An interesting paper that asserts the use of “Back Radiation” is in error. ( H/t to JWR in comments on WUWT
It’s long, but I think it is worth it. The author uses a lot of exclamation points, which is a common habit in non-native speakers of English from some particular cultures, but do try to get past that. The math looks right to me.
http://www.tech-know-group.com/papers/IR-absorption_updated.pdf
He also uses a ‘shorthand’ where several terms in T^4 are presented as a single symbol. Yes, it makes the writing more compact, but for those of us who do ‘visual thinking’ we can’t just see the 4th power in the equations and have to keep remembering it…
Some selected quotes:
Introduction
It has been argued by Claes Johnson that what is called in climate circles “back-radiation of heat” is not a physical phenomenon. [1, 2, 3] Heat flows and radiates spontaneously only from warm to cold. The fact that for some cases between two plates e.g. the surface of the earth and the representation of the atmosphere by one single slab, the formulation for heat flow with the non-physical back-radiation of heat gives the same temperature distribution as the formulation with the correct interpretation of the law of Stefan-Boltzmann (SB), makes some people to believe that backradiation of heat exists and heat can flow spontaneously from cold to warm! It will be shown in this paper that in the one-slab model for a semitransparent atmosphere with the so-called two-stream formulation and thereby back-radiation of heat, a spurious absorption occurs, twice as high as compared to the one-stream formulation from warm to cold according to the Second Law of Thermodynamics.
A simple proof of the fact that back-radiation of heat does not exist!
But hasn’t ‘back radiation’ been measured?
Still others claim that they have measured back-radiation of heat!
Claes Johnson [4] has argued that pyrgeometers do not measure heat fluxes but rather frequencies which can be related to temperature. A micro-processor converts the signal by means of SB to Watt/m^2: it is called “back-radiation of heat” from the colder sky to the warmer surface of the planet! See also Douglas Cotton [15]. In a blog by John O’Sullivan [5] are reported discussions between IRthermometer manufactures and Alan Siddons and the experiments of Nasif Nahle.
We conclude that back-radiation has not been confirmed experimentally.
About 1/2 way down the paper the author finds a way to calculate heat flow that happens by ‘means other than radiation’ in a semi-transparent atmosphere. (It’s a somewhat impressive feat… but one where I’m still looking at the formulas to try to find an error as it just seems a bit counter intuitive that you can calculate that from a radiation oriented model… but I’ve not found an error… yet…)
Note the scale difference of the x-axes in the two figures: the IR-sensitive trace gases emit to higher levels and to outer space about 10 times the amount they absorb! The difference is transferred by molecular collision from the 99% bulk of the atmosphere to the IR- sensitive trace gases. That heat arrives at the bulk of the atmosphere by “mechanisms other than radiation”! As we will see later, about 60% from the surface by convection of sensible and latent heat and the other 40% by absorption of SW sunlight by aerosols at different heights of the air column (see also appendix 2). If there were not an atmosphere with a lapse rate defined by thermodynamics
All in all, an interesting paper.
And one that, should it stand up to close inspection, will likely become a bedrock paper of the “convection and evaporation does it” folks.
The whole notion of “Back Radiation” always annoyed me. First off, there’s that Second Law problem of heat flow from cold to hot. Then there’s just this feeling that the wave function of a particle trying to emit a photon is not going to be happy doing an overlap with an incoming photon / wave function of ‘back radiating’ heat without just rejecting the whole thing. Yes, you can end run around that with the assertion that the outgoing comes from one molecule while the ‘back radiation’ is absorbed into some other molecule and then ‘they talk’… but that just ignores the implications of the ‘two slit’ experiment that the wave functions have more geographic coverage than that ( i.e. go through both slits with wide physical separation… at least until ‘observed’.)
So that whole ‘back radiation’ idea just seemed wrong to me. The flux of photons / wave functions would be too high (especially in a multi layer system) and just the flux density ought to lead to paradox issues or some kind of ‘symptom’… (unless one does a lot of ‘hand waving’…) Intuitively it just feels right to think that nature works on a ‘net net’ basis and doesn’t shovel vast numbers of wave functions back and forth waiting for a solution to be observed… Then again, Q.M. can be very non-intuitive…
At any rate, the paper deserves inspection.
