Collapse or abrupt weakening of the Atlantic Meridional Overturning Circulation (AMOC) could cause severe, hemispheric-scale impacts including cooling of Northern Europe and disruption to tropical rainfall. Modeling suggests that Stratospheric Aerosol Injection (SAI) would likely reduce AMOC decline (except under Southern Hemisphere-only injection) by counteracting the key drivers of weakening in the North Atlantic Ocean—surface warming and freshening (reduced saltiness)—that control how warm water transported north by AMOC sinks before circulating back south, a process known as deep convection. However, the modeled effectiveness of SAI at preventing AMOC slowdown or eventual collapse remains highly uncertain and depends critically on deployment strategy, timing, and magnitude (Bednarz et al., 2025; Futerman et al., 2025; Pflüger et al., 2024; Xie et al., 2022; Zhao et al., 2025). In summary, there is confidence that SAI would reduce or prevent AMOC slowdown, but the extent to which it would be able to do this, and how this would depend on injection strategy, warming scenario, and timing of SAI onset, is not well constrained.
A second, related tipping risk applies to deep-water formation in the North Atlantic subpolar gyre (SPG), which may be subject to a tipping point after which convection collapses (Loriani et al., 2025). SPG tipping could occur on time-scales much faster than full AMOC collapse, and would both contribute to AMOC decline and cause North Atlantic cooling and associated climate impacts (Sgubin et al., 2017). At present, there is very little direct modeling evidence for SAI's impact on SPG tipping, but, as with AMOC as a whole, it is likely that SAI would reduce the risk of collapse (Futerman et al., 2025; Pflüger et al., 2024).
