Methane study reveals serious new climate threat

Issue 

Millions of tonnes of the potent greenhouse gas methane have apparently begun leaking from the seabed beneath wide areas of the Arctic Ocean, the British Independent reported on September 23.

Scientists on board the research ship Yakov Smirnitsky recently finished taking precise measurements of methane along Russia's entire northern coastline. Conducted under the International Siberian Shelf Study 2008, the research revealed methane concentrations as much as 100 times background levels, with the largest anomalies tens of thousands of square kilometers in extent.

"We have found elevated levels of methane above the water surface and even more in the water just below", researcher Dr Orjan Gustafsson of Stockholm University told the British Independent in an email. "It is obvious that the source is the seabed."

In some places, the gas was evidently bubbling from the sea floor in volumes too great to be dissolved by the surrounding water. Echo-soundings detected "methane chimneys" reaching all the way to the surface.

Methane, which has the chemical formula CH4, is produced when organic matter decays in an environment poor in oxygen. Vast quantities of methane are locked in the permafrost — frozen earth and swamps — of Arctic landmasses.

Increases in average Arctic temperatures, of some 4°C over recent decades, are now causing the permafrost to melt in summer across wide areas. As a result, growing amounts of Arctic methane are reaching the atmosphere.

Permafrost also extends far onto the shallow seabed of the Arctic continental shelf, where it was flooded as sea levels rose at the end of the last ice age. Until recently, scientists thought the permafrost would form a secure "lid", keeping the methane in undersea sediments from being released.

As related by the Independent, studies in the 1990s by Dr Igor Semiletov of the Far Eastern Branch of the Russian Academy of Sciences showed no elevated methane levels.
By 2003, the picture had changed. In expeditions to the Laptev Sea off Siberia, Semiletov began finding methane "hot spots" in increasing numbers. Now, the voyage of the Yakov Smirnitsky has yielded evidence that the "lid" is leaking methane across broad regions of the continental shelf.

Semiletov, who is helping prepare the findings of the Siberian Shelf Study for publication, suggests that as permafrost melts on land, rivers are discharging warmer water in growing volumes into the Arctic Ocean. Together with increased warming of ocean waters by the sun as the area of sea ice shrinks, this may be responsible for piercing the undersea permafrost and allowing methane to escape.

The thought of massive additional quantities of methane entering the atmosphere from Arctic sediments is one to ruin the sleep of climate change scientists.

Methane is often described as a greenhouse gas "twenty-five times more powerful" than carbon dioxide (CO2). But this calculation, which averages greenhouse impacts over 100 years, largely misses the point.

Unlike CO2, which once released remains in the atmosphere for centuries, methane is mostly broken down after 10 years and almost completely gone after 20. But so powerful are the greenhouse effects of methane over these 20 years — 72 times the impact of CO2 over the same period — that a large "burst" of methane into the atmosphere could cause rapid warming.

This, in turn, would melt more permafrost and release more methane. And plenty would still remain to be released — as noted by the Independent, the amount of carbon present in Arctic methane is believed to exceed that in the earth's coal deposits.

Methane in the atmosphere has more than doubled since pre-industrial times. At its present level, of about 2 parts per million, it is the second most powerful greenhouse gas after CO2, accounting for around 20% of the global warming effect. Between 1999 and 2007, atmospheric methane was roughly static, probably as a result of improved industrial and landfill practices and the decline of natural wetlands, an important methane source. But, for the last 18 months or so, the level has again been rising.

The sudden welling up of methane from the Arctic seabed is an ominous sign. Climate scientists will now be watching intently as the researchers involved in the Siberian Shelf Study try to work out how many millions of tonnes of the gas are being released.

Ending the danger from Arctic methane will require lowering temperatures across the region, and restoring sea ice in the Arctic Ocean to something like its earlier extent. For this to happen, big cuts in the atmospheric concentrations of major greenhouse gases will be essential.