A primary reason for the destruction of the rain forest in countries like Costa Rica, Colombia, Brazil, Malaysia, Thailand, and Indonesia, is to provide grazing land for cattle, virtually all of which goes not to the poor in these third world nations, but rather is exported to richer countries like the United States. In fact, in the past 25 years almost half of the tropical rain forests of Central America have been razed, mostly in provide beef to North America. The impact is enormous. Every day more of these species are being pushed to extinction as a result of Americans' animal-centered diet. The clearing of these forests also leads to a great deal of erosion, increases runoff which causes flooding, takes away the wood peasants often rely upon for fuel, and has been blamed for decreased rainfall.
Animal agriculture is also a major cause of global warming.
On the one hand, the earth relies upon its rain forests to cycle carbon dioxide, the primary greenhouse gas, out of the atmosphere. The destruction of these forests for livestock production and the resulting buildup of carbon dioxide in the atmosphere is the cause of global warming. On the other hand, livestock production worldwide is the single largest source of emissions of methane, one of the most potent global warming pollutants. By emitting greenhouse gases and destroying our rainforests, we cause climactic changes which can kill off countless species, cause widespread droughts and storms, and flood large areas of land. The dangers are many and severe, and we directly cause them every time we eat a hamburger.