Any change in the balance between the quantity of energy absorbed compared to the amount emitted, affects climate. The "greenhouse effect" is concerned with the infrared radiation given off by the earth. Part of this radiation is absorbed by the atmosphere, rather than being lost to space. The gases in the atmosphere that absorb infrared light primarily are water (H2), carbon dioxide (CO2), ozone (O3), nitrous oxide (NO2), methane (CH4) and CFCs. These gases act as a sort of insulating blanket for the earth, in the same way they would act to lessen heat loss from a greenhouse, hence the name 'greenhouse effect'.