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At a glance - Is the CO2 effect saturated?

Posted on 9 January 2024 by John Mason, BaerbelW

On February 14, 2023 we announced our Rebuttal Update Project. This included an ask for feedback about the added "At a glance" section in the updated basic rebuttal versions. This weekly blog post series highlights this new section of one of the updated basic rebuttal versions and serves as a "bump" for our ask. This week features "Is the CO2 effect saturated?". More will follow in the upcoming weeks. Please follow the Further Reading link at the bottom to read the full rebuttal and to join the discussion in the comment thread there.


At a glance

This myth relies on the use (or in fact misuse) of a particular word – 'saturated'. When someone comes in from a prolonged downpour, they may well exclaim that they are saturated. They cannot imagine being any wetter. That's casual usage, though.

In science, 'saturated' is a strictly-defined term. For example, in a saturated salt solution, no more salt will dissolve, period. But what's that got to do with heat transfer in Earth's atmosphere? Let's take a look.

Heat-trapping by CO2 in the atmosphere happens because it has the ability to absorb and pass on infra-red radiation – it is a 'greenhouse gas'. Infra-red is just one part of the electromagnetic spectrum, divided by physicists into a series of bands. From the low-frequency end of the spectrum upwards, the bands are as follows: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays. Gamma rays thus have a very high-frequency. They are the highest-energy form of radiation.

As our understanding of the electromagnetic spectrum developed, it was realised that the radiation consists of particles called 'photons', travelling in waves. The term was coined in 1926 by the celebrated physicist Gilbert Lewis (1875-1946). A photon's energy is related to its wavelength. The shorter the wavelength, the higher the energy, so that the very high-energy gamma-rays have the shortest wavelength of the lot.

Sunshine consists mostly of ultraviolet, visible light and infra-red photons. Objects warmed by the sun then re-emit energy photons at infra-red wavelengths. Like other greenhouse gases, CO2 has the ability to absorb infra-red photons. But CO2 is unlike a mop, which has to be wrung out regularly in order for it to continue working. CO2 molecules do not get filled up with infra-red photons. Not only do they emit their own infra-red photons, but also they are constantly colliding with neighbouring molecules in the air. The constant collisions are important. Every time they happen, energy is shared out between the colliding molecules.

Through those emissions and collisions, CO2 molecules constantly warm their surroundings. This goes on all the time and at all levels in the atmosphere. You cannot say, “CO2 is saturated because the surface-emitted IR is rapidly absorbed”, because you need to take into account the whole atmosphere and its constant, ongoing energy-exchange processes. That means taking into account all absorption, all re-emission, all collisions, all heating and cooling and all eventual loss to space, at all levels.

If the amount of radiation lost to space is equal to the amount coming in from the Sun, Earth is said to be in energy balance. But if the strength of the greenhouse effect is increased, the amount of energy escaping falls behind the amount that is incoming. Earth is then said to be in an energy imbalance and the climate heats up. Double the CO2 concentration and you get a few degrees of warming: double it again and you get a few more and on and on it goes. There is no room for complacency here. By the time just one doubling has occurred, the planet would already be unrecognisable. The insulation analogy in the myth is misleading because it over-simplifies what happens in the atmosphere.

Please use this form to provide feedback about this new "At a glance" section. Read a more technical version below or dig deeper via the tabs above!

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In case you'd like to explore more of our recently updated rebuttals, here are the links to all of them:

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Antarctica is gaining ice
CRU emails suggest conspiracy
What evidence is there for the hockey stick
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The greenhouse effect and the 2nd law of thermodynamics
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What's the link between cosmic rays and climate change?
Is Al Gore's An Inconvenient Truth accurate?
Are glaciers growing or retreating?
Ocean acidification: global warming's evil twin
The human fingerprint in global warming
Empirical evidence that humans are causing global warming
How do we know more CO2 is causing warming?
Explaining how the water vapor greenhouse effect works
The tricks employed by the flawed OISM Petition Project to cast doubt on the scientific consensus on climate change
Is extreme weather caused by global warming?
How substances in trace amounts can cause large effects
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Is CO2 a pollutant?
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Evidence for global warming
Has the greenhouse effect been falsified?
Does breathing contribute to CO2 buildup in the atmosphere?
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What is methane's contribution to global warming?
Plants cannot live on CO2 alone
Is the CO2 effect saturated?


