Ice sheets and glaciers are shrinking. But we can still slow that process dramatically, study finds

BUFFALO, N.Y. — New research from a large international community of scientists predicts that sea level rise from the melting of ice could be halved this century if the world meets the Paris Agreement target of limiting warming to 1.5 degrees Celsius. That’s relative to projections based on countries’ current pledges to reduce emissions of heat-trapping gases.

The study, published in Nature on May 5 and led by Tamsin Edwards, PhD, reader in climate change at King’s College London, explores the land ice contribution to sea level in the 21st century arising from the world’s glaciers and the Greenland and Antarctic ice sheets. Edwards is the lead author on the paper, “Projected land ice contributions to twenty-first-century sea level rise,” and worked with more than 80 authors internationally.

Contributors included University at Buffalo climate scientist Sophie Nowicki, PhD, the paper’s second author. Nowicki led the Ice Sheet Model Intercomparison Project for phase 6 of the Coupled Model Intercomparison Project (ISMIP6), a major international effort that provided key data for the study. UB’s Center for Computational Research (CCR) facilitated the research by providing resources for data storage and sharing.

The new study in Nature uses a large number of computer models combined with statistical techniques, making predictions for the latest socio-economic scenarios to inform the Intergovernmental Panel on Climate Change's Sixth Assessment report, which will be published later this year.

The research predicts that if the world can limit global warming to 1.5 degrees Celsius, Greenland Ice Sheet losses would fall by 70%, and glacier losses by half, compared with current emissions pledges (called nationally determined contributions). For Antarctica, the predictions did not produce a clear link between the volume of ice loss and different emissions scenarios. This is because it is unclear whether snow falling in the cold interior of the ice sheet will offset melting at the coasts. However, under a “pessimistic” storyline, with much more melting than snowfall, Antarctic ice losses could be five times larger.

Edwards, director of the King’s Climate Hub, says, “Ahead of COP26 this November, many nations are updating their pledges to reduce greenhouse gas emissions under the Paris Agreement. Global sea level will continue to rise, even if we halt all emissions now, but our research suggests we could limit the damage: If pledges were far more ambitious, central predictions for sea level rise from melting ice would be reduced from 25 centimeters to 13 centimeters in 2100, with a 95% chance of being less than 28 centimeters rather than the current upper end of 40 centimeters. This would mean a less severe increase in coastal flooding.” (COP26 is the 2021 United Nations Climate Change Conference.)

“This study is important because the statistical techniques used — called emulation — allowed us to explore many more different futures than possible with the numerical ice sheet and glacier models,” says Nowicki, Empire Innovation Professor in the Department of Geology in the UB College of Arts and Sciences, and in the UB RENEW Institute. “This is because numerical modeling takes a lot of time and computer resources and so we are limited in the number of simulations that we can do.

“These numerical simulations, however, are the key input for the emulator. ISMIP6 gave key inputs for this study, providing 600 sea level rise projections from the Greenland and Antarctic ice sheets from 27 international ice sheet models. The first ISMIP6 workshop that I organized was 7 years ago, and it took us as a community this whole time to get here.”

The study adds to evidence — such as a 2020 study on the Greenland Ice Sheet led by UB geology professor Jason Briner, PhD — indicating that reductions to emissions of heat-trapping gases can have an important impact on how much sea levels rise this century.

Glaciers and ice sheets are currently responsible for around half of global sea level rise, with most of the rest arising from expansion of the oceans as they warm. Previous predictions had used older emissions scenarios, and could not explore uncertainty about the future as thoroughly due to the limited number of simulations. This statistically-based study updates the scenarios, and combines all sources of land ice into a more complete picture that predicts the likelihood of different levels of sea level rise.

“We used a larger and more sophisticated set of climate and ice models than ever before, combining nearly 900 simulations from 38 international groups using statistical techniques to improve our understanding of uncertainty about the future,” Edwards says. “Antarctica is the ‘wildcard’ of sea level rise: difficult to predict, and critical for the upper end of projections. In a pessimistic storyline, where Antarctica is very sensitive to climate change, we found there is a 5% chance of the land ice contribution to sea level rise exceeding 56 centimeters in 2100 even if we limit warming to 1.5 degrees Celsius. Coastal flood management must therefore be flexible enough to account for a wide range of possible sea level rise, until new observations and modeling can improve the clarity of Antarctica’s future.”