Global measurements of atmospheric methane have revealed a sharp decrease in the growth rate in the Northern Hemisphere during 1992. The average trend for the Northern Hemisphere during 1983–1991 was (11.6±0.2) ppbv yr−1, but the increase in 1992 was only (1.8±1.6) ppbv. In the Southern Hemisphere, the average increase (1983–1991) was (11.1±0.2) ppbv yr−1, and the 1992 increase was (7.7±1.0) ppbv. Various possibilities for a change in methane sources or sinks are discussed, but the most likely explanation is a change in an anthropogenic source such as fossil fuel exploitation, which can be rapidly and easily affected by man's activities.
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