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Climate models show that the largest uncertainties in the 21st century dynamic sea level (DSL) projections are in the high latitudes of the North Atlantic and Southern Oceans. We conduct an intermodel singular value decomposition analysis and find that the DSL uncertainties in these two oceans are both intrinsically connected to the uncertainty in the change of the Atlantic meridional overturning circulation (AMOC). We further conduct a freshwater hosing experiment to show that the AMOC decline not only accounts for the dipole pattern in the DSL change in the North Atlantic but also remotely induces a poleward shift in the Southern Hemisphere westerlies that helps build a belted pattern of DSL change in the Southern Ocean. Our results suggest that reducing the intermodel spread in the change of the AMOC can greatly improve the consistency of DSL projection among models not only in individual basins but over the global ocean.

Plain Language Summary State-of-art climate models project distinct patterns of regional sea level change. Most of these patterns arise from a dynamic change in the ocean, which has been named the dynamic sea level (DSL) change. However, climate models project different regional DSL changes in the 21st century, especially those in the North Atlantic and Southern Oceans. Any connection between intermodel uncertainties in the DSL projections in different basins has largely been ignored. We argue here that the change in the Atlantic meridional overturning circulation (AMOC) is a key factor that controls the intermodel uncertainty of regional DSL projections on a global scale. A weakening AMOC alters the DSL pattern in the North Atlantic and concurrently remotely affects the DSL over the Southern Ocean. In particular, we find that a decline in the AMOC could cause a poleward shift of the Southern Hemisphere westerly winds and thereby lead to a zonal belt-like change of the DSL in the Southern Ocean. These results imply that improving the intermodel consistency of the projected changes in the AMOC will greatly improve the reliability of future sea level projections on a global scale.