Increased methane in the atmosphere – what is the cause?

For the past ten years methane levels have remained rather stable, while carbon dioxide levels have risen. Now it seems that methane levels are on the rise, especially around the Arctic region.

Methane, you will remember is a greenhouse gas which is about forty times more potent than carbon dioxide but fortunately it is no where near as long lived in the atmosphere as the dreaded CO2. Methane is present in very small quantities, measured in nanomoles per parts billion (carbon dioxide is measured in parts per million) but so potent is it that it is estimated to be responsible for 20% of the greenhouse gas direct radiative forcings. Currently methane is in the air at around 1770 parts per billion although the concentration varies according to latitude.

It had been on an upward trend in the 1980s, slowed its growth in the 1990s and remained virtually stable this millennium but is not increasing its presence in the atmosphere.

There has to be a reason why methane concentrations are increasing around the North Pole. The most likely source of the additional methane comes from the permafrost.

Permafrost is soil at or below freezing for two years or more. It mostly exists at the land close to the North and South poles and in mountainous regions. It covers 20% of the earth’s land and its depth varies according to how long the land has been exposed to cold. It takes 350 years to get permafrost 80 metres deep, but as the climate gets warmer so the permafrost melts.

If you visit Fairbanks Alaska in summer, you will be in the warmth of the sun and pestered perhaps by mosquitoes, but you will never be more than a few meters away from permanently frozen land under your feet.permafrost has been “moving” northwards in the northern hemisphere for some years.

Permafrost holds trapped methane in it, caused by microorganisms reacting with decaying vegetation and the methane is held frozen in the permafrost. As permafrost melts so the methane melts and is released and that is what scientists at the US Oceanographic and Atmospheric Administration think is happening causing a half percent increase in methane in the atmosphere.

There are ways of measuring the molecular structure of the methane to see if it is formed biologically and preliminary tests by researchers at the University of Royal Holloway indicate that the methane at the polar regions is predominantly from biogenic sources.

It may not be caused by permafrost melting; another possibility is that recent warmer and wetter weather for the past few years in extreme northern lands have enabled the microorganisms to produce more methane than they usually do. Others speculate that the increased methane may result from the drastic reduction in Arctic summer ice, which may have increased the release of methane from seawater.

The worse scenario is that methane is being released from warming seas. These hold more methane than the permafrost.

Whatever the cause, increased atmospheric methane does not bold well for the future of life as we know it. We have enough problems with rising carbon dioxide emissions. We need more atmospheric methane like we need another hole in the head.


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