Musings from the Chiefio 
Anyone who thinks “back radiation” isn’t real is merely displaying his ignorance. The Schwarzschild equation is firmly established as the basic theory of radiative heat transfer; it is as solid a theory as there is in quantum mechanics. Get over it! And the theory isn’t even that hard to understand for anyone who has studied physics. Next I’m gonna hear that you think Darwinian Evolution is “just a theory.” :)
[Reply: Well, they are all “just theories”. Some much more founded than others. Take that Schwarzchild equation. Works well in Q.M. Now explain why Q.M. doesn’t ‘play well’ with General Relativity. Or just take the “double slit” experiment. Explain please how the particle, or wave, or wavicle, or partiwave, or whatever it really is; can be both “going through both slits” and “only going through one slit” and how it can change upon observation. Explain how it can propagate BACK in time to BEFORE the moment of observation. (That fun little bit was recently demonstrated…) So the simple fact, unpleasant as it may be, is that we really have no clue what reality is made of, or how it works. We have two very nice theories that give some predictability in some contexts; and are mutually antagonistic. Oh Dear, as they say…
Per Darwin: In fact, his theory of evolution is “just a theory” and has two very simple “misses”. One real and demonstrated, one hypothetical.
First off, gradual evolution of species doesn’t cover the great leaps in speciation. Sorry, just doesn’t. Something is missing. Now I think I know what that something is, but I could be wrong, and it’s not in Darwin’s Theory anyway. I think it’s inter-species hybridization and transgenic gene migration. Lots of recent work support those two, yet by definition the biologist say that an inter-species hybrid can’t be a “new species”, so they’ve defined themselves out of natures playground… ( Look at the genome of archaea, then some of the bacteria and plants. There are HUGE chunks of “out of place” genetics only well explained if you allow for one species to have ‘picked up a chunk’ from another species – or entirely different kingdom in some cases. It’s a bit “unexplained ooopsy” in evolution…) It is highly likely that humans are just such an inter-species hybrid. It is absolutely the case that the mustards / cabbages / turnips are collective such a product (see the “Triangle of Wu”). Yet it is not part of Darwin’s Theory. Meaning his theory is flawed (at best).
Now, the other minor problem: It’s theoretical, but quite possible to have “directed genetic modification”. We are presently doing it wholesale to crops and farm animals. Nothing AT ALL prevents the History Channel Wet Dream Space Aliens Made Us image of our development. Yes, there is little to no evidence for it. But lack of evidence is not evidence of absence. We have many ‘legends’ or ‘myths’ (some call them “religion” in some cases) that say advanced beings came down from space and fiddled with the local primate genetics to “make us”. You can put some various interpretations on those written records. (From ancient “sci fi”, to mythical fantasy, to God Did It, to Space Aliens really did come and this is the best write up the locals could make.) But nothing prevents that from being a “possible”. In which case Darwin’s Theory will take another hit.
So, just like Q.M. and General Relativity, Darwin’s Theory does cover part of the case rather well. Species DO slowly drift over time in response to outside pressures and genetic mutation. But it fails dismally on the “great leaps” of genetics. While I think the answer is “interspecific crosses”, we can’t rule out “directed development”. That, BTW, is why I firmly support teaching “Intelligent Design” in Science classes (though I’d put emphasis on the potential for Space Aliens as as a thought device – they are an hypothetical example of ‘intelligent design’). Because it would demonstrate just how to approach ANY theory, even Darwin’s Holy Evolution Theory. Toss crap at it and see what sticks. NOTHING is so Holy as to be above imaginative and rational questioning. No questions, you never learn anything. (What would we learn? I have no idea. Perhaps that interspecific hybrids are absolutely critical to the “punctuated equilibrium with drift” that is evolution. Or perhaps that a million years ago some wandering Space Aliens with a sense of humor mixed some chimps genes with Orangutans and amped up the brain size just because they were bored. Or maybe even that neither of those is enough and something more Divine is needed to make all the bits fit. See, that’s the thing about knowing that ALL theories ought to be open to challenge. You don’t presuppose to know what the “right answer” will be…)
So back at the point of my post. Since we don’t really know how the parti-wave / wave-icle gets through two slits by only passing through one, nor how it communicates backwards in time to tell itself what to do AFTER it is observed… we can’t really know that something similar isn’t happening with “back radiation”. (In fact, I’d be astounded if it didn’t. How could the same parti-wave photons that do that trick with two slits NOT do it with two ‘surfaces’?…) So I could easily imagine a case where the “back radiating” wave function “communicates” with the “out radiating” wave function and they just agree not to violate the 2nd law of thermodynamics and not transfer energy / heat from colder to hotter. As we can’t measure that ‘communications’ without changing it, it’s not possible (yet) to know for sure. So you have a nice theory, that even works for a lot of the cases, and can even be measured in some cases; that just might not quite fit in this case.
