Futhermore,farm animals add to the problem of global warming. All livestock animals such as cows, pigs, and sheep release methane by expelling gas from their bodies. One cow can produce up to sixty liters of methane each day. Methane gas is the second most common greenhouse gas after carbon dioxide. Many environmental experts now believe that methane is more responsible for global warming than carbon dioxide. It is estimated that twenty-five percent of all methane released into the atmosphere comes from farm animals.