New projections of ice loss and sea level change

A special investigation presents new estimates on melting ice sheets and sea level rise. The international effort ISMIP6, led by NASA and with several NESSC-researchers from Utrecht University, has published new projections of the effect of greenhouse gas emissions on Greenland and Antarctica’s role in sea level rise. The estimations are based on the IPCC carbon dioxide emissions scenarios, and are beyond the amount that has already been set in motion by Earth’s warming climate. The results have been published in a special issue of the journal The Cryosphere.

The research is a result of the Ice Sheet Model Intercomparison Project (ISMIP6), which brings together more than sixty ice, ocean and atmosphere scientists from three dozen international institutions and is led by NASA’s Goddard Space Flight Center. “The strength of ISMIP6 was to bring together most of the ice sheet modeling groups around the world, and then connect with other communities of ocean and atmospheric modelers as well, to better understand what could happen to the ice sheets,” says NESSC-researcher Heiko Goelzer, now at NORCE Norwegian Research Centre. Goelzer led the Greenland ice sheet ISMIP6 effort.

Two scenarios
The ISMIP6 team investigated two different IPCC scenarios: one with carbon dioxide emissions increasing rapidly, another with lower emissions. In the high emissions scenario, the researchers found that the mass loss of the Greenland ice sheet would lead to an additional global sea level rise of about 9 centimeters by 2100. In the lower emissions scenario, the loss from the ice sheet would raise global sea level by about 3 centimeters.

Ice loss from the Antarctic ice sheet is more difficult to predict: In the west, warm ocean water erode the bottom of large floating ice shelves, causing ice loss, while the vast East Antarctic ice sheet can gain mass, as higher temperatures cause increased snowfall. The results point to a greater range of possibilities, from an ice sheet change that decreases sea level by almost 8 centimeters to increasing it by 30 centimeters by 2100.

Improving projections
“It took over six years of workshops and teleconferences with scientists from around the world working on ice sheet, atmosphere, and ocean modeling to build a community that was able to ultimately improve our sea level rise projections,” tells project leader Sophie Nowicki at NASA. “The reason it worked is because the polar community is small, and we’re all very keen on getting this problem of future sea level right. We need to know these numbers.”

The new results will help inform the Sixth IPCC report which is scheduled for release in 2021/2022.

Special issue | The Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6)
The Cryosphere, 2020

The future sea-level contribution of the Greenland ice sheet: a multi-model ensemble study of ISMIP6
ISMIP6 Antarctica: a multi-model ensemble of the Antarctic ice sheet evolution over the 21st century