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Last Updated: Wednesday, 22 November 2006, 08:50 GMT
Global methane rise slowing down

Farmer with cow manure. Image: AP
Farmers reduce emissions and make money by collecting methane
The rise in concentrations of the greenhouse gas methane in the atmosphere has slowed down considerably in recent years, research suggests.

Scientists say levels have been stable for about seven years following a steep rise during the last century.

Researchers believe the slowdown may be due to measures aimed at reducing the release of methane from gas pipelines, paddy fields and landfill sites.

The findings are published in the journal Geophysical Research Letters.

The study also found that major forest fires, such as occurred in Indonesia in 1997 and 1998, produce significant quantities of methane.

If one really tightens emissions, we will gain some ground on global warming
Sherwood Rowland
"Methane is not as significant a greenhouse gas as carbon dioxide, but its effects are important," said Sherwood Rowland from the University of California at Irvine, US.

"The world needs to work hard to reduce emissions of all greenhouse gases."

Professor Rowland was a member of the four-person team on this project, and a Nobel laureate for his work on the ozone layer.

Breaking down

Methane is the second most important gas contributing to the human-made greenhouse effect after carbon dioxide. Current concentrations are about 150% above pre-industrial levels.

But because methane is broken down relatively easily, atmospheric concentrations would return to pre-industrial levels within about a decade if the various sources of production linked to human activities could be eliminated.

Graph of methane concentrations
This has led some scientists and policymakers to suggest that cutting emissions of methane could be a more effective way of curbing climate change than focusing on carbon dioxide.

Measures adopted in various parts of the world include sealing leaks in gas pipelines, capturing and using methane from landfill sites and farm effluent, and changing farming practices to reduce emissions from rice paddies.

The latest research suggests these measures are working, with concentrations unchanged over the last seven years.

If this trend continues, it suggests that temperature rises over the next few decades could be marginally lower than previously predicted, even though emissions of other greenhouse gases including carbon dioxide are rising.

"If one really tightens emissions, the amount of methane in the atmosphere 10 years from now could be less than it is today," observed Professor Rowland.

"We will gain some ground on global warming if methane is not as large a contributor in the future as it has been in the past century."

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