Kevin Kilty
I’d say there is no one who writes comments in threads at WUWT who doesn’t believe that radiation provides the beginning and end points of Earth’s climate. Insolation provides energy input to drive the climate, and radiation takes away waste heat at the top of atmosphere (TOA), whatever TOA means for outgoing LWIR (more about this in a moment). Figure 1 shows, using Kelvin’s statement of the Second Law of Thermodynamics, how any heat engine, climate included, must work. It must procure energy from a hot place, whether or not we can call this a reservoir in the sense of thermodynamics, or not. Some of that energy is converted to work. The remainder is discarded into a cold place, with the same statement about whether or not that is a “reservoir”.
Figure 1. An engineered heat engine (Figure 1A) moves heat in the direction it would flow spontaneously but redirects some to do external work. By the first law Work=Qh-Qc, but by the second it can be no greater than Work=Qh(1-Tc/Th) where the temperature factor is Carnot’s theorem. In the atmosphere (Figure 1B) Work is done internal to the system and the dissipation of this work as heat may feed back into the so-called reservoirs so that the Carnot factor no longer really applies. Figure 1C simply shows what occurs in a power plant where flow-work is what runs the turbine.
However, there is endless discussion at WUWT, bordering on argument at times, about what goes on with regard to radiation, particularly the CO2 contribution, in the intermediate air.
The community here at WUWT are largely climate skeptics which means they tend to discount the importance of CO2. Fine. However, whether one seeks to discount or magnify the influence of CO2, one is obliged to use physically relevant arguments to do so. I hope to deep six a number of talking points that occur over and over with as rational an explanation of things as I can muster.
Transmittance measured and calculated
Let me begin with a diagram showing data collected in a laboratory. This is from the NIST website. Figure 2 shows the transmittance of IR radiation through a sample column of CO2 and Nitrogen, measured with an IR spectrometer. Transmittance is defined in terms of power transmitted by a beam of radiation. Thus, the deep troughs indicate energy per unit time that has been redirected from the beam. Where has it gone?
Figure 2. The IR spectrum of CO2. For reference with Figures 3 and 4 the deep troughs are located at 15um (667 inverse cm), 4.26um (2350 inverse cm) and 2.7um (3,700 inverse cm).
First, let’s examine how well a calculating engine, MODTRAN, reproduces this same picture. The pertinent parameters of the path through the sample tube in the spectrometer were 2.6 cm-atm of CO2 (the 200mmHg sample of CO2 was augmented with N2 gas to a total pressure of 600mmHg so that even the pressure broadening is representative). Figure 3 shows how the MODTRAN version at Spectral Sciences, Inc. does with parameters adjusted for 2.6cm-atm CO2.
Figure 3. Source of IR is a blackbody spectrum at 298K which tails-off strongly below 4um wavelength. CO2 at 26ppm and 1 km of pathlength is 2.6cm-atm approximately.
Looks pretty close, does it not? What it says, implicitly, is that while the path length for each plotted wavelength of EM radiation contains the same concentration of CO2, we get hugely different results. Concentration doesn’t matter because the cross-section for absorption varies hugely by wavelength. Claims that CO2 can’t matter much because it is a minor chemical constituent are simply wrong.
In fact, with this version of MODTRAN I can easily check whether or not Beer’s law works. Beer’s law is defined in terms of Absorbance. Absorbance is equal to -Log(Transmittance). At a wavelength of 4.71 um, these three models of atmosphere provide the indicated transmittances:
1700cm-atm H2O, 0ppm CO2, 20km path, T=0.741
0cm-atm H2O, 400ppm CO2, 20km path, T=0.919
1700cm-atm H2O, 400ppm CO2, 20km path, T=0.708
Beer’s Law calculated for this situation is in order 0.741×0.919=0.68
And the resulting transmittance is 0.68. Comparing 0.68 to 0.708 is well within the uncertainty of all things considered. So, MODTRAN looks like a pretty solid calculator when it comes to transmittance. We will examine radiance calculations shortly, but let’s return to the NIST data. Now back to answer the question about where does this energy go?
Where does the redirected energy go?
There are really only two possible responses to the step beyond absorption. The radiant energy is either scattered into other directions other than forward, or it is absorbed by CO2 and stored as molecules with elevated energy. Scattering is nearly zero because of the size discrepancy between the EM radiation and the molecular scale. CO2 strongly absorbs radiation at the wavelengths of those deep transmittance throughs in Figure 2. Now what is the next step in the chain of conversions?
