Published online 17 December 2008 | Nature | doi:10.1038/news.2008.1314


Arctic warming spurs record melting

Greenland and Siberia see rapid changes.

Record melting in northern Greenland and the widespread release of methane gas from formerly frozen deposits off the Siberian coast suggest that major changes are sweeping the Arctic, researchers say.

The recent observations, reported on 16 December at the autumn meeting of the American Geophysical Union in San Francisco, California, have surprised scientists who — although used to Arctic changes — did not expect to see them so dramatically over the past year.

Parts of southwestern Greenland, along with the northern part of the island's ice cap, saw record melting in summer 2008.ESA

"Five years ago, I was not sure it's very serious, but now I'm sure something is going on and we should warn people," says Igor Semiletov from the University of Alaska in Fairbanks, chief scientist of the International Siberian Shelf Study, an oceanographic expedition that surveyed the entire Siberian coastline this summer. The study found methane bubbling up from the seafloor over hundreds of square kilometres in the Laptev and East Siberian Seas, according to Semiletov (see Fears surface over methane leaks).

Changes a-coming

Water measurements indicate that methane concentrations were up to 200 times higher than the background levels, he says. In earlier, less extensive studies in the 1990s, Semiletov did not find such significant releases of methane. "Based on the newly obtained data, we suggest an increase of methane releases from the East Siberian Arctic Shelf," he says.

Methane is a potent greenhouse gas, and scientists estimate that the Arctic permafrost — both on land and underwater — could hold trillions of tons of methane stored mostly in the form of frozen gas hydrates, says Semiletov. The submerged permafrost is on the threshold of melting, and air temperatures in the East Siberian Arctic Shelf have increased by as much as five degrees Celsius over the last decade, he says. "We didn't know that this huge carbon pool is extremely vulnerable."

The impact of such methane releases remains unknown, however. At this point, researchers lack enough data to say whether enough methane is escaping from the Siberian continental shelf to affect the globe, says Edward Brook of Oregon State University in Corvallis, who says he has not seen the new data that Semiletov presented.

In a report also released on 16 December by the US Climate Change Science Program, Brook and his colleagues concluded that a catastrophic release of methane is very unlikely this century, although they project that climate change will speed up methane emissions from hydrates and other sources. The report calls for more monitoring of atmospheric methane to determine if any abrupt changes are developing.

Not-so-icy north

Across the Arctic from Siberia, Greenland was also keeping researchers busy this summer, as satellite measurements revealed record melting along the far northern margin of its ice cap. In most summers, temperatures rise enough to permit melting in that region on only 10–15 days on average. But in 2008, the melt period totalled 35 days. "It's a place where you do not expect to see this extreme melting because it's a northern area," says Marco Tedesco of the City College of New York, who analyzed microwave data collected by a defence meteorological satellite.

Record melting also happened last summer along the edge of southwestern Greenland, Tedesco reported. The changes in 2008 mark a continuation of rapid climate change in Greenland over the past few years. Estimates based on satellite measurements of the entire ice cap suggest that the island is now losing hundreds of billions of tons of ice each year. In another example of extreme changes, a 29-square-kilometre patch broke off the end of the Petermann glacier in northern Greenland during the summer of 2008.

"We're now seeing the emergence of the Arctic amplification that we've been projecting," says Julienne Stroeve of the National Snow and Ice Data Center at the University of Colorado at Boulder.


Climate models have projected that greenhouse gases should warm the Arctic far more than the rest of the globe because the loss of sea ice allows heat to penetrate the oceans, which drives up regional temperatures and causes further melting. In 2007 the amount of summertime sea ice dropped to a record low, followed by near-record ice loss in 2008. 

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