Livestock’s role in climate change
by Frank Mitloehner, Ph.D., and Sara Place, Ph.D. Student – Department of Animal Science, University of California, Davis
Highlights
Growing concern about global climate change has spurred evaluations of livestock agriculture’s contribution; however, the complexity and variation in beef production systems makes the quantification of greenhouse gas (GHG) emissions difficult. Several recent publications have used Life Cycle Assessments (LCA) that employ “cradle-to-the-grave” accounting of GHGs from inputs and outputs over the entire beef production chain.
The application and comparisons between these existing LCAs can be limited due to differences in their scope and scale. Reporting carbon dioxide equivalent (CO2-eq1) emissions per unit of production (i.e. per pound of beef) can clarify some of the discrepancies and allow for comparisons.
To best evaluate U.S. beef production systems, models that can predict the complex bio-geochemical processes involved in the entire beef product life cycle are needed. Research that improves predictions of these processes, will advance our ability to identify major GHG sources and mitigate life cycle emissions on a per unit of output basis.
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Introduction
In 2006, the United Nations’ Food and Agriculture Organization (FAO) published a comprehensive global Life Cycle Assessment (LCA) of livestock agriculture’s environmental impact called Livestock’s Long Shadow: Environmental Issues and Options (LLS). LLS concluded that global livestock agriculture contributes 18 percent of the anthropogenic (human-caused) GHGs and stated that livestock contribute more to climate change than the global transportation sector; however, the global transportation sector was not evaluated with a LCA. The LLS conclusion has been extensively quoted in the popular press and is influencing public policy.
Discussion
LLS included land use change as an indirect CO2-eq [or CO2 equivalent emissions. To simplify the reporting the global warming potential (GWP) of GHGs other than CO2 over a specified period of time, it is common practice to convert the total effects of nitrous oxide (N2O) and methane (CH4) into CO2 equivalents. The Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report estimates the 100 year GWP of CH4 and N2O as 21 and 310 times greater than CO2, respectively.] emission source from global livestock production. Land use change is when land that is a carbon “sink” (a net sequester of CO2 from the air into the soil such as the the Amazon rainforest) is converted into a carbon source (the rainforest is clear cut to graze cattle, greatly reducing the CO2 sequestered and causing methane (CH4) emissions, 21 times more potent a GHG than CO2, from the enteric fermentation of the cattle). Deforestation alone represents 34 percent of the total GHGs attributed to livestock production in LLS. While land use changes are a serious environmental threat in some developing nations, they do not represent a significant GHG source in U.S. livestock production systems, as the total area of forestland in the U.S. has been relatively stable since the 1920’s and has increased by 1 percent since 1987.
Other comprehensive assessments of livestock agriculture relative to the United States and California have concluded that direct livestock emissions (from manure and enteric fermentation) account for less than 3 percent of total U.S. and California anthropogenic GHG emissions. For context, the U.S. Environmental Protection Agency (EPA) estimates cars and light trucks are responsible for approximately 26 percent of CO2-eq.1 emissions in the United States. Thus, proportions of GHGs from transportation and livestock agriculture are significantly different in the United States compared to LLS’s global assessment, due to differences between developing and developed nation’s transportation infrastructures and populations.
Conclusions
When focusing in on the U.S. beef industry, it becomes apparent that assigning a “one-size-fits-all” GHG emissions factor produced per animal would be inaccurate. Accurately modeling life-cycle emissions will require accounting for the complex bio-geochemical processes that occur from extensive cow-calf operations to intensive feedlot operations. With a powerful enough model, strategies could be developed to reduce the life cycle environmental impact of a pound of beef while optimizing business sustainability and animal welfare. However, a comprehensive, collaborative scientific research effort is needed to better understand the emissions and nutrient flows in the beef production system, as well as the actual development of a model.
Historically, great progress has already been made to improve the environmental efficiency of beef production in the United States. According to the U.S. Department of Agriculture, the total number of beef cattle in the United States reached its peak in 1975 with a population of 140.2 million head. Since then, the population has steadily declined, with the 2008 population at approximately 103.3 million; however, the amount of beef produced has remained relatively stable. The record cattle population of 1975 produced 54.7 billion pounds of beef, while the 2008 population, with 37 million fewer head, produced 54.2 billion pounds of beef (USDA, 2009). This sustained trend means the beef industry has been able to produce more beef per animal, thereby decreasing the amount of feed and excretion needed to produce each pound of beef by diluting out animal maintenance costs. More improvements in efficiency at the ranch or feedlot level can be made by advancing genetics, nutrition, animal health, etc. to dilute maintenance costs further to lower the life cycle GHGs per unit of beef.
Often overlooked in LCAs, waste at the consumer level includes emissions from the entire life cycle of the product; consequently, reducing final product waste could have a far greater climate change impact than improvements at the farm level. A 1997 USDA report estimated that 16 percent of edible red meat was lost at the retail, consumer and foodservice levels (Kantor et al., 1997). This waste represents a total loss of the product’s nutritional value and the natural resources required throughout the entire production process. A complete LCA of livestock industries should account for final product waste to determine the effect of reducing waste vs. mitigation strategies at the farm level on a GHGs per unit of output basis.
In summary, global GHG percentage estimates, such as the LLS 18 percent figure, are inappropriate to apply at the regional level due to differences in production systems and livestock’s relative GHG contribution in developed versus developing nations. A complete LCA of the livestock industry is needed, as the end of the product’s life cycle may be the most important part of its environmental impact. With accurate, dynamic models, a holistic analysis of the beef production system would be possible and mitigation strategies could be developed to reduce GHGs per unit of output. A thorough scientific understanding of livestock’s climate change impact, taking into account its historical progress for context, would best serve the public’s simultaneous needs for safe, high quality food products and environmental stewardship.
Additional Resources
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USDA. 2009. Cattle: National Statistics. National Agriculture Statistics Service, U.S. Depart. of Agriculture. http://www.nass.usda.gov Accessed Aug. 3, 2009
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