Climate Intervention: Reflecting Sunlight to Cool Earth (2015)

CHAPTER FIVE

Way Forward

Most discussions of the climate change challenge focus on addressing greenhouse gas emissions and their impacts: for example, the scale of infrastructure that would need to be rebuilt in order to curtail emissions in a meaningful way; the expense of carbon dioxide removal (CDR), carbon capture and sequestration (CCS), and other techniques; and the major social disruption of adaptation for a global population concentrated near sea level. Against that backdrop, the issues surrounding albedo modification stand in stark contrast. By comparison, increasing Earth’s reflectance of global radiation, at least approximately, requires no major retooling of the energy infrastructure, is relatively easy to accomplish (e.g., could be undertaken by a subnational organization), and has lower direct costs when compared to either mitigation or adaptation. The committee therefore focused on what scientific knowledge would be needed to decide whether albedo modification could be deployed responsibly, safely, effectively, and with predictable and desirable outcomes.

There are both theoretical and observational reasons to believe that albedo modification has the potential to act rapidly to offset some of the consequences of global warming at a relatively low cost, albeit with high risks of unintended consequences. If less energy from the Sun is absorbed by the Earth system, the surface of Earth will cool on average. This is clearly demonstrated by the history of past volcanic eruptions. For example, the eruption of Mount Pinatubo in the Philippines in 1991 injected large amounts of sulfur dioxide into the stratosphere that increased Earth’s albedo and decreased the amount of sunlight absorbed, causing the atmosphere to cool an estimated 0.3°C over a period of 3 years. Other eruptions, such as Tambora in 1815, caused global climatic anomalies that led to widespread crop failure and famine. Overall, it is difficult to compare the injection of an aerosol plume from a single volcanic eruption to repeated aerosol injections that result in a more sustained albedo modification.

Modeling studies have also shown that large amounts of cooling, equivalent in scale to the predicted warming due to doubling the CO₂ concentration in the atmosphere, can be produced by the introduction of tens of millions of tons of aerosols into the stratosphere. Increasing the reflectivity of low clouds is another strategy that could cool the planet within a year or two from the onset of the intervention. Although there are many reasons to be cautious in interpreting model results, climate simulations can extend scientific understanding of albedo modification to timescales beyond those observed with volcanic eruptions. Preliminary modeling results suggest that albedo

modification may be able to counter many of the damaging effects of high greenhouse gas concentrations on temperature and the hydrological cycle and reduce some impacts to sea ice. Models also strongly suggest that the benefits and risks will not be uniformly distributed around the globe.

Feasibility studies suggest that it may be technically possible to introduce aerosols into the stratosphere that can produce significant cooling (on the order of 1 W/m² or larger) with little or no major technological innovations required. Direct costs of deployment of a stratospheric aerosol layer of sufficient magnitude to offset global mean radiative forcing of CO₂ have been estimated to be orders of magnitude less than the cost of decarbonizing the world’s economy. Although these cost estimates do not include an appropriate monitoring system or indemnification for damages from albedo modification actions, they are small enough that decisions are likely to be based primarily on considerations of potential benefits and risks, and not primarily on the basis of direct cost.

Despite some initial research advances discussed in Chapter 3 of this report, much remains unknown about albedo modification. Proposed albedo modification approaches introduce environmental risks and political ramifications associated with intended and unintended consequences; these risks are not well understood and generally unquantified. These gaps in understanding present significant barriers and risks to deploying the range of albedo modification strategies under consideration. As such, the committee identifies a set of measured steps intended to improve our understanding of albedo modification, while underscoring that other efforts to mitigate climate change should remain the primary focus.

ALBEDO MODIFICATION WITHIN A PORTFOLIO OF CLIMATE RESPONSES

Avoiding greatly increased risk of damage from climate change will require a portfolio of response strategies. The deployment of any climate response strategy requires consideration of many factors: How effective is the strategy at achieving predictable and desirable outcomes? How much does the strategy cost to implement at a scale that matters? What are the risks for unintended consequences and opportunities for co-benefits? What governance mechanisms are in place to ensure safety, equity, and other ethical aspects are considered? The committee evaluated CDR and albedo modification within this broader portfolio of climate response.

Despite the growing recognition of these risks, global society has yet to adequately implement the well-known strategies for mitigating climate change (e.g., reducing GHG emissions by conserving energy and developing carbon-free energy sources).

