FROM:

http://blogs.nature.com/news/blog/2006/02/methane_burps_disproved.html ' 

Now that most scientists agree human activity is causing the Earth to warm, the central debate has shifted to when we will pass the tipping point and be helpless to stop the runaway global warming.

There are enormous quantities of methane trapped in permafrost and under the oceans in ice-like structures called clathrates. The methane in Arctic permafrost clathrates is estimated at 400 billion tons.

Methane is more than 20 times as strong a greenhouse gas as CO2, and the atmosphere currently contains about 3.5 billion tons of the gas.

The highest temperature increase from global warming is occurring in the arctic regions-an area rich in these unstable clathrates. Simulations from the National Center for Atmospheric Research (NCAR) show that over half the permafrost will thaw by 2050, and as much as 90 percent by 2100.

Peat deposits may be a comparable methane source to melting permafrost. When peat that has been frozen for thousands of years thaws, it still contains viable populations of bacteria that begin to convert the peat into methane and CO2.

Western Siberia is heating up faster than anywhere else in the world, having experienced a rise of some 3C in the past 40 years. The west Siberian peat bog could hold some 70 billion tons of methane. Local atmospheric levels of methane on the Siberian shelf are now 25 times higher than global concentrations.

By the way, warmer temperatures and longer growing seasons have caused microbial activity to increase dramatically in the soil around the world. This, in turn, means that much of the carbon long stored in the soil is now being released into the atmosphere.
Releases of methane from melting oceanic clathrates have caused severe environmental impacts in the past. The methane in oceanic clathrates has been estimated at 10,000 billion tons.

55 million years ago a global warming chain reaction (probably started by volcanic activity) melted oceanic clathrates. It was one of the most rapid and extreme global warming events in geologic history.

Humans appear to be capable of emitting CO2 in quantities comparable to the volcanic activity that started these chain reactions. According to the U.S. Geological Survey, burning fossil fuels releases more than 150 times the amount of CO2 emitted by volcanoes.

Human methane sources, such as rice paddies and livestock, have already more than doubled the methane concentration in the atmosphere from pre-industrial levels.

Methane in the atmosphere does not remain long, persisting for about 10 years before being oxidized to CO2 (a greenhouse gas that lasts for hundreds of thousands of years). Chronic methane releases oxidizing into CO2 contribute as much to warming as does the transient methane concentrations.

To summarize, human activity is causing the Earth to warm. Bacteria converts carbon in the soil into greenhouse gasses, and enormous quantities are trapped in unstable clathrates. As the earth continues to warm, permafrost clathrates will thaw; peat and soil microbial activity will dramatically increase; and, finally, vast oceanic clathrates will melt. This global warming chain reaction has happened in the past.

Atmospheric concentrations of CO2 rose by a record amount over the past year. It is the third successive year in which they have increased sharply. Scientists are at a loss to explain why the rapid rise has taken place, but fear the trend could be the first sign of runaway global warming.

Posted by: Brad Arnold | February 15, 2006 08:06 AM