The Greenland ice sheet is the second largest ice mass on Earth after Antarctica - and it is rapidly becoming smaller. The loss in Greenland has increased about sixfold since the 1980s, warns now an international research team, which has evaluated data from the years 1972 to 2018.
Accordingly, the ice mass on the island increased in the 1970s. But since 2010, the ice sheet lost an average of about 290 gigatons - that is, billions of tons - in mass per year, as the researchers around Eric Rignot and Jérémie Mouginot from the University of California at Irvine reported in the journal "Proceedings of the National Academy of Sciences".
Among other things, the team has combined ice thickness, mass and flow rate measurements for 260 glacier regions in Greenland. According to the authors, the new study now provides an assessment of ice sheet development over the past 46 years. Depending on the technology used, the available data series were 20 to 30 years shorter.
The new data show that the island's ice mass rose by 47 gigatons per year in the first decade of the 1972 to 1980 survey. For comparison: Lake Constance contains almost 50 gigatons of water.
In the period between 1980 and 1990, the annual ice loss in Greenland was 51 gigatons. In the following decade, from 1990 to 2000, the year-on-year loss of 41 gigatons was slightly lower, before rising sharply: to 187 gigatonnes per year between 2000 and 2010 and then, from 2010 to 2018, to 286 gigatons per year. The annual ice loss is thus currently greater than in the Antarctic.
A team around Eric Rignot had only calculated the ice loss there in January. Accordingly, the Antarctic lost in the years 2009 to 2017 about 252 billion tons of ice per year. According to the researchers, not only the West Antarctic but, surprisingly, the eastern part of the continent, which until now has been regarded as relatively stable, are also affected.
Strong sea level rise over the past eight years
While the melting of Arctic sea ice floes has no impact on sea level, thawing in Greenland and the Antarctic contributes to a rise in water levels. The loss of mass of the glaciers in Greenland since 1972 corresponds to a sea level rise of 13.7 millimeters, write Rignot and colleagues. About half of this is attributable to the past eight years.
However, the development of individual glacier regions is very different: for example, the areas of Jakobshavn-Isbrae, Steenstrup-Dietrichson and Humboldt lost a great deal of ice, while others increased in mass or remained similar. "This result illustrates how risky it is to extrapolate ice loss based on the trend of a few glaciers," say the researchers.
Ultimately, the development of glaciers depends on various factors. In addition to the melting of the ice, these include, in particular, the constantly changing flow velocity of the ice streams that lead from the interior of the island into the sea. Researchers have recently reported that the Jakobshavn-Isbrae has even grown again recently. This has to do with a changed ocean current in the Atlantic. However, the glacier is not saved with that, in the long term it is likely to shrink again.