The greenhouse effect is the natural warming of the earth's atmosphere. Carbon dioxide and other gases, called "greenhouse gases," let energy from the sun pass through to warm the earth. The gases then traps the heat when it tries to rise into the atmosphere. The greenhouse effect keeps the planet warm. Researchers who study this must rely on climate models. Climate models are computer programs that can copy the world's climate system. The greenhouse effect is very important to our planet and is one of the things that allow earth to even exist.