks. We introduce SRM in a simple economic model of climate change that is designed to explore the interaction between uncertainty in the climate’s response to CO2 and the risks of SRM in the face of carbon-cycle inertia. The fact that SRM can be implemented quickly, reducing the effects of inertia, makes it a valuable tool to manage climate risks even if it is relatively ineffective at compensating for CO2-driven climate change or if its costs are large compared to traditional abatement strategies. Uncertainty about SRM is high, and decision makers must decide whether or not to commit to research that might reduce this uncertainty. We find that even modest reductions in uncertainty about the side- effects of SRM can reduce the overall costs of climate change in the order of 10%.” Moreno-Cruz and Keith 2012 , abstract.

6.“SRM has a greater potential for doing harm [than CDR] if the science is not thoroughly researched” Solar Radiation Management Governance Initiative 2011 p.8

7.GAO 2010 reports U.S. federal agencies provided $83.5 million in funding for CDR across fiscal years 2009 and 2010, compared to $949,000 for SRM. Table 1, p. 19.

8.“The fact that SRM can be implemented quickly, reducing the effects of inertia, makes it a valuable tool to manage climate risks even if it is relatively ineffective at compensating for CO2-driven climate change or if its costs are large compared to traditional abatement strategies. Uncertainty about SRM is high, and decision makers must decide whether or not to commit to research that might reduce this uncertainty. We find that even modest reductions in uncertainty about the side- effects of SRM can reduce the overall costs of climate change in the order of 10%.” Moreno-Cruz and Keith 2012 , abstract.

9.“Several historic volcanic eruptions—Tambora in 1815 (preceding the “Year Without a Summer” in Northern Europe and the Northeastern US in 1816), Krakatau in 1883, El Chicón in 1982, and Pinatubo in 1991—have been associated with short-term (∼1 to 3 year) subsequent hemispheric cooling. It has been generally accepted that the eruptions caused the cooling (and spectacular sunrises and sunsets) by injecting aerosols into the troposphere and lower stratosphere, and that these effects diminished as the aerosols were removed from the atmosphere by sedimentation or scavenging by hydrometeors.46
As the most recent event, Mt. Pinatubo is also the most thoroughly studied of these major volcanic eruptions.
Figure 3 shows the correlation between increased atmospheric aerosol concentration from the eruption (measured by aerosol optical thickness) and the consequent average global cooling. In 1991, Pinatubo injected about 10 million tons of sulfur (10 TgS) into the stratosphere in the form of SO2 (which is ~20% of annual global tropospheric sulfur emitted as SO2 by the burning fossil fuels47.) Ground based measurements have shown that at peak loading (immediately following the eruption) the shortwave planetary albedo very briefly increased by 0.02 above its “normal” value of about 0.30 as a result of the stratospheric aerosols formed, equating to a ~5% net decrease in the amount of sunlight reaching Earth’s surface.48 At the same time, the peak stratospheric loading also converted an additional ~20% of the total incident sunlight from direct to diffuse illumination (for a clear sky), causing an increase of up to ~300% in the amount of clear sky diffuse sunlight reaching Earth’s surface at some locations.49 As the aerosol loading of the stratosphere diminished to background levels over several years, the corresponding effects also disappeared with no evidence of a lasting impact.50
As a result of the Mt Pinatubo eruption, the 1992 global mean temperature of the Earth decreased by about 0.5 ºC. This cooling has been simulated with a fairly high degree of fidelity in several different climate models, using estimates of sulfur injection or the radiative effects of that sulfur as the forcing variables. However, the thermal inertia due to the oceans’ large heat capacity smoothes and delays the climate response to a change in radiative forcing. As a consequence, had the Pinatubo stratospheric aerosol loading been sustained indefinitely, the cooling would have been some six-times greater than the transient 0.5ºC observed.
This “natural experiment” provides strong evidence that stratospheric aerosols (and sulfate aerosols in particular) would diminish absorption of solar radiation by the Earth, and that the lifetime of the aerosols in the stratosphere is of the order of one to two years (although there can be substantial variation depending on aerosol particle size, latitude and altitude of injection51.) Moreover, these natural experiments also illuminate the possible unexpected consequences of injecting aerosols into the stratosphere. For example, the eruption is thought to have diminished stratospheric ozone by about 3% on average (about 5% near the poles and 2% near the equator), while land plants are thought to have grown more vigorously after the eruption due to the increase in diffuse sunlight. (For example, Gu et al (2003)52 have suggested that the increase in diffuse sunlight allowed more light to penetrate forest canopies, more than offsetting the effects of reduced direct and total sunlight.) ” Blackstock et al. 2009, pg 13.

