on other aspects of the earth system, including ecosystems on land and in the oceans. Because the coupled human-environment system is large and complex, it is impossible to fully anticipate all consequences of a geoengineering intervention in advance, or any other type of intervention for that matter. Nevertheless, it is possible to predict and anticipate some of these consequences through a combination of analysis; small-scale de minimis experiments; and climate, Earth system, and integrated assessment modeling. Again, in the case of stratospheric sulfur aerosol injection options, experiments that evaluate how increases in diffuse solar radiation would affect ecosystem productivity or how stratospheric particles might affect the ozone layer could be carried out. Similarly, modeling studies and analysis of observations around volcanic eruptions may provide insight into the changes to be expected in the hydro-logic cycle from SRM.
Develop metrics and methods for informing discussions and decisions related to "climate emergencies." There are at least two components to this research need. For use of SRM as a potential "backstop option" in the case of an emerging "climate emergency," improved observations and understanding of climate system thresholds, reversibility, and abrupt changes (see Chapter 6)—for example, observations to let us know when an ice sheet or methane hydrate field may become unstable (e.g., Khvorostyanov et al., 2008; Shakhova et al., 2010)—could inform societal debate and decision making about needs for deployment of a climate intervention system. Second, there is no consensus on what constitutes a "climate emergency," nor is there a consensus regarding when an SRM deployment might be warranted. The notion of an "emergency" is not simply a scientific concept, but one that involves both scientific facts and human values—quite similar to discussions about "dangerous interference in the climate system" (e.g., Dessai et al., 2004; Gupta and van Asselt, 2006; Hansen, 2005; Lorenzoni et al., 2005; Oppenheimer, 2005; Smith et al., 2009). To some people, losing Arctic ecosystems constitutes a climate emergency, whereas to others the declaration of an "emergency" might require widespread loss of human life. Therefore, to inform a broader discussion of how society wants to address issues of risk, climate intervention cannot be studied in isolation but must be placed in a broader context considering, for example, drivers of climate change, climate consequences, sociopolitical systems, and human values.
Develop and evaluate systems of governance that provide models for decision making about whether, when, and how to intentionally intervene in the climate system. Because decisions about intentional alteration in the climate system will have widespread consequences, options for governance, including different types of institutions, assigned decision makers, procedures, norms, and rules and regulations, will be needed and can be provided through analysis. Much can be learned, for exam ple, by studying past environmental and national security agreements, the siting and deployment of large-scale technology, and the conditions under which cooperation or conflict develops. Further research can help elucidate when and what type of governance might be useful not only for deployment but also for field experiments that can be reasonably expected to involve risks of negative consequences. Decisions about intentional interventions in the climate system require not only an understanding of the physical climate system response but also how these climate responses affect differentially vulnerable people and things people need or care about such as food and water security.
Improve detection and attribution of climate change so as to provide an adequate baseline of observations of the "nonengineered" system with which to compare observations of the "engineered" system. Just as it is a nontrivial exercise to quantitatively attribute observed climate change among different climate forcing agents, distinguishing the effects of intentional climate intervention from other causes of climate change to ascertain the effectiveness of SRM approaches is a nontrivial task. Detection and attribution of climate change, and evaluation of all actions taken to respond, including initial testing, will require enhanced observing systems and analyses covering a wide array of climate and other environmental variables, especially more complete observations of energy flows in Earth's climate system. In particular, preparations are needed to carefully observe the effects of the next major volcanic eruption.
Measure and evaluate public attitudes and test communication approaches to effectively inform and engage the public in decision making. Past experience with large and potentially dangerous technologies (or technologies perceived as dangerous) shows the importance of involving the public in advancing ideas and deliberations regarding testing or deployment of climate engineering approaches (see references above). However, little is known at this time about how different publics would perceive such large-scale interventions, what their attitudes are, how they should be engaged, and how best to communicate the complex issues concerning climate engineering. Also, attitudes and communicative approaches are likely to change over time and require periodic reassessment.
Develop an integrated research effort that considers the physical, ecological, technical, social, and ethical issues related to srm. Much of the research and observations needed to advance the scientific understanding of SRM approaches are also needed to advance general understanding of the climate system and related human and environmental systems. Examples of dual-purpose research include studies of the climate effects of aerosols, cloud physics, and how ecosystems, ocean circulation, permafrost, and ice sheets respond to changes in temperature and precipitation.
There is, however, additional research that would be needed to support full evaluation of SRM approaches (just as there is with other options for limiting the magnitude of future climate change), including a variety of social, ecological, and physical sciences (see Chapter 4). Such an effort would no doubt draw on many of the experts already engaged in climate change research, but would also need to engage new disciplines and expertise to aid in issues related to governance, public acceptance, and ethics.
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