Dlugokencky, E. J.,
L. M. P. Bruhwiler, J. W. C. White, L. K. Emmons,
Paul C. Novelli,
Stephen A. Montzka,
Kenneth A. Masarie,
Patricia M. Lang,
A. M. Crotwell,
John B. Miller and L. V. Gatti, (2009), Observational constraints on recent increases in the atmospheric CH4
burden,
Geophysical Research Letters, 36, L18803, 10.1029/2009GL039780
Measurements of atmospheric CH4 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,
CH4 increased by 8.3 ± 0.6 ppb. CH4 mole fractions
averaged over polar northern latitudes and the Southern
Hemisphere increased more than other zonally averaged
regions. In 2008, globally averaged CH4 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
CH4 from biomass burning. The most likely drivers of the
CH4 anomalies observed during 2007 and 2008 are
anomalously high temperatures in the Arctic and greater
than average precipitation in the tropics. Near-zero CH4
growth in the Arctic during 2008 suggests we have not yet
activated strong climate feedbacks from permafrost and
CH4 hydrates.