10.“It appears to be technically feasible to engineer an increase in albedo, a planetary brightening, as a means to offset the warming caused by carbon dioxide (CO2) and other greenhouse gases through Solar Radiation Management (SRM) (Keith and Dowlatabadi 1992; Keith 2000; Crutzen 2006; Shepherd et al. 2009). However, the cooling produced by SRM does not exactly compensate for the warming caused by CO2-driven climate change; and any particular method of SRM will no doubt entail other risks and side-effects (e.g. Bala et al. 2008; Ricke et al. 2010). Nevertheless, SRM may be a useful tool to mange climate risks (Wigley 2006).” Moreno-Cruz and Keith 2012 , pgs 1-2.

“Two strategies to reduce incoming solar radiation—stratospheric aerosol injection as proposed by Crutzen and space-based sun shields (i.e., mirrors or shades placed in orbit between the sun and Earth)—are among the most widely discussed geoengineering schemes in scientific circles. While these schemes (if they could be built) would cool Earth, they might also have adverse consequences.” Robock 2008.

“Although using solar-radiation management (SRM) to lower the average planetary temperature is not a new idea7, it has recently become the focus of greater attention. Several prominent climate scientists have raised it as a feasible, and potentially necessary, strategy for avoiding catastrophic impacts of climate change (for example, rapid sea-level rise, rapid and large increase in emission of methane from high latitudes)1–3. Research on SRM is still in its infancy, but so far modelling studies suggest that, although significant hydrological anomalies would be associated with stratospheric albedo modification, even at the regional level, such a geoengineered world bears much closer resemblance to a low-CO2 world, than either world bears to an unmodified high-CO2 world4–6 . Increasing planetary albedo does not mitigate impacts directly related to elevated CO2 , such as acidification of the surface ocean8 .” Ricke, Morgan, and Allen 2010, pg 537.

11.“2. Continued ocean acidification. If humans adopted geoengineering as a solution to global warming, with no restriction on continued carbon emissions, the ocean would continue to become more acidic, because about half of all excess carbon dioxide in the atmosphere is removed by ocean uptake. The ocean is already 30 percent more acidic than it was before the Industrial Revolution, and continued acidification threatens the entire oceanic biological chain, from coral reefs right up to humans.” Robock 2008, pg 15.

12.“Recent research has highlighted risks associated with the use of climate engineering as a method of stabilizing global temperatures, including the possibility of rapid climate warming in the case of abrupt removal of engineered radiative forcing. In this study, we have used a simple climate model to estimate the likely range of temperature changes associated with implementation and removal of climate engineering. In the absence of climate engineering, maximum annual rates of warming ranged from 0.015 to 0.07 °C/year, depending on the model’s climate sensitivity. Climate engineering resulted in much higher rates of warming, with the temperature change in the year following the removal of climate engineering ranging from 0.13 to 0.76 °C. High rates of temperature change were sustained for two decades following the removal of climate engineering; rates of change of 0.5 (0.3,0.1) °C/decade were exceeded over a 20 year period with 15% (75%, 100%) likelihood. Many ecosystems could be negatively affected by these rates of temperature change; our results suggest that climate engineering in the absence of deep emissions cuts could arguably constitute increased risk of dangerous anthropogenic interference in the climate system under the criteria laid out in the United Nations Framework Convention on Climate Change.” Ross and Matthews 2009.

