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« The Crazy Gang | Main | Nordhaus and the sixteen »
Wednesday
Apr042012

Another rebuttal

Richard Betts points us to this paper by a group of climatologists who seek to rebut Richard Lindzen's talk at the House of Commons the other day. The authors are, in the main, familiar names. John Mitchell and Brian Hoskins featured regularly in the Climategate emails and both were involved in the coverups too; Eric Wolff made a couple of brief visits to BH in the wake of the Cambridge Conference last year, but was put off by the over-hostile reaction from commenters; Tim Palmer has been mentioned on the pages of BH a couple of times. Keith Shine is less familiar to me although he too has been mentioned before as one of the members of the Royal Society's advisory panel on climate change (as indeed are most of the others).

With my current focus on climate models, here's an interesting excerpt:

At every stage models should be evaluated by exhaustive comparison with observations. The models encapsulate our understanding of the basic science of the climate system, including for example, Newton’s laws of motion, the laws of thermodynamics and the quantum theory of radiation. When deficiencies are found at one level then improvements are sought and the lessons learnt should cascade to models at other levels. This is, of course, the ideal: the actual development of the science is rather more irregular but very definitely in this direction. Even the models at the more complete and complex end contain many uncertainties and deficiencies, which are widely recognised within the modelling community, but they are the best guide we have as to how the climate system may change in the future. Their results are not to be accepted in an unquestioning manner; they should be analysed in detail, with the dominant processes behind any climate variability and change thoroughly investigated using observations and simpler models in the hierarchy.

I think the words "out of sample" need inserting in a couple of places in that paragraph. I think it would also have helped if Hoskins had reiterated his earlier clarification about the limitations of climate models - namely that they are "lousy".

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    [...]- Bishop Hill blog - Another rebuttal[...]

Reader Comments (212)

Jorge: Apr 6, 2012 at 12:49 PM. "The second disc must also be radiating 100W from the inner face, all of which, must be arriving at the inner face of the original disc. This disc now has to radiate 200W to equal the 100W from the heater plus the 100W from the inner surface of the second disc."

Jorge, we started with 100W; now we've got 400W going to and fro just by introducing a passive disc. Where is the source of the extra watts?

Also, imagine letting the gap between the discs close up to make a single disc. The temperature of the original disc would then (apparently) suddenly drop from 243.7K to 204.9K at the moment of closure. Maybe the imagined "internal" temperature of the combined disc is still 243.7K where the original disc's inner surface used to be (perhaps).

Apr 7, 2012 at 12:45 PM | Unregistered Commentersimon abingdon

Whereas I don't really mind a little drift off-topic, as there are only a few of us left reading this, I have a personal prefence against daft thought experiments based on hypothetical situations which will not in any case translate to the real world.

Can't we find something to measure? What does the Trenberth budget look like with upgoing IR reduced by the amount of 'back-radiation'? If the net upgoing IR is reduced that way, rather than by proposing actual down-welling IR which really ought to be cancelled out, will there not be a lot of heat left at the surface which has to leave by convective or evaporative means? Is this what mydog is getting at, or have I got the wrong end of the stick? Please do not reply with an ideal black body in a vacuum thought experiment.

Apr 7, 2012 at 2:00 PM | Unregistered CommenterRhoda

mydogsgotnonose

I am sorry if I inadvertently posed a particularly difficult problem. My intent was to produce a very simple one!

However by the end of your post you had not actually shown your own calculation for the temperature of disc 1 and simply suggest that both discs will be near 204.9K.

Thank you for the link to the MIT page. They rather helpfully do a calculation of the heat transfer between the inner and outer walls of a thermos flask where both walls are at a different temperature. They calculate the heat flowing from the inner (hot) wall to the outer (cooler) wall using exactly the equation that I used apart from a modification that allows for the non-unity emissivity in their case. You will see that the denominator in their equation becomes unity when the emissivities of both surfaces are equal to one.

I am left with the conclusion that the only way to achieve a heat transfer of 100W from disc 1 to disc 2 is for disc 1 to be at 243.7K if disc 2 is at 204.9K.

You will, I hope, forgive me if I continue to use the equation provided by MIT rather than your assertion that both discs will be near 204.9.

To simon,

I have no idea where all the extra Watts come from but the calculations show that you will not transfer the 100W from one disc to the other without the temperature difference. It does seem odd that the difference would suddenly drop to zero if the two discs made a good thermal contact but the rules for conduction are not the same as radiation.

To everybody,

I apologise for going off topic and will move this to unthreaded if there is any interest in pursuing this rather technical exchange.

Jorge

Apr 7, 2012 at 2:10 PM | Unregistered CommenterJorge

Hi Barry (ref. Apr 6 at 10:46 PM), are you addressing your “ .. Please.. ! Why not always take this discussion to the discussion thread... ” to the moderator or to me? If the former then I always prefer to leave it to that person to complain (unless of course you are one of the moderators).

As for “ .. It allways dominates/distracts from the actual topic at hand .. ” I’d hardly say that one comment in 203 was dominating anything here.

