# Albedo shouldn't change the temperature

1. Oct 31, 2013

### DrDress

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. Oct 31, 2013

### dauto

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.

3. Oct 31, 2013

### DrDress

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.