Changing methane lifetime: Possible cause for reduced growth

We present a 3-D model study, where the focus:is on CH4 lifetime and variat ions related to changes in the global distribution of OH. The observed CH4 concentration and estimates of the anthropogenic emissions of CO, NOx and N MHC'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 concen tration has:increased by 0.43%/yr . Combining the calculated change in CH4 lifetime and the observed CH4 conc entration the yearly average CH4 emission from 1980-96 is calculated to inc rease 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 198 0-90. The key to the changing oxidation of CH4 is the increasing anthropoge nic emissions in SE-Asia, which more than compensate for the declining emis sions seen over Europe and N-America.