People at WUWT now claim, rightly so, that this absorbed radiation very quickly passes into the kinetic energy of nitrogen in the case of Figure 2, but into Oxygen and Nitrogen in the case of the atmosphere. This is a good thing.
Energy quickly leaves the CO2 molecules into a sea of energy shared among molecular rotations, vibrations, and speed. It is not a one-way evolution of exchanges, because down at the molecular level, what proceeds in one direction goes just as surely in the opposite, maybe at a different rate. So, evolution proceeds toward a distribution of energy by all conversion means until it is a stationary distribution – an equilibrium state. This is the Boltzmann distribution, and the atmosphere arrives there through a detailed balance of energy exchanges. Once we arrive at the Boltzmann distribution it becomes possible to speak of a “temperature” of the ensemble of molecules in near equilibrium with the sea of EM radiation within it.
I never see any reference to Boltzmann distribution, or Maxwell distribution (molecular speeds) or concept of detailed balance, even though these concepts are central to understanding both the concept of temperature (especially LTE) and radiance in the atmosphere.
The background blackbody radiation from the Earth’s surface, along with emitted radiance from nearby atmosphere, simply replaces energy lost from the local atmosphere by various means. This sum total of interactions, and the rates at which they occur, keeps the atmosphere in local thermodynamic equilibrium (LTE).
So, rather than the rapid conversion of absorbed radiation from CO2 to other molecules and other forms of energy preventing back radiation, this conversion makes possible the calculation of radiance of the atmosphere by knowing only its temperature and composition. Some of that radiance goes back to the surface.
Accurate transmission calculations, and radiance calculations from specified chemistry and temperature allow MODTRAN to act as a useful transport modeler.
A couple of other things to discuss
There is often an insistence that molecules in a cold atmosphere can’t radiate to a warmer surface because doing so would violate the Second Law of Thermodynamics. Thus, the greenhouse effect is impossible. Moreover a few people deny that a warmer instrument can measure LWIR originating from a colder place.
This insistence shows a misunderstanding of the concept of “temperature”. Molecules don’t have a temperature; they have only energy. The second law applies to temperature which is only meaningful for a large ensemble of molecules. Energy can travel anywhere, bulk heat can, spontaneously, only travel toward cold from hot, unless one forces its travel the other direction with input of work (refrigerators and heat pumps).
Another insistence by folks who overvalue CO2 is that LWIR cannot travel from the surface directly to space because it gets absorbed and much is returned to Earth. Here is how one set of professional climate scientists phrased it.
“… infrared emission from the surface is mostly absorbed in the atmosphere and cannot radiate directly to space. In turn, the atmosphere radiates both up (to space) and down (to the surface). The surface therefore receives a double whammy of radiation from both the Sun and the atmosphere…”
This represents a belief that cooling of the Earth takes place at a mythical level way up high where the temperature is 255K.
This actual level from which radiation heads to space, the cold “reservoir” that allows the atmospheric heat engine, is exceedingly complex and includes even the Earth’s surface in places and at times. Let’s use MODTRAN once again to show its two end-member clear sky models. Figure 4 shows these.
Transmittance from surface to space averaging between 14% and 32% is not negligible. Yet, there are other instances, not covered by models in MODTRAN, where average transmittance is likely higher. Portions of surface above 2,000 meters elevation, for example, are above the bulk of moist air.
The subtropics, where the furthest reach of the Hadley cell returns to Earth, is composed of air that has been substantially dried by tropical precipitation. It is very transparent to LWIR. It is also an interesting case of where dynamics and radiation meet to cooperate in cooling the Earth. The descending air is kept warm through work performed on it by the surrounding atmospheric pressure, (or by gravity if one insists on that explanation that requires further elaboration), and radiates this work away as heat freely to space.
Even in wavelength ranges where the atmosphere is very opaque (many optical depths from surface to space) to the ballistic passage of IR radiation, there is still a flow of radiant energy that more nearly resembles diffusion, or conductive heat flow, with conductivity proportional to temperature cubed – the Rosseland approximation.
Figure 4A.
Figure 4 A and B. These represent end member clear sky models available in MODTRAN. Note that the Arctic winter atmosphere has ample windows that are highly transmissive and can easily present over 30% average transmittance. Even the moist Tropical atmosphere, though, has 14% average transmittance.
Is CO2 a negligible influence?
