A guest post by Ken Coffman and Mikael Cronholm
In clicking around on the Internet, I found an outstanding paper called Thermodynamics of Furnace Tubes – Killing Popular Myths about Furnace Tube Temperature Measurement written by Mikael Cronholm. The paper was clever and wise…and made a lot of sense. Clearly Mikael knows a lot about infrared radiation and I’m a guy with questions. A match made in heaven?
We exchanged e-mails. I want to be clear about this…Mikael corrected some of my wrong ideas about IR. I’ll repeat that for the slow-witted. Some of my ideas about infrared radiation were wrong. I am considered a hard-headed, stubborn old guy and that’s completely true. However, I want to learn and I can be taught, but not by knuckleheads spewing nonsense and not by authoritarians who sit on thrones and toss out insults and edicts.
Ken Coffman (KLC) is the publisher of Stairway Press (www.stairwaypress.com) and the author of novels that include Hartz String Theory and Endangered Species.
Mikael Cronholm (MC) is an industry expert on infrared radiation, a licensed, level III Infrared Training Center Instructor and holds two Bachelor of Science degrees (Economics and Business Administration).
The following is a summary of our conversation.
KLC: Hello Mikael. I found your paper called Thermodynamics of Furnace Tubes and I found it very informative, practical and interesting. I hope you’ll bear with me while I ask a couple of dumb questions. I am an electrical engineer, so I have some knowledge about thermodynamics of conduction and convection, but not so much about IR radiation. In return for your time, I would be happy to make a donation to the charity of your choice.
If I take an inexpensive IR thermometer outside, point it at the sky and get a temperature reading of minus 25°C, what am I actually measuring? Is there anything valid about doing this?
MC: Just as a matter of curiosity, how did you find my paper? I checked your website and I guess this has to do with the Dragon, no? If you want to make a donation I would be happy to receive that book. If you can, my postal address is at the bottom. I don’t follow the debate more than casually, but I am a bit skeptical to all the research that is done on climate change…it seems that the models are continuously adjusted to fit the inputs, so that you get the wanted output…and they argue “so many scientists agree with this and that”…well, science is not a democracy…anyway…
About radiation, then. There is more to this than meets the eye. Literally!
Looking at the sky with an infrared radiometer you would read what is termed “apparent temperature” (if the instrument is set to emissivity 1 and the distance setting is zero, provided the instrument has any compensation). Your instrument is then receiving the same radiation as a blackbody would do if it had a temperature of -25°C, if that is what you measure. It is a quasi-temperature of sorts, because you don’t really measure on a particular object in any particular place, but a combination of radiation, where that from outer space is the lowest, close to absolute zero, and the immediate atmosphere closest to you is the warmest. (I have once measured -96°C on the sky at 0°C ground temperature.) What we have to realize though, is that temperature can never be directly measured. We measure the height of a liquid in a common thermometer, a voltage in a thermocouple, etc, and then it is calibrated using the zeroth law of thermodynamics and assuming equilibrium with the device and the reference.
KLC: Global warming (greenhouse gas) theory depends on atmospheric CO2 molecules absorbing IR radiation and “back radiating” this energy back toward the earth. If you look at the notorious Ternberth/Keihl energy balance schematic (as shown in Figure 1 of this paper: http://www.cgd.ucar.edu/cas/Trenberth/trenberth.papers/TFK_bams09.pdf ), you see the back radiation is determined to be very significant…more than 300W/m2. From your point of view as an IR expert, does this aspect of the global warming theory make any sense?
MC: The paper you sent me mentions Stefan-Boltzman’s law, but it does not talk about Planck’s law, which is necessary to understand what is happening spectrally. I suggest you read up on Planck and Stefan-Boltzman at Wikipedia or something. Wien’s law would be beneficial as well—they are all connected.
Planck’s law describes the distribution of radiated power from a blackbody over wavelength. You end up with a curve for each blackbody temperature. The sun is almost a blackbody, so it follows Planck quite well, and it has a peak at about 480nm, right in the middle of visual (Wien’s law determines that). The solar spectrum is slightly modified as it passes through the atmosphere, but still pretty close to Planckian. When the radiation hits the ground, the absorbed part heats it. The re-radiated power is going to have a different spectral distribution, with a peak around 10um (micrometer). Assuming blackbody radiation it would also follow Planck’s law.
S-B’s law is in principle the integral of Planck from zero to infinity wavelength. Instruments do not have equal response from zero to infinity, but they are calibrated against blackbodies, and whatever signal they output is considered to mean the temperature of the blackbody. And so on for a number of blackbodies until you have a calibration curve that can be fitted for conversion in the instrument.
That means that the instrument can only measure correctly on targets that are either blackbodies, or greybodies with a spectral distribution looking like a Planck curve, but at a known offset. That offset is emissivity, the epsilon in your S-B equation in that paper. It is defined as the ratio of the radiation from the greybody to that of the blackbody, both at the same temperature (and wave length, and angle…). Some targets will not be Planckian, but have a spectral distribution that is different. If you want to measure temperature of those, you need to measure the emissivity with the same instrument and at a temperature reasonably close to the one you will measure on the target later.
