Personally, I think we underestimate these changes, because we tend to project them linearly from known factors. However, physical systems typically go through phase changes at different energy levels. Phase changes tend to happen quickly, and are accelerated by positive feedback mechanisms.

For example, I see it as unlikely that we can currently model the rate of change accurately when sea level has already risen by 1m.

This study suggests that experts’ judgments of uncertainties in projections of the ice sheet contribution to SLR have grown during the last 6 y and since publication of the AR5. This is likely a consequence of a focused effort by the glaciological community to refine process understanding and improve process representation in numerical ice sheet models. It may also be related to the observational record, which indicates continued increase in mass loss from both the AIS and GrIS during this time. This negative learning (36, 37) may appear a counter intuitive conclusion, but is not an uncommon outcome: as understanding of the complexity of a problem improves, so can uncertainty bounds grow.