5 march 2009

[In our appeal written a year ago, “Global Warming Threatens the Future of the Earth. Act now before it is too late”, we mentioned the danger that 70 billion tons of methane under the Siberian permafrost might be released by global warming. We were right about the danger, but wrong about the amount. The Siberian shelf contains not 70 billion, but 1,400 billion tons of methane. And global warming may have already begun to melt it.]

Sleeping Giant?

Nature Reports Climate Change, 5 March 2009

Amanda Leigh Mascarelli reports on the race to understand a ticking time bomb.

In 2007, scientists scouting the icy waters of the Arctic Ocean began to notice some troubling signs. In about half of their seawater chemistry samples, the concentration of dissolved methane was two to ten times higher than in samples taken during previous years from the same locations. Then, last summer, they observed large rings of gas — sometimes as wide as 30 centimetres in diameter — trapped in ice, as well as methane plumes bubbling to the surface over hundreds of square kilometres of the shallow waters along the Siberian Shelf.

The team, from Russia and other nations, presented their results at the American Geophysical Union's Fall Meeting in December, where scientists cautiously voiced their concerns that large quantities of methane are becoming destabilized as the planet — and the ocean — heat up. Researchers have long speculated that warming could unleash vast stores of the greenhouse gas from where it lies frozen beneath the sea floor and locked up in Arctic soils. If those deposits were to melt, it would almost certainly trigger abrupt climate change. Methane heats the atmosphere with an efficiency 25 times that of carbon dioxide, and its release could put in motion a positive feedback loop in which warming releases methane, causing further warming, which liberates even more of the gas.

Whether that's already happening is anyone's guess....But the findings are part of a growing trend in which scientists are turning their attention to a threat conceivably worse than carbon dioxide. Though human activity has boosted atmospheric concentrations of methane by 150 per cent since the Industrial Revolution — mostly through agriculture and farming, the creation of landfills, biomass burning and fossil fuel use — that's nothing compared with the quantities that could be released from frozen deposits in the ground. "These deposits rival fossil fuels in terms of their size. It's like having a whole additional supply of coal, oil and natural gas out there that we can't control," says James White, a geochemist at the University of Colorado, Boulder....

Rich in organic material from dead plant and animal matter, thawed-out permafrost becomes alive with methane-producing microbes, which release the gas to the atmosphere. Some have compared it to unplugging a giant freezer: Warming temperatures could free up ancient carbon that's been safely tucked away for many thousands of years. "We've been putting carbon in this bank for 10,000 years," says White. "It's so cold that it doesn't decay away. But as the climate warms up, you start to take it out of the bank."

Although the rapid release of methane may sound like science fiction, it is not wholly far-fetched: methane has been suspected in nearly all of the dramatic warming spells in Earth's history. What's troubling to some is how little is currently known about the gas and its potential response to warming. "It's frightening that we can't even say what the background is," says Martin Kennedy, a geologist from the University of California, Riverside. "That's what's so alarming about the state of the field right now."

Loosening the lid

The Siberian Shelf alone harbours an estimated 1,400 billion tonnes of methane in gas hydrates, about twice as much carbon as is contained in all the trees, grasses and flowers on the planet. If just one per cent of this escaped into the atmosphere within a few decades, it would be enough to cause abrupt climate change, says Shakhova...

[For more on methane hydrates and polar melting, see "Climate Emergency" on Campaign Against Climate Change

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