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

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

Ice is constantly flowing from Greenland’s melting glaciers at an accelerating pace, causing dramatic sea levels worldwide. New results published in the magazine Nature on Nov. 9 indicate that existing models have underestimated how much ice will be lost in the 21st century. The contribution to sea level rise will therefore be considerably higher.

By 2100, the Northeast Greenland ice flow will contribute six times as much to rising sea levels as previous models suggested, between 13.5 and 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 over the past 50 years. Scientists from Denmark, the United States, France and Germany conducted the study.

“Our previous predictions of ice loss in Greenland up to 2100 have been vastly underestimated,” said first author Shfaqat Abbas Khan, a professor at DTU Space.

“Models are mainly geared to observations at the front of the ice sheet, which is easily accessible and where a lot is visibly happening.”

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 research is based in part on data gathered from a network of precise GPS stations reaching up to 200km inland on the Northeast Greenland Ice Stream – located behind the glaciers Nioghalvfjerdsfjord Gletscher and Zachariae Isstrøm, one of the most hostile and remote areas of the world. the earth. The 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’re seeing is happening at the front as far back as the heart of the ice sheet,” Khan said.

“We see that the entire basin is becoming thinner and that the surface speed is increasing. Each year, the glaciers we have studied have retreated further inland, and we predict this will continue for decades and centuries to come. Under the current climate forcing, it is hard to imagine how this withdrawal could stop.”

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

Significant contribution to rising sea levels

In 2012, after a decade of melting, the floating extensions of Zachariae Isstrøm collapsed, and the glacier has been retreating inland at an accelerating rate ever since. And while winter 2021 and summer 2022 have been particularly cold, the glaciers continue to retreat. Since northeast Greenland is a so-called Arctic desert – in places only 25mm falls per year – the ice sheet is not regenerating enough to soften the melt. However, it is not easy to estimate how much ice is lost and how far in the ice sheet the process takes place. The interior of the ice sheet, which moves at less than a meter per year, is difficult to control, limiting its ability to make accurate projections.

“It’s really amazing that we can detect a subtle change in speed from highly accurate GPS data, which eventually, when combined with a model of ice flow, informs us about how the glacier is sliding on its bottom,” said study co-author Mathieu Morlighem. a professor of earth sciences at Dartmouth College.

“It is possible that what we find in northeast Greenland is also happening in other parts of the ice sheet. Many glaciers have been accelerating and thinning near the rim in recent decades. GPS data helps us detect how far this acceleration is propagating inland, possibly 200-300 km from the coast. If true, the contribution of ice dynamics to Greenland’s overall mass loss will be greater than what current models suggest.”

The Zachariae Isstrøm was stable until 2004, followed by a gradual retreat of the ice front until 2012, when much of the floating sections became detached. Since more accurate observations of ice velocity changes have been incorporated into models, it is likely that the IPCC’s estimates of 22-98 cm global sea level rise will need to be corrected upwards.

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

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

Reference: “Extensive Thinning and Acceleration of the Northeast Greenland Ice Flow” by Shfaqat A. Khan, Youngmin Choi, Mathieu Morlighem, Eric Rignot, Veit Helm, Angelika Humbert, Jérémie Mouginot, Romain Millan, Kurt H. Kjær and Anders A Björk, Nov 9, 2022, Nature.
DOI: 10.1038/s41586-022-05301-z