DTU Space

Ice melting at increasing rate

Tuesday 23 Mar 21

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René Forsberg
Professor
DTU Space
+45 45 25 97 19

Contact

Shfaqat Abbas Khan
Professor
DTU Space
+45 45 25 97 75

All measurements of the Greenland ice sheet indicate it is melting faster than previously thought.

The melting of the Greenland ice sheet has accelerated since the 1990s. The continent lost 4,300 km3 of ice between 1992 and 2018. This is equivalent to 4,300 ice cubes, 1 km in height, width, and depth, having melted and run into the oceans as extra water. Just over three such ice cubes melt each week on average. This melting has contributed to an 11 mm rise in sea level during the period.

These were the conclusions of one of the most comprehensive international studies on ice melting in Greenland to date, which was published in late 2019. The study found that Greenland is losing its ice seven times faster than in the 1990s. At that time, around 38 billion tonnes of ice melted each year. By 2018, this figure had grown to 254 billion tonnes of ice per year.

The study also concluded that the melting ice sheet is contributing to sea level rises that are now close to the UN climate change panel’s most pessimistic scenarios (RCP8.5). The expected melting of the ice sheet could bring the rise in global sea levels up to around 67-70 cm in the year 2100.

Aerial measurements of the ice sheet

Almost 90 researchers from 50 international organizations contributed to the Ice Sheet Mass Balance Intercomparison Exercise (IMBIE) study in Greenland. Among them were several researchers from DTU Space, including René Forsberg, who heads the European Space Agency’s (ESA) Climate Change Initiative for Greenland.

They process data from the various satellite missions and coordinate DTU’s work with aerial measurements of the ice sheet and sea ice in the Arctic and Antarctica. The aerial measurements are used to validate the satellite measurements that are registering the current ice changes.

The measurements are made using a small Twin Otter aircraft, equipped with laser scanning and various radar systems. The flights have often been coordinated with research teams on the ice, as well as other airborne missions, including from NASA. The combination of surface, aerial, and satellite measurements ensures that a picture of the ice height and changes can be formed with only a few centimetres of variation, when all the data is subsequently processed and analysed. 

All measurements of the Greenland ice sheet and Antarctica suggest that the ice caps are melting faster than previously assumed.

This photo was taken over Antarctica, where DTU Space performed measurements similar to those in Greenland.

GPS stations in Greenland

Another professor at DTU Space—Shfaqat Abbas Khan—also participated in the large IMBIE study, the results of which confirm the findings in several of his previous joint research projects, which also demonstrated accelerating melting of the ice sheet. Shfaqat Abbas Khan analysed data from the approx. 60 unmanned GPS stations spread around the perimeter of the Greenland ice sheet.

“A GPS station measures with millimetre accuracy, and not just its near vicinity. It is sensitive in a radius of up to 100 km,” says Shfaqat Abbas Khan, who has used the measurements to calculate the rises in the Greenlandic bedrock, which moves up as the heavy ice cap melts. The GPS measurements supplement the satellite measurements, which are also taken in the perimeter zone of the ice sheet.

Future satellite missions 

DTU works closely with ESA, including on the CryoSat-2 radar mission. Since 2010, this has been measuring the thickness of sea ice in the Arctic Ocean and the elevation changes in the polar ice sheet with great precision. DTU is also participating in the scientific work on a number of new satellite missions, monitoring ice changes at the North and South Poles and changes in the global sea level.

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