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Comments 1 to 15:

  1. The sceptics claim that the CO2 warming effect is already saturated or is close to being saturated is clearly false. It seems to originate with the assertion that the surface receives about 3.7 W/m2 more energy each time CO2 is doubled ie: a logarthmic curve. This means eventually it would take a huge volume of additional CO2 (presumably over a long time period) to add an extra 3.7W / m2. Which they suggest means the effect is essentially then saturated, but without specifying a precise number (how convenient of them).

    I see that the article mentions that this assertion about a logarithmic relationship may have been proven false by He et al. 2023, (?) and it also depends on emissions trajectories and other factors, but assuming the logarithmic relationship is simplistically true a look at radiative forcing versus CO2 concentration below and a bit of maths and its obvious the warming effect is not saturated and we are not yet near saturation:

    My back of envelope maths: In 1960s CO2 was 320 ppm ppm so doubling would be 640 ppm at around roughly year 2100 assuming BAU emissions. This coincides with the IPCC warming projection of 3 - 5 degrees C by 2100.

    The next doubling is from from 640 to 1280 is a larger volume of CO2 and would presumably take longer to around year 2300 assuming the same BAU CO2 growth trend and other things being equal. Projections of warming by the IPCC by 2300 are not surprisingly around 8 - 10 degress C for this further doubling of CO2. Such a quantity of CO2 is large but may possibly be feasible given reserves of fossil fuels and uncertainties arount that.

    The next doubling from 1280 to 2560 would lead to something like 15 degrees C and is a huge volume of CO2 that would take many centuries and would almost certainly exhaust reserves of fossil fuels, and most probably well before 15 degrees is reached. We could say this is the point of saturation in a practical sense. Its of no comfort because we would have had at least 5 degrees of warming and probably more, and not even factoring in tipping points.

    Someone check my maths its very rough, but the sceptics claims are clearly false and meaningless.

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  2. I think this is where data from paleoclimatology can help as well.  Three recent studies have looked at the earth's temperature vs CO2 during the Cenozoic period, Rae et al.Honisch et al., and Tierney et al. .  Each of those show that the temperature of ancient earth continues to rise as CO2 increases.  As I understand it the first two are based solely on proxy data while the Tierney effort includes modeling to try and correlate the data geographically and temporally.

    All of these are concerned with earth system sensitivities that include both short term climate responses plus slower feedback processes that can take millenia, e.g. growth and melting of continental ice sheets. Both Rae and Honisch include reference lines for 8 C / doubling of CO2. In both cases, almost all the data lie below those reference lines suggesting that 8 C / doubling is an upper bound or estimate of earth's equilibrium between temperature and CO2. Also notice that there quite is a bit of spread in the data.

    In contrast, when Tierney et al. include modeling they get a much better correlation of T and CO2. They find that their data is best correlated with 8.2 C / doubling, r = 0.97.  Again, this represents an equilibrium that can take millenia to achieve but does to my way of thinking represent "nature's equilibrium" between T and CO2. 

    In these comparisons, the researchers define changes in temperature relative to preindustrial conditions, CO2 = 280 ppm. For Tierney's correlation then on geological timescale, the temperature would increase by 8.2 C at 560 ppm.  At our present value of 420 ppm there would be 3.7 C of apparent warming potential above our 1.1 C increase already achieved as of 2022, i.e., global warming in the pipeline if you will.

    Bottom line, based on paleoclimatological data, there is no apparent saturation level of CO2.

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  3. When I first sat up and took notice of global warming was when I started reading palaeoclimate studies (a very long time ago now). As a geologist trained to read 'what rocks have to tell', I quickly realised we were heading straight for trouble. Big trouble.

