Earth’s atmosphere is slightly warmer than what it should be due to direct solar heating because of a mild case of greenhouse effect. The ground is heated by visible and (some) infrared light from the Sun. The heated surface emits infrared light. The majority of Earth’s atmosphere (N2 and O2) are not good greenhouse gas. The most important greenhouse gases are: H2O – Water vapor; CO2 – Carbon Dioxide and CH4 – methane. Most of the greenhouse heating of Earth’s atmosphere is due to Water vapor absorption of IR radiation emitted by Earth, and then transferring the energy to the surrounding air molecule.