Greenhouse Effect

The greenhouse effect refers to circumstances where the short wavelengths of visible light from the sun pass through a transparent medium and are absorbed, but the longer wavelengths of the infrared re-radiation from the heated objects are unable to pass through that medium. The trapping of the long wavelength radiation leads to more heating and a higher resultant temperature. Besides the heating of an automobile by sunlight through the windshield and the namesake example of heating the greenhouse by sunlight passing through sealed, transparent windows, the greenhouse effect has been widely used to describe the trapping of excess heat by the rising concentration of carbon dioxide in the atmosphere. The carbon dioxide strongly absorbs infrared and does not allow as much of it to escape into space.

Sunlight warms your car
Increasing atmospheric carbon dioxide
Global warming
Role in the absence of water on Venus?
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Greenhouse Effect Example

Bright sunlight will effectively warm your car on a cold, clear day by the greenhouse effect. The longer infrared wavelengths radiated by sun-warmed objects do not pass readily through the glass. The entrapment of this energy warms the interior of the vehicle.

Short wavelengths of visible light are readily transmitted through the transparent windshield. (Otherwise you wouldn't be able to see through it!)




Shorter wavelengths of ultraviolet light are largely blocked by glass since they have greater quantum energies which have absorption mechanisms in the glass. Even though you may be uncomfortably warm with bright sunlight streaming through, you will not be sunburned.

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Blackbody radiation concepts
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Increase in Greenhouse Gases

The increase in the concentration of carbon dioxide, one of the three major atmospheric contributers to the greenhouse effect has been carefully documented at the Mauna Loa Observatory in Hawaii. The 1990 rate of increase was about 0.4% per year. The interesting cyclic variations represent the reduction in carbon dioxide by photosynthesis during the growing season in the northern hemisphere.

Current analysis suggests that the combustion of fossil fuels is a major contributer to the increase in the carbon dioxide concentration, such contributions being 2 to 5 times the effect of deforestation (Kraushaar & Ristinen).

Increase in Atmospheric Carbon Dioxide

Trefil reports the concentration of carbon dioxide in the atmosphere today as 360 parts per million compared to 315 ppm in 1958 when modern measurements were initiated. Measurements of air bubbles trapped in the Greenland ice sheet indicate concentrations of 270 ppm in preindustrial times.

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References
Kraushaar & Ristinen

Trefil
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Contributers to Greenhouse Effect

Increase in greenhouse gasesGreenhouse effect
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Reference
Kraushaar & Ristinen
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Global Warming

An issue of major concern is the possible effect of the burning of fossil fuels and other contributers to the increase of carbon dioxide in the atmosphere. The action of carbon dioxide in trapping infrared radiation is called the greenhouse effect. It may measurably increase the overall average temperature of the Earth, which could have disastrous consequences. Sometimes the effects of the greenhouse effect are stated in terms of the albedo of the Earth, the overall average reflection coefficient.

Increase in greenhouse gasesGreenhouse effect
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Reference
Kraushaar & Ristinen
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