OSLO (Reuters) – Large amounts of a powerful Siberia, raising fears of far bigger leaks that could stoke , scientists said.are bubbling up from a long-frozen seabed north of
It was unclear, however, if the Arctic emissions of methane gas were new or had been going on unnoticed for centuries -- since before theof the 18th century led to wide use of fossil fuels that are blamed for .
The study said about 8 million tonnes of methane a year, equivalent to
the annual total previously estimated from all of the world's oceans,
were seeping from vast stores long trapped under permafrost below the
seabed north of Russia.
"Subsea permafrost is losing its ability to be an impermeable cap,"
Natalia Shakhova, a scientist at the University of Fairbanks, Alaska,
said in a statement. She co-led the study published in Friday's edition
of the journal Science.
The experts measured levels of methane, a gas that can be released by
rotting vegetation, in water and air at 5,000 sites on the East
Siberian Arctic Shelf from 2003-08. In some places, methane was
bubbling up from the seabed.
Previously, the sea floor had been considered an impermeable barrier
sealing methane, Shakhova said. Current methane concentrations in the
Arctic are the highest in 400,000 years.
"No one can answer this question," she said of whether the venting was
caused by global warming or by natural factors. But a projected rise in
temperatures could quicken the thaw.
"It's good that these emissions are documented. But you cannot say they're increasing," Martin Heimann, an expert at the Max Planck Institute for Biogeochemistry in Germany who wrote a separate article on methane in Science, told Reuters.
"These leaks could have been occurring all the time" since the last Ice
Age 10,000 years ago, he said. He wrote that the release of 8 million
tonnes of methane a year was "negligible" compared to global emissions
of about 440 million tonnes.
Shakhova's study said there was an "urgent need" to monitor the region
for possible future changes since permafrost traps vast amounts of
methane, the second most common from human activities after carbon dioxide.
Monitoring could resolve if the venting was "a steadily ongoing
phenomenon or signals the start of a more massive release period,"
according to the scientists, based at U.S., Russian and Swedish research institutions.
The release of just a "small fraction of the methane held in (the) East Siberian Arctic Shelf sediments could trigger," they wrote.
The shelf has sometimes been above sea level during the earth's
history. When submerged, temperatures rise by 12-17 degrees Celsius
(22-31 F) since water is warmer than air. Over thousands of years, that
may thaw submerged permafrost.
About 60 percent of methane now comes from human activities such as
landfills, cattle rearing or rice paddies. Natural sources such as
wetlands make up the rest, along with poorly understood sources such as
the oceans, wildfires or termites.
Most studies about methane focus on permafrost on land. But the shelf
below the Laptev, East Siberian and Russian part of the Chuckchi sea is
three times the size of Siberia's wetlands.