Continued Atlantic overturning circulation even under climate extremes

The Atlantic Meridional Overturning Circulation (AMOC), crucial for transporting heat northward across the Atlantic Ocean, is expected to weaken due to global warming, with implications for global climate. It is uncertain, however, how much it will weaken or if it may even completely collapse this century. Hence, we assess the AMOC's ability to withstand extreme increases in greenhouse gases and freshwater forcing in the North Atlantic by examining the upwelling pathways that return deep waters of the AMOC to the surface in 34 CMIP6 climate models. Our findings show that upwelling in the Southern Ocean, maintained by persistent overlying westerly winds, prevents a total AMOC collapse and impacts its future strength. This Southern Ocean upwelling must be balanced by downwelling in the Atlantic or Pacific oceans, so only the development of a strong Pacific Meridional Overturning Circulation (PMOC) could enable an AMOC collapse. While a PMOC does appear in nearly all models, it is insufficient to offset the upwelling in the Southern Ocean, suggesting an AMOC collapse this century is unlikely. We uncover novel stabilising mechanisms that enhance the resilience of the AMOC, with implications for its past and future change. Our findings highlight the critical need for improved observation-based estimates of the Indo-Pacific and Southern Ocean circulations to reduce uncertainty in AMOC projections.