Doest that mean I’m signing up to say “THAT, That’s the RIGHT one!”? Nope. It just means I’m looking at it and saying: “Hmmmm… Interesting math. Looks like it could explain some things. Don’t see anything that tosses it out immediately (given the context of strange things that wave functions do in time and space…)… So maybe it needs a closer look. Can anyone see something wrong in the math that I missed?” But what’s really really clear, is that tossing it out WITHOUT a look means you learn nothing. WHAT you learn is as yet unknown. It might be a new bit of math that shows the error. It might be a new bit of experimental physics that proves back radiation exists. Or it might be an ‘edge case’ of Q.M. where it doesn’t do quite what we expected. Perhaps even something as simple as two slits in a bit of paper in front of a light bulb…
But you go ahead and be all sure and certain that you are Master Of The Universe with full and complete mastery of all aspects of physics and biology. (After all, you read it in a book and the professor told you it was true.) Me? I’m going to “Trust, but verify”. And that “verify” part means questioning. Testing. Asking uncomfortable, and sometimes even silly questions. For the simple reason that we KNOW we are wrong. Q.M. and G.R. are in conflict. Something is wrong. Darwin and punctuated speciation are in conflict. Something is wrong. AGW and 16 years of no warming are in conflict. Something is wrong. Unlimited Quantitative Easing ala Keynes and continuing Stagflation are in conflict. Something is wrong. And that makes for a much more interesting world than the one where the Master Of The Universe keeps screwing up while being certain it isn’t THEIR fault… ]
EM – I was taught that everything radiates, so those waves do travel around. A hotter body radiates more than a colder one, so the heat transfer is just the difference between radiation and reception. You can effectively “focus cold” using a concave mirror (the mirror blocks off a large part of the incident radiation, and the cold thing at the other focus absorbs far more than it radiates), and on a clear summer’s night you can set a bucket of water in the middle of a ring of bales of straw and make ice. The sky is cold.
It’s hard to keep track of all those quanta flying around, and Nature doesn’t make things simple by only working out what is needed to be sent out in any particular direction.
@ Simon – it seems that we should be able to regulate earths temperature by big mirrors in space. Hot or cold, just change the source. Seems like it would be possible, if Global warming existed.
Simon; I know the theory is correct but have you done it? This is so cool I may have to try it next summer, if I can remember! Making ice in a bucket on a mid summers night would greatly enhance my status as a wizard. ;-) pg
Bob – it’s already been proposed as part of geoengineering to cool the planet, but it would be quite expensive. As it turns out, they may well be useful to warm it, too, and provide better regulation as the Sun varies. Since they only need to vary the radiation level by the odd 0.5% or so, judging by past variations, they wouldn’t be as expensive as was proposed. We still need a cheaper way to get to space than one-time rockets, but those seem to be coming.
Just have the orientation and maybe orbit as variable, and it should work.
I concur with Simons first comment. I did a few years work on heat sinks for high power LEDs, so I know about thermal transfer and black body radiation. The second-law versus back radiation argument seems to be based entirely on inter-discipline jargon differences, with each side reaching the same end using different words and hating each other over it. Net heat always goes hot to cold, yes. Rate of heat transfer between A and C can be slowed by what’s happening at B. Hot stuff radiates indiscriminately in whatever direction that’s convenient. The result is a net evening of heat, and given that most of the universe is empty, everything should eventually approach bupkis degrees Kelvin.
