A DRAMATIC DECREASE IN THE GROWTH-RATE OF ATMOSPHERIC METHANE IN THE NORTHERN-HEMISPHERE DURING 1992

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.