Legacy of stratospheric aerosol injection for limiting global warming

Despite significant advances in low emissions and renewable technologies, global warming is expected to exceed 2 degree and breach the Paris Agreement. Here we applied an Earth system model to simulate stratospheric aerosol injection (SAI) in idealized overshoot scenarios. The objective is to evaluate the impacts of avoiding temperature overshoot using SAI under optimal conditions. Three injection locations were tested: the tropics, and the northern and southern hemispheres’ mid-latitude.  While the global mean temperature overshoot can be avoided, regional climatic responses vary considerably depending on the injection location. For example, in the subpolar northern hemisphere, the long-term temperature evolution over the next centuries following SAI cessation is highly sensitive to the SAI-induced changes in the Atlantic Meridional Overturning Circulation (AMOC) evolution. This, in turn, alters long-term projections of Arctic sea-ice and permafrost dynamics. The global warming-induced shift in the Intertropical Convergence Zone (ITCZ) can either be amplified or offset depending on the location of SAI implementation. These results re-emphasize the challenge of avoiding regional disparity introduced by SAI. Our experiments suggest that SAI application would affect both the short- and long-term feedback processes in the Earth system with legacies lasting long after its termination.