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How Green is My Diet?
by Wendy Priesnitz

How Green is My Meat Diet?

Q: A friend recently told me that she has stopped eating meat because it contributes to global warming. That seems a bit far-fetched to me so I’m wondering if you can set the record straight by connecting the dots between environment and diet.

A: Surprisingly, what we choose to eat has one of the biggest impacts on the environment, including the climate, of any human activity.

A 2006 Italian study published in the European Journal of Clinical Nutrition evaluated the environmental impact of various dietary patterns combined with different food production systems. Researchers examining the impact of a typical week’s eating showed that plant- based diets are better for the environment than those based on meat. An organic vegan diet had the smallest environmental impact and all non-vegetarian diets required significantly greater amounts of environmental resources, such as land and water. But the most damaging food was beef, with up to 100 calories of grain required to produce four calories of beef.

More recent Japanese research assessed the effects of beef production (including the effects of producing and transporting feed) on global warming, water acidification and eutrophication, and energy consumption – in other words, the total environmental load on a portion of beef. Published in Animal Science Journal in August, 2007, research by the National Institute of Livestock and Grassland Science found that producing a kilogram of beef leads to the emission of greenhouse gases with a warming potential equivalent to 36.4 kilograms of carbon dioxide – more than driving for three hours while leaving all the lights on back home. They also found that a kilo of beef releases the equivalent of 340 grams of sulphur dioxide and 59 grams of phosphate, and consumes 169 megajoules of energy.

The calculations, which are based on standard industrial methods of meat production in Japan, did not include the impact of managing farm infrastructure and transporting the meat, so the total environmental load is even higher when they are factored in. Since global beef consumption is rising dramatically, meeting this demand will no doubt require that animals be reared more intensively and cheaply with factory farming, creating further pollution, water and land usage problems.

The environmental load is so high, in fact, that in a 2005 study, University of Chicago researchers suggested that going vegan would reduce one’s environmental footprint by more than if they switched to a hybrid vehicle. Gidon Eshel and Pamela Martin told a meeting of the American Geophysical Union that they studied the amount of fossil fuel needed to cultivate and process various foods, including running agricultural machinery, providing food for livestock and irrigating crops. They found that the typical American diet, about 28 percent of which comes from animal sources, generates the equivalent of nearly 1.5 tonnes more carbon dioxide per person per year than a vegan diet with the same number of calories. By comparison, the difference in annual emissions between driving a regular car and a hybrid car is just over 1 tonne.

In fact, farmed animals produce more greenhouse gas emissions (18 percent) than the world’s entire transportation system (13.5 percent,) according to the Food and Agriculture Organization of the United Nations (FAO.) Most of the greenhouse gas emissions from cattle are in the form of methane released from the animals’ digestive systems. According to a 2003 report issued by the EU’s Environment and Agriculture Informal Ministerial Councils, along with nitrous oxide, methane is the real threat to global warming from agriculture. Methane has 23 times the global warming impact of carbon dioxide and a single cow can produce as much as 500 liters of methane per day.

Cattle manure contains other problematic pollutants like nitrous oxide (which is considered to be almost 300 times as damaging to the climate as carbon dioxide) and ammonia (which contributes to acid rain.) In a 2006 report Livestock’s Long Shadow – Environmental Issues and Options, the FAO pointed out that farming animals also generates greenhouse gas emissions through the manufacture of fertilizers to grow feed crops, industrial feed production and the transportation of both live animals and their carcasses across the globe.


Rearing animals for food causes a variety of other environmental issues besides contributing to global warming. Much of the world is running out of fresh water. In an alert issued last March, the FAO estimated that by 2025 there will be 1.8 billion people living with absolute water scarcity and two thirds of the world’s population could be living under water-stressed conditions.

Scientists agree that farming accounts for around 70 percent of all fresh water withdrawn from lakes, waterways and aquifers and that meat production, especially the feeding of cattle, is a particularly water-intensive process. The FAO says that livestock production accounts for over eight percent of global human water consumption. Depending on a variety of factors, a kilogram of beef is estimated to require upwards of 13,000 liters of water, compared to the 1,000 to 2,000 liters required to produce a kilo of wheat.

Livestock production also contributes to water pollution, with manure, antibiotics and hormones entering the water cycle alongside chemicals from tanneries, fertilizers and the pesticides used to spray feed crops. In a 2005 report entitled Facts About Pollution from Livestock Farms, the Natural Resources Defense Council noted that in the Gulf of Mexico, pollutants in animal waste have contributed to a “dead zone” where there is not enough oxygen to support aquatic life. During the summer of 2004, this dead zone extended over 5,800 square miles.

Land Use

According to the Center for Sustainability and the Global Environment at the University of Wisconsin, 40 percent of the earth’s entire land surface is used for agriculture, and 70 percent of all agricultural land is used for farming animals. Much of this is grazing land that would otherwise host a natural habitat such as rainforest. Livestock production is reportedly responsible for 70 percent of the deforestation of the Amazon rainforest. Aside from contributing to the loss of biodiversity, deforestation increases greenhouse gas emissions by releasing carbon previously stored in the trees.

