The Arctic methane time bomb is bigger than scientists once thought and primed to blow, according to a study published today (Nov. 24) in the journal Nature Geoscience.
About 17 teragrams of methane, a potent greenhouse gas, escapes each year from a broad, shallow underwater platform called the East Siberian Arctic Shelf, said Natalia Shakova, lead study author and a biogeochemist at the University of Alaska, Fairbanks. A teragram is equal to about 1.1 million tons; the world emits about 500 million tons of methane every year from manmade and natural sources. The new measurement more than doubles the team's earlier estimate of Siberian methane release, published in 2010 in the journal Science.
"We believe that release of methane from the Arctic, in particular, from the East Siberian Arctic Shelf, could impact the entire globe, not just the Arctic alone," Shakova told LiveScience. "The picture that we are trying to understand is what is the actual contribution of the to the global methane budget and how it will change over time."
Waiting to escape
Arctic permafrost is an area of intense research focus because of its climate threat. The frozen ground holds enormous stores of methane because the ice traps methane rising from inside the Earth, as well as gas made by microbes living in the soil. Scientists worry that the warming Arctic could lead to rapidly melting permafrost, releasing all that stored methane and creating a global warming feedback loop as the methane in the atmosphere traps heat and melts even more permafrost.
Researchers are trying to gauge this risk by accurately measuring stores of methane in permafrost on land and in the ocean, and predicting how fast it will thaw as the planet warms. Though methane gas quickly decays once it escapes into the atmosphere, lasting only about 10 years, it is 30 times more efficient than carbon dioxide at trapping heat (the greenhouse effect).
Shakova and colleague Igor Semiletov of the Russian Academy of Sciences first discovered methane bubbling up from the shallow seafloor a decade ago in Russia's Laptev Sea. Methane is trapped there in ground frozen during past ice ages, when sea level was much lower.
In their latest study, Shakova and her colleagues reported thousands of measurements of methane bubbles taken in summer and winter, between 2003 and 2012.
But the team also sampled seawater temperature and drilled into the ocean bottom, to see if the sediments are still frozen. Most of the survey was in water less than 100 feet (30 meters deep).
The shallow water is one reason so much methane escapes the Siberian shelf — in the deeper ocean, as methane-eating microbes digest the gas before it reaches the surface, Shakova said. But in the Laptev Sea, "it takes the bubbles only seconds, or at least a couple of minutes, to escape from the water column," Shakova said.