Melting ice sheets in Greenland and Antarctica could raise sea levels by an additional 44 cm by 2100

Melting ice sheets in Greenland and Antarctica could raise sea levels by an additional 44 cm by 2100

VUB ice sheet models contributed to large-scale NASA study

If greenhouse gas emissions continue at the current rate, the combined melt water of the Greenland and Antarctic ice sheets could contribute to an additional 44 cm in sea level rise by 2100, that is, on top of the sea level rise from recent global warming. This new estimate is the result of an international collaboration between more than 60 ice, ocean and atmosphere scientists, including scientists from the Vrije Universiteit Brussel. The results of this Ice Sheet Model Intercomparison Project (ISMIP6), led by NASA's Goddard Space Flight Center, are being published in a special issue of The Cryosphere magazine today.

“The strength of this project is that, for the first time, almost all existing ice sheet models carried out the same experiments under the same climate scenarios so that we can build a better picture of the uncertainty caused by differences in ice dynamics and future ocean and atmospheric conditions. This is a big step towards better being able to better inform the IPCC," says VUB glaciologist Philippe Huybrechts.

The results of the study are in line with estimates from the recent Intergovernmental Panel on Climate Change (IPCC) report on the oceans and cryosphere in 2019. This report stated that melting from the ice sheets could contribute to a third of the total sea level rise. The ISMIP6 team examined two of the scenarios put forward by the IPCC: one with a rapid increase in carbon emissions and another one with lower emissions. "One of the biggest uncertainties around the future sea level rise is how much ice sheets will contribute to the rise," says project leader and ice scientist Sophie Nowicki. "And how much the ice caps will contribute depends on what the climate will do."

Climate models

Different ISMIP6 groups worked on different aspects of the project. A first group of scientists selected the most reliable climate models for the polar regions, which were used as input for the ice sheet models. Another group calculated how higher ocean temperatures might contribute to increased ice shelf melting and increased erosion of glaciers that reach into the sea. The study comprised a total of 13 Antarctica and 14 Greenland ice sheet models. The VUB team performed calculations with their ice sheet models for both ice sheets. The VUB's three-dimensional flow models were developed more than 30 years ago and were the only ones of their kind for a long time. They were the foundation for the sea level projections of the polar ice sheets calculated in earlier IPCC climate reports.

The ISMIP6 team determined that the melting water of the Greenland ice sheet would lead to an additional sea level rise of on average 9 cm, with an uncertainty of ± 5 cm, by 2100 in a high-emission scenario. In the lower emissions scenario, the ice sheet loss is likely to increase the global sea level by about 3 cm, with an uncertainty of about ± 1.5 cm. This rise comes on top of the 6 mm sea level rise that is already unavoidable due to the global warming that has accumulated since the beginning of the Industrial Revolution. The ISMIP6 team also analysed the Antarctic ice sheet, which is much more difficult to project. In West Antarctica, warm ocean currents are melting the bottom of large, floating ice shelves, while the huge East Antarctic ice sheet may gain in mass as warmer temperatures are increasing snowfall there. It’s why their results cover a wider range of possibilities: from a 30 cm rise in sea level by 2100, to a drop of 8 cm. The regional projections show the greatest impact in West Antarctica, with a sea level rise of up to 18 cm by 2100 in the warmest conditions. For both ice sheets, the projections range between 0 and 20 cm in the low-emissions scenario, and -4 to +44 cm in the high-emissions scenario.

How should we interpret these results?

Observations from the last 40 years are close to, and even slightly above, the upper limit of the model results for the high emissions scenario. Failure to significantly reduce greenhouse gas emissions in the short term makes the sea level rise close to the maximum projected in the ISMIP6 study a possible outcome. The low emissions scenario assumes that the targets to keep warming below 2°C, as outlined in the Paris Climate Agreement, are met. In that case, it is even possible that the contribution from both ice sheets together will be close to zero as the increased snowfall in Antarctica might still compensate for increased melting in Greenland,” says Philippe Huybrechts.

The results of this study will be used in the sixth IPCC report, to be published in 2022.

Contact:

Philippe Huybrechts - philippe.huybrechts@vub.be - 0474993395

Jonas Van Breedam - jonas.van.breedam@vub.be - 0494602514

 

Links to the publication in The Cryosphere:

https://tc.copernicus.org/articles/14/3071/2020/

https://tc.copernicus.org/articles/14/3033/2020/

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