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Is the CO2 effect saturated?

What the science says...

Select a level... Basic Intermediate Advanced

The notion that the CO2 effect is 'saturated' is based on a misunderstanding of how the greenhouse effect works.

Climate Myth...

CO2 effect is saturated

"Each unit of CO2 you put into the atmosphere has less and less of a warming impact. Once the atmosphere reaches a saturation point, additional input of CO2 will not really have any major impact. It's like putting insulation in your attic. They give a recommended amount and after that you can stack the insulation up to the roof and it's going to have no impact." (Marc Morano, as quoted by Steve Eliot)

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!


Further details

This myth relies on the use of a word – saturated. When we think of saturated in everyday use, the term 'soggy' comes to mind. This is a good example of a word that has one meaning in common parlance but another very specific one when thinking about atmospheric physics. Other such words come to mind too. Absorb and emit are two good examples relevant to this topic and we’ll discuss how they relate to atmospheric processes below.

First things first. The effect of CO2 in the atmosphere is due to its influence on the transport of 'electromagnetic radiation' (EMR). EMR is energy that is moving as x-rays, ultraviolet (UV) light, visible light, infrared (IR) radiation and so on (fig. 1). Radiation is unusual in the sense that it contains energy but it is also always moving, at the speed of light, so it is also a form of transport. Radiation is also unusual in that it has properties of particles but also travels with the properties of waves, so we talk about its wavelength.

The particles making up radiation are known as photons. Each photon contains a specific amount of energy, and that is related to its wavelength. High energy photons have short wavelengths, and low energy photons have longer wavelengths. In climate, we are interested in two main radiation categories - firstly the visible light plus UV and minor IR that together make up sunshine, and secondly the IR from the earth-atmosphere system.

The Electromagnetic Spectrum

Fig. 1: diagram showing the full electromagnetic spectrum and its properties of the different bands. Image: CC BY-SA 3.0 from Wikimedia.

CO2 has the ability to absorb IR photons – it is a 'greenhouse gas'.So what does “absorb” mean, when talking about radiation? We are all familiar with using a sponge to mop up a water spill. The sponge will only absorb so much and will not absorb any more unless it's wrung out. In everyday language it may be described, without measurements, as 'saturated'. In this household example, 'absorb' basically means 'soak up' and 'saturated' simply means 'full to capacity'. Scientific terms are, in contrast, strictly defined.

Now let's look at the atmosphere. The greenhouse effect works like this: energy arrives from the sun in the form of visible light and ultraviolet radiation. A proportion reaches and warms Earth's surface. Earth then emits the energy in the form of photons of IR radiation.

Greenhouse gases in the atmosphere, such as CO2 molecules, absorb some of this IR radiation, then re-emit it in all directions - including back to Earth's surface. The CO2 molecule does not fill up with IR photons, running out of space for any more. Instead, the CO2 molecule absorbs the energy from the IR photon and the photon ceases to be. The CO2 molecule now contains more energy, but that is transient since the molecule emits its own IR photons. Not only that: it's constantly colliding with other molecules such as N2 and O2 in the surrounding air. In those collisions, that excess energy is shared with them. This energy-sharing causes the nearby air to heat up (fig. 2).

CO2 heat transfer

Fig. 2: The greenhouse effect in action, showing the interactions between molecules. The interactions happen at all levels of the atmosphere and are constantly ongoing. Graphic: jg.

The capacity for CO2 to absorb photons is almost limitless. The CO2 molecule can also receive energy from collisions with other molecules, and it can lose energy by emitting IR radiation. When a photon is emitted, we’re not bringing a photon out of storage - we are bringing energy out of storage and turning it into a photon, travelling away at the speed of light. So CO2 is constantly absorbing IR radiation, constantly emitting IR radiation and constantly sharing energy with the surrounding air molecules. To understand the role of CO2, we need to consider all these forms of energy storage and transport.

So, where does 'saturation' get used in climate change contrarianism? The most common way they try to frame things is to claim that IR emitted from the surface, in the wavelengths where CO2 absorbs, is all absorbed fairly close to the surface. Therefore, the story continues, adding more CO2 can’t make any more difference. This is inaccurate through omission, because either innocently or deliberately, it ignores the rest of the picture, where energy is constantly being exchanged with other molecules by collisions and CO2 is constantly emitting IR radiation. This means that there is always IR radiation being emitted upwards by CO2 at all levels in the atmosphere. It might not have originated from the surface, but IR radiation is still present in the wavelengths that CO2 absorbs and emits. When emitted in the upper atmosphere, it can and will be lost to space.

