Different Strategies of Stratospheric Aerosol Injection Would Significantly Affect Climate Extreme Mitigation

Stratospheric aerosol injection (SAI) has been proposed as a potential supplement to mitigate some climate impacts of anthropogenic warming. Using Community Earth System Model ensemble simulation results, we analyze the response of temperature and precipitation extremes to two different SAI strategies: one injects SO2 at the equator to stabilize global mean temperature and the other injects SO2 at multiple locations to stabilize global mean temperature as well as the interhemispheric and equator-to-pole temperature gradients. Our analysis shows that in the late 21st century, compared with the present-day climate, both equatorial and multi-location injection lead to reduced hot extremes in the tropics, corresponding to overcooling of the mean climate state. In mid-to-high latitude regions, in comparison to the present-day climate, substantial decreases in cold extremes are observed under both equatorial and multi-location injection, corresponding to residual winter warming of the mean climate state. Both equatorial and multi-location injection reduce precipitation extremes in the tropics below the present-day level, associated with the decrease in mean precipitation. Overall, for most regions, temperature and precipitation extremes show reduced change in response to multi-location injection than to equatorial injection, corresponding to reduced mean climate change for multi-location injection. In comparison with equatorial injection, in response to multi-location injection, most land regions experience fewer years with significant change in cold extremes from the present-day level, and most tropical regions experience fewer years with significant change in hot extremes. The design of SAI strategies to mitigate anthropogenic climate extremes merits further study. Injecting SO2 into the stratosphere to deflect incoming sunlight back to space has been proposed as a possible means to counteract anthropogenic warming. Previous studies focused on the response of the mean climate change to SO2 injection. Here we analyze how SO2 injection would affect climate extremes using two sets of climate model simulations under a high-CO2 scenario. In one set of simulations, SO2 is injected into the stratosphere at the equator to stabilize global mean warming at the present-day level; in another set of simulations, SO2 is injected into the stratosphere at four different latitudes to stabilize global mean temperature, interhemispheric temperature gradient, and equator-to-pole temperature gradient at the same time. Our analysis shows that both equatorial injection and multi-location injection can help reduce temperature and precipitation extreme events induced by global warming, but their effectiveness varies across different regions. In general, compared to equatorial injection, multi-location injection can be more effective in stabilizing climate extremes at the present-day level over most regions. This is consistent with the fact that multi-location injection exhibits smaller changes in mean climate state than that of the equatorial injection relative to the present-day state. We examine the climate extreme response to two stratospheric aerosol injection (SAI) strategies: equatorial injection and multi-location injection The response of climate extremes to SAI shows similar characteristics to mean climate response Multi-location injection is more effective in stabilizing climate extremes at the present-day level