Greenland lost a record amount of ice in 2019, researchers reported Thursday. Nearly half of it was lost in July, when the region roasted from an unusual heat wave.
The net ice loss of more than 530 billion metric tons was more than twice the annual average since 2003, the scientists said. In July, when warm air from Europe moved north, leading to temperatures that were well above normal and causing widespread surface melting of the ice sheet, the loss was roughly equal to the average loss in a full year.
Ingo Sasgen, a geoscientist at the Alfred Wegener Institute in Bremerhaven, Germany, and the lead author of a paper describing the findings in the journal Communications and Environment, said with the warmth last summer, he and his colleagues suspected that 2019 would be a bad one for the ice sheet.
They analyzed data from a pair of satellites that precisely measure the gravitational pull, and thus the mass, of the area they are orbiting over.
“It took us some time to analyze it and quantify it robustly, but it turned out to be another record melt year,” Dr. Sasgen said. In the previous record year, 2012, the net loss was about 460 billion metric tons.
Yara Mohajerani, a postdoctoral researcher at the University of Washington who was not involved in the study, said it was “part of a series of studies that have shown the same thing,” including work that he did that reported record ice loss in summer 2019.
Greenland’s ice sheet is nearly two miles thick in places, and if all the ice were to melt, sea levels would rise about 24 feet, or about 7.5 meters.
That would take centuries. But since the 1990s, as the Arctic has warmed faster than any other part of the planet, ice loss from Greenland and its contribution to sea level rise have accelerated. At the current rate of loss, Greenland’s ice accounts for about one-quarter inch per decade of the global total increase of about one and a quarter inches per decade.
But ice loss can vary from year to year. In their paper, Dr. Sasgen and his colleagues found that net loss in 2017 and 2018 was about half the annual average since 2003.
So far in 2020, he said, net ice loss appears to be a little below average.
Both 2017 and 2018 had colder-than-usual summers, Dr. Sasgen said, when cold air flowed from the north along the west coast of Greenland, reducing ice loss. But in 2019 that circulation pattern was reversed, with warm air coming from the south.
Similar reversals have happened before. “It was really fascinating that it jumped again from very cold historic conditions to a record melt year,” he said.
The shift to north-flowing air occurs when a region of high-pressure air, a result of changes in the jet stream, lingers over Greenland. Referred to as a “block,” these zones of stationary air have become more frequent in the Arctic, and while there is debate as to why, many scientists are increasingly seeing a link to global warming that is made worse by sea-ice loss in the Arctic Ocean.
“It’s very clear that the last 10, 15, 20 years have produced more stationary wave patterns and more blocking situations over Greenland,” Dr. Sasgen said. “There’s a very likely chance it’s connected to sea-ice loss. But it’s really hard to prove.”
In Greenland, ice loss results from runoff of surface meltwater and from discharge of ice from glaciers that serve as outlets for the ice sheet, connecting it to the ocean. Accumulation results from snowfall that, compressed over years, eventually becomes ice. When runoff and discharge exceed accumulation, the result is net loss.
A paper published last week in the same journal showed that ice discharge from outlet glaciers, which includes both calving of icebergs and underwater melting, had increased by about 14 percent since the 1980s.
Most of the increase was from 2000 to 2005, and discharge rates have remained relatively consistent at this higher level since then, said the study’s lead author, Michalea King, who recently earned her doctorate from Ohio State University and will soon be a researcher at the University of Washington.
The increase in ice discharge, coupled with the trend toward increasing meltwater runoff over the past several decades, make it increasingly unlikely that Greenland will have years with a net ice gain, Dr. King said.
“It’s kind of a double whammy,” she said. “Only one of every 100 years would we expect to have mass gain.”
The new paper, which Dr. King contributed to, illustrates that point, she said. While the abnormal cold summers of 2017 and 2018 led to more ice accumulation and less surface melt runoff, “even with all of that they’re still mass-loss years,” she said, largely because of the higher glacier discharge rate.
“Mass loss is not going away anytime soon,” Dr. King said. “But of course we have control over the rate" by taking steps to mitigate climate change.
“It’s not a throw-your-hands-up kind of situation,” she said.
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