Gavin Cawley explains the radiative greenhouse effect

Here are 2 key issues that you must address when trying to defend the radiative “Greenhouse” hypothesis:

1. How does 240 W m-2 absorbed solar radiation get converted into 342 W m-2 IR back radiation without violating the Energy-Conservation Law?
2. Why there is such a POOR relationship between and global T for past 70 My?
  • Gavin Cawley Retweeted eli rabett

    The answer is still the same as the last time you ignored it

    Gavin Cawley added,

    eli rabett @EthonRaptor
    As Eli has pointed out many times, the 240 W/m2 is the solar input, not the energy the surface and the atmosphere exchange. 462 W/m2 enters the atm from the surface, 79 from the sun = 541 W/m2. 342…

    Gavin, this is not sensible answer to my 1st question, but a CIRCULAR argument! Can’t you see it? The 342 W m-2 IR back radiation cannot be explained by surface LW emissions, because then the question becomes, where does the 398 W m-2 surface LW radiation come from?

    I seem to remember I have already explained this to you at least once. Here is the thought experiment. Imaging a black body in a vacuum containing a 1W constant power heat source. Eventually it will reach an equilibrium temperature at which it radiates 1W out into the (1/n)

    vacuum. Now put a thin shell surrounding, but not touching the sphere, of the same blackbody material. The outgoing sphere will heat the shell, and it too will begin to radiate heat until it too reaches thermal equilibrium. Now the shell will radiate equally out into the (2/n)


    vacuum and inwards towards the sphere. As the sphere is now receiving 1W from the heat source AND the “back-radiation” from the shell, it must end up at a higher equilibrium temperature than in the absence of the shell. There is now an exchange of (3/n)

    radiation between the sphere and the shell, where the outbound radiation is in excess of 1W, because it also has to radiate away the energy received as back-radiation from the shell. You can make this radiation arbitrarily higher by adding more and more (4/n)

    shells. This doesn’t contravene any laws of thermodynamics as no energy is created (except that from the 1W heat source), just large exchange fluxes. In this thought experiment, the 1W heat source corresponds to the visible/UV radiation from the sun, to which the “shell” (5/n)

    of the atmosphere is transparent. (6/6)

But the troposphere isn’t a vacuum, so Gavin’s thought experiment needs to account for convection and latent heat transport, which together shift 2x the energy radiation does.

obviously doesn’t understand the purpose of a thought experiment, which is to present a very simple explanation of one aspect of the system under consideration, without extraneous detail, so that one aspect can be understood. If you want a fll model use a GCM.

Sadly in my experience, this is what happens pretty much every time I use a thought experiment in discussing climate on-line. It is almost as if someone is actively trying to avoid acknowledging the single aspect illustrated by the thought experiment! ;o)

It’s not any aspect of planetary atmospheres, because planetary atmospheres, by definition, are not vacuums. Your thought experiment is irrelevant (and misleading).

Do you agree that the physics of the thought experiment, as given, are correct?

Yes. Here’s a thought for the day. If the ‘atmospheric window is only 40W going upwards from surface, then it can’t be 340W going downwards from cloud base to surface as NASA and IPCC energy budget diagrams erroneously illustrate.

I’m glad you agree. So you agree also that the atmosphere, being warmer than absolute zero, radiates IR photons downwards to the surface? I’d be happy to discuss your digression later, provided you continue the discussion of the key point first.

A lot of the downward radiaton from cloud base is due to latent heat release from condensing water vapour, not surface LW emission being returned.

well duh! Do you agree that there is back-radiation from the atmosphere to the surface, yes or no?

“Well duh” doesn’t cut it Gavin. If a lot of the 340W at cloud base is due to latent heat release, then the atmospheric window is a lot bigger than 40W in reality.

Back radiation is due to the temperature of the atmosphere, the transfer mechanism that spreads heat through the atmosphere is irrelevant to the existence of back-radiation.

Yes, everthing radiates according to its temperature. And the atmosphere is at the the temperature it’s at due to the effect of the Sun and the pressure gradient causing adiabatic compression heating which impedes surface>air conduction

via Tallbloke’s Talkshop

November 2, 2018 at 03:59AM

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