When you include all the energy transfers related to the CO2 absorption of IR radiation – the transfer to other molecules, the emission, and both the upward and downward energy fluxes at all altitudes - then we find that adding CO2 to our current atmosphere acts to inhibit the transfer of radiative energy throughout that atmosphere and, ultimately, into space. This will lead to additional warming until the amount of energy being lost to space matches what is being received. This is precisely what is happening.

The myth reproduced at the top – incorrectly stating an analogy with roof insulation in that each unit has less of an effect - is misleading. Doubling CO2 from 280 ppm to 560 ppm will cause a few degrees of warming. Doubling again (560 to 1130 ppm) will cause a similar amount of additional warming, and so on. Many doublings later there may be a point where adding more CO2 has little effect, but recent work has cast serious doubt on that (He et al. 2023). But we are a long, long way from reaching that point and in any case we do not want to go anywhere near it! One doubling will be serious enough.

Finally, directly observing the specific, global radiative forcing caused by well-mixed greenhouse gases has - to date - proven elusive. This is because of irregular, uncalibrated or limited areal measurements. But very recently, results have been published regarding the deep reinterrogation of years of data (2003-2021) from the Atmospheric Infrared Sounder (AIRS) instrument on NASA's Aqua Satellite (Raghuraman et al. 2023). The work may well have finally cracked the long-standing issue of how to make finely detailed, consistent wavelength-specific measurements of outgoing long-wave radiation from Earth into space. As such, it has opened the way to direct monitoring of the radiative impact (i.e. forcing + feedback) of greenhouse gas concentration changes, thereby complimenting the Keeling Curve - the longstanding dataset of measured CO2 concentrations, down at the planet's surface.

Note: Several people in addition to John Mason were involved with updating this basic level rebuttal, namely Bob LoblawKen Rice and John Garrett (jg).

Last updated on 31 December 2023 by John Mason. View Archives

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Further reading

V. Ramanthan has written a comprehensive article Trace-Gas Greenhouse Effect and Global Warming.

Further viewing

Video by Rosh Salgado on his "All about Climate" YouTube channel in which he debunks Will Happer's claim that the CO2 effect is saturated in the atmosphere:

Comments

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Comments 626 to 650 out of 653:

  1. Eclectic @625,

    Of course, there is the point as to whether you should be referring to that paper as Wijngaarden & Happer (2020). Academic work is usually only dated if it is properly published or if it is presented at a conference. Otherwise it would be demoted to being a working paper which is thus not complete and thus not properly dateable. And I would suggest that up-loading a paper onto Cornell University's "free distributon service" arXvi doesn't count as 'publication', it being no-more 'published' than this comment I post here at SkS.

    But the proof of the pudding and all that....

    Whatever tha nature of a piece of work's origin, it is its usefulness to the science that is the proper measure of it. A look at google scholar for Wijngaarden & Happer (unpublished) 'Dependence of Earth’s Thermal Radiation on Five Most Abundant Greenhouse Gases' shows today just four citations, which is pretty rubbish. And one of those is a reference from a further Wijngaarden & Happer paper posted @arXvi which is but an updated version of the same while accounting for two more GHGs, CF4 & SF6. Of the remaining three, one explicitly styles itself a working paper. (I note its reference list is stuffed full of denialist nonsense: Koonin & Jon-boy Christy, Lewis & Dicky Lindzen, McIntyre & McKitrick & Monckton, Svensmark & Woy Spencer.) The final two citations do initially appear to be by published work. But in tracking down both ♣Pascal Richet (2021): 'Climate and the temperature-CO2 relationship An epistemological re-examination of the ice core message', History of Geo- and Space Sciences, Vol 12, pp97-110. and ♣David Coe; Fabinski, Walter & Weigleb, Gerhard (2021): 'The Impact of CO2, H2O and Other "Greenhouse Gases" on Equilibrium Earth Temperatures'  Int J. Atmos. & Oceanic Sci.,Vol 5, Issue 2, pp29-40. I see either a blank space in the pp97-110 page-numbering or the pages pp29-41 taken by another paper. So it appears that the final two citations have failed to gain publication; not so uncommon with denialist works which both these final two citing paper evidently are. (An on-line French version of the first of these two simply presents a common climate myth while a posting of the second's Abstract still visible on a denialist website shows its finding is an ECS=+0.5ºC.)

    ....turns out to be a large bowl of rather-sticky humble pie.

  2. MA Rodger @626 :   Thank you.  You are as always, a grand source of climate information and analysis.  Encyclopedic !

    Yes, I am guilty of being insufficiently attentive to the non-publication status of the Wijngaarden & Happer paper.  And yes, the paper seems to have drifted toward oblivion during the past year ~ even within the hallowed precincts of Wattsupia University.

