Scientists refer to the reflectivity of a surface as its albedo. Snow and ice have high albedo relative to soil and water. The average albedo can be measured for any area that contains a diversity of surfaces.
We can measure the albedo of the various planets in our solar system, by calculating the amount of sunlight energy they receive at their distance from the Sun, and the amount that we can see reflected from their surface.
But, what is the overall albedo of the Earth? If we get far enough away from our planet, we can measure its reflected sunlight in a radiometer that takes in a view of the entire Earth. Alternatively, a clever way to measure Earth’s albedo is to record the intensity of Earthshine that is reflected off a New Moon. Both methods indicate that the Earth reflects about 30% of the incoming solar radiation back out to space.
Some of that reflectivity comes from the tops of clouds in our atmosphere, some from snow and ice on the surface, and some from particulate materials in the atmosphere. For the latter, volcanoes and air pollutants contribute to Earth’s reflectivity.
Could changes in reflectivity be involved with current observations of global warming? Probably not. Through air pollution, Earth’s albedo has increased in recent years, reducing the warming of the surface by about 1.2 Watts per square meter. But, that is less than the warming due to increasing concentrations of carbon dioxide and other greenhouse gases in our atmosphere — about 2.3 Watts per square meter.
Without this small increase in albedo, what we call global dimming, the Earth would be warming even faster than we measure.
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Photo, taken on October 17, 2000, courtesy of the NASA Goddard space Flight Center via Flickr.
Earth Wise is a production of WAMC Northeast Public Radio. Support for Earth Wise comes from the Cary Institute of Ecosystem Studies in Millbrook, NY.