Figure 1.2: The Earth’s
annual and global mean energy balance. Of the incoming solar radiation, 49% (168
Wm-2) is absorbed by the surface. That heat is returned to the atmosphere
as sensible heat, as evapotranspiration (latent heat) and as thermal infrared
radiation. Most of this radiation is absorbed by the atmosphere, which in turn
emits radiation both up and down. The radiation lost to space comes from cloud
tops and atmospheric regions much colder than the surface. This causes a greenhouse
effect. Source: Kiehl and Trenberth, 1997: Earth’s Annual Global Mean Energy
Budget, Bull. Am. Met. Soc. 78, 197-208.