The result may be circumstances in the future that are sufficiently adverse that intervention in the climate system to reverse or reduce these effects may be deemed necessary. Such climate intervention could be achieved through two classes of strategies—albedo modification and carbon dioxide removal. These strategies carry very different costs and risks (see Table 5.1).

TABLE 5.1 Overview of General Differences between Carbon Dioxide Removal Proposals and Albedo Modification Proposals

NOTE: GHG stands for greenhouse gases released by human activities and natural processes and includes carbon dioxide, methane, nitrous oxide, chlorofluorocarbons, and others. The committee intends to limit discussion to proposals that raise the fewest problematic issues, thus excluding ocean iron fertilization from the CDR list. Each statement may not be true of some proposals within each category.

To be effective, carbon dioxide removal should be pursued collectively by a number of international participants. In contrast, albedo modification could be undertaken unilaterally. The environmental and climate system consequences of albedo modification are as yet poorly characterized, and the governance issues are complex as well. Some forms of carbon dioxide removal also involve environmental risk, for example from changes in ocean ecology or induced seismicity from underground injection of CO₂ or from the use of inappropriate reservoirs. The barriers to deployment of CDR approaches are largely related to high costs, slow implementation, limited capacity, and policy considerations. As is true for mitigation and adaptation, society must take advantage as soon as possible of CDR strategies that can help avoid the worst effects of warming. We will lose this opportunity if society delays in research and development to lower the technical barriers to efficacy and affordability of CDR for deployment.

One of the main findings is that albedo modification does not address in any way the fundamental cause of climate warming: excess greenhouse gases in the atmosphere. Thus, deployed in isolation, albedo modification has no exit strategy. Using the simple home heating analogy introduced in Chapter 1, if the blinds in the overinsulated house were made of some fragile substance that deteriorated over time, they would need to be frequently replaced and kept drawn indefinitely because albedo modification alone only masks the problem. If sulfate aerosols were injected into the stratosphere, interruption of the aerosol injection would return the planet rather rapidly to the state that it would have been in had there been no intervention, risking dramatic ecologic and agronomic impacts. In addition, albedo modification does nothing to address ocean acidification, another impact of greenhouse gas emissions that is predicted to have serious consequences for ocean ecosystems. For these reasons, albedo modification is no substitute for mitigation. Hence, in order to avoid serious longer-term problems, any future decision to embark on aerosol injection should be paired with efforts to mitigate greenhouse gas emissions, remove carbon dioxide from the atmosphere, or both. Indeed, the degree to which those mitigation and CDR strategies are successful would affect how aggressively and for how long albedo modification would need to be sustained.

A further risk involves the deployment of albedo modification without adequate development of emissions mitigation and carbon dioxide removal as viable exit strategies. If albedo modification were to be used to reduce peak warming significantly or to offset the effects of substantial additional CO₂ emissions, then there is no good exit strategy unless economically viable CDR technologies become available. For this reason development of CDR should go hand in hand with consideration of the scope of safe application of albedo modification techniques.

As discussed in Chapters 2 and 3, if albedo modification were to be deployed, the albedo-modified world would not constitute a return to the preindustrial low-CO₂ state. It would be an altered climate state that, like the unmodified high-CO₂ state, has no analogue within preindustrial times spanning the rise of human civilization. Models can help inform judgments about whether the albedo-modified state might be preferable to an unmodified high-CO₂ state. According to various simple statistics, it can be said that the albedo-modified state is in some sense “closer” (in terms of mean surface temperature and precipitation) to the preindustrial state than is the unmodified high-CO₂ state. But simple statistics are not necessarily the ones that will prove most salient to those who may face the need to make a decision about the amount of albedo modification to deploy, or to those affected by the decisions. How much albedo modification is considered optimal will vary from region to region, and trade-offs between regions will be difficult to make. How should disparities in wealth and ability to adapt to climate change be taken into account, or the dependence of some regions on critical circulations like monsoons? The subject of metrics for use in the decision process is an area that requires much further research. Although modeling results can help inform judgments of how much albedo modification to deploy, decisions will ultimately involve values and relative acceptability of various kinds of risks—factors that are outside the scope of science. But one thing is certain: the more albedo modification that is deployed, the greater the deviation of the modified state from the preindustrial state, and the greater the risks. This underscores a recurring theme in this report, that the potential availability of albedo modification in the portfolio of responses to global warming does not constitute a license for unbounded CO₂ emissions.

