a, Observed ice surface elevation (Bedmap2, ref. 1), regridded to 16 km. Grounding lines are shown in white; surface-height contours are given every 250 m. b, Modelled ice surface elevation of the reference state serving as initial configuration for the hysteresis experiments. Grounding lines are shown in white; surface-height contours are given every 250 m. c, Modelled minus observed (Bedmap2) ice surface elevation. d, Scatter plot for comparison of modelled and observed ice thickness for each grid cell. Red identity line illustrates where modelled ice thickness would perfectly match the observations. RMSE, root-mean-square error.