The regional hydroclimate response to stratospheric sulfate geoengineering and the role of stratospheric heating

Geoengineering methods could potentially offset aspects of greenhouse gas-driven climate change. However, before embarking on any such strategy, a comprehensive understanding of its impacts must be obtained. Here, a 20-member ensemble of simulations with the Community Earth System Model with the Whole Atmosphere Community Climate Model as its atmospheric component is used to investigate the projected hydroclimate changes that occur when greenhouse gas-driven warming, under a high emissions scenario, is offset with stratospheric aerosol geoengineering. Notable features of the late 21st century hydroclimate response, relative to present day, include a reduction in precipitation in the Indian summer monsoon, over much of Africa, Amazonia and southern Chile and a wintertime precipitation reduction over the Mediterranean. Over most of these regions, the soil desiccation that occurs with global warming is, however, largely offset by the geoengineering. A notable exception is India, where soil desiccation and an approximate doubling of the likelihood of monsoon failures occurs. The role of stratospheric heating in the simulated hydroclimate change is determined through additional experiments where the aerosol-induced stratospheric heating is imposed as a temperature tendency, within the same model, under present day conditions. Stratospheric heating is found to play a key role in many aspects of projected hydroclimate change, resulting in a general wet-get-drier, dry-get-wetter pattern in the tropics and extratropical precipitation changes through midlatitude circulation shifts. While a rather extreme geoengineering scenario has been considered, many, but not all, of the precipitation features scale linearly with the offset global warming.