Greenland ice sheet melting faster until 2100 | Polarjournal
Every summer, the Greenland ice sheet melts at its surface and the water runs off either on top of or underneath the ice sheet. In recent decades, this melting process has increased more and more and has now overtaken the formation of new ice in many places in Greenland. Picture: Michael Wenger

In the Arctic, ice is melting away rapidly both on the sea and on land due to global warming. Scientists are paying particular attention to the ice sheets on the mainland, as their melting is causing sea levels to rise. The Greenland Ice Sheet plays the leading role. Previous model calculations predicted that by the year 2100 the melting processes on Greenland could cause the global sea level to rise by up to 10 centimetres. But a new study now shows that the increase can be as much as 18 centimeters. The reason for this is better model calculations.

The model that produced the new results is the same one that was used for the last climate report of the IPCC (Climate Change Panel). The large-scale study, led by the Laboratory of Climatology of the University of Liège and resulting in two publications, “fed” the MAR model with the latest findings and results of other research groups and concluded that Greenland’s ice sheet would melt 60 percent more than previously assumed in the “worst case scenario”. “While our MAR model suggested that in 2100 the surface melting of the Greenland ice sheet would contribute to a rise in the oceans of around ten centimetres in the worst-case scenario (if we don’t change our habits), our new projections now suggest a rise of 18 centimeters,” explains lead author of one study, Dr. Stefan Hofer of the University of Oslo. His work was published in Nature Communications and predicts sea level rise.

The animation shows the differences between the two calculations (left: old prediction, right: new prediction) and how the melting of the Greenland ice sheet looks much stronger with the new findings. The more blue, the greater the difference between ice formation and melting Image: University of Liège

According to the research group, the new findings on the influence of cloud cover and feedback mechanisms of faster melting sea ice have resulted in an amplification of warming by 1.3°C, which leads to the result of more rapidly rising sea levels. This statement was supported by the research of the second research group of Dr. Xavier Fettweis from the University of Liège. They had compared the original MAR model with several new models and figured out how the differences in the two results came about. In doing so, they compared the model predictions with the current situation. “It would now be interesting to analyse how these future projections are sensitive to the MAR model that we are developing by downscalling these scenarios with other models than MAR as we have done on the present climate,” explains Dr. Fettweis. The aim of this new project is to be able to assess global changes of te cryosphere with fully quantified uncertainties and thus to make better and more reliable predictions of local, regional and global sea-level rise.

Sea levels rise when ice from Greenland’s glaciers reaches the sea through calving and melts there. Due to warming, which affects the glaciers at different levels, this process accelerates, the glaciers lose more ice and thus the Greenland ice sheet loses mass. Because there is not enough snow falling at the back to compensate for the melt. Picture: Michael Wenger

In their new project, however, the group around Xavier Fettweis does not only want to investigate the influences of cloud cover and enhanced sea ice mechanisms. The catabatic winds that roar from the interior of the ice sheet to the coast are also to be included. He hopes that this will provide an even more robust statement of the MAR model and thus also for the IPCC report. “Knowing that the wind influences the melting of the ice sheet, it is important to have the most reliable models possible,” he concludes.

Greenland’s ice sheet is up to 3,200 metres thick in its centre and then flattens out towards the edges. This means that air masses that cool and sink in the centre of the island become faster and faster towards the edge and reach gale force on the coast as katabatic winds. This has an influence on the melting of the surface. Picture: Michael Wenger

Dr Michael Wenger, PolarJournal

Links to the studies:

Hofer, S., Lang, C., Amory, C. et al. Greater Greenland Ice Sheet contribution to global sea level rise in CMIP6. Nat Commun 11, 6289 (2020). https://doi.org/10.1038/s41467-020-20011-8

Fettweis et al. (2020)The Cryosphere, 14, 3935-3958, GrSMBMIP: intercomparison of the modelled 1980-2012 surfacemass balance over the Greenland Ice Sheet; https://doi.org/10.5194/tc-14-3935-2020

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