Scientists have long believed that thawing
permafrost in Arctic soils could release huge amounts of methane, a
potent greenhouse gas. Now they are watching with increasing concern as
methane begins to bubble up from the bottom of the fast-melting Arctic
30 Oct 2008: Report
For the past
15 years, scientists from Russia and other nations have ventured into
the ice-bound and little-studied Arctic Ocean above Siberia to monitor
the temperature and chemistry of the sea, including levels of methane,
a potent greenhouse gas. Their scientific cruises on the shallow
continental shelf occurred as sea ice in the Arctic Ocean was rapidly
melting and as northern Siberia was earning the distinction — along
with the North American Arctic and the western Antarctic Peninsula —of
warming faster than any place on Earth.
Until 2003, concentrations of methane had remained relatively
stable in the Arctic Ocean and the atmosphere north of Siberia. But
then they began to rise. This summer, scientists taking part in the
six-week International Siberian Shelf Study discovered numerous areas,
spread over thousands of square miles, where large quantities of
methane — a gas with 20-times the heat-trapping power of carbon dioxide
— rose from the once-frozen seabed floor.
These “methane chimneys” sometimes contained concentrations of
the gas 100 times higher than background levels and were so large that
clouds of gas bubbles were detected "rising up through the water
column," Orjan Gustafsson of the Department of Applied Environmental
Science at Stockholm University and the co-leader of the expedition,
said in an interview. There was no doubt, he said, that the methane was
coming from sub-sea permafrost, indicating that the sea bottom might be
melting and freeing up this potent greenhouse gas.
Gustafsson said he makes no claims that the methane release “is necessarily driven by global warming.”
The route of the Jacob Smirnitskyi, a
Russian research vessel that traveled along the Russian Arctic coast
this summer as part of the International Siberian Shelf Study.
Scientists detected extremely high levels of methane in the sea during
the six-week voyage. The purple grid shows areas where researchers
But a growing body of data showing that more methane is emanating from
the rapidly thawing Arctic Ocean has caught the attention of many
climate scientists. Could this be the beginning, they wonder, of the
release of vast quantities of sub-sea Arctic methane long trapped by a
permafrost layer that is starting to thaw?
In recent years, climate scientists have been concerned about
a so-called “methane time bomb” on land, which would be detonated when
warming Arctic temperatures melt permafrost and cause frozen vegetation
in peat bogs and other areas to decay, releasing methane and carbon
dioxide. Now come fears of a methane time bomb, part two, this one
bursting from the sea floor of the shallow Arctic continental shelf.
The Arctic sea floor contains a rich, decayed layer of vegetation from
earlier eras when the continental shelf was not underwater.
So little data is available from the Arctic Ocean that no
scientists dare say with certainty whether the world is watching the
fuse being lit on a marine methane time bomb. But researchers such as
Natalia Shakhova —a visiting scientist at the University of Alaska in
Fairbanks and a participant in some of the Siberian Shelf scientific
cruises — are concerned that the undersea permafrost layer has become
unstable and is leaking methane long locked in ice crystals, known as
"Now come fears of a methane time bomb, part two, this one bursting from the sea floor of the shallow Arctic continental shelf."
One thing is certain: the shallow Siberian Shelf alone covers
more than 1.5 million square kilometers (580,000 square miles), an area
larger than France, Germany, and Spain combined. Should its permafrost layer thaw,
an amount of methane equal to 12 times the current level in the
atmosphere could be released, according to Shakhova. Such a release
would cause “catastrophic global warming,” she recently wrote in
Geophysical Research Abstracts. Among the many unanswered questions is
how quickly — over years? centuries? — methane releases might occur.
Said Gustafsson, “The conventional view is that the permafrost
is holding these large methane reservoirs in place. That is a view that
we need to rethink and revise.”
What concerns some scientists is evidence from past geological
eras that sudden releases of methane have triggered runaway cycles of
climate upheaval. Martin Kennedy, a geologist at the University of
California at Riverside and lead author of a paper published in Nature
in June, speaks in near-doomsday terms, warning that rising methane
emissions — from land and sea — threaten to radically destabilize the
climate. Ice core studies in Greenland and Antarctica have shown that
Earth’s climate can change abruptly, more like flipping a switch than
slowly turning a dial.