So, of course, the whole principle behind the greenhouse effect is that shorter wavelengths from the sun penetrates the atmosphere easily, whereas the re-radiated power—being at a longer wavelength—is reflected back at a higher degree. I have no dispute about that fact. It is reasonable. So I think the Figure 1 you refer to is correct in principle. My immediate question is raised regarding the numbers in there though. The remaining 0.9 W/m2 seems awfully close to what I would assume to be the inaccuracies in the numbers input to calculate it. You are balancing on a very thin knifes edge with such big numbers as inputs for reaching such a small one. An error of +/- 0.5% on each measurement would potentially throw it off quite a bit, in the worst case. But I don’t know what they use to measure this, only that all the instruments I use have much less accuracy than that. But with long integration times…well, maybe…but there may be an issue there.
KLC: I am interested in some rather expensive thermopile-based radiation detectors called pyrgeometers (an example is the KippZonen CGR 3 instrument http://www.kippzonen.com/?product/16132/CGR+3.aspx).
If a piece of equipment like this is pointed into the nighttime sky and reads something like 300W/m2 of downwelling IR radiation, what is it actually measuring? If I built a test rig from IR-emitting lightbulbs calibrated to emit 300W/m2 and placed this over the pyrgeometers, would I get the same reading?
MC: “What is it actually measuring?” Well, probably a voltage from those thermopiles…and that signal has to be calibrated to a bunch of blackbody reference sources to covert it either to temperature or blackbody equivalent radiation.
Your experiment will fail, though! If you want to do something like that, you have to look at a target emitting a blackbody equivalent spectrum, which is what the instrument should be calibrated to. IR light bulbs emitting 300W/m2 is simply impossible, because 300W/m2 corresponds to a very low temperature! Use S-B’s law and try it yourself. Like this: room temp, 20°C = 293K. The radiated power from that is 293K raised to the power of 4. Then multiply with sigma, the constant in S-B’s law, which is 5.67*10-8, and you get 419 W/m2 or something like that, it varies with how many decimals you use for absolute zero when you convert to Kelvin. For 300 W/m2 radiation I get -23.4°C at 300 W/m2 when I calculate it (yes, minus!). Pretty cool light bulb.
I don’t know what your point is with that experiment, but if it is to check their calibration you need a lot more sophisticated blackbody reference sources if you want to do it at that temperature. But you could do a test at room temperature though. Just build a spherical object with the inside painted with flat black paint, make a small hole in it, just big enough for your sensor, and measure the temperature inside that sphere with a thermocouple, on the surface. Keep it in a stable room temperature at a steady state as well as you can and convert the temperature to radiation using S-B’s law. You should get the same as the instrument. Any difference will be attributable to inaccuracy in the thermocouple you use and/or the tested instrument. Remember that raising to the power of 4 exaggerates errors in the input a lot!
I hope I have been able to clarify things a little bit, or at least caused some creative confusion. When I teach thermography I find that the more you learn the more confused you get, but on a higher level. Every question answered raises a few more, which grows the confusion exponentially. It makes the subject interesting, though.
Let me know if you need any more help with your project!
KLC: I found your paper because one of the FLIR divisions is local and I was searching their site for reference information about IR radiation. I know what a 100W IR lamp feels like because I have one in my bathroom. If someone tells me there is 300W/m2 of IR power coming from space, and I hold out my hand…I expect to feel it. What am I missing?
MC: Yeah, you put your hand in front of a 100W bulb, but how big is your hand…not a square meter, I’m sure. It is per area unit, that is one thing you are missing. The 100W of the bulb is the electrical power consumption, not the emitted power of the visual light from it. That’s why florescent energy-saving lamps as opposed to incandescent bulbs give much more visual light per electrical Watt, because they limit the radiation to the visual part of the spectrum and lose less in the IR, which we cannot see anyway. The body absorbs both IR and visual, but a little less visual.
And, here is the other clue. Your light bulb radiation in your bathroom is added to that of the room itself, which is 419 W/m2, if the room is 20°C. Your 300 W/m2 from space is only that. You will feel those 300 W/m2, sure. It will feel like -25°C radiating towards your hand. But you don’t feel that cold because your hand is in warmer air, receiving heat (or losing less) from there too.
Actually, we cannot really feel temperature—that is a misconception. Our bodies feel heat flow rate and adjust the temperature accordingly. It is only the hypothalamus inside the brain that really has constant temperature. If you are standing nude in your bathroom, your body will radiate approximately 648 W/m2 and the room 419 W/m2, so you lose 229 W/m2. That is what you feel as being cooled by the room, from radiation only. Conduction and convection should be added of course. The earth works the same way—lose some, gain some. It is that balance that is being argued in the whole global warming debate.
KLC: I still feel like I’m missing something. IR heat lamps are pretty efficient, maybe 90%? Let’s pick a distance of 1 meter and I want to create a one-square meter flooded with an additional 300W/m2. It must be additional irradiation, doesn’t it? That’s going to take a good bunch of lamps and I would feel this heat. However, I go outside and hold out my hand. It’s cold. There’s no equivalent of 300W/m2 heater in addition to whatever has heated the ambient air.
Perhaps I’m puzzled by something that is more like a flux…something that just is as a side-effect of a temperature difference and not really something that is capable of doing any work or as a vehicle for transporting heat energy.
It’s a canard of climate science that increasing atmospheric CO2 from 390PPM to 780PPM will raise the earth’s surface temperature by about 1°C (expanded to 3°C by positive feedbacks). From my way of thinking, the only thing CO2 can do is increase coupling to space…it certainly can’t store or trap energy or increase the earth’s peak or 24-hour average temperature.
Any comments are welcome.
