The fate of the Greenland Ice Sheet in a geoengineered, highCO2 world

Abstract

Solar radiation management (SRM) geoengineering has been proposed as one means ofhelping avoid the occurrence of dangerous climate change and undesirable state transitions(‘tipping points’) in the Earth system. The irreversible melting of the GreenlandIce Sheet is a case in point—a state transition that could occur as a result ofCO2-driven elevated global temperatures, and one leading to potentially catastrophic sea-levelrise. SRM schemes such as the creation of a ‘sunshade’ or injection of sulfate aerosols intothe stratosphere could reduce incoming solar radiation, and in theory balance, in aglobal mean, the greenhouse warming resulting from elevated concentrations ofCO2 in the atmosphere. Previous work has highlighted that a geoengineered world would have:warming towards the poles, cooling in the tropics, and a reduction in the globalhydrological cycle, which may have important implications for the Greenland IceSheet. Using a fully coupled global climate model in conjunction with an icesheet model, we assess the consequences for the mass balance of the GreenlandIce Sheet of the reorganization of climate patterns by the combination of highCO2 and geoengineering. We find that Greenland surface temperature and precipitation anomalies,compared to the pre-industrial situation, decrease almost linearly with increasing levels of SRMgeoengineering, but that these combine to create a highly non-linear response of the ice sheet.The substantial melting of the Greenland Ice Sheet predicted for four times pre-industrialCO2 levels is prevented in our model with only a partial application of SRM, and hence withouthaving to fully restore the global average temperature back to pre-industrial levels. Thissuggests that the degree of SRM geoengineering required to mitigate the worst impacts ofgreenhouse warming, such as sea-level rise, need not be as extensive as generally assumed.