Environmental Impact of Meat Production - Energy Consumption and Greenhouse Gas Emissions

Energy Consumption and Greenhouse Gas Emissions

At a global scale, it has been estimated that livestock (including poultry) contribute, directly and indirectly, to about 9% of total anthropogenic carbon dioxide emissions, 37% of anthropogenic methane emissions and 65% of anthropogenic nitrous oxide emissions, which together amount to about 18% of anthropogenic greenhouse gas emissions estimated as 100-year CO₂ equivalents. Because these emission percentages include contributions associated with livestock used for production of draft power, eggs, wool and dairy products, the percentages attributable to meat production alone are significantly lower. The indirect effects contributing to these percentages include emissions associated with production of feed consumed by livestock and carbon dioxide emission from deforestation in Central and South America, attributed to livestock production. Mitigation options for reducing methane emission from ruminant enteric fermentation include genetic selection, immunization, rumen defaunation, diet modification and grazing management, among others. The principal mitigation strategies identified for reduction of agricultural nitrous oxide emission are avoiding over-application of nitrogen fertilizers and adopting suitable manure management practices.

At a national level, livestock represents up to half of New Zealand's greenhouse gas emissions. Livestock sources (including enteric fermentation and manure) account for about 3.1 percent of US anthropogenic greenhouse gas emissions expressed as carbon dioxide equivalents, according to US EPA figures compiled using UNFCCC methodologies. Not all forms of meat and animal–based foods affect the environment equally. One study estimates that red meats are 150% more greenhouse gas intensive than chicken or fish. According to another research group, the ranking of some food products in relation to greenhouse gas emissions is lamb (#1), beef (#2), cheese (#3), and pork (#4). However, such ranking may not be broadly representative. Among sheep production systems, for example, there are very large differences in both energy use and prolificacy; both factors strongly influence emissions per kg of lamb production.

Because a large fraction of GHG emissions attributed to livestock production involves methane (from enteric fermentation and manure management), care is appropriate in considering contributions of these emissions to global warming. Relative to carbon dioxide, atmospheric methane has a 100-year global warming potential of 25 (including indirect effects on ozone and stratospheric water vapor). Methane emission from livestock and other anthropogenic sources has contributed substantially to past warming; however, it is of much less significance for current and recent warming. This is because there has been relatively little increase in atmospheric methane concentration in recent years, with total methane sources, estimated at 582 Tg per year, being nearly balanced by methane sinks, estimated at 581 Tg per year. In a tabulation by the IPCC, estimates of methane emission from global livestock range from 80 to 115 Tg per year.

Data of a USDA study indicate that about 0.9 percent of energy use in the United States is accounted for by raising food-producing livestock and poultry. In this context, energy use includes energy from fossil, nuclear, hydroelectric, biomass, geothermal, technological solar, and wind sources. (It excludes solar energy captured by photosynthesis, used in hay drying, etc.) The estimated energy use in agricultural production includes embodied energy in purchased inputs.

Intensification and other changes in the livestock industries influence energy use, emissions and other environmental effects of meat production. For example, in the US beef production system, practices prevailing in 2007 are estimated to have involved 8.6 percent less fossil fuel use, 16.3 percent less greenhouse gas emissions, 12.1 percent less water use and 33.0 percent less land use, per unit mass of beef produced, than in 1977. These figures are based on analysis taking into account feed production, feedlot practices, forage-based cow-calf operations, backgrounding before cattle enter a feedlot, and production of culled dairy cows.