MC: Efficiency of a lamp depends on what you want, if heat is what want then they are 100% efficient, because all electrical energy will be converted to heat, the visible light as well, when it is absorbed by the surrounding room. If visible light is required, a light bulb loses a lot of heat compared to an energy saving lamp. Energy cannot be created or destroyed—first law of thermodynamics.
When you say W/m2 you ARE in fact talking about a flux (heat flow is what will be in W). If you have two objects radiating towards each other, the heat flow direction will be from the hotter one, radiating (emitting) more and absorbing less, to the cooler one, which radiates less and absorbs more (second law of thermodynamics). The amount of radiation emitted from each of them depends on two things ONLY, the temperature of the object and its emissivity. So radiation is not a side effect to temperature, it is THE EFFECT. Anything with a temperature will radiate according to it, and emissivity. (If something is hotter than 500°C we get incandescence, emission of visible light.) Assuming an emissivity of unity, which is what everyone seems to do in this debate, the radiation (flux. integrated from zero to infinity) will be equal to what can be calculated by Stefan-Boltzmann’s law, which is temperature in Kelvin, raised to the fourth power, multiplied by that constant sigma. It’s that simple!
With regard to your thought experiment, it is always easier to calculate what an object emits than what it absorbs, because emission will be spreading diffusely from an object, so exactly where it ends up is difficult to predict. I am not sure where you are aiming with that idea, but it does not seem to be an easy experiment to do in real life, at least not with limited resources.
CO2 is a pretty powerful absorber of radiated energy, that fact is well known. Water vapor is an even stronger absorber. In the climate debate it is also considered a reflector, which probably also true, because that is universal. Everything absorbs and reflects to a degree. So I guess that the feedback you mention has to do with the fact that increasing temperature increases the amount of water vapor, which increases absorption, and so on. But my knowledge is pretty much limited to what happens down here on earth, because that is what matters when we measure temperature using infrared radiation. However, it is important to remember, again, that we talk about different spectral bands, the influx is concentrated around a peak in the visual band and the outgoing flux is around 10 micrometer in the infrared band, and the absorption may not be the same.
With so many scientists arguing about the effects of CO2 I am not the one to think I have the answers. I really don’t know what the truth is. And the problem that all these scientists have is that they will never be able to test if their theories are correct, because the time spans are too long. For a theory to be scientifically proven, it has to be stipulated and tested, and the test must be repeatable and give the same results in successive tests for the theory to be proven.
If not, it is not science, it is guessing.
More like a horoscope…
George Smith says…
Every single additional molecule of H2O or cO2 that is added to the atmosphere WILL reduce the amount of incoming solar energy that reaches the surface of the planet to warm it.
That assertions is not valid for CO2, which is an absolutely-blind cat to short wavelength IR quantum/waves incomming from the Sun.
It’s a one-eyed cat towards long wavelength IR quantum/waves; nevertheless, it only absorbs a little from this spectral band because its absorptivity, taking into account the mean free path lenght and the crossing lapse time of IR quantum/waves IN the atmosphere, is quite low: 0.004. Taking into account the whole column of air, the CO2 Pp and actual temperatures of the atmosphere -not that of an idealized blackbody because CO2 is not a blackbody neither it “resembles” a blackbody, the total emissivity of the carbon dioxide is no more than 0.002.
As a way of comparison, the total emissivity of water vapor is 0.7, the total emissivity of moistened clay with organic materials is 0.95. The total emissivity of liquid water is 0.96. These observed and verified facts transform the CO2 into a feeble one-eyed cat.
Alternatively, the delay that a molecule of carbon dioxide causes to the emission of electrons and photons, after having absorbed a photon, is measured in attoseconds (as), i.e. 10^-18 of a second; consequently, there is no way for the atmospheric carbon dioxide to “hold” the absorbed energy for periods longer than 20 ± 5 as.
😐
marky48, you had more in your hip pocket than you let on. I read the article that you posted and found it very compelling. I am much more inclined to this, if you are willing to show the same courtesy- http://journals.ametsoc.org/doi/full/10.1175/1520-0469%281999%29056%3C1649%3ATWVACS%3E2.0.CO%3B2 The article you posted assumes that Co2 increase precedes temperature but makes little case to inform on that point. This is a vital to the discussion. It would certainly resolve all the debate on this thread.
Mikael Cronholm says:
February 15, 2011 at 8:59 pm
Re “IR is deep body penetration”
Too generic a statement. IR is a very broad spectrum. Some IR may penetrate deeply, you may want to inform me exactly which wavelengths, if you know, I am truly interested (not sarcastic, I promise). But certainly NOT the kind of IR we look at with thermal imagers. From Hollywood people “know” that we can see through wall and stuff with IR. That is probably where that BS comes from originally. It is BS though, no less.
I give you pukkha medical references which contradict your claim that UV penetration and Visible light penetration greater than IR, practical applications, and you want me to find all the detail. You’re the expert on IR, so you say. These examples falsify your claims.
If you don’t believe condensing steam will give off huge amounts of latent heat, put the kettle on and when it boils, stick your finger right in the steam that comes from it you will find out.”
?!! Where did I say I thought that? Again, you show yourself apt to avoid what is actually being said by creating a straw man. Re saunas:
My point was, because you imagined that an IR sauna would be like a toaster I find it impossible to take your claim that you are an expert about IR, seriously.
I’m sorry, that’s how it looks from where I’m standing. You may well be an expert in some applications of IR, but you cannot expect me to think that you understand it fully. I cannot be sure that your statements about it in areas where you are not an expert are anything but assumptions, as I have already found to be the case where other scientific disciplines using IR contradict you.
