Guest post by Reed Coray
The following example illustrates the issues I have with reasoning often used to argue that increasing the amount of CO2 in the Earth’s atmosphere will increase both the Earth’s surface temperature and the Earth’s atmosphere temperature. Immediately following is a direct quote from URL
http://www.school-for-champions.com/science/heat_transfer_earth.htm
“The present situation is that there has been an increase in infrared-absorbing gases in the atmosphere, such as carbon dioxide (CO2) and methane (CH4). Energy that would normally escape into space is absorbed by these molecules, thus heating the atmosphere and spreading through convection currents. The average temperature of the atmosphere has increased 0.25 °C since 1980, mainly attributed to an increase in infrared-absorbing gases in the atmosphere.”
Although the above statement makes no direct reference to Earth surface temperature, I believe it carries the implication that greenhouse gases in the Earth’s atmosphere increase the Earth’s surface temperature.
I make two comments: the first is relevant only if the above implication is valid, the second is relevant independent of the validity of the implication. First, placing matter adjacent to a warm surface such that the matter is capable of absorbing/blocking radiation to space from the warm surface can lead to a decrease in the warm surface’s temperature. Second, increasing the amount of the absorbing/blocking matter can lower the temperature of the absorbing/blocking material.
Take for example an internal combustion engine whose metal surface is exposed to a vacuum. In addition to doing useful work, the engine produces thermal energy (heat). That thermal energy will produce a rise in the temperature of the engine’s surface such that in energy-rate equilibrium the rate energy is radiated to space from the engine’s surface is equal to the rate thermal energy is generated within the engine. By attaching radiating plates to the engine’s surface, some of the energy radiated to space from the engine’s original surface will be absorbed/blocked by the plates; but because thermal energy can be transferred from the engine to the plates via both radiation and conduction, the temperature of the engine’s original surface will be lowered. This is the principle of an air-cooled engine[1]: provide a means other than radiation of transferring heat from an engine to a large surface area from which heat can be removed via a combination of conduction, convection and radiation, and the engine’s surface temperature will be lowered.
If plates at a temperature lower than the original engine surface temperature are attached to the engine, it’s true that the temperature of the plates will increase to establish energy-rate equilibrium. Once energy-rate equilibrium is established, however, increasing the plate radiating area (adding additional matter that blocks more of the energy radiated from the original engine surface) will likely lower the plate temperature.
Thus, blocking the amount of surface radiation escaping to space does not necessarily increase the surface temperature; and increasing the amount of radiation blocking material does not necessarily increase the temperature of that material. In both cases (the Earth/Earth-atmosphere and the internal combustion engine in a vacuum), the heat eventually escapes to space–otherwise the temperature of the Earth’s surface and the engine would continue to rise indefinitely. The difference isn’t that the energy doesn’t eventually escape to space (it does in both cases), the difference is in the path the energy takes to reach space. The amount of generated thermal energy in conjunction with the path the thermal energy takes to get to space determines temperatures along the path; and adding more material may increase or decrease those temperatures. To say that “Energy that would normally escape into space is absorbed by these molecules, thus heating the atmosphere…” by itself is unwarranted; because an equivalent statement for the case of adding extra plate material to the engine would be “Energy that would normally escape to space from an engine with small attached plates is absorbed by additional plate material, thus heating the plates…” For air-cooled engines, this statement is not true—otherwise the plate surface area of air-cooled engines would be as small as possible.
It’s fairly easy to visualize why (a) adding thermally radiating plates to an air-cooled engine might decrease the engine’s surface temperature, and (b) increasing the area of the radiating plates might decrease the plate temperature. It’s not so easy to visualize, and may not be true, why (a) adding greenhouse gases to the Earth’s atmosphere decreases the Earth’s surface temperature; and (b) increasing the amount of atmospheric greenhouse gases lowers the temperature of the Earth’s atmosphere. I now present one possible argument. I do not claim that the argument is valid for greenhouse gases in the Earth’s atmosphere, but I do claim that the argument might be valid, and can only be refuted by an analysis more detailed than simply claiming “Energy that would normally escape into space is absorbed by these molecules, thus heating the atmosphere.”
If we assume that (a) matter cannot leave the Earth/Earth-atmosphere system, and (b) non-greenhouse gases radiate negligible energy to space, then for a non-greenhouse gas atmosphere the only way thermal energy can leave the Earth/Earth-atmosphere system to space is via radiation from the surface of the Earth. The rate radiation leaves the surface is in part a function of both the area and temperature of the surface. For a greenhouse gas atmosphere, energy can leave the Earth/Earth-atmosphere system to space both via radiation from the Earth’s surface and radiation from greenhouse gases in the atmosphere. Suppose it is true that the density of greenhouse gases near the Earth’s surface is such that radiation emitted from low-altitude greenhouse gases does not directly escape to space, but is in part directed towards the Earth’s surface and in part absorbed by other atmospheric greenhouse gases. As the atmospheric greenhouse gas density decreases with increasing altitude, radiation emitted from high-altitude greenhouse gases can directly escape to space.
