Life cycle assessment for livestock: a complex issue

Discussions about global climate change have spurred evaluations of livestock agriculture's contribution; however, the complexity and variation in livestock production systems makes the quantification of greenhouse gas (GHG) emissions difficult. Several recent publications have used Life Cycle Assessments (LCAs) that employ ‘cradle-to-the-grave’ accounting of GHGs from inputs and outputs over the entire livestock production chain. An LCA for dairy and beef production can include the GHGs produced from the production of forages and grains (emissions from the soil, fertilizer and burning fossil fuels), from the cattle directly (emissions from manure and feed fermentation in the rumen) and from processing and transporting the beef or dairy products to the consumer (emissions from burning fossil fuels and refrigeration). The sum of the GHGs from all of these sources would be considered the total ‘life cycle’ emissions or carbon footprint for livestock production.

The application and comparisons between these existing LCAs can be limited because of differences in their scope and scale. Reporting GHG missions per unit of production (e.g. per kg of beef, or liter of milk) can clarify some of the discrepancies and allow for comparisons across current production systems or comparisons of current v. historical livestock production.

Global v. regional assessment of livestock's carbon emissions

Much of the discussion about livestock agriculture's contribution to climate change stems from a United Nations Food and Agriculture Organization (FAO) report titled ‘Livestock's Long Shadow’ (LLS; Steinfeld et al., Reference Steinfeld, Gerber, Wassenaar, Castel, Rosales and de Haan2006). This report determined the climate change impact of global livestock production using a true LCA. Included in the LLS's calculations were crop production, land-use change (e.g. clearing rainforest to establish pastures and cropland), the animals themselves and the transportation of final products. In the executive summary of the LLS report, the authors concluded that globally 18% of human-caused GHG emissions could be attributed to livestock agriculture, and this had a larger share than transportation. However, the authors of LLS made this claim without actually conducting a similarly comprehensive LCA for the global transportation sector. Unfortunately, the ‘livestock v. transportation’ statement has been extensively quoted in the popular press (Bittman, Reference Bittman2008; Rosenthal, Reference Rosenthal2008; Chang, Reference Chang2009) and has been influencing public policy. Furthermore, the media applied the 18% global figure regionally, which has caused much confusion at the consumer level.

LLS (Steinfeld et al., Reference Steinfeld, Gerber, Wassenaar, Castel, Rosales and de Haan2006) included land-use change as an indirect GHG 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 e.g. 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; Intergovernmental Panel on Climate Change (IPCC), 2007). Deforestation alone represents 34% of the total GHGs attributed to livestock production in LLS (Steinfeld et al., Reference Steinfeld, Gerber, Wassenaar, Castel, Rosales and de Haan2006). Although land-use changes are a serious environmental threat in some developing nations, they do not represent a significant GHG source in the developed world. For example, the total area of forestland in the United States has been relatively stable since the 1920s and has actually increased by 1% since 1987 (Smith et al., Reference Smith, Vissage, Darr and Sheffield2001).

Other comprehensive assessments of livestock agriculture relative to the California and United States Environmental Protection Agency (CEPA, 2008; US EPA, 2009) have concluded that direct livestock emissions (from manure and enteric fermentation) account for less than 3% of total United States and California anthropogenic GHG emissions (Pitesky et al., Reference Pitesky, Stackhouse and Mitloehner2009).

For context, the US EPA estimates cars and light trucks are responsible for approximately 26% and electricity for 31% of GHG emissions in the United States (US EPA, 2009). Thus, proportions of GHGs from transportation and livestock agriculture are significantly different in the United States compared with the LLS's global assessment, because of differences between developing and developed nations’ transportation infrastructures and populations.

Intensification equates to mitigation of environmental impacts

Although we differed with the authors of LLS on their carbon footprint comparison of livestock v. transportation and with the usefulness and correctness of their 18% figure, we do agree with their overall concern that satisfying upcoming animal protein demands will pose a challenge to the environment. Global animal protein production is projected to double from its year 2000 levels by 2050 and the majority of this livestock production growth will occur in the developing world. Much of the growth in the global livestock sector will occur in areas that are currently forested (e.g. parts of South America and South East Asia), which will create pressure to rely on deforestation to facilitate increased livestock production. It has been well-established that significant reductions of carbon sequestering forests will have large effects on global climate change; therefore, avoiding deforestation is paramount.

Historically, great progress has already been made to improve the environmental efficiency of cattle production in the developed world and lessons can be learned in much of the developing world. According to the United States Department of Agriculture (USDA), the total number of beef cattle in the United States peaked 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 24 million tons of beef, whereas the 2008 population, with 37 million fewer head, produced again 24 million tons of beef (USDA, 2009). This sustained trend means that the beef industry has been able to produce more beef per animal unit, thereby decreasing the amount of feed and excretion required to produce each unit of beef by diluting out animal maintenance costs (reducing the proportion of feedstuffs required to keep the animal alive relative to the total feedstuffs consumed).

By examining the historical trends in dairy production in the developed world, it becomes clear that there has been a marked improvement in efficiency, leading to reductions in numbers of animals required to produce a given amount product that satisfies the nutritional demands of society. To emphasize this point, today one California cow produces the same amount of milk as five of her peers in Mexico. Capper et al. (Reference Capper, Cady and Bauman2009) provided a historical perspective: compared with 1944, the 2007 US dairy industry reduced its GHG emissions per unit of milk by 63%. This reduction was achieved through improved nutrition, management, genetics, etc., born through scientific research that has lead to dramatic improvements in milk production per cow.

According to LLS, intensification of livestock production provides large opportunities for climate change mitigation and can reduce deforestation to establish pastures, thus becoming a long-term solution to more sustainable livestock production. Indeed, the authors of LLS are currently working on a follow-up paper to LLS titled ‘Shrinking the Shadow’, which will focus on how advanced biotechnologies, improved genetics, nutrition and comprehensive waste management already utilized in many parts of the developed world can be applied effectively worldwide.

Although the extraordinary reduction in the US beef and dairy industry's carbon footprint over time may be viewed by some as a vindication of modern production practices, attention should be given to the areas of opportunity that still exist, including transition cow management, lameness, respiratory disease and reproductive failure. Improving these and other areas on US beef and dairy farms should allow for further reductions in carbon footprint per unit of meat or milk, and these areas often intersect with another hot issue that livestock industries face: animal welfare.

Consumer waste: an important contributor to livestock system's carbon footprint

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% of edible red meat was lost at the retail, consumer and foodservice levels (Kantor et al., Reference Kantor, Lipton, Manchester and Oliveira1997). This waste represents a total loss of the product's nutritional value and the natural resources required throughout the entire production process, and, consequentially, has a greater GHG impact than waste earlier in the production chain (e.g. a loss of feed due to spoilage at a feedlot). A complete LCA of livestock industries should account for final product waste to determine the effect of reducing consumer and retail waste v. mitigation strategies at the farm level on GHG emissions per kg of beef.