Raising livestock also contributes to rising global temperatures. Animals such as cows, pigs, and sheep release methane—a greenhouse gas that causes global warming—when they pass wind, with one cow producing an estimated 500 liters of methane each day. A 2006 report by the Food and Agriculture Organization (FAO) says that livestock farming accounts for 37 percent of all methane production, and warns that methane may have a more damaging effect on the
atmosphere than carbon dioxide.