Now it’s not impossible that since (a) in addition to radiation, heat is transferred from the Earth’s surface to greenhouse gases via conduction, and (b) convection currents (i) circulate the heated greenhouse gases to higher altitudes where energy transfer to space can take place and (ii) return cooler greenhouse gases to the Earth’s surface, that the process of heat transfer away from the Earth’s surface via greenhouse gases is more efficient than simple radiation from the Earth’s surface. Many engines are cooled using this concept. Specifically, a coolant is brought into contact with a heated surface which raises the coolant’s temperature via conduction and radiation, and the coolant is moved to a location where thermal energy transfer away from the coolant to a heat sink is more efficient than direct thermal energy transfer from the heated surface to the heat sink.
One way to realize increased thermal transfer efficiency would be to use a coolant, such as greenhouse gases, that efficiently radiates energy in the IR band (i.e., radiates energy at temperatures around 500 K). Another way would be to spread the heated coolant over a large surface area. Since surface area increases with increasing altitude, thereby providing expanded “area” (in the case of a gas, expanded volume) from which radiation to space can occur, it’s not clear to me (one way or the other) that greenhouse gases won’t act as a “coolant” reducing both the temperatures of the Earth’s atmosphere and the Earth surface.
[1] It’s true that for most air-cooled engines the main transfer of heat from the engine plates is via a combination of (a) conduction of heat to the air near the plates, and (b) convection that replaces the warm air near the plates with cooler air. To aid this process, a fan is often employed, or the engine is located on a moving vehicle and the vehicle’s motion through an atmosphere provides the flow of air across the plates. Although conduction/convection may be the primary means of heat dissipation from the plates, radiative cooling also dissipates heat.
In light of the discussions re: TOA, WRT: CO2, temperature, thermosphere, etc. I will drag this out again, since it never seems to be part of the discussion, yet is observationally based and makes some interesting points, eg. cooling thermosphere (2°K attributable to CO2), shrinking of thermosphere due to low UV output, etc.
Shrinking atmospheric layer linked to low levels of solar radiation
AGU Release No. 10–28
26 August 2010
For Immediate Release
WASHINGTON—Large changes in the Sun’s energy output may cause Earth’s outer atmosphere to contract, new research indicates. A study published today by the American Geophysical Union links a recent, temporary shrinking of a high atmospheric layer with a sharp drop in the Sun’s ultraviolet radiation levels.
The research indicates that the Sun’s magnetic cycle, which produces differing numbers of sunspots over an approximately 11-year cycle, may vary more than previously thought.
“Our work demonstrates that the solar cycle not only varies on the typical 11-year time scale, but also can vary from one solar minimum to another,” says lead author Stanley Solomon, a scientist at the National Center for Atmospheric Research’s High Altitude Observatory. “All solar minima are not equal.” Researchers from the University of Colorado at Boulder (CU) also contributed to the project.
The findings may have implications for orbiting satellites, as well as for the International Space Station. The fact that the layer in the upper atmosphere known as the thermosphere is shrunken and less dense means that satellites can more easily maintain their orbits. But it also indicates that space debris and other objects that pose hazards may persist longer in the thermosphere.
“With lower thermospheric density, our satellites will have a longer life in orbit,” says CU professor Thomas Woods, a co-author. “This is good news for those satellites that are actually operating, but it is also bad because of the thousands of non-operating objects remaining in space that could potentially have collisions with our working satellites.”
The Sun’s energy output declined to unusually low levels from 2007 to 2009, a particularly prolonged solar minimum during which there were virtually no sunspots or solar storms. During that same period of low solar activity, Earth’s thermosphere shrank more than at any time in the 43-year era of space exploration.
The thermosphere, which ranges in altitude from about 90 to 500 kilometers (55 to more than 300 miles), is a rarified layer of gas at the edge of space where the Sun’s radiation first makes contact with Earth’s atmosphere. It typically cools and becomes less dense during low solar activity. But the magnitude of the density change during the recent solar minimum appeared to be about 30 percent greater than would have been expected by low solar activity.
The study team used computer modeling to analyze two possible factors implicated in the mystery of the shrinking thermosphere. They simulated both the impacts of solar output and the role of carbon dioxide, a potent greenhouse gas that, according to past estimates, is reducing the density of the outer atmosphere by about 2 percent to 5 percent per decade.
