How meat contributes to global warming

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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 Nathan Fiala

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.

Burgers or Tofu?Annual beef consumption per capita varies from 120

pounds in Argentina and 92 pounds in the U.S. to only a pound in the

small eastern European country of Moldova; the average is about 22

pounds per person per year. The colors of the countries and the

distortions of their usual shapes reflect the amount by which beef

consumption per capita varies from the world average. World beef

consumption per capita is growing, particularly in Asia, because of

economic development: as peo¬ple earn higher incomes, they purchase

foods they find more desirable.

Eating and Driving: An Atmospheric Comparison The greenhouse gas

emissions from producing various foods can be appreciated by

comparing them with the emissions from a gasoline-powered passenger

car that gets 27 miles per gallon. The estimated emissions from food

production incorporate the assumption that 1,000 kilograms of carbon

per hectare per year (about 2,700 pounds of carbon dioxide per acre

per year) would have been absorbed by forests or other vegetation if

the land had not been cleared for annual food crops or fodder.

Greenhouse gases—carbon dioxide (CO2) and methane, for instance—trap

solar energy and warm the earth's surface. Quantities of greenhouse

gases are often expressed as the amount of CO2 that would have the

same global-warming potential: their CO2 equivalent.

The High (Greenhouse Gas) Cost of Meat Worldwide meat production

(beef, chicken and pork) emits more atmospheric greenhouse gases

than do all forms of global transportation or industrial processes.

On the basis of data from the United Nations Food and Agriculture

Organization (FAO) and the Emission Database for Global Atmospheric

Research, the author estimates that current levels of meat

production add nearly 6.5 billion tons of CO2-equivalent greenhouse

gases every year to the atmosphere: some 18 percent of the worldwide

annual production of 36 billion tons. Only energy production

generates more greenhouse gases than does raising livestock for food.

A Growing Appetite World beef production is increasing at a rate of

about 1 percent a year, in part because of population growth but

also because of greater per capita demand in many countries.

Economic analysis shows that if all beef were produced under the

economically efficient feedlot, or CAFO (concentrated animal feeding

operation), system—which generates fewer greenhouse emissions than

many other common husbandry systems do—beef production by 2030 would

still release 1.3 billion tons of CO2-equivalent greenhouse gases.

If current projections of beef consumption are correct, even under

the feedlot production system the buildup of CO2-equivalent

greenhouse gases could amount to 26 billion tons in the next 21

years.

Prime Cuts: How Beef Production Leads to Greenhouse Gases The

largest fraction of the greenhouse effect from beef production comes

from the loss of CO2-absorbing trees, grasses and other year-round

plant cover on land where the feed crops are grown and harvested.

Second most important is the methane given off by animal waste and

by the animals themselves as they digest their food. This analysis

of the U.S. feedlot beef production system was done by ecological

economist Susan Subak, then at the University of East Anglia in

England.

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

Greenhouse Hamburger " .

http://www.sciam.com/article.cfm?id=the-greenhouse-hamburger