This essay began as a project to summarize estimates of climate sensitivity and the ways of arriving at it. However, the number of ways of arriving at that number is amazingly large. The methods have become more sophisticated over time; and more expensive! And definitions expanded the effort further by focusing on either the transient or equilibrium values. And then worrying about minor constituents of the atmosphere expanded it further, and on and on.
Soon I felt like someone auditing a Chicago election – the accounting mattered less than who decided what details went into the accounting. However, the topic of climate sensitivity ties in well, and generates two more comments of note.
A Baseline Value of Climate Sensitivity
The effect of adding a step increase in CO2 from 400 to 800 ppm does the following. It produces a step decrease in outgoing LWIR at the top of the (tropical) atmosphere (TOA) by 3.3W/m2.[1] Obviously, the First Law of Thermodynamics applied to this situation reveals that as output is restricted a little, but insolation remains constant, the amount of stored energy in the surface and atmosphere must rise a small amount too.
Just figuring Stefan-Boltzmann (SB) feedback alone suggests a need to raise surface temperature by 0.55C to restore output at TOA. MODTRAN calculations, though, reveal that balance isn’t restored entirely by this adjustment. Through trials I find that the surface temperature must adjust by 0.76C to restore TOA balance. By this point, though, SB applied to the ground surface shows that it radiates 4.5W/m2 – 1.2W/m2 more than the simple application of SB suggests.
People have commented that this presents a paradox, “Where does the additional radiant energy come from?” The answer is that it comes back to the surface from the atmosphere. There is no paradox. It is simply the reality of dealing with boundary problems when an LWIR active atmosphere occupies the space near a boundary.
It is no different than engineers applying a coating to a surface to make an object behave thermally in a different way. This surface coating for the Earth is its atmosphere.
Now further exploration using MODTRAN is warranted because it is perfectly reasonable to suppose that increasing surface temperature will lead to increased absolute humidity with its attendant enhanced LWIR absorption.
The U of Chicago version of MODTRAN allows one to calculate the effect of a constant relative humidity with increased profile temperature. Modeling as before one finds that the surface temperature has to be increased by 1.21C to restore the original LWIR output at TOA. At this point the surface emitted energy according to SB (with emissivity=0.97) is 7.2 W/m2.
This range of values 0.76 to 1.21 centigrade, I feel, provides a useful baseline of what will happen with 2XCO2, as long as the entire process is radiation bound.
The additional comment I would make takes me back to my original motivation of look at climate sensitivity. It is a rejoinder to the often repeated reference to “Simpson and Brunt from 1938”; that atmospheric dynamics makes prediction of what 2XCO2 will do meaningless.
After Moller in 1963 spooked everyone by concluding that an atmosphere with a variable relative humidity could lead to a surface temperature that was “arbitrary[2], Manabe and Wetherald undertook an effort to model the atmosphere that was sophisticated by 1967 standards.[3] They built a model using a 1-D finite differencing algorithm that included either 9 or 18 atmospheric layers and considered the effects of clouds, CO2, ozone, and water vapor either in constant RH or constant vapor pressure models. Their effort was complicated at this time because in addition to addressing the long-time worry over CO2 warming, there was an additional worry over the SuperSonic Transport (SST) adding water vapor to the stratosphere. What they found, however, was that reasonable distributions of absolute humidity would lead to 1.3 degrees centigrade warming while reasonable assumptions about relative humidity would lead to 2.3 degrees centigrade.
Spencer and Christy [4] (also open access) describe the construction of a 1-D model of vertical heat transport starting with the deep ocean and proceeding through the atmosphere. Their model involves three oceanic layers, three atmospheric layers. Having made this model and verifying it. They then considered estimates of energy imbalance made in various ways (satellite radiometery, Argo floats, borehole measurements, etc) and determined what climate sensitivity values produce a consistent story between energy imbalance, their 1-D model, and observed Earth temperatures since either 1970 or 1850 depending on data source, and also consistent with the two-sigma uncertainties in all quantities.
Their results range from 1.86 to 2.49 degrees centigrade per doubling of CO2. Lewis and Curry (2018)[5] found similar values using similar means. Three dimensional computer climate models produce greater climate sensitivity estimates (up to 5K) still. Yet then using these exact codes within the context of Earth system models produce much less warming (3.3K).[6] It is as though one can’t get a reasonable value of climate sensitivity without including every influence from the biosphere, cryosphere, oceans and atmosphere, because then one misses significant negative feedbacks. But in answer to Simpson and Brunt, despite many attempts to determine climate sensitivity in various ways, nothing seems lower than my baseline from radiation alone.
