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Water vapour overlooked as greenhouse gas ?

  1. Feb 9, 2006 #1
    Hello all
    It seems that water vapour doesn't figure in greenhouse gas calcs & global warming. This site claims..
    "Water vapor overwhelms
    all other natural and man-made greenhouse contributions."

    Are they right ?
  2. jcsd
  3. Feb 9, 2006 #2
    Hi Robin and most welcome here,

    No water vapor is not overlooked. Actually it’s a very *hot* issue. The guys of that site are probably exagarating a little. Here are other data:


    The global warmers know those properties of water vapor very well. The assumption is positive feedback. If there is more CO2, it gets warmer due to GHG effect, so more water evaporates, so more greenhouse effect and more warming and hence... Positve feedback is thought to be seen in the ice cores and during volcanic eruptions. But the story is probably a lot more complicated.

    The problem with this positve feedback is saturation and the latent heat. Saturation means that even when a lot more greenhouse gas is added, the effect will not increase that much, because most of the effect is already there. next, the latent heat is taken up during evaporation. So more water vapor also means more (latent) heat removed, this tempers the feedback. Then, when the water vapor condenses again, the heat is released but mainly to non radiating normal gasses in the atmosphere, N2 and O2, unable to radiate the heat and hence not contributing to the greenhouse effect. Secondly, the clouds that are formed increase the albedo, are decreasing the warming on Earth. So all in all the water vapor apparently has a nett negative feedback, reducing the already negliglible effect of greenhouse forcing due to CO2.

    It's the lack of clouds (and consequently change in reflecivity – albedo) that causes global warming as you can see here:

  4. Feb 10, 2006 #3


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    I think water vapor's GHG power is totally overlooked by most of the public that believe what they hear on the news.
  5. Feb 13, 2006 #4
    I believe the whole idea that we'd ever have to worry about greenhouse gases is bunk. We don't have a dense enough atmosphere for the gases to affect the temperature. I think it's silly that we're still pursuing the idea that these gases can trap light energy instead of reflecting it, because our sun gives off way more energy in other forms as well.
  6. Feb 13, 2006 #5


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    They do, but if I'm not mistaken, the question is by how much? Do they have a noticeable affect, or almost none?

    Like what? CMEs?
  7. Feb 14, 2006 #6
    No, I meant it gives off a lot of other energy in it's day to day radiance, most notably electricity. :tongue2:
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