Between 1978 and 1987 atmospheric methane levels increased by more than 1% per year (Global Average). After 1987 methane continued to increase but at a slower rate. Now, recent measurements (Simpson et al., 2006) report that data for the years 1998 through 2005 show a rather abrupt halt to the rise in this powerful greenhouse gas. Reasons for this change, according to the authors, may be repairs to leaky oil and gas lines and storage facilities and reduced emissions from rice paddies, coal mining and natural gas production. (UCAR Quarterly, Fall 2006). These results suggest that human intervention might play a strong role in reducing further increases in this greenhouse gas.
Simpson, I. J., F. S. Rowland, S. Meinardi, and D. R. Blake, 2007: Influence of biomass burning during recent fluctuations in the slow growth of global tropospheric methane. Geophys. Res. Lett. 33, L22808, doi:10.1029/2006GL027330.
UCAR Quarterly: http://www.ucar.edu/communications/quarterly/fall06/