Notes:
1-The range of values for the decline in outgoing LWIR is 1.8 to 3.5 W/m2 through the full suite of MODTRAN models. Not as great as the Tropical model value, but not insignificant either.
2- F. Möller, On the influence of changes in the CO2 concentration in air on the radiation balance of the Earth’s surface and on the climate, Journal of Geophysical Research, 1 July 1963 https://doi.org/10.1029/JZ068i013p03877
3-Syukuro Manabe and Richard T. Wetherald, Thermal Equilibrium of the Atmosphere with a Given Distribution of Relative Humidity, Journal of the Atmospheric Sciences, Page(s): 241–259, 01 May 1967 DOI: https://doi.org/10.1175/1520-0469
4-Roy W. Spencer and John R. Christy, Effective climate sensitivity distributions from a 1D model of global ocean and land temperature trends, 1970–2021, Theoretical and Applied Climatology (2024) 155:299–308
https://doi.org/10.1007/s00704-023-04634-7
5-Nicholas Lewis and Judith Curry, 2018, The Impact of Recent Forcing and Ocean Heat Uptake Data on Estimates of Climate Sensitivity, Journal of Climate, 6051–6071
DOI: https://doi.org/10.1175/JCLI-D-17-0667.1
6-See for instance at The Geophysical Fluid Dynamic Lab and note the table of models.
For those wishing to pursue some challenging explanation of LTE:
Hermann Harde, Radiation and Heat Transfer in the Atmosphere: A Comprehensive Approach on a Molecular Basis, International Journal of Atmospheric Sciences, 27 October 2013 https://doi.org/10.1155/2013/503727
From the article:” At this point the surface emitted energy according to SB (with emissivity=0.97) is 7.2 W/m2.”
What is the emissivity of CO2 at temperature less than 30 C and pressures at or less than 1 atmosphere?
We have seen that CO2 is a lousy blackbody with full column emissivity somewhere between .002 and .2. The value we have developed above, .02, falls in this range.
Emissivity of CO2 | geosciencebigpicture
Since gases DO NOT emit radiation in curves similar to black body or grey body radiators (i.e., radiate according to the the SB equation), it is meaningless to ask about their effective emissivity.
You mean the emissivity charts in my heat transfer book are meaningless?
I think a better way to put it is that gases emit at given frequency bands with a certain emissivity. Outside those bands, you can not use SB because they don’t emit with an expected Planck curve causing different emissivity values from those at their frequency bands. It is one reason people say SB works for dense material, liquids and solids, but not gases. This should keep one from simply adding the intensity of a gas to the intensity of a solid to generate a Planck curve.
Followed this morning’s CrossFit session with a visit to the HOA pool.
Beautiful blue sky, light breeze, 83 F.
Jumped onto the pool.
Wow, cold shock to the system.
Water is 84 F!!
Body is 98 F.
Which way does heat flow?
Body to water.
There is no surface radiation let alone “back” radiation.
Heat transfer modes: conduction from contact & convection from movement especially the nozzles pumping in even warmer water.
Stand in the shallow end where the breeze cools exposed body by conduction, convection, advection, latent evap & radiation.
To what temperature?
Why the wet bulb, of course, at which the body now also radiates.
Stretch out on chaise lounge to dry in the sun.
Heat transfer modes: conduction from contact + convection & advection from movement + radiation now at skin temp + minor latent.
Radiation does not function separately from the kinetic modes and Earth’s surface cannot upwell an “extra” 396 W/m^2 out of thin air as a BB. The kinetic modes control the temperature & radiation goes along for the ride.
Science, it’s everywhere.
I read it all and my takeaway is how can the tests of a CO2+Nitrogen mix that is entirely unlike the actual atmosphere be relevant? To determine what CO2 does in the Earth’s atmosphere one should run tests using a sample of what’s easily available everywhere – air.
Then to test the effects of 2x CO2 it might be easiest to create “synthetic air” by putting together an exact same volume sample with all the same gasses – but each reduced fractionally and proportionally to make room for the added CO2.
Only then, by testing actual air, and what it would really be like with 2x (or more) CO2, can you really say “This is the effect in IR that doubling CO2 should have.”.
Thank you for this reminder of basic physics which I had the opportunity to learn in engineering school.
I would make just a point about back radiation :
So, the fact that there is a back radiation from the atmosphere towards the ground (and no doubt : there is one) doesn’t mean that there is an energy transfer from the atmosphere to the ground.
For this energy transfer to exist (and then a plausible warming), the downard – upward fluxes balance must be positive (i.e. downwards).