Temperature, heat, power and energy jargon gets mangled, mixed, misused and applied selectively to score empty points just as economics wonks do by interchanging fiscal debt, fiscal deficit, trade deficit, etc. Its rarely worth stepping into the ring because of all the slippery blood on the mat.
pg – I haven’t tried it but a friend of mine did a long time ago. It needs a clear cloudless night, since the clouds will reflect the ground heat back in. If all you can see is sky/stars, and it’s clear bright stars rather than high mist, it will work. I’ve never had a stock of straw bales around, but I expect it would work with hay too, so I’ll maybe test it myself next summer (I’d forgotten about it till prodded).
Re: ego engineering with space reflectors
Larry Niven Ringworld. Read it almost 30 years ago, but the day/ night was built with tinfoil rectangles.
@Simon; back in the days I designed solar collectors for heating water I learned that deep space represented a, -176dF window that your flat plate collector looked at during the night sky. Certainly cold enough to freeze an unprotected water filled panel if the air temperature did not provide backup heating. In cool temperatures it is called a radiation frost where surfaces freeze even though the air temperature is above freezing. As you know, we circulate air in vineyards and orchards to prevent surface freezes in the spring. The sun may heat the ground in daylight but space cools it a night. Only the insulation provided by the atmosphere above, keeps us from boiling by day and freezing at night. pg
SOMEBODY out there PLEASE REMIND us to do the experiment. I live at 2000feet in the woods. IT would work here if anywhere! 8-) pg
If you want to experience the whopping lack of “back radiation” please visit POTOSÍ/BOLIVIA in July. During a clear night with minimum air movement in July when the thermometer reading is just about minus eight degrees Celsius (~ +17° F) you get the impression that your bone marrow has been replaced by liquid nitrogen. It feels a lot colder than e. g. minus eight degrees Celsius in FRANKFURT A. M./GERMANY under a dense cloud cover in January.
I never understood the “back radiation” conjecture:
Why should some vicious molecules like CO2 , H2O or CH4* when struck by heat radiation from the earth “stand their ground” and kick the radiation/energy right back to the emitter (without an exothermic reaction) whilst other, meeker ones, just get all jittery and – “bullying” – impart their energy to slower i. e. colder molecules?
*) http://epa.gov/climatechange/ghgemissions/gases/ch4.html :
“Methane (CH4) is the second most prevalent greenhouse gas emitted in the United States from human activities. In 2010, CH4 accounted for about 10% of all U.S. greenhouse gas emissions from human activities. Methane is emitted by natural sources such as wetlands, as well as human activities such as leakage from natural gas systems and the raising of livestock. Natural processes in soil and chemical reactions in the atmosphere help remove CH4 from the atmosphere. Methane’s lifetime in the atmosphere is much shorter than carbon dioxide (CO2), but CH4 is more efficient at trapping radiation than CO2. Pound for pound, the comparative impact of CH4 on climate change is over 20 times greater than CO2 over a 100-year period.”
Muchos saludos,
don Matías.
S 17°, W 66°,
2’590 m. AMSL.
Don Matias,
If you aim a laser pointer into the sun (from outer space) do the photons turn around and come back to you? Or do your laser’s photons continue until they get to the sun and “hit something” while the sun’s photons travel the opposite direction and “hit you”? Or do the “light waves” going in opposite directions add destructively with equal-frequency counterparts and offset each other? If the latter, would a spectrometer behind your laser pointer measure a notch at the laser frequency? (No).
There are lots of analogies that refer to models that are backed by equations, but in the end the sun “gets energy” from the laser and you “get energy” from the sun, and likely the balance will be uneven with a net transfer taking place from “hot” to “cold”.
