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.
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 online journal Nature Communications. An international team of researchers from a number of institutions – headed by DTU Space – 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.
Indication of future ice mass loss scenario
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.
“The ice mass loss here gives a very good picture of the situation in the rest of Greenland and the Arctic region, and guides us on what the likely future scenario will be,” says Shfaqat Abbas Khan.
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.
“We’re seeing that a small change in the global temperature is having a major impact and resulting in somewhat higher increases in the Arctic region, which, in turn, leads to large-scale ice mass loss,” says Shfaqat Abbas Khan.
“This ice mass loss of just over eight millimetres corresponds more or less to the worst-case future scenario we have for the period between now and towards 2100. But this future scenario is based on a calculation that an average Greenland temperature increase of 8-9 degrees is required to melt this much ice. Not the 1.5 degrees.”
Worse than the UN’s most extreme scenario
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. Recent research shows that the increase in the Arctic region will be up to about 8.3 degrees Celsius.
In the IPCC’s scenario, the ice mass loss from the three Greenland glaciers is only 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.
“Our results provide important insights on how Greenland glaciers responded in the past and, therefore, how sensitive these glaciers could be in the future,” says Professor at the University of Bristol in the UK Jonathan Bamber, another contributor to the project and the scientific article.
This makes Shfaqat Abbas Khan conclude that the IPCC’s climate scenarios underestimate how much the seas will rise.
“If we look 100 years ahead with a scenario in which the temperature rises by about 8.3 degrees in Greenland, we will not – as previously assumed – only see sea level rise of 9-15 millimetres from these glaciers. We will rather see perhaps three or four times as much,” he says.
According to the scientists this is also going to be the case for the rest of the Greenland ice sheet. In other words, the results suggest that the ice sheet contribution could be several times larger than what the models currently project for the whole ice sheet.
“Therefore, we believe that the models should be expanded and updated with this new knowledge to become more correct. They are currently not accurate because the present data sets are deficient. By looking back 100-130 years and using this data in the models, you can get a more realistic picture when looking 100 years ahead,” says Shfaqat Abbas Khan.
The ice sheet models used by the IPCC in its sea level rise scenarios are based primarily on satellite data going back only about 20-30 years.
New satellite data and old aerial photos
The researchers have laboriously collected data from 1880 to the present day. And then fed the data into an ice mass loss model. Many different data types make up the new picture.
“It has been an extensive and exciting piece of detective work. To arrive at the new picture of the ice mass loss, we’ve used satellite data from recent times, older aerial photos and everything we’ve been able to find of records in the form of, for example, historical photos from expeditions showing where the glacier front was,” says Shfaqat Abbas Khan.
The researchers have then performed various analyses, including based on position and height coordinates on maps, and have seen how this has changed over time based on the available data sources. For example, the height of the ice, the extent in relation to recognizable points and how the ice margin has receded inland relative to the coastline.
An in this way they have been able to establish a unique and thorough picture of the historic ice loss in Greenland.
Danish and international cooperation on climate change research
The new study in Nature Comunications – Centennial response of Greenland’s three largest outlet glaciers – is a result of an international cooperation headed by DTU Space.
Danish contributors apart from DTU/DTU Space are: University of Copenhagen, University of Aalborg, University of Aarhus and GEUS.
International contributors are, among others, University of Bristol (UK), University of California and Ohio State University (US), The Alfred Wegener Institute (GER) and Université Grenoble Alpes (FR) as well as research institutions in China.
DTU Space contributes to the green transition by, among other things, conducting research, develop technology and monitoring the consequences of climate change on Earth. This knowledge is for example being used in climate models and to find solutions to handle and mitigate climate change.
We develope and build space-based technology, for example for satellites that monitor changes in the world’s oceans sea levels, the melting of ice at the poles and the earth’s forest and land areas. And we use this and other partners’ technology – which is typically part of ESA and NASA missions – to conduct climate change research. We do not only collect earth data from space, but also via aircraft, drones and by measurements on land and water, for example on the ice sheet in Greenland.
In the new study we have used satellite data as well as old aerial photos and maps from previous expeditions in Greenland to get an overview of how three large glaciers in Greenland have melted historically in order to better understand what may happen to them in next 100 years. The animation below shows how one of the three glaciers – Jakobshavn Isbræ in western Greenland – has retreated for more than 130 years. (Animation: DTU Space)
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