Is CO2 Warming a Mirage?

Reader and contributing author Ed Caryl sends another essay, and warns it may be controversial for the obsessed among us who insist a catastrophe is coming.

Is CO2 Warming a Mirage?

By Ed Caryl

There are three levels in the atmosphere where CO2 could act: at the surface, in the troposphere, and high in the atmosphere where radiation to space is greater than thermal absorption. In each location the conditions are different, and the way CO2 acts is different.

At the surface, the CO2 “back radiation” has been a mystery to many, this author included. Some argue that such a thing doesn’t exist, that it is against the second law of thermodynamics. It does exist, but the mechanism does not work very often, or exactly as advertised. This article will throw you some curves, and many numbers, but will stay away from complicated mathematics. Complex math is unnecessary.

First, the basics: CO2 is a three-atom molecule. It can be visualized as one carbon atom with two oxygen atoms attached, one on each side, in a straight rod configuration. As such, it is “non-polarized”, that is the charges on each atom balance, and the charge on the whole molecule appears to be zero as viewed from any angle. Thus, it has only two modes of vibration when excited by infrared radiation (IR). It can vibrate in and out along the long axis, like a rod that has been struck on one end, or it can vibrate parallel to the axis, like a rod that has been struck in the middle.

The vibration mode along the long axis is only excited in an asymmetric mode, where the end atoms move together in the same direction at the same time. The symmetrical stretch, where the oxygen atoms both move away from the carbon atom then back towards it, does not expose any charge, so doesn’t radiate or absorb radiation.

Figure 2. The vibration modes of CO2. From the top, only the 2nd and 3rd modes contribute to CO2’s IR activity. (Source: Chemwiki, UC Davis)

Figure 3 below shows radiation transmitted by the atmosphere. Conversely, that part that is not transmitted is absorbed. Note: only two peaks of CO2 act to absorb radiation that water vapor does not. Those peaks are at 4.25 µm and 15 µm. The 4.25-µm peak occurs at a wavelength that has little long-wave radiation by the earth.

Figure 3: Source Wikimedia Commons.

The 15-µm peak is the only one that is important in the greenhouse gas discussion. The atmospheric transmission at that frequency is such that less than 5% of the radiation gets through a 1-meter path at one atmosphere with the normal amount of CO2. This means that any radiation from the ground at the wavelengths that CO2 will absorb and re-radiate will be intercepted very close to the ground, most of it within a meter. The standard story is that when the energy is re-radiated, half goes up and half goes back down to the ground. But here is the rest of the story:

When a CO2 molecule is irradiated, it takes from 7 to 15 microseconds (a microsecond is 10-6 seconds) before it re-radiates. In air at standard pressure (1000 millibars), the air molecules are undergoing 1010 (10 billion) collisions per second. This means that before the CO2 molecule can get rid of the energy by re-radiating, it has very probably gotten rid of the energy thermally by colliding with other air molecules, oxygen and nitrogen, that do not re-radiate, about 100,000 times. It is true that some CO2 molecules will gain energy by these same collisions, at room temperature about 5% are excited at any time, but most of them lose the energy thermally before they can radiate.

At the surface, the ground is radiating long wave IR into the atmosphere. But, as described above, that radiation does not go very far. Half of it is absorbed in a few centimeters. If “back radiation” exists, some of the energy would be returned to the ground, but on the way back to the ground, CO2 molecules would absorb an additional fraction. That heat is then further absorbed by more thermal collisions with other air molecules. In any case the result is heated air.

This is especially visible above dark, flat surfaces, like asphalt roadways, or flat gravel deserts, if conditions favor, as an interior mirage, as in figure 1. An interior mirage occurs when the air at ground level is hotter than the air above it, making the ground level air less dense, thus with a lower index of refraction. This acts as a crude lens, making things higher up in the background, like the sky, hills, or higher background objects appear as if they were inverted at ground level. The sky or distant terrain can sometimes look like rippling water in this situation.

