Stratospheric circulation response to stratospheric aerosol injections remains uncertain.

Abstract Mitigating global warming through stratospheric aerosol injection (SAI), which aims to reproduce the cooling effects of tropical volcanoes on surface climate, is emerging as a potential strategy for limiting near–surface global warming to around 1.5–2◦C above pre–industrial levels. However, knowledge of how the stratospheric circulation will respond to SAI, and the resulting feedback on surface climate and weather, remain highly uncertain. Here, we quantify the stratospheric circulation response to the 1991 Mount Pinatubo eruption and compare its response to a future global warming scenario with and without tropical SAI. We show that the shallow branch of the stratospheric circulation slows down in climate models and observations following tropical aerosol perturbations due to reduced lower stratospheric planetary and gravity wave breaking. However, the depth and strength of the deep branch response is highly uncertain. Climate models show a strengthening of the deep branch due to enhanced middle/upper stratospheric planetary and gravity wave breaking, contrasting with the observed weakening of the deep branch induced by reduced planetary and gravity wave forcing. As interest in SAI continues to grow, our results demonstrate the urgent need to study the impact of gravity/planetary wave uncertainty on ozone recovery, surface climate and weather.