As concern grows over the possibility of altering the Earth's climate, a major uncertainty exists in computer models used to study the Earth's atmosphere, regarding our current understanding of clouds and our ability to simulate their effect on climate. A number of recent observations and computer simulation studies, however, have shed light on the important role of clouds in determining the present and future climate of our atmosphere.
Data from the National Aeronautics and Space Administration's (NASA's) Earth Radiation Budget Experiment have been used to obtain an accurate picture of how clouds affect our present global climate system [Ramanathan, 1989]. The effect of clouds on solar and thermal radiation entering and leaving our climate is known as cloud forcing. Low clouds generally cool the Earth's surface, while high clouds warm the climate system. For the entire planet, however, the cooling effect of low clouds is stronger than the warming effect from high clouds, so that overall, clouds cool the climate.