Chapter 2, Part 2

Energy Balance

Radiation and Absorption

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.

Blackbody Radiation

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?

Selective Absorbers

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.

Absorption in the Atmosphere

Greenhouse Effect

Energy Balance

Solar Wind


	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.