Climate response to off-equatorial stratospheric sulfur injections in three Earth system models – Part 2: Stratospheric and free-tropospheric response

We also find a large spread in the magnitudes of the tropicallower-stratospheric warming amongst the models, driven by microphysical,chemical, and dynamical differences. These lead to large differences instratospheric water vapor responses, with significant increases instratospheric water vapor under SAI in CESM2 and GISS that were largely notreproduced in UKESM. For ozone, good agreement was found in the tropicalstratosphere amongst the models with more complex microphysics, with lowerstratospheric ozone changes consistent with the SAI-induced modulation ofthe large-scale circulation and the resulting changes in transport.

Incontrast, we find a large inter-model spread in the Antarctic ozoneresponses that can largely be explained by the differences in the simulatedlatitudinal distributions of aerosols as well as the degree ofimplementation of heterogeneous halogen chemistry on sulfate in the models. The use of GISS runs with bulk microphysics demonstrates the importance ofmore detailed treatment of aerosol processes, with contrastingly differentstratospheric SAI responses to the models using the two-moment aerosoltreatment; however, some problems in halogen chemistry in GISS are alsoidentified that require further attention.

Overall, our results contributeto an increased understanding of the underlying physical mechanisms as wellas identifying and narrowing the uncertainty in model projections of climateimpacts from SAI.