文档介绍：72 SCIENTIFIC AMERIC A N February 2009 M ost of us are aware that our cars, our coal-generated electric power and even our cement factories ad - versely 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, speci !cally, the meat in them cause more greenhouse gas - es —carbon dioxide (CO 2), methane, nitrous ox - ide, and the like —to spew into the atmosphere than either transportation or industry. (Green - house gases trap solar energy, thereby warming the earth’s surface. Because gases vary in green - house potency, every greenhouse gas is usually expressed as an amount of CO 2 with the same global-warming potential.) The FAO report found that current produc - tion levels of meat contribute between 14 and 22 percent of the 36 billion tons of “CO 2-equiva - lent” 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 environmen - tal costs: transportation, refrigeration and fuel for farming, as well as methane emis