You can claim until you’re blue in face that UV and Visible light penetrate deeper than IR, and arrogantly demean me as “unteachable” about IR because you are the expert, but the fact remains that what I have found from real science contradicts you and putting me down doesn’t change that.
I haven’t made any claim to be an expert, I have said that I make judgements about conflicting statements by assessing these using what common sense I have. And I find this a continuing struggle in this argument because I do not have the easy familiarity with scientific terms, and certainly not its language of maths, of many here, I have to look everything up.. However, it’s obvious to me, using this method of common sense, that what you say about penetration is contradicted, here, by people who use actual knowledge of light penetration in their medical practice.
Common sense tells me you can’t both be right.
Your throwaway that this must be some deeply penetrating NIR and that you don’t care to explore it is insulting. One the one hand you expect me to take whatever you say about IR as coming from an expert and accept without question your claim that UV and Visible light penetrate more deeply and then get annoyed when your expertise is shown limited. I can understand you’d be annoyed, but I was also under the impression from what you had also said that you were willing to explore admitting that you didn’t know everything about IR. So I’m confused. Which makes it impossible for me now to take anything you say about IR as fact. I am quite practiced, through examining assumptions in the AGW arguments, in starting from ignorance every time I ask a question and not expecting provable facts in reply..
..because my interest is to gain understanding of the argument and so far, as majority others here have found, assumptions are frequently bandied about as scientific fact by AGW and closer inspection shows they are not.
One thing I thought, if you’re still willing to explore this, is that far IR being close to Microwave could be penetrating in much the same way. As I said before re your wondering why microwaves in the atmosphere don’t cook us, it could be just the difference in concentration.
Re Herschel, you say that what he was measuring was in near IR and that if he’d moved it further away it would have disappeared completely, but, near IR is still IR, and this was hotter than the other colours, whatever that means. The claim in AGW is that glass is opaque to IR, so this is an important point, for me, in understanding the statements pro and con. And, is it proved that it was near IR he was measuring and not, say, mid IR or even far IR? I am having little joy with searching for this information, if you have it handy somewhere as actually tested please give me the link.
You give a figure where glass becomes opaque to IR which some sources say is still in the near IR band, while others say this is mid IR, while others.. Most, of the pages I’ve looked at, have far IR beginning at 3 microns.
OK, I think I might have found a page that understands glass and IR:
http://www.nrc-cnrc.gc.ca/eng/ibp/irc/cbd/building-digest-60.html
“Absorption of radiant energy by glass varies with the wave length of the radiation and the absorption characteristics of the glass. It may be seen in Figure 1B that 1/4-inch plate glass is essentially transparent to all of the solar spectrum except the short-wave ultra-violet. It is less transparent, however, to wave lengths over about 3 microns and opaque to wave lengths over 4.5 microns. This means that solar radiation can pass through glass to heat surfaces inside a building, but longer wave length radiation from objects in the building is absorbed by the glass. This accounts in part for the common “greenhouse effect,” or the ability of an unheated glass-enclosed space to experience a rapid temperature rise during hours of sunshine and retain its heat during the night. It should be noted that absorption of radiation causes the glass temperature to rise, and transmitted radiation causes a heat gain the building interior.”
So, glass of the common soda-lime lets in some far IR, that dubbed thermal, about 1.5 microns of its spectrum, that glass isn’t opaque to IR until 4.5 microns.
If the rest is absorbed by the glass, heating it, isn’t this also delivering IR into the greenhouse?
It says further:
“Thermal Conductivity
the thermal conductivity (k) of soda-lime glass at between 5 and 7 Btu/hr sq ft °F/in. is higher than that of insulating materials, but much lower than that of most metals. Glass of normal thickness offers neglibible resistance to heat transfer between the inside and outside of a building and the thermal resistance of a pane is predominantly due to the surface films.”
Which might mean something to the majority posting on these boards, but all that I grasp from it is that “Glass of normal thickness offers neglible resistance to heat transfer between inside and outside of a building and the thermal resistance of a pane is predominantly due to the surface films.”
So, does this falsify the AGW claim that glass is opaque to incoming IR and traps outgoing, or not?
And even if it was wholly opaque to all IR, does it matter since the heated glass itself will be emitting IR into the greenhouse? All it would do, istm, is delay some thermal energy transfer.
I suppose I now have to look up the emissivity of glass..
Oh shhugar, I messed up the italics again. Sincere apologies, will stop and think before posting in the future, I didn’t check.
Very sloppy on your part Mr. Matter. You immediately got sidetracked from the simple and iron-clad point I made (and as a commenter mentioned) you didn’t bother to quote me which provided cover for your conversational detour. So, let’s recap …
Then I said …
I’ll make it crystal clear …
Let the Earth have no atmosphere and we shall call the EMR striking the Earth as X,
Let the Earth have its present or any atmosphere and we shall call the EMR striking the Earth as Y,
I ask you now: Is … X < Y … or … X = Y … or … X > Y? There is only one answer. X > Y.
P.S. Therefore your last sentence is wrong …
(well you certainly employ vague yet enigmatic use of the terms sunlight, and then light wouldn’t you say?)
Let’s avoid confusion. If a single photon of any part of the EMR spectrum is either reflected or absorbed and re-radiated to space, (i.e., it never gets here!), then, the net EMR is reduced, period. The point (as I was responding to Matt) is that there is no way that any matter (Atmosphere) placed in between the Sun and the Earth can ever increase the amount of EMR we receive. It is theoretically possible (but highly unlikely) for it to be EQUAL, but not GREATER.
