For comparison, that’s roughly half of a recent estimate for ice loss for all of Antarctica (159 billion metric tons). It takes 360 gigatons of ice to lead to one millimeter of sea level rise, which implies that the Alaska region alone may have contributed several millimeters in the past few decades.
“Despite Greenland’s ice covered area being 20 times greater than that of Alaska, losses in Alaska were fully one third of the total loss from the ice sheet during 2005-2010,” wrote the authors, led by Chris Larsen of the University of Alaska at Fairbanks’s Geophysical Institute. The study was published in Geophysical Research Letters.
The paper used data from airborne altimeters as part of NASA’s Operation IceBridge to examine 116 Alaska glaciers, including both coastal or “tidewater” glaciers, but also glaciers that terminate in lakes or on land. The examined glaciers represented 41 percent of the total area of glaciers in the Alaska region, which the study defined as also including parts of British Columbia and the Yukon Territory. Then calculations were performed to estimate mass loss for the whole of the region’s glaciers.
“This is the first estimate ever where we’ve gone glacier by glacier through the whole region, all 25,000 plus glaciers are estimated individually, and then we sum them up,” says Shad O’Neel, a study co-author with the U.S. Geological Survey. And the result in terms of total glacial ice loss, he says, is that “we’re getting a bigger number than the community had thought before.”
In particular, Alaska appears to be punching well above its weight in losing ice and contributing to sea level rise. Mountain glaciers worldwide contain just a tiny fraction of the ice contained in the great ice sheets of Greenland and Antarctica, says O’Neel, but they’re currently contributing about as much as those ice sheets to sea level rise. And when it comes to mountain glaciers, he continues, Alaska is “11 percent of the area, and 25 percent of the water going to sea level rise.”
The estimate of 75 gigatons or billion metric tons of ice loss is subject to some uncertainty — the authors say they could have erred by 11 gigatons in either direction.
One Alaska glacier, the massive marine terminating Columbia Glacier, has been losing ice rapidly — the study estimates that it has been losing 4 billion metric tons per year.
In a recent NASA visualization, the agency used satellite imagery to capture Columbia glacier’s dramatic retreat. Here’s what it looked like in July of 1986:
And here’s what it looked like in July of 2014:
Somewhat surprisingly, though, other tidewater glaciers weren’t found to be retreating as much as Columbia — though the majority of those surveyed were losing mass. But the bulk of the remaining ice loss came from lake-terminating glaciers and especially fully land based ones, which, the study noted, “tend to show steady change more directly coupled and proportional to variations in climate.” Ice loss from these latter two types of glaciers, the study found, was “extremely high … occurring at nearly double the rate found over the period 1962-2006.”
Overall, there was dramatic variability in what all the different glaciers were doing, but the net result was the same — gigantic mass loss. “Alaska will continue to be a primary contributor to global [sea level rise] through the end of this century,” the study concludes.
Moreover, the fact that so much of the melting is coming from land-based glaciers, whose melt rate so closely tracks overall temperatures, suggests that with a warming climate, ice loss should continue or accelerate. Looking forward, then, Alaska’s contributions will still continue to be quite large.
“We’re still in the realm of half of Greenland’s contribution, even though we’re much, much smaller,” says O’Neel. “The Alaska region is not going to be marginalized in the sea level budget.”
The research emerges after a record hot month for the state of Alaska — May 2015 was the hottest May in records going back 91 years. At the same time, North America saw its third lowest level of May snow cover on record this year, and much of the low snow cover occurred in Alaska as well.
“The lack of snow means that the glaciers can initiate melt more rapidly,” says study co-author Anthony Arendt, a research scientist at the University of Washington in Seattle. “Because snow is much more reflective than an ice surface, so we’re already getting down to the glacier ice.
“So if it’s a warm summer this will be a pretty bad year for the glaciers in Alaska,” says Arendt.
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