Their work built on several recent studies. Earlier this year, a team of scientists from the Naval Research Laboratory and George Mason University, measuring changes in satellite drag, estimated that the density of the thermosphere declined from 2007–2009 to about 30 percent less than that observed during the previous solar minimum in 1996. Other studies by scientists at the University of Southern California and CU, using measurements from sub-orbital rocket flights and space-based instruments, have estimated that levels of extreme-ultraviolet radiation—a class of photons with extremely short wavelengths—dropped about 15 percent during the same period.
However, scientists remained uncertain whether the decline in extreme-ultraviolet radiation would be sufficient to have such a dramatic impact on the thermosphere, even when combined with the effects of carbon dioxide.
To answer this question, Solomon and his colleagues used a computer model to simulate how the Sun’s output during 1996 and 2008 would affect the temperature and density of the thermosphere. They also created two simulations of thermospheric conditions in 2008—one with a level that approximated actual carbon dioxide emissions and one with a fixed, lower level.
The results showed the thermosphere cooling in 2008 by 41 kelvins (about 74 degrees Fahrenheit) compared to 1996, with just 2 K attributable to the carbon dioxide increase. The results also showed the thermosphere’s density decreasing by 31 percent, with just 3 percent attributable to carbon dioxide. The results closely approximated the 30 percent reduction in density indicated by measurements of satellite drag.
“It is now clear that the record low temperature and density were primarily caused by unusually low levels of solar radiation at the extreme-ultraviolet level,” Solomon says.
Woods says the research indicates that the Sun could be going through a period of relatively low activity, similar to periods in the early 19th and 20th centuries. This could mean that solar output may remain at a low level for the near future.
“If it is indeed similar to certain patterns in the past, then we expect to have low solar cycles for the next 10 to 30 years,” Woods says.
The study, published in Geophysical Research Letters, was funded by NASA and by the National Science Foundation.
paulinuk says:
July 23, 2012 at 9:41 am
Tim Folkerts “Yes, if you look closely enough you can find IR from room temperature N2 and O2, but it is orders of magnitude less intense than the IR from CO2, O3, CH4, etc”.
Thanks Tim, but you havn’t given me experimental evidence to back that up.The experiment I was considering was impracticable but this is more manageable: create a vacuum in a metal chamber cooled down to near absolute zero (like deep space); introduce a jet of diatomic N2 at 15c into the chamber and measure the watts of IR coming off the the jet . Do the same for triatomic Co2. You say CO2emission of IR is orders of magnitude higher, could be, I’m not sure about that.
I am, Tim’s right. Go to Hitran, look at the line browser for N2, you’ll see a solitary band just below 4 microns with a peak intensity ~10^-28. Do the same for CO2 you’ll see bands covering all wavelengths from 0.5-50 microns many of which exceed 10^-25 and some (including the 15 micron band) exceed 10^-19, i.e. nine orders of magnitude!
Your experiment has a flaw however, the N2 will most likely emerge as a liquid spray!
I saw a very dramatic illustration of this when a large tank of N2 at 3500psi outside my building blew its safety valve sending a very impressive, supersonic spray of liquid N2 tens of feet in the air, it lasted long enough for the fire brigade to arrive. 🙂
cba says:
July 24, 2012 at 6:19 am
Note that only about 2/3 of this is ghgs and clouds and aerosols etc. make up the other 1/3 and also that only 0.61 or 61% (239/391) of what leaves the surface escapes to space.
Your whole analysis is flawed because it assumes that the marginal effect of adding the next ppm of CO2 is the same as the average effect of all the existing CO2 which is clearly not correct.
It would be the same as my assuming that my retirement fund will earn at the same rate next year as the average of the last 30 years!
Steve Keohane says
http://wattsupwiththat.com/2012/07/21/some-thoughts-on-radiative-transfer-and-ghgs/#comment-1042947
that is interesting, especially in the light of my own results
http://wattsupwiththat.com/2012/07/21/some-thoughts-on-radiative-transfer-and-ghgs/#comment-1040910
\
if you can follow what my results mean:
we are on a path of (natural) global cooling, most probably due to increasing ozone (due to that shrinkage?)
I guess it will last until 2045, give or take one or two years
I HOPE NONE OF YOU GUYS HERE ARE GOING TO CLAIM NOW THAT THIS COOLING MUST BE AGC?
Phil: “Go to Hitran, look at the line browser for N2, you’ll see a solitary band just below 4 microns with a peak intensity ~10^-28. Do the same for CO2 you’ll see bands covering all wavelengths from 0.5-50 microns many of which exceed 10^-25 and some (including the 15 micron band) exceed 10^-19, i.e. nine orders of magnitude!”
