Researchers have recalculated the loss of ice in Greenland since 1972 when the first Landsat satellites were photographed regularly. And, unsurprisingly, the results of
their study, published Monday in the Proceedings of the American Academy of Sciences (PNAS), are anything but encouraging.
"When you look back over several decades, it's better to sit in your chair before looking at the results, because it's a bit scary to see how fast it's changing," said French glaciologist Eric Rignot, co-author. from the study with colleagues in California, Grenoble, Utrecht and Copenhagen. The phenomenon affects "the four corners of Greenland, not just the warmer parts in the South," says the specialist.
More and more reliable methods
Measuring melting ice in Greenland or Antarctica is a relatively accurate exercise in 2019, thanks to an arsenal of satellites, weather stations and sophisticated climate models. Glaciologists thus have three methods.
Satellites simply measure altitude, and its variations, with a laser. If a glacier melts, the satellite sees its altitude drop. A second technique, since 2002, is to measure earth gravity variations. The mountains do not move (almost) not, it is the movements and transformations of water that explain them. Finally, scientists have developed so-called mass balance models. They compare what accumulates on Greenland (rain, snow) to what comes out (rivers of ice), and calculate what remains.
Ice melts six times faster than in the 1980s
These models, confirmed with field measurements, have become very reliable since the mid-2000s, says Eric Rignot, about 5 to 7% margin of error, against 100% a few decades ago. The team used these models to "go back in time" and reconstruct in detail where the ice of Greenland was in the 1970s and 1980s.
The result is that in the 1970s, Greenland gained an average of 47 gigatonnes of ice a year (Gt / yr), before losing an equivalent volume in the 1980s. Melting continues at this rate in the 1990s , before a strong acceleration from the 2000s (187 Gt / year) and especially since 2010 (286 Gt / year).
The ice melts six times faster today than in the 1980s, say the researchers. The glaciers of Greenland alone would have helped raise the level of the oceans by 13.7 millimeters since 1972.
As a similar work of the same team for Antarctica, this study provides a longer context for the rapid melting observed in Greenland in recent years. "The glacial melting observed over the past eight years is equivalent to that of the previous four decades," says Amber Leeson of Lancaster University.