This phenomenon does not happen everywhere, only where conditions are right to hold the hot air at the surface and where IR heating is high. Any vertical relief, such as sloping ground, trees, grass, brush or other vegetation, will encourage convection and interfere with the radiation, and the warmer air will rise away from the surface. Lighter surfaces and vegetation also have less emissivity, thus there is less IR to interact with CO2. It does not happen over water, ice, or snow. Over those surfaces, another type of mirage happens, a superior mirage.

Figure 4. This is a superior mirage of Point Reys National Seashore seen in the background from San Francisco Bay. The image is not inverted. Point Reys is over 50 kilometers away, and over the horizon from this location. Source: Wikipedia Commons.

A superior mirage occurs when the air is colder and denser at the surface than higher up, and refracts a distant image along the surface, sometimes one that is over the actual horizon, making it visible as in Figure 4. This is an indication that IR heating is not taking place. We know that IR heating will not take place over ice or snow, because both the temperature and the emissivity are low. It does not take place over water because the water temperature and air temperature over it are usually very close. Any heat generated by IR is lost to water evaporation.

What happens to an inferior mirage when CO2 increases? The atmosphere becomes a bit more opaque at the wavelengths where CO2 absorbs energy, and the height where the energy is absorbed lowers slightly. Instead of 95% absorbed at 1 meter, we have 95% absorbed at 80 cm. Only where it is absorbed changes, not how much. There would be little difference in appearance of the mirage, and no difference in heating.

What happens further up in the atmosphere? For that I bow to others. It involves a concept called Local Thermodynamic Equilibrium. Tom Vonk has a good explanation here. The CO2 in the atmosphere is in Local Thermodynamic Equilibrium (LTE) up to about 100 km. If the atmosphere is in LTE, an increase in CO2 does nothing. It is only at the top of the atmosphere that CO2 can radiate heat to space, and more CO2 there will result in more radiation.

At the top of the atmosphere (TOA), if there is more CO2, there is more long-wave radiation to space, and the high atmosphere cools. Google Local Thermodynamic Equilibrium on the web; you will see many articles talking about non-Local Thermodynamic Equilibrium. Many of these are discussing cooling at the TOA by ozone, CO2, and other processes.

Some readers will say that my explanation is wrong; that an inferior mirage is simply from the surface heating the air by conduction. Air is an insulator. There is some heating of the air by convection, especially if the surface is sloping or irregular, but most of the air heating is by radiation.

There is no “back radiation” if the air is cooler than the surface, because heat (radiation) cannot flow from a cooler body (the air) to a warmer body (the ground surface). There is only radiation upward from the hot ground to the cooler air, which is then absorbed by the CO2 in the air. If the air happens to be warmer than the ground, then radiation can flow the other way and heat the ground, but this is rare. For a good tutorial on the subject of heat flow, go to this site, and download Chapter 26 – Heat Transfer.

In summary: The ground surface is heated only by solar shortwave radiation. This heats the ground, which then radiates long wave IR back into the atmosphere. At the wavelengths where CO2 and water vapor are opaque, this IR is absorbed and heats the atmosphere. If CO2 increases, only the height at which this happens changes. This height is very close to the surface, on the order of 1 meter or less. Back radiation only happens if the air is warmer than the ground. At elevations above 1 meter, the atmosphere is in LTE and increased CO2 does nothing. At the TOA, increased CO2 can radiate to space, cooling the TOA.

Increased CO2 warming is nothing but a mirage.

193 responses to “Is CO2 Warming a Mirage?”

  1. Brian G Valentine

    About all I can add to that is, what was to have been the most reliable information about the distribution of CO2 in the atmosphere, the Orbiting Carbon Observatory, (which went down in the ocean about a minute and a half after lift off)

    – would have STILL required modeling of CO2 transport in the atmosphere to describe the distribution.

    (The OCO zeroed right in on the major source of carbon dioxide, mission successful.)

    Anyway the assumption is counter intuitive to what we know about the influence of gravity on the atmosphere. Enough said.

    “Put your trust in your judgment, not your Google Scholar.”

