Clearing the Air: Livestock's Contribution to Climate Change

Abstract The United Nations, Food and Agricultural Organization [ FAO, Steinfeld, Gerber, Wassenaar, Castel, Rosales, and de Haan (2006) . Livestock's Long Shadow. Food and Agriculture Organization of the United Nations] report titled Livestock's Long Shadow (LLS) stated that 18% (approximately 7100 Tg CO 2 -eq yr − 1 ) of anthropogenic greenhouse gases (GHGs) are directly and indirectly related to the world's livestock. The report's statement that livestock production is responsible for a greater proportion of anthropogenic emissions than the entire global transportation sector (which emits 4000–5200 Tg CO 2 -eq yr − 1 ) is frequently quoted in the public press [ Fox News and Kroll (2009) . A Tearful, Reluctant Farewell to My Favorite Food: Meat; LA Times (2007) . A warming world; pollution on the hoof; livestock emissions are a leading source of greenhouse gases. One solution may be to eat less meat, Los Angeles; NY Times, Op-ed. (2009) . Meat and the Planet. New York City] and continues to inform public policy. Recent estimates by the United States Environmental Protection Agency [ EPA, Hockstad, Weitz (2009) . Inventory of U.S. greenhouse gases and sinks: 1990–2007. Environmental Protection Agency] and the California Energy Commission [ CEC—California Energy Commission (2005) . Inventory of California Greenhouse Gas Emissions and Sinks: 1990 to 2002 Update] on the impacts of livestock on climate change in the United States and California have arrived at much different GHG estimates associated with direct livestock emissions (enteric fermentation and manure), totaling at less than 3% of total anthropogenic GHG and much smaller indirect emissions compared to the global assessment. Part of the difference of the global versus national predictions is due to the significant weight that has been assigned to the category of “land-use change” patterns related to livestock production (mainly deforestation). Furthermore, LLS attempts a life cycle assessment for global livestock production but does not use an equally holistic approach for its transportation prediction numbers. The primary focus of the present paper is to examine the relative contributions of livestock to climate change at different geographical and production scales. [ Note : CO 2 equivalents (CO 2 -eq.) represent the total impact (radiative forcing) of GHG in the atmosphere, thereby making it possible to determine the climate change impact of one GHG versus another EPA [ EPA and Holtkamp, Irvine, John, Munds-Dry, Newland, Snodgrass, and Williams (2006) . “Inventory of U.S. Green House Gases and Sinks: 1996–2006.”]. The definition of the Global Warming Potential (GWP) for a particular GHG is the ratio of heat trapped by one unit mass of the GHG to that of one unit mass of CO 2 (the GWP of CO 2 is one) over a specific period of time [IPCC (2001). IPCC Third Assessment Climate Change 2001. A Report of the Intergovernmental Panel on Climate Change]. The 100-year GWP for CH 4 and N 2 O are 23 times and 296 times the GWP of CO 2 , respectively [IPCC (2001). IPCC Third Assessment Climate Change 2001. A Report of the Intergovernmental Panel on Climate Change]. Therefore, for simplicity sake it is common practice to combine the total effects of CO 2 , CH 4 , and N 2 O into CO 2 equivalents (or CO 2 -eq).]