If it were not for the natrural greenhouse effect, the Earth would be like the moon, too cold to support life. The average temperature of the Earth's surface with the greenhouse effect is 15 degrees Celsius. Without the natural greenhouse effect, the temperature would be -18 degrees Celsius. The natural greenhouse effect works because tiny quantities of greenhouse gases in the atmosphere trap the sun's heat, warming land, air and water. Without these greenhouse gases, the sun's heat would escape into space.
Greenhouse gases are both natural and manmade.
Carbon dioxide or CO2 is the most important natural and manmade greenhouse gas, and the major contributor to global warming. Plants and animals release CO2 as they breathe. Methane is produced naturally when vegetation is burned, digested or rotted without the presence of oxygen. Today, large amounts of methane are released by rice paddies, grazing cattle, rotting material in garbage dumps or landfills, and by fossil fuels. You have probably heard of CFCs because of the damage they are doing to the ozone layer.