Greenland outlet glaciers may be melting more quickly than predicted

Publiceret 17-11-2020
News

Greenland ice mass loss can contribute to sea level rise that surpass the most extreme scenario from the UN body on climate, the IPCC. According to new research headed by DTU and with contributions from GEUS, current climate models underestimate how fast the ice is melting in the Arctic.

The Jakobshavn Isbrae in Western Greenland has been retreating for more than 130 years as illustrated in this animation. (Credit: DTU Space)
The Jakobshavn Isbrae in Western Greenland has been retreating for more than 130 years as illustrated in this animation. Credit: DTU Space

Meltwater from the Greenland ice sheet represents the largest contribution to current global sea level rise. But there may very well be mechanisms that are not picked up by the current models for how fast the ice is melting in Greenland. This is suggested by new results from a groundbreaking international research project headed by DTU Space and with participation from GEUS. It appears that the ice is melting at a much higher rate and will contribute more to future sea level rise than previously assumed.

The researchers have studied the ice mass loss rates for three large outlet glaciers in Greenland over the past 100 years. It turns out that the three outlet glaciers—Jakobshavn Isbrae in Western Greenland as well as Helheim and Kangerlussuaq Glacier in Eastern Greenland—have lost ice corresponding to a sea level rise of 8.1 millimetres.

This equals 2,930 ice cubes of 1x1x1 kilometres having melted in the period between 1880 and 2012.

“It turns out that the ice has melted at a much higher rate than we’ve previously assumed. We have acquired this new and more detailed picture by studying ice mass loss over a very long period of time and by analysing old maps, aerial photos, and satellite measurements of the three outlet glaciers,” says Professor at DTU Space Shfaqat Abbas Khan, who has headed the research project.

These new findings have just been published in the international scientific journal Nature Communications. An international team of researchers from a number of institutions have carried out the extensive work with collection of maps, aerial photos, and satellite data, etc. to be able to piece together the unique historical picture of the ice mass loss.

“The three large outlet glaciers in Greenland together drain approximately 12 per cent of the area of the Greenland Ice Sheet. We can see that - between 1880 and 2012 - the three outlet glaciers have overall resulted in a global sea level rise of 8.1 millimetres,” says Kurt H. Kjær, Professor at the GLOBE Institute at the University of Copenhagen, who has also contributed to the scientific article in Nature Communications.

The ice mass loss from the three outlet glaciers constitutes a large and ‘representative’ proportion of the total ice mass loss for the Greenland Ice Sheet.

Tremendous ice loss in response to a small fraction of the climate change

Over the same period from 1880 to 2012 the average global temperature has increased by approximately 1.1 degrees Celsius. However, the temperatures develop very differently in various parts of the world. In Greenland, the average temperature has increased by approximately 1.5 degrees Celsius.

In the most extreme climate change scenario that the UN’s Intergovernmental Panel on Climate Change (IPCC) considers (called RCP8.5), there is a global average temperature increase of around 3.7 degrees Celsius by 2100 compared to today.

In the IPCC’s scenario, the ice mass loss from the three Greenland glaciers is expected to contribute to a global seal level rise of between 9.1 and 14.9 millimetres. The researchers have now shown that just a 1.5 degrees Celsius warming of Greenland has resulted in a sea level rise of 8.1 millimetres.

“The scale of ice loss being documented - nearly three thousand cubic kilometers - is difficult to comprehend. But the main concern is that this tremendous ice loss occurred in response to a climate change that is just a small fraction of the climate change that we anticipate over the next century,” says William Colgan co-author and Senior Researcher at GEUS.