Best regards, Pete Ridley

Apr 7, 2012 at 4:23 PM | Unregistered CommenterPete Ridley

Apr 7, 2012 at 11:18 AM | Registered CommenterMike Jackson

"Martin A
I must say "thermal impedance" wasn't a phrase I'd come across (which is probably hardly surprising!) but when I went a-googling there it is.
I think this probably has the best definition."


Thank you Mike. Of course thermal resistance is used everyday in calculating the benefit of thermal insulation - where things are pretty well linear and thermal flux is proportional to temperature difference.

Its use in thermal transfer by radiation as mentioned by MDGNN, where things are nonlinear, is something I had not come across.

Apr 8, 2012 at 3:14 PM | Unregistered CommenterMartin A

Martin A
I'm not sure about this, and as a non-scientist I'm probably asking a very stupid question.
Climate itself may well be chaotic since it consists of an almost infinite number of variables but would it not be fair to say that the variables themselves are linear to the extent that they must obey the laws of physics (or in this case, specifically thermodynamics)?
So is thermal flux not always proportional to temperature difference?
It seems to me that mdgnn's argument is that the Laws are to a large extent immutable and that climate scientists assume that "in this case it's different". Which is why I'm more or less on his side in this debate.

Apr 8, 2012 at 3:59 PM | Registered CommenterMike Jackson

Mike Jackson

There are many linear relationships between variables in physics but heat transfer by radiation is definitely not one of them.

This is an abstract from an interesting review of the history behind the fourth power law.

"Since the 1700s, natural philosophers understood that heat exchange between two bodies was not precisely linearly dependent on the temperature difference, and that at high temperatures the discrepancy became greater. Over the years many models were developed with varying degrees of success. The lack of success was due to the difficulty obtaining accurate experimental data, and a lack of knowledge of the fundamental mechanisms underlying radiation heat exchange. Josef Stefan,
of the University of Vienna, compiled data taken by a number of researchers who used various methods to obtain their data, and in 1879 proposed a unique relation to model the dependence of radiative heat exchange on the temperature: the T4 law."

http://webpages.uidaho.edu/~crepeau/ht2009-88060.pdf

This is the basis for the calculations I did on my disc example This has seemed to be fairly immutable up to now and I really think mdgnn is wrong to say the two discs will be nearly the same temperature. Having said that, it is true that the behaviour of radiation in gases is much more complicated, particularly when particles like cloud droplets or aerosols are involved. That kind of stuff is above my pay grade and mdgnn may be right in that area.

Jorge

Apr 8, 2012 at 8:14 PM | Unregistered CommenterJorge

Simon Abingdon, your questions are reasonable; indeed the second question is a particularly good one.

1) Where is the source of the extra watts? A reasonable question, but they don't actually need a source! This radiation is just bouncing around, not going anywhere: there is still just 100W coming in and 100W going out.

2) Also, imagine letting the gap between the discs close up to make a single disc... An excellent question: clearly when the discs touch they just merge into one and will form a single disc at the original temperature. But it seems physically unreasonable that there is a discontinuous jump from T2 down to T1 exactly when the discs touch: instead there must be some smooth transition between the two regimes which occurs when the discs are "near enough". So what defines near enough? Off the top of my head I would guess that this must happen when the separation between the discs is no longer large compared with the wavelength of the infrared radiation: the standard radiative picture will only apply in the far field limit when concepts like photons are good ones, and not in the near field limit where you would have to use some sort of direct EM coupling treatment. (As I said this is off the top of my head, but i doubt it's far wrong.)

Apr 8, 2012 at 8:45 PM | Registered CommenterJonathan Jones

@Jonathan Jones Apr 8, 2012 at 8:45 PM.

Thank you for your time and trouble in replying.

When you say "This radiation is just bouncing around, not going anywhere: there is still just 100W coming in and 100W going out", I cannot then see why the temperature of disc1 should be raised (and I'm assuming that such is indeed the case).

So you see I'm still struggling. (See the unthreaded exchange between Jorge and myself).

Apr 9, 2012 at 3:29 PM | Unregistered Commentersimon abingdon

@Simon Abingdon, thanks, I have replied on unthreaded.

Apr 9, 2012 at 4:48 PM | Registered CommenterJonathan Jones

Apr 8, 2012 at 3:59 PM Mike Jackson

So is thermal flux not always proportional to temperature difference?

Mike,

Thermal conduction is pretty well linear - the heat flowing through a wall is proportional to the difference in temperature between its two surfaces.

But thermal radiation is decidedly nonlinear. The heat radiated by a hot body is proportional to its absolute temperature raised to the fourth power, so it is very far from being proportional to the absolute temperature itself.

Apr 10, 2012 at 5:10 PM | Unregistered CommenterMartin A

So is thermal flux not always proportional to temperature difference?


[cont'd]

So if you have two bodies one at temp T1 the other at temp T2, close to each other, the net heat radiated from the hotter one to the less hot one involves a pair of terms, one with T1 raised to the power 4 and the other involving T2 raised to the power 4. So it is definitely not a case of being proportional to the temperature difference (T1 - T2).

Apr 10, 2012 at 5:13 PM | Unregistered CommenterMartin A

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