Optimal Observation Locations for Early Warning of the Onset of an AMOC Collapse

Abstract

There is increasing concern that the Atlantic Meridional Overturning Circulation (AMOC) will start to collapse this century having disrupting societal impacts worldwide. Although several available reconstructions appear to indicate a gradual weakening of the AMOC over the last century, the proximity to a possible tipping point associated with the onset of the collapse remains unknown. Here, we use results of an AMOC collapse, simulated in the Community Earth System Model (CESM), to identify currently observed regions and variables that can serve as early warning signals for this collapse. Optimal regions are identified using equilibrium CESM simulations and quasi-equilibrium forcing conditions. Salinity data near the southern boundary of the Atlantic Ocean turn out to give optimal early warning signals for the AMOC collapse in the CESM and provide adequate estimates of its onset time. The results are important for the design of a future early warning system of AMOC tipping.