Reconciling the changes in atmospheric methane sources and sinks between the Last Glacial Maximum and the pre-industrial era

We know from the ice record that the concentration of atmospheric methane, [CH(4)], at the Last Glacial Maximum (LGM) was roughly half that in the pre-industrial era (PI), but how much of the difference was source-driven, and how much was sink-driven, remains uncertain. Recent developments include: a higher estimate of the LGM-PI change in methane emissions from wetlands-the dominant, natural methane source; and the possible recycling of OH consumed in isoprene oxidation-the principal methane sink. Here, in view of these developments, we use an atmospheric chemistry-transport model to re-examine the main factors affecting OH during this period: changes in air temperature and emissions of non-methane volatile organic compounds from vegetation. We find that their net effect was negligible (with and without an OH recycling mechanism), implying the change in [CH(4)] was almost entirely source driven-a conclusion that, though subject to significant uncertainties, can be reconciled with recent methane source estimates. Citation: Levine, J. G., E. W. Wolff, A. E. Jones, L. C. Sime, P. J. Valdes, A. T. Archibald, G. D. Carver, N. J. Warwick, and J. A. Pyle (2011), Reconciling the changes in atmospheric methane sources and sinks between the Last Glacial Maximum and the pre-industrial era, Geophys. Res. Lett., 38, L23804, doi: 10.1029/2011GL049545.