Mass loss reversibility of the West Antarctic Ice Sheet

Over the last two decades, the contribution of the West Antarctic Ice Sheet (WAIS) to sea level rise (SLR) has doubled. Current observations show that grounding-line retreat is highly discontinuous and strongly modulated by ocean variability, with the strength and timing of decadal extremes exerting a greater influence than long-term mean changes. Here, we analyse the future behaviour of the WAIS by incorporating multiple random realizations of plausible climate scenarios in Kori-ULB ice-sheet model simulations. We further develop a statistically robust metric to assess grounding line stability in a spatial context, not only in the time domain as currently expressed in terms of SLR uncertainties. We thus define a “safety band" as the location where grounding line retreat is still reversible. Beyond this band, glaciers undergo a self-sustained retreat irrespective of ambient climate conditions. On the contrary, grounding lines that remain within this band still allow for glacier slowdown and even re-advance in the absence of ocean melt or if sub-shelf accretion occurs. The window for effective climate mitigation therefore remains open only while the grounding line stays within this safety band. Our results provide a robust metric for assessing glacier stability and highlight the need to account for climate variability in sea-level rise projections.