Methane is leaking into the atmosphere from unstable permafrost in the Arctic Ocean faster than scientists had thought and could worsen global warming, a study said Thursday.

From 2003 to 2008, an international research team led by University of Alaska-Fairbanks scientists Natalia Shakhova and Igor Semiletov surveyed the waters of the East Siberian Arctic Shelf, which covers more than 772,200 square miles (two million square kilometers) of seafloor in the Arctic Ocean.

"This discovery reveals a large but overlooked source of methane gas escaping from permafrost underwater, rather than on land," the study said.

"More widespread emissions could have dramatic effects on global warming in the future."

Earlier studies in Siberia had focused on methane escaping from thawing permafrost on land.

Scientists have long thought that the permafrost under the East Siberian Arctic Shelf acted as an impermeable barrier that sealed in methane, a powerful greenhouse gas 30 times more potent that carbon dioxide.

But the research team's observations showed that the permafrost submerged on the shelf is perforated and leaking large amounts of methane into the atmosphere.

More than 80 percent of the deep water and more than half of surface water had methane levels around eight times higher than found in normal seawater, according to the study published in the journal Science.

The researchers warned that the release of even a fraction of the methane stored in the shelf could trigger abrupt climate warming.

"Ocean-bottom permafrost contains vast amounts of carbon, and experts are concerned that its release as methane gas would lead to warmer atmospheric temperatures, thus creating a positive-feedback loop that would lead to more methane escaping from the permafrost and more global warming," they said.

Current average methane concentrations in the Arctic average about 1.85 parts per million, the highest in 400,000 years, said Shakhova.

Concentrations above the East Siberian Arctic Shelf are even higher, and scientists are concerned because the undersea permafrost "has been showing signs of destabilization already," she added.

"If it further destabilizes, the methane emissions... would be significantly larger."

Geological records indicate that atmospheric methane concentrations have varied between about .3 to .4 parts per million during cold periods to .6 to .7 parts per million during warm periods.