​More than 99% of the earth's ice is found in the ice sheets covering Antarctica and Greenland. Under the effect of climate change, their melting, even partial, will contribute significantly to a rise in sea level. By how much?
For the first time, glaciologists, oceanographers and climatologists from 13 countries have joined forces to produce new projections under CMIP5 and CMIP6 scenarios (see below). Their simulations are organized as part of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6).

Simulations indicate that the melting of the Antarctic ice sheet could contribute up to 30 cm to sea level rise from 2015 to 2100 but could also mitigate it by up to 7.8 cm at best. Indeed, certain models and scenarios predict that snow accumulation could exceed the loss due to ice melt.
This very significant uncertainty is explained by the melting of the lower extensions of the ice sheet over the ocean (ice shelves) - a poorly understood mechanism governed by changes in the ocean. These floating extensions, whose surface areas can be as large as half that of France, are contrary to the melting of the cap. Assuming their imminent disappearance, projections indicate a sea level rise of several meters over 500 years!
For the Arctic, over 2015-2100, the Greenland ice sheet would contribute between 1.5 cm and 14 cm, depending on the trajectory of greenhouse gas emissions due to human activity.

To refine these estimates, scientists are working on a new generation of climate models that will describe the cryosphere, along with the atmosphere, ocean and biogeochemistry.

CMIP5 and CMIP6

The Coupled Model Intercomparison Project (CMIP) is part of the World Climate Research Programme (WCRP). Its aim is to coordinate climate simulations carried out by different research groups in order to better evaluate and understand the differences between climate models. Specifically, it makes it possible to determine uncertainty due to model imperfections in the prediction of climate change at work. CMIP5, the fifth and most recently completed phase of the project involved nearly 20 research centers around the world and nearly 50 climate models. The results of the simulations are taken into account in the assessment by the Intergovernmental Panel on Climate Change on the state of knowledge on climate. CMIP6 is currently underway.