The Green House Gases

The most known cause is the green house effect and that happens when the sunlight reaches the earth, it warms it up and some of it get absorbed and most of it reflected by the earth as longer waves than the usual sunlight is. Some of the reflected sunlight is absorbed also by the atmosphere before they are lost in the space but the green house gasses absorbs it more and act like a mirror and resend it back again to the earth which keeps the earth more warmer than the normal rate because the heat is kept in the earths atmosphere and the main reason behind it is the human behavior.