13.“Effects on regional climate. Geoengineering proponents often suggest that volcanic eruptions are an innocuous natural analog for stratospheric injection of sulfate aerosols. The 1991 eruption of Mount Pinatubo on the Philippine island of Luzon, which injected 20 megatons of sulfur dioxide gas into the strato- sphere, produced a sulfate aerosol cloud that is said to have caused global cool- ing for a couple of years without adverse effects. However, researchers at the National Center for Atmospheric Research showed in 2007 that the Pinatubo eruption caused large hydrological responses, including reduced precipitation, soil moisture, and river flow in many regions.5 Simulations of the climate response to volcanic eruptions have also shown large impacts on regional climate, but whether these are good analogs for the geoengineering response requires further investigation.
Scientists have also seen volcanic eruptions in the tropics produce changes in atmospheric circulation, causing winter warming over continents in the Northern Hemisphere, as well as eruptions at high latitudes weaken the Asian and African monsoons, causing reduced precipitation.6 In fact, the eight-month- long eruption of the Laki fissure in Iceland in 1783–1784 contributed to famine in Africa, India, and Japan.
If scientists and engineers were able to inject smaller amounts of stratospheric aerosols than result from volcanic eruptions, how would they affect summer wind and precipitation patterns? Could attempts to geoengineer isolated regions (say, the Arctic) be confined there? Scientists need to investigate these scenarios. At the fall 2007 American Geophysical Union meeting, researchers presented preliminary findings from several different climate models that simulated geoengineering schemes and found that they reduced precipitation over wide regions, condemning hundreds of millions of people to drought.” Robock 2008, pg 15.

“We find that if there were a way to continuously inject SO2 into the lower stratosphere, it would produce global cooling. Tropical SO2 injection would produce sustained cooling over most of the world, with more cooling over continents. Arctic SO2 injection would not just cool the Arctic. Both tropical and Arctic SO2 injection would disrupt the Asian and African
summer monsoons, reducing precipitation to the food supply for billions of people. These regional climate anomalies are but one of many reasons that argue against the implementation of this kind of geoengineering.” Robock, Oman, and Stenchikov 2008, abstract.

14.“One additional risk associated with geoengineering strategies is a potential for conflict. This is because geoengineering might “succeed” for some, while causing negative effects for others. Who would decide about an appropriate level of geoengineering? Would the decision be arrived at in a civil way?” Keller conversation.

“18. Control of the thermostat. Even if scientists could predict the behavior and environmental effects of a given geoengineering project, and political leaders could muster the public support and funding to implement it, how would the world agree on the optimal cli- mate? What if Russia wants it a couple of degrees warmer, and India a couple of degrees cooler? Should global climate be reset to preindustrial temperature or kept constant at today’s reading? Would it be possible to tailor the climate of each region of the planet independently without affecting the others? If we proceed with geoengineering, will we provoke future climate wars?” Robock 2008, pg 17.

15.“20. Unexpected consequences. Scientists cannot possibly account for all of the complex climate interactions or pre- dict all of the impacts of geoengineering. Climate models are improving, but scientists are discovering that climate is changing more rapidly than they predicted, for example, the surprising and un- precedented extent to which Arctic sea ice melted during the summer of 2007. Scientists may never have enough confidence that their theories will predict how well geoengineering systems can work. With so much at stake, there is reason to worry about what we don’t know.” Robock 2008, pg 17.

16.“The primary loss mechanism for sulphur species from the stratosphere is believed to be the sedimentation of the aerosol particles. Particle sedimentation is governed by Stokes’ equation for drag corrected to compensate for the fact that in the stratosphere at higher altitudes the mean free path between air molecules can far exceed the particle size, and particles fall more rapidly than they would otherwise. The aerosol particles settle out (larger particles settle faster), gradually entering the troposphere, where they are lost via wet and dry deposition processes.
Examples of the nonlinear relationships between SO2 mass injection, particle size and visible optical depth as a function of time assuming idealized dispersion can be found in Pinto et al. (1998). These are detailed microphysical simulations, although in a one-dimensional model with specified dispersion. The rate of dilution of injected SO2 is critical owing to the highly nonlinear response of particle growth and sedimentation rates within expanding plumes; particles have to be only 10 mm or less to fall rapidly, which greatly restricts the total suspended mass, optical depth and infrared effect. The mass limitation indicates that 10 times the mass injection (of say Pinatubo) might result in only a modestly larger visible optical depth after some months.” Rasch et al. 2008, pg 4012.

