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yellow, and the peak emission range of outgoing radiation is colored blue (though of course some emission occurs from both sources outside those ranges)[1].



Fig. 4.2


Note the fact that incoming solar radiation is not absorbed efficiently by any molecule, whereas outgoing radiation is efficiently absorbed by a number of molecules, particularly carbon dioxide, nitrous oxide, water vapor, and ozone. This is the source of the greenhouse effect.

A more apt metaphor for the effect, then, might be the “one-way mirror” effect. Rather than acting like a greenhouse (which suppresses convection), the presence of a heterogeneous atmosphere on Earth acts something like an array of very small one-way mirrors, permitting virtually all incoming radiation to pass relatively unimpeded, but absorbing (and later re-radiating) much of the energy emitted by the planet itself. Of course this too is just a metaphor, since true mirrors are reflective (rather than radiative), and changing the reflection profile of the system (as we’ve seen) changes the albedo, not the radiative values. Moreover,


  1. Figure adapted from Mitchell (op. cit.)

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