Arctic methane chimneys raise fears of runaway climate change
by James Randerson
Scientists claim to have discovered evidence for large releases of methane into the atmosphere from frozen seabed
stores off the northern coast of Siberia.
A large injection of the gas -- which is 21 times more potent as an atmospheric heat trap than carbon dioxide -- has
long been cited by climate scientists as the potential trigger for runaway global warming. The warming caused by the
gas could destabilise permafrost further, they fear, leading to yet more methane release.
But climate experts have expressed caution at the claims, which have yet to be published in a peer reviewed
scientific journal. Methane release from stores of so-called gas hydrates, that can form on land or under the sea, is
not new to researchers. Huge quantities are known to exist in the Arctic, but special circumstances would need to
exist for significant releases to occur.
"Methane release has been known for a number of years now," said geologist Dr Lorenz Schwark at the University of
Cologne, Germany. "There are various areas around the world that have been studied in detail."
He said the process of methane release from hydrates had been filmed by robotic vehicles off the coast of Vancouver
Island in Canada, for example.
"The problem is that in the Russian or in the Siberian Arctic on land and in the sea there is very little coverage by
hard data and there are hardly any measurements. And therefore there is a lot of speculation going on."
In most cases, methane released from the sea bed is consumed by micro-organisms as it bubbles up to the surface. But
if it is released quickly enough it could make it into the atmosphere.
"The most likely process where this happens -- and there is geological evidence that it has happened in the past --
is when the methane gas hydrate layer in the sediment destabilises on a slope. And then we have a slope failure, a
landslide underwater," Dr Schwark said.
"As long as the scientists in the Siberian Arctic are not able to report very strong increases in submarine
landslides and slope failures, I wouldn't expect that the release into the atmosphere is so severe that it is really
very serious at the moment," Schwark added.
The scientists who have studied methane levels along Russia's northern coastline are aboard the Russian research ship
Jacob Smirnitskyi.
Oerjan Gustafsson of Stockholm University in Sweden told in an e-mail from the vessel: "An extensive area of intense
methane release was found. At earlier sites we had found elevated levels of dissolved methane. Yesterday, for the
first time, we documented a field where the release was so intense that the methane did not have time to dissolve
into the seawater but was rising as methane bubbles to the sea surface. These 'methane chimneys' were documented on
echo sounder and with seismic [instrument]."
At some locations he said concentrations of the gas were 100 times the background level. These anomalies were
documented in the East Siberian Sea and the Laptev Sea, covering several tens of thousands of square
kilometres.
Gustafsson added: "The conventional thought has been that the permafrost 'lid' on the sub-sea sediments on the
Siberian shelf should cap and hold the massive reservoirs of shallow methane deposits in place. The growing evidence
for release of methane in this inaccessible region may suggest that the permafrost lid is starting to get perforated
and thus leaking methane."
Estimates for the amount of carbon locked up in the hydrates vary from 500 to 5,000 gigatons.
Scientists predict that warming will release some of these deposits, but modelling the temperature rise that would
trigger significant releases has proved extremely difficult.