Rise in Atmospheric Methane Points to Arctic Wetlands

Methane rise points to wetlands
By Richard Black
Environment correspondent, BBC News website

Higher atmospheric levels of the greenhouse gas
methane noted last year are probably related to
emissions from wetlands, especially around the Arctic.

Scientists have found indications that extra amounts
of the gas in the Arctic region are of biological
origin.

Global levels of methane had been roughly stable for
almost a decade.

Rising levels in the Arctic could mean that some of
the methane stored away in permafrost is being
released, which would have major climatic
implications.

The gas 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.

Northern lights

Indications that methane levels might be rising after
almost a decade of stability came last month, when the
US National Oceanic and Atmospheric Administration
(Noaa) released a preliminary analysis of readings
taken at monitoring stations worldwide.

Noaa suggested that 2007 had seen a global rise of
about 0.5%.

Some stations around the Arctic showed rises of more
than double that amount.

One is the station at Mount Zeppelin in Svalbard,
north of Scandinavia.

In addition to the long-term monitoring carried out
there by Norway and Sweden, a British team has
recently started gathering samples and analysing 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.

I think 2007 is probably down to wetland emissions
Ed Dlugokencky, Noaa
“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.

“The results we have so far imply a predominantly
biogenic source,” she told BBC News.

The researchers also match methane levels with wind
direction, so they can see where the gas is being
produced. This analysis also implies a source in the
Arctic regions, rather than one further afield such as
the additional output from Asia’s rapid
industrialisation.

Warm and wet

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.”

Dr Dlugokencky 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.

A further possibility is that the gas is being
released in increasing amounts from permafrost as
temperatures rise.

Researchers will be keeping a close eye on this year’s
data which will indicate whether 2007 was just a blip
or the beginning of a sustained rise.

Methane concentrations had been more or less stable
since about 1999 following years of rapid increases,
with industrial reform in the former Soviet bloc,
changes to rice farming methods and the capture of
methane from landfill sites all contributing to the
levelling off.

In the recent past, concentrations have risen during
El Nino events, whereas the world is currently amid
the opposite climatic pattern, La Nina.

Solid evidence

An upturn in 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 temperatures still higher.

A particularly pertinent question is whether methane
is being released from hydrates on the ocean floor.

These solids 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.

In collaboration with other British institutions, Dr
Fisher’s team will begin work this summer sampling
water near hydrate deposits to look for indications of
gas emerging.

Richard.Black-INTERNET@bbc.co.uk

Story from BBC NEWS:
http://news.bbc.co.uk/go/pr/fr/-/2/hi/science/nature/7408808.stm

Published: 2008/05/23

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