Impacts and state-dependence of AMOC weakening in a warming climate

Abstract

All climate models project a weakening of the Atlantic Meridional Overturning Circulation (AMOC) strength in response to greenhouse gas forcing. However, the climate impacts of the AMOC decline in relation to other drivers of climate change, cannot be assessed from existing Coupled Model Intercomparison Project (CMIP) simulations. To address this issue, we conduct idealized experiments using the EC-Earth3 climate model. We compare an abrupt 4xCO2 simulation with an identical one, except we artificially fix the AMOC strength at preindustrial levels. With this design, we can formally attribute differences in climate change impacts between these two experiments to the AMOC decline. In addition, we quantify the state-dependence of AMOC impacts by comparing the aforementioned experiments with a preindustrial simulation in which we artificially reduce the AMOC strength. Our findings demonstrate that AMOC decline impacts are state-dependent, thus understanding AMOC impacts on future climate change requires targeted model experiments.