Impacts, effectiveness and regional inequalities of the GeoMIP G1 to G4 solar radiation management scenarios

We evaluate the effectiveness and the regional inequalities of solar radiation management (SRM) in compensating for simultaneous changes in temperature and precipitation caused by increased greenhouse gas concentrations. We analyze the results from Earth System Models under four Geoengineering Model Intercomparison Project (GeoMIP) experiments with a modified form of the Residual Climate Response approach. Each experiment produces 50 model yrs of simulations: 13 models completed experiment G1 (offsetting 4 × CO2 via solar reduction); 12 models completed experiment G2 (offsetting CO2 that increased by 1% per year); 3 models completed experiment G3 (offsetting increasing radiative forcing under RCP4.5 with increasing stratospheric aerosol); and 7 models completed experiment G4 (injection of 5 Tg SO2 a− 1 into the stratosphere). The regional inequalities in temperature and precipitation compensation for experiments G1, G3 and G4 are significantly different from their corresponding noise backgrounds for most models, but for G2 they are not significantly different from noise. Differences in the regional inequalities and the actual effectiveness among the four SRM scenarios are not significant for many models. However, in more than half of the models, the effectiveness for temperature in the solar dimming geoengineering scenarios (G1 and G2) is significantly higher than that in the SO2 geoengineering scenarios (G3 and G4). The effectiveness of the four SRM experiments in compensating for temperature change is considerably higher than for precipitation. The methodology used highlights that a large across-model variation in the treatment of key geoengineering processes (such as stratospheric aerosols) and the quantification of damage caused by climate change creates significant uncertainties in any strategies to achieve optimal compensation effectiveness across different regions.