Environmental Protection

What is the albedo effect and what does it have to do with global warming?
Answered by HowStuffWorks
  • HowStuffWorks

    HowStuffWorks

  1. The Earth's tropical forests located near the equator absorb carbon dioxide (CO2), in the process decreasing the temperature. This is referred to as carbon sequestering. Because of this effect, some people have advocated planting new trees and the prevention of deforestation as effective means of fighting global warming. The actual total effect, however, of trees on the climate -- specifically, on temperature -- is extremely complex.

    Trees regulate the climate in several ways:

    • They reduce air pollution. Tree leaves remove particles and pollution from the air, such as dust, ozone and carbon monoxide. They also remove carbon dioxide and can sequester between 35 and 800 pounds (15.9 to 363 kilograms) of it, depending on the size of the tree [source: EPA]. By absorbing carbon dioxide -- a greenhouse gas -- through photosynthesis, they reduce the level of greenhouse gases in the atmosphere, which many people hope will help mitigate the effects of human carbon emissions and reduce global warming.
    • They lower temperatures by cooling the air through transpiration. During this process, water that was drawn from the soil by a tree evaporates from its leaves. Trees also reduce surface and air temperatures in urban areas that typically trap heat.
    • When strategically planted near buildings, they reduce energy usage by shading the buildings in warm months and protecting them from winds in cold months.
    • The leaves of trees absorb sunlight.

    According to a recent study, forests that are located farther from the equator trap heat and increase the temperature, in what is called the albedo effect. Albedo is a measurement of reflectivity, expressed as a ratio between 0 and 1, which respectively correspond to total absorption of electromagnetic radiation (such as sunlight) and to total reflectivity. The tops of trees tend to have a low albedo, absorbing this radiation and heating the surrounding areas. So while trees are very helpful in removing carbon from the atmosphere and preventing global warming in other ways, the albedo effect may actually cancel out the positive benefits of afforestation. Within the next century, trees may actually increase temperatures by as much as 10 degrees Fahrenheit (5.5 degrees Celsius) [source: Lawrence Livermore National Laboratory].

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