Future sea-level rise may be much higher than thought: Greenland ice loss ‘vastly underestimated’

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

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

By 2100, the Northeast Greenland Ice Stream will contribute six times more to sea level rise than previous models suggested, adding 13.5 to 15.5 mm (0.53 to 0.61 in ), according to the new study. This is equivalent to the contribution of the entire Greenland ice sheet in the last 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 greatly underestimated,” said first author Shfaqat Abbas Khan, professor at DTU Space.

“The models mostly fit the observations at the front of the ice sheet, which is easily accessible and where, visibly, a lot is happening.”

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

Ice loss occurs more than 200 km inland

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

“Our data shows us that what we see happening at the front reaches the heart of the ice sheet,” Khan said.

“We can see that the entire basin is thinning and the surface velocity is accelerating. Each year the glaciers we’ve studied have retreated further inland, and we predict this will continue for decades and centuries to come. Under current climate forcing, it is difficult to conceive of how this retreat could be stopped.”

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

Significant contribution to sea level rise

In 2012, after a decade of melting, the floating extents of Zachariae Isstrøm collapsed and the glacier has since retreated inland at an accelerated rate. And although the winter of 2021 and the summer of 2022 have been particularly cold, the glaciers continue to retreat. Because northeast Greenland is a so-called arctic desert (in some places precipitation is as little as 25 mm a year), the ice sheet is not regenerating enough to mitigate the melting. However, estimate the amount of ice that is lost and to what extent the process occurs in the ice layer. The interior of the ice sheet, which moves at less than a meter per year, is difficult to monitor, limiting the ability to make accurate projections.

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

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

The Zachariae Isstrøm remained stable until 2004, followed by the 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, the IPCC estimates of sea level rise between 22 and 98 cm are likely to need to be revised upwards.

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

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

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