The domestic animal population has increased by 0.5 to 2.0 percent per day during the last century, according to the Environmental Protection Agency (EPA) report Policy Options for Stabilizing Global Climate (Lashof and Tirpak 1990). The report shows the upward trend in domestic animal populations. One result of this population increase is that emissions from livestock have become a significant source of atmospheric methane.

U.S. Environmental Protection Agency: Ruminant Livestock. Frequently Questions: Questions and answers about how methane is produced from livestock and what measures can be done to reduce these emissions. Resources and Tools: Information and models to measure and evaluate livestock production impacts on methane emissions.