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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.