Measurements (see Earth energy budget by NASA) show that this balance is negative (upwards) which means that the atmosphere absorbs some energy emitted by the ground and this energy is :
To be more specific, lets imagine that the two upward and downward fluxes are equal :
May be of interest :
My stance :
Anyway, thanks for your great presentation.
Say what?
You are hopelessly confusing the fact that (a) radiation energy is emitted from any matter having a temperature above absolute zero (per SB equation), independent of whether or not another body of matter exists external to it at any temperature, with the calculation of (b) the net exchange of radiation energy between two or more bodies that have view factors of each other.
In case (b), a colder radiating body can and will deliver energy to a hotter body and this does NOT violate the Second Law of Thermodynamics.
With this understanding, “back radiation” (atmosphere-to-ground) is no different from direct radiation from a warm atmosphere to the ground, independent of the ground being hotter or colder than the atmosphere.
I’m confusing nothing and you (at least) misunderstood my post. Read it again but first, you should read (and understand) Michael Modest’s or Jean Taine’s reference books on radiative heat transfer.
Between 2 objects, only the net radiative heat transfer matters : your case (b). Here the 2 objects are the Earth’s ground and the atmosphere. The flux emitted from one or the other may be arbitrarily high (there is not only the proper (often assumed BB) emission at stake, but also reflexion, absorption, transmission between the 2 objetcs so the 2 measured fluxes ARE NOT merely the assumed BB – black body – emission of each one of the 2 objects. BTW the atmosphehre doesn’t behave as a BB).
In the case of the Earth’s surface and the atmosphere, the radiative fluxes balance, and thus the radiative energy transfer is upward so the atmosphere doesn’t radiatively warm the surface.
The basic confusion (as many do) is to believe that each of the fluxes are physically energy transfers : they are NOT despite the fact that each object may emit as a BB.
The only case where this assumption is almost correct is when an object emits into space (at 2.7K) as the fluxes balance is almost equal to the radiative flux of the object.
In the Earth energy budget, separating the 2 radiative fluxes between the surface and the atmosphere is misleading on purpose (before 2009, the NASA Earth budget showed only the fluxes balance which is the actual upward net radiative energy transfer from the surface to the atmosphere). I assume this trick is made because most people confuse radiative fluxes with radiative energy transfers and thus believe that the atmosphere can radiatively warm the ground (i.e. can increase its temperature) : this is wrong.
According to the NASA Earth’s energy budget, the only thing the atmosphere can do is to slow down the surface cooling.
For example, two same plates at 100°C facing each other and emitting as BBs DO NOT warm each other since the net radiative heat transfer is, by symmetry, 0 W (if they could warm each other, their own temperatures would indefinitely increase and thus their radiative emission and so on, which is obviously not the case).
The only physical radiative energy transfer to take into account is the fluxes balance and it goes only in one direction : only one object can be warmed, the coldest.
Another way to understand it is that there is no net radiative energy transfer between objects in an isolated room at a constant and uniform 22°C temperature, despite the fact that each one may emit assumedly as a BB.
Again, according to your understanding of radiative transfer, if a colder object could warm a warmer one by radiating (assumedly) as a BB then 2 objects at the same temperature should warm each other. Thus, each of the objects in the room should warm the others and should soon or later exceed 22°C and thus indefinitely increase the isolated room’s temperature.
This is obviously wrong and doesn’t only violate the second law of thermodynamics but almost all the observations and basic laws of physics (energy conservation, …).
Conversely, if you take only the actual radiative heat transfers between the objects (as fluxes balances) you will find that they are all of 0 W with no warming between objects and the isolated room will stay at 22°C, which is what is observed and is consistent with the second law of thermodynamics.
“According to the NASA Earth’s energy budget, the only thing the atmosphere can do is to slow down the surface cooling.”
You nailed it. CO2 is *NOT* a source of heat. Anything it sends toward the earth is simply returning part of what the earth has already emitted.
This can be easily seen in my attached, primitive graph for nighttime temperatures. Slower cooling emits more heat (the area under the temperature curve) than faster cooling. That “more” heat is Planck’s “compensation” for reflected heat returned toward the source.
The temperature curves for both fast cooling and slower cooling NEVER go positive, meaning the radiation from CO2 never actually “raises” the temperature of the earth.