    Nevertheless, there is a scientific duty to keep a weather eye in the direction of all fringe-dwellers, just in case there really might develop "a small cloud on the horizon".   ~Improbable though that might be.

    In one sense, the main obfuscation in the W & H paper is the prominent semantic mis-use of the term "saturation".   That is a matter which seems to have misled the propagandist Dr David Wojick (or perhaps he - and his Heartland colleagues - are being disingenuous in not seeing through it. A novel thought! )

  3. MA Rodger @626

    I am brought to this site/thread by searching on the Coe, Fabinski, Gerhard paper http://www.sciencepublishinggroup.com/journal/paperinfo?journalid=298&doi=10.11648/j.ijaos.20210502.12

    This does indeed seem to have been published, albeit in an open access "journal" - so I am slightly puzzled by what you wrote - indeed your link takes me not to pages 29-41 as writ, but to different pages (and indeed to a different article). The "climate change denying" article does indeed appear at pages 29-40 in the same journal. The author list is shorter.

    The publication status and page numbering is all nit-picking (by me) - I mention it just for completeness. I am more interested in knowing whether there is a simple rebuttal to the analysis in said article. I am not a practising scientist and my maths and physics are rather rusty. I can see that the claims in the article fall into the "CO2 is saturated" category. It appears to present a sophisticated numerical demonstration of this saturation and I'm interested to know where it might be wrong (or not). Can anyone oblige?

     

    Response:

    [BL] Link activated.

    The web software here does not automatically create links. You can do this when posting a comment by selecting the "insert" tab, selecting the text you want to use for the link, and clicking on the icon that looks like a chain link. Add the URL in the dialog box.

  4. Andrewhoward:

    I just read the abstract you linked.  I noted that the three authors have no experience in atmospheric sciences.  They claim that doubling CO2 would result in a 0.5C increase in surface tempeatures with other human generated gasses being insignificant.  Since the temperature has already risen 1C and we have not reached a doubling yet it seems to me that their analysis is obviously incorrect.

    Why do you think that this example from persons unskilled in the art of atmospheric science is worth our time to analyze?  The IPCC report is compiled by experts in the field, not beginners. 

    I continue to be amazed at conservative people in the USA who refuse to accept data from scientists and then dose themselves with dangerous drugs that have been shown to have no effect against covid.  The same argument applies to "papers" by unskilled people like the one cited by Andrewhoward.  MARodger can ddress what mistakes were made in the "paper".

  5. Andrewhoward:

    I have downloaded the paper and will try to look at it. Michael Sweet has noted the lack of background of the three authors. Also note that the page you linked to provides received, accepted, and publication dates:

    • Received August 2, 2021.
    • Accepted August 11, 2021.
    • Published August 23, 2021.

    Nine days for an editor to look at a paper, send it to reviewers, get reviews back, evaluate the reviews, and get the authors to address any deficiencies in the paper and resubmit a revised paper, assess the revisions, and accept the final paper? I don't think so.

    This tells me that the journal has essentially no review process in place, and will publish pretty much anything.

    And the company that "publishes" the journal (Science Publishing Group, also known as SciencePG and SciPG) is on Beall's list of potentially predatory publishers:

    https://beallslist.net/

    The chances that this paper represents a noteable scientific advancement is pretty close to zero.

    ...but I will try to read the paper.

  6. andrewhoward @628,
    Concerning the 'nit-picking', back in September there was no sign of the Coe et al paper [full paper here] but instead another paper occupying those pages. It thus appeared at that time to be somewhat more than 'nit-picking'. There since has been some page re-numbering by the journal which isn't very professional and the side-bar buttons for 'Submit a Manuscript' and 'Become a Reviewer' and even 'Launch a New Journal' suggest a title that is more vanity publishing than serious science.

    This would not be the first time denialists have accessed HITRAN to produce a pack of nonsense. Their description shows them calculating how much surface radiation is absorbed by the various GHGs and ignoring the emissions from the atmosphere. It is the density/temperature of the GHGs where they emit into space that determines the GH-effect so the paper's calculations are simple nonsense.

    In terms of their basic findings, they find H2O alone would provide 91.8% of the GH-effect, CO2 alone would provide 24.7% but when added to H2O, CO2 would provide an additional 7.7%. The CH4 & N2O alone value isn't expressly given while their additional contribution is 0.5%.
    This is all very silly. This RealClimate post provides a more conventional set of findings but includes further contributions to the GH-effect. Thus the CO2 percentages do not look greatly different. But H2O alone is given as just 66% and while the 'Other GHG' (which would be more than just CH4 & N2O but they would be the lion's share) provide an additonal 2%.

