Mapping tipping risks from Antarctic ice basins under global warming

Abstract

The Antarctic Ice Sheet is known to be subject to several self-sustaining feedback mechanisms which can accelerate ice loss and could lead to unstable retreat under continued global warming. It is therefore considered one of the core tipping elements in the Earth system. This means that ice loss in certain regions—once triggered—might in effect be irreversible. Here we analyse the distinct nature and risk of potential long-term ice loss for each individual Antarctic ice drainage basin under different levels of global warming. Depending on the topographic structures as well as atmospheric and oceanic boundary conditions, we find that the dominance of different surface and ice-dynamic processes in some basins results in a rather gradual decline with increasing warming, whereas other basins are characterised by a critical threshold or tipping point, beyond which large parts of the basin eventually disintegrate. Yet other basins show a combination of gradual decline and tipping behaviour. Of the basins displaying tipping dynamics, the lowest warming threshold is found for the Amundsen Sea Embayment sector of West Antarctica around 1 °C of global warming above pre-industrial levels, consistent with earlier findings. Further marine ice-sheet regions in West and East Antarctica—together corresponding to almost 5 metres global sea-level contribution—are prone to tipping below 4 °C. Other ice basins remain stable up to 7 or even 8 °C. The strongest impact in terms of sea-level rise can be expected from the Totten basin where, once its critical threshold is exceeded, at least 90 % of the ice basin (corresponding to 6 metres sea-level equivalent) eventually collapses. We combine the identified warming thresholds and the respective global sea-level impact in a risk map, showing that the highest risk occurs for the Thwaites / Pine Island basin in West Antarctica and Wilkes basin in East Antarctica. Our results imply that the Antarctic Ice Sheet does, in fact, not act as a single tipping element, but rather as a set of interacting tipping elements across drainage basins.