Geoengineering strategies are increasingly considered as tools to mitigate impacts of climate change. A rapidly increasing body of research focuses on success of interventions on the climate system and on optimizing implementation strategies such as increasing atmospheric albedo by stratospheric aerosol injection. These studies suggest that climate geoengineering could lower global mean temperatures while keeping atmospheric CO2 concentration elevated. However, geoengineering may substantially alter global and regional precipitation regimes with potentially large and unintended consequences for ecosystems which are as of yet barely understood. We investigated consequences of geoengineering on global drylands where water is the most frequent limiting resource, using a daily time step, multiple soil layer simulation model of ecosystem water balance. We simulated how changes in precipitation and temperature after stratospheric aerosol injection, obtained from the Geoengineering Model Intercomparison Project (GeoMIP), influenced temporal and spatial patterns of evapotranspiration and ecological drought. We evaluated responses under two GeoMIP scenarios: G3, which balances radiative forcing under RCP4.5 by increasing stratospheric aerosol injection, and G4, which reduces radiative forcing by injecting stratospheric sulfate aerosols at a constant rate.
Results/Conclusions
Global mean temperature increased less under G3 (0.21±0.39 C) and G4 (0.27±0.43 C) than under RCP4.5 (0.83±0.29 C) for mid-century projections. Global mean changes, however, mask important regional variation, particularly for precipitation and ecological drought. Preliminary results suggest a smaller increase of mean annual precipitation for Mongolian drylands under G3 and G4 compared to conditions under RCP4.5, whereas for Australian drylands models suggest on average no change in precipitation under RCP4.5, a modest decrease under G3, and a modest increase under G4. Number of days when ecological drought co-occurs with warm temperatures increased substantially across all scenarios in Mongolia (14±8 days) whereas the G4 scenario projected a smaller increase (14±17 days) than under either G3 or RCP4.5 (22±17 days) for Australian drylands. If transpiration increases due to CO2 fertilization outweigh reductions in temperature-related mortality and in reduced infiltration due to increased biomass, then ecological droughts may decrease regionally despite higher biomass density. Therefore, the projected changes in ecological drought and water uptake show strong regional patterns. Our simulations highlight the changes in evapotranspiration and the extent of ecological droughts under global albedo modification, with important implications for the distribution of plant functional types.