Melting of permafrost could trigger rapid global warming warns UN
February 21, 2008
Vast amounts of methane, a greenhouse gas 23-25 times more potent than carbon dioxide, are locked in the deep sea and in the frozen soils of Siberia, Northern Europe, and North America, but warming could trigger rapid thawing that would release billions of tons into the atmosphere.
"Methane release due to thawing permafrost in the Arctic is a global warming wildcard," stated The UNEP Year Book 2008. "The balance of evidence suggests that Arctic feedbacks that amplify warming, globally and regionally, will dominate during the next 50 to 100 years. As warming continues, these feedbacks will likely intensify. We may be approaching thresholds that are difficult to predict precisely, but crossing such thresholds could have serious global consequences."
Change in duration of snow-covered ground north of 50°N. The number of days in a year in which the ground is snow covered has decreased by an estimated average of 7.5 days from 1970 to 2000. Source: Euskirchen and others 2007, image courtesy of UNEP
The report also noted that methane hydrates "are a potentially large stockpile of clean-burning fuel, if ways can be found of mining them safely and economically." Already firms are looking at strategies for exploiting methane hydrates as an energy source.
Hydrates store immense amounts of methane, with major implications for energy resources and climate, but the natural controls on hydrates and their impacts on the environment are very poorly understood.
Gas hydrates occur abundantly in nature, both in Arctic regions and in marine sediments. Gas hydrate is a crystalline solid consisting of gas molecules, usually methane, each surrounded by a cage of water molecules. It looks very much like water ice. Methane hydrate is stable in ocean floor sediments at water depths greater than 300 meters, and where it occurs, it is known to cement loose sediments in a surface layer several hundred meters thick.
The worldwide amounts of carbon bound in gas hydrates is conservatively estimated to total twice the amount of carbon to be found in all known fossil fuels on Earth.
This estimate is made with minimal information from U.S. Geological Survey (USGS) and other studies. Extraction of methane from hydrates could provide an enormous energy and petroleum feedstock resource. Additionally, conventional gas resources appear to be trapped beneath methane hydrate layers in ocean sediments.
IMAGE AND CAPTION TEXT COURTESY OF USGS
Most methane emissions never reach the atmosphere -- they are broken down by ultraviolet radiation. For methane that does reach the atmosphere, the gas has a lifetime of about eight years. In contrast, carbon dioxide can last a century in the atmosphere. As such, atmospheric methane levels can be quickly reduced, while carbon dioxide accumulates and presents a long-term problem. Still, methane levels have more than doubled since the beginning of the Industrial Revolution in the 18th century, and annual emissions have again begun to creep up after declining in the 1990s. Further, when methane oxidizes, its carbon element still affects the climate as carbon dioxide. The U.N. report notes "the consequences of increased amounts of methane entering the atmosphere depend on whether it is released instantaneously or at a slow, chronic pace."