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A post (below) on the Bishop Hill blog relating to climate change asserts that no warming effect can be attributed to CO2. I don't know whether the author is really a physicist but it sounds impressive (Plank spectra and black-body radiation etc). Can someone explain in layman's language whether the assertions are valid.

Quote from http://www.bishop-hill.net/blog/2012/4/5/greenhouse-reversal.html

There is no greenhouse, so it can't be reversed.

Many so-called skeptics are not really basing their arguments on the true
physics of the atmosphere. By failing to do so, they are demonstrating
that they also have fallen for the IPCC bluff that radiation from a cooler
atmosphere (including so-called backradiation, but also initial radiation)
can transfer thermal energy to a warmer surface.

This is not correct physics and the sooner this is made clear to the
public the better. True physics, backed up by basic phenomena such as the
fact that radiation in a microwave oven is not absorbed in the usual sense
of the word, shows why this is the case. No one has ever proved anything
to the contrary in any empirical experiment, and never will.

The only thing any such radiation from the atmosphere can do is slow down
that third or so of surface cooling which occurs by way of radiation that
does not escape to space via the atmospheric window. Radiation from the
atmosphere can have absolutely no effect on evaporative cooling, chemical
processes or sensible heat transfer. These non-radiative components plus
the radiation to space make up about 70% of all surface
cooling. Furthermore, the effect of carbon dioxide with its limited
frequencies is far less than a true blackbody, and less per molecule than
water vapour. No gas can radiate outside its Planck spectrum (ie more than
a true blackbody) and so there is no way that carbon dioxide (1 in 2,500
molecules) can contribute a very large amount of radiation anyway.

The other cooling processes merely accelerate and compensate for any
minuscule slowing of radiative cooling. Thus there is absolutely no
warming attributable to carbon dioxide. It is time for sceptics to get
their facts right and stop giving in to part of the hoax. Only truth will
prevail in the long run. 

EDIT: The author of the blog post was 'Doug Cotton', who has published a related paper at http://principia-scientific.org/publications/psi_radiated_energy.pdf and has a website at http://climate-change-theory.com/

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If you want answers drawing from a credible source, we can have this migrated to Skeptics.SE.. –  Manishearth Apr 8 '12 at 17:24
    
I imagined that a forum inhabited by physicists was the most credible source :-) The statements above seem so authoritative and are stated from the perspective of a physicist (apparently). Since physics is by and large a matter of fact not opinion, I wondered if the statements above are really fact or fiction. –  William Morris Apr 8 '12 at 18:10
    
(1) we're not a forum. Beware, you may be banned for saying that ;-) (2) Yep, but climate change can get controversial, and IIRC opinion is divided on it, even within the physics community. And the opinion guides the fact that'sused :/ .Skeptics.SE would have given you a referenced answer--then again, it wouldn't be hard to find comtradictory scientific publications--and might look at it neutrally. –  Manishearth Apr 8 '12 at 18:46
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Oh come on, nobody gets banned for calling this site a forum ;-) (although of course we'd prefer you didn't). And welcome to Physics Stack Exchange, William! Like Terry said in his answer, kudos to you for asking for a review of the claim. –  David Z Apr 8 '12 at 19:00
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@manishearth: there really isn't any division or controversy over the basic facts of climate change. The idea that any controversy exists is purely a political fabrication. The details are certainly complex, but the fundamental rules of thermodynamics and absorption spectra have been settled science for over a century. –  Colin K Apr 8 '12 at 19:14

2 Answers 2

up vote 4 down vote accepted

The article you quoted frankly reads very poorly. It quotes a lot of stuff without once noting that greenhouse effects absolutely are real and critical to the earth being habitable. I don't know who this fellow is, but if he posted here directly I'd give it an instant negative vote.

You, sir, I'm giving a thumbs up for taking the trouble to ask in a forum where you are likely to get some answers. More people should do that when they hear odd science claims!

Now, with that said, it's absolutely true that both carbon dioxide and methane are bit players in the overall greenhouse effect.