  2. Rob Honeycutt

    Brian said… “Put your trust in your judgment, not your Google Scholar.”

    That’s very un-scientific of you. Trust your judgement over decades of research?

    1. Brian G Valentine

      Your clear, unbiased, rational, considered, skeptical, and most critical of your own views.


      1. Rob Honeycutt

        Did you even think to try reading any of the papers SoD has pointed you to? You might find your judgement improve if you do.

  3. Dana

    SoD, I must say, I’m very impressed. Not only do you really know your stuff, but you have the patience of a saint. When people think they’ve disproven decades-old physics, or assume that scientists make stupid mistakes in their fundamental observations, it just bugs the hell out of me. Scientists don’t just jump from grade school to the observatory, they spend their lives researching this stuff. If you think you’ve figured out some obvious fundamental error that thousands of these scientists haven’t, the odds are pretty damn good that you’re full of sh*t.

    Personally when I come to a different conclusion than the experts, my first reaction isn’t “these scientists must be idiots!”, it’s “okay, what did I do wrong?”. And 99 times out of 100, The mistake is mine.

  4. Interglacial John

    Wow! I cannot believe CO2 has not completely done us in already. Can you imagine? Billions of years of CO2 just swirling around in it’s deadly dance, sometimes at levels 20 times higher than today! EEEK!!! Thank God the CO2 fairies were there to save the Earth from that evil gas. It is truly a miracle this rock is not burnt to a crisp right now, because we know for a fact that the “thousands of scientists” could not possibly be wrong, that has never happened before. Golly gee Wally, I sure hope mom doesn’t find out.

  5. ScienceofDoom

    Earlier (12. Februar 2011 at 21:48) I said:

    “DirkH suggested that the paper, “A new one-dimensional radiative equilibrium model for investigating atmospheric radiation entropy flux” by Wu & Liu indicates that current radiative transfer theory is still in need of work.

    As many people here, including DirkH and the author of the article, are well-versed in the field of radiative transfer I look forward to a summary of what the paper demonstrates about the standard theory regarding radiative transfer.

    Afterwards, I will make my comments and the readers can compare.”

    DirkH, can you confirm whether or not you are going to explain how this paper demonstrates a problem with the current theory of radiative transfer in the atmosphere?

  6. Bomber_the_Cat

    I thought this was a very promising article Ed until I got to “There is no “back radiation” if the air is cooler than the surface, because heat (radiation) cannot flow from a cooler body (the air) to a warmer body (the ground surface)” .
    At this point I had an internal groan, for here you destroy your credibility by denying established physics. And, judging by the comments you received, look what’s happened since.
    In your response to the first commentator you immediately contradict yourself and say “The cooler object can influence by back radiation the temperature of a warmer object”. Indeed, as ‘Brian H’ points out in his first comment, radiation doesn’t know where it’s come from or where it’s going and “If the CO2 output happens to strike a warmer spot, that spot will become even warmer”. This does not in any way infringe the 2nd Law of thermodynamics, just a schoolboy misunderstanding of it.
    No serious sceptic denies that CO2 has some warming effect. What they do deny is that further increases in CO2 will have anything other than a benign marginal effect, well within the natural variations of climate. There is no need to resort to back-street science to justify this.
    We know that, without mythical feedback effects, a doubling of CO2 will lead to a global temperature increase of only 1 deg. Celsius.This is what the mathematics show and this is what is published in the IPCC reports. Indeed, even the arch-warmist Stephen Schnieder said in a peer-reviewed paper, Schneider S. & Rasool S., “Atmospheric Carbon Dioxide and Aerosols – Effects of Large Increases on Global Climate”, Science, vol.173, 9 July 1971, p.138-141
    “We report here on the first results of a calculation in which separate estimates were made of the effects on global temperature of large increases in the amount of CO2 and dust in the atmosphere. It is found that even an increase by a factor of 8 in the amount of CO2, which is highly unlikely in the next several thousand years, will produce an increase in the surface temperature of less than 2 deg. K.”

