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PMEL Publications Abstract

FY 2026

Arctic sea ice meltwater as a forcing and feedback on the Atlantic Meridional Overturning Circulation

Hankel, C., W. Cheng, and C.M. Bitz

J. Climate, 39(8), 1821–1839, doi: 10.1175/JCLI-D-25-0254.1, View article at AMS (external link) (2026)

Recent work has shown that the weakening of the Atlantic meridional overturning circulation (AMOC) under anthropogenic climate change is sensitive not only to the amount of atmospheric CO2 increase but also to the rate of CO2 increase. In this work, we explicitly test whether a previously proposed AMOC–sea ice feedback controls the AMOC’s sensitivity to the rate of CO2 increase using mechanism-denial experiments in a global climate model. We find that when the AMOC–sea ice feedback is suppressed, the AMOC is nearly insensitive to the rate of CO2 increase, supporting the hypothesis that this feedback is the primary reason for the AMOC’s sensitivity to the rate of CO2 increase. Additionally, we show that the reduction of sea ice meltwater in the North Atlantic that is caused by the retreat of Arctic sea ice in a warming climate constitutes a large strengthening forcing on the AMOC, reducing the total amount of AMOC weakening by nearly half. The strong influence of sea ice meltwater on the AMOC—both in its role as a forcing and a feedback—occurs through the ability of the meltwater to modulate how much surface water mass transformation occurs via ocean heat loss to the atmosphere over the deep convection zones in the North Atlantic. This work demonstrates that Arctic sea ice–AMOC interactions are a first-order control on future AMOC weakening and highlights the importance of constraining present-day sea ice meltwater fluxes to assess their potential counteracting influence on the weakening of Earth’s AMOC.

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