Mitigating global drought extremes through stratospheric aerosol geoengineering: spatial and socioeconomic disparities

As global temperature rises, the severity and frequency of droughts are projected to increase. Stratospheric aerosol injection (SAI) has been proposed as a potential solution to reduce surface temperatures, but its effectiveness in alleviating drought extremes remains unclear. Here, we assess the global impacts of SAI on drought extremes based on experiments from the Geoengineering Model Intercomparison Project phase 6 (GeoMIP6) and the Geoengineering Large Ensemble Project (GLENS). By 2100, the frequency of extreme droughts is projected to increase by 7.33 % under the high-emission Shared Socioeconomic Pathways 5 (SSP5-8.5) scenario relative to present day. SAI reduces this increase by 1.99 % in GeoMIP6, and by 1.80 % in GLENS compared with Representative Concentration Pathways 8.5 (RCP8.5). Attribution analyses show that SAI-induced cooling alone reduces extreme drought frequency by 3.42 % in GeoMIP6 and 4.28 % in GLENS relative to their respective high-emission scenarios, outweighing the 2.12 % increase driven by SAI-induced precipitation reductions under the same conditions. However, these rainfall deficits lead to substantial inequities in drought exposures. Compared to developed nations, countries with less development experience smaller reductions, or even increases, in economic and population exposure to extreme drought under SAI relative to SSP5-8.5 or RCP8.5. These findings suggest that the current SAI strategies in GeoMIP6 and GLENS may induce the risk of unintentionally worsening regional hydroclimatic disparities.