It is the committee’s assessment that there is no substitute for dramatic reductions in emissions of CO₂ and other greenhouse gases to mitigate the negative consequences of climate change at the lowest probability of risk to humanity. Mitigation, although technologically feasible, has been difficult to achieve for political, economic, and social reasons that may persist well into the future. Whatever we do as a society, some adaptation will be necessary, but the degree to which it is needed depends on the amount of climate change and the degree to which future emissions of CO₂ and other greenhouse gases are reduced. Although there are ongoing efforts at climate adaptation in many communities, both humans and ecosystems face substantial challenges in adapting to the varied impacts of climate change over the coming century. For that reason, it is prudent to examine other options for limiting the risks from climate change, even as mitigation and adaptation remain the primary emphasis.

Recommendation 1: Efforts to address climate change should continue to focus most heavily on mitigating greenhouse gas emissions in combination with adapting to the impacts of climate change because these approaches do not present poorly defined and poorly quantified risks and are at a greater state of technological readiness.

ALBEDO MODIFICATION PRESENTS POORLY UNDERSTOOD RISKS

Proposed albedo modification approaches introduce environmental, ethical, social, political, economic, and legal risks associated with intended and unintended consequences that could differ in various parts of the world. Some of the risks from albedo modification can be anticipated. Observed side effects from volcanic eruptions include stratospheric ozone loss, changes to precipitation (both amounts and patterns), and likely increased growth rates of forests caused by an increase in diffuse solar radiation. Because volcanic eruptions are brief events, they are not perfect analogues for the full effects of sustained albedo modification deployment. Models also indicate that there would be consequences of concern (e.g., some ozone depletion and a weakening of global precipitation). Albedo modification does nothing to reduce the buildup of atmospheric CO₂, which is already changing the makeup of terrestrial ecosystems and causing ocean acidification and associated impacts on oceanic ecosystems.

Another risk is that the success of albedo modification could reduce the incentive to curb anthropogenic CO₂ emissions and that albedo modification would instead be deployed with ever increasing intensity. The committee considers it to be irrational and irresponsible to implement sustained albedo modification without also pursuing emissions mitigation, carbon dioxide removal, or both. Nonetheless, climate models indicate that the combination of large-scale albedo modification with large-scale CO₂ increases could lead to a climate with different characteristics than the current climate. Without reductions in CO₂ levels in the atmosphere, the amount of albedo modification required to offset the greenhouse warming would continue to escalate for millennia, generating greater risks of negative consequences if it is terminated for any reason (e.g., undesirable side effects, political unrest, and cost), because the effects of the forcing from the CO₂ concentrations present at the time of termination will be rapidly revealed.

It is not possible to quantify or even identify other environmental, social, political, legal, and economic risks at this time, given the current state of knowledge about this complex system. The uncertainties in modeling of both climate change and the consequences of albedo modification make it impossible today to provide reliable, quantita-

tive statements about relative risks, consequences, and benefits of albedo modification to the Earth system as a whole, let alone benefits and risks to specific regions of the planet. To provide such statements, scientists would need to understand the influence of various possible activities on both clouds and aerosols, which are among the most difficult components of the climate system to model and monitor. Introducing albedo modification at scales capable of substantial reductions in climate impacts of future higher CO₂ concentrations would be introducing a novel situation into the Earth system, with consequences that are poorly constrained at present.

Gaps in our observational system also present a critical barrier to responsible deployment of albedo modification strategies. Currently, observational capabilities lack the capacity to monitor the evolution of an albedo modification deployment (e.g., the fate of the aerosols and secondary chemical reactions), its effect on albedo, or its environmental effects on climate or other important Earth systems. An international forum for cooperation and coordination on any sort of climate intervention discussion and planning is lacking.

Given the enormous uncertainties outlined in the previous chapters, what is known today about the climate system, and the alternatives available to humankind to slow or reverse the buildup of greenhouse gases, this committee does not believe that there is sufficient knowledge of the proposed albedo modification techniques to advocate the deployment of albedo modification at this time.