Now unless you are planning on telling us that CO2 does not intercept a single photon of any part of the EMR spectrum traveling from the Sun to the Earth, (not a single photon? CO2 is a perfect insulator?), then only one statement can be held as true: CO2 decreases the net EMR transmitted from the Sun to the Earth (even if it is a single photon). You certainly are not proposing there is no downstream infrared from the Sun are you?
The current controversy seems to lie in the energy balance of the photons that actually make it here through the atmospheric ‘wall’. On this I agree with the crude blanket analogy, the energy bounces around here a little longer than it would were there no atmosphere, CO2 or not. That means that if you switch off the Sun, we’ll take just a little longer to freeze to death. How much longer? Who cares. Not long enough though.
I can comment about what marky48 has in his “hip pocket”. The reference he provided was from a polite and helpful (and uncredited) suggestion at RC by the eminent Dr. Raymond Pierrehumbert. To be precise, here is a quote of that helpful suggestion.
[Response: I’m averse to polluting myself by wading into the sewer of pseudoscience over there [at WUWT], but perhaps somebody with more fortitude would do me the favor of going over there and posting a link to my Physics Today article on infrared radiation. (available at http://geosci.uchicago.edu/~rtp1/papers/publist.html ) Maybe then they’d learn something (though I doubt it). –raypierre]
George E Smith seems to be saying that CO2 (and H2O) are double edged swords.
That is, every extra molecule of CO2 contributes to keeping some fraction of incoming radiation from making it to to surface (approximately half of what is intercepted is re-radiated, although some of it contributes to heating the atmosphere), while it also contributes to keeping some of the outgoing energy in the atmosphere for a while longer.
To Ken Coffman
Raymond Pierrehumbert’s paper is loaded with cherry picking and assumptions carefully crafted together by him to try and prove that CO2 is far more important to the greenhouse effect on earth than it really is.
I doubt he has ever spent even a day working out in the field with IR measuring equipment to directly measure parts of the greenhouse effect.
He’s a typical pencil pusher with no primary experience with real data and the instruments used to obtain that real data.
Thanks for that reference, Ken Coffman, and to you too, Domenic. Care to respond marky? The sequence of events is still critical to the discussion.
Sad and weak the Pierrehumbert would rather dismiss than engage. I think that Mr. Cronholm has shown here that he has some cogent knowledge that I think Mr. Pierrhumbert needs to address. And of course my question on the sequence of events regarding Co2 and temperature.
I hope all those contributing here haven’t moved on as this thread has been most interesting.
Domenic says:
RE: Raymond Pierrehumbert’s paper
” . . . prove that CO2 is far more important to the greenhouse effect on earth than it really is . . ”
What aspects do you find to be cherry picking and assumptions. I ask because of my lack of knowledge and no expert application. Is Domenic alone is his opinion of Pierrehumbert’s paper? Are there any other opinions supporting Pierrehumbert’s view?
The closing paragraph seems to sum up Pierrehumbert’s argument. I was wondering, based on all that I’ve read here, why this is the first I’ve read re: what Pierrehumbert refers to as the ‘bite of IR spectrum” and how that “bite” increases as CO2 increases?
RE: Pierrehumbert:
“The CO2 greenhouse effect is directly visible in satelite observations of the bite taken out of the IR spectrum near 667cm-1, a feature whose details agree precisely with results of calculations based on first-principles radiative transfer calculations. Laboratory spectroscopy demonstrates that the width of the bite will increase as CO2 increases, and warming inevitably follows as a consequence of well-established energy-balance principles . . .” (last line) “the basic radiative physics of the anthropogenic greenhouse effect is unassailable.”
Ready to learn more . . .
-Barn
“”””” Richard Sharpe says:
February 16, 2011 at 7:45 am
George E Smith seems to be saying that CO2 (and H2O) are double edged swords.
That is, every extra molecule of CO2 contributes to keeping some fraction of incoming radiation from making it to to surface (approximately half of what is intercepted is re-radiated, although some of it contributes to heating the atmosphere), while it also contributes to keeping some of the outgoing energy in the atmosphere for a while longer. “””””
Richard, that is precisely what I am saying BUT !! Let’s keep a proper perspective. I think the “back of the envelope” chicken scratchings I did, show that perhaps CO2 is not a big culprit as far as lowering the incoming; but the effect is incontrovertible; it is real. The issue is much more important for H2O, because there is a lot more of it; it is never less than the amount of CO2, and it varies widely geographically, and with weather.
In the long haul, there can be no doubt, that an increase in H2O on a global scale, and over climatically meaningful time scales; must reduce to total solar energy that reaches the earth surface; where it can be stored in the oceans, or in the land materials. Sooner or later, that must mean a cooler earth.
I should add one further clarification. The main solar spectrum portion that is intercepted by H2O, and the same is true for the CO2, is longer than 0.75 microns, and as long as 4.0 microns. It would NOT be correct to say that this is deposited “Deep” in the oceans, like the bulk of the solar energy is.
As every scuba diver knows, the red end of the spectrum disappears first as you go deeper, and 750 nm is a quite deep red; so we are talking metres to tens of metres; but not hundreds. We know that H2O has its very strongest spectral absoption at 3.0 microns, where maybe a couple of percent of solar energy still is to be found. At that wavelength the water absorption coefficient, is about 9,000 cm^-1, so the 1/e absorption depth is just 1.1 microns, or 5.5 microns for 99% extinction.
