The Sun serves as the primary source of energy for Earth's climate. Some of the incoming sunlight is reflected directly back into space, especially from bright surfaces such as ice and clouds, and the rest is absorbed by the surface and atmosphere. Much of this absorbed solar energy is re-radiated as heat (longwave or infrared radiation). The atmosphere in turn absorbs and re-radiates heat, some of which escapes into space. Any disruption to this balance of incoming and outgoing energy will affect the climate. For example, small changes in the energy output from the Sun will directly affect this balance. (More on royalsociety.org)