Source: NASA/USGS, NASA Goddard Space Flight Center Scientific Visualization Studio, and NSIDC
This interactive activity adapted from NASA and the U.S. Geological Survey illustrates the concept of albedo—the measure of how much solar radiation is reflected from Earth's surface. The balance between the amount of solar radiation reflected and absorbed by Earth's surface plays an important role in regulating global temperature. Learn about how Earth materials, such as snow, ice, and water, differ in their ability to reflect and absorb the Sun's energy and how melting polar ice creates a positive feedback loop that accelerates global warming. Investigate how the presence of pollution, such as soot, lowers the albedo of ice and further increases melting. In addition, observe the decline in Arctic sea ice cover from 1979–2007 and the effect of melting ice on sea levels.
Different features of Earth (such as snow, ice, land, ocean, and clouds) have different albedos—the percentage of solar radiation reflected back into space. For example, land and ocean have low albedos (typically about 10 to 40 percent is reflected back into space) and absorb more energy than they reflect, while snow, ice, and clouds have high albedos (typically 70 to 90 percent) and reflect more energy than they absorb. Overall, Earth's average albedo is about 30 percent; in other words, about 30 percent of incoming solar radiation is reflected back into space, and 70 percent is absorbed.
Earth's radiation budget is a concept that helps us understand how much energy Earth receives from the Sun, and how much energy Earth radiates back to outer space. Depending on the balance, Earth may be experiencing a net warming or a net cooling. Over the past century, there has been a net warming, which has caused Earth's temperature to increase by about 0.8°C.
An increase in global temperature causes snow and ice to melt, which decreases the extent to which they cover the surface, which then decreases Earth's albedo. This decrease in albedo means more energy is absorbed, which causes further warming and in turn causes more melting. This ice-albedo positive feedback loop accelerates change in global temperature and is, therefore, a critical concept to understand when trying to predict global climate change.
Human activities that create pollution influence the energy balance. For example, when we burn coal, oil, wood, and other fuels, the carbon by-product, soot, is released into the atmosphere and eventually deposited back on Earth. The dark particles land on snow and ice, and decrease albedo. Wearing a black shirt (which absorbs radiation) on a sunny day will make you feel warmer than if you wore a white shirt (which reflects radiation). Similarly, the darkened snow and ice absorb more radiation than pure snow and ice. In addition, as the snow and ice melt, the soot embedded in the snow is left behind and becomes more concentrated on the surface, further accelerating warming.
Aerosols (tiny particles in the air) also alter the amount of radiation absorbed and reflected by the atmosphere. Some aerosols, such as soot, absorb radiation; they have a warming effect. However, light-colored aerosols, such as sulfates, increase the amount of solar radiation that is reflected; they have a cooling effect. Currently there is a partial balance between dark and light aerosols, but their overall effect is similar to what happens after a large volcanic eruption: particles in the air reduce the amount of solar energy that reaches Earth's surface. This effect, known as global dimming, appears to have been masking the full impact of global warming. In the 1990s, as efforts to decrease the amount of air pollution reduced the particulates in the air, studies showed an increase in solar radiation. Ironically, reduced particulate emissions may cause Earth's temperature to rise faster than many earlier models predicted.
Academic standards correlations on Teachers' Domain use the Achievement Standards Network (ASN) database of state and national standards, provided to NSDL projects courtesy of JES & Co.
We assign reference terms to each statement within a standards document and to each media resource, and correlations are based upon matches of these terms for a given grade band. If a particular standards document of interest to you is not displayed yet, it most likely has not yet been processed by ASN or by Teachers' Domain. We will be adding social studies and arts correlations over the coming year, and also will be increasing the specificity of alignment.