West Antarctic Ice Retreat Temporarily Halted with Transient Rheology in Future Climate Projections

Abstract. Projections of sea-level change and Antarctic Ice Sheet (AIS) stability under anthropogenic climate change hinge upon accurately describing physical feedbacks that link ice dynamics (marine and terrestrial) with the gravitational, rotational and deformational response of the solid Earth to ice and ocean loading changes. In turn, the rate of AIS melting can lower the rate of global mean temperature rise, by promoting sea ice growth and amplifying Earth’s albedo. The marine West Antarctic Ice Sheet (WAIS) is vulnerable to runaway grounding line retreat. However, the rapid viscoelastic rebound of the bedrock in response to ice retreat has been shown to stabilize its grounding line, aided by the low-viscosity mantle beneath the WAIS. Such bedrock deformation is typically modelled with idealized Maxwell viscoelasticity, despite that rock deformation experiments show that additional “transient” creep mechanisms occur over societally relevant (~decadal-centennial) timescales that are missing from the Maxwell model. Here, we simulate future AIS evolution, coupled with self-consistent solid Earth deformation and sea level change, for various emissions scenarios (RCP 2.6, 4.5, 8.5), incorporating transient deformation. This more complete treatment of solid Earth deformation delays grounding line retreat as compared to Maxwell projections, with differences of tens of kilometres persisting for decades at Pine Island and Thwaites Glaciers. Though transient deformation slows glacier retreat, it is unable to prevent the bulk of ice loss and sea-level rise on longer, centennial timescales. Even still, deviations in AIS meltwater flux with transient deformation could affect the pace of global temperature rise in climate model predictions.