Can we save Antarctica with geoengineering? The response of the Antarctic Climate to stratospheric sulfate aerosol injection simulated in CESM.

Observations show that the Antarctic Ice Sheet is already responding rapidly to climate change. With many of the continent's ice sheets now losing mass, this has accelerated in recent years. The loss of ice sheets could impact the rest of the world through its contributions to rising sea levels, which currently threaten many coastal communities. As the ice shelves retreat they can become unstable, possibly leading to a tipping point where even lowering global mean temperatures cannot stop further ice sheet loss. While geoengineering has been proposed as a possible tool for reducing climate risks, its potential to avoid irreversible climate impacts associated with the Antarctic region have received minimal attention. Here we investigate the impact of geoengineering using stratospheric aerosol injections on the Antarctic climate in experiments where the amount of sulphate injected is controlled with a feedback algorithm maintaining global mean surface temperature and its interhemispheric and equator-to-pole gradients at the present day levels. Previous studies showed that while this method successfully maintains the above temperature targets, important changes can occur to other parts of the climate system (e.g. Arctic polar vortex, Hadley circulation) which are less constrained by the large-scale surface temperature changes or respond at different timescales. Here we show that while our geoengineering simulations project a cooling over the Antarctic during austral summer, there is a general warming in the Antarctic during the rest of the year compared to the present day. We explore the associated impacts on the Antarctic sea-ice, snowfall and melt, as well as discuss the changes in the potential drivers of these responses, including changes in the radiative fluxes, atmospheric circulation and ocean processes. The results will thus constitute an important contribution towards assessing the impacts of sulfate aerosol geoengineering on the Antarctic system and improve our understanding of the relative importance of various drivers and physical processes for the short- and long-term climate variability in the region.