Even if greenhouse gas emissions stopped immediately, Greenland’s ice loss would raise the global sea level by a good 27 centimeters, most of it within this century.
The estimate is not based on calculations with computer models, but on measurements from the years 2000 to 2019. A group led by Jason Box from the Geological Survey of Denmark and Greenland in Copenhagen has published their results in the journal “Nature Climate Change”.
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The researchers explain that model calculations cannot be used to predict exactly what will happen to the Greenland ice sheet as a result of global warming. They therefore also pursued an approach in which the amount of ice that has become unstable due to global warming is determined by measurements on site and by satellite.
Specifically, they determined a snow line of the ice sheet, which lies between the higher central area of the ice, where fallen snow does not melt even in summer, but is compacted into ice with further snowfall. At the lower edge of the ice sheet, some of the snow that fell in winter and the ice underneath are melting away. This will continue even if the regional climate does not warm up further.
Box and colleagues determined the proportion of this ice to be 3.3 percent of the total ice mass. That corresponds to 110,000 cubic kilometers of ice. “Our observations suggest that most of the induced sea-level rise will occur in this century,” Box said.
Furthermore, the measurements show that the ice losses in the south and west of the island are considerably greater than in the east and north. The scientists write that computer models do not represent these differences well.
The 27 centimeters are a minimum estimate. “Realistically, that number will more than double this century,” Box says. The researchers arrived at this higher estimate by basing the calculation on data from 2012 with the highest melt rate measured to date. In this case, the melting of the Greenland ice sheet would result in a sea level rise of more than 78 centimeters.
As examples of recent processes driving ice retreat, the researchers cite the loss of floating ice shelves, an acceleration of internal ice movement, more rain on the surface, and a biologically induced darkening of the ice surface, which increases heat absorption and melting.
The Greenland ice sheet covers a good four-fifths of the total area of the world’s largest island. Its area is about five times the size of Germany. Only the Antarctic ice sheet is larger. The island is particularly badly affected by climate change, as the Arctic is warming significantly more than any other region on earth.
The Greenland ice sheet is currently the main contributor to sea level rise. Its melting has already caused around 1.2 centimeters of global sea level rise within almost 20 years, as the Danish Polar Portal announced in February. Since the start of corresponding measurements in April 2002, the Greenland ice sheet has lost around 4,700 gigatons – enough to put the entire United States half a meter under water. One gigatonne equals one billion tons.