Abstract

Geoengineering by injection of aerosol into the stratosphere has been proposed as a countermeasure to anthropogenic global warming. Although global cooling should result, a geoengineered climate will not be the same as the preindustrial climate. In this presentation I will focus on the impacts of stratospheric aerosol geoengineering on the dynamics of the stratosphere. Geoengineering aerosols produce tropical radiative heating, which increases the stratospheric pole-Equator temperature gradient in the lower stratosphere, intensifying the stratospheric polar vortex. Similar intensifications are seen following volcanic eruptions. However, using geoengineering to counterbalance a substantial greenhouse gas radiative forcing has a larger and more persistent effect on the stratosphere than a transient volcanic aerosol layer. Here, I describe the effect of geoengineering on the frequency and dynamics of stratospheric sudden warming events. There are also related changes in the latitude of the tropospheric jets which act to amplify, not minimise, the response to greenhouse warming. I will also discuss the effect of geoengineering on the Brewer-Dobson circulation and the potential for formation of polar stratospheric clouds.