Greenhouse effect: Difference between revisions
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== The Physics of the Greenhouse == | == The Physics of the Greenhouse == | ||
The essential condition for a greenhouse effect is the presence in a planetary atmosphere of gases that absorb (and emit) in the [[thermal radiation]] band of the planetary surface, or lower atmospheric levels. Frequently, the greenhouse gases will be transparent, or nearly so, to incoming solar radiation (ozone is an exception). The surface thermal radiation band will be in the long-wave [[infrared radiation| infrared]] region (3.5 µm - 100 µm). | The essential condition for a greenhouse effect is the presence in a planetary atmosphere of gases that absorb (and emit) in the [[thermal radiation]] band of the planetary surface, or lower atmospheric levels. Frequently, the greenhouse gases will be transparent, or nearly so, to incoming solar radiation (ozone is an exception). The surface thermal radiation band will be in the long-wave [[infrared radiation| infrared]] region (3.5 µm - 100 µm). The greenhouse gases are triatomic (or more, but note the exception for [[Titan]]) molecules which absorb energy into a variety of rotational, bending, and stretching modes. Common solar-system gases that meet the requirements are [[water]] (H<sub>2</sub>O), [[carbon dioxide]] (CO<sub>2</sub>), [[ozone]] (O<sub>3</sub>), and [[methane]] (CH<sub>4</sub>). For Earth, H<sub>2</sub>O, CO<sub>2</sub>, and O<sub>3</sub> provide most of the greenhouse. Common diatomic gases, such as [[nitrogen]] (N<sub>2</sub>) and [[oxygen]] (O<sub>2</sub>) do not have a strong enough dipole to interact well with infrared. | ||
== References and Notes == | == References and Notes == | ||
Revision as of 22:28, 5 February 2007
This article is a stub and is being actively worked on.
The Greenhouse Effect (or "atmospheric effect") is a general attribute of planets and moons with atmospheres. It is an imbalance between surface radiation and top-of-atmosphere radiation due to the presence of greenhouse gases. For example, in the case of the Earth, the surface emits 390 W/m2[1] (averaged over a year and the whole surface), but the emission at the top of the atmosphere is 235 W/m2, giving a global-average greenhouse effect of 155 W/m2[2]. The top-of-atmosphere outgoing radiation balances the incoming 235 W/m2 of solar radiation (342 W/m2 incident minus 107 W/m2 reflected). The term "greenhouse effect" is something of a misnomer, since actual greenhouses operate by a different mechanism.
The Greenhouse and the Planets
The Physics of the Greenhouse
The essential condition for a greenhouse effect is the presence in a planetary atmosphere of gases that absorb (and emit) in the thermal radiation band of the planetary surface, or lower atmospheric levels. Frequently, the greenhouse gases will be transparent, or nearly so, to incoming solar radiation (ozone is an exception). The surface thermal radiation band will be in the long-wave infrared region (3.5 µm - 100 µm). The greenhouse gases are triatomic (or more, but note the exception for Titan) molecules which absorb energy into a variety of rotational, bending, and stretching modes. Common solar-system gases that meet the requirements are water (H2O), carbon dioxide (CO2), ozone (O3), and methane (CH4). For Earth, H2O, CO2, and O3 provide most of the greenhouse. Common diatomic gases, such as nitrogen (N2) and oxygen (O2) do not have a strong enough dipole to interact well with infrared.
References and Notes
External Links
Additional Bibliography
- Houghton, JT, 19977. The Physics of Atmospheres, 3rd Ed, Cambridge Univ. Press.
- Thomas, GE, and K Stamnes, 1999. Radiative Transfer in the Atmosphere and Ocean, Cambridge Univ. Press.