Is the amplitude of the methane seasonal cycle changing?

Twelve years of atmospheric CH4 data from a globally distributed set of sampling sites ranging in latitude from 82°N to 90°S are analyzed to determine if a statistically significant trend in the peak-to-peak seasonal cycle amplitude exists. Two analysis methods are used. Agreement between amplitude trends determined by the two methods is reasonable. Trends in amplitude determined from sampling sites of similar latitude are not consistent, except in the high southern latitudes, so we focus on the latitude zone 30–90°S, where CH4 destruction is the primary factor determining the seasonal cycle amplitude. In this high southern hemisphere latitude zone, the trend in seasonal cycle amplitude is not statistically different from zero. Statistical uncertainties in the peak-to-peak seasonal cycle amplitude suggest that the observations are consistent with the change in the amplitude expected due to the increasing burden of atmospheric CH4, but not with an increase in the globally averaged OH concentration.