Pollution

Methane levels hold steady

Levels of the greenhouse gas methane have plateaued for the first time in about 200 years, shows a report in Geophysical Research Letters. Methane is second only to carbon dioxide in contributing to our planet's warming. The gas - belched out by fossil-fuel burning, rice paddies, festering farm manure and landfill sites - has been accumulating since the industrial revolution. Now the tide may be turning, say Ed Dlugokencky of the National Oceanic and Atmospheric Administration (NOAA) in Boulder, Colorado, and his team. They found that levels steadied between 1999 and 2002, according to measurements from 43 ground-based stations around the world.
The reason for the change is unclear. Dlugokencky believes that a big contributing factor was the break-up of the Soviet Union in 1991. Oil and gas production fell, and the industry became more efficient at plugging gas leaks from pipes and wells.
Experts say the plateau is no cause for complacency. Increasing fossil-fuel consumption in developing nations, or renewed drilling for natural gas, might boost methane again. "The trajectory is still moving up," says David Blake, an atmospheric chemist at the University of California, Irvine.
The finding highlights how small steps to cut methane emissions could slow global warming, he says. Leaking gas pipelines could be capped and incentives introduced to encourage landfill owners and farmers to use methane to run power generators.
Earlier studies hinted at a slowing in the long-term rise in methane - but Dlugokencky's conclusion is based on particularly frequent and accurate measurements..
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