Hitran is a computer program used to calculate spectral line emissions due to internal changes in a molecule or atom? Does it calculate broadband thermal emission solely due to the temperature of the gas as well ( ie the motion of molecules, containing charge, relative to one another, the blackbody type)? That’s the type I’m interested in, the temperature dependent type .
cba says “I believe the project giving observational information is ARM”
Do you or anyone have a link to a published paper of observations that show increased GHGs raise the “location” and thereby lower the temp of outgoing radiation?
paulinuk says:
July 25, 2012 at 10:45 am
Phil: “Go to Hitran, look at the line browser for N2, you’ll see a solitary band just below 4 microns with a peak intensity ~10^-28. Do the same for CO2 you’ll see bands covering all wavelengths from 0.5-50 microns many of which exceed 10^-25 and some (including the 15 micron band) exceed 10^-19, i.e. nine orders of magnitude!”
Hitran is a computer program used to calculate spectral line emissions due to internal changes in a molecule or atom? Does it calculate broadband thermal emission solely due to the temperature of the gas as well ( ie the motion of molecules, containing charge, relative to one another, the blackbody type)? That’s the type I’m interested in, the temperature dependent type .
Gases don’t emit as blackbodies at atmospheric conditions, spectral line emissions are temperature dependent however.
”
Phil. says:
July 25, 2012 at 9:43 am
cba says:
July 24, 2012 at 6:19 am
Note that only about 2/3 of this is ghgs and clouds and aerosols etc. make up the other 1/3 and also that only 0.61 or 61% (239/391) of what leaves the surface escapes to space.
Your whole analysis is flawed because it assumes that the marginal effect of adding the next ppm of CO2 is the same as the average effect of all the existing CO2 which is clearly not correct.
It would be the same as my assuming that my retirement fund will earn at the same rate next year as the average of the last 30 years!
”
**************
No! you have missed something critical. This has nothing to do with ppm of co2 other than the doubling from the rise of the industrial results in a change of power absorption of 3.7 W/m^2 – using the standard accepted value. What it does assume is the same assumption as made by the ipcc which is 1 W/m^2 of forcing is the same as some other cause of a 1 W/m^2 change. I am using the averages for sensitivity but suffice to say that if the next 1 W/m^2 change in absorption does not cause roughly the same change in temperature as any other, then there is no such thing as a sensitivity and that the ipcc is fatally flawed in a fundamental assumption which negates their whole theory’s foundation. Also, since adding W/m^2 to the total is associated with increasing T, then the fractional changes of both will become smaller as more W/m^2 are added and the temperature rises which suggests that any changes now should be less than those changes at lower temperatures and power absorption levels. And, finally, if there is significant variation from this average such that there is higher sensitivity, it means there are a lot of W/m^2 related temperature increases that must be LESS sensitivity than the average and as mentioned in the last sentence, it is more believable that the most recent changes in W/m^2 wll result in the least effect. That is essentially that the last added W/m^2, if different from the average should be lower in sensitivity than that of the first few or middle few.
As for your retirement fund, it is producing artificially low results due to conscious decisions from governments to screw you in order to spend more money they do not have. Or put another way, the socialists are running out of other people’s money.
“””””…..paulinuk says:
July 25, 2012 at 10:45 am
Phil: “Go to Hitran, look at the line browser for N2, you’ll see a solitary band just below 4 microns with a peak intensity ~10^-28. Do the same for CO2 you’ll see bands covering all wavelengths from 0.5-50 microns many of which exceed 10^-25 and some (including the 15 micron band) exceed 10^-19, i.e. nine orders of magnitude!”
Hitran is a computer program used to calculate spectral line emissions due to internal changes in a molecule or atom? Does it calculate broadband thermal emission solely due to the temperature of the gas as well ( ie the motion of molecules, containing charge, relative to one another, the blackbody type)? That’s the type I’m interested in, the temperature dependent type ……”””””
PaulinUK, as you said, Hitran is a computer program used to calculate “spectral line emissions” (absorptions too) due to atomic or molecular structure; ergo it is based on quantum mechanics.
Black body radiation on the other hand has nothing whatsoever to do with quantum mechanics, or for that matter with atomic or molecular structure, or even with atoms or molecules.
For starters, a “Black Body” as used in science discussions, is a completely fictitious and fictional object, that does not exist anywhere, nor have any experimental data been gathered of such a contraption since none exist, or ever have existed.
