On the predictability of Antarctica's contribution to sea level rise

Antarctica’s contribution to global sea-level rise is accelerating, yet projections from ice-sheet models continue to span a wide range despite sustained advances in resolution and physical realism. Using a coordinated ensemble of simulations from the H2020 European PROTECT project, we assess both the ability of six state-of-the-art ice-sheet models to reproduce observed Antarctic mass loss since the early 1990s and the extent to which present-day behaviour constrains future evolution.

Across most of the ice sheet, model agreement with observations is limited, reflecting strong sensitivity to model structure and internal dynamics rather than to external forcing alone. In sharp contrast, the Amundsen Sea sector of West Antarctica exhibits a persistent and robust relationship between modelled present-day mass-loss rates and projected sea-level contribution that extends to the end of the twenty-first century and beyond. This sector emerges as the only region where contemporary observations retain demonstrable predictive power for long-term outcomes, while elsewhere compensating processes dominate. Our results identify a fundamentally regional limit of predictability for the Antarctic Ice Sheet, highlighting where emergent constraints can meaningfully inform projections—and where uncertainty is likely irreducible with current models and observations.