With increased societal urgency to limit rising global temperatures, solar geoengineering strategies are attracting considerable attention. Studies suggest that geoengineering such as albedo management, i.e., increasing atmospheric albedo by stratospheric aerosol injections, may feasibly lower global mean temperatures without requiring reductions in atmospheric CO2 concentrations. Much research focuses on implementation optimization and on the overall potential to moderate or eliminate temperature increases. However, geoengineering may have potentially important unintended consequences for the Earth system, most of which remain poorly characterized. One of these unintended consequences is altered patterns of precipitation and drought, which may be particularly important for dryland ecosystems. We simulated daily ecosystem water balance with a process-based model across global drylands to evaluate how albedo management (represented by the Geoengineering Model Intercomparison Project – GeoMIP – scenarios) may impact the frequency of extreme events and the duration of ecological droughts at different soil depths. 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
Our simulation results suggested that albedo management may exacerbate frequency of extreme events and duration of ecological droughts in excess of 50% compared to baseline climate change impacts by mid-21st century across substantial areas in every dryland region (on average, 9% and 8% of dryland area for extreme events and 34-44% and 12-15% for ecological droughts under G3 and G4 respectively). Additionally, we found that climate and region poorly explained (< 25-54%) how albedo management scenarios modify baseline impacts on drought, suggesting that localized impacts of albedo management on ecosystems may be difficult to anticipate with climate studies alone. Our simulations highlight the sub-regional spatial heterogeneity among areas where albedo management achieves the goal of reducing the severity of climate change impacts vs. areas where it exacerbates baseline climate change and may further increase drought conditions. These results have important implications for dryland ecosystem functioning and the distribution of plant functional types. The discrepancy between unintended, but sizeable negative ecosystem impacts in drylands and global success in reducing temperature increases calls for an improved understanding of geoengineering impacts beyond large scale and averaged climate characteristics and underscores the need for a full consideration of ecohydrological processes and ecosystem properties.