Changes

===Infrared radiation===

===Infrared radiation===

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 with this theory is called the [[Anthropogenic global warming theory|anthropogenic greenhouse effect]].

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 with this theory is called the [[Anthropogenic global warming theory|anthropogenic greenhouse effect]].