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This picture of the Andes Mountains between Chile and Argentina in South America was taken from the International Space Station in December 2000. Glaciers and snow top many of the high mountain peaks. Lakes in the valleys between mountains collect the water that melts from the snow and ice each spring and summer. Scientists have found that the smaller glaciers in this area are melting quickly as the Earth becomes warmer.
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NASA Earth Observatory

Albedo

This picture shows a part of the Earth surface as seen from the International Space Station high above the Earth. A perspective like this reminds us that there are lots of different things that cover the Earth. Soil, rocks, water, forests, snow, and sand - they all look different from above. They also have different ways of dealing with the solar energy that gets to our planet. Dark colored parts of the planet surface reflect very little of the solar energy that hits them. Light colored parts of the planet surface reflect almost all of the solar that hits them.

The amount of energy reflected by a surface is called albedo. Albedo is measured on a scale from zero to one (or sometimes as a percent).

  • Very dark colors have an albedo close to zero (or close to 0%).
  • Very light colors have an albedo close to one (or close to 100%).

Because much of the land surface and oceans are dark in color, they have a lower albedo and absorb a large amount of the solar energy that gets to them, reflecting only a small fraction of the energy. Forests have low albedo, near 0.15. The snow and ice, on the other hand, are very light in color. They have very high albedo, as high as 0.8 or 0.9, so they reflect most of the solar energy that gets to them, absorbing very little.

The combined effect of the albedo of all these surfaces is called the planetary albedo. Earth's planetary albedo is about 0.31. That means that about a third of the solar radiation that gets to Earth is reflected out to space and about two thirds is absorbed. The Moon's albedo is 0.07, meaning that only 7% of the energy that gets to it is reflected. The albedo of distant planets, so distant that they are difficult to study with telescopes, can be a very helpful to scientists trying to figure out what materials are at the planet surface. Something that absorbs all radiation would have an albedo of 0 and be called a black body.

Earth's climate is affected by the amount of solar radiation that is reflected back out to space and the amount of solar radiation that is absorbed. If Earth's climate is colder and there is more snow and ice on the planet, more solar radiation is reflected back out to space and the climate gets even cooler. On the other hand, when warming causes snow and ice to melt, darker colored Earth surface and ocean are exposed and less solar energy is reflected out to space causing even more warming. This is known as the ice-albedo feedback.

Clouds in Earth's atmosphere have an important effect on albedo, reflecting a large amount of solar energy out to space. While different types of clouds reflect different amounts of solar energy, their combined effect is huge. If there were no clouds in our atmosphere, Earth's average albedo, which is about 0.31, would drop by half.

 

Last modified May 13, 2011 by Jennifer Bergman.

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA