Exploring Earth System Model Forcings for Ice Sheet Tipping Point Experiments in TIPMIP-ICE

The Tipping Points Modelling Intercomparison Project (TIPMIP) uses Earth System models (ESMs) and stand-alone models to assess tipping point risks. Within TIPMIP-ICE, stand-alone ice sheet models are forced with temporally extended atmospheric and oceanic output from multiple TIPMIP ESMs, making the choice of forcing a critical source of uncertainty.

We explore TIPMIP ESM results in Antarctica for the historical period as well as under positive and zero emission scenarios to (1) decide on suitable forcing data for ice sheet simulations and to (2) understand simulated ice sheet changes in relation to the ESM forcing. The analysis focuses on ocean potential temperature and salinity at the Antarctic continental shelf depth, near-surface air temperature, and precipitation as key fields for sub-shelf melt, surface mass balance, and ice sheet stability. It includes a comparison to observations and an assessment of multi-model differences under positive and zero emissions scenarios. 

Comparing historical runs (1981-2010) to observations reveals oceanic temperature biases across the ESMs of up to +4°C/-2°C. Under an idealized positive emission experiment to +2°C of global mean warming, preliminary results show spatial variability across basins in Antarctica. Different models follow distinct atmosphere-ocean warming trajectories, resulting in different forcing patterns for ice sheet models. 

These distinct warming trajectories could impact the risk of ice sheet tipping dynamics in TIPMIP-ICE, particularly the grounding-line stability of Antarctica. They underline the importance of having a diverse set of ESM forcings to enable future evaluation of  feedbacks associated with tipping dynamics of the ice sheets such as melt-elevation feedback or marine ice sheet instability (MISI). Ongoing work extends this analysis to additional ESMs and to Greenland.