Recommendation 3: Albedo modification at scales sufficient to alter climate should not be deployed at this time. ¹

• Albedo modification strategies for offsetting climate impacts of high CO₂ concentrations carry risks that are poorly identified in their nature and unquantified.
• Deployment at climate-altering amplitudes should only be contemplated armed with a quantitative and accurate understanding of the processes that participate in albedo modification. This understanding should be demonstrated at smaller scales after intended and unintended impacts to the Earth system have been explicitly documented, both of which are lacking.
• There is significant potential for unanticipated, unmanageable, and regrettable consequences in multiple human dimensions from albedo modification at

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¹ Note that Recommendation 2 involves CDR only. It is found in the Summary of this report and is discussed in more detail in Chapter 5 of the companion report, Climate Intervention: Carbon Dioxide Removal and Reliable Sequestration.

• climate-altering scales, including political, social, legal, economic, and ethical dimensions.

• Current observing systems are insufficient to quantify the effects of any intervention at present. If albedo modification at climate-altering scales were ever to occur, it should be accompanied by an observing system that is appropriate for assessing the impacts of the deployment and informing subsequent actions.
• If research and development on albedo modification were to be done at climate-altering scales, it should be carried out only as part of coordinated national or international planning, proceeding from smaller, less risky to larger, more risky projects; more risky projects should be undertaken only as information is collected to quantify the risks at each stage.

THE NEED FOR MORE RESEARCH ON ALBEDO MODIFICATION

As described in Chapter 4, the issue of “moral hazard” is a potentially serious risk associated with any decision to pursue research on albedo modification. Several authors have examined this issue, but overall, the scholarship on this topic is relatively limited. The early results have been mixed thus far on the severity of these risks, including studies that argue there is a low risk (Kahan et al., 2014; Reynolds, 2014) and those that argue it is quite high (Lin, 2013b). Early empirical evidence shows that geoengineering is likely to pose a moral hazard for some people much more than others (Corner and Pidgeon, 2014). The moral hazard risk has potentially kept more albedo modification research from being done up to now, as described by Morgan et al. (2013):

With an appreciation of the severity of these potential risks, the committee argues that, as a society, we have reached a point where the severity of the potential risks from climate change appears to outweigh the potential risks from the moral hazard associated with a suitably designed and governed research program. Overall, it is important to understand whether and to what extent albedo modification techniques are viable (Keith et al., 2010; Morgan et al., 2013). Furthermore, there is the possibility that some actor (person, organization, country) may unilaterally decide to apply one of these techniques without sufficient knowledge about its potential unintended consequences, thus putting the world at risk (Morgan et al., 2013).

Research on albedo modification techniques would allow the scientific community to learn more about the risks and benefits of these proposed approaches, which could better inform societal decisions without the scale of risks associated with deployment. One of the foremost goals of research on albedo modification should be to understand how viable these techniques are, including a better understanding of the feasibility, verifiability, consequences (intended and unintended), and efficacy of the various proposed albedo modification strategies. Indeed, current implementation options are clearly crude and method development would provide less risky options for society and state actors.

To date, very limited research has been undertaken to gain insight about whether, and how well, strategies for albedo modification might work and the intended and unintended consequences of such strategies. For example, federal investments specifically addressing albedo modification or carbon dioxide removal have been “modest” (Bracmort and Lattanzio, 2013). The U.S. Global Change Research Program (USGCRP) reported that the annual U.S. budget for climate change research exceeded $4 billion for fiscal years 2009 and 2010 (USGCRP, 2010). Of that, the U.S. Government and Accountability Office (GAO) reported about $100 million was spent during the same period on research activities “relevant to geoengineering” (GAO, 2010) and indicated that the majority of that budget focused on either mitigation strategies (e.g., carbon capture and sequestration) or basic science, and estimated that about $2 million were directed to “albedo modification and less conventional CDR approaches,” so less than 0.1% of the U.S. climate change budget focused on the strategies discussed in our report.

Much of the required research on albedo modification overlaps considerably with basic scientific research that is needed to improve understanding of the climate system. Most notably, research on clouds and aerosols has the potential to advance climate research while also contributing to understanding of the effects and unintended impacts of albedo modification approaches. A number of actions can promote such “multiple-benefit research”—research that can contribute to a better understanding of the viability of albedo modification techniques and a better understanding of basic climate science—such as maintaining continuous measurements of the top-of-atmosphere radiation budget, developing improved space-borne instruments to discriminate the processes leading to changes in Earth’s radiation budget, monitoring ocean-atmosphere energy exchange through programs such as the Argo float system, and improving methods of data assimilation and data analysis to make optimal use of observations in detecting and attributing albedo and climate responses.

