Heat is created by the sun. But the reason the world is getting hotter is not because the sun is getting hotter, it is because the layer that blocks the sun's vicious rays is disapearing. This layer is called the ozone.
Greenhouse gases is man-made pollution which is destroying the Ozone. The ozone is a layer around the Earth which stops the hottest of suns rays getting to us and setting fire to us and stopping us from being sizzled.