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Peer Review

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Notes

Executive summary:

Although the workshop did not address the issue of the circumstances under which solar radiation management should be deployed, participants’ views on this matter appeared to span the gamut including (i) never, (ii) only in the event of an imminent climate catastrophe, (iii) as part of a transition to a low-carbon-emission economy, and (iv) in lieu of strong reductions in greenhouse gas emissions. More importantly, the discussion illuminated important differences in the economic and political implications of solar radiation management depending on whether deployment occurred in the face of imminent climate emergency or was implemented preemptively well in advance of crisis conditions. Thus the circumstances under which solar radiation management might be deployed could have major implications for its economic and policy implications.
Possible risks, uncertainties, and objections
One major focus of the workshop was to identify the factors that might militate against research or deployment of solar radiation management technology. Participants noted several such potential objections. These included:
• Solar radiation management systems are unlikely to perfectly reverse all climate consequences of greenhouse gases and could introduce new changes in regional or seasonal climate, so some climate change might be expected even with the deployment of such systems.
• Modeling indicates that if a solar radiation management system were shut down suddenly after prolonged operation the climate system could warm very rapidly.
• Injecting sulfur into the stratosphere would likely diminish spring Northern Hemisphere stratospheric polar ozone levels, although the amount of diminution is currently uncertain and extreme Antarctic-style depletion is unlikely.
• Solar radiation management will neither reverse nor exacerbate non-climate effects of CO2 including fertilization of the land biosphere and acidification of the ocean.
The workshop scope focused on preliminary characterization of some elements of a possible solar radiation management research program. Research into solar radiation management could have implications for other approaches to addressing climate change and could have various political consequences, both domestically and internationally. These considerations may be important, but were beyond the scope of our workshop.