Direct and indirect metabolic CO₂ release by humanity

The direct CO₂ released by respiration of humans and domesticated animals, as well as CO₂ derived from the decomposition of their resulting wastes was calculated in order to ascertain the direct and indirect metabolic contribution of humanity to CO₂ release. Human respiration was estimated to release 0.6 Gt C year^-1 and that of their associated domestic animals was estimated to release 1.5 GtC year ^-1, to which an indirect release of 1.0 Gt C year_-1, derived from decomposition of the organic waste and garbage produced by humans and their domestic animals, must be added. These combined direct and indirect metabolic sources, estimated at 3.1 GtC year^-1, have increased 7 fold since pre-industrial times and are predicted to continue to rise over the 21st century.