Northeast Greenland’s ice loss is vastly underestimated

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Ice is continuously flowing from melting Greenland glaciers at an accelerating rate, dramatically raising global sea levels. New results released [DATE] in Nature 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, ice flow from northeast Greenland will contribute six times more to sea level rise than previous models suggested, adding between 13.5 and 15.5mm, according to the new study . This is equivalent to the total contribution of the Greenland ice sheet over the past 50 years. The research was conducted by researchers from Denmark, the United States, France and Germany

“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.”

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 basin is thinning and the surface velocity is accelerating. Each year, the glaciers we have studied have retreated further inland, and we expect this to continue. over the decades and centuries to come. Under the current climate forcing, it is difficult to conceive how this retreat could stop.”

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’s possible that what we find in northeast Greenland is happening in other areas of the ice sheet. Many glaciers have been accelerating and thinning near the margin in recent decades. The data GPS help 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 greater 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. .”

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