    When Coe et al address ECS, they are entirely off with the fairies. It is well known that the forcing from 2xCO2 increases global temperatures by +1ºC. These jokers manage to find just +0.4ºC, a certain maker of 'idiots-at-work'. Coe et al say ECS estimates range from +1.5ºC to +4.5ºC. The usual best estimate is seen as +3ºC, thus a trebling of the CO2 warming through feedbacks. The statement by Coe et al that "More recent work, however, suggests ECS values of less than 1degC" is plain wrong - a cherrypick of fellow denialist work. Coe et al prattle through a pack of nonsense to turn the climate feedback from a best estimate +200% into just +12.4%. Of course, if such a crazy finding were in the slightest bit serious, it would need nailing down and strongly justifying. But Coe et al jump straight to what is the purpose of their task and so predictably conclude "There is no impending climate emergency and CO2 is not the control parameter of global temperatures."

  7. As a quick follow-up, the same journal in a 2019 issue has the following:

    Human CO2 Emissions Have Little Effect on Atmospheric CO2, Edwin C Berry

    This paper has been previously discussed at SkS on the human emissions of CO2 post:

    https://skepticalscience.com/argument.php?p=7&t=352&&a=16#137046

    More evidence that the "journal" in question will accept all sorts of crackpottery.

  8. ...and another comment on the Berry paper is here:

    https://skepticalscience.com/news.php?n=4842#136000

  9. MA Rodger links to a 2005 RealClimate post that discusses the relative importance of CO2 and water vapor in IR transfer. A more recent journal paper on the subject is:

    Schmidt, G. A., Ruedy, R. A., Miller, R. L., and Lacis, A. A. (2010), Attribution of the present‐day total greenhouse effect, J. Geophys. Res., 115, D20106, doi:10.1029/2010JD014287.

    Gavin Schmidt is, over course, the one that wrote the RealClimate post, too.

    Discussion of water vapour vs. CO2 belongs on the following thread, though:

    https://skepticalscience.com/water-vapor-greenhouse-gas.htm

  10. I have now read enough of the Coe et al paper to form an evaluationbased on its content, rather than its origin.

    As MA Rodger says, they ignore emissions from the atmosphere - although they do use terms that suggest they've at least heard of it. The bizarreness of their model show up early,in section 1.4 "The Impact of Retained Energy". They are talking about IR energy absorbed by the atmosphere, and state (p31):

    "What happens to this absorbed energy? Some will be retained by the atmosphere/earth system, and some will be re-radiated by the atmosphere through to space.

    This is not even wrong. If the earth/atmosphere system were constantly retaining energy, it would be constantly warming. They have completely confused the effect of re-radiation downwards as if it is some permanent retention of energy. It is not. That energy joins the rest of the energy, to be re-radiated again and eventualy lost to space. At equilibrium, no "retention of energy" is happening and gains from the sun equal losses to space and temperatures are constant.

    They intoduce n as an "energy retention factor", and start talking about atmospheric absorption fractions, but all of that is already built into the "earth emissivity" term they use in equation 1 (the standard zero-dimensional model). They have also completely ignored the fact that vertical energy transfer in the atmosphere includes convection - probably part of the "complex atmospheric thermodynamics" that they explicitly ignore.

    All of these extra terms they introduce are smoke and mirrors. They argue that the real atmosphere is far too complex to model, and then create a simple model that is far too wrong.

    The rest of their manipulations of HITRAN data and "atmospheric absorption calculations are all just hand-waving and not worth any further examination.

  11. andrewhoward @628 - a more specific answer to your specific question could go something like this:

    In terms of mass & volume, water vapour is much more prevalent (~80-90%).

    However, the radiative importance is less due to molecule structure. One way to quantify this is to take a radiation model and remove each long-wave absorber and see what difference it makes to the amount of long-wave absorbed. This gives the minimum effect from each component.

    The complementary calculation, using only each particular absorber in turn, gives the maximum effect. Generally these will not be equal because of overlaps in the absorbing spectra. The radiation at particular frequencies can either be absorbed by water vapour or any other GHG.

  12. The approach described by cph - add absorbers one at a time, subtract one at a time - is indeed the methodology used in the Schmidt et al paper I linked to in comment #634.

  13. After much reading, it occurs to me that because H2O absorbs IR in such a wide array of wavelengths, including 15µm, and is so overwhelmingly prevalent being 95% of all "Greenhouse Gases", might it absorb almost all of the 15µm radiation available, leaving an insignificant amount to be absorbed directly by CO2 and other IR sensitive gases. Could this render CO2 just another molecule in the air and make it virtually impossible to measure any effect of CO2 related to atmospheric temperature making the "CO2 greenhouse effect" an unprovable theory? Isn't H2O the primary reason we have such a moderate climate?

