Loss of Greenland ice sheet set record in ’19
Greenland lost a record amount of ice in 2019, researchers reported last week. 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,” 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 whowas 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 1/4 inch per decade of the global total increase of about 1-1/4 inches per decade.
But ice loss can vary from year to year. In their paper, Sasgen and his colleagues found that net loss in 2017 and 2018was 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, Sasgen said, when cold air flowed fromthe north along thewest 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 globalwarming that is made worse by seaice loss in the Arctic Ocean.
“It’s very clear that the last 10, 15, 20years have produced more stationary wave patterns and more blocking situations over Greenland,” 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 melt water 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.