Changes

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.<ref>D. Hartmann, Global Physical Climatology</ref> 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.

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.<ref>D. Hartmann, Global Physical Climatology</ref> 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:

[[Richard Lindzen]] wrote (in 1992):

: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. [http://www.cato.org/pubs/regulation/regv15n2/reg15n2g.html]

: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. [http://www.cato.org/pubs/regulation/regv15n2/reg15n2g.html]

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.

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.