So the mathematical theories of black body radiation, going back to Sir James Jeans, and Lord Raleigh, and of course Wiens, and probably earlier, and eventually Max Planck, are statistical mechanical classical physical discussions of a hypothetical object that totally absorbs ALL electromagnetic radiation that falls on it, in terms of a structure of that body simply consisting of “particles” which are in mechanical collision with each other under the laws of Newtonian mechanics (dynamics); which processes manifest themselves as the “Temperature” of that collection of particles. Concepts such as translational and rotational degrees of freedom of such particles (three of each), as well as the concept of equipartition of energy (average), assigning 1/2 kT to each such DOF, and the statistical distributions of such, were studied to create the various theories of how the spectrum of emission and absorption from such bodies should look. There isn’t even any implied mechanism for why energy should be absorbed or emitted; well because the device is totaly fictional anyway.
Planck of course put the icing on the cake, by simply insisting that emission or absorption at ANY frequency or wavelength must consist of an integral number of units of hf (or nu) at that specific frequency.
Note that this does NOT quantize the energy into discrete spectral lines; ANY frequency is possible, so ANY PHOTON ENERGY is possible, so there is nothing to relate to any physical atom or molecule or its electronic structure.
As you point out this hypothetical emission is entirely a consequence of TEMPERATURE which requires only that there be a very large number of PARTICLES IN CONSTANT COLLISIONS WITH EACH OTHER, which is after all why we call it THERMAL RADIATION when talking about actual real physical emissions of EM radiation from real bodies INCLUDING ORDINARY NEUTRAL GASES..
Despite the protestations of Myrrh and others; “Thermal Radiation” has nothing to do with the human sensory mechanism of feeling warm. The 2.7 Kelvin microwave background radiation is “Thermal radiation” and it isn’t going to warm diddley squat, except maybe somebody’s cryostat at say 5 microKelvins.
The magnificence of black body radiation is that something so non existent, can form one of the most important planks of modern Physics.
But no, HITRAN cannot compute thermal radiation even from atmospheric gases, because thermal radiation doesn’t have anything to do with quantum mechanics, or electron energy levels, and molecular structure; it is purely a consequence of Hertz/Maxwellian theory of electromagnetism, and plain ordinary Newtonian mechanics of electric charge carrying bodies in collision.
I explained how all that happens some time ago somewhere here at WUWT. As I recall, I made a screwup, in that which even Phil, did not call me on. I mentioned the Biot-Savart law as being germane to the subject (maybe it is), but that was a misconstrusion due to advancing old age, and was an incorrect reference. The law which I intended to refer to, which I mistakenly referred to as the BS law (the real one) is the law of electrostatics, that says there is no net effect inside a closed conductor carrying an electric charge. The same principle aplies to gravitation, so as you go deeper into the earth, the shell of mass external to you (earth radius wise) produces no net gravitational effect on you, so you get lighter as you dig deeper.
The electric effect applies to thermal radiation origins, because neutral atoms in free flight (between collisions) look roughly like a spherical electron charge cloud, similar to the charged conductor, and inside that cloud of course you have an atomic nucleus which is also charged; but which must be essentially unaware of the existence of that electron cloud, since there is no net electric field due to the electrons, inside the cloud to affect the nuclear charge.
But once atoms come into collision range, then of course all hell breaks loose, and both the electron clouds, and the nuclei, undergo accelerations and decelerations, and of course distortion in the case of the electron cloud, and per Hertz/Maxwell, that is going to create a giant radio station that will broadcast EM programming for eons, until the two colliding atoms take leave of each other, and go their separate ways, and then the station goes off the air to eventually fire back up again on another channel, when the next collision takes place.
Compared to the first 10^-43 seconds after the big bang, when all the interesting archeo-Physics happened, the broadcasting era of a couple of atoms in collision at +Kelvin Temperatures, is almost an eternity of interesting phenomena.
George E. Smith; says:
July 25, 2012 at 12:42 pm
I will quibble a small amount with your comment in two areas. In heat transfer, thermal radiation is defined and microwaves, UV, X-rays etc are not thermal radiation. Second solids such as metals which give off thermal radiation don’t have particles in constant collisons. They are in a lattice structure that vibrates, but the particles don’t necessarily collide. Electrons can move from lattice to lattice within the solid.
Although I don’t follow Myrrh his comment about thermal radiation was seconded by an astrophysist at NASA on an episode of “Universe”. So he can be forgiven for that.
”
Hockey Schtick says:
July 25, 2012 at 11:22 am
cba says “I believe the project giving observational information is ARM”
Do you or anyone have a link to a published paper of observations that show increased GHGs raise the “location” and thereby lower the temp of outgoing radiation?