So to some extent much of that lost solar energy, would have been absorbed in shallower water, and would likely have given rise to enhanced evaporation from the surface; which is pretty much what the returned LWIR from the atmosphere does also.
We should note that both GHG absorption of LWIR, and similar absorption of incoming solar energy HEAT THE ATMOSPHERE. They do NOT heat the ground. Once the atmosphere is heated; regardless of means; the ambient LWIR radiation which is going in all directions, is a function only of that atmospheric Temperature; and quite independent of what heated the atmosphere.
As others constantly point out here; convection and evaporation and other energy transport mechanisms are perhaps more important to the earth cooling process, at least at living elevations. I don’t ignore those effects; I just don’t dwell on them; since absolutely none of that is in any way affected by GHGs or the Greenhouse effect. That is purely a radiation phenomenon; which is why I concentrate my thoughts on the radiant energy processes. I’m happy that others do keep track of the other thermal processes, and the various circulations like ENSO and AMO etc.
Water really is THE double edged sword, since it is the only condensing GHG; and in liquid or solid form as clouds, I’m convinced it ALWAYS cools the earth; NEVER warms it. Those high clouds that we associate with humid balmy nights; are a consequence of the earlier surface conditions (Temperature and Humidity); they are NOT the cause of those surface conditions.
I think a lot of my own confusion comes from buying into the warmist strategy of counting photons: up, down and sideways. You get yourself into a tangled mess and into the mysterious “back radiation” and equally mysterious “net radiation”. We have a choice–we can think of photons as particles or waves. So, what if we imagine waves instead of photons? When we do this, I think the picture becomes much more clear.
The amount of radiation emitted from each of them depends on two things ONLY, the temperature of the object and its emissivity. So radiation is not a side effect to temperature, it is THE EFFECT.
– Mikael Cronholm
If we think of waves like lines of flux, then they point from the warm body toward the cold body (and there are none when the bodies have equal temperatures). We have radiation and nothing like anti-radiation. Given this mental model, (ignoring temperature inversions for now) is there any way for atmospheric CO2 to increase the temperature of the earth’s surface? It can modify the cooling rate, but it cannot increase the temperature. So, global warming with more and more record high temperatures? This is not something CO2 can do.
This is a point made over and over from different points of view in the Slaying the Sky Dragon book. I, for one, am looking forward to Mikael’s comments about this book, good, bad or indifferent.
“”””” Mikael Cronholm says:
February 15, 2011 at 6:34 pm
@ur momisugly George E. Smith, February 15, 2011 at 11:54 am
I just want to say I appreciate your input in this comment a lot. I have that solar spectrum curve in front of me if I close my eyes. And when I remind myself that the darn thing is in a logarithmic scale, all those numbers you give make a lot of sense. Thanks for that!
My only slight objection is here:
““Heat” is NOT energy in the form of photons. Heat is purely MECHANICAL KINETIC ENERGY in the form of molecular or atomic vibrations due to collisions between particles (of matter) Sans matter; there is NO “HEAT”. Heat is characterized by TEMPERATURE.”
Agreed to the most part. It is the last sentence I am a little bothered with. Heat and temperature are connected in such a way that they co-vary depending on heat capacity, BUT with the exception of latent heat during phase change. If you observe a temperature change you can safely assume that the amount of heat it the object has also changed, but if you have a change in heat it may not necessarily cause a change in temperature, if there is phase change going on. “””””
Mikael, what I meant by that statement, is simply this. “HEAT” (energy) is nothing more nor less, than the total kinetic energy
of all of the particles of matter in the “sample”. That total energy, and its distribution as to particle velocity is defined by the Temperature. The Maxwell-Boltzmann distribution of velocities is defined by the Temperature (in gases).
The average KE per particle is simply 3kT/2. That is for the translational energy (in three axes). Some molecules will also have rotational degrees of freedom, so they can have more energy per particle, and one can calculate the RMS velocity as sqrt(3kT/m) where m is the particle mass.
One can calculate the velocity distribution (ideal gas) in the form:-
(1/N)dN/dv =4piv^2(m/2pikT)^3/2. exp(-mv^2 /2kT) which is the M-B distribution.
As to these curves; My most uesful source of (somewhat dated) thermal data is “The Infra-Red Handbook”, and I have several Optics Handbooks that I use at work all the time, that have a lot of stuff. Another VERY useful curve to have is a Normalized Back-Body Radiation curve. Normalized in the sense that the wavelenght axis is normalized to the peak wavelength, so the peak is at 1.0, and the spectral radiant emittance is also normalized to the value at the peak wavelength so it also is 1.0.
There is such a curve in “Modern Optical Engineering by Warren J. Smith; published by McGraw Hill. It is his Fig 8.7 I have an old copy and also a new copy and the curve is in both. He plots wavelength from 0.1 to 50 (times the peak) and relative spectrale mittance from 0-1 (linear) and also from 1.0-10^-5 (logarithmic), and then he has a nifty scale of fraction of total energy emitted below, going from 10^-6 (at 0.24 of peak wavelenght) up to 99% at 8.0 times peak.
So I don’t really have to eyeball that much; I can read it off the graph. Since we can’t cut and paste pictures here, it is hard to show people this data. But if you care to give Anthony permission to send me your e-mail address, I’d be happy to snap some digital photos of some of these uesful graphs, and e-mail them to you.