This is also the reason that CO2 has not resulted in a statistically significant (i.e. outside the natural variance) global increase in Tmax. We are *not* seeing consistently higher Tmax temperatures than we did 90 years ago. We *are* seeing statistically significant increases in Tmin resulting in longer growing seasons globally, due to the slower cooling rate. Tmax is pretty much limited by T^4. The sun’s insolation is pretty constant so at the point where the joules-in from the sun trigger a temperature on earth where T^4 gives the same amount of joules-out, the earth’s temperature stops going up. It’s why T_max just doesn’t continue to go up till sunset happens
“You nailed it. CO2 is *NOT* a source of heat. Anything it sends toward the earth is simply returning part of what the earth has already emitted.”
Otherwise known as recycling, so the Earth will be warmer than it would have been if, in the absence of CO2, that IR will have reached space.
“warmer than it would have been”
These are the operative words. All these words are saying is that the object cools at a slower rate. The temperature gradient remains negative, it never goes positive due to reflected heat. Even with a perfect reflector the temperature gradient would only go to zero, it will not go positive.A negative gradient means COOLING.
Losing less heat due to radiation while at the same time absorbing the same amount of solar means that the surface temperature will increase, i.e. warming.
Losing heat is cooling. It does *NOT* cause an increase in temperature. It only results in slower cooling. The temperature gradient does not reverse and become positive.
See the attached graph. The heat lost is proportional to the area under the temperature curves. Which curve has the largest area under it? The fast cooling curve? The slow cooling curve?
Please note that in neither case does the slope of the temperature curve go positive.
The surface, ocean and land, can store heat through conduction to a different location. If you examine land, the surface can conduct heat to 2 in, 5 in, even 20 in deep. That is heat that is not radiated at any given time.
Dealing with black bodies, Planck says this in relation to entropy.
Your assumption here is that heat can flow from cold to hot. Notice I said heat and not energy. Under the assumption that the earth and insolation are in equilibrium, which if they are not, the whole evaluation of what occurs on this planet can never be determined accurately, then what occurs between the surface and the atmosphere becomes a two-body problem. As a consequence, what you propose requires that entropy decreases with heat (not energy) flowing from cold to hot.
Lastly, your assumption requires that equilibrium between the surface and the atmosphere can never be reached. That is the consequence of cold warming hot.
Back radiation violates LoT 2.
Not that it matters.
There is no 396 BB & no 333 back.
I like to see photos of the Earth taken from spacecraft. I am able to “see” them because energy in the “visible” wavelengths is radiating from Earth. I can see “colors” because some substances absorb some wavelengths and reject others. Even the nighttime Earth shows red to white points of visible energy. The spectrum of energy from the Sun shows that about 40% of incoming energy is in the visible wavelengths. I have yet to see a similar spectrum of outgoing energy, but it seems to me that a study of energy balance that refers to all outgoing energy as LWIR is an unnecessary simplification.
Speaking of wavelengths, CO2, and all other non-condensing GHGs, can absorb energy only from certain, very small, bands of wavelengths from the Sun’s spectrum, in other words, a very small portion of the Sun’s energy. That being so, if the existing concentration of GHG is sufficient to capture all the energy available in those limited wavelengths, then the atmosphere is indeed “saturated” and no further “heat” can make the “oceans boil” no matter how much extra CO2 is added, nor how and how quickly that CO2 can pass on its energy to the rest of the air.
Ummmm . . . there is a difference between energy reflected in the visible range of the human eye and energy emitted in the visible range of human eye. The average temperature of Earth’s surfaces (around 15 degrees-C, or 290 K), is far too low for it to emit light in the human-visible part of the EM spectrum.
Energy emitted by Earth’s atmosphere and surfaces (land and water) falls almost entirely within the wavelength range of 7–20 microns, in the LWIR range and far away from the range of visible light. Contrary to what you assert, outgoing energy as LWIR is not “an unnecessary simplification”.
See attached graph.
Spencer has convective cooling about 1/2 of greenhouse warming. If greenhouse warming increases so should comvective cooling, reducing warming by about 1/2.
https://www.drroyspencer.com/2024/08/yes-the-greenhouse-effect-is-like-a-real-greenhouse-and-other-odds-and-ends/
Harold The Organic Chemist Says:
ATTN: Kevin
RE: CO2 Can Not and Does Not Cause Warming of The Air.
RE: H2O Can and Does Cause Warming of Air.
At the Mauna Loa Obs. in Hawaii, the concentration of CO2 in dry air is currently 431 ppmv. One cubic meter of this air has a mass of 1,290 g and contains a mere
0.85 g of CO2 at STP. This tiny amount of CO2 in air can not absorb enough out-going long wavelength IR light at 667 wavenumbers to heat up such a large mass of air. Photons at 667 wavenumbers are low energy photons.
