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Climate Intervention: Reflecting Sunlight to Cool Earth (2015)

Chapter: Appendix E: Discussion of Feasibility of Albedo Modification Technologies

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Suggested Citation:"Appendix E: Discussion of Feasibility of Albedo Modification Technologies." National Research Council. 2015. Climate Intervention: Reflecting Sunlight to Cool Earth. Washington, DC: The National Academies Press. doi: 10.17226/18988.
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APPENDIX E

Discussion of Feasibility of Albedo Modification Technologies

Assessing an albedo modification strategy’s feasibility (ignoring the extremely important need for appropriate governance issues dealt with elsewhere in this document) hinges upon

  • Developing a theoretical and conceptual framework for a particular strategy for producing an albedo modification and
  • Identifying system components and means that are critical to testing the scientific and physical concepts important to the strategy, and the technology necessary for implementing those strategies.

It is worth noting that the implementation details, and costs needed to test the underlying concept, would differ significantly from those that would be employed if the strategy were to be used at a larger scale. Assessing the conceptual feasibility of a strategy need not initially use the same implementation methods that would be considered feasible for a larger-scale implementation. So it is necessary to distinguish between assessing the “scientific feasibility” of a strategy (e.g., what calculations, instrument developments, laboratory and field experiments are needed to demonstrate an understanding of underlying physics to produce an intended perturbation to albedo in a particular region and time) and the “practical feasibility” issues associated with a larger deployment (e.g., Is it possible? And what would the cost be for a deployment intended to affect the planetary albedo sufficiently to counter some fraction the radiative forcing arising from increasing greenhouse gases?).

Understanding both types of feasibility studies is important and they can be considered in parallel. The scientific feasibility studies would provide better information for more realistic estimates of costs and practical strategies to produce a measurable effect on the climate processes. These studies would also examine local impacts to radiative forcing, quantify the intended changes, and assess whether models are capable (or not) of simulating and predicting the statistical characteristics of those changes to the climate processes to demonstrate some physical understanding of the climate process being manipulated. The process is necessarily iterative. The first step

Suggested Citation:"Appendix E: Discussion of Feasibility of Albedo Modification Technologies." National Research Council. 2015. Climate Intervention: Reflecting Sunlight to Cool Earth. Washington, DC: The National Academies Press. doi: 10.17226/18988.
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uses theory, existing analogues in the real world (e.g., volcanoes and ship tracks), and both process and climate models to provide a “zero-order guess” at the amplitude of the induced perturbation to component processes and the “fast” response of the climate system (the so-called “adjusted radiative forcing”). These modeling studies and analyses of existing analogues provide basic estimates of relevant forcing, as well as the local responses guiding estimates of costs, and implementation details, but there is a limit to their utility. There can easily be flaws in physical understanding expressed in models or overlooked issues that were not considered. At some point more stringent assessments would require that laboratory and field experiments would be needed to make sure that initial estimates are realistic and robust across location, climate regimes, and seasons.

If exploratory field experiments were successful in producing the desired effect on the component behavior, they would (a) provide information needed to characterize the potential for a particular strategy (perhaps for only a subset of important regimes or seasons) to produce a significant radiative perturbation; (b) provide a mechanism for estimating the cost of inducing such a change; and (c) identify the immediate, local impact of those changes on that component of the climate system. Exploration of albedo modification to other regimes, locations, and season might then be considered to identify their potential to produce radiative forcing, and eventually consideration of slower feedbacks, and consequences to the climate system become important considerations.

Feasibility estimates should thus be contingent upon (1) first-guess estimates based on models and measured analogues found in our current environment; (2) staged series of laboratory and de minimus field experiments designed to test basic understanding and components important to the strategy, and the overall robustness, of the models; (3) updated estimates of feasibility produced by improved knowledge from the de minimus field experiments; and (4) testing of the robustness of the mechanisms as the amplitude of forcing and temporal and areal extent are increased, where nonlinearities become important. Eventually, as the amplitude of the forcing is increased, assessing the feasibility of the strategy becomes primarily a signature detection problem—that of teasing out a signal (the climate response to a perturbation) in the presence of the background “noise” of natural climate variability (MacMynowski et al., 2011).

Suggested Citation:"Appendix E: Discussion of Feasibility of Albedo Modification Technologies." National Research Council. 2015. Climate Intervention: Reflecting Sunlight to Cool Earth. Washington, DC: The National Academies Press. doi: 10.17226/18988.
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Page 239
Suggested Citation:"Appendix E: Discussion of Feasibility of Albedo Modification Technologies." National Research Council. 2015. Climate Intervention: Reflecting Sunlight to Cool Earth. Washington, DC: The National Academies Press. doi: 10.17226/18988.
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Page 240
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The growing problem of changing environmental conditions caused by climate destabilization is well recognized as one of the defining issues of our time. The root problem is greenhouse gas emissions, and the fundamental solution is curbing those emissions. Climate geoengineering has often been considered to be a "last-ditch" response to climate change, to be used only if climate change damage should produce extreme hardship. Although the likelihood of eventually needing to resort to these efforts grows with every year of inaction on emissions control, there is a lack of information on these ways of potentially intervening in the climate system.

As one of a two-book report, this volume of Climate Intervention discusses albedo modification - changing the fraction of incoming solar radiation that reaches the surface. This approach would deliberately modify the energy budget of Earth to produce a cooling designed to compensate for some of the effects of warming associated with greenhouse gas increases. The prospect of large-scale albedo modification raises political and governance issues at national and global levels, as well as ethical concerns. Climate Intervention: Reflecting Sunlight to Cool Earth discusses some of the social, political, and legal issues surrounding these proposed techniques.

It is far easier to modify Earth's albedo than to determine whether it should be done or what the consequences might be of such an action. One serious concern is that such an action could be unilaterally undertaken by a small nation or smaller entity for its own benefit without international sanction and regardless of international consequences. Transparency in discussing this subject is critical. In the spirit of that transparency, Climate Intervention: Reflecting Sunlight to Cool Earth was based on peer-reviewed literature and the judgments of the authoring committee; no new research was done as part of this study and all data and information used are from entirely open sources. By helping to bring light to this topic area, this book will help leaders to be far more knowledgeable about the consequences of albedo modification approaches before they face a decision whether or not to use them.

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