May 2010 Issue

Meat Takes Heat — Evidence Suggests Livestock Contribute Significantly to Global Warming
By Rita E. Carey, MS, RD, CDE
Today’s Dietitian
Vol. 12 No. 5 P. 36

Research is providing reason to believe that reducing worldwide production and consumption of animal products may benefit the environment in a big way.

The relationships among human populations, ecosystems, and global warming are complex and at times uncertain. But the major cause of climate change seems clear: Human activities, especially those based on the burning of fossil fuels, have emitted enough heat-trapping gases over the last 200 years to alter the planet’s usual climatic patterns. Reducing the use of fossil fuels is a top strategy for those working to arrest climate change, but the technology and infrastructure needed to significantly alter the industrialized world’s reliance on coal, oil, and gas have been slow to develop.

What if the most expedient way to reduce greenhouse gas (GHG) production is simply to eat less meat? Would worldwide dietary change be easier to accomplish than weaning humans off fossil fuels? Substantial evidence suggests that livestock production is a major source of GHG emissions. Therefore, changing the way we produce, transport, and eat animal products, as well as the amount we produce, transport, and eat, could diminish agricultural contributions to global warming. Dietitians already encourage people to eat less meat to safeguard their health. For some, protecting the planet may be an even more potent catalyst for lifestyle change. 

More Meat, Please
Almost 40 years ago, Frances Moore Lappé wrote a book that has likely changed the way millions of people think about food. In Diet for a Small Planet, Lappé wrote of the unseen negative global environmental and social consequences of Western meat-centric diets and provided a solid argument supporting the healthfulness of vegetarianism, which was considered nutritionally inadequate by many experts at the time. Since the first edition was published in 1971, 3 million copies of Diet for a Small Planet have been sold, and other authors have written extensively on the subject.

The work of Lappé and others has undoubtedly raised awareness of the negative impacts of Western diets on the health of ecosystems, communities, and individuals around the world. Their research has bolstered popular support for vegetarian diets, which, interestingly, some experts today consider to be nutritionally superior.

But the global popularity of meat-based Western diets has not waned over the last 40 years, and worldwide consumption of animal products has increased, not decreased. 

A 2002 joint World Health Organization (WHO)/Food and Agriculture Organization (FAO) of the United Nations report on global and regional food consumption patterns and trends stated that the combined effects of worldwide population growth, urbanization, and rising incomes have significantly increased the global demand for animal protein since 1964. In fact, according to WHO/FAO statistics, meat consumption in developing countries increased from 10.2 kg/person/year to 36.7 kg/person/year between 1964 and 1999. Industrialized countries increased their intake from 61.5 kg/person/year to 88.2 kg/person/year in the same time period. The same 2002 WHO/FAO report estimated an increase in annual global meat production from 218 million tons in 1999 to 376 million tons by 2030. A report published in 2009 by the World Watch Institute estimated global meat production at 275 million tons in 2007 and predicted a doubling of worldwide meat production over the next 40 years.

A Diet With Unexpected Consequences
As meat production and consumption increase worldwide, demands on natural systems inevitably increase as well. The sheer number of animals being raised for human consumption is enough to give one pause. Livestock account for 20% of the Earth’s land-based animal biomass.1 The land they and their feed crops occupy was once inhabited by diverse wildlife and plant cover. Consequently, the World Wildlife Fund identifies livestock production and agriculture in general as the “world’s largest driver of habitat and biodiversity loss.”

The impact of livestock production on land, air, and water quality have been well documented. According to the FAO, grazing lands occupy 26% of the Earth’s surface; feed crop production requires about one third of all arable land; and the expansion of grazing land for cattle in Latin America is the key factor in tropical deforestation there.1 Furthermore, about 70% of all grazing land is seriously degraded due to soil erosion and the loss of natural carbon-sequestering pasture. More than 8% of all human water use is dedicated to livestock, mostly for irrigating land used to grow feed crops. The FAO considers livestock production the single largest source of water pollutants, including antibiotics, hormones, nitrates, pesticides, and sediments from eroded lands. The livestock sector is also responsible for two thirds of all anthropogenic ammonia production, a significant contributor to acid rain.1

Meat and Global Warming: The Big Picture
Global warming has recently been added to the list of negative environmental impacts engendered by extensive worldwide livestock production. In its 2006 report “Livestock’s Long Shadow. Environmental Issues and Options,” the FAO estimated that livestock alone is responsible for 18% of all global GHG emissions, including 9% of carbon dioxide, 37% of methane, and 65% of nitrous oxide emissions.1

However, these estimates are greater than those some other organizations have made. For example, the Pew Center on Global Climate Change estimates total emissions from all agricultural activities at only 14%. The GHG levels calculated in “Livestock’s Long Shadow” are higher because, according to the FAO, scientists considered emissions from every step involved in livestock production and included GHG sources not considered in other reports. For example, they included emissions from feed production (including chemical fertilizer production and application, deforestation, and pasture degradation) through animal production (including enteric methane gas production by animals and nitrous oxide emissions from manure) and carbon dioxide produced from the transportation and processing of animal products.

