Changing methane lifetime: Possible cause for reduced growth

We present a 3‐D model study, where the focus is on CH 4 lifetime and variations related to changes in the global distribution of OH. The observed CH 4 concentration and estimates of the anthropogenic emissions of CO, NO x and NMHC's, for the period 1980–96 is used to calculate changes in OH and in CH 4 lifetime. The model suggests that CH 4 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 CH 4 lifetime and the observed CH 4 concentration the yearly average CH 4 emission from 1980–96 is calculated to increase by 0.67%/yr. A moderate decrease in CH 4 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 CH 4 is the increasing anthropogenic emissions in SE‐Asia, which more than compensate for the declining emissions seen over Europe and N‐America.