Comparing Climate Impacts of Stratospheric Aerosol Injection using Different SO2 Injection Strategies in UKESM1

Stratospheric Aerosol Injection (SAI) is a proposed method of climate intervention which aims to reduce the impacts of human-induced global warming by reducing surface temperatures. Many studies have demonstrated that SAI would successfully reduce global mean temperatures, however the choice of injection latitude and strategy results in a diverse range of climate impacts, including the significant impact of SAI on atmospheric circulation and the resulting changes to regional climate variability. This study intends to evaluate the differences between two injection strategies using the Met Office's UK Earth System Model (UKESM1). The first applies a feedback controller (e.g. MacMartin et al., 2013; Kravitz et al., 2017) to the G6sulfur scenario to adjust the injection of SO2 at four latitudes (30°N, 15°N, 15°S, 30°S) and controls for three temperature targets - global mean, a measure of interhemispheric balance and a measure of the polar to tropics ratio. This is compared to G6sulfur which has a global mean temperature target and prescribes the injection of SO2 between 10°N and 10°S. We reveal an overcooling of the tropics and residual warming of polar regions occurs in the equatorial injection strategy which is ameliorated when using the controller at four latitudes. We examine the precipitation response and find that utilizing multiple injection latitudes lessens potentially damaging reductions in precipitation across the Amazon and equatorial Africa. Additional potential impacts on the stratosphere and atmospheric circulation will also be explored.

MacMartin, D. G., et al. (2014). Climate Dynamics 43(1): 243-258.

Kravitz, B., et al. (2017). Journal of Geophysical Research: Atmospheres 122(23): 12,616-612,634.