The Normalized Planck curve is very useful. A lot of people are not aware that the Planck curve is a function of the single variable lambda.T, which is also a consequence of Wien’s Displacement Law; lambdamax.T is a constant (2897.8 micron.Kelvins)
Also the peak spectral radiant emittance is 1.288 e-11. T^5 W/m^2micron^-1
Most people know that 25% of the BB spectrum radiation is emitted below the peak wavelength. The actual number is extremely close to 25%; but I have never actually done the integration to find out if that is exact; and if any of the PhD physicists out there know; they aren’t telling anybody. But everybody should know that 25% :75% before and after the wavelength peak. And only 1% below 1/2 of the peak wavelength, and 1% left above 8 times the peak.
So it is kind of interesting that the solar spectrum long wavelength tail dies at about 4.0 microns, and the short wavelngth edge of the earth emitted LWIR also dies at about 4.0 microns; which is where the CO2 peak that is dominant on Venus, sits. So that particular CO2 band doesn’t have much influence on earth; well unless you are doing one of those fraudulent heat lamp CO2 absorption demos.
A couple of things are clear from Pierrehumbert’s piece;
First, that CO2 is the sine qua non of the greenhouse effect. He declares that, absent CO2, all the water woud be ice. CO2 transforms water into a greenhouse gas.
Secondly, he finds it confusing, too, as he says “Carbon dioxide is just planetary insulation”.
If there’s any doubt as to his slant on the whole story, there’s his statement that “CO2 accounts for about a third of the clear-sky greenhouse effect in the tropics and a somewhat greater portion in the drier, colder extratropics; the remainder is mostly due to water vapor.”
“The remainder” is a surprising phrase to use to describe upwards of 60% of the whole. It’s not that it’s false, just that it suggests some attitude.
He declares that the basic radiative physics is unassailable, but he implies that every aspect of the AGW hypothesis is equally sound, by association.
“”””” Nasif Nahle says:
February 15, 2011 at 9:18 pm
George Smith says…
Every single additional molecule of H2O or cO2 that is added to the atmosphere WILL reduce the amount of incoming solar energy that reaches the surface of the planet to warm it.
That assertions is not valid for CO2, which is an absolutely-blind cat to short wavelength IR quantum/waves incomming from the Sun. “””””
Nasif, you are apparently determined to completely ignore the significant CO2 absorption bands, at 1.8, 2.7 and 4.0 Microns wavelength which certainly address incoming solar spectrum energy. So I stand by my statement; but I anxiously await your contrary data that would show I am incorrect.
I am not claiming this has any significance when considering the mass of the earth…but I found it interesting. Yes, I know this is contrary to my thoughts about viewing IR radiation as waves.
Light seems such a “flimsy” thing it is probably difficult to imagine it pushing on anything, or at any rate pushing very hard. And yet, the radiation force on the earth due to the sun is on the order of an impressive 100,000 tons! This is equivalent, for example, to a fully loaded aircraft carrier.
– Paul J. Nahin, Oliver Heaviside, The Life, Work, and Times of an Electrical Genius of the Victorian Age
The degenerate bending mode of CO2 is the usual 15 micron band. The strongest CO2 absorption band is the assymmetrical stretch mode, where all three atoms are in longitudinal motion along the axis of the CO2 molecule. That is observed at 2345 cm^-1 which is 4.26 microns wavelength.
The symmetrical stretch mode where the C atom is stationary is predicted at about 6.3 microns; but is IR inactive since the dynamic dipole moment is zero.
Can we simply look at Dr. Pierrehumbert’s first two sentences?
In a single second, Earth absorbs 1.22 x 10^17 joules of energy from the Sun. Distributed uniformly over the mass of the planet, the absorbed energy would raise Earth’s temperature to nearly 800,000K after a billion years, if Earth had no way of getting rid of it.
– Raymond T. Pierrehumbert, Infrared radiation and planetary temperature
Beyond the silly, speculative nature of Dr. Pierrehumbert’s thought experiment, he imagines an earth at a much greater temperature than the source of the energy…the sun. Maybe this is simply the pragmatic engineer in me, but I would never dream up an analogy like that. Nothing good can come of imagining this scenario…it’s like a signpost on the road to madness.
“”””” Oliver Ramsay says:
February 16, 2011 at 9:58 am
A couple of things are clear from Pierrehumbert’s piece;
First, that CO2 is the sine qua non of the greenhouse effect. He declares that, absent CO2, all the water woud be ice. CO2 transforms water into a greenhouse gas. “””””
If ALL of the water on earth was ice; then there would be no clouds and very little water vapor in the atmosphere, and suddenly we would have the full sun beaming down on the surface at closer to the 1362 W/m^2, than 1000 W/m^2 like it does now. That would be the mother of all climate forcings, since even now, the sun can heat the land surface to over 60 deg C during the day. With no clouds, there’d be no snow in the main land areas of the earth; the boiling sun would melt all that so it could run into the oceans and freeze.
What Peter Humbug is missing, is that water ice simply is not all that reflective. Fresh snow just a few minutes old may have 80% solar reflectance; but it quickly drops to a fraction of that once the sun gets on it. Sea ice looks quite bright; but only when compared to sea water, which is near black (3% reflectance).
It is quite clear that CO2 does virtually nothing to keep the Temperature up at nighttime in a high arid desert. Freeze all the oceans, and CO2 won’t do a damn thing about unfreezing them.
But the sun beating down on the ice so the surface melts, and refreezes, creating an anechoic optical trap that conducts light and heat to great depths. And the sun would evaporate all kinds of water vapor off the top of that ice even if there was not a single .molecule of CO2 in the atmosphere.