Of necessity, much of this multiple-benefit research would be part of a comprehensive climate research portfolio or research program aimed at other purposes (e.g., effect of

volcanic eruptions on aerosols). Such research projects and data sets should be identified for their multiple benefits and prioritized to aid in understanding effectiveness and consequences of albedo modification. In addition, there is research that is specific to learning about albedo modification techniques (e.g., mechanisms for delivering sulfate aerosol precursors to the stratosphere) that would not fit under this description of multiple benefit and is therefore unlikely to be supported without a research program focused on climate intervention. The committee argues that these research topics specific to albedo modification should also be identified and prioritized as part of a larger research effort on albedo modification, and they should be tasked to the relevant federal agencies for possible support within existing or expanded programs. Focusing on basic science related to albedo modification will hopefully minimize fears that resources are being used to support a potential near-term albedo modification deployment plan. Box 5.1 lists a number of important research areas.

The development of a research program on albedo modification may involve modeling, field research, satellite measurements, and laboratory studies. As such, this research will likely involve the efforts of multiple agencies, laboratories, and universities. It would be useful to have some coordination among the research efforts of these multiple organizations to avoid duplication and ensure that the most important questions are addressed. Although other organizations could perhaps fill this coordinating role, the USGCRP is the most obvious possibility and is a logical choice given the overlap of many research topics with the climate change research agenda. USGCRP coordinates and integrates federal research on changes in the global environment and their implications for society.² Thirteen federal departments and agencies participate in the USGCRP and also interact with a wide variety of related groups, including international organizations; national, state, tribal, and local governments; businesses; professional and other nonprofit organizations; the scientific community; and the public.

Any future decisions surrounding the use of albedo modification will need to be based on more than just scientific theories. Research results on efficacy, environmental impacts, and unintended consequences will need to be integrated with social, ethical, political, and legal discussions. A governance structure for albedo modification research will be needed within the United States and likely coordinated internationally before field studies of any significant magnitude are attempted. U.S. participation in “scenario planning” can be extremely valuable for identifying gaps in planning and understanding and thus can guide future science investments. Interdisciplinary research is also needed concerning understanding issues associated with deployment of albedo modification should it ever be deemed desirable. How should leaders weigh

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² See http://www.globalchange.gov/about/overview.

Scientists have explored only a few issues relevant to climate intervention by albedo modification to date. More knowledge about particular climate processes and better climate models are needed. Climate models—a computational tool used to synthesize knowledge of the climate system—are incomplete and approximate representations of the real world. Climate models require more development before they can be used to quantify the risks in projections of climate impacts from albedo modification. Improvement may come from climate models and through theory, field studies, detailed process modeling, and laboratory experiments. The following areas would benefit from more attention:

Clouds, aerosols, and cloud-aerosol interactions are some of the more important climate components that need attention and improvement, because these basic Earth system components are central to the albedo modification strategies that appear most promising. Viability of particular strategies cannot be assessed until there is confidence in treatment of these components in climate models; many consequences that would arise from employing a strategy cannot be quantified without an accurate characterization of these important climate features. Work in this area would also be relevant to climate and climate change problems generally.

Regular and systematic evaluation of simulated albedo modification strategies would help in characterizing model uncertainty and climate consequences and risks. Models should be compared carefully with each other with more attention to understanding the reasons for model differences when an albedo modification scenario is employed.

The impacts of albedo modification on a variety of climate features that have not yet been examined, or have only been examined superficially to date, should be studied in more detail. It would be useful to explore and characterize consequences to these features (e.g., El Niño–Southern Oscillation, ecosystems) and to have the scientific community identify other possible consequences.

It would be useful to compare climate model process representations to more detailed and accurate “process models” that are too expensive to afford for climate change calculations. It would also be useful to systematically compare both global models and expensive process models to existing field experiment data and satellite data relevant to stratospheric aerosol and marine cloud-brightening strategies.

