Nonlinear Sea Level Rise

Nonlinear sea-level rise is sea-level change that departs from a constant linear trend, most importantly the observed acceleration of global-mean rise. Satellite altimetry from 1993 shows the rate climbing from about 2.1 mm per year early in the record to over 4 mm per year recently, an acceleration near 0.08 mm per year squared, driven by faster ice-sheet mass loss and ocean warming. Projections under high-emission scenarios are strongly nonlinear because ice-sheet instabilities can add a long tail. Treating the rise as linear underestimates future levels and the change in extreme return periods, so allowance and adaptation planning must use the curved trajectory.