PNNL

Abstract

Geoengineering methods could potentially offset aspects of human induced climate change associated with rising greenhouse gases. However, before embarking on any such strategy, a comprehensive understanding of its impacts must be obtained. Here, the predicted hydroclimate changes that occur when greenhouse gas driven warming under a high emissions scenario is offset with stratospheric sulfate aerosol geoengineering are investigated using a large ensemble of simulations with the Community Earth System Model and the Whole Atmosphere Community Climate Model as its atmospheric component. Notable features of the 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. The soil desiccation that occurs with global warming is, however, largely offset by the geoengineering with the notable exception of 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 in which 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 the simulated hydroclimate change, resulting in a general dry-get-wetter, wet-get-drier pattern in the tropics and in extra-tropical precipitation changes through mid-latitude circulation shifts. While this study evaluates a rather extreme geoengineering scenario, many, but not all, of the precipitation features scale linearly with the degree of offset global warming.