”
************************
They do show differences between areas with little and lots of h2o vapor and different surface temperatures. What one sees is bands of wavelengths which are lower in magnitude than the theoretical power curve for the surface where the surface basically matches the power curve in areas not subject to ghg absorption. The lower magnitudes for the bands correspond to a temperature curve that is for a lower temperature such as at some altitude. The whole thing is not a bb curve at some temperature and hence some altitude. These can be calculated and constructed that look rather close to the measured values. Good luck trying to find very small changes like a 3.7 W/m^2 increase in absorption due to a co2 doubling (using the calculated ones). I doubt the measurements exists to permit one to look at two measured curves with enough difference in co2 concentrations to really see anything.
The whole thing about ghgs raising the location and lowering the T of the outgoing radiation is a nonreal hansen dellusion with no meaning. For clear sky you will have a bb curve with ground temperature and with some missing chunks that are actually reduced temperature emissions. For cloudy skies you will have the surface temperature of the cloud tops with much smaller amounts of absorption chunks missing because most of the ghg effects are below the cloud tops.
Rough balance dictates there be about 239 W/m^2 escaping from the Earth/atmosphere to match the 239 W/m^2 of incoming solar power absorbed by the Earth/atmosphere system. Looking at clear skies, one finds about 265 W/m^2 escaping from the average surface T of 288.2k. You’ll note that cloudy skies have to be somewhat below 239 W/m^2 in order for the average to come up as 239 W/m^2 with about 62% cloudy skies. On average, this would be about 223 W/m^2 which would correspond to about -22 deg C if there were no ghg absorption occurring about here. It’s prbably closer to around 273k for the average cloud top and that there is probably around 80 to 100 w/m^2 of absorption – but these are extremely crude guesses just to complete the rough idea.
George E. Smith +2
George E. Smith says: “Black body radiation on the other hand has nothing whatsoever to do with quantum mechanics … “
Say what!?
Black body radiation was the START of quantum mechanics! Planck’s efforts to understand BB radiation lead him to propose quantization of energy. Without quantum mechanics, you invariably get the “ultraviolet catastrophe”.
“For starters, a “Black Body” as used in science discussions, is a completely fictitious and fictional object, that does not exist anywhere, nor have any experimental data been gathered of such a contraption since none exist, or ever have existed.”
I suppose you could say this, in the same way you could say there is no “uniform sphere” ( they are made up of discrete atoms) or “frictionless surface” (there is always SOME friction) or “AC current in the form of a sine wave” (sine waves are infinite, but all currents have to start and stop sometime). But these are still extremely useful approximations.
The fact is, there are surfaces that are close enough to black bodies that there is no experimental way to measure the imperfections — small openings into large cavities . You might look up “cavity radiation”.
“it [BB radiation] is purely a consequence of Hertz/Maxwellian theory of electromagnetism, and plain ordinary Newtonian mechanics of electric charge carrying bodies in collision.”
Not even close. Classical physics utterly fails to explain BB radiation. It leads to the “ultraviolet catastrophe”.
“As you point out this hypothetical emission is entirely a consequence of TEMPERATURE which requires only that there be a very large number of PARTICLES IN CONSTANT COLLISIONS WITH EACH OTHER, which is after all why we call it THERMAL RADIATION when talking about actual real physical emissions of EM radiation from real bodies INCLUDING ORDINARY NEUTRAL GASES.
No. The emission of photons is NOT “entirely” a consequence of temperature. Temperature is only half of the story. The other half is the quantum mechanical properties of the material.
Materials can only emit or absorb photons with energies corresponding to energy changes within the material.
For hydrogen atoms, these are the quantized energies of the electron jumping between levels, as given by the Bohr Model (as predicted by quantum mechanics).
For other monatomic gases with more electrons, the electrons can jump in to lots of different levels allowing lots of different wavelengths (as predicted by quantum mechanics).
For molecules, you add in bending and spinning, giving a whole new set of energy levels (you guessed it — as predicted by quantum mechanics).
For solids, the the discrete energy levels get spread out into bands, allowing them to potentially absorb photons over a wider set of frequencies (based once again on quantum mechanics).
* The material determines WHICH energies of photons can be emitted.
* The BB radiation curve determines the MAXIMUM intensity of photons that can be emitted at each frequency.
You need to know BOTH the temperature AND the the quantum mechanics of the material to predict the thermal radiation.
For example, CO2 emits and absorbs pretty well near 15 um. So warm CO2 will emit 15 um photons at rates approaching those of an ideal BB. CO2 emits poorly near 8 um. So warm CO2 will emit 8um photons at rates much below those of an ideal BB.
N2 emits poorly throughout the IR wavelengths, so it will emit photons much at rates much below those of an ideal BB at ANY IR wavelengths. Yes, N2 (or H2 or O2) emits IR “thermal radiation”, but at rates so much below those of CO2 or H2O or the ground so as to be insignificant.
