Projected land ice contributions to twenty-first-century sea level rise.

Abstract

The land ice contribution to global mean sea level rise has not yet been predicted1 using ice sheet and glacier models for the latest set of socio-economic scenarios, nor using coordinated exploration of uncertainties arising from the various computer models involved. Two recent international projects generated a large suite of projections using multiple models2-8, but primarily used previous-generation scenarios9 and climate models10, and could not fully explore known uncertainties. Here we estimate probability distributions for these projections under the new scenarios11,12 using statistical emulation of the ice sheet and glacier models. We find that limiting global warming to 1.5degrees Celsius would halve the land ice contribution to twenty-first-century sea level rise, relative to current emissions pledges. The median decreases from 25to 13centimetres sea level equivalent (SLE) by 2100, with glaciers responsible for half the sea level contribution. Theprojected Antarctic contribution does not show a clear response to the emissions scenario, owing touncertainties in the competing processes of increasing ice loss and snowfall accumulation in a warming climate. However, under risk-averse (pessimistic) assumptions, Antarctic ice loss could be five times higher, increasing the median land ice contribution to 42centimetres SLE under current policies and pledges, with the 95th percentile projection exceeding half a metre even under 1.5degrees Celsius warming. This would severely limit the possibility of mitigating future coastal flooding. Given this large range (between 13centimetres SLE using the main projections under 1.5degrees Celsius warming and 42centimetres SLE using risk-averse projections under current pledges), adaptation planning for twenty-first-century sea level rise must account for a factor-of-three uncertainty in the land ice contribution until climate policies and the Antarctic response are further constrained.