Farmland that could grow grain and other human food crops is also a casualty of the livestock industry. According to the FAO, one third of the land suitable for growing crops globally is used to produce animal feed.

Feeding cattle takes up so much land because they are inefficient converters of feed to meat. Thomas White, a professor in the Department of Economics and Global Studies at Assumption College in Worcester, Massachusetts, described just how inefficient in his paper “Diet and the Distribution of Environmental Impact” published in 2000 in Ecological Economics. He says that cattle require approximately seven kilos of grain in order to generate one kilo of beef and pigs require four kilos of grain for one kilo of pork.

When cattle are allowed to overgraze, the result is soil erosion, desertification and deforestation. The FAO says that 20 percent of the world’s grazing land has been designated as degraded due to the rearing of animals for meat.


Many people who give up meat end up eating more fish, which is a healthy source of essential fatty acids (although some fatty fish retain pollutants, making their health benefits questionable). However, eating fish isn’t without its environmental problems. Over-fishing is threatening the existence of many fish species, a trend that we’ve been tracking for many years here in Natural Life. Fishing practices like bottom trawling cause untold damage to non-target species and destroy the fragile ecosystem of the seabed. It’s been called “underwater strip mining.”

The aquaculture industry has experienced huge growth. However, fish farming can pollute rivers and streams, while harming wild fish. Plus, feeding farmed fish can be problematic, intensifying pressure on the ocean stocks. The Worldwatch Institute says, for example, that it takes five tonnes of wild-caught fish to feed each tonne of farmed salmon.

Then there is the need to fuel the fishing fleets. A paper entitled “Fuelling Global Fishing Fleets” published in the journal Ambio calculates that fisheries account for about 1.2 percent of global oil consumption and directly emit over 130 million tonnes of carbon dioxide into the atmosphere.

What About Organics?

Generally, small, mixed farms and those operated in a sustainable manner, such as organically or biodynamically, are more environmentally friendly than large-scale factory farms. But the research as to whether or not organically-raised meat generates lower levels of greenhouse gas emissions is uneven. A 2003 Swedish study that was recently cited in the New Scientist, suggested that organic beef, raised on grass rather than concentrated feed, emits 40 percent less greenhouse gases and consumes 85 percent less energy than non-organic beef. But a 2000 Swedish study from the Department of Applied Environmental Sciences at Goteborg University compared organic and conventional dairy production and found a much less dramatic difference. Life Cycle Assessment of Milk Production concluded that the organic system  generated slightly fewer greenhouse gas emissions than the conventional. Carbon dioxide and nitrous oxide levels were lower, largely due to the absence of energy intensive nitrate fertilizers, but methane emissions were higher in the organic system due to the cattle’s higher intake of roughage fodder.

A French study published in Ecosystems and Environment in 2005 compared organic and conventional pork production. It found that per kilogram of pig, climate change emissions were highest for the organic system, but on a per-hectare basis, the lowest emissions were found in the organic system.

There is also a large body of literature focusing on other farming techniques that either require lower energy inputs or that lead to fewer emissions of greenhouse gas emissions. They include harnessing the methane and other animal wastes for biomass energy. One report cited in the New Scientist in 2003 described research from Belgium that indicated switching animals from regular feed to a diet laced with fish oil could cut the amount of methane they emit by nearly half. But then there is the fishery problem….

One prominent ecologist, who says that raising cattle is the most damaging aspect of agriculture, believes that eating lower on the food chain is becoming increasingly important. Dr. Robert Goodland, who was the Environmental Advisor to the World Bank for 25 years and now advises the UN World Summit on Sustainable Development, has concluded that diet does, indeed, matter because a diet containing meat requires up to three times as many resources as a vegetarian diet. He has advocated a food conversion efficiency tax. The least efficient converters (pork, beef) would be highly taxed; more efficient converters (poultry, eggs, dairy) would be moderately taxed. Most efficient converters (ocean fish) would be taxed lowest and grain for human consumption would not be taxed at all.

Dr. David Fraser of the University of British Columbia’s Animal Welfare Program agrees that economics may be the answer: Higher prices for meat products might allow for better treatment of animals and the environment.

Nevertheless, it does appear to be a good practice for the health of people and the ecosystem to feed grain and vegetables directly to people, rather than to livestock. But even vegetarians can decrease their impact on global warming by eating organic, seasonal, locally-grown produce wherever possible.

Learn More

The Pros and Cons of Grass-Fed Beef by Gene Sager in Natural Life Magazine, November/December 2008

The Omnivore's Dilemma: A Natural History of Four Meals by Michael Pollan (Penguin, 2007)

Food Rules: An Eater's Manual by Michael Pollan (Penguin, 2009)

Animal, Vegetable, Miracle: A Year of Food Life by Barbara Kingsolver (Harper Perennial, 2008)

Eating to Save the Earth by Linda Riebel and Ken Jacobsen (Celestial Arts, 2002)

Six Arguments for a Greener Diet by Michael Jacobson (CSPI, 2006)

The Vegan Sourcebook by Joanne Stepaniak (McGraw-Hill, 2000)

Wendy Priesnitz is the Editor of Natural Life Magazine and a journalist with over 40 years of experience. She has also authored 13 books. Visit her website.


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