When sunlight reaches the Earth’s surface, some of it is absorbed and some is reflected. The relative amount (ratio) of light that a surface reflects compared to the total incoming sunlight is called albedo. Surfaces with high albedos include sand, snow and ice, and some urban surfaces, such as concrete or light-colored stone. Surfaces with low albedos include forests, the ocean, and some urban surfaces, such as asphalt.
Albedo is important to Earth scientists because it plays a significant role in our planet’s average surface temperature. When a surface reflects incoming sunlight, it sends the energy back to space, where it doesn’t affect temperature or climate. When a surface absorbs light, however, solar energy is turned into heat. If the surface is snow or ice, it may melt; otherwise, the surface’s temperature rises.
A surface’s albedo may change depending on the angle of the incoming sunlight and the satellite’s viewing angle. These maps show the albedo that would be observed at each location at noon local solar time—in other words, as if the Sun were directly overhead at every location.
In addition, the same surface may not have the same albedo for all wavelengths of light. Consider leaves: they look green because they are reflecting a lot of the green wavelengths of light falling on them. So, they have a high albedo in green wavelengths. But we know they are absorbing other wavelengths of visible light for photosynthesis, so in those wavelengths (mostly red and blue), leaves have a low albedo.
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