inversely proportional to its absolute temperature (Box 8.1: Wien's law). Radiating bodies also emit energy in proportion to the fourth power of their temperatures (Box 8.1: Stefan-Boltzmann law).

Incoming solar radiation has a maximum wavelength around 0.5 microns (0.0000005 meters) with 44% in the visible, 48% in the infrared, and the remainder in the ultraviolet regions of the electromagnetic spectrum (Figs. 8.7 and 8.8a). When this solar radiation reaches the Earth system, around 26% is immediately reflected by clouds and scattered through the blue sky back into space. Another 4% of the solar radiation is reflected at the Earth's surface, primarily from white ice-covered regions, which have high albedo or reflectance. Incoming solar ra-

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