LONDON: Methane, the second most common greenhouse gas from human activities after carbon dioxide, is bubbling out from the frozen Arctic much faster than expected and could stoke global warming, scientists have warned.

A study by researchers from the University of Fairbanks in Alaska showed that methane, trapped in the permafrost -- soil at or below the freezing point of water for two or more years -- over time and now 8 million tonnes of it is seeping out every year due to rising temperatures.

According to co-author of the study Natalia Shakhova, "Release of just a small fraction of the methane held in East Siberian Arctic Shelf sediments could trigger abrupt climate warming".

"Subsea permafrost is losing its ability to be an impermeable cap."

"The amount of methane currently coming out of the East Siberian Arctic Shelf is comparable to the amount coming out of the entire world's oceans," she wrote in journal Science.

Shakhova said there was an 'urgent need' to monitor the region for possible future changes since permafrost traps vast amounts of methane, the Daily Mail reported.

According to Martin Heimann from the Max Planck Institute there is, however, no proof they are increasing. "These leaks could have been occurring all the time since the last Ice Age 10,000 years ago."

The release of eight million tonnes of methane a year was "negligible" compared to global emissions of about 440 million tonnes, he said.