The main greenhouse is water vapor, by about two orders of magnitude. My recollection without looking it up is that 97 to 98 percent of the greenhouse effect is caused by water vapor. This is why it gets so cold in the desert at night, for example.

The Nobel-prize winning models for global warming do not invoke direct warming from carbon dioxide. Instead, they postulate and model using computer programs the idea that the very small additive impacts of carbon dioxide, methane, and other minor greenhouse gases throw off the balance of the major player, water vapor. I do not know how they do that part of the model. It has to be complicated, since water vapor levels vary with near-fractal complexity from day to day and from region to region.

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Thanks for the reply. I have added some references I found to other work by the blog post author. –  William Morris Apr 8 '12 at 20:50
    
But certain geologists disagree on the fact that the present increase in global temerature is because of increase in greenhouse gases. They say that earth actually have a cycle of heat and ice ages. So, what we are seeing is actually those rather than an effect of greenhouse emission. –  Vineet Menon Apr 9 '12 at 6:16
    
I have doubts about your numbers and corresponding picture you paint here. If we go by the most widely accepted IPCC scenarios and models, then the radiative forcing from CO2 alone contributes about 1 degree C. Although there are contributions from other gases, this is over half of the total anthropogenic forcing value. Then water vapor has the effect of increasing this to 5-7 degrees C. This corresponds to 700-800 ppm CO2 and can be verified with Wikipedia and 10 cells of calcs in Excel. Now, this is my conceptual picture and I think it conflicts with what you wrote. –  AlanSE Apr 9 '12 at 13:19
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Hey, Terry--- you're answer is good, +1, but the CO2 is not negligible, as AlanSE says. Could you modify it a bit? You can get rough estimates for CO2 impact from ice-core data, and they match observations from human-generated CO2, so the complicated models are not necessary. But they do give confidence in the projections of warming, and the location of the warming. –  Ron Maimon Apr 13 '12 at 20:19
    
Ron, will do, I'm not happy with my lack of specs either. I've read papers that had specifics on relative roles and recall what they looked like, but I need to dig them up and find out the details. The ones I saw were not from the ice core data - those are absolutely fascinating for multiple reasons - but from a physical properties analysis. Sometime this week; I won't be happy myself until I can recover the specifics of what I was paraphrasing from memory. –  Terry Bollinger Apr 16 '12 at 2:46

Let's look a bit closer at the claims of Doug Cotton, and of Claes Johnson, whose work Doug relies upon. It's important because this is one of the strongest claims made by those who choose to reject the notion of anthropogenic climate change.

Here's the core claim, from Doug Coton:

The assumption is made that so-called "backradiation" from a cold atmosphere is able to transfer thermal energy to a surface which is warmer than the source of the radiation. This is a physical impossibility as is proven theoretically by Prof Claes Johnson and empirically by Prof. Nasif Nahle

The claim, contradictory to over a century of thermodynamics, is that a body will only radiate heat towards bodies colder than it, and never towards bodies hotter than it. Note that this is not a claim about net heat transfer, but about any radiated heat.

Apparently, this happens through the following mechanism according to Professor Claes Johnson:

[a body] reads the temperature of the surrounding from its spectrum, and then decides to cool or warm depending on its own temperature

The Johnson/Cotton theory is that almost everyone other than them misinterprets the Stefan-Boltzmann Law, and that there is no such thing as photons of infra-red radiation.

And the problem with all of this is that this is an extraordinary claim that lacks any evidence at all. Thermodynamics, the theory of photons, and of black-body radiation, have all made astonishingly successful predictions, and are supported by many decades of empirical evidence.

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Thanks. I'd also got the feeling from reading Cotton's paper that he is not to be taken seriously, but I don't have the theoretical background to contradict his claims. However, common sense leads me to think that the atmosphere will radiate in all directions, including towards the earth, whatever their relative temperatures, so his claim that the earth cannot be affected by the CO2 in the atmosphere is clearly nonsense. I've seen various discussions indicating that the anti-warming community rejects his thesis too. –  William Morris Apr 9 '12 at 21:57

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