First, cattle themselves are a source of methane, which has a much more significant greenhouse warming effect than carbon dioxide. As they digest food, cattle produce around 18 percent of the methane in the atmosphere caused by human activity. In addition, tropical rain forest is burned and cut down in order to grow crops to feed cattle. This burning adds carbon dioxide to the atmosphere, and the forest can no longer capture carbon dioxide and produce oxygen. Lastly, raising animal protein, with its requirement of oil-based chemicals and fuel, uses more energy. In all these ways, our hunger for cheap meat adds to the global warming problem