All the gases and stuff in the air get trapped in the atmosphere. All the suff is usually of course absorbed by plants and trees but there is too much. Usually the heat would escape the earth or something but the gases sort of act as a protective layer keeping and trapping all of the heat here. This is usually a good thing but it depends on how you treat it. Look at the planet venus. It is the hottest in our solar system, due to the Greenhouse effect. But still if we didn't have it our planet would freeze, and plants would die. Well in the end I guess so would we.