@ P.G and Simon
I have inadvertently done the “make-ice-above freezing-air-temperature” experiment many times, though never in the summer. As an amateur astronomer I used to spend many nights beneath a clear sky and often would get the “radiation frost” on the tops of cars and other flat surfaces, especially those oriented slightly toward the north. For such accidental freezing the temperature would have to get down to about 5C — but it was still always fun to see it happen! I seem to remember that the miners in Chile at the Atacamba Desert used radiation to make ice at night. The process (IIRC — it was almost 50 years ago that I read this!) was to dig a ditch oriented roughly east-west, with the north side of the ditch slightly higher. (Remember, they are in the Souther Hemisphere and their visible “cold pole” is to the south.) They would place metal pots of water in the ditch and would have lumps of ice by sunrise. Neat trick. I think that Simon is right about the mirror; a large mirror should produce ice at its focus even in warmer weather.
Sir Arthur Milne, 1922:
“Milne’s work on the atmospheres of stars extended work done earlier by Schuster in 1905 and by Schwarzschild in 1906. Schuster had studied the transfer of radiation where it was assumed that no absorption was taking place in the atmosphere, while Schwarzschild studied equilibrium states for radiation in an absorbing atmosphere. Milne combined the two approaches and came up with an integral equation of great mathematical interest which is now known as Milne’s integral equation. ”
http://www-history.mcs.st-andrews.ac.uk/Biographies/Milne.html
Miskolczi claims that Milne’s equation leads to a discontinuity at the surface and tried to fix it with his theory while at NASA but was prevented from publishing. The link I had to slides about his theory vanished.
Here’s an interesting comment by Dr. Roy Spencer on Miskolczi, arguing that back and forth of IR radiation are NEARLY equal while Miskolczi argues they must be completely equal…
Read it yourself…
http://www.drroyspencer.com/2010/08/comments-on-miskolczi%E2%80%99s-2010-controversial-greenhouse-theory/
The back radiation is in fact not very different from the concept of forward and backward travelling waves in a waveguide or on a cable. That interpretation is based on an impedance and a fixed frequency, but you could do the same for any impedance with very different results, except for the total energi flow, which is the same however you choose the impedance.
With many frequencies involved it gets more complicated, but in principle the same.
You can always divide an energy flow in two flows at opposite directions, some gives meaning and some not, but the so called back radiation is a very good way of understanding what goes on.
Back radiation is very real when you concider a radiating object and a perfect mirror. So don’t tell me it does not exist.
I have asked Claes to explain me how a mirror can avoid back radiation, but he has not answered.
Chiefio,
Thanks for asking an interesting question:
“Or just take the “double slit” experiment. Explain please how the particle, or wave, or wavicle, or partiwave, or whatever it really is; can be both “going through both slits”
This one perplexed even Albert Einstein so I will be surpised if your readers can come up with a convincing explanation. Professor Gilbert Stead summed it up in doggerel many years ago:
http://www.haverford.edu/astronomy/songs/cavendish/hv.htm
Here is the final verse:
“There would be a mighty clearance,
We should all be Planck’s adherents
Were it not that interference
Still defies “h v.”
Jason – just a note on the video you attached. The guy there uses an infrared thermometer and believes the readings from it, but doesn’t take into account the different emissivities of the surfaces he’s measuring. He needs to use a contact thermometer (thermocouple, Mercury, alcohol or suchlike) to get an accurate temperature. It looks like a good system apart from that niggle, but you’ll need some storage of both heat and “cold”, probably large insulated water tanks, to make the system work well and supply you with both hot water and air conditioning.
Nice story about Chile. pg can enhance his “wizard” reputation with that, too.
I pointed my infrared thermometer at the wall – it reads 6.2°C (it’s not a warm day today). I then pointed it directly upwards at the sky (mainly blue sky, few clouds), and it reads -34.5°C. The ground is somewhere around 1.2°C in the shade (North side of building, so has been in shade all day so far), 12.5°C in the sun. The air temperature is 9.5°C, for interest. Damn – what’s the temperature today?
In order to measure the temperature using infrared, it must be pretty obvious that the infrared must be heading towards me – back-radiation is indeed real. Considering the wide variations I measured on grass, concrete, gravel (though I should have used a contact thermometer for the things I can touch) setting an “average” ground temperature for today would be complex. The only way I could get that would possibly be from high above with an infrared thermometer that averaged the emissions (so a hotter but lower-emissivity surface would register less, maybe, than a cooler but higher-emissivity surface). That way I would at least get a measurement of “how cold it feels on the ground” which is maybe of more interest.
