Melting Away

Nicolo E. DiGirolamo, SSAI/NASA GSFC, and Jesse Allen, NASA Earth Observatory

This summer’s record-breaking drought and heat, which a growing number of scientists have tied to climate change, have been difficult for many Americans to ignore. But the impacts felt in the lower 48 states may pale in comparison to those being seen in Arctic regions around the world. The Arctic region is warming three or four times as fast as global average rates, scientists found last year.

Nowhere is this warming more visible than in Greenland. New research has found that the surface of Greenland’s ice sheet is melting at startling rates. Not only has this year’s thaw set new records for ice melt, but it’s done so nearly four weeks before Greenland’s “melting season,” which usually extends into early September.

Cumulative melting by the first week in August already broke records set in 2010 for the entire season, research by Marco Tedesco, assistant professor of earth and atmospheric sciences at The City College of New York, shows.

“With more yet to come in August, this year’s overall melting will fall way above the old records. That’s a goliath year—the greatest melt since satellite recording began in 1979,” said Tedesco, whose research was corroborated by Thomas Mote, Ph.D., professor of geography at the University of Georgia, using a similar analysis.

This summer, a barrage of studies and events has drawn attention to sea ice melting in Greenland and across the Arctic region. In July, an iceberg twice the size of Manhattan broke off from northwest Greenland’s Petermann glacier. Last month, NASA researchers reported that melting had spread to 97% of the surface of Greenland’s ice sheet, noting that in an average year only half of the ice sheet’s surface melts.

Greenland’s ice sheet is enormous, consisting of so much water that if all of the ice melted, sea levels around the world would rise by more than 20 feet.

Tedesco’s new research examined both the extent and the duration of thaws, creating a so-called “cumulative melting index.” This index help gauge how much of the melting waters is likely to re-freeze on land or permanently flow into the ocean.

His study does not imply that this runoff into the seas will grow substantially in the short run. The satellite images show the surface of the ice sheet, rather than melting of the base of the glaciers perched on the island of Greenland. Surface melting can be trapped in ponds atop frozen ice sheets or land. This year’s surface melting mostly created a layer of slush that can become an icy crust when it refreezes – but very likely it did not add to the runoff of meltwater that makes sea levels rise, Tedesco said.

But the satellite images are no surprise to many living in the region. Residents in one Greenland town, Kangerlussauq, have said that this year’s melting in their area is the largest in recent memory. The town made headlines worldwide when a major bridge was wiped out on July 11 as melting ice flooded the Watson river.

Across the Arctic, sea ice is melting unusually fast this year. Only 1.9 million square miles of the ocean were covered in ice during one five-day period this month, the fourth-lowest level ever measured, data from the U.S. National Snow and Ice Data Center in Boulder, Colorado, shows—and summer is not yet over.

With regards to Greenland, scientists from NASA point to a combination of factors, including natural variation in weather patterns. “Ice cores from Summit show that melting events of this type occur about once every 150 years on average. With the last one happening in 1889, this event is right on time,” said Lora Koenig, a Goddard glaciologist and a member of the team that released the NASA report. “But if we continue to observe melting events like this in upcoming years, it will be worrisome.”

Tedesco agreed that larger historic patterns could be at play but said that the overall context showed a warming trend. “We have to be careful, because we are only talking about a couple of years, and the history of Greenland happened over millennia,” Tedesco said. “But as far as we know now, the warming that we see in the Arctic is responsible for triggering processes that enhance melting and for the feedback mechanisms that keep it going.”

“Looking over the past few years, the exception has become part of the norm,” he added.