Climate change means that polar terrestrial* ice sheets are melting. Accurate calculations about the rate of ice-melt are clearly crucial for estimates of future sea-level rise.

Climate 'modelers' take into account the 'non-linearity' of the ice melt, bearing in mind that the ice has different properties when it's under pressure, or in contact with bedrock (or both).

Current computational models assume that the 'non-linearity' (n) = 3.

A 2018 study published in Geophysical Research Letters, which examined actual (rather than theoretical) ice flows in Greenland, found that the n = 3 assumption could be wrong - possibly invalidating the current models.

What can be inferred is that the internal deformation of ice plays a bigger role than hitherto assumed. Considering the importance of correctly predicting ice sheet behavior and related sea level rise, with results of models feeding into global political-economical decisions, it is imperative that ice flow modelers start considering n = 4, at least as an alternative to only n = 3."

Source : Greenland Ice Sheet: Higher Nonlinearity of Ice Flow Significantly Reduces Estimated Basal Motion Geophysical Research Letters, Volume 45, Issue 13 p. 6542-6548,

* Note : Only terrestrial ice melting (Greenland, Antarctica etc etc ) contributes to sea level rise. The melting of floating sea-ice caps and icebergs - for example at the North Pole - have almost no effect on the levels.