The -34.5°C from the blue sky is interesting, and it’s not something I’ve thought to do before today – that’s surely cold enough to make ice. I’ll try to remember to do this when there are clouds up there, as well, and report the reading from that.
Back radiation has been measured. It definitely exists. An excited CO2 molecule will emit a photon in a random direction. Sometimes, it will point towards the surface of the Earth. When it hits the surface, the surface will absorb the energy, thus heating the surface.
Imagine a uniformly lit wall. If you point a parabolic mirror, the distance from the wall being the focal point, at the wall, there will be a brighter spot at the focal point. This is just the way photons work.
That being said, CO2 makes the Earth’s surface a little warmer, but if the Sun goes out, CO2 won’t keep us warm very long. Ultimately, the CO2 gets its energy from the Sun.
Oh, the measured back radiation …
http://www.skepticalscience.com/print.php?r=92
Interesting link, leads to this paper from Chen , see fig 3
Click to access pdf_conf_p50_s9_01_harries_v.pdf
SkepticalScience has cunningly shown some manipulated data. Large parts of the spectrum emit MORE than they used to, compensating for any increased CO2/CH4 GHG backradiation.
…and interestingly the stuff that skepticalscience cites does ignore the major absorption bands of water vapor.
http://www.senseair.se/senseair/gases-applications/water/
So these were studies to promote the CO2AGW talking points; NOT studies to assess radiative balance in a scientific way.
@gallopingcamel says: 9 December 2012 at 6:03 am
“just take the “double slit” experiment”
I have no problem with that outcome in My philosophy of physics.
The energy/mass of a photon or other “particle” is contained in its’ EMF field or bubble. This “wave” of energy is a ball or bubble of influence that effects other things as it passes. The act of measurement adsorbs that energy and creates the appearance of a “particle” in the detector. A detector requires a unit of energy to displace an electron in it to signal detection. This problem of “particle” or “wave” is a concept problem of interpretation of detection results, think spinning bubble of Electro-Motive Force. Wave or particle is just a point of perception. pg
Since the back-radiation spectrum is taken over the Arctic, there isn’t much in the way of water vapor. The problem I see with the Trenberth energy balance diagram is that green house gases should be radiating more energy up than down. So if there are 324 w/m2 down, there should be more than that going up. That should be what is really happening in the atmosphere.
I am not sure that back radiation measured over the pole would be valid for measurement over the equator. It would appear to me that back radiation would be strongest where the incoming radiation was the strongest.
Far too much of Climate Science is based on Rubber Rulers and assumptions of fact. pg
Also, Dirk, note this is an emission spectrum, not absorption.
Back radiation over the equator would be greater due to more water vapor in the atmosphere there.
jim2 says:
9 December 2012 at 3:12 pm
“Also, Dirk, note this is an emission spectrum, not absorption.”
Same frequencies, same magnitude.
Dirk – WRT magnitude – 100% absorption = 0 % emission and vice versa. So absorption and emission are complements of each other, not equal.
Sorry Dirk – scratch that last comment. I was thinking of an absorption spectrometer – ghost of my days as a chemist.
Politics was always behind:
ERBS observations have also been used to determine how human activities such as the use of chlorofluorocarbons (CFCs) and the burning of fossil fuels affect Earth’s radiation balance. Data on the ozone layer provided by ERBS was key in the international community’s decision-making process during the Montreal Protocol Agreement, which has resulted in a near elimination of CFCs in industrialized countries. It was ERBS data, in part, that led to the understanding that CFCs deplete atmospheric ozone concentrations.
I was thinking of Kirchhoff’s law – equal absorption and emission at local thermal equilibrium. Basically GFG molecules work to scatter IR photons.
Dirk – you are right. And that’s why Trenberth’s diagram is wrong. The GHG part should be emitting in all directions. Less than half will be directed towards the Earth and more than half will directed towards space. Net cooling.