Small field studies would be useful that explore issues that are as yet poorly understood but influence the viability of candidate albedo modification strategies. Some studies could operate using “measurements of opportunity” by making measurements downwind of volcanoes or polluters. But there are issues that can be understood more thoroughly, and more easily via field studies making controlled emissions to the atmosphere (see Chapter 3), through injections of aerosols in the lower stratosphere or below marine clouds. The committee feels strongly that large experiments with the potential to influence climate are not appropriate and would need strict governance to be considered further. Small-scale field studies designed to clarify the mechanisms important to a particular strategy may be useful, provided they fit within the context of current research structures.

the relative risks of an immediate climate crisis versus the need to maintain albedo modification over many centuries? How could society design institutions capable of maintaining such an enormous undertaking over that timescale?

Recommendation 4: The committee recommends an albedo modification research program be developed and implemented that emphasizes multiple-benefit research that also furthers basic understanding of the climate system and its human dimensions.

• If future decision makers reach a point that they are contemplating adopting albedo modification, or assessing such an adoption by others, they will need to assess a wide range of factors, both technical and social, to compare the potential benefits and risks of an albedo modification deployment. These factors would include an assessment of the expected climate with only emissions reductions and CDR (including risks from continued greenhouse gas emissions with no intervention), the expected effects from starting albedo modification, the expected effects from terminating albedo modification, ethical issues, and social responses.
• The goal of the research program should be to improve understanding of the range of climate and other environmental effects of albedo modification, as well as understanding unintended impacts.
• U.S. research on albedo modification should be supported by a number of scientific research agencies in a coordinated manner. The U.S. Global Change Research Program could provide valuable oversight and coordination to ensure that the aspects of the research that are of benefit to both basic climate science and understanding of albedo modification are taken into account.
• Small-scale field experiments with controlled emissions may for some situations with some forms of intervention be helpful in reducing model uncertainties, validating theory, and verifying model simulations in different conditions. Experiments that involve release of gases or particles into the atmosphere (or other controlled perturbations) should be well enough understood to be benign to the larger environment, should be conducted at the smallest practical scales, should be designed so as to pose no significant risk, and should be planned subject to the deliberative process outlined in Recommendation 6.

Recommendation 5: The committee recommends that the United States improve its capacity to detect and measure changes in radiative forcing and associated changes in climate.

• A new generation of short-wavelength (albedo) and long-wavelength (outgoing infrared) space-based instruments should be developed and deployed that can measure radiative forcing with an accuracy of better than 1 W/m², including hyperspectral instruments that could improve discrimination of the processes that cause changes in radiative forcing. Such instruments would significantly improve understanding of the effects of clouds and stratospheric aerosols on climate, improve the ability to predict the effects of albedo modification, and provide an ability to detect large-scale albedo modification by rogue actors.
• An observational capability should be developed to make better use of future major volcanic eruptions to improve understanding of the effects of stratospheric aerosols on climate. This would involve space-based sensors and rapidly deployable ground-based and airborne sensors for monitoring stratospheric aerosols.

GOVERNANCE CONSIDERATIONS

Some types of research into intentional albedo modification will likely have legal, ethical, social, political, economic, and other important ramifications. Albedo modification research must abide by existing laws, regulations, and policies that apply to research broadly and its impacts on worker safety, the environment, and human and animal welfare. However, such research is not specifically addressed by any federal laws or regulations.

Given the perceived and real risks associated with some types of albedo modification research, open conversations about the governance of such research, beyond the more general research governance requirements, could encourage civil society engagement in the process of deciding the appropriateness of any research efforts undertaken.

“Governance” is not a synonym for “regulation.” Depending on the types and scale of the research undertaken, appropriate governance of albedo modification research could take a wide variety of forms, ranging from the direct application of existing scientific research norms, to the development of new norms, to mechanisms that are highly structured and extensive. The most appropriate type of governance structures for albedo modification research will potentially depend on the nature and scale of that research. It is not the purview of the committee to make an assessment or recommendation of the appropriate structure. However, the committee does believe that governance considerations should be targeted at ensuring civil society involvement in decision making through a transparent and open process. It should focus on en-

abling safe and useful research on the viability and impacts of albedo modification strategies (e.g., the efforts of the Solar Radiation Management Governance Initiative³). Ultimately, the goal is to ensure that the benefits of the research are realized to inform civil society decision making, the associated challenges are well understood, and risks are kept small.

To date most investigations of the efficacy and likely impacts, environmental and otherwise, of albedo modification have been confined to computer simulations and observations of volcano, ship track, and other analogues. Such work will and should continue and it can provide additional understanding that can inform future decisions on whether albedo modification can safely address some of the worst impacts of climate change without other impacts that are unacceptable. However, in addition to these approaches, some controlled emissions experiments on smaller scales (e.g., estimated forcing well below natural variability) in the environment may be proposed to understand fundamental processes that may be complex and poorly characterized at present.