I still can’t understand why anyone with common sense would say a big ball of nitrogen,hydrogen or oxygen gas in space at say 1,000c wouldn’t burn your backside off if you were daft enough to get close to it but CO2 would.
Tim Folkerts,
You asked about the next question. Here is Question 2. Imagine an alternate Earth. Earth 2 has the same atmosphere as Earth 1, but one small difference at the surface. The surface of Earth 2 emits no IR at 15 microns.
At TOA, will Earth 2 either-
A. Emit no IR in the 15 micron band.
B. Emit the same amount of 15 micron IR as Earth 1.
C. Emit a smaller amount of 15 micron IR than Earth 1.
D. None of the above.
paulinuk says: July 25, 2012 at 2:17 pm “I still can’t understand why anyone with common sense …”
As someone who has studied and taught physics over the years, I can assure you that people’s “common sense” is notoriously poor and should not be counted on for discerning anything but the simplest of physics problems.
Even basic Newtonian mechanics defied common sense until a few hundred years ago (and still defies the common sense of many people). Throw in quantum mechanics (of molecular vibrations and photons) and you can pretty much figure that common sense is of no use.
“Here is Question 2….”
B. The outgoing IR would be the same (at least to a very good approximation). No 15 um photons from the surface escape to outer space. All of the 15 um photons that do escape are already coming from cool CO2 in the upper troposphere, so the spectrum as seen from high above the earth would be the same.
To extend the “bank of lights” analogy from above, you turned off one of the lights (ie the light that shines 15 um photons) that was already being blocked by a dimmer light above it. Whether or not that particular “light” at the surface is on or off makes no difference.
“””””…..mkelly says:
July 25, 2012 at 1:34 pm
George E. Smith; says:
July 25, 2012 at 12:42 pm
……”””””
Electromagnetic radiation is involved in HEAT TRANSFER in exactly the same manner that grocery shopping carts are involved in HEAT TRANSFER. Both are processes for transporting ENERGY. In the first case the energy is conveyed by an electromagnetic field wave, which knows absolutely nothing about TEMPERATURE, which occurs precisely nowhere in Maxwell’s equations, so EM radiation can’t transport “heat”, only ENERGY. We get NO HEAT from the sun; we make it ALL here on earth by wasting the incoming EM energy .
The grocery cart transports HEAT in the form of presto logs to throw in your fireplace, or steak, to munch on, or alcohol to wake you up. Those things themselves are not heat; they just contain energy which can be converted into waste heat. EM radiation isn’t heat either, it’s energy that can be wasted in many ways to result in heating.
By the way, what is it that locates the atoms in those solids, so they stay in those nice lattices, and stops them from colliding with each other. ?
“””””…..Tim Folkerts says:
July 25, 2012 at 2:12 pm
George E. Smith says: “Black body radiation on the other hand has nothing whatsoever to do with quantum mechanics … “
Say what!?
Black body radiation was the START of quantum mechanics!…..”””””
Well Tim , you got into this by yourself, so I’ll let you enjoy it.
Seems to me that MATTER which IS ENERGY was quantized, long before Max Planck ever heard of quantum mechanics, which had to wait till after wave mechanics came along.
So we see that Max was the CO2 of black body radiation. He used quantum mechanics to explain BB radiation, even before quantum mechanics existed.
How many quantum numbers are involved in the Planck quantum mechanics of black body radiation ?
“””””…..No. The emission of photons is NOT “entirely” a consequence of temperature. …..”””””
Well you have never heard or read me EVER saying that Tim; to recapitulate,
from Tim Folkerts…..”No. The emission of photons is NOT “entirely” a consequence of temperature. ”
from George E. Smith…..”As you point out this hypothetical emission is entirely a consequence of TEMPERATURE which requires only that there be a very large number of PARTICLES IN CONSTANT COLLISIONS WITH EACH OTHER…”
Tim, “>>>THIS<<>>THE<<< EMISSION OF PHOTONS". Words have meaning; use MY words; they mean what I say.
The first is a restricted special case; even a hypothetical one. The second is an all inclusive general case.
The first (black body radiation) is entirely a consequence of Temperature; the second that you cite of molecular and atomic electron energy level changes, is first order quite unaffected by Temperature; but is dependent on material properties.
BB radiation is quite independent of material properties; being fictional there is no prescribed material it applies to.
Planck's quite arbitrary hypothesis that the energy at some radiated frequency be in chunks of some integer multiple of THAT frequency, did nothing to restrict the possible radiated frequencies (or absorbed); all frequencies are possible, as are all energies.
Quantum mechanics restricts both the frequencies and the energies to only certain allowed values. All other values are forbidden.
