Engineering with stratospheric aerosols to avoid climate emergencies

Proposals to engineer a solution to global warming are becoming more common, yet there is much to explore before the viability and potential unintended consequences are known to any degree of confidence. It has been suggested that so-called climate emergencies, such as melting Arctic sea ice and polar ice sheets, and food crisis due to a heated tropics, could be avoided by cooling the planet through some feat of engineering. Model results indicate that managing the amount of sunlight to reach Earth's surface would alleviate warming due to anthropogenic emissions of greenhouse gases. However, climate is a complex system, at its most sensitive in the high latitudes, but responding globally. We use the Community Climate System Model 3 (CCSM3) global climate model to investigate the use of stratospheric sulfate aerosols, one proposed implementation of geoengineering. We evaluate model simulations with combinations of doubled CO2 with imposed stratospheric sulfate to investigate the effects on global climate. We further explore the sensitivity of the climate system to model configuration by running a suite of simulations with no sea-ice or ocean dynamics, with sea-ice dynamics but no ocean dynamics, and with both ice and ocean dynamics.

Results indicate that the stratospheric sulfate layer is at least partially effective at recovering modern values of sea-ice area, temperature, and precipitation, but that these results are limited to global and annual means and depend on model configuration. We find that some regional, specifically high latitude, temperature changes in a geoengineered and warmed world are of the order of 20-50% of the changes in a warmed world alone. We also find that the temperature spread among one model (CCSM3) with and without sea ice dynamics and ocean circulation feedbacks is roughly 25% of the spread of temperature differences in all IPCC AR4 models. The most uncertain regions coincide with regions where climate emergencies may occur and geoengineering could be used, providing little confidence that geoengineering to solve these climate issues would behave as anticipated.