Within this range, there are considerable problems in assigning emissions to single causes. There are three main sources of livestock-related carbon dioxide emissions. Firstly, all domesticated animals emit carbon dioxide as part of basic metabolic function or respiration, estimated at a total of 2.8 billion MT annually. Secondly, carbon dioxide emissions result from biomass burning, part of which can be attributed to land clearing and bush fires for pasture and enhancing pasture growth. Thirdly, carbon dioxide is released in relation to livestock-related consumption of fossil fuel for heating, manufacturing of machinery and production of feed, etc.
Carbon dioxide is the least aggressive of the greenhouse gases but is emitted in large quantities.
However, unlike the emission from fossil fuels, the same grasslands and forests recapture part of these emissions. Leaving aside respiration of domesticated animals, livestock can be associated with about 15 to 20 percent of total carbon dioxide emissions. When the carbon sequestration capacity of natural and improved grassland is considered, the contribution to the net increase in carbon dioxide concentrations in the atmosphere is probably much smaller. There are however, notable differences between the systems. Grazing systems, with little fossil fuel inputs and often considerable sequestration are likely to have a positive carbon balance whereas this balance is likely to turn negative as intensity and commercial inputs increase, such as in industrial systems.