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  4. I am not science trained but trying to understand. This rebuttal doesn't mention the alleged evidence presented in the paper "Climatic consequences of the process of saturation of radiation absorption in gases" by Kubicki and others - or does it?  The current denialism talking point is that additional CO2 has now been shown to have no additional warming effect, and claims new proofs of this:

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  5. re - # 4: I've just taken a look at that paper. The reason we didn't mention it was that it came out very recently.

    This however is part of the conclusion:

    "However, the intention of the authors of this article is not to encourage anyone to degrade the natural environment. Coal and petroleum are valuable chemical resources, and due to their finite reserves, they should be utilized sparingly to ensure they last for future generations. Furthermore, intensive coal mining directly contributes to environmental degradation (land drainage, landscape alteration, tectonic movements). It should also be considered that frequently used outdated heating systems burning coal and outdated internal combustion engines fueled by petroleum products emit many toxic substances (which have nothing to do with CO2). Therefore, it seems that efforts towards renewable energy sources should be intensified, but unsubstantiated arguments, especially those that hinder economic development, should not be used for this purpose."

    In scientific literature, a conclusion should be about the work that was done, and not an arm-waving diatribe! The Introduction likewise gives its first 400 plus words over to arm-wavy waffle about the IPCC. I'm surprised it got beyond peer review on that basis. Indeed, its submission/acceptance dates (Received 4 December 2023, Accepted 11 December 2023) suggests it never was reviewed. In most cases a period of months divides those two dates because the peer review process is quite slow. These are all warning signs that 'something is up' with this item.

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  6. Theo Simon @4 :

    As John Mason says @5 , there are certainly some Red Flags attached to that Kubicki paper ~ including it's citations of papers by Harde; by Humlum; and by Idso . . . those prominent luminati of the Alternate Universe.

    Theo, to save your reading time in future ~ whenever you see a "gotcha" article in NoTricksZone .com , claiming that the mainstream science (of anything) is quite wrong . . . then there's a roughly 99% probability that the article is a load of taurine excrement [abbreviation = BS ].

    Reading the cited [Kubicki] article's Abstract quickly demonstrates that the authors have simply failed to understand the basic physics of the atmosphere & GreenHouse Effect [abbreviation = GHE ].   And this first impression gets confirmed by reading the article's Conclusions, which are comprised of an excessive amount of word salad and bizarro politics.

    Kubicki et al. seem to have discovered ideas that have been well & truly debunked . . . many decades ago.   If only the authors had troubled to have their "novel" ideas reviewed by experts, before presenting their paper to the world !   They could have saved themselves so much embarrassment, as well as saving dollars.

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  7. Thanks, I did notice that it was taking a position, which I took as a red flag.  But I struggled to understand if it was making new claims regarding saturation, based on new experimental evidence, or if the explanations on this page essentially cover it already.  

    I'd be very interested to know how valid this papers arguments are and if they have been rebuffed, or found wanting in peer review, as I think this line of attack will be a very popular one in the coming months. I've already met it from numerous trolls elsewhere who currently think it's their "gotcha!"

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  8. Denialist "Gotcha" papers pop up most years, gain a lot of traction in those circles and then decay away to hardly anything, then that's it until the next one comes along!

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  9. Theo Simon @7 :

    Theo, please don't waste your time (or anyone's) in going through the details of that Kubicki  paper.

    It is just like when you encounter someone's submitted "paper" showing (with an avalanche of complex mathematics & diagrams) why his design for a Perpetual Motion Machine is certain to work beautifully, as soon as he gets finance to build it.   You yourself know that there must be one or more errors buried away in the midst of his presentation ~ but why would you bother to search?  Life is too short and precious, to spend time dissecting some crackpot ideas which have already been proven to be fundamentally flawed.   Proven and re-proven to be garbage.

