Sources, sinks, and seasonal cycles of atmospheric methane

It is shown that a lifetime of approximately 8 years is most consistent with the observed latitudinal variation of atmospheric methane, requiring the current global emissions of methane to be around 550 teragrams per year. The repeating pattern of a rapid rise of CH4 concentrations in the fall in the Northern Hemisphere indicates a large fall source at latitudes above 30 deg N. The remaining observed seasonal variations are seen as consistent with the seasonal cycle of OH, which removes methane from the atmosphere. An extensive set of self-consistent measurements of methane is reported and analyzed, revealing that methane has increased during the past 3-4 years at rates of 1-1.9 percent per year all over the world at sites ranging from inside the Arctic Circle to the South Pole. The observational results are used in estimating the sources, sinks, and seasonal cycles of CH4 and the effects of human activities on its atmospheric abundance.