Identifying climate impacts from different Stratospheric Aerosol
Injection strategies in UKESM1
Abstract
Stratospheric Aerosol Injection (SAI) is a proposed method of climate
intervention aiming to reduce the impacts of human-induced global
warming by reflecting a portion of incoming solar radiation. Many
studies have demonstrated that SAI would successfully reduce global-mean
surface air temperatures, however the vast array of potential scenarios
and strategies for deployment result in a diverse range of climate
impacts. Here we compare two SAI strategies - a quasi- equatorial
injection and a multi-latitude off-equatorial injection - simulated with
the UK Earth System Model (UKESM1), both aiming to reduce the
global-mean surface temperature from that of a high-end emissions
scenario to that of a moderate emissions scenario. Both strategies
effectively reduce global mean surface air temperatures by around 3°C by
the end of the century; however, there are significant differences in
the resulting regional temperature and precipitation patterns. We
compare changes in the surface and stratospheric climate under each
strategy to determine how the climate response depends on the injection
location. In agreement with previous studies, an equatorial injection
results in a tropospheric overcooling in the tropics and a residual
warming in the polar regions, with substantial changes to stratospheric
temperatures, water vapour and circulation. However, we demonstrate that
by utilising a feedback controller in an off-equatorial injection
strategy, regional surface temperature and precipitation changes
relative to the target can be minimised. We conclude that moving the
injection away from the equator minimises unfavourable changes to the
climate, calling for a new series of inter-model SAI comparisons using
an off-equatorial strategy.