Correspondence with Pierrehumbert on Back Radiation

Here is a response on my letter to Raymond Pierrehumbert:

Dear Claes,

“Back radiation” is simply the name given to the downward infrared flux evaluated at the surface.  The flux computation (in any direction) proceeds directly from the Planck distribution, Kirchoff’s Laws, and measured emissivities of the atmospheric constituents.  These have been established beyond doubt, both by theory and measurements, so if you have come to a conclusion that “back radiation” doesn’t exist, there is clearly an error in your calculation, and I’m afraid I have other things I need to be doing and can’t take the time to plow through it and see where it is.  “back radiation” doesn’t exist as a concept distinct from radiation fluxes in general, so it is impossible to “disprove” its existence without throwing out the whole of radiative transfer theory as well — which is about as well established as the Newton’s Laws of Motion.  

There have been a great many fallacious arguments about back radiation that have appeared in the past.  The following blog post has useful citations to the literature on radiative transfer, and also some discussion of where some of the other attempts to “disprove” back radiation have gone wrong. 

http://scienceofdoom.com/roadmap/back-radiation/

Perhaps studying those will help you spot the error in your own derivation.

m.v.h.

—Ray Pierrehumbert

Here is my response and continued correspondence:

Dear Raymond:

Thanks for your answer. I understand that you base your climate science on a non-physical incorrect form of Planck's and Stefan-Boltzmann's radiation laws, where physical net heat transfer from warm-to-cold is artificially decomposed into two opposite transfers warm-to-cold and cold-to-warm. This is artificial as a procedure performed by symbols on a piece of paper, because heat transfer cold-to-warm violates the 2nd law of thermodynamics. If you do not make a clear distinction between symbolic manipulation and physics, gross mistakes can be made. 

The correct forms of Planck's and Stefan-Boltzmann's laws can only be understood by properly understanding the proofs of these laws. I thus ask you about your proof of these laws? What is it based on? What are the main arguments? I don't ask you to read my proof. I only ask you about your own. Since this is central to climate science and you represent the expertise, you must be willing to give an answer. 

Looking forward to your reply,

Sincerely, Claes

Claes,

If you think you have a theory of radiative transfer that gives completely different results from that developed by Planck, Einstein and Chandrasekhar, you’d better be ready to show that it can account for the way stars shine, their photospheric temperature, the cosmic microwave background radiation, the successful retrieval of temperature in the atmosphere by satellite measurements of outgoing infrared and microwave radiation, the successful match of the spectrum of OBSERVED downward radiation flux to the ground and about a hundred thousando other ways that radiative transfer is applied throughout physics — and not just in climate problems.  Again, I urge you to study the basic physics and take another look at your derivation to see where you have gone wrong. Until you do, there is no point in continuing this discussion.

—Ray Pierrehumbert

Dear Raymond

I asked you about your proof of Planck's and Stefan-Boltmann's laws, but did not get any answer.

So I repeat my question. I don't think that you as leading climate scientist are in a position, where you can simply close the discussion without giving a proper answer to my question.

Looking forward to your reply.

Sincerely, Claes

From Pierrehumbert:

Oh for goodness sakes, “my” proof of Plank’s radiation law (and Kirchoff’s law) is no different from Einstein’s or the proof you will find in any elementary statistical physics textbook. Let me put this in the simplest terms I can:  a body with a temperature radiates.  In local thermodynamic equilibrium the radiation emitted is isotropic. That means some of the radiation flux is downwards. The sum of all the downward radiation flux reaching the ground from each layer of the atmosphere is what is commonly called “back radiation” it depends only on the temperature and composition of the atmosphere, and is completely independent of how the atmospheric temperature is maintained.  In particular, it  doesn’t require you to keep track of what happens to the radiation emitted upwards from the ground (that’s part of the separate computation of what maintains the atmospheric temperature.  

If you are underneath something with a nonzero temperature that has a nonzero emissivity, it is going to warm you. You will experience the downward flux. This is routinely measured at any number of observing stations around the globe (for references see the link I sent you earlier).  If you think you have a way of making the emitted thermal radiation anisotropic, good luck with making that consistent with the observed properties of the Universe and the objects of which it is composed.  

For the record, while back-radiation is important in determining the surface energy balance of a planet, the greenhouse effect can be understood more simply in terms of the top-of-atmosphere energy budget (which is purely radiative), and the vertical structure of the atmosphere as determined by the adiabat. (As explained in Ch. 3 and 4 of my book, Principles of Planetary Climate).  

Please do not expect any more correspondence from me. I’ve already put more time into this than I can spare.

My answer to Pierrehumbert:

OK Raymond you refer to Einstein, but he did not give any proof of Planck's and Stefan-Boltzmann's laws (including back radiation). You say: A body with temperature radiates. I ask you: Radiates into what? Into an environment at 0 K? Into an environment at higher temperature? After insisting heavily that "back radiation" is real, you take a step back and say that after all the "greenhouse effect", does not depend on any "back radiation". What is the logic? 

Raymond, what you are saying does not make any sense, and I understand that you cannot continue the discussion. But you cannot stop the world nor scientific evidence:  "Back radiation" is non-physical illusion. How come you invest all your money into such a hopeless non-physical idea, which not even Einstein did embrace?  

It may well be that we will meet in person in connection with the new statement on the scientific basis of climate change to be issued by KVA/Henning Rodhe, and then the discussion will continue.  

Sincerely, Claes

Summary: 

Pierrehumbert does not answer my question. The only reference given is to the blogosphere http://scienceofdoom.com/roadmap/back-radiation/. The derivation of Planck's law by statistical physics says nothing about back radiation. I think that it is possible to properly understand the meaning of a mathematical theorem only if you know a proof and a physical law only if you know the arguments behind the law. To read a physical law like a lawyer reads a judiciary law seeking the meaning by inspecting the symbolic wording, can easily lead to misinterpretation confusing symbols with physics. This mistake is done in the case of "back radiation". A related logical fallacy is to say that if Einstein's or Planck's proofs say nothing about the non-existence of "back radiation" as physical reality, then it follows that "back radiation" is a real phenomenon. This is an elementary form of "argumentum ad ignorantiam"; the less you know, the more sure you can be that you are right.

PS See later post on phlogiston theory and "back radiation".