Stability and reversibility of ice sheets in climate overshoot scenarios

Mass loss from ice sheets under the ongoing anthropogenic warming is a major contributor to sea-level rise. Previous studies suggest that global warming exceeding 2 °C could push the marine-based West Antarctic Ice Sheet beyond a critical threshold, triggering irreversible retreat and multi-meter rise in the global-mean sea-level. Climate overshoot scenarios are a key focus of CMIP7, yet most existing work on the reversibility of ice sheets is based on quasi-equilibrium simulations, with much less attention paid to ice sheets' stability and reversibility under century-scale transient climate forcing. Here we use climate and ice sheet models to simulate the evolution of the Antarctic and Greenland ice sheets under multiple climate overshoot scenarios. Results show that net-negative emissions in overshoot pathways can substantially reduce ice loss from the Greenland Ice Sheet, but are less effective in mitigating retreat of the West Antarctic Ice Sheet. This indicates that the West Antarctic Ice Sheet may also exhibit a tipping behavior under overshoot scenarios, and that achieving carbon neutral early is crucial to avoiding a potential catastrophic sea-level rise.