May 23, 2008
Wetlands May Cause Rise in Methane Levels
Emissions from wetlands around the Arctic may be responsible for higher atmospheric levels of the greenhouse gas methane that were noted last year.
Extra amounts of the gas in the Arctic region are of biological origin, according to scientists.
For nearly a decade global levels of methane had remained mostly stable.
Rising levels in the arctic indicate that some of the methane stored away in permafrost is being released, which would result in major climatic implications.
Methane is about 25 times more potent than carbon dioxide as a greenhouse gas, though it survives for a shorter time in the atmosphere before being broken down by natural chemical processes.
The U.S. National Oceanic and Atmospheric Administration (NOAA) released a preliminary analysis of readings taken at monitoring stations worldwide, which indicated that methane levels might be rising after almost a decade of stability.
In 2007, NOAA suggested a global rise of around 0.5%.
Some stations around the Arctic, such as the one at Mount Zeppelin in Svalbard, north of Scandinavia, showed rises of more than double that amount.
Norway and Sweden have been carrying out long-term monitoring around the Arctic. A British team has recently started gathering samples and analyzing them in a way that could reveal where the methane is coming from.
Methane produced by bacteria contains a high proportion of molecules with the lighter form (isotope) of carbon, carbon-12, rather than the heavier form, carbon-13.
"Anything where bacteria form methane, you get depletion in C-13 because methanogens (the bacteria) preferentially use C-12," said Rebecca Fisher from Royal Holloway, University of London, who has been running the Svalbard experiments.
She said the results they have so far imply a predominantly biogenic source.
The researchers can see where the gas is produced by matching methane levels with wind direction. This analysis also implies a source in the Arctic regions, rather than one further afield such as the additional output from Asia's rapid industrialization.
Ed Dlugokencky, the scientist at NOAA's Earth System Research Laboratory (ESRL) who collates and analyses data from atmospheric monitoring stations, agrees that the 2007 rise has a biological cause.
"We're pretty sure it's not biomass burning; and I think 2007 is probably down to wetland emissions," he said.
"In boreal regions it was warmer and wetter than usual, and microbes there produce methane faster at higher temperatures."
He also suggested that the drastic reduction in summer sea ice around the Arctic between 2006 and 2007 could have increased release of methane from seawater into the atmosphere.
It is also possible that the gas is being released in increasing amounts from permafrost as temperatures rise.
Researchers will analyze this year's data to determine whether 2007 was just a blip or the beginning of a sustained rise.
Before rapid increases such as industrial reform in the former Soviet bloc, changes to rice farming methods and the capture of methane from landfill sites, methane concentrations had been mostly stable since 1999.
Recently, concentrations have risen during El Nino events, whereas the world is currently amid the opposite climatic pattern, La Nina.
Increased methane concentrations emissions could have significant implications for the Earth's climatic future.
A sustained release from Arctic regions or tropical wetlands could drive a feedback mechanism, whereby higher temperatures liberate more of the greenhouse gas, which in turn forces higher temperatures.
It is still unsure whether methane is being released from hydrates on the ocean floor.
Hydrates are formed from water and methane under high pressure, and may begin to give off methane as water temperatures rise.
The amount of the gas held in oceanic hydrates is thought to be larger than the Earth's remaining reserves of natural gas.
Fisher's team will begin work this summer sampling water near hydrate deposits to look for indications of gas emerging. They will be collaborating with other British institutions.
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