The Atlantic Meridional Overturning Circulation (AMOC) is projected to weaken under anthropogenic warming in CMIP5 and CMIP6, with most climate-model projections primarily driven by greenhouse-gas emission scenarios that do not explicitly include observationally constrained, time-evolving freshwater input from the Greenland Ice Sheet. This omission of key freshwater forcing may lead to an underestimation of the possibility of persistent AMOC weakening in the future. Here we use a fully coupled climate model forced with a basin-resolved, seasonally varying reconstruction and projection of Greenland freshwater fluxes from 1950 to 2300 to assess the maximum extent to which realistic freshwater input can modify the AMOC response under CO₂-driven warming. We find that high atmospheric CO₂ concentration alone weakens the AMOC, but does not sustain this weakening once the imposed warming stabilizes. It is the sustained Greenland freshwater input that drives the more persistent AMOC weakening. Only the combined CO₂ and freshwater forcing can reproduce an SST pattern more consistent with the observed AMOC cold blob, with subpolar cooling and enhanced warming along the Gulf Stream region, which is not reproduced by either forcing alone. The mixed-layer-depth change under combined forcing is consistent with the real-world observational trend, highlighting changes in deep-water formation that are central to sustaining the AMOC. The consistency between our results and observations gives a warning that the real world may already be on track toward a future with significant AMOC decline. These results demonstrate that Greenland freshwater forcing is not a secondary perturbation to CO₂-driven climate change, but a critical component of future AMOC projections. Incorporating realistic, time-evolving ice-sheet freshwater input into climate simulations is therefore essential for assessing the future AMOC destiny and its wider climate impacts.


 

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