Greenland ice sheets are melting six times faster than they did in the 1980s, which scientists say is worrisome because if the rate of ice melt speeds up further, the losses could be enormous.
A team of researchers from University of California at Irvine sought to recalculate the amount of ice lost in Greenland since 1972, which was the year that the first Landsat satellites entered orbit to photograph the massive Danish island from space.
The results of the study help experts put dramatic changes to Greenland's contribution to global sea level rise into a longer-term context. Combined with the rate of ice melt in Antarctica, the findings portend a bleak future.
How Scientists Measured Greenland Ice Melt
Methods and equipment that scientists use to measure the rate of melting ice is much more precise in 2019 compared to 47 years ago thanks to satellites, weather stations, and climate models.
Now, in the new study, a group of glaciologists led by Eric Rignot employed three methods to measure the rate of ice melting in Greenland.
The first method makes use of satellites that measure altitude with a laser. The satellite picks up the reduced height of the melting glaciers.
The second technique involves measuring changes in gravity because loss of ice can be detected thru a decrease in gravitational pull. This second technique has been in practice since 2002 using NASA satellites.
Lastly, Rignot and his colleagues developed so-called mass balance models, which compare the amount of mass accumulated in the form of rain and snow with the amount of mass lost in the form of ice river discharges. This subtraction method helps calculate the amount of ice left in Greenland.
All three methods have been confirmed reliable and precise since the 2000s, said Rignot. These techniques boast a 5 to 7 percent margin of error, compared to 100 percent margin of error a few years ago.
Greenland Ice Is Melting 6 Times Faster
Rignot said they went back in time to reconstruct Greenland's ice levels in the 1970s and 1980s. The limited data available in these periods such as aerial photos, medium-quality satellite photos, ice cores, and other observations helped refine scientists' calculations.
What Rignot and his team found was that during the 1970s, Greenland accumulated 47 gigatonnes of ice per year on average. In the 1980s, Greenland then lost an equivalent volume.
By the 1990s, the rate of melting continued before it accelerated in the 2000s at 187 gigatonnes of ice per year and increasing more in 2010 at 286 gigatonnes of ice per year.
This meant that Greenland ice is melting six times faster than in the 1980s. What's more, Greenland's ice melt have contributed to a 13.7 millimeter rise in sea levels since 1972, scientists explained.
The findings of the study provide experts with a longer term view of the rapid ice melt that has occurred in Greenland in recent years.
"When you look at several decades, it is best to sit back in your chair before looking at the results, because it is a bit scary to see how fast it is changing," said Rignot.
He added that the ice melt is something that affects the four corners of Greenland, not just the warmer parts of the south. Furthermore, combined with the rate of ice melt in Antarctica, the findings explain why global sea level rise has increased in the past decades.
Meanwhile, details of the new study are available in the journal Proceedings of the National Academy of Sciences (PNAS).
Photo: NASA Goddard Space Flight Center | Flickr