    Current predictions of climate catastrophe depend solely on there being a positive feed-back effect, in which this fractional temperature rise will release more CO2 from the oceans, more methane from the permafrost and so on, thus producing runaway catastrophic warming. This is pure speculation. We have never witnessed such an effect in geological history although past temperatures on this planet have been much higher and CO2 levels have been much higher. This positive feedback, or ‘climate sensitivity’, is not based on experiment nor observation. It remains an unfounded conjecture in conflict with all known observations.
    This is the Achilles heel in the warmist argument. Don’t get distracted into on to the wrong ground.
    Life on our planet has managed to survive with levels of CO2 much higher than the present level, which are historically low.

    1. Ed Caryl

      There is no contradiction between those two statements. What i meant was, on balance, heat doesn’t flow from a cooler object to a warmer object. But a cooler object in proximity to a warm object will result in less heat flow from the warmer object. Yes, heat is flowing from the cool object, but more heat is flowing from the warm object. The resulting heat flow is the difference. In the case of CO2 in air and the ground surface, what is the mass difference? What is the ratio of heat flowing upward and heat flowing downward, due to CO2?

  7. AlecM

    Sorry to upset the party but I’ve concluded IPCC ‘science’ is wrong for different reasons. Leaving aside palaeo-climate data, the only ‘evidence’ for high-feedback CO2-AGW is ‘cloud albedo effect’ cooling, 1.75 times raw median AGW [figure 4, AR4]. If it’s wrong, ‘climate sensitivity’ is much lower than claimed. Yet by c.2003 NASA knew there was no experimental proof of it:

    So, it’s purely theoretical. But look at thick clouds about to rain. They get darker underneath, higher albedo, yet the theory predicts the reverse so it’s wrong. The bottom line is this ‘cooling’ is imaginary. So what really happens? The models use one or other ‘two-stream approximations’. Sagan’s version is eq. 19:

    It’s a monotonic function which apparently fits data but because it assumes just one optical process, asymmetrical diffuse scattering, it goes the wrong way when you ‘pollute’ thicker clouds. You correct the physics by adding direct backscattering.

    When the plane wave interacts first with droplets in line of sight, 3% is backscattered, 97% forward scattered, a narrow lobe, relative peak 10^7 at 15 microns, 10^5 at 5 microns [polluted] and 10^10 at 200 microns [about to rain]. If you assume the same backscattering at the next interaction, 3% of 10^10 is a very large number. It’s a cone because of dispersion, wider for small droplets. Glider pilots above rain clouds can be temporarily blinded so it’s a powerful effect.

    As it falls significantly as droplet size decreases, it’s another form of AGW. At a best guess, reducing droplet size from 15 to 5 microns decreases it by a factor of c.3 and a starting albedo of say 0.7 falls to .56, transmitted energy increases by 43% [0.3 to 0.43]. It’s also self limiting [albedo asymptotes to just over .5] and reversible.

    So, we can have a Miskolczi GH effect control system and account for AGW which heated the oceans from the 1980s to 2003 then levelled off. Was it mainly the rise of the Asian Brown Cloud decreasing low level cloud albedo! I could be deluded though. Go ahead and prove me wrong!

  8. Gene Beljaeff

    Great discussion.

    I am not a scientist, but here’s a Thought Experiment:

    If you had an Infrared camera which was only sensitive at 15-µm, and pointed at the ground, what would it see at:
    a) 1/2 meter from the ground
    b) 1 meter from the ground
    c) 100 meters from the ground
    d) 10,000 meters from the ground

    Would c & d look the same?
    Would anything farther than about 1 meter show no radiation?


  9. Bob Armstrong

    Like so many battling this GlobalStatistStupidity , I can pursue it only in my literally “free” time . So I’ve only just now finished reading the post . But I wanted to comment that this is the best presentation of much of the classical basic physics of the situation , and Figure 3 , which I wish I had seen nearer 2007 when it appears to have been published , the best instantaneously understandable presentation of why additional amounts of the green gas upon which life is built can have very little effect on temperature . I’m adding it and a link to it and this article to my planetary temperature page .

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