Radiative effects of decreased North America and European aerosols weaken the AMOC via wind-driven freshwater advection

Growing observational and modeling evidence suggests that the Atlantic Meridional Overturning Circulation (AMOC) has weakened since the 1980s, with reductions in North American and European (NAEU) aerosols identified as a potential contributing factor. Here we use fully coupled climate model experiments to demonstrate that the radiative forcing associated with decreased NAEU aerosols weakens the AMOC by enhancing freshwater transport from the Arctic and subtropical regions into the deep convection region. Reduced aerosol loading induces large-scale atmospheric circulation adjustments, including cyclonic wind stress anomalies over the Arctic Ocean and the subtropical North Atlantic. Over the Arctic Ocean, the cyclonic wind stress anomaly weakens the Beaufort Gyre, releasing freshwater that accumulates north of the Canadian Arctic Archipelago and Greenland. This freshwater is then exported through Baffin Bay into the Labrador Sea, suppressing deep convection there. Simultaneously, enhanced cyclonic wind stress over the subtropical North Atlantic weakens the North Atlantic Current (NAC), reducing the northward transport of saline water and promoting the freshwater accumulation within the subpolar gyre. This freshwater anomaly is then advected toward the Labrador Sea, further suppressing deep convection and weakening the AMOC. Together, our results identify a remotely driven pathway through which reductions in NAEU aerosols weaken the AMOC via wind-driven freshwater advection. The robustness of this mechanism is further supported by the multi-model ensemble mean from the Coupled Model Intercomparison Project Phase 6 (CMIP6) simulations, which exhibits consistent oceanic and atmospheric circulation responses.