Quantifying uncertainties in the Antarctic ice sheet response to climate overshoot scenarios

The Antarctic Ice Sheet (AIS) could contribute tens of centimetres to global sea level rise by 2100, and metres by 2300, substantially increasing coastal flooding worldwide. Policymakers have identified overshoot of 1.5°C warming, and how this would increase the risk of tipping points such as Antarctic ice sheet instability (which may occur between 1°C and 2°C warming), as priority areas for assessment. Key questions include: how much overshooting 1.5°C would increase AIS losses compared with no overshoot, and whether reversing climate change could stabilise the AIS once instabilities are triggered. Understanding is currently limited, as previous studies have used idealised scenarios and not substantially explored model uncertainties, but initial simulations and physical understanding suggest that reversing global warming could even worsen ice sheet decline, as cooling temperatures limit precipitation but instabilities continue.

This project will address these questions using BISICLES, a state-of-the-art ice sheet model. Building on previous projects, we will extend small ensembles to more comprehensively explore the AIS response under overshoot and non-overshoot scenarios up to 2300, and estimate the increased risks of ice losses and irreversible sea level rise. Running perturbed parameter ensembles with BISICLES, in combination with machine learning emulation, will allow us to explore, and quantify, climate and ice sheet model uncertainties and sensitivities regarding potential tipping points and irreversibility.

This integration of simulations and emulation under policy-focused overshoot scenarios will yield new insights into the AIS’s long-term behaviour, addressing policymaker priorities on overshoot impacts and tipping points and their implications for sea level rise.