Methane (CH4) is a potent greenhouse gas. The concentration of methane in the atmosphere plateaued from about 1999 to 2007, but since 2007 it began rising again. The sources of the increase are not clear. The primary sources of atmospheric methane are oil and gas production and agriculture, primarily livestock. Recent research has suggested that existing bottom-up inventories (IPCC 2006) of livestock methane emissions are too low. In this study, recent changes in animal body mass, feed quality and quantity, milk productivity, and management of animals and manure have been used to calculate new livestock methane emissions factors for enteric fermentation in cattle, and for manure management in cattle and swine. Using the new emissions factors, researchers have found that global livestock emissions are probably 11% greater than those calculated using the IPCC 2006 emissions factors. In 2011 the new global estimates for annual livestock CH4 emissions comprise one-fifth of total annual global methane emissions. However, with the new estimates the annual increase in livestock emissions accounts for one half to three-fourths of the global increases from all sources since 2007.
This suggests that livestock CH4 emissions may be a major contributor to the observed increases in emissions in the 2000s to 2010s. Revised methane emissions factors and spatially distributed annual carbon fluxes for global livestock, Julie Wolf, Ghassem R. Asrar and Tristram O. West, Carbon Balance and Management 2017 12:16, doi 10.1186/s13021-017-0084-y