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Melting permafrost methane emissions: The other threat to climate change

15 September 2006

A frozen peat bog covering the entire sub-Arctic area of Western Siberia, the size of France and Germany, contains billions of tonnes of greenhouse gas that is melting for the first time since it was sequestered more than 11,000 years ago before the end of the last ice age.

Researchers Sergei Kirpotin of Tomsk State University in Siberia, and Judith Marquand of Oxford University first reported in 2005 that one million square kilometres of permafrost had started to melt.

Such an unprecedented thaw could dramatically increase the rate of global warming.

A study published in the September 7th issue of Nature authored by Katey Walter of the University of Alaska, and Jeff Chanton of Florida State University reports that greenhouse gas is escaping into the atmosphere at a frightening rate.

When Siberian permafrost melts, carbon buried since the Pleistocene era is bubbling to the surface of lakes, and dissipating into the atmosphere as methane, a greenhouse gas 23 times more potent than carbon dioxide.

Global warming gases trapped in the soil is being released from thawing permafrost at five times the rate previously thought.  Researchers warn it may set off a climate change time bomb.

With a more accurate method of measuring methane bubbling from two Siberian thaw lakes, the researchers revealed the world's northern tundra as a much larger source of methane release.  New calculations show the levels of methane emissions from northern wetlands 10 to 63 percent higher than the previous estimates.

Researchers have studied a unique Siberian permafrost called yedoma which is a frozen tundric dust, deposited during the last glacial age.  It is rich in biomass such as plant roots and animal bones, with a carbon content 10 to 30 times higher than average deep soils.

When organic matter decomposes in air, the gas produced escapes as carbon dioxide. However much of the yedoma in Siberia lies at the bottom of thaw lakes, and when it decomposes under water, provides microbes with feedstock that produce methane.

Methane is a much more potent greenhouse gas than carbon dioxide, but it has a shorter life of about a decade.  Ultimately it oxidizes to become carbon dioxide which then stays in the atmosphere for more than a hundred years.

The study of greenhouse gases released from land is exceedingly complex because soils vary considerably.

It has been known for some time that a huge amount of organic carbon is trapped in Siberian tundra. The more plentiful yedoma is a vast reservoir of carbon that has been neglected in most analyses of climate change.

An estimated 500 gigatons of carbon have been flash frozen in yedoma regions, and 900 tons in permafrost worldwide.  This large store would more than double the amount of carbon in the atmosphere today if it is released.

Thousands of lakes in eastern Siberia have disappeared during the last 30 years.  This apparent contradiction is because the two events represent opposite ends of the same process called thermokarsk.

Higher air temperatures first create frost-heave, transforming flat permafrost into hollows and hummocks known as salsas.  As the permafrost melts, water collects on the surface, forming ponds that do not drain because of the frozen bog beneath.  The ponds combine into larger lakes until the last permafrost melts and the lakes drain underground.