Response of High Latitude Seasonal Cycle to Stratospheric Aerosol Geoengineering

Stratospheric sulfate aerosol injection has been proposed as a means to reduce some undesired impacts of anthropogenic climate change. Here we examine the effect of stratospheric aerosol injection on the high latitude seasonal cycle using results from the Stratospheric Aerosol Geoengineering Large Ensemble simulations (GLENS). In GLENS, the rate and location of sulfate dioxide injection are adjusted interactively to maintain the level of global mean temperature, interhemispheric temperature gradient, and equator-to-pole temperature gradient simultaneously at their 2020 levels under the background RCP8.5 scenario. During 2075-2095, the changes in many climate fields decrease under GLENS relative to that of RCP8.5 simulation. However, we show that relative to the baseline simulation (ensemble mean of RCP8.5 simulations during 2010-2030), substantial shifts in the seasonal cycle occur in GLENS. Many high-latitude regions experience relatively warmer winters and cooler summers. The shift in the temperature seasonal cycle has a significant effect on snow depth and sea ice. For example, compared to the baseline, Arctic sea ice extent increases in summer but decreases in winter. In places such as Helsinki and Stockholm, a slightly warmer winter in response to GLENS would cause a considerable decrease in the snow depth relative to baseline. We also compare our results with other relevant simulations to better understand the underlying mechanisms of the high-latitude seasonal cycle shift in response to stratospheric aerosol geoengineering. Seasonal variation of solar irradiance and the dynamic effect of stratospheric heating both appear to play a critical role in modulating the seasonal shifts of high latitude climate.