It is a myth that warming of permafrost (permanently frozen sub-soil) by itself releases methane. Permafrost is simply permanently frozen ground. As the permafrost in places such as Siberia and Alaska is melting, however, methane is being released in massive quantities. So what is happening?
The earth is much cooler at present than it has been for much of the planet’s history, and has been cooling since the end of what is colloquially termed the last Ice Age. For most of the earth’s history, for periods of hundreds of millions of years long, the global average temperature has been 22 degrees Celsius, whereas at present it is around 13.8 deg C. These long periods are interrupted by occasional Ice Ages lasting a couple of million years or so. In the eyes of geologists we are in an Ice Age now, because the temperature is relatively row and there is ice at the poles. What we call the last Ice Age, geologists call the last glaciations, and the period we are currently in, is an inter-glacial warm period.
During the warm times there have been extensive forests in the cold places such as Antarctica, Siberia, Greenland, Alaska and the North of Canada. In fact, for long periods of time the flora in these areas was sub-tropical. As the temperatures cooled and these regions began to be covered with ice, the forests died. Their remains became peat bogs, and were trapped in permafrost.
A peat bog is basically a compost heap in which the vegetation has not completely decomposed, and like all compost heaps, it generates methane and carbon dioxide. What has happened in the peat bogs of Alaska, Canada and Siberia, for example, is that the peat, and its methane, have been trapped in permafrost for many thousands of years, and now that is changing. The climate is warming again, and the permafrost is melting, and as it melts the trapped methane is being released.
The remains of the forests cover incredibly large areas. The peat bogs in Siberia, for example, are the size of France and Germany combined (over a quarter of a million square miles), while the peat bogs of Canada cover approximately 12% of the country’s area. Billions of tonnes of methane are trapped in these areas, and is being released as the permafrost melts and the peat begins to decompose again.
The peat bogs are the main source of methane trapped in the permafrost. If the peat is wet, methane is the major gas released. If dry, the major gas tends to be carbon dioxide. They are a reminder that we are actually living in a cool period, and there have been sub-tropical forests in places we associate with ice, blizzards and permafrost.
References:
http://www.newscientist.com/article/mg18725124.500
http://www.geocraft.com/WVFossils/Carboniferous_climate.html
http://news.nationalgeographic.com/news/2004/01/0115_040115_siberianpeatbog.html
http://www.geocraft.com/WVFossils/ice_ages.html
http://news.mongabay.com/2006/1012-ucla.html
