Constraining the onset of future irreversible retreat of Thwaites Glacier, Antarctica

The Antarctic Ice Sheet is susceptible to instability-driven ice loss triggered by ocean-induced melting in the vicinity of its grounding lines. When engaged in such a retreat, ice loss – and consequentially sea-level rise – can hardly be reversed over millennial time scales. With dedicated ice-sheet model experiments, we delineate the possible future onset of irreversible grounding-line retreat at Thwaites Glacier. We determine the grounding-line location where ice loss becomes irreversible and calculate thresholds in ice loss and ocean-driven melting. For the model realization that is most sensitive to ocean-induced changes, critical grounding line positions may be reached within 25 years under ocean warming of 0.5°C above present, while the least sensitive realization does not enter irreversible retreat before 150 years under 3°C of temperatures above present. We highlight that Thwaites is currently in an imbalance such that any overshoot beyond present-day will lead to an earlier onset of irreversible retreat.