In air at 21° C and 70% RH, the concentration of H2O is 17,780 ppmv. One cubic meter of this air has a mass of 1,200 g and contains 14.3 g of H2O and 0.79 g of CO2. To the first approximation and all things being equal, the proportion of the greenhouse effect (GHE) due to H2O is given by:
GHE = moles H2O/(moles H2O+moles CO2)= 0.79/(0.79+0.0178)=0.98 or 98%.
This calculation assumes that a molecule of H2O and CO2 absorb about the same amount of out-going long wavelength IR light emanating from the earth’s warm surface. Actually, H2O absorbs more IR light than CO2. As I mentioned in my comment above, greenhouse effect due to H2O is variable and depends on local RH, and it is not the main process for warming of the air. The main process for warming of the air is: (1) sunlight heats the earth’s surfaces, (2) air contacts warm surfaces and warms up by conduction, and (3) the warm air rises up by convection and heats up the atmosphere.
You should not any more time and effort on this CO2 nonsense.
I guess I am more pessimistic that the current group of commentators.
Arguments here seem to ignore or oversimplify very complex concepts.
First, all the energy arriving from the sun is in the form of electromagnetic waves with a vast breadth of the spectrum and they are all “energy”.
The irradiated object has fiercely complex thermodynamic properties which vary vertically and horizontally and unevenly in both dimensions.
All “forms” of energy exchange operate significantly in this complex system.
Conduction, convection and radiation are not simple.
Much published analysis deals with these by ignoring more than is included.
Now, take water for example. a body of ice absorbs energy without changing its temperature until it is all melted, a body of water absorbs energy while evaporating without changing temperature – “latent heat” are the weasel words for this property. Water and convection: within a certain temperature range, water becomes less dense until it becomes ice and so a mass of water under gravity and the Coriolis phenomenon will rise or fall with slight temperature changes, and just a mention that fluid flow which is turbulent differs enormously from laminar flow.
Now, take a look at radiation. So many studies or analyses look at spectral bands associated with intrinsic properties of individual elements and compounds while radiation of infinitely variable wavelength is also of enormous significance in energy transfers.
Also, from outer space the earth is a glowing orb of blue-white and the light is a combination of lots of emission bands of specific molecules and black-body rainbow emission.
Lastly, the substances involved in these multiply complex energy exchanges change in their relative concentration depending on “temperature”.
So water and carbon dioxide and methane and ozone all change – they are dependent variables, not CONTROL variables.
Good luck with finding a mathematical equation which includes all these discontinuous variables in our lifetime, or ever.
“Much published analysis deals with these by ignoring more than is included.”
100%. Climate science calls these “simplifying assumptions”.
Things like: “all measurement uncertainties are random, Gaussian, and cancel”. “Cloud cover can be parameterized into an “average” global constant.” “numbers is just numbers” “an average is a physical measurement and not just a statistical descriptor” “averaging readings can increase resolution of measurement instruments”
Flux_radiant = f[ ε(x,y,t), σ, T(x,y,t)^4]
Good luck defining those to a granularity capable of determining radiation differences in the units digit over any time period you want to look at! If you can’t do that then it’s not possible to determine Joules-in vs joules-out to see if there is actually an increase or a decrease in the heat energy of the earth over the time period of the lowest frequency cycle involved.
Another simplifier is, ‘air temperature projection means are accurate because the errors offset, and all the base-state error is subtracted away in the anomalies.’
Right! And every probability distribution is Gaussian for that to occur. LOL.
Right! Because subtraction cancels errors just like a Gaussian distribution does. LOL.
no wonder there is debate. there is so much out there to unpack.
Saturated above 300ppm CO2 experiments.
https://iowaclimate.org/2024/04/22/3-physicists-use-experimental-evidence-to-show-co2s-capacity-to-absorb-radiation-has-saturated/
Supported here with ECS ~1.4 and a calculated GHG effect not =33C.
https://archive.org/details/RadiationPhysicsConstraintsOnGlobalWarmingCo2IncreaseHasLittleEffect/mode/1up
A 2026 paper indicating CO2 saturation above 300ppm and has been a since 1960.
https://doi.org/10.53234/scc202603/23
The absorption by carbon dioxide of infrared light radiated from the earth derived from Beer’s Law shows that 99% of IR,from 2390 to 2275 cm-1, radiated from the earth is absorbed in the lowest 25 m of the atmosphere.
