Future sea level rise could be much higher than predicted – Greenland ice loss ‘grossly underestimated’

A new study combined GPS, satellite data and numerical modelling. It revealed that northeast Greenland’s ice loss could be six times greater by the end of the century than previously thought.

Ice is continuously flowing from melting Greenland glaciers at an accelerating rate, dramatically raising global sea levels. New findings published in the journal Nature on November 9 indicate that existing models have underestimated the amount of ice that will be lost in the 21st century. Therefore, its contribution to sea level rise will be significantly higher.

By 2100, the northeast Greenland ice stream will contribute six times more to sea level rise than previous models suggested, adding between 13.5 and 15.5 mm (0.53 to 0.61 inches), according to the new study. This is equivalent to the total contribution of the Greenland ice sheet over the past 50 years. Scientists from Denmark, the United States, France and Germany conducted the research.

“Our previous projections of ice loss in Greenland until 2100 are grossly underestimated,” said first author Shfaqat Abbas Khan, a professor at DTU Space.

“The models are mostly tuned to observations at the front of the ice sheet, which is easily accessible and where obviously a lot is going on.”

Animation of modeled frontal positions from 2007 to 2100. A Landsat-8 image from 2017 is used as background. The color indicates the surface speed. Credit: Animation by Shfaqat Abbas Khan, DTU Space, Denmark

Ice loss occurs more than 200 km inland

The study is partly based on data collected from a network of precise GPS stations reaching up to 200 km inland on the northeast Greenland Ice Stream, located behind the Nioghalvfjerdsfjord glaciers. Gletscher and Zachariae Isstrøm, one of the harshest and most remote terrains on Earth. GPS data was combined with surface elevation data from the CryoSat-2 satellite mission and high-resolution digital modeling.

“Our data shows us that what we see happening at the front goes way back to the core of the ice sheet,” Khan said.

“We can see that the whole pelvis is getting thinner and the surface speed is accelerating. Each year, the glaciers we have studied have retreated further inland, and we expect this to continue for decades and centuries to come. Under the current climatic forcing, it is difficult to conceive how this decline could stop.

Animation of modeled surface elevation change from 2007 to 2100. A Landsat-8 image from 2017 is used as the background. The colors indicate the change in elevation of the surface. Negative values ​​indicate a thinning/lowering of the surface. Credit: Animation by Shfaqat Abbas Khan, DTU Space, Denmark

Significant contribution to sea level rise

In 2012, after a decade of melting, the floating extensions of Zachariae Isstrøm collapsed and the glacier has since retreated inland at an accelerating rate. And if the winter of 2021 and the summer of 2022 were particularly cold, the glaciers continue to retreat. Since northeast Greenland is a so-called arctic desert – rainfall is as low as 25mm per year in places – the ice cap is not regenerating enough to mitigate the melting. However, it is not easy to estimate the amount of ice loss and how far the process is occurring in the ice sheet. The interior of the ice sheet, which is moving less than a meter per year, is difficult to monitor, limiting the ability to make accurate projections.

“It is truly amazing that we are able to detect a subtle velocity change from high precision GPS data, which ultimately, when combined with an ice flow model, tells us how the glacier slips on his bed,” said co-writer Mathieu Morlighem. , professor of earth sciences at Dartmouth College.

“It is possible that what we find in northeast Greenland is happening in other areas of the ice sheet. Many glaciers have accelerated and thinned near the margin in recent decades. GPS data helps us detect how far inland this acceleration propagates, potentially 200-300 km from the coast. If this is correct, the contribution of ice dynamics to Greenland’s overall mass loss will be larger than current models suggest. »

The Zachariae Isstrøm remained stable until 2004, followed by a steady retreat of the ice front until 2012, when a large part of the floating sections disconnected. As more accurate observations of ice speed change are included in the models, it is likely that IPCC estimates of a global sea level rise of 22-98cm will need to be corrected upwards.

“We project profound changes in global sea level, more than currently predicted by existing models,” said co-author Eric Rignot, professor of Earth system science at the University of California, Irvine.

“Data collected from the vast interior of ice sheets, such as those described here, help us to better represent the physical processes included in numerical models and in turn provide more realistic projections of global sea level rise. .”

Reference: “Extensive inland thinning and speed-up of Northeast Greenland Ice Stream” by Shfaqat A. Khan, Youngmin Choi, Mathieu Morlighem, Eric Rignot, Veit Helm, Angelika Humbert, Jérémie Mouginot, Romain Millan, Kurt H. Kjær and Anders A Bjørk, November 9, 2022, Nature.
DOI: 10.1038/s41586-022-05301-z