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Albedo shouldn't change the temperature

  1. Oct 31, 2013 #1
    I've never understood why changing the albedo of an object will change the temperature of the object.

    As I understand it the albedo is a factor that determines the amount of light reflected off the surface. This means that a low albedo will mean that more light-energy is absorbed. Thermal equilibrium is then achieved when absorbed light-energy equals the energy lost through black-body radiation, determining the temperature. However I've read in an introductory geophysics book the black-body radiation is modified by the exact same factor (I think there was even a simple convincing proof), so that a low-albedo object will radiate at a higher rate. I've haven't been able to find any other sources on the matter. In this case the factor will cancel out, yielding the same temperature, albeit at a slower equilibrium time. I've even simulated this on a computer once.

    So what's up!? I'm really puzzled by this.
  2. jcsd
  3. Oct 31, 2013 #2
    That's because that fact that you read in this introductory book isn't exactly correct. Albedo is a function of wavelength and is perfectly possible for a surface to have high albedo at visible wavelength (reflecting sun's light) while having low albedo a IR wavelength being efficient IR emitter.
  4. Oct 31, 2013 #3
    I knew that the factor was wavelength dependent and suspected that it could have some effect. But this means that the typical approach to albedo problem is a little one sided, at least. For example saying that if the earth is covered in snow (giving an albedo of 0,8-0,9 for visual light) will cause the earth temperature to drop. This is not necessarily true, until you also supply the albedo for the expected black body radiation wavelength.
    Well thanks for the answer.
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