|
|
|
|
All things radiate and absorb radiation. |
|
This includes the sun, the earth, and our
atmosphere. |
|
When the rate of absorption of solar radiation
equals the rate of emission of infrared earth radiation, radiative
equilibrium is achieved. |
|
|
|
|
|
|
An object that is a perfect absorber and a
perfect emitter, is called a blackbody. |
|
If the earth behaves a blackbody with no
atmosphere, then radiative equilibrium will be attained at –18C or 0F. |
|
The correct average temperature is 15C or
59F. Why? |
|
|
|
|
Kirchoff’s law: Good absorbers are good emitters
at a particular wavelength, and poor absorbers are poor emitters at the
same wavelength. |
|
With the
selective absorption, the average surface temperature is 15C or 59F. |
|
|
|
|
|