Global Methane Emissions From Terrestrial Plants

Measurements reported earlier this year suggest that terrestrial plants are significant emitters of methane on a global scale under ambient conditions. This report is of considerable interest since one, it was thought that most major sources of methane have been identified, and two, nearly all natural sources of methane are mediated by bacteria under anoxic conditions. In the original announcement, the authors estimated a mean global emission rate of 149 Tg/yr from this source. If true, the magnitude of this source would push the sum of the known methane sources beyond the constraint set by the atmospheric burden and would force reassessment of the methane budget. The attempt to confirm these measurements is ongoing and we report the results of recent work. In addition we discuss new techniques to extrapolate the emissions from the local to the global scale. If we apply these techniques to the emission rates as first reported, we estimate the global emission rate from terrestrial plants to be 15 to 40 Tg/yr. These are significantly less than the original estimates and could be readily accomodated within the current methane budget without recourse to major revisions.