Difference between revisions of "Greenhouse effect"
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| − | The '''greenhouse effect''' refers to the retention of heat at the [[Earth]]'s surface and in the [[atmosphere]] which results when gas molecules reduce the escape of [[infrared radiation]] into [[outer space]]. The greenhouse effect was discovered in 1824 by [[Joseph Fourier]]. | + | The '''greenhouse effect''' refers to the retention of heat at the [[Earth]]'s surface and in the [[atmosphere]] which results when gas molecules reduce the escape of [[infrared radiation]] into [[outer space]]. The greenhouse effect was discovered in 1824 by [[Joseph Fourier]]. |
These [[greenhouse gas]] molecules (principally [[water]], [[carbon dioxide]], and [[methane]]) | These [[greenhouse gas]] molecules (principally [[water]], [[carbon dioxide]], and [[methane]]) | ||
Revision as of 23:29, August 8, 2007
The greenhouse effect refers to the retention of heat at the Earth's surface and in the atmosphere which results when gas molecules reduce the escape of infrared radiation into outer space. The greenhouse effect was discovered in 1824 by Joseph Fourier.
These greenhouse gas molecules (principally water, carbon dioxide, and methane) absorb and re-emit longwave infrared rays emitted from the earth's surface into the atmosphere (see radiational cooling).
Sunlight falling on the surface of a planet is primarily in the visible part of the spectrum. The surface absorbs some of the incident sunlight, and some is reflected, depending on the reflectivity of the surface (see albedo). The reflected light mostly passes through the atmosphere back to space. The absorbed light warms the surface.
Any body with a temperature radiates according to Planck's law, [1] and the Earth is no exception. Due to its relatively low temperature, the emission from the ground is in the infrared (IR) part of the electromagnetic spectrum. Greenhouse gases, by definition, are good absorbers at these wavelengths. The gas absorbs the IR radiation, and emits IR radiation, both up and down. Because these gases are above the surface, they are at a lower temperature than the surface, so they emit at a different frequency. The net effect is that energy is retained by the Earth system, warming it.[2] This is the natural greenhouse effect, which allows the Earth to be habitable. When the atmospheric composition is changed by human activity resulting in increases in greenhouse gases, the warming associated is called the anthropogenic greenhouse effect.
Richard Lindzen wrote:
- The main absorbers of infrared in the atmosphere are water vapor and clouds. Even if all other greenhouse gases (such as carbon dioxide and methane) were to disappear, we would still be left with over 98 percent of the current greenhouse effect. [2]
This insulating effect has been compared to a blanket or to the glass walls and roof of a greenhouse, but the process is not the same.
See also
Notes
- ↑ Thermodynamics says that any body with a temperature above absolute zero will radiate its energy away. [1]
- ↑ D. Hartmann, Global Physical Climatology
