AMOC stability amid tipping ice sheets: the crucial role of rate and noise

Abstract

The Atlantic Meridional Overturning Circulation (AMOC) has recently been categorized as a core tipping element as, under climate change, it is believed to be prone to critical transition implying drastic consequences on a planetary scale. Moreover, the AMOC is strongly coupled to polar ice sheets via meltwater fluxes. On the one hand, most studies agree on the fact that a collapse of the Greenland Ice Sheet would result in a weakening of AMOC. On the other hand, the consequences of a collapse of the West Antarctica Ice Sheet are less well understood. However, some studies suggest that meltwater originating from the Southern Hemisphere is able to stabilize the AMOC. Using a conceptual model of the AMOC and a minimal parameterization of ice sheet collapse, we investigate the origin and relevance of this stabilization effect in both the deterministic and stochastic cases. While a substantial stabilization is found in both cases, we find that rate- and noise-induced effects have substantial impact on the AMOC stability, as those imply that leaving the AMOC bistable regime is neither necessary nor sufficient for the AMOC to tip. Also, we find that rate-induced effects tend to allow a stabilization of the AMOC in cases where the peak of the West Antarctica Ice Sheet meltwater flux occurs before the peak of the Greenland Ice Sheet meltwater flux.