Scientists have found more than 150,000 sites in the Arctic where methane is seeping into the atmosphere, according to a report published Sunday in the journal Nature Geoscience.

Aerial and ground surveys in Alaska and Greenland revealed that many of the methane seeps are located in areas where glaciers are receding or permafrost is thawing as the climate warms, removing ice that has trapped the potent greenhouse gas in the ground.

Researchers at the University of Alaska and Florida State University say the amount of methane being released from the seeps now is relatively small but could grow in coming decades as climate change intensifies, shrinking the ice that has prevented ancient deposits of the heat-trapping gas from reaching the atmosphere.

"As permafrost thaws and glaciers retreat, it is going to let something out that has had a lid on it," said lead author Katey Walter Anthony of the University of Alaska.

Scientists have long known of the existence of methane seeps in the Arctic, but the new study is one of the first to map them over large areas.

Walter Anthony and her colleagues used airplanes to fly over 6,700 lakes in Alaska during the winters of 2008, 2009 and 2010.

The survey revealed 77 previously unknown seep sites, which the scientists narrowed down to 50 lakes they visited on foot.

They documented the seeps they found, using carbon-dating to determine the age of methane released at the sites. The scientists performed the same analysis at 25 lakes in western Greenland.

Seep sites in Alaska tended to occur where permafrost is thawing or at the edges of receding glaciers. In Greenland, the scientists found seeps in places where glaciers have retreated over the past 150 years, since the end of the Little Ice Age.

The researchers calculate that methane seeps in Alaska alone are releasing 250,000 metric tons of methane into the atmosphere each year, 50 to 70 percent more than previously estimated.

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500