PNNL

Abstract

Based on observations of large volcanic eruptions1 and dedicated model simulations2, solar radiation management by stratospheric sulfate aerosol injection (SRM-SAI) is thought to be one of the most promising methods to counteract anthropogenic global warming3. However, coordinated simulations of SRM-SAI using Earth System Models (ESMs) reveal fundamental uncertainties in the climate response to geoengineering, including global cooling and any resulting risks to natural and human ecosystems. Here we identify an emergent relationship4,5,6,7 linking the long-term global land surface cooling due to SRM-SAI and the short-term cooling following the 20th century major volcanic eruptions across an ESM ensemble. This emergent relationship, combined with observations and reanalysis, is used to constrain the global land surface temperature (GLST) response to reduced downward solar radiation. Based on these constraints, we find that GLST decreases by approximately 0.43 K per W.m-2 ([0.18,0.67]), which is 22% smaller in magnitude than the model mean of an unconstrained ensemble of ESMs simulating SRM-SAI and 46% smaller in magnitude than some past estimates8. These new estimates may affect how trade-offs between cost, risk and effectiveness of SRM-SAI might be considered.