George E. Smith's comment
This comment is from the same source as the Richard S Courtney comment but I feel it is well worth a read in its own right. George seems to write more directly to the layman than Richard. Or that is just my own bias showing.
Quote:George E. Smith says:
July 15, 2011 at 11:34 am
First let me say that Richard (S. Courtney) is much closer to this subject than I am, and further more, I don’t have any access to some teracomputer or any modtran calculations of what CO2 or any other so-called GHG such as H2O or O3 is supposed to absorb in the way of electro-magnetic radiation energy.
The news that such absorption of energy does not alter the atmospheric Temperature, is indeed a surprising revelation to me. But then I had always had this simplistic view, that “Temperature” was simply a measure of the purely mechanical energy stored in atoms or molecules (materials), by reason of the various modes of atomic or molecular “vibrations/rotations/translations/whatever”, so that Temperature has no meaning whatsoever in the absence of physical materials, and in particular is not a property of electro-magnetic radiation, as described by James Clark Maxwell, and his famous equations.
But every credible plot that shows the spectrum of incoming solar energy, outside earth’s atmosphere (air mass zero TSI of about 1362 W/m^2 (according to a recent NASA report), shows a nearly black body like curve corresponding (roughly) to about a 6,000 K black body Planck radiation curve.
But at the earth surface under normal incidence (air mass one), the spectrum is very different, although still somewhat BB like. The shorter wavelength regions (blue-green) are considerably attenuated evidently as a result of first, absorption by Ozone (O3); and please note, when I use the term “blocked”, I do not mean to the point of total extinction; only some photons are blocked, and in their case, it most certainly is to the point of extinction; those are permanently removed from the incoming solar spectrum stream. And of course there is the very important primarily Raleigh scattering of the blue-green region of the spectrum, which results in the day sky being blue, rather than black with stars.
This blue sky is itself instructive, because it converts a nearly collimated near point source of blue-green radiation (sunlight) into a nearly isotropic diffuse source of same spectrum radiation that fills the whole sky.
Moreover, as anyone who has ever flown to Hawaii, in daylight can attest, the blue sky looks the same looking down, as it does looking up. When you look up in daylight, the black sky with stars, is completely washed out by the blue scattered light. Well actually you can observe the stars n broad daylight, if you can just point your telescope to the exact direction of the star; they then become quite visible.
And when looking down, you do not see the black ocean (2% reflectance) or the wind blown white cap “stars”. Once again, if you can point your telescope downwards, and focus on one of those ocean stars, they too become quite visible.
The whole point of this explanation, is that any isotropic source of radiant energy looks the same from any direction. Skiers and other snow bunnies know full well what a white out looks like.
This is exactly why the isotropic thermal radiation (LWIR) from the atmosphere is a roughly 50-50 split of upwards, versus downwards. It matters not a jot, whereabouts in the altitude range some sample atmospheric layer is, the isotropic emissions from THAT layer split about 50-50, upwards versus downwards. There is nothing magic about that particular sample layer, when it comes to absorption and emission of EM radiations. The layer above, and the layer below, will do exactly the same thing; doesn’t matter whether we talk about a 100 metre thick layer of a 100 micron layer; its nearest neighbor layers, will absorb and emit pretty much the same.
But, as I pointed out, the upper layer (100 microns) is both colder, and lower density, as compared to the adjacent lower layer (100 microns), so the molecular or atomic absorption spectral lines or bands will be narrower for the upper layer, than they are for the lower layer. A given radiated spectrum, will be less gutted by a narrower absorption band above, than a wider one below. This near 50-50 split applies to every single layer, of whatever thickness, but the escape path upwards, is slightly favored, over the downward path, where recapture is more likely.
But the bottom line end result, is that about half of the total isotropic emissions from the atmosphere must escape to space, and about half will eventually reach the surface; with the caveat, that we are talking about radiation effects only. Other energy bled off as a result of thermal (heat) processes is a different isue.
So when the dust settles, ANY solar energy, that is extracted from the incoming nearly collimated sunbeam, by H2O,O3, or CO2, and is subsequently re-incarnated in some form as atmospheric LWIR emission, will have half escape to space, and only half reach the ground; which in my system of mathematics is ALWAYS a net loss of solar energy to the earth.
Water in any form anywhere in the atmosphere MUST always result, in a net loss of solar energy to planet earth; and you don’t need any modtran or teracomputer to see that. Clouds also, whatever they may do to LWIR radiation ALWAYS result in LESS solar energy reaching the surface, where it can be stored as part of earth’s energy budget. Nobody ever observed it to warm up in the shadow zone of a cloud. The Temperature always drops; it never increases; despite what LWIR from the surface may get returned from that cloud; ANY cloud, ANYWHERE.
And for the legal disclaimer; the intrusion of some other warm AIR mass from some other region is a convection process, and unrelated to solar energy blockage.
CO2 comes from coal, coal comes from fossilised trees, fossilised trees come from living trees, living trees growth comes from CO2 therefore coal is carbon neutral. ...from here