Energy and Mass Transfer in the Atmosphere

The fraction of electromagnetic radiation from the sun that is reflected by Earth s surface, called albedo, varies with the nature of the surface, from freshly plowed black topsoil with a low albedo of only about 2.5% to fresh snow at about 90%. Human activities in the anthrosphere affect albedo by measures such as cultivating soil and paving large areas. 

The maintenance of Earth s heat balance to keep temperatures within limits condncive to life is very complex and not well understood. Geological records show that in times past Earth was sometimes relatively warm and that at other times there were ice ages in which much of Earth s surface was covered by ice a kilometer or two thick. The differences in average Earth temperature between these extremes and the relatively temperate climate conditions that we now enjoy are a matter of only 

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