A detailed assessment of global methane production through enteric fermentation by domestic animals and humans is presented. Measured relations between feed intake and methane yields for animal species are combined with population statistics to deduce a current yearly input of methane to the atmosphere of 74 Tg (1 Tg = 1012 g), with an uncertainty of about 15%. Of this, cattle contribute about 74%. Buffalos and sheep each account for 8–9%, and the remainder stems from camels, mules and asses, pigs, and horses. Human CH4 production is probably less than 1 Tg per year. The mean annual increase in CH4 emission from domestic animals and humans over the past 20 years has been 0.6 Tg, or 0.75% per year. Population figures on wild ruminants are so uncertain that calculated CH4 emissions from this source may range between 2 Tg and 6 Tg per year. Current CH4 emission by domestic and wild animals is estimated to be about 78 Tg, representing 15–25% of the total CH4 released to the atmosphere from all sources. The likely CH4 production from domestic animals in 1890 was about 17 Tg, so that this source has increased by a factor of 4.4.

A brief tentative discussion is also given on the potential CH4 production by other herbivorous fauna, especially insects. Their total CH4 production probably does not exceed 30 Tg annually.