Global warming refers to the gradual heating up of the Earth. What is supposed to happen is the Earth should give off the energy it takes in and maintain its temperature. During the summer it does heat up, but then loses this heat during the winter. Overall, the annual energy should be balanced, what is taken in should be equal to what is given off.
Part of the process of handling heat is a marvelous circulation system whereby excessive heat at the equator is shared with the poles. Air aloft moves in a manner to help keep the Earth from really overheating at the equator, and from getting much colder at the poles.