The Earth's Climate

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Albedo

Albedo is a physical value that indicates the quantity of incident sunlight reflected by a given surface. In relation to the climate, this is an important variable because it expresses the proportion of solar radiation reflected into space by the Earth's surface and atmosphere, which therefore does not heat the planet.

Albedo is a dimensionless quantity. Its value is expressed either by a percentage between 0 and 100 representing the percentage of light reflected in relation to the quantity received, or by a figure between 0 and 1 correspondind to the fraction of reflected light.

Consequently, a perfectly white surface reflects all light, and its albedo is 100%. Conversely, a perfectly black surface reflects no light and thus absorbs all of the solar radiation it receives. Its albedo is 0%.

To give a few examples, the oceans have an albedo of 5 to 10%, sand between 25 and 40%, ice about 60%, and fresh thick snow up to 90%. The continents have a higher albedo than the oceans, which is why in satellite photos the land is lighter than the bodies of water. All surfaces combined, the Earth's average albedo is 30%.

The melting of the icecaps and variations in the use of land, as in the case of massive deforestation, affect the planet's albedo, which in turn impacts its energy exchanges and thus its climate. Changes in the cloud cover affect the Earth's albedo and the transmission of infrared radiation, thus modifying the greenhouse effect and the terrestrial cycles of heat and water exchange.

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