While many previous studies of the impacts of climate change geoengineering have focused on scenarios involving near-median estimates of climate sensitivity to GHG forcing, those of us in the field know that climate forcing sensitivity remains a highly uncertain scientific construct (see, for example, J. Hansen, et al., Earth’s Energy Imbalance and Implications, 11 Atmospheric Chemistry & Physics 13421-13449 (2011). A new study in Nature Climate Change uses a perturbed-physics ensemble model to assess the response of the climate to the solar radiation management geoengineering approach of aerosol dispersion (SRM-S) in the stratosphere to a range of greenhouse-gas climate sensitivities. Among the take-aways from the study:
- SRM-S is likely to be less effective in ameliorating regional impacts of climate change than mitigation in higher-sensitivity scenarios, “precisely when SRM-S seems most likely to be deployed.”
- Interregional heretorogeneities associated with SRM-S would also be greater under high sensitivity scenarios
- On the other hand, the potential for SRM-S to ameliorate climate change, including at the regional level, increases with climate sensitivity. On average, SRM-S is projected in a high sensitivity scenario to reduce regional rates of temperature change by more than 90% and precipitation change by more than 50%. By contrast, regional rates of warming and precipitation under the highest sensitivity scenario are twice as high in the highest-sensitivity model in the study’s ensemble than in the lowest-sensitivity scenario;
- SRM-S thus least effective in returning regional climates to baseline conditions, but is also most effective in reducing regional relative to the no SRM-S alternative.
A number of geoengineering studies in recent years have discussed potential negative regional impacts associated with deployment. This study adds to the equitable component fo the debate. On one hand, it appears that effective mitigation responses would produce better results in many regions under a high climate-sensitivity scenario; however, SRM-S is also most effective in reducing change relative to a no-SRM-S alternative. This article could generate some interesting discussion. Does the fact that SRM-S’s effectiveness is at its apogee at the point where it’s most likely to be deployed (under a climate crisis scenario) cut against it as a policy option, or does the fact that SRM-S is the fact that SRM-S is most powerful in reducing climate change relative to a non-SRM-S alternative under such a scenario, does it cut in favor of SRM?