German researchers have identified a previously unknown emitter of methane, a potent greenhouse gas. The culprit: ordinary plants.
The first hints arrived last year when the European Space Agency's ENVISAT satellite detected huge clouds of methane above forested areas. Scientists could not understand where the gas came from, because they thought methane was produced only in oxygen-poor environments like swamps and rice paddies, where decomposition occurs. To investigate, geochemist Frank Keppler and his colleagues at the Max Planck Institute for Nuclear Physics placed a variety of plants in test chambers and filled the rooms with methane-free air. He was amazed to see chemical sensors in the room quickly begin detecting methane. "At the moment, it is a mystery," he says. "If you look at the textbooks, you will see that it was not envisioned that this could happen."
Turning up the heat seems to increase the rate at which the plants produce methane, Keppler says, which could explain why atmospheric levels of methane were high hundreds of thousands of years ago when global temperatures were balmy. The new finding also adds a twist to our understanding of Earth's climate. Methane is the second biggest contributor to global warming, and although Keppler doesn't think we should stop planting trees, he says we need to factor them into our projections. "If global warming continues, we could get a higher flux of methane from the plants," he says. "We could get a massive feedback reaction."