Atmospheric warming
Greenhouse gasesA greenhouse gas is a gas that absorbs and emits radiation in the infrared range. The main greenhouse gases in the Earth's atmosphere are water vapour, carbon dioxide, methane, nitrous oxide, and ozone. Without greenhouse gases, the Earth's surface would average about -19 oC instead of 14 oC. |
Contribution of each gas/vapour to atmospheric warming
Source: Wikipedia |
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Warming due to greenhouse gasesA guitar string, or a closed pipe, will resonate at exact frequencies. It is the same with molecules. Each photons is a packet of electromagnetic radiation of specific frequency. If a frequency is the same as any of the resonant frequencies of the molecule, then the molecule will vibrate and warm the surrounding molecules by re-emitting the radiation in a random direction .
Carbon dioxide (above), water vapor, methane, nitrous oxide, and a few other gases are greenhouse gases. They all are molecules composed of more than two component atoms, bound loosely enough together to be able to vibrate with the absorption of heat. In O2, N2, H2, the (moderate) vibration of the two atoms does not entail any movement of charge, so no absorption or emission of electromagnetic radiation. The peak of the thermal IR emission from the Earth's surface is very close to a strong vibrational absorption band of CO2, 67 cm−1.
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Each molecule that can vibrate due to elastic bonds between it's atoms, will do so at its own frequencies. Those frequencies are absorbed and re-emittted producing characteristic spectra. |
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Warming by water vapourThe amount of water vapour in the atmosphere depends on temperature, and how much water there is available to be evaporated. Warming by greenhouse gases, increases the amount of water vapour, thus producing a positive feedback effect that increases temperature even more. The average residence time of a water molecule in the atmosphere is only about nine days. |
Small technical detail..Air does not hold water vapour, it coexists with it. At say 20 oC, the water vapour above a pool of water will be the same in a vacuum, or an atmosphere of any gases. |
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Meet the moleculesThis table is from: http://chemistry.beloit.edu/Warming/pages/molecule.html
ppm = parts per million (106), ppb = parts per billion (109), ppt = parts per trillion (1012). * The Global Warming Potential (GWP) is used to contrast different greenhouse gases and provides a simple measure of the radiative effects of various greenhouse gases relative to CO2 defined as 1. Atmospheric lifetime is used to characterize the decay of an instanenous pulse input to the atmosphere, and represents the time the input would take to decay to 0.368 (1/e) of its original value. One hundred year time horizon GWPs and atmospheric lifetimes taken from Table 2.14, Intergovernmental Panel on Climate Change, Climate Change 2007: The Physical Science Basis, IPCC WG1 AR4 Report. See also http://cdiac.esd.ornl.gov/pns/current_ghg.html
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