The extreme weather event that caused widespread melting across the Greenland ice sheet last week, sending temperatures soaring above the freezing mark at the highest point on the island, may have ended, but the melt season overall — which has about 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 (NSIDC) in Boulder, Colo., Greenland has already lost a total of over 250 billion tons from a combination of melt runoff and low total snowfall earlier in the season. That’s enough to fill more than 90 million Olympic-size 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 from 12 billion to 24 billion tons of ice per day, which was about 6 to 18 billion tons above the typical rates seen on these dates seen during the period from 1981-2010.
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 which terminate 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 time period, NSIDC reported.
“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 and 2019 may exceed that.
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.
A broader look at the Arctic reveals a spiral of climate feedbacks at work
A combination of natural climate variability, such as a pattern of atmospheric pressure known as the North Atlantic Oscillation, plus long-term global warming has led to a much warmer than average summer melt season in Greenland and throughout the Arctic.
In response to the above average temperatures, Arctic sea ice is well on its way to one of the five lowest levels on record since satellite records began in 1979. Ice-free areas feature much above average sea surface temperatures, which is reinforcing the transport of mild air into the region, and helping to melt more sea ice. Sea ice ended the month of July at a record low, and was continuing to drop sharply into early August.
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. This was first seen in 2018, and no longer appears to be a fluke.
In addition, a widespread outbreak of Arctic wildfires has been billowing smoke across the Greenland ice sheet and other parts of the Arctic, where soot deposition darkens the ice surface and melts it faster.
Another feedback involves natural darkening of the ice cover, since above average temperatures tend to reduce the reflectivity, or albedo, of the ice, thereby melting more of it as incoming solar energy is readily absorbed. Satellite imagery shows broad regions of dark ice across Greenland, particularly in western areas.
The rate and extent of present-day sea ice loss is unprecedented in at least 1,500 years, according to a 2017 report.