To put livestock’s impact into perspective, the Pew Center report on global climate change estimates that global transportation systems contribute 13% of all GHG emissions, heating and cooling of residential buildings produce 8%, and general industry weighs in at 19%. Remarkably, according to these numbers, livestock production alone may contribute more to global warming than the burning of fossil fuels for transportation. 

The FAO report places the livestock sector of agriculture on equal footing with the other major drivers of climate change: transportation and industry. However, some scientists disagree with the FAO estimates and believe that livestock production is the major GHG emitter on the planet. A study published by the World Watch Institute in late 2009 challenges the FAO report and suggests that as much as one half of global GHG production may be attributable to the livestock sector of agriculture. In “Livestock and Climate Change. What If the Key Actors in Climate Change Are … Cows, Pigs, and Chickens?” researchers with the World Watch Institute calculated that “livestock and their by-products actually account for at least 32,564 million tons of CO2 equivalents per year, or 51 percent of annual worldwide GHG emissions.” (The term CO2 equivalents converts the impact of all global GHGs, including methane and nitrous oxide, to an equivalent impact from carbon dioxide).

The report’s authors back up their claim with a thorough review of the direct and indirect sources of GHG emissions from livestock and conclude that the FAO and other organizations have underestimated and overlooked some sources while assigning others to the wrong sectors. After considering overlooked respiration from livestock, overlooked land use, undercounted methane and other sources such as underestimated tons of global livestock produced, their estimate of GHG emissions from livestock is nearly five times the FAO’s calculation. (The FAO estimates 7,516 million metric tons of CO2 equivalents produced in the livestock sector of agriculture per year.)

On the Cutting Edge of Change
Calculating the tons of GHGs globally produced and attributing these emissions to their correct sources and categories is apparently a tricky business. When all is said and done, however, it seems clear that the global yen for meat is having a negative impact on the climate. Perhaps humans need to eat less meat and the livestock sector of agriculture needs to make changes to the way it produces meat and other animal products to reduce the effects of this major player in climate change.

Stonyfield Farm, the world’s largest organic yogurt manufacturer, began studying the impact of its operations on climate change in the early 1990s. As a result, the company identified a number of GHG emission sources in milk production, including methane and nitrous oxides from manure, carbon dioxide and other emissions from the multiple processes involved in feed production, carbon dioxide emissions from milk transport and refrigeration, and methane produced during ruminant digestion (ie, cow burps). The company discovered that enteric methane emissions from cows topped the list of GHG emitters in its operations. In fact, on a sample Wisconsin dairy, it calculated that 38% of emissions were enteric, 34% were from manure, 23% from farm electricity, and the remainder from milk and feed transport. The company was able to develop solutions to reduce emissions from all sources except the major one. 

Danone, Stonyfield’s parent company, had already developed a pilot program in France to reduce enteric methane production in cows. Stonyfield Farm decided to follow Danone’s lead and undertake a similar program in the United States. The company has since discovered that by changing what it feeds dairy cows (a diet higher in natural sources of omega-3 fatty acids), it can reduce methane production by as much as 18%, with an average of 12%. As a bonus, cows fed this alternative diet produce milk that contains 29% more omega-3 fatty acids than milk produced in cows fed a standard diet.

Nancy Hirshberg, Stonyfield Farm’s vice president of natural resources, says, “Our research validated our beliefs that ‘we are what they eat,’ meaning how cows live and what you feed them has a profound impact on our health and the health of the planet.” In other words, an 18% reduction in methane gas emissions may not sound like much, but when companies as large as Stonyfield Farm and Danone decide to make changes to their operations to reduce their carbon footprint, the global ramifications are considerable.

What level of individual diet change could reduce the effects of livestock on global warming? The authors of “Livestock and Climate Change” estimate that a 25% reduction in livestock production alone may yield, at minimum, a 12.5% reduction in global anthropogenic GHG emissions. This level of reduction is similar to that expected to be negotiated by countries participating in the recent round of climate talks in Copenhagen, Denmark. In other words, by reducing our worldwide production and consumption of animal products by only 25%, we may benefit from the greatest and quickest possible reduction in global GHG emissions. 

Final Thoughts
Global climate change was not a topic of concern 40 years ago and thus was not mentioned as a potential consequence of livestock production in Diet for a Small Planet. Times have changed, and as the world rushes to find ways to reduce GHG production and slow climate change, we need to take a critical look at the negative atmospheric impacts of agriculture. Certainly international equity and food security issues need to be considered with any proposed changes in global industries and economies. The Western world can lead the way in reducing emissions from every sector, including agriculture. Americans can certainly afford to eat less meat and other animal products. We can also pressure large agricultural companies to change their operations in many ways that reduce GHG emissions and likely save those companies money in the long run.

Changing cultural expectations and beliefs about meat is a more difficult challenge and in this area, dietitians can lead the way. After all, if the numbers cited previously are accurate, changing what we eat and how we produce a major source of food for a growing global population may be the quickest way to ameliorate human-induced climate change.

— Rita E. Carey, MS, RD, CDE, is a clinical dietitian and diabetes educator at Yavapai Regional Medical Center and the Pendleton Wellness Center in Prescott, Ariz.


1. Food and Agricultural Organization of the United Nations. Livestock’s long shadow: Environmental issues and options. 2006. Available at: Accessed December 12, 2009.