Swamps and rice paddies are known to produce methane through bacterial action in anoxic environments. But Frank Keppler of the Max Planck Institute for Nuclear Physics in Heidelberg, Germany, and his colleagues now find that a wide variety of plant species emit methane under normal physiological conditions in the presence of oxygen (Nature 2006, 439, 187). The researchers estimate that 10-30% of the annual amount of methane entering Earth's atmosphere comes from living plants and dead plant material in aerobic environments. David C. Lowe of the National Institute of Water & Atmospheric Research, in Wellington, New Zealand, writes in a related commentary that the findings help "to account for observations from space of inexplicably large plumes of methane above tropical forests." The observation also suggests that rapid deforestation may be responsible for the observed slowdown in the growth rate of methane in the atmosphere in recent years, Lowe adds, which may impact global warming.