Direct and indirect metabolic CO<sub>2</sub> release by humanity

Abstract. 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 Gt C 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 Gt C year−1, have increased 7 fold since pre-industrial times and are predicted to continue to rise over the 21st century.