How stable is the Atlantic meridional ocean circulation when interacting with polar ice sheets?

The Atlantic meridional overturning circulation, the Greenland and Antarctic ice sheets have been identified as parts of the climate system that can potentially react nonlinearly to climate change albeit on very different time scales. While critical thresholds remain difficult to quantify from existing observations for all of these subsystems, they certainly do not stand on their own. In fact, the AMOC and polar ice sheets form an intricate network of multiscale systems, with interactions that can be stabilizing or destabilizing, the latter opening the possibility of cascading tipping events.

The interaction between Greenland ice sheet and AMOC on the larger scale shows the possibility of a collapse of the AMOC once a critical amount or rate of freshwater has entered the North Atlantic. This interaction also involves smaller scales, because the Greenland meltwater needs to reach the deep-water formation regions in the North Atlantic subpolar gyre, exhibiting substantial variability in the critical regions. Moreover, the Greenland ice sheet acts on slower time scales than the AMOC, such that these two systems can form an ‘accelerating cascade’. Specfically, when tipping of the ice is underway, the ‘coupling’, i.e. the freshwater flux into the North Atlantic is at maximum. These properties have consequences for the possibility of early warning predictions; in accelerating cascades early warning signs can break down due to lack of extrapolation.

On the other hand, West Antarctic Ice Sheet melting may be able to to stabilize the AMOC. Here, we investigate through a hierarchy of models of the AMOC and idealized forms of polar ice sheet collapse, the origin and relevance of stabilization and destabilization effects. In both deterministic and stochastic conceptual models, we find that rate- and noise-induced effects have substantial impact on the AMOC stability. Moreover, rate-induced effects can stabilize the AMOC depending on the relative timing of the peak meltwalter fluxes from both ice sheets.