Just Wondering

This is a comment from Anthony Watt’s blog.

Arthur Glass (03:11:29) :

Not immediately germane, but if hydrogen powered engines emit H2O, aren’t they worse polluters than the internal combustion engine, since water vapor is a much more powerful ‘greenhouse’ gas than CO2?

http://wattsupwiththat.wordpress.com/2008/06/24/reader-poll-james-hansen-calls-for-trials-of-energy-executives-what-next/#comments

For some background into atmospheric absorption efficiency of common gases compared to the  electromagnetic spectrum, this graph is valuable:

spectral_absorption click on graphic to enlarge.

Note the CO2 peak at 15 microns is the only significant one, as the 2.7 and 4.3 micron CO2 peaks have little energy to absorb in that portion of the spectrum.  But the H2O (water vapor) has many peaks from .8 to 8 microns, two that are fairly broad,  and H2O begins absorbing almost continuously from 10 microns on up, making it overwhelmingly the major “greenhouse gas”.

Source:http://wattsupwiththat.wordpress.com/2008/06/21/a-window-on-water-vapor-and-planetary-temperature-part-2/

 

Water vapour

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3 Responses to Just Wondering

  1. Josh says:

    Ha ha! That\’s funny. A couple more points to consider:1) H2O is the dominant GHG in large part because of volume. As I\’ve heard you mention before, by volume it\’s at about 90% of the GHGes. A bit harded to make a dent in that number, especially when you\’re competing against oceans. (Also, at 90% of volume it\’s only 40-70% of the total effect, while CO2 is 9-30% at 10% or less by volume.)2) H2O shelf life is measured in days, where CO2 is in decades or centuries. H2O leaves the atmosphere pretty quickly.3) H2O doesn\’t go up past the tropopause (8-16km) – too cold. It condenses and falls back into the ocean. CO2 can go much higher.Do those have any effect on your wondering?

  2. David says:

    Clicked on "no name " to reach Josh\’s space. Hi Josh.
    The entry wasn\’t saying that CO2 was dominant because of volume but because of the physics as displayed in the graphic.
    The quote above is from Anthony Watts.
     
          "Note the CO2 peak at 15 microns is the only significant one, as the 2.7 and 4.3 micron CO2 peaks have little energy to absorb in that portion of the spectrum.  But the H2O (water vapor) has many peaks from .8 to 8 microns, two that are fairly broad,  and H2O begins absorbing almost continuously from 10 microns on up, making it overwhelmingly the major “greenhouse gas”."
     
    The part about the water vapour from fuel cells is, of course, just a joke to brighten your day.
     
     
           

  3. Josh says:

    Poe\’s Law. Hard to tell the jokes from the serious when the serious is just as silly.

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