    NoTricksZone  is a cynical recycler of nonsenses, to get clicks & profits ~ and happily recycles any garbage which the climate-science denialists themselves keep recycling at intervals.   But I admit to some interest in the psychology of how & why some people with science degrees, even professorships - usually Emeritus types - manage to delude themselves in various ways.  Yes, they are often misreported . . . and yet they seem mostly motivated by rather extremist political views and are handicapped by their own Motivated Reasoning.

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  10. Addendum:

    Theo Simon @7 and earlier :-

    I should have mentioned that, if you still have a nagging doubt and wonder if Kubicki et al. have really made an astounding breakthrough ~ then the easy course for you is to put your feet up and relax and observe for 6 or 7 months.

    Because in October or November this year (2024) the Nobel Committee will maybe  be announcing Kubicki & colleagues have won the Nobel Prize in Physics.   If that were to happen . . . then all over the world, the enjoyers of scrambled eggs would celebrate a collapse in the price of their favorite egg-dish . . . as a million physicists wipe all the egg off their own faces.   And the name Kubicki will rival the fame of Einstein !    (Excuse my flippancy.)

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  11. Theo:

    Taking a quick look at that paper, I see it refers to Angstrom's work in 1900 to support their "saturation" argument. This is already discussed in the Advanced tab of the detailed "Is the CO2 effect saturated?" post that this at-a-glance introduces. Short version - we've learned a few things since Angstrom wrote his paper in 1900.

    Searching the recent paper for "saturation", it seems that they are using the typical fake skeptic approach that applies the Beer-Lambert law (which is exponential in nature, and a standard part of radiation transfer theory) to the atmosphere as a whole. That is - they look at whether or not IR radiation can make it through the atmosphere in a single pass.

    To nobody's surprise, this turns out to not be the case - IR radiation in the bands absorbed by CO2 rarely makes it directly from the earth's surface to space. The energy in the photons needs to go through a series of absorption/re-emission cycles as it gradually works its way up through the atmosphere. When these processes are included in the calculations, it turns out that this particular flavour of the "saturation" argument falls flat on its face, and adding more CO2 (compared to our current levels) does indeed have an effect.

    Executive Summary: the authors of that paper have no idea how the greenhouse effect works, as Eclectic has stated.

    Read the full rebuttal here for more discussion - and the details of the Beer-Lambert Law are also discussed in this SkS blog post.

    Elsevier is usually considered a reputable publisher, but they screwed up on this one. The rapid passage from "received" to "accepted" is indeed a red flag. The journal - Applications in Engineering Science - is clearly an off-topic journal for this paper. On the page I link to, it mentions "time to first decision" as 42 days, and "review time" of 94 days. If you click on "View all insights", you get to this page that also gives "Submission to acceptance" as 77 days, and "acceptance to publication" as five days. The seven days for this paper (from "received" to "accepted") is, shall we say, a bit shorter than usual?

    It is worth noting that several other papers in the same issue also have very short times between "received" and "accepted". Of the four I looked at, none of them had any indication that the authors were asked to revise anything, which is rather unusual. Someone at that journal is in a rush.

    (If you click on "What do these dates mean?", below the title/author section of the web page for the appear, it specifically states that "received" is the date of the original submission, and they will say "revised" if a more recent version is submitted - e.g. after review.)

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  12. Thanks Bob - and all of you - for taking the time to answer me.  I'm just one of many lay people trying to raise the awareness, and we don't always have sufficient science training to be sure of our ground, so it's very helpful when you engage, without too much impatience!   Thanks for all you are doing.

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  13. The paper Kubicki et al (2024) 'Climatic consequences of the process of saturation of radiation absorption in gases' is utter garbage from start to finish. When something is so bad, it is a big job setting straight the error-on-error presented.

    As an exemplar of the level of nonsense, consider the opening paragraph, sentence by sentence.

    Due to the overlap of the absorption spectra of certain atmospheric gases and vapours with a portion of the thermal radiation spectrum from the Earth's surface, these gases absorb the mentioned radiation.

    I'd assume this is saying that the atmosphere contains gases (or "vapours" if you are pre-Victorian) which absorb certain IR wavelengths emitted by the Earth's surface. Calling this "overlap" is very odd.

