Greenhouse Effect 

The atmosphere conserves the heat energy of Earth because it absorbs radiation selectively. Most of the solar radiation in clear skies is transmitted to Earths surface, but a large part of the outgoing terrestrial radiation is absorbed and reradiated back to the surface. This is called the GREENHOUSE effect. A greenhouse permits most of the short-wave solar radiation to pass through the glass roof and sides, and to be absorbed by the floor, ground or plants inside. These objects reradiate energy at their tempera-tures of about 300K, which is a higher temperature than the energy that was initially received. The glass absorbs the energy at these wavelengths and sends part of it back into the greenhouse, causing the inside of the structure to become warmer than the outside. The atmosphere acts similarly, transmitting and absorbing in somewhat the same way as the glass. If the greenhouse effect did not exist, Earths tempera-ture would be 35C cooler than the 15C average temperature we now enjoy, because the insolation would be reradiated back to space. 

Of course, the atmosphere is not a contained space like a greenhouse because there are heat transport mechanisms such as winds, vertical currents, and mixing with surrounding and adjacent cooler air.

Figure 1-2-7.Radiation balance in the atmosphere.

a balance is maintained between incoming and outgoing radiation. This section of the lesson explains the various radiation processes involved in maintaining this critical balance and the effects produced in the atmosphere.

We have learned that an object reradiates energy at a higher temperature. Therefore, the more the Sun heats Earth, the greater the amount of heat energy Earth reradiates. If this rate of heat loss/gain did not balance, Earth would become continuously colder or warmer.

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