I make it a rule to never stand between someone and the edge of the cliff they want to charge over.
@HenryP says, July 25, 2012 at 10:44 am
http://www.agu.org/journals/gl/gl0419/2004GL021042/2004GL021042.pdf
http://asd-www.larc.nasa.gov/~kratz/ref/p28jgr.pdf
http://www.agu.org/journals/gl/gl1115/2011GL048061/2011GL048061.pdf
“”””” u need to know BOTH the temperature AND the the quantum mechanics of the material to predict the thermal radiation……”””””
So we have one of these experimental near black body radiators Tim; you recommended I look up cavity radiation (I didn’t bother), and it is so close to a perfect black body that we can’t measure the discrepancy; I think you said something along those lines. So we have Planck’s exquisitely perfect formula for the black body radiation spectrum, containing nothing but fundamental constants of classical Physics, and an actual real faux black body made of actual quantum mechanical materials, which we haven’t even specified; apparently don’t need to know it’s so close to perfect. So now when do the quantum mechanical properties of these quite unknown and unspecified materials get to play their part in determining the radiation spectrum of our near but not exact simulated black body radiator.
How many possible ways, and material lists are there for building a near perfect black body radiator, all of which seem to behave the same regardless of their quite different quantum mechanical properties. Well it’s a rhetorical question Tim; no need to answer
I might come back to see who wants to join you.
Classical Physics/thermodynamics/chemistry is all that is required to analyze and explain: weather, global climate systems, heat flow, temperature differentials, and so forth. No blackbody exists in natrure anywhere period, and even with corrections to gray bodies, more are needed for the more true colored bodies. QM is not needed to be invoked at all for climate science or meteorology. Now for some of the cool underpinnings, wacky counter-intuitiveness of the small constituent world, or to make lasers for that matter, QM is then necessary. Nothing George E. Smith said is wrong. I would add mkelly’s minor corrections especially regarding solids like metals.
And of course there are many unknowns with climate because it would take tens of thousands of thermodynamics equations to truly understand the complexities/dynamic turbulent flows to actually arrive a true “global mean temperature” which we CANNOT do.
Hmm, not sure why WordPress eat the YouTube link. Here is the same link as https so WordPress hopefully won’t try to expand it: https://www.youtube.com/watch?v=EEFQHDSYP1I
Tim Folkerts, thanks for answering. Yes , B should be the answer to question 2. (C could also be correct if the small amount of 15 um IR that makes it directly to space from the surface of Earth 1 is taken into account).
Question 3 references Question 2. An alternate Earth 3 is the same as Earth 2, except that it has double the amount of O2 in the atmosphere.
At Earth 3 TOA, is the amount of outgoing 15 um photons –
A. The same as Earth 2.
B. Greater than Earth 2.
C. Less than Earth 2.
George, I suspect a lengthy debate about quantum mechanics will not be productive here. I suspect we both understand it pretty well. Let’s start by what I think we can agree on.
I think we can agree that “ideal” BB thermal radiation (eg in an infinitely large, perfectly conducting cavity) is an abstract idea, that leads to thermal radiation with a specific mathematical form that depends only on temperature. (And if I misread your statements and thought you were discussing actual thermal radiation when you were thinking about Ideal BB thermal radiation, I apologize.)
I think we can agree that any actual materials (or actual cavities) will emit thermal radiation that is strictly less than the BB radiation at any every wavelength.
I hope we can agree that the ground is pretty close to the the ideal BB curve for thermal IR; CO2 is close to the ideal BB curve for a few bands; N2 is never close to the the deal BB curve. (This is all that really matters for the climate discussions.)
There are several finer points where I would disagree with you (eg the wavelengths are indeed quantized in Plank’s theory but the size of the cavity, but they are typically so closely spaced that it doesn’t really matter; or that the mere fact that atoms are quantized implies that they are part of “quantum machanics”). These sorts of subtle ideas would require a face-to-face meeting to explain just what we mean and what assumptions we are making, and then to iron out any remaining differences.
And none of these fine points are particularly critical.
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There IS one other place where do I take exception to your writing. It is mostly a matter of semantics, but you say “We get NO HEAT from the sun; we make it ALL here on earth by wasting the incoming EM energy .”
“Heat” is a very problematic concept, but traditionally in thermodynamics “heat” means “energy in transit due to a temperature difference” or “the processes that transfer energy from one system to another system due to differences in temperature” — which includes conduction, convection, AND radiation.
* There is no heating of the earth by the sun via conduction.
* There is no heating of the earth by the sun via convection.
* There IS heating of the earth by the sun via radiation.
So thermal photons would traditionally be considered “heat” (whereas fluorescence or lasers would not).