Observational constraints on recent increases in the atmospheric CH4 burden

Measurements of atmospheric CH 4 from air samples collected weekly at 46 remote surface sites show that, after a decade of near‐zero growth, globally averaged atmospheric methane increased during 2007 and 2008. During 2007, CH 4 increased by 8.3 ± 0.6 ppb. CH 4 mole fractions averaged over polar northern latitudes and the Southern Hemisphere increased more than other zonally averaged regions. In 2008, globally averaged CH 4 increased by 4.4 ± 0.6 ppb; the largest increase was in the tropics, while polar northern latitudes did not increase. Satellite and in situ CO observations suggest only a minor contribution to increased CH 4 from biomass burning. The most likely drivers of the CH 4 anomalies observed during 2007 and 2008 are anomalously high temperatures in the Arctic and greater than average precipitation in the tropics. Near‐zero CH 4 growth in the Arctic during 2008 suggests we have not yet activated strong climate feedbacks from permafrost and CH 4 hydrates.