Atmospheric Methane Rising

Atmospheric Methane Rising

“CSIRO, the Commonwealth Scientific and
Industrial Research Organisation, is Australia’s
national science agency and one of the largest
and most diverse research agencies in the world.”
over the past year, the total sources have overwhelmed
the total sinks, and methane has again started to rise.”

CSIRO News Release
30 October 2008

Global methane levels on the rise again

After eight years of near-zero growth in
atmospheric methane concentrations, levels have
again started to rise.

“This is not good news for future global
warming,” says CSIRO’s Dr Paul Fraser, who
co-authored a paper to be published in
Geophysical Research Letters, a journal of the
American Geophysical Union.

“Over recent years, the growth of important
greenhouse gases, namely methane and the CFCs,
had slowed. This tended to offset the increasing
growth rate of carbon dioxide that results mainly
from large increases in the consumption of fossil
fuels, particularly in the developing world.

“Now that methane levels have resumed their
growth, global warming may accelerate.”

Methane is the second most important greenhouse
gas in the atmosphere after carbon dioxide,
accounting for nearly 20 per cent of global
warming since the industrial revolution.

Methane is emitted to the atmosphere from natural
wetlands, rice fields, cattle, forest and
grassland fires, coal mines, natural gas leakage
and use, and other sources.

“Over the past decade these methane sources have
been close to balancing the absorption of methane
through atmospheric oxidation and into dry soil,”
Dr Fraser says.

“This fragile balance has resulted in little
growth of methane in the atmosphere. Apparently
some sources have been increasing, such as from
fossil fuel use, cattle, and rice, while others
have been decreasing, particularly natural
tropical wetlands. However, over the past year,
the total sources have overwhelmed the total
sinks, and methane has again started to rise.”

Dr Fraser says that recent analyses of global
data by CSIRO and collaborators at the
Massachusetts Institute of Technology, Scripps
Institution of Oceanography and the University of
Bristol suggest that the methane increase is, at
least in part, due to methane releases in the
high latitudes of the Northern Hemisphere.

“Such increases have been predicted as rapid
Arctic ice melting creates more high latitude
wetland sources,”  says Dr Fraser.

“A possible additional cause of the methane
increase is that atmospheric oxidation may be
weakening, for reasons as yet unknown, although
recovery from ozone depletion, which is predicted
to have commenced, may be involved.”

The Intergovernmental Panel on Climate Change
(IPCC) has identified the need to understand
causes of the variations of methane growth rates
as a priority area of research. “The reality is
that scientists have only a very basic
understanding of these methane variations,” Dr
Fraser says.

“In order to predict the future contribution of
methane to climate change, continuing
high-quality observations, in particular in
tropical and boreal locations, are required as
input to, and verification of, sophisticated
climate models.”

The Centre for Australian Weather and Climate
Research is a partnership between CSIRO and the
Bureau of Meteorology.


M. Rigby, R.Prinn, P. Fraser, P. Simmonds, R.
Langenfelds, J. Huang, D. Cunnold, P. Steele, P.
Krummel, R.Weiss, S. O’Doherty, P. Salameh, H.
Wang, C. Harth, J. Mühle, L. Porter.  Renewed
growth of atmospheric methane. Journal of
Geophysical Research. 28 pages 2008


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