Antarctic marine-based ice destabilized when warming outpaces solid-Earth feedbacks

The Antarctic Ice Sheet is expected to be the largest contributor to sea-level rise over the coming centuries. Previous equilibrium ice-sheet simulations have suggested that this is due to crossing a bifurcation point associated with marine ice-sheet instability. Here we investigate whether sectors vulnerable to this instability can undergo rate-induced tipping, whereby rapid forcing and slow bedrock uplift trigger self-sustained retreat before the bifurcation point is reached. We test this with an ice-sheet model coupled to a glacial isostatic adjustment model, sampling the uncertainty in mantle viscosity. We find that slow bedrock adjustment weakens the stabilizing effect of glacial isostatic adjustment, allowing grounding lines to reach retrograde bed slopes more readily and triggering self-sustained retreat below the bifurcation threshold. Although the West Antarctic Ice Sheet is subject to a bifurcation, it is unlikely to experience rate-induced tipping because of the low mantle viscosity beneath the region. In contrast, the Recovery and Aurora subglacial basins are likely to undergo such a transition even under warming rates lower than those observed today. Depending on mantle viscosity, this mechanism can reduce the critical global mean temperature anomaly by up to 0.5 K, with important implications for the long-term evolution of the Earth system. Delayed bedrock uplift can allow rapid warming to trigger Antarctic Ice Sheet retreat before classical instability thresholds are reached, lowering critical warming thresholds by up to 0.5 K in East Antarctica, according to coupled model simulations.