Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 6 4 2006 10.5194/acpd-6-5867-2006 http://www.atmos-chem-phys-discuss.net/6/5867/2006/ http://www.atmos-chem-phys-discuss.net/6/5867/2006/acpd-6-5867-2006.html http://www.atmos-chem-phys-discuss.net/6/5867/2006/acpd-6-5867-2006.pdf 5867 5875 2006-07-07 Stable isotopes provide revised global limits of aerobic methane emissions from plants D. F. Ferretti J. B. Miller J. W. C. White K. R. Lassey D. C. Lowe D. M. Etheridge University of Colorado, Boulder, CO, USA National Institute of Water and Atmospheric Research Ltd, Wellington, New Zealand National Oceanographic and Atmospheric Administration, Boulder, CO, USA Marine and Atmospheric Research, Commonwealth Scientific and Industrial Research Organisation, Aspendale, Victoria, Australia Recently Keppler et al. (2006) discovered a surprising new source of methane – terrestrial plants under aerobic conditions, with an estimated global production of 62–236 Tg yr^−1 by an unknown mechanism. This is ~10–50% of the annual total of methane entering the modern atmosphere and ~30–100% of annual methane entering the pre-industrial (0 to 1700 AD) atmosphere. Here we test this reported global production of methane from plants against ice core records of atmospheric methane concentration (CH₄) and stable carbon isotope ratios (δ¹³CH₄) over the last 2000 years. Our top-down approach determines that global plant emissions must be much lower than proposed by Keppler et al. (2006) during the last 2000 years and are likely to lie in the range 0–46 Tg yr^−1.