From Climatic Drivers to Antarctic Ice Sheet Response: Improving Accuracy in Sea Level Rise Projections

Sea level rise, mainly caused by the melting of glaciers and ice sheets and the expansion of seawater when it warms, is one of the biggest threats imposed on us by climate warming. Today, we expect sea levels to rise by about 60 cm by the end of this century. Still, if the rate of greenhouse gas emissions remains high, uncertainties in the Antarctic Ice Sheet (AIS) behavior could mean a rise of as much as 5 meters by 2150. Such a high increase in sea level would be catastrophic for many low-lying regions across the globe. But how likely will it be? The AIS holds about 90% of all the ice on Earth. If it were all to melt, sea levels would rise about 58 meters. Therefore, predicting how much of the AIS might melt is critically important for governments and policymakers, aiding them in strategizing greenhouse emissions reduction and mitigation. The AIS mainly gains mass through accumulating snow and loses it through its interactions with the Southern Ocean. Predictions about the AIS's mass change are based on ice sheet models that use outputs from climate models. While climate models are good at predicting large-scale climate changes, they struggle with small-scale oceanic processes that bring heat to melt the ice, leading to substantial uncertainties in projections of Antarctica's contribution to sea level rise. By combining glaciology and oceanography, sophisticated numerical modelling, and statistical analysis techniques, this project (CLIM2Ant) will improve projections of Antarctica's contribution to sea level rise. Our project outcomes will directly contribute to future assessments of ice sheet sea-level contributions.

The Antarctic Ice Sheet (AIS) stores a large amount of freshwater. If melted completely, it would contribute58 m to global mean sea level rise. According to IPCC AR6, a rise of up to 5 m by 2150 cannot be ruled out under a high-emission scenario due to the large uncertainty related to AIS processes. Such a strong increase in sea level would be catastrophic for many low-lying regions worldwide, but how likely is it? The AIS gains mass mainly through snow accumulation and loses mass through iceberg calving and ocean-induced basal melting of its floating parts. Future projections of AIS mass balance are based on ice sheet model simulations forced by climate model outputs. Climate models can properly project large-scale climate changes but struggle to represent small-scale coastal processes that bring heat to the ice sheet margins. This leads to poor representation of basal melting and thus substantial uncertainties in projections of Antarctica's contribution to sea level rise. Climate models also suggest compensating mass change under climate warming in Dronning Maud Land: increased basal melting and more snowfall. This project brings together glaciology and oceanography, sophisticated numerical modelling and statistical analysis techniques to address these two key uncertainties of sea level rise projections: 1) Our combined approach of ocean model downscaling and statistical emulation enables us to assess future ocean-induced AIS mass loss more accurately and thus reduce uncertainties in its contribution to sea level rise. 2) Our regional fine-resolution coupled ice sheet-ocean model enables us to provide improved projections for ice mass balance and ice sheet movement in the Norwegian administrated Dronning Maud Land sector of Antarctica. Our project outcomes will directly contribute to future assessments of ice sheet sea-level contributions and address two of the goals of the EU Decade for Ocean Research: a predicted ocean and an accessible ocean.