PNNL

Abstract

Stratospheric sulfate aerosol geoengineering has been proposed as a potential strategy to reduce the impacts of climate change. Here we investigate the impact of stratospheric aerosol geoengineering on the terrestrial hydrological cycle. We use the Geoengineering Large Ensemble (GLENS), which involves a 20-member ensemble of simulations using the Community Earth System Model with the Whole Atmosphere Community Climate Model, in which sulfur dioxide (SO2) was injected into the stratosphere at four different locations, to maintain global mean surface temperature, and also the interhemispheric and equator-to-pole temperature gradients at values representative of 2020 (“baseline”) under the Representative Concentration Pathway 8.5 (RCP8.5). Under RCP8.5, annual mean land precipitation and evapotranspiration (ET) increase by 12% each. Under GLENS, the hydrological cycle is suppressed compared to the baseline, with end-of-century decreases of 1.4% (12±5 mm year-1) and 3.3% (18±2 mm year-1) in global mean, annual mean precipitation and ET over land, respectively. Geoengineering effectively maintains global mean total column soil moisture, though there is significant regional variability. Summertime soil moisture is reduced by 42±11 kg m-2 (3.5%) and 27±16 kg m-2 (2.1%) in India and the Amazon, respectively, which is dominated by the decrease in precipitation. We also compare these regional changes in soil moisture under GLENS with an equatorial-only SO2 injection case and find a similar sign in residual changes, although the magnitude of the changes is larger in the equatorial run.