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<http://www.sciam.com/sciammag>Scientific American Magazine -  February 4, 2009

How Meat Contributes to Global Warming

Producing beef for the table has a surprising environmental cost: it 
releases prodigious amounts of heat-trapping greenhouse gases

By Katherine Harmon

	Most of us are aware that our cars, our coal-generated 
electric power and even our cement factories adversely affect the 
environment. Until recently, however, the foods we eat had gotten a 
pass in the discussion. Yet according to a 2006 report by the United 
Nations Food and Agriculture Organization (FAO), our diets and, 
specifically, the meat in them cause more greenhouse gases carbon 
dioxide (CO2), methane, nitrous oxide, and the like to spew into the 
atmosphere than either transportation or industry. (Greenhouse gases 
trap solar energy, thereby warming the earth's surface. Because gases 
vary in greenhouse potency, every greenhouse gas is usually expressed 
as an amount of CO2 with the same global-warming potential.)

	The FAO report found that current production levels of meat 
contribute between 14 and 22 percent of the 36 billion tons of 
"CO2-equivalent" greenhouse gases the world produces every year. It 
turns out that producing half a pound of hamburger for someone's 
lunch a patty of meat the size of two decks of cards releases as much 
greenhouse gas into the atmosphere as driving a 3,000-pound car 
nearly 10 miles.

	In truth, every food we consume, vegetables and fruits 
included, incurs hidden environmental costs: transportation, 
refrigeration and fuel for farming, as well as methane emissions from 
plants and animals, all lead to a buildup of atmospheric greenhouse 
gases. Take asparagus: in a report prepared for the city of Seattle, 
Daniel J. Morgan of the University of Washington and his co-workers 
found that growing just half a pound of the vegetable in Peru emits 
greenhouse gases equivalent to 1.2 ounces of CO2 as a result of 
applying insecticide and fertilizer, pumping water and running heavy, 
gas-guzzling farm equipment. To refrigerate and transport the 
vegetable to an American dinner table generates another two ounces of 
CO2-equivalent greenhouse gases, for a total CO2 equivalent of 3.2 
ounces.

	But that is nothing compared to beef. In 1999 Susan Subak, an 
ecological economist then at the University of East Anglia in 
England, found that, depending on the production method, cows emit 
between 2.5 and 4.7 ounces of methane for each pound of beef they 
produce. Because methane has roughly 23 times the global-warming 
potential of CO2, those emissions are the equivalent of releasing 
between 3.6 and 6.8 pounds of CO2 into the atmosphere for each pound 
of beef produced.

	Raising animals also requires a large amount of feed per unit 
of body weight. In 2003 Lucas Reijnders of the University of 
Amsterdam and Sam Soret of Loma Linda University estimated that 
producing a pound of beef protein for the table requires more than 10 
pounds of plant protein with all the emissions of greenhouse gases 
that grain farming entails. Finally, farms for raising animals 
produce numerous wastes that give rise to greenhouse gases.

	Taking such factors into account, Subak calculated that 
producing a pound of beef in a feedlot, or concentrated animal 
feeding operation (CAFO) system, generates the equivalent of 14.8 
pounds of CO2 pound for pound, more than 36 times the CO2-equivalent 
greenhouse gas emitted by producing asparagus. Even other common 
meats cannot match the impact of beef; I estimate that producing a 
pound of pork generates the equivalent of 3.8 pounds of CO2; a pound 
of chicken generates 1.1 pounds of CO2-equivalent greenhouse gases. 
And the economically efficient CAFO system, though certainly not the 
cleanest production method in terms of CO2-equivalent greenhouse 
emissions, is far better than most: the FAO data I noted earlier 
imply that the world average emissions from producing a pound of beef 
are several times the CAFO amount.


Solutions?

	What can be done? Improving waste management and farming 
practices would certainly reduce the "carbon footprint" of beef 
production. Methane-capturing systems, for instance, can put cows' 
waste to use in generating electricity. But those systems remain too 
costly to be commercially viable.

	Individuals, too, can reduce the effects of food production 
on planetary climate. To some degree, after all, our diets are a 
choice. By choosing more wisely, we can make a difference. Eating 
locally produced food, for instance, can reduce the need for 
transport though food inefficiently shipped in small batches on 
trucks from nearby farms can turn out to save surprisingly little in 
greenhouse emissions. And in the U.S. and the rest of the developed 
world, people could eat less meat, particularly beef.

	The graphics on the following pages quantify the links 
between beef production and greenhouse gases in sobering detail. The 
take-home lesson is clear: we ought to give careful thought to diet 
and its consequences for the planet if we are serious about limiting 
the emissions of greenhouse gases.

Note: This article was originally printed with the title, "The 
Greenhouse Hamburger".