WASHINGTON — The extreme weather event that caused widespread melting across the Greenland ice sheet last week, with temperatures soaring above the freezing mark at the highest point on the island, may have ended.
But the melt season overall — which has 35 to 40 days to go — is poised to set a new and more significant record.
According to the National Snow and Ice Data Center in Boulder, Colo., Greenland has already lost a total of over 250 billion tons from a combination of melt runoff and low total snowfall this season. That’s enough to fill more than 90 million Olympic-sized swimming pools. Or to put it another way, that much water could sustain the global population’s water intake for more than 40 years.
During the extreme melt event last week, Greenland lost 12 to 24 billion tons of ice per day, which was 6 to 18 billion tons above the typical rates seen on these dates seen during the period from 1981 to 2010.
All told, a computer model that tracks ice mass gained or lost by snowfall and snow and ice melt, but does not include the ice mass lost by glaciers that end in the ocean waters, found that the ice sheet lost a total of about 55 billion tons through melt runoff during the extreme melt event, which was about 40 billion tons more than the 1981 to 2010 average for the same period, the data center said.
‘‘The glacier flow system also contributes to loss and will likely add another 60 to 100 billion tons of loss (as icebergs),’’ said Ted Scambos, a senior research scientist at the University of Colorado.
According to Scambos, 2012 eventually reached 300 billion tons of surface ice mass loss from Greenland. The rate of ice loss in Greenland has increased sixfold since the 1980s, according to a recent study, with the ice sheet responsible for raising global sea levels by 13.7 millimeters since 1972, half of which occurred in just the past 8 years.
Also, as of this week, there is no sea ice off the shores of Alaska, something that has never occurred before so early in the melt season. Ice has even pulled back again from the coastal waters north of Greenland, which had long been a refuge for the oldest and thickest ice cover.