The greenhouse effect is a natural phenomenon that enables life to propagate in Earth. During the day, the Sun provides energy through sunlight. Note that the Sun's energy is obtained from the nuclear fusion of hydrogen to helium. So, sunlight contains radiation at very high temperatures. In order to regulate heat, the atmosphere allows only some of the heat to be absorbed into the surroundings, but blocking the rest and reflecting it back to space. During night time, without the Sun giving energy, greenhouse gases in the atmosphere has 'reserved' heat that is trapped in the atmosphere. So, the greenhouse gases (like water vapor and carbon dioxide) maintains the average temperature of the Earth's atmosphere at around 33°C.
