The Influence of Increased CO₂ Concentrations on AMOC Interdecadal Variability Under the LGM Background

This study explores the impact of rising CO2 levels on the Atlantic meridional overturning circulation's (AMOC) interdecadal variability within the context of the Last Glacial Maximum (LGM) background climate. Under heightened CO2 concentrations, the AMOC interdecadal variability intensifies dramatically, which is very different from the future warming case that shows a weakening of AMOC interdecadal variability in response to increased CO2 concentration. This unexpected phenomenon primarily results from the extensive retreat of sea ice, which exposes a larger portion of the ocean surface to efficiently feel the heat flux fluctuations from atmospheric processes. These findings underscore the significance of background climate conditions in shaping AMOC responses to increased CO2 and emphasize the necessity of considering these nuances to develop a more accurate understanding of AMOC dynamics in an evolving climate. Plain Language Summary The Atlantic meridional overturning circulation (AMOC) is an important component of the Earth system, and its interdecadal variability is predicted to be significantly weakened under future warming scenarios. In this paper, we analyze the response of AMOC interdecadal variability to rising CO2 levels under the background of the Last Glacial Maximum (LGM) and find that the AMOC interdecadal variability is intensified under increased CO2 , which is totally different from its response at the background of modern climate. Analyses suggest that this unexpected result is mainly caused by dramatic sea ice retreat, which exposes much seawater to efficiently receive large fluctuations of heat flux from atmospheric forcing. The findings reveal that the response of AMOC to increased CO2 and relevant dominant mechanism differs significantly under different climate conditions.