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Why do scientists disagree about whether the Atlantic Meridional Overturning Circulation could shut down completely?

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Map of the North Atlantic Ocean showing major ocean currents, with warm currents like the Gulf Stream and North Atlantic Drift highlighted in pink and cold currents in blue. Arrows indicate current directions and relative speeds, connecting the eastern coasts of North America, the western coasts of Europe and Africa, and the Arctic region. — Gulf Stream Major warm and cold currents of the North Atlantic Ocean.

Scientists disagree on the potential for a complete collapse of the Atlantic Meridional Overturning Circulation (AMOC) primarily due to differences in how they interpret climate models and the complex variables involved in ocean circulation.1

Those who predict a potential collapse often rely on models showing that increased freshwater input—driven by melting glaciers in Greenland—reduces surface water salinity and density, thereby inhibiting the sinking mechanism that drives the current.1

Conversely, other researchers argue that the AMOC remains largely stable and that extreme collapse projections are based on oversimplified models. These experts suggest that freshwater inputs from the north could be offset by the melting of the West Antarctic Ice Sheet. They posit that this additional freshwater would cool the Southern Ocean, potentially strengthening the AMOC by increasing the density gradient between surface and deep waters in the North Atlantic. While there is a consensus that the AMOC will continue to weaken, the likelihood of a total shutdown remains a subject of significant scientific debate.1