FIGURE 2.1. The Earth radiates energy at the same rate it is received from the Sun. The Earth's emission temperature is 255 K, and that of the Sun is 6000 K. The outgoing terrestrial radiation peaks in the infrared spectrum; the incoming solar radiation peaks at shorter wavelengths, in the visible spectrum.
infrared (IR). But the atmosphere is strongly absorbing at these wavelengths due to the presence of trace gases—principally the triatomic molecules H2O and CO2—which absorb and emit in the infrared, thus raising the surface temperature above that of the emission temperature, a mechanism that has become known as the greenhouse effect.
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