Dangerous consequences of geoengineering implementation and termination for species and ecological systems

Background/Question/Methods:   Geoengineering to reduce solar radiant input to Earth’s surface (albedo modification) has been advocated as a way to reduce the greatest impacts of climate change by the injection of reflective sulfate aerosols into the stratosphere. The effects of geoengineering on global and regional temperatures and precipitation have been modeled and studied extensively. However, almost nothing is known about the potential ecological risks of implementing geoengineering. If sulfate aerosol injections were to be abruptly terminated for political, economic, or other reasons, climate change would be very rapid and in places, dramatic changes would occur in a short time. We adopt a scenario in which implementation begins in 2020, continuation is maintained for 50 years, and then geoengineering is abruptly terminated. While implementation reduces average temperatures globally, temperatures continue to rise under geoengineering continuation if CO₂ emissions continue. We investigated climate velocities—the speed with which organisms and ecological systems would have to move to track their current climates—for the implementation, continuation and termination of geoengineering.

Results/Conclusions:   Geoengineering implementation is predicted to increase precipitation velocities substantially, with drying in biotically vulnerable areas over the Amazon, Siberia and southeast Africa. Under RCP4.5 (an emissions stabilization scenario, with total radiative forcing stabilized by 2100), temperature velocities are predicted to increase to a global median of 4.0 km yr^-1. However, velocities could increase to 10.1 km yr^-1 after sudden termination of geoengineering, with 29% of the land surface predicted to have more than double both temperature and precipitation velocities predicted for RCP4.5. In multiple regions including biodiversity hotspots, we project that sudden termination will cause temperature velocities to more than triple those predicted for RCP4.5 (i.e. ‘business as usual’ with moderate CO₂ emission reduction). Finally, for many regions, termination would cause temperature and precipitation velocities to pull species and communities in divergent directions, with high potential for fragmentation of communities and ecosystems. Geoengineering is not an easy fix for greenhouse gas climate change, but represents a very serious threat to species and community persistence, including those in the most biodiverse regions on Earth.