Global warming begins with the greenhouse effect, which is caused by the interaction between Earth's atmosphere and incoming radiation from the sun.
Solar radiation passes through the atmosphere to the surface of Earth, where it is absorbed and then radiated upward as heat. Gases in Earth's atmosphere absorb about 90 percent of this heat and radiate it back to the surface, which is warmed to a life-supporting average of 59 F (15 C). This very helpful process is called the greenhouse effect.