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Does my gas cause global warming? Belches and flatulence are harmless, right? Wrong! When cattle and sheep burp and pass gas, the entire planet reels. (Earth Science: Global Warming * Methane Gas).

HERE'S WHY: LIVESTOCK GAS IS HIGH IN METHANE, a colorless, odorless gas. Methane is also a potent, greenhouse gas, and once spewed into the atmosphere, it absorbs heat radiating from Earth's surface (see SW 9/3/01). That's why methane is a major contributor to the planet's increasing temperature rise--or global warming. Molecule for molecule, methane's heat-trapping power in the atmosphere is 21 times stronger than carbon dioxide, the most abundant greenhouse gas.

With 1.3 billion cows belching almost constantly around the world (100 million in the U.S. alone), it's no surprise that methane released by livestock is one of the chief global sources of the gas, according to the U.S. Environmental Protection Agency (EPA). Other prime methane sources: petroleum drilling, coal mining, solid-waste landfills, rice paddies, and wetlands.

Greenhouse gases like methane and carbon dioxide make up only a scant part of Earth's atmosphere, which is 78 percent nitrogen and nearly 21 percent oxygen. And without greenhouse gases to trap the sun's heat and warm the planet, life as we know it couldn't exist. But in the last 200 years, human activity that requires burning oil, natural gas, and coal for energy has magnified the greenhouse effect.

Atmospheric concentrations of methane have more than doubled in the last two centuries. Blame for this often focuses on big industry and gas-guzzling vehicles. But agriculture plays a major role, too. In the past 40 years alone, the global cattle population has doubled.


Cows much mostly grass and hay--yet they grow big and hefty. Why? Because of the rumen; the first and largest of a cow's four stomachs. The rumen holds 160 liters (42 gallons) of food and billions of microbes. These microscopic bacteria and protozoa (single-celled organisms that reproduce by dividing) break down cellulose (plant-wall substance) and fiber into digestible nutrients. "A cow couldn't live without its microbes," says animal nutrition expert Dr. Floyd Byers of the U.S. Department of Agriculture.

As the microbes digest cellulose, they release methane. The process, called enteric fermentation, occurs in all animals with a rumen (cows, sheep, and goats, for example), and it makes them very gassy. "It's part of their normal digestion process," says Tom Wirth of the EPA. "When they chew their cud, they regurgitate [spit up] some food to rechew it, and all this gas comes out." The average cow expels 600 liters of methane a day, climate researchers report.


"Methane production is a waste of energy that we want to redirect into more production of meat and milk," says Byers. So scientists are devising ways to reduce and recycle emissions from livestock and their waste:

* Studies show poor livestock nutrition leads to excess methane production. Supplementing cattle feed with urea (nitrogen-rich compound found in urine) can lower methane by 25 to 75 percent.

* Australian farmers are testing vaccine drugs that trigger sheep and cow immune systems to fight off some rumen microbes. The vaccine doesn't eliminate gas, but lowers the methane content by up to 20 percent.

* A Minnesota farmer is harnessing methane from the manure of his 850 cows and using the gas to generate electricity. With each cow pooping about 45 kilograms (100 pounds) of manure a day, he's easily able to power his farm--and the homes of 78 neighbors!


Cross-Curricular Connection

Math: Answer these questions: The cow population has doubled in the last 40 years to 1.3 billion cows worldwide. How many cows existed 40 years ago? If the population growth rate triples, how many cows will there be 40 years from now?


Did You Know?

* In the U.S., there are two head of cattle for every five humans. Even more surprising, one cow's rumen houses more bacteria than there are people on Earth!

* Human activities--from energy production to agriculture--produce approximately 60 percent of the world's methane.

* It takes 2.4 kilowatt-hours (kwh) of electricity to burn a 100-watt lightbulb for a day. The electrical energy available in one cow's daily poop: 3.0 kwh.

National Science Education Standards

Grades 5-8: structure and function in living systems * structure of the Earth system * natural hazards * transfer of energy

Grades 9-12: natural and human-induced hazards * environmental quality * energy in the Earth system * chemical reactions * the cell * the interdependence of organisms


Michigan State University's Microbe Zoo Web site: dlc-me/zool

The U.S. Environmental Protection Agency's Ruminant Livestock Efficiency Program:

Directions: Answer the following questions using complete sentences.

1. How do methane and other greenhouse gases in the atmosphere contribute to global warming?

2. Why are cows, sheep, and other animals with rumen gassy?

3. In what ways are scientists and farmers trying to reduce methane emissions from cow gas and solid waste?


1. Greenhouse gases like methane and carbon dioxide trap the sun's heat in atmosphere, which helps keep the planet warm. But an excess of greenhouse gases can cause the planet to overheat.

2. The rumen houses billions of microbes that help cows and sheep digest fiber and cellulose. But as the microbes break down plant matter, they release lots of methane gas. The gas build-up causes ruminants to belch almost constantly.

3. To reduce methane emissions, livestock farmers supplement their animals' diet with urea. Others are trying a vaccine that can lower methane emissions. And some farmers are harnessing methane from cow manure and using it to generate power.
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Article Details
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Author:Masibay, Kim Y.
Publication:Science World
Geographic Code:1USA
Date:Jan 21, 2002
Previous Article:Snowboard superstar. (Physical Science: Newton's Law of Motion).
Next Article:Gross out? (You Can Do It).

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