for National Geographic News
Human-caused methane gas, a contributor to global warming, is on the rise in Earth's atmosphere, a new study says. But declines in methane emissions from wetlands are painting a deceptively rosy picture, researchers say.
After rising during the 1980s, the growth of methane in the atmosphere slowed during the 1990s, providing a bright spot in an otherwise gloomy global warming forecast.
And while methane concentrations in Earth's atmosphere have remained stable, the study suggests the news isn't as good as scientists once thought.
(Rekated: "Global Warming Feedback Loop Caused by Methane, Scientists Say" [August 29, 2006].)
Writing in tomorrow's issue of the journal Nature, researchers say that human-caused methane emissions began rising again in 1999, possibly tied to China's booming economy.
The increase has been masked, however, by a drop in methane emissions from wetlands as they dried out, especially in the Northern Hemisphere and possibly due to global warming.
"Atmospheric methane levels may increase again in the near future if wetland emissions return to their mean 1990s levels," the authors write.
Philippe Bousquet, a physicist and chemist at the University of Versailles and the Laboratory of the Sciences of the Climate and the Environment in Gif-sur-Yvette, France, co-authored the study.
"It's important to know if methane is going to stabilize or to increase again, because methane is about 20 times more efficient [at trapping heat] in the atmosphere than CO2 [carbon dioxide, another greenhouse gas]," he said.
"So if it continues to increase, it can have some climate change consequences," he added.
Where Methane Comes From
Since preindustrial times the amount of methane in Earth's atmosphere has nearly tripled.
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