Albedo

The albedo is a measure of reflectivity of a surface or body. It is the ratio of electromagnetic radiation (EM radiation) reflected to the amount incident upon it. The fraction, usually expressed as a percentage from 0% to 100%, is an important concept in climatology and astronomy. This ratio depends on the frequency of the radiation considered: unqualified, it refers to an average across the spectrum of visible light. It also depends on the angle of incidence of the radiation: unqualified, normal incidence. Fresh snow albedos are high: up to 90%. The ocean surface has a low albedo. Earth has an average albedo of 37-39% whereas the albedo of the Moon is about 12%. In astronomy, the albedo of satellites and asteroids can be used to infer surface composition, most notably ice content. Enceladus, a moon of Saturn, has the highest known albedo of any body in the solar system, with 99% of EM radiation reflected.

Related Topics:
Reflectivity - Electromagnetic radiation - Climatology - Astronomy - Frequency - Visible light - Earth - Moon - Enceladus

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Human activities have changed the albedo (via forest clearance and farming, for example) of various areas around the globe. However, quantification of this effect is difficult on the global scale: it is not clear whether the changes have tended to increase or decrease global warming.

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The "classical" example of albedo effect is the snow-temperature feedback. If a snow covered area warms and the snow melts, the albedo decreases, more sunlight is absorbed, and the temperature tends to increase. The converse is true: if snow forms, a cooling cycle happens. The intensity of the albedo effect depends on the size of the change in albedo and the amount of insolation; for this reason it can be potentially very large in the tropics.

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