Greenland loses more ice cream than expected

Researchers are correcting ice loss by 20 gigatons per year

The glaciers of Greenland are in acute distress due to global warming. © Ingo Sasgen / AWI
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False model calculation: The Greenland glaciers are melting faster than previously thought. This shows a comprehensive analysis of GPS data. Accordingly, the ice sheet loses 272 gigatonnes of mass per year - that's about 20 gigatons more than previous calculations have shown. Accordingly, a mistake has crept into the current models, as researchers report in the journal "Science Advances".

Greenland's ice is the second largest reservoir of water ice on our planet - and one that is gnawing climate change. Global warming is making the Greenland glaciers increasingly unstable, causing the ice giants to melt. The ice sheet has been losing ground for years. Researchers have calculated that from the glaciers every year as much meltwater flows as in five Lake Constance fits.

How strong is the land?

Now, however, the extent of ice loss could be even greater. Because the previous calculations have ignored a crucial point, as researchers report to Shfaqat Abbas Khan of the Technical University of Denmark.

The geoscientist and his colleagues used a new network of GPS stations to accurately measure how much the Earth's crust is rising in Greenland. Such land elevations are an indication of how much ice loss a region has experienced in the past: A powerful ice sheet pushes the ground down and lets it sink. If the ice melts, the country lifts up with a time delay.

Seven percent faster

The measurements reveal that the crustal uptake is significantly higher than assumed in previous model calculations. Accordingly, the subsoil of Greenland sometimes lifts up to twelve millimeters per year. This result indicates a more massive glacial decline since the last ice age, writes the team. display

If one corrects the current calculations by this new value, it shows: The ice mass has not decreased in the period from 2004 to 2015 by an average of 253 gigatons per year - but by 272 gigatons. Greenland ice melts seven percent faster than expected. Based on the new data, researchers now conclude that the melting Greenland ice has caused a sea-level rise of 4.6 meters since the glacial maximum in the last ice age. So far, experts expected a rise of 3.2 meters.

Hotspot as a source of error

But how did the mistake in previous calculations come about? Khan and his colleagues explain that: The rate of uplift depends not only on the strength of the ice sheet but also on the nature of the lithosphere and here the Models probably ignored a peculiarity: The subsoil under Gr nland slipped over about 40 million years ago in the course of the large plate movements over a "hotspot" in the earth's mantle.

Today, Iceland is home to its volcanoes and hot springs over this hotspot. From these millions of years of heating up of the Greenland underground, a thinner lithosphere leads than, for example, under Scandinavia, and with false information about the thickness of the lithosphate Also, the calculations of the land survey in Gr nland are incorrect.

Northwest and southeasts particularly affected

However, the deviation of about 20 gigatons per year is not particularly dramatic, says co-author Michael Bevis of Ohio State University: "It's a rather small correction." For the researchers, the new results are nevertheless of great Their importance: Thanks to GPS data, they are now better able to identify the regions in which global warming has eaten the most on the ice, and where it has a particularly strong impact today.

Thus Khan's team found particularly strong deviations in the northwest and in the southeast of Gr nland. This is where the country stands out most and even today, in those regions where the glaciers calve directly into the ocean, the largest ice mass losses take place. According to the new results, the climate sensitivity of these regions is probably even higher than expected, the researchers say. "Presumably, dwindling greenland ice will continue to rise sea level for centuries, " they conclude. (Science Advances, 2016)

(German Research Center for Geosciences GFZ / The Ohio State University / University of Bristol, 22.09.2016 - DAL)