Changing methane lifetime: Possible cause for reduced growth

Abstract

We present a 3‐D model study, where the focus is on CH4 lifetime and variations related to changes in the global distribution of OH. The observed CH4 concentration and estimates of the anthropogenic emissions of CO, NOx and NMHC's, for the period 1980–96 is used to calculate changes in OH and in CH4 lifetime. The model suggests that CH4 lifetime has decreased by 0.49%/yr, while the annual global average OH concentration has increased by 0.43%/yr. Combining the calculated change in CH4 lifetime and the observed CH4 concentration the yearly average CH4 emission from 1980–96 is calculated to increase by 0.67%/yr. A moderate decrease in CH4 emissions is obtained towards the end of the period, 0.53%/yr from 1993–96 compared to 0.69%/yr from 1980–90. The key to the changing oxidation of CH4 is the increasing anthropogenic emissions in SE‐Asia, which more than compensate for the declining emissions seen over Europe and N‐America.