The ocean heat valve: AMOC and planetary energy budget during abrupt glacial climate change

During the Ice Ages, abrupt climate changes co-occurred with switches in Atlantic Meridional Overturning Circulation (AMOC) strength. The thermal bipolar seesaw has served as a seminal conceptual framework to explain the global extent of these events, calling on interhemispheric redistribution of heat to explain the observed north-south temperature pattern. Here we summarize an emerging alternative framework centered instead on the global ocean heat content (OHC) and planetary energy budget, which we illustrate using simulations of spontaneous abrupt climate change in three climate models. In all models, the AMOC strength sets the OHC trend via the rate of North Atlantic heat loss, coupled to the top-of-the-atmosphere energy budget through radiative feedbacks. Antarctic and Greenland temperatures, as recorded in ice cores, are shown to reflect OHC and the rate of North-Atlantic heat loss, respectively. Under intermediate glacial climate states, global ocean heat uptake cannot reach steady-state with the bimodal rate of North Atlantic heat loss causing instability. Our synthesis suggests that the AMOC serves as a heat valve that alters planetary temperature by changing the radiative balance. This implies amplified planetary heat uptake in response to projected future AMOC weakening.