[tt] methane release increasing

[Eugen Leitl]

http://www.independent.co.uk/news/science/exclusive-the-methane-time-bomb-938932.html

Exclusive: The methane time bomb

Arctic scientists discover new global warming threat as melting permafrost
releases millions of tons of a gas 20 times more damaging than carbon dioxide

By Steve Connor, Science Editor

Tuesday, 23 September 2008

Preliminary findings suggest that massive deposits of subsea methane are
bubbling to the surface as the Arctic region becomes warmer and its ice
retreats


The first evidence that millions of tons of a greenhouse gas 20 times more
potent than carbon dioxide is being released into the atmosphere from beneath
the Arctic seabed has been discovered by scientists.

The Independent has been passed details of preliminary findings suggesting
that massive deposits of sub-sea methane are bubbling to the surface as the
Arctic region becomes warmer and its ice retreats.

Underground stores of methane are important because scientists believe their
sudden release has in the past been responsible for rapid increases in global
temperatures, dramatic changes to the climate, and even the mass extinction
of species. Scientists aboard a research ship that has sailed the entire
length of Russia's northern coast have discovered intense concentrations of
methane – sometimes at up to 100 times background levels – over several areas
covering thousands of square miles of the Siberian continental shelf.

In the past few days, the researchers have seen areas of sea foaming with gas
bubbling up through "methane chimneys" rising from the sea floor. They
believe that the sub-sea layer of permafrost, which has acted like a "lid" to
prevent the gas from escaping, has melted away to allow methane to rise from
underground deposits formed before the last ice age.

They have warned that this is likely to be linked with the rapid warming that
the region has experienced in recent years.

Methane is about 20 times more powerful as a greenhouse gas than carbon
dioxide and many scientists fear that its release could accelerate global
warming in a giant positive feedback where more atmospheric methane causes
higher temperatures, leading to further permafrost melting and the release of
yet more methane.

The amount of methane stored beneath the Arctic is calculated to be greater
than the total amount of carbon locked up in global coal reserves so there is
intense interest in the stability of these deposits as the region warms at a
faster rate than other places on earth.

Orjan Gustafsson of Stockholm University in Sweden, one of the leaders of the
expedition, described the scale of the methane emissions in an email exchange
sent from the Russian research ship Jacob Smirnitskyi.

"We had a hectic finishing of the sampling programme yesterday and this past
night," said Dr Gustafsson. "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 [instruments]."

At some locations, methane concentrations reached 100 times background
levels. These anomalies have been seen in the East Siberian Sea and the
Laptev Sea, covering several tens of thousands of square kilometres,
amounting to millions of tons of methane, said Dr Gustafsson. "This may be of
the same magnitude as presently estimated from the global ocean," he said.
"Nobody knows how many more such areas exist on the extensive East Siberian
continental shelves.

"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 leak methane... The permafrost now has
small holes. We have found elevated levels of methane above the water surface
and even more in the water just below. It is obvious that the source is the
seabed."

The preliminary findings of the International Siberian Shelf Study 2008,
being prepared for publication by the American Geophysical Union, are being
overseen by Igor Semiletov of the Far-Eastern branch of the Russian Academy
of Sciences. Since 1994, he has led about 10 expeditions in the Laptev Sea
but during the 1990s he did not detect any elevated levels of methane.
However, since 2003 he reported a rising number of methane "hotspots", which
have now been confirmed using more sensitive instruments on board the Jacob
Smirnitskyi.

Dr Semiletov has suggested several possible reasons why methane is now being
released from the Arctic, including the rising volume of relatively warmer
water being discharged from Siberia's rivers due to the melting of the
permafrost on the land.

The Arctic region as a whole has seen a 4C rise in average temperatures over
recent decades and a dramatic decline in the area of the Arctic Ocean covered
by summer sea ice. Many scientists fear that the loss of sea ice could
accelerate the warming trend because open ocean soaks up more heat from the
sun than the reflective surface of an ice-covered sea.