Aerosol–cloud interactions influence the climate response to AMOC weakening

The Atlantic Meridional Overturning Circulation (AMOC) strongly influences regional climate, yet how atmospheric aerosols and aerosol–cloud interactions respond to its weakening remains largely unexplored. Using an aerosol-climate model, we examine how a 60  % AMOC weakening affects aerosols, clouds, and radiation. The weakening drives a hemispheric aerosol redistribution through purely dynamical pathways, increasing the Northern Hemisphere aerosol burden by 41  % through enhanced Saharan dust emissions and longer lifetimes under suppressed wet deposition. Averaged over 40–90° N, in-cloud droplet number increases by 10  % in warm clouds and 11  % in mixed-phase clouds, while enhanced dust ice-nucleating particles raise mixed-phase ice crystal number by 32  % , promoting the Wegener–Bergeron–Findeisen process and reducing mixed-phase total water path by 8  % . A kernel decomposition shows substantial regional cloud radiative responses, particularly over the North Atlantic, but opposing contributions largely cancel in the global mean, leaving a small net cloud radiative response of +0.21Wm-2. This near cancellation reflects subpolar low-cloud brightening offset by optical thinning of mixed-phase and ice clouds, partly driven by dust-induced glaciation, together with opposing tropical cloud changes from the southward ITCZ shift. This small global mean cloud contribution contrasts with previous studies of AMOC weakening, in which cloud changes contribute a net positive radiative feedback on the surface response. Of the cloud, aerosol and surface-albedo contributions diagnosed here, the largest effect comes from the enhanced shortwave reflection by expanded sea-ice and snow cover (−0.83 W m ⁻² ), followed by the effective radiative forcing due to dust aerosol–radiation interactions (ERFari, −0.23 W m ⁻² ). Combined with the cloud contribution, these terms sum to −0.86 W m ⁻² . This estimate excludes the longwave response to the cooling, including the Planck and lapse-rate responses, which is not decomposed here.