Of the total direct radiative forcing of long-lived greenhouse gases (2.45 Wm-2), almost 20% is attributable to methane (CH4), according to the 1995 report of the Intergovernmental Panel on Climate Change (IPCC 1995). Since the mid-1700s, the atmospheric concentration of methane has increased by about 145% (IPCC 1995). Thus, an understanding of the various sources of methane is important.
Atmospheric methane is produced both from natural sources (e.g., wetlands) and from human activities (see global methane cycle, from Professor W.S. Reeburgh at the University of California Irvine). Total sources of methane to the atmosphere for the period 1980-1990 were about 535 (range of 410-660) Tg (1 Teragram = 1 million metric tons) CH4 per year, of which 160 (110-210) Tg CH4/yr were from natural sources and 375 (300-450) Tg CH4/yr were from anthropogenic sources (IPCC 1995). The anthropogenic sources are further broken down into 100 (70-120) Tg CH4/yr related to fossil fuels and 275 (200-350) Tg CH4/yr from biospheric sources.
Trends Online includes estimates from Stern and Kaufmann, on a year-by-year basis, of global emissions of methane from various anthropogenic sources (flaring and venting of natural gas; oil and gas supply systems, excluding flaring; coal mining; biomass burning; livestock farming; rice farming and related activities; and landfills). Their total estimated anthropogenic sources for the 1980s (about 320-360 Tg CH4/yr) are consistent with the corresponding range reported by the IPCC (1995), as are their estimates for the emissions related to fossil-fuels (about 70-80 Tg CH4/yr).
We urge readers to credit the principal investigators and their organizations (listed at the beginning of each Methods section) when using these data. The proper citation for each record is listed at the bottom of each section. Users are encouraged to contact the principal investigators before applying the data in specific model exercises or research exercises.
31 August 1998