17.“We find that if there were a way to continuously inject SO2 into the lower stratosphere, it would produce global cooling. Tropical SO2 injection would produce sustained cooling over most of the world, with more cooling over continents. Arctic SO2 injection would not just cool the Arctic. Both tropical and Arctic SO2 injection would disrupt the Asian and African summer monsoons, reducing precipitation to the food supply for billions of people. These regional climate anomalies are but one of many reasons that argue against the implementation of this kind of geoengineering.” Robock, Oman, and Stenchikov 2008, abstract.

18.“Moreover, these natural experiments also illuminate the possible unexpected consequences of injecting aerosols into the stratosphere. For example, the eruption is thought to have diminished stratospheric ozone by about 3% on average (about 5% near the poles and 2% near the equator), while land plants are thought to have grown more vigorously after the eruption due to the increase in diffuse sunlight.” Blackstock et al. 2009, pg 13.

19.“How to respond to climate change tail-area events such as climate sensitivity? One potential response, analyzed by some, is geoengineering. For example, increasing the aerosol concentration in the stratosphere would increase the Earths albedo and cool, on average, the Earth’s surface. However, this geoengineering approach can have potentially severe negative side effects, such as abrupt warming in case the geoengineering is stopped or changing precipitation patterns. One additional risk associated with geoengineering strategies is a potential for conflict. This is because geoengineering might “succeed” for some, while causing negative effects for others. Who would decide about an appropriate level of geoengineering? Would the decision be arrived at in a civil way?” Keller conversation.

20.Solar Radiation Management Governance Initiative 2011.

21.GAO 2010:

Table 1, pg 19.

“We identified approximately $100.9 million in geoengineering-related funding across USGCRP agencies in fiscal years 2009 and 2010, with about $1.9 million of this amount related to research directly investigating a particular geoengineering approach. The other roughly $99 million was related to research concerning conventional mitigation strategies that could be applied directly to a particular geoengineering approach or basic science that could be applied generally to geoengineering.” pg 18.

22.Parker conversation.

23.“The Fund for Innovative Climate and Energy Research (FICER) exists to accelerate the innovative development and evaluation of science and technology to address carbon dioxide and other greenhouse gas emissions and their environmental consequences…Grants for research are provided to the University of Calgary from gifts made by Mr. Bill Gates from his personal funds…Since its inception in 2007, FICER has given out grants to 13 research projects and various scientific meetings totaling $4.6 million.” Fund for Innovative Climate and Energy Research.

“David Keith and Ken Caldeira and a couple of other people receive money for research from Bill Gates through the Fund for Innovative Climate and Energy Research.” Parker conversation.

24.We augmented Andrew Parker and David Keith’s list by searching for funding information for other geoengineering research programs we were aware of, incorporating U.S. funding information, and requesting further input from the public geoengineering Google group. (The two threads on the topic are here and here.)

25.For instance, there are three projects that we believe have funding, but for which we do not have any funding info, which are currently counted as providing $0.

26.“The Expert Panel highly recommends research into climate engineering strategies. Of the strategies that the Expert Panel considered, solar radiation management methods – especially marine cloud whitening – appear to show the greatest promise. The Expert Panel notes that, compared with other solution categories, geo-engineering reduces the risk of ‘pork barrel politics’ and lowers transaction costs. In the case of a low-probability, high-impact situation, climate engineering could play a crucial role because of its speed. The Expert Panel notes that a short-term focus on research into climate engineering would be beneficial in establishing the limitations and risks of this technology, and the identification of these should happen sooner rather than later. They find that research into air capture would be useful as air capture appears to have potential as a backstop technology. ” Copenhagen Consensus on Climate: Findings of the Expert Panel.