Predicting the Antarctic sea level contribution to sea level rise with emulation

The Antarctic ice sheet has the potential to be a major contributor to future global sea level rise, but this has been difficult to predict, in part due to the combination of expected ice mass loss and snowfall accumulation. A great deal of uncertainty arises from the large variation of atmospheric and oceanic changes across climate models, and sensitivity to ocean changes across ice sheet models, but these uncertainties cannot be fully sampled because the models are too computationally expensive.

Here we make projections of Antarctica’s contribution to global sea level rise based on the simulations of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6). Using a Gaussian process emulator, a statistical approximation of expensive computer models, we estimate probability distributions by sampling uncertainties in future climate and ice sheet sensitivity to ocean warming far more thoroughly than the original ISMIP6 ensemble could. We find a sea level contribution of 4 cm (5^th-95th percentile range -5 to 14 cm) sea level equivalent by 2100 under current emissions policies, increasing to 21 cm (5^th-95th percentile range 7 to 43 cm) if we use the subset of climate models, ice sheet models and ice sheet/ocean sensitivity values that lead to the highest sea level contributions.

We then compare the output from this emulator to a linear mixed model emulator, which  incorporates a random effect to represent the variation arising from different ice sheet models. We do this for all three Antarctic regions (West and East Antarctica, and the Peninsula) under two greenhouse emissions scenarios (SSP1-26 and SSP5-85). Both methods produce similar probability distributions of sea level contribution in 2100, demonstrating that differences in statistical models are not dominating the results.