A new study shows the East Antarctic Ice Sheet, once thought to be stable, may be melting faster than expected.
Torsten Blackwood/Pool/Getty Images
By Alex Fox
Antarctica’s melting ice, which has caused global sea levels to rise by at least 13.8 millimeters over the past 40 years, was long thought to come from primarily one place: the unstable West Antarctic Ice Sheet. Now, scientists studying 40 years of satellite images have found that the East Antarctic Ice Sheet—considered largely insulated from the ravages of climate change—may also be melting at an accelerating rate. Those results, at odds with a large 2018 study, could dramatically reshape projections of sea level rise if confirmed.
“If this paper is right, it changes the ball game for sea level rise in this century,” says Princeton University climate scientist Michael Oppenheimer, who was not involved in the new work. East Antarctica’s ice sheet holds 10 times the ice of its rapidly melting neighbor to the west.
The West Antarctic Ice Sheet, whose base is below sea level, has long been considered the most vulnerable to collapse. With an assist from gravity, a deep current of warm water slips beneath the sheet, melting it from below until it becomes a floating shelf at risk of breaking away. In contrast, frigid temperatures and a base mostly above sea level are thought to keep the East Antarctic Ice Sheet relatively safe from warm water intrusion. A collaboration of more than 60 scientists last year, published in Nature, estimated that the East Antarctic Ice Sheet actually added about 5 billion tons of ice each year from 1992 to 2017.
But as climate change shifts wind patterns around Antarctica, some scientists think warm water carried by a circular current off the continental shelf will start to invade East Antarctica’s once unassailable ice. “People who study Antarctic ice know that East Antarctica has the potential to start losing significant amounts of ice, but it’s never been clear how fast that would [happen],” Oppenheimer says.
To find out how fast that ice loss is happening, glaciologist Eric Rignot of the University of California, Irvine, and colleagues combined 40 years of satellite imagery and climate modeling. The models were used to estimate annual snowfall, which over time adds ice to the region’s glaciers. Then, the team measured the speed of ice flowing out to sea by tracking visual landmarks on the glaciers through time. This allowed them to estimate how much ice each of the continent’s many glaciers sent out to sea each year from 1979 to 2017. By subtracting the amount of ice added annually by snow from the amount of ice lost to sea, the researchers determined how much ice was gained or lost.
“After staring at satellite photos for hours you go a little cross-eyed, but it’s basic statistics—you beat down the noise by adding more data points,” Rignot says. “Tracking down these old satellite photos and spending months analyzing by hand was worth it to create this long-term record.”
Overall, the study found that Antarctica now sends six times more ice plunging into the sea each year than it did in 1979. During the 40-year period of the study, Antarctica added 13.8 millimeters to sea level, with the majority coming from West Antarctica. But East Antarctica, particularly the area known as Wilkes Land, was responsible for more than 30% of Antarctica’s contribution to sea level rise, the researchers report today in the Proceedings of the National Academy of Sciences. “The more we look at this system the more we realize this is a fragile system,” Rignot says. “Once these glaciers are destabilized there is no red button to press to stop it.”
If intensifying polar winds are responsible for the intrusion of warm waters beneath East Antarctica, the situation is likely to get worse, Rignot says. The increasing strength of those winds is owed in part to the contrast in temperature between Antarctica and the rest of the world. As greenhouse gases warm much of the planet, this temperature differential is likely to intensify, driving even stronger westerlies, he adds.
But the bold new results won’t be accepted without a fight, says glaciologist Richard Alley of Pennsylvania State University in University Park, who was not involved in either study. “There will be a lot of comparisons between the methods used to create these estimates and those in the [previous study],” he says. In addition to the ice-tracking method used in the current paper, the previous one also gathered two other measurements: one that estimated ice loss by repeatedly “weighing” the ice sheet via satellite, and one that estimated changes in elevation on the glacier’s surface from planes and satellites.
No matter the outcome, Rignot hopes the study brings greater attention to a part of Antarctica that has traditionally been understudied. Helen Fricker, a glaciologist at the Scripps Institution of Oceanography in San Diego, California, agrees. “We need to monitor the entirety of Antarctica and we just can’t do that without international cooperation,” Fricker says. “We can’t take our eyes off this ice.”
Source: Science Mag