There are two significant facts about methane in terms of global warming. It is about 20 times more potent as a greenhouse gas than carbon dioxide, and there are massive stores of it locked away under the permafrost of the northern hemisphere.
Methane is produced naturally by the decay of water-logged vegetation. Over thousands of years it has accumulated under the ground at northern latitudes and has effectively been taken out of circulation by the permafrost acting as an impermeable lid.
What makes methane so potentially dangerous is that its release from under the now-leaking permafrost could accelerate global warming, which in turn would speed the melting of the permafrost and release even more methane. Scientists believe this has happened in the geological past with devastating consequences for the global climate and life.
Like carbon dioxide, average methane concentrations in the atmosphere have risen significantly since the Industrial Revolution, increasing from about 700 parts per billion (ppb) in 1800 to about 1,790ppb today. Much of this increase is down to human activities, notably oil and gas exploration, and agriculture.
For the past 10 years, average global methane concentrations have levelled out, probably because of improvements in Russian gas exploration. However, for the first time in more than a decade, scientists recorded an increase in global methane in 2007 and are set to measure a further increase this year.
Scientists at the US National Oceanic and Atmospheric Administration (NOAA) have identified the Arctic as a potentially important new source of methane as temperatures in the region increase; it is one of the most rapidly warming places on Earth. "We're on the look-out for the first sign of a methane release from thawing Arctic permafrost. It's too soon to tell whether last year's spike in emissions includes the start of such a trend," said NOAA's methane expert Ed Dlugokencky last April.
The good news about methane is that it is quickly degraded in the environment, with an average lifetime of about 12 years, compared to the 100 years of carbon dioxide. The bad news is that we do not understand how the methane stores in the north will behave as the region experiences more extensive thaws. The fear is that the amounts released will make global warming far worse than expected.
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