Sudden Ice Melt Seen on 97% of Greenland
Nearly the entire Greenland ice sheet experienced surface melting over just a few days in mid July, an extremely rare event that has not occurred since 1889, according to measurements reported by NASA scientists.
And while the melting episode cannot be linked directly to global warming, it appears to fit into a dramatic trend: a long-term warming of the Arctic that is two to three times faster than the global average.
“This is more like weather,” said glaciologist Eric Rignot, a researcher at UC Irvine and the Jet Propulsion Laboratory who specializes in polar ice. “You’re looking at an unusually warm summer. But if you look at the recent record, there have been very warm summers in 2010 and also in 2009. If you look at the trend for the past 20 years, it’s not surprising we have a warm summer in 2012; we’ve had a lot of warm summers lately.”
About half the surface of the Greenland ice sheet melts every summer on average. But between July 8 and July 12, satellite measurements show, the melting soared, jumping from 40 percent to an estimated 97 percent, a team of scientists from NASA and several universities reported this week.
That included coastal areas as well as the top of the huge ice dome over Greenland, some two miles thick.
“It was actually so bad this year, airplanes could not land and takeoff at the summit because it was too wet,” said Rignot, who has studied polar melting extensively but was not involved in the latest report on the sudden Greenland melting.
According to ice core readings from Greenland, such extensive melting has not occurred since 1889, roughly in line with scientists’ expectations of such a melt about every 150 years.
But if such widespread and rapid melting becomes more frequent in the years ahead, that could amount to a worrisome trend, glaciologist Lora Koenig of NASA’s Goddard Space Flight Center, part of the team that analyzed the melting data, said in a NASA statement.
The melting also is continuing, said Rignot, who will soon be traveling to the Greenland coast to conduct a survey of Greenland glaciers, part of an attempt to learn how quickly they are melting when they come into contact with ocean water.
“Some people are asking me if this is going to be a record melt year,” he said. “It’s not over yet. I’m sure there already has been a large increase in melt this year, but how much exactly we’ll have, we’ll have to wait till the end of September (to find out).”
Surface melting also can feed on itself by darkening the ice surface, an effect noted on Greenland in a study by the National Oceanic and Atmospheric Administration earlier this year.
While Arctic melting is pronounced, and while significant glacial melting is being seen in the Antarctic as well, more data is needed, Rignot said, before a strong connection can be made between global warming and changes seen in the Antarctic.
“The melting in the Antarctic is more complex,” he said. “It’s not a result of increasing air temperature. Changes there are driven by the dynamics of glaciers interacting very strongly with the ocean.”