Ice loss from northeast Greenland was significantly underestimated

Ice continues to flow from Greenland’s melting glaciers at an accelerating rate, dramatically raising global sea levels. New results were published today at Nature show that existing models have underestimated how much ice will be lost during the 21st century. Therefore, its contribution to sea level rise will be significantly higher.

By 2100, the Northeast Greenland Current will contribute six times more to sea level rise than previous models suggested, adding between 13.5 and 15.5 mm, according to the new study. This is equivalent to the contribution of the entire Greenland ice sheet over the past 50 years. The research was carried out by researchers from Denmark, the United States, France and Germany

“Our previous predictions of Greenland ice loss by 2100 are greatly underestimated,” said first author Shfaqat Abbas Khan, 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 based in part on data collected from a network of precise GPS stations reaching up to 200 kilometers inland in the Northeast Current of Greenland – located behind the Nioghalvfjerdsfjord Gletscher and Zachariae Isstrøm glaciers, one of the most hostile and remote lands of the Earth. GPS data was combined with surface elevation data from the CryoSat-2 satellite mission and high-resolution numerical modeling.

“Our data shows that what we see happening at the front extends far back into the heart of the ice sheet,” Khan said.

“We can see that the entire basin is thinning and the surface velocity is accelerating. Every year the glaciers we studied are retreating further inland, and we predict that this will continue in the coming decades and centuries. Under today’s climate conditions, it is difficult to conceive how could stop this retreat.”

Significant contribution to sea level rise

In 2012, after a decade of melting, the floating reaches of Zachariae Isstrøm collapsed and the glacier has since retreated inland at an accelerated rate. And although the winter of 2021 and summer of 2022 were particularly cold, the glaciers continue to retreat. Since northeast Greenland is a so-called arctic desert—precipitation is as low as 25 mm per year in places—the ice sheet is not regenerating enough to moderate the melting. However, estimating how much ice is lost and how far into the ice sheet the process occurs is not easy. The interior of the ice sheet, which moves at less than a meter per year, is difficult to track, limiting the ability to make accurate projections.

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

“It’s possible that what we’re finding in northeast Greenland may be happening in other areas of the ice sheet. Many glaciers have been accelerating and thinning near the margin in recent decades. GPS data is helping us trace how far this acceleration is spreading inland, possibly 200 –300 km from the coast. If this is correct, the contribution of ice dynamics to the total mass loss of Greenland will be greater than current models suggest.”

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

“We predict profound changes in global sea levels, more than are currently predicted by existing models,” said Eric Rignot, a professor of Earth systems science at the University of California, Irvine.

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