The overall effect of all clouds together is that the Earth's surface is cooler than it would be if the atmosphere had no clouds.
The shortwave rays from the Sun are scattered in a cloud; many of the rays return to space. The resulting ΓÇ£cloud albedo forcing,ΓÇ¥ taken by itself, tends to cause a cooling of the Earth.
When a cloud absorbs longwave radiation emitted by the EarthΓÇÖs surface, the cloud re-emits a portion of the energy to space and a portion back toward the surface. The intensity of the emission from a cloud varies with its temperature and also depends upon several other factors, such as the cloudΓÇÖs thickness and the makeup of the particles that form the cloud.
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This process is called ΓÇ£cloud greenhouse forcingΓÇ¥ and, taken by itself, tends to cause a heating or ΓÇ£positive forcingΓÇ¥ of the EarthΓÇÖs climate. Usually, the higher a cloud is in the atmosphere, the colder is its upper surface and the greater is its cloud greenhouse forcing.
