Effect of model initialisation on committed sea level contribution from the Amundsen Sea Sector

The West Antarctic Ice Sheet (WAIS) is losing ice and its annual contribution to sea level is increasing. The biggest changes are found in the Amundsen Sea sector of WAIS, which contains two of the most rapidly thinning ice streams, Pine Island Glacier (PIG) and Thwaites Glacier (TG). The future behaviour of these glaciers will impact societies worldwide, yet deep uncertainty remains in the expected rate of ice loss. One prominent question is whether the retreat in this region has already passed a tipping point. In ice-sheet projections using the WAVI model, Thwaites Glacier continues to retreat even in an unrealistic scenario of zero oceanic melting, implying that a tipping point has already been passed. Here, we investigate the robustness of this conclusion to the choices made during the ice sheet model initialisation. In particular, we explore the effects of internal ice temperature, ice shelf extent and initial ice damage on forward runs of the WAVI model under the zero-melt scenario (with no evolving damage). We repeat these experiments for initialisations at different time points within the last ~30 years to assess whether the ice damage in this region passed a tipping point within this timeframe.