Role of Atlantic multidecadal variability in modulating Arctic sea ice loss and wetting.

Arctic precipitation has increased in recent decades (hereafter, Arctic wetting), but the drivers remain uncertain. Using observations, reanalyses, and single-model initial-condition large ensembles (SMILEs), we show that enhanced evaporation due to sea ice loss has been the primary driver of Arctic wetting during 1979-2024, especially in the Atlantic sector. However, the externally forced component in most SMILEs explains only ~69% of sea ice loss and 75% of wetting in the observations and reanalyses. Further analysis reveals that the observed transition of one of the Northern Hemisphere's interdecadal internal variability-Atlantic multidecadal variability (AMV)-from a negative to a positive phase substantially enhanced Arctic sea ice loss, thereby accelerating wetting by about 31%. Under SSP3-7.0, if the AMV switches phase in the near future from the current +1 to a -1 standard deviation anomaly, then the rates of Arctic sea ice loss and wetting would slow by nearly 29 and 33%, respectively, relative to the externally forced response alone. These results underscore the pivotal role of AMV in modulating Arctic sea ice loss and wetting and highlight the need to account for AMV phase changes in near-term Arctic climate projections.