Uncertainty in Future Southern Ocean Warming and Antarctic Ice Shelf Melting Due to Meltwater-Driven Climate Feedbacks

The increasing release of meltwater from Antarctica represents one of the most profound yet uncertain consequences of global climate change. The lack of interactive ice sheets in state-of-the-art climate models, including those participating in the Coupled Model Intercomparison Project (CMIP6), combined with the inadequate representation of key processes driving ice shelf basal melting, prevents the direct calculation of ice-ocean feedbacks and leaves a high uncertainty on the magnitude and impacts of meltwater discharge. Previous studies that explored meltwater impacts produced partially contradictory findings, largely relied on experiments with single models, had inconsistent experimental designs, and imposed varying freshwater forcing rates. To address these shortcomings, this study employs results from the new  "Southern Ocean Freshwater Input from Antarctica” (SOFIA) initiative to assess the effect of meltwater-induced ocean warming on basal melting and potential future Antarctic mass loss. We evaluate the ocean response to meltwater across a suite of 10 CMIP6 models and compare it to future scenarios simulations without additional meltwater (SSP5-8.5), assessing model bias and both meltwater- and global warming-induced anomalies in the Southern Ocean. Applying these anomalies to a regional basal melting parameterization, constrained by a new observational hydrographic climatology, our findings reveal that meltwater feedbacks amplify warming on the continental shelf and enhance ice loss in many sectors around Antarctica. However, in the West Antarctic regions where the greatest ice mass loss was observed in recent years, most models show either cooling or reduced warming on the shelf, hence indicating a negative feedback due to the meltwater input. Consistent with previous studies, we confirm that regional disparities are driven by advection and acceleration of the Antarctic Slope Current. Our results suggest that mass loss from East Antarctica will become increasingly important under future global warming. The meltwater-induced feedback causes an additional 750 Gt/year of ice loss in the multi-model median response to our perturbation experiments. For comparison, observations estimate current anomalous ice shelf loss at approximately 1,000 Gt/year, while SSP5-8.5 simulations, which account for global warming without additional Antarctic meltwater, project an anomalous 3,400 Gt/year of ice loss by the end of the century.