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Potent greenhouse-gas methane has been rising

Methane levels in the atmosphere rose in 2007 after 10 years. Scientists are trying to find out why.

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One of a handful of gases that appear in tiny amounts but are far more potent warming agents than CO2, methane's climate significance – along with other trace gases and black carbon soot – have led some researchers to suggest that clamping down quickly on these emissions could buy some time to deal with the thornier problem of reducing CO2 emissions.

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Countries are currently negotiating a new climate agreement to take effect after 2012. Several key players, including the European Union, argue that to avoid dangerous climate change, the world must hold the increase in global average temperatures to between 3.6 and 5.4 degrees Fahrenheit by 2100. That means stabilizing CO2 concentrations at about 450 p.p.m.

Recently, however, a team led by James Hansen at the National Aeronautics and Space Administration's Goddard Institute for Space Studies in New York have begun to argue that the CO2 target must be 350 p.p.m. or less to account for additional, long-term amplifying effects of warming.

Without seriously tackling methane and these other sources of warming, "our CO2 requirements could be ... tougher than the 350 target," Dr. Hansen says. Making serious reductions in methane, tropospheric ozone (to which methane contributes), and black soot, he continues, could ease the requirements on CO2 by some 25 p.p.m.

More research needed

At least for several developed countries, much of that low-hanging fruit may already have been picked, according to Michael Prather, an atmospheric chemist at the University of California at Irvine and a lead author on last year's IPCC reports. The flat trends in methane over the past eight years defied previous IPCC projections.

The reasons, he says, could range from changes in energy demand in Russia after the fall of the Soviet Union to a push by industry in the US and Europe to tackle methane from leaky pipelines, landfills, and other sources as their first cut at controlling greenhouse gases.

The uptick NOAA detected "is a surprise," he says. "But in some sense it could mean that we're just back to normal."

The task now, Dlugokencky and others say, is to conduct detailed analyses of last year's methane samples to try to identify the sources – Northern Hemisphere versus Southern and natural versus human generated.

In addition, some researchers are calling for many more sampling sites. This, they say, would allow monitoring of emission-control efforts in various regions and figuring out whether critical feedback mechanisms, such as thawing permafrost, are finally their heat-trapping inventory to the atmosphere.