for National Geographic News
Editor's Note: Published on January 11, the original version of this story misinterpreted a scientific study as saying that plants contribute to global warming. According to a later press release by the study's authors, that characterization was inaccurate, and we have amended our story.
Grasses and other green growth may produce 10 to 30 percent of Earth's annual methane output, a new study reports.
Until the data were unveiled in this week's Nature, scientists had believed that plant-related methane formed only in oxygen-free environments, such as bogs.
But a team of European researchers identified a large range of plants that release methane under normal growing conditions. The gas also seeps from dead plant material.
David Lowe is an atmospheric chemist with the National Institute of Water and Atmospheric Research in Wellington, New Zealand. He wrote a review article accompanying the study.
According to Lowe, "We now have the specter that new forests might increase greenhouse warming through methane emissions rather than decrease it by being sinks for carbon dioxide."
"The identification of a new source should prompt a reexamination of the global methane budget."
The potentially enormous natural source of greenhouse gases had thus far escaped notice, which experts say is not surprising.
Thomas Roeckmann, a study co-author and atmospheric scientist with the Institute for Marine and Atmospheric Research in Utrecht, the Netherlands, said a very close look was needed to spot the emissions.
"The emissions per plant are rather small, and one has to look quite carefully to detect the increase above the high natural background of [methane]," he said. "So you would not find those emissions by chance."
Estimating the total global production of methane and other greenhouse gasses is far from an exact science, Lowe said.
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