"As a result, sub-sea permafrost has warmed up to minus 1 degree Celsius [30 degrees Fahrenheit]," Semiletov said. "It's very, very close to the thawing point."
Underneath the permafrost are stores of methane, the same as the natural gas people use for cooking and heating.
There are also methane hydrates, a solid that forms when methane and water mix in cold temperatures. The hydrates release gas as they warm.
"It was assumed that these stores of methane have not been leaking, because the sub-sea permafrost served as a lid keeping hydrates and natural gas in place," Semiletov said.
But now global warming may be starting to release these stores of methane into the atmosphere.
Regions farther from the Equator generally are experiencing more warming, and the Arctic is warming fastest of all.
"Springtime air temperatures on the East Siberian Arctic shelf [have] increased up to 5 degrees Celsius [9 degrees Fahrenheit]," Semiletov said. "It's a hot spot."
In comparison, the world as a whole has warmed about 1.25 degrees Fahrenheit (0.7 degrees Celsius) since pre-industrial times.
If abrupt methane release became widespread, it could create a feedback loop that would lead to even more drastic global warming.
"Our early observations in 1994 to 1999 didn't reveal a widespread enhanced dissolved methane concentration" along the Siberian coast, Semiletov said.
"With this newly obtained data, we suggest an increase of methane release from the East Siberian Arctic shelf," he said.
"We have obtained a drastic increase of air methane in some sites—sometimes up to four times higher than the background [global average]."
Vladimir Romanovsky, a permafrost expert also at the University of Alaska, Fairbanks, says the study is worrying.
"It has very serious implications for changes in greenhouse gases," Romanovsky said, adding that the releases described should be monitored more closely.
"It could be very important, but we still need some numbers to see how big [of a problem] it is."
Carolyn Ruppel is a geophysicist with the U.S. Geological Survey who is based in Woods Hole, Massachusetts.
"The nature of the shallow Arctic continental shelves means that they have the potential to release significant methane now and into the future," said Ruppel, who was not involved in the study.
But there are a number of places this methane could be coming from, she said.
"Quantifying the contribution of each potential methane source will be a major challenge."