Examples of experiments that have been proposed are found in Table 4.1, along with the advances in scientific understanding related to the albedo modification and climate science generally that are anticipated from these experiments. The committee recommends that the serious deliberative process related to the larger governance discussion include discussions of if and how the different scales of this type of research should be pursued and governed. Subsequent to a deliberative process, judging the merits of individual proposals for these types of experiments is best done through the existing mechanisms of peer review.

If there were to be considerations of implementation, scaling up to the larger-scale experiments would best be done in the context of a goal-driven engineering development plan. Such a plan would prioritize investments in key “show-stopper” questions while minimizing cost and risk, rather than being driven by individual investigators.

Recommendation 6: The committee recommends the initiation of a serious deliberative process to examine (a) what types of research governance, beyond those that already exist, may be needed for albedo modification research and (b) the types of research that would require such governance, potentially based on the magnitude of their expected impact on radiative forcing, their potential for detrimental direct and indirect effects, and other considerations.

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³ See http://www.srmgi.org/.

• If a new governance structure is determined to be needed based on deliberations among governance experts and civil society representatives, the development of the governance structure should consider the importance of being transparent and having input from a broad set of stakeholders to ensure trust among the stakeholders and appropriate consideration of all dimensions.
• Such a governance structure should consider setting clear and quantitative guidelines for experimentation and be responsive to domestic and international laws and treaties.
• The deliberative process should consider focusing on research activities that involve injecting material into the atmosphere, for example aerosol-producing substances injected into the upper atmosphere or cloud-brightening substances injected near the surface.
• If a program of research in albedo modification includes controlled-emission experiments, it should provide for a sufficiently specific governance regime to at least define the scale of experiments at which oversight begins.
• The approach to governance should consider the need for increasing supervision as the scope and scale of the research and its potential implications increase, including the amount of material emitted, the area affected, and the length of time over which emission continues.
• The goal of the governance should be to maximize the benefits of research while minimizing risks.
• The United States should help lead the development of best practices or specific norms that could serve as a model for researchers and funding agencies in other countries and could lower the risks associated with albedo modification research.

CONCLUDING THOUGHTS

Addressing the challenges of climate change requires a portfolio of actions that carry varying degrees of risk and efficacy. CDR strategies and other technologies and approaches that reduce net emissions (e.g., carbon capture and sequestration, non-carbon-based energy, and energy efficiency improvements) offer the potential to slow the growth and reverse the increase of CO₂ concentrations in the atmosphere. The lowest-risk CDR strategies are currently limited by cost and at present cannot achieve the desired result of removing climatically important amounts of CO₂ beyond the significant removal already performed by natural processes. However, with declining costs and stronger regulatory commitment, atmospheric CO₂ removal could become a valuable component of the portfolio of long-term approaches to reducing CO₂ concentrations in the atmosphere and associated impacts. Overall, there is much to

be gained and very low risk in pursuing multiple parts of a portfolio of CDR strategies that demonstrate practical solutions over the short term and develop more cost-effective, regional-scale, and larger solutions for the long term.

In contrast, even the best albedo modification strategies are currently limited by unfamiliar and unquantifiable risks and governance issues rather than direct costs. The committee reiterates that it is opposed to large-scale deployment of albedo modification techniques, but it does recommend further research, particularly multiple-benefit research that furthers the basic understanding of the climate system and seeks to quantify the potential costs, consequences (intended and unintended), and risks from these proposed albedo modification techniques.

Climate change is a global challenge that will require complex and comprehensive solutions, which in turn will require that people of many nations work together toward common objectives. For the outcome to be as successful as possible, any climate intervention research should be robust and likely to yield valuable scientific information, international in nature, and open. The impacts of any potential future climate interventions should be honestly acknowledged and fairly considered. The committee firmly believes that there is no substitute for dramatic reductions in CO₂ emissions to mitigate the negative consequences of climate change at the lowest probability of risk to humanity. However, if society ultimately decides to intervene in Earth’s climate, the committee most strongly recommends any such actions be informed by a far more substantive body of scientific research—encompassing climate science and economic, political, ethical, and other dimensions—than is available at present.