Sea-level contribution from Thwaites Glacier doubles in an observation-constrained ice-sheet model

Abstract Thwaites Glacier is a major contributor to Antarctic mass loss and a key source of uncertainty in future sea-level rise. Ocean-driven melting at its grounding line drives rapid retreat, yet most models treat the transition between grounded and floating ice as a sharp boundary, neglecting kilometer-scale seawater intrusions recently observed beneath grounded ice. Here we incorporate actively melting grounding zones into a calibrated ice-sheet model and reproduce nearly three decades of observed retreat, thinning, and acceleration, but only when grounding zones are represented as 2–5 km wide regions with melt rates of 110 m/yr. Extending this model forward, we show that grounding-zone processes govern detachment from stabilizing ridges, enabling unpinning as early as 2038 and producing 30+-6 mm of global mean sea-level rise by 2100 - approximately double previous projections even without additional climate warming.