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Discussion > Where has all my Back Radiation gone?

I had a bad dream last night. I dreamt I was a born again 100% non sceptical warmist zealot tasked with preparing a presentation showing the effect of back radiation from CO2 on Global Warming.

I'd start with Trenberth's cartoon showing that energy flux at the surface of 390Wm^2 is some 40% greater than insolation of 240Wm^2, and that this is all simply explained by Back Radiation from CO2.

A quick look at the properties of CO2 would show an emissivity of 0.001 [for a presentation I'll call this 0.01] and, being a gas, emitted radiation [stick to Back Radiation] would be in all directions with perhaps at best 10% having any meaningful interaction with the surface.

I'd set up the model with 1m^2 of the surface radiating with a flux of 240Wm^2

To demonstrate the principle I'd initially assume emissivity of 1 - or better still represent CO2 as a perfect reflector with 100% of Back Radiation directed to the surface.

Obviously the reflector must be less than 1m^2 or I'd end up with 480Wm^2 so I'd have to resize it to represent the atmospheric concentration of CO2 of .039% which leaves me with a reflector size of 0.00039m^2.

This means a Back Radiation of 0.039% of 240Wm^2, that is 0.0936Wm^2.

Multiply that by emissivity of 0.01 and multiply by 10% to allow for the multi direction nature of the 'Back Radiation' and I end up with a total Back radiation of 0.0000936Wm^2 [0.000039%].

Bugger!, Where has all my Back Radiation gone?

I started out looking for 40% and end up with nowt.

Apr 21, 2012 at 9:05 AM | Unregistered CommenterRKS

Since you moaned that nobody took you up on your thread:

You have made three basic mistakes which misrepresent your case:

1. Treating CO2 as a reflector. It is not.
2. Equating proportion of flux with concentration of CO2.
3. Assuming only 10% of back radiation reaches the surface


1. CO2 does not reflect LWR. It absorbs it, and either re-emits it, or the energy is converted to heat (kinetic energy) by collision with other air molecules. We know it doesn't refelct it because if it did, the spectrum of wavelenths would resemble that which is emitted from the surface (almost black body planck curve) - but it does not - it shows radiation only in the bands of emissivity for H2O and CO2 and minor components from other gases.

2. Things emit photons according to their temperature. CO2 at a certain temperature emits a certain flux of energy according to that temperature, not its concentration within some other enert gas. If you had one molecule of CO2, it would be emitting at the same flux level as a cubic meter, as a million cubic meters. You cannot multiply flux by the concentration of CO2. You have misunderstood flux, which already contains a term for area which removes the size considerations. Your adjustment of your 'reflector' size to compensate for low concentration has no basis in reality.

3. In an atmospheric energy model, there are only two directions which matter - up and down. What escapes to space, and what is bounced back to the surface. You have assumed that in any 'reflection' event (actually an absorption and re-emission) that 10% of the time the direction of the photon will be towards the ground. This is correct. Unfortunately for yout thesis, the ones going out sideways (not aimed at the ground) are absorbed by other molecules, which then re-radiate it. Eventually, the photon either hits the ground again, or escapes into space. The sideways ones count towards both of these.

May 23, 2012 at 3:55 PM | Unregistered CommenterTheBigYinJames

May 23, 2012 at 3:55 PM | TheBigYinJames>>>

You didn't read what I actually wrote James, you must use your imagination to take part in the mind game.

I used an a ridiculously large imaginary value for emissivity, and then suggested that instead of relying on emissivity we might imagine the result if we actually used a mirror to reflect ALL surface radiation.

If you don't see the mind game you won't understand the post.

All properties are maxed to the impossible to see what happens.

And of course don't forget in reality that only 8% of surface radiation lies within the main CO2 emissivity wavelength band.

As I said on another post, if you can get that 8% to increase surface flux by 40% you're onto a pretty good energy source,

May 24, 2012 at 12:22 AM | Unregistered CommenterRKS

All this mind games stuff... you're not David Icke are you?

OK, Hottel is my achilles heel, I admit it. There is something wrong with his maths, but I can't see what it is. The reason I doubt his maths is because we can measure the amount of CO2 emitted flux and it's way way above what his straight emissivity and partial pressure calculations would suggest.

This suggests that either the measurements are wrong due to instrument design (mydogsgotnonose) or there's something wrong with the conclusions drawn from Hottel's formulae. I have a suspicion his effects are based on a unit of gas, e.g. 1m^3, and are not scaled up properly to a 15km atmosphere, but I can't prove it. There was a long long LONG thread on this at scienceofdoom where they argued over a difference in the partial pressure units, which were out by a factor of 1000 depending on which side you believed.

May 24, 2012 at 8:35 AM | Unregistered CommenterTheBigYinJames

TBYJ "The sideways ones count towards both of these." Also the up ones. An outward bound photon in the lower troposphere has to run the gauntlet of billions of H2O and CO2 molecules to get to the upper atmosphere. It is far more likely to end up back at the surface than to escape.

RKS Only 8% may lie within the main absorption band; but that is already saturated. Additional warming due to additional CO2 is - I believe (don't quote me) caused by more efficient absorption in the other, partially absorbed, wavelengths.

May 26, 2012 at 5:51 PM | Unregistered Commenterlogicophilosophicus

Let's simplify it

Carbon dioxide, CO 2 is not pollution of any kind.
Carbon dioxide cannot do what is claimed by government and Greens.
It is impossible for humans to control carbon dioxide levels in the air.
To attempt to control carbon dioxide levels in the air is futile.
It is an act of selfish, weak, cowardly stupidity to lie to divert funds from real environmental
and humanitarian needs. It is shameful and inhumane.

Jun 18, 2012 at 10:48 PM | Unregistered CommenterDAVID SPURGEON