https://pubs.acs.org/doi/10.1021/ed074p316
For a concentration of 400 ppm for which the mass of CO2 in the atmosphere is ~ 6 kg/m2, the saturation limit is exceeded 4- fold. Thus, the carbon dioxide additionally emitted into the atmosphere does not absorb further thermal radiation.
https://ph.pollub.pl/index.php/iapgos/article/view/2998/2729
The problem with jar experiments like Foote used is that they don’t demonstrate how CO2 traps heat, but rather demonstrate that CO2 has a higher molar mass than air. The same experiment with Argon which has no IR absorption does the same thing. https://pubs.acs.org/doi/10.1021/acs.jchemed.8b01057
Back-radiation lab experiment work confirms that increasing levels of CO2 at current levels in the atmosphere cannot significantly contribute to warming by more back-radiation.
https://www.scirp.org/journal/paperinformation?paperid=136478
Further back-radiation effect on air temperature simulation experiments showed that the temperature with CO2 only increased very slightly, about 0.5%. whereas the formulas used by IPCC give very large temperature changes.
https://www.scirp.org/journal/paperinformation?paperid=99608
Can’t find any other example of an “open-system” controlled lab experiment, but this one produced data proved that water vapor constituted ~95% of the natural greenhouse gases, and that CO2 at its current atmospheric concentration (0.042%) had no measurable effect on the absorption temperature. In this laboratory test, a 15-fold increase only raised the absorption temperature by 1.2˚F. This means the IPCC’s mathematical model is off by a factor of 31 times.
https://www.scirp.org/journal/paperinformation?paperid=145896
As many have suggested for years, another analysis appears the total net ECS around 0.76C +/-0.08 / 2xCO2 is likely and benign…. lost in the noise….along with saturation in hottest zone.
https://wattsupwiththat.com/2026/03/21/chasing-elusive-climate-sensitivity/
CO2 radiative ECS impact lower than many claim.
https://www.academia.edu/168964539/The_Thermodynamic_Short_Circuit_of_the_Lower_Troposphere_The_Fallacy_of_Macroscopic_Opacity_and_the_Kinetic_Destiny_of_Infrared_Energy?fbclid=IwdGRjcASkDZBjbGNrBKQNg2V4dG4DYWVtAjExAHNydGMGYXBwX2lkDDM1MDY4NTUzMTcyOAABHnuE-abLSUIt1qcncf9MzpR5pudwS7eXIdlU7y6gKL_h_Zcp1oHjPwuNSL11_aem_BRiIjXVsinn50IGQiVvTEA
Here, the researcher finds the impact of carbon dioxide is minimal because the mole fraction and partial pressure of CO2 is negligible. If we were to replace the atmosphere by one fully made up of carbon dioxide, the lapse rate would be faster.
https://doi.org/10.4236/acs.2020.101003
Role of trace gases in storage of heat and radiative energy balance exchanges. The contribution of CO2 to heat storage is negligible.
https://systems.enpress-publisher.com/index.php/TSE/article/view/10356
Equilibrium thermodynamics clearly show that Earth’s atmosphere would be isothermal at equilibrium with or without GHG’s.
https://www.frontiersin.org/journals/complex-systems/articles/10.3389/fcpxs.2025.1617092/full
These experiments found that short-term warming after adding heavier gases was mainly caused by suppression of convection, not by a greenhouse effect.
https://scienceofclimatechange.org/wp-content/uploads/SCC-Vol.6.1-09_Schnell-Harde.pdf
Earth’s climate is set by a balance between incoming solar and outgoing infrared radiation but it follows a simple linear function of surface temperature not the runaway quadratic thermal blockbody emission function.
https://www.pnas.org/doi/full/10.1073/pnas.1809868115
If energy could flow from a cold system to a warm system without work there would be refrigerators without power cords.
I have not seen any.
You?
The CO2 argument largely ignores degrees of freedom. You cannot change one thing and assume all else remains equal. The system will change everything to try and achieve least effort.
We hear about back radiation. What about back conduction and back convection? Conduction and convection carry energy from the atmosphere to the surface no different than back radiation. Temperature does not care how energy moves.
What about energy CO2 absorbs via conduction and convection and then radiates to space. This is energy the atmosphere would not lose otherwise and is thus a cooling effect of CO2 that increases with increasing CO2
Over 200 comments and scientific arguments. So where are we?
(I think all four apply)
If I might add one.