So you take out the CO2 and you get a little bit less cloud cover globally; but I doubt that the global Temperature would be perceptively different.
Our comfortable temperature range at todays orbital values, depends almost entirely on the Physical Properties of the H2O molecule.
This of course could be disproven by simply publishing some peer reviewed, and experimentally observed data, that shows the global Temperatures foillowing the atmospheric CO2; for any period of history, and any time offset, between the Temperature and the CO2. So far we’ve seen no such data.
“”””” Robert Clemenzi says:
February 15, 2011 at 1:11 am
George E. Smith says:
“So whatever your particles are emitting downwards, they must be emitting a like amount upwards; which escapes to space.”
Actually, the lower atmosphere is mostly IR opaque with a few windows. For most of the spectra were absorption occurs, 99% of the available energy is absorbed within 20 meters of the surface. In the “wings” it requires about 500 meters to absorb 99%. From this, I deduce that very little radiation from the lower troposphere ever gets to space. Based on my analysis of lapse rate plots, it is pretty obvious that, near the surface, the atmosphere is IR opaque and the net radiation is toward the surface. Since it is opaque, the radiation emitted toward space is simply reabsorbed within a few meters. At the tropopause, the atmosphere becomes IR transparent and a significant amount of energy is emitted into deep space. “””””
If the earth atmosphere is IR Opaque, then exactly how does LWIR from the upper atmospehre or even clouds ever reach the surface; and what is the directional selective mechanism, which causes the LWIR radiation to be concentrated downwards. The emissions from the surface are most definitely concentrated in the upwards direction. Emissions FROM the heated atmosphere itself are quite clearly isotropic; so they are not biassed donwwards. If anythign the escape path to space is favored over the downward path to the surface; simply based on the change in absorption line bradening due to Temperature and Pressure (collision broadening). Higher atmospheric layers are colder and lesss dense, so their absorption and emission lines are narrower than closer to the surface where the density (collision rate) and Temperature (Doppler broadening) are increased.
There’s no possible way the atmospheric radiated thermal spectrum can be concentrated downwards. The phenomenon is not optically different from the Raleigh scattering at short wavelengths; which makes the sky blue (daytime). The Raleigh scattering is also greater at ground level compared to the upper Troposphere, yet the blue sky looks the same upwards and downwards, except at the boundaries of the atmosphere (outer space, or the ground).
The earth’s atmosphere isn’t even vaguely IR opaque; well not until you get out beyond any CO2 bands and only H2O is IR absorbing.
The surface emitted spectrum goes from about 5.0 microns to about 80 microns for 98% of the emitted energy, and CO2 only grabs a small chunk of that in the 13.5 to 16.5 micron range. We are talking about a global “heating” source that has an average Temperature of 288 K, and radiates about 390 W/m^2. An ordinary one pint (250 cc) drinking water bottle is what is typically causing global warming via LWIR “heating”
To Oliver Ramsay
And he completely downplays any effects of nitrogen.
We live at the bottom of an ocean composed mainly of nitrogen which in itself is a huge heat sink moderating temperature, and subject to all the fluid and thermal properties as would a liquid in an ocean.
1 atmosphere of pressure = 10.3 m (34 ft) of water.
The atmosphere, mostly nitrogen, is ‘approximately’ the equivalent of the earth being covered in an additional 34 ft of water. Everywhere.
I don’t think nitrogen has ever been properly characterized for thermal radiation properties into the long wavelengths, lets say 8 microns and more. But that is absolutely necessary to characterize it’s insulating, or greenhouse properties.
I can’t find any data. In the past, there was simply never any need to do it. Now there is. Both N2 and O2 need to be fully characterized for absorption, emittance, reflectance, and transmission in the long wavelengths.
You will find a lot on the short wavelength response of N2 (O2, CO2, etc), but not long wavelengths. That is because short wavelength response is extremely easy to do. A high temp source is easy to build (a light bulb, hot plate, etc) and direct the thermal radiation through a room temp gas sample. Or send any other high energy particles through the gas sample.
The low temp characterizations have never been done because those are much more difficult measurements to make. You need a low temp sensor, as close to 3 or 4 kelvin as possible to simulate outer space background thermal radiation, and then have the gas sample and a 290 K or so radiation source emit through the gas. Or vice versa.
oops forgot to add
The reason N2 and O2 need long wavelength characterizations is because there are MASSIVE amounts of it in our atmosphere. Even small absorption, reflection, etc amounts, because there is so much of it, will totally swamp any puny CO2 effects.
These ivory chair pundits in academia need to get real….
No. I’m sorry. This is as far as I’m reading. This man is not a scholar, he’s a clown. That’s not an insult, it’s an observation. I suppose Physics Today is a peer-reviewed journal. Lovely.
An atmosphere is a mixed gas of matter and photons.
– Dr. Raymond T. Pierrehumbert
Ken Coffman says:
February 16, 2011 at 11:55 am
No. I’m sorry. This is as far as I’m reading. This man is not a scholar, he’s a clown. That’s not an insult, it’s an observation. I suppose Physics Today is a peer-reviewed journal. Lovely.
An atmosphere is a mixed gas of matter and photons.
– Dr. Raymond T. Pierrehumbert
————————————
If only he’d continued thus ” An atmosphere is a mixed gas of matter and photons, dreams and aspirations, airplanes and the rumble of history….etc” he could have been a poet or philosopher (neo-post-mod).