“I’m very concerned that we’re near the threshold and we’re
going to see the tipping point in 20 years,” Kennedy warns. Temperature
increases in the Arctic of a just few degrees could unleash the huge
storehouse of methane, which some have estimated would be comparable to
burning all recoverable stocks of coal, oil, and natural gas.
concerns some scientists is evidence from past geological eras that
sudden releases of methane have triggered runaway cycles of climate
Kennedy’s Nature article bases his warnings on a long-ago event. Sediment samples gathered in south Australia led Kennedy’s team to theorize that a catastrophic era of
global warming was triggered some 635 million years ago by a gradual —
and then abrupt — release of methane from frozen soils, bringing an end
to “Snowball Earth,” when the entire planet was encrusted in ice. He
sees similarities in the mounting threats of thawing terrestrial and
marine permafrost today. The question, he asks, is what will set the
process in motion and when.
“Do we have a substantial risk of crossing one of these
thresholds?” he asked in an interview. “I would say yes. I have
absolutely no doubt that at the current rate of [greenhouse gas
emissions] we can cross a tipping point, and when that occurs it’s too
late to do anything about it.”
As with much climate research, the science is complex and
opinions can vary dramatically. David Lawrence of the National Center
for Atmospheric Research in Boulder, Colorado, is concerned, but not
alarmed. Lawrence was lead author of a paper in Geophysical Research
Letters, also published in June, that documented the consequences of
the record loss of Arctic sea ice in 2007. Based on climate models,
Lawrence and his team theorized that during periods of rapid sea-ice
loss, temperatures could increase as far as 900 miles inland,
accelerating the rate of terrestrial permafrost thaw. From August to
October of 2007, they reported, temperatures over land in the western
Arctic rose more than 4° F above the 1978-2006 average.
“If you give it [the land] a pulse of warming like that it
could lead to increased degradation of permafrost,” Lawrence said in an
interview. “It’s not quite a runaway situation, but it does accelerate
once it starts to thaw and accumulates heat.”
Arctic soils hold nearly one-third of the world’s supply of
carbon, remnants of an era when even the northern latitudes were
covered with lush foliage and mammoths ranged over grassy steppes.
Scientists estimate that the Siberian tundra contains as much buried
organic matter as the world’s tropical rain forests.
Disappearing Arctic sea ice — summer ice extent was at its
lowest level in recorded history in 2007 and almost hit that level in
2008 — also will warm the Arctic Ocean, since a dark, ice-free sea
absorbs more solar radiation than a white, ice-covered one. In
addition, warmer waters are pouring in from rivers in rapidly warming
land regions of Alaska, Canada, and Russia, also increasing sea
"Scientists are stepping up their monitoring of the land and the sea in the Arctic."
Rising ocean and air temperatures mean not only the continuing
disappearance of Arctic sea ice — many scientists now think the Arctic
Ocean could be ice-free in summer within two decades — but
also mean that permafrost on the sea floor could thaw more quickly.
Scientists are unsure how rapidly the subsurface permafrost is thawing,
or the exact causes. One possible cause could be geothermal heat
seeping through fault zones. In any case, scientists agree that Arctic
sub-sea permafrost — with a temperature of 29° F to 30° F— is closer to
thawing than terrestrial permafrost, whose temperature can drop as low
as 9.5° F.
At this point, scientists are stepping up their monitoring of
the land and the sea in the Arctic, watching to see if either time bomb
— terrestrial or marine — is showing signs of going off. So far, data
are scarce and monitoring networks don’t exist. “That makes it very
difficult to understand and evaluate the future,” Lawrence said.
Although scientists know that methane has been released in the region’s
water for eons, they are unsure if the new findings represent a
short-term spike or long-term trend.
Pending more research, Orjan Gustafsson shares Lawrence’s
caution. When he was asked how close Earth may be to a tipping point of
irreversible climate change, he replied: “Everyone would like to know
the answer to that. I don’t think anyone can say.”
the article is reprinted from Yale Environment 360 e360.yale.edu