flacaltenn
Diamond Member
This is an hilarious thread! Could gslack be any dumber? And I see Old Rocks still doesn't understand the difference between warm and warming.
Hey flac- I have a more serious question for you. Why do you think the speed of the CO2 molecules in the atmosphere affects the absorption/emission spectra? Blackbody radiation is a function of the average kinetic motion of all the molecules (temperature) but specific ab/em is based on the molecule itself. Other than slight momentum transferred (entropy is always hiding in the background) specific transfers lose no energy and 'slightly linger wavelenths' are not an option.
Missed your post Ian.. Some troll recently uncovered it for me..
I don't know that it affect the spectra of emission/abs. But speed is related to the Kelvin Temp of the gas molecules, and thus emission rates. Thus it's the other way around perhaps.. A hotter gas travels faster and emits MORE than a cooler gas.
If there's any shift in spectra -- it's tiny due to Doppler of motion and negligable -- but maybe I'm overlooking something.
BlackBody doesn't apply to a gas molecule, If it DID --- a shift in Kelvin Temp WOULD shift the emission/abs spectra slightly as shown in the traditional graphs. For a gas -- those lines of em/abs are fixed by atomic alignment. (I think)..
All objects emit blackbody radfiation. Even a GHG free atmosphere would warm the surface. Should we split hairs by considering BB radiation to be a product of conduction? Slightly inelastic collisions that produce radiation according to the kinetic speed of the participants?
Anyways, the surface absorbs all BB radiation directed at it from the atmosphere but the reverse is not true. GHGs increase the amount of surface BB radiation absorbed, and if a collision occurs with an excited molecule then that energy is added to the thermal total. Otherwise it gets spit out inn a random direction, some escaping and some returning to the surface.
We know by experiment that the 15 IR is absorbed to extinction in roughly ten meters. I would like to know how quickly it gets totally thermalized. I cannot see the mechanism by which runaway warming would occur. The eight percent of surface BB radiation that is affected by CO2 is already stopped within the first few tens of meters. Any further dispersion would be superfluous. The bottleneck is near-surface and countered by water transporting the energy to the cloud tops where air density negates much of the ability of CO2 to stop radiation produced by the releaase of latent heat.
Just sayin'.
I'm not doubting that gases have the ability to radiate.. It's just that RIGOROUSLY -- they are not BBodies.. In fact, rigorously, the earth is a GREY body because it reflects some of the incident radiation.. In fact most diatomic gases are completely transparent to the IR emission band of the Earth.
If the 15 IR has such a short pathway -- must be due to water vapor, no? And that is a variable that's hard to isolate.. I doubt CO2 alone could extinguish that frequency at 50 meters. And just because it's been thermalized at a short distance, doesn't mean it isn't acting as an insulator to "re-radiate" at 15 IR further up into the atmos.
We know that there is only about one and half bands in the CO2 emission spectra that ISN'T covered by water vapor. In essence --- CO2 becomes the "free safety" of the defense.. The last man between that emission band and the dark of space. So you STILL have to calculate the amount of stopping power at those bands NOT covered by water vapor. (although they are at higher frequencies where Earth BBody emission goes down.. )
I'm doubting the few "tens of meters" number because I glanced at the absorpt. charts and the 15u IR band for CO2 is about 1/2 covered by water vapor.
But you are wise to question the thermal absorption power of a gas that has only 4 or 5 effective frequencies of absorption..
Tell me -- is the 8% the calculated amount of radiation CAUGHT by CO2 over the entire emission spectra of the Earth Surface? Because I could easily believe it's that low and that more of the Greenhouse is water vapor than has been estimated.
BUT IN THAT CASE --- the 8% number already INCLUDES all of the absorption from CO2..