    This leads to an increase in their temperature and the re-emission of radiation in all directions, including towards the Earth.

    The absorption if IR does lead to "an increase in their temperature" but the emission from atmospheric gases is determined by its temperature. Absorbed IR only very rarely results in a re-emission of IR (and if it does, the IR energy is not cause "increase in their temperature").

    As a result, with an increase in the concentration of the radiation-absorbing gas, the temperature of the Earth's surface rises.

    This is not how the greenhouse effect works. For wavelengths longer than the limit for its temperature defined by 'black body' physicis (for the Earth, about 4 microns), the planet emits IR across the entire spectrum. The level of emission depends on the temperature of the point of emission which for wavelengths where greenhouse gases operate is not the surface but up in the atmosphere. For IR in the 15 micron band, CO2 will result in emissions to space from up in the atmosphere where it is colder and thus where emissions are less. If adding CO2 moves the height of emission up into a colder altitude, emissions will fall and the Earth then has to heat up to regain thermal equilibrium. 

    Due to the observed continuous increase in the average temperature of the Earth and the simultaneous increase in the concentration of carbon dioxide in the atmosphere, it has been recognized that the increase in atmospheric carbon dioxide concentration associated with human activity may be the cause of climate warming.

    This was perhaps true before the 1950s but the absorption/emission of IR by various gasses was identified and measured when the USAF began to develop IR air-to-air missiles. The warming-effect of a doubling of CO2 (a radiative forcing of +3.7Wm^-2) has been established for decades.

    So just like debating science with nextdoor's cat, taking the heed the whitterings of Messers Kubicki, Kopczyński & Młyńczak is a big big waste of time.

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  14. Thanks for that, MA Rodger @13.

    Possibly - just possibly - the ultimate Thumbs-Down on the Kubicki et al. paper . . . is that it has not been trumpeted at WUWT  website (which usually trumpets any crackpot paper which seems "anti-mainstream" science.    And that's despite many of the WUWT  denizens regularly/continually asserting that the CO2-GreenHoouse Effect was now irrelevant (because "saturated") or was always non-valid anyway.

    Now perhaps I have failed to remember "Kubicki" being a Nine-Day Wonder at WUWT   ~ or perhaps I failed to notice "Kubicki" among the mountainous garbage-pile accumulating at WUWT.   But as a final check, I used the WUWT  Search Function . . . and turned up Nothing.

    Something of Contrarian pretensions would need to be pretty bad, not to get 15-minutes of fame at WUWT.    But maybe I speak too soon?

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  15. Eclectic @14,

    You say the work of these jokers Kubicki, Kopczyński & Młyńczak failed the WUWT test, being too bonkers even for Anthony Willard Watts to cope-with. I would say Watts has happily promoted work just as bonkers in the past.

    And as you say, there is no WUWT coverage of this Kubicki et al 2024 paper although Google shows it is mentioned once in one of the comment threads, as is an earlier paper from the same jokers. Indeed, there are two such earlier papers from 2020 and 2022. Thankfully, these are relatively brief and thus they easily expose the main error these jokers are promoting.

    In Kubicki et al (2020) they kick-off by misusing the Schwarzschild equation. The error they employ even gets a mention within this Wiki-ref which says:-

    At equilibrium, dIλ = 0 even when the density of the GHG (n) increases. This has led some to falsely believe that Schwarzschild's equation predicts no radiative forcing at wavelengths where absorption is "saturated".

    They then measure the radiation from the Moon through a chamber either filled with air or with CO2 and show there is no difference and thus, as their misuse of Schwarzschild suggests, that the Earth's CO2 is "saturated." In preparing for this grand experiment, they research the thermal properties of the Moon as an IR source and thus tell us:-

    The moon. The temperature of its surface varies a lot, but for the part illuminated by the Sun, according to encyclopaedic information, it may slightly exceed 1100ºC.

    This well demonstrates that these jokers are on a different planet to us as it is well know our Moon only manages 120ºC under the equatorial noon-day sun.

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