    Response:

    This cannard is off-topic here. Please see the myth "Water vapour is the most powerful greenhouse gas". Read the article and if you have further doubts, please raise them there but only after studying the resources supplied.

    And see also https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2010JD014287

     

  14. Likeitwarm @638,

    While your "canard" is off-topic on this thread, a direct response to it is not.

    The 15 micron absorption band of CO2 is about 3 microns of the spectrum (roughly 13.5µm to 16.5µm). While this waveband does sit in the edge of the big H2O radiation 'window' which stretches from 6µm to 16.5µm (termed a 'window' as it allows incoming radation in from space) and thus CO2 narrows that 'window', this is not the essential part of the operation of CO2 as a greenhouse gas.

    The essential mechanism is that the CO2 greenhouse effect operates higher up in the atmosphere, above the bulk of of the atmospheric water vapour.  Thus it is CO2 which determines the altitude from which the IR in this band is emitted into space, thus the amount of this IR emitted into space (determined by the atmospheric temperature of the point of emission) and thus it is CO2 which determines the amount of greenhouse warming from this waveband.

  15. The sort-of-on-topic aspect of it is that a common error in looking at greenhouse gas absorption is to think of the atmosphere as a monolithic single layer. By only considering fluxes at the bottom (surface) and top (loss to space), people tend to lead themselves down many paths of misunderstanding. This is the most common error in most "saturated" arguments, and it plays a part in the "water vapour..." arguments as well.

    Although simplified versions of radiative transfer can be useful in early learning stages, those simplified versions are not what drives climate models. You will see frequent references to MODTRAN in this forum. With the online version in the link I just gave, you can try various assumptions you wish to explore and see how a full radiative transfer model actually responds.

    As well as absoprtion, the changes in emission are also important - and also need more than a "single layer" approach.

  16. As MA Rodger @638 points out, the CO2 greenhouse effect operates above the bulk of atmospheric water vapor, or atmospheric H20 in any phase.  This is consistent with The Science of Doom website which states

    The key point behind all the detail is that the top of atmosphere radiation change (as CO2 changes) is the important one. The surface change (forcing) from increasing CO2 is not important, is definitely much weaker and is often insignificant. Surface radiation changes from CO2 will, in many cases, be overwhelmed by water vapor.

    Water vapor does not overwhelm CO2 high up in the atmosphere because there is very little water vapor there – and the radiative effect of water vapor is dramatically impacted by its concentration, due to the “water vapor continuum”.

    So my question is if the CO2 greenhouse effect operates high in the atmosphere where there is very little H2O in any form,  how is it possible for this greenhouse warming to cause further evaporation of condensed H2O (ie. liquid water or ice) in order to complete the water vapor feedback loop discussed in the debunking of Climate Myth 36?  For this, it seems we do need the "single layer" model mentioned by BoB Loblaw @640.  Otherwise, there is no correlation between the H20 and CO2 greenhouse warmings, and the controlling GHG would simply be the stronger of the two.

  17. No, OldHickory, you do not need a single-layer model. The entire atmosphere is coupled together as a series of layers. What happens in one layer (e.g. the upper atmosphere) then affects the fluxes with the layer below it, which affects the fluxes within the layer below that, etc. The net energy flux - all fluxes, radiative and convective - needs to adjust so that all layers are in local equilibrium (steady mean temperature).

    What happens at the top of the atmosphere affects the entire profile, so that the lower layers (and surface) increase in temperature, which leads to more evaporation (where water is available). That increased evaporation leads to global average higher water vapour. That is the feedback loop.

    It is an entire coupled system. Not one or two layers.

  18. Regardless of where the CO2 greenhouse warming takes place, it will still saturate if enough CO2 is added. It is the very strong (but narrow) absorption lines in the IR spectrum of CO2 that makes it so easy for its greenhouse effect to saturate, and has nothing to do with location.  Therefore, we should expect that adding more CO2 to the atmosphere would not cause much more warming, either at the surface, high in the atmosphere, or anywhere in between.

  19. OldHickory @643 ,

    your final sentence is simply wrong.

    It is a verbal/semantic problem which has confused you.  Saturation is a term with several meanings ~ but if you look at the actual mechanism of the Greenhouse Effect (for all greenhouse gasses), then you will see that the important factor is the average inter-molecular distance between "greenhouse" molecules at the so-called Top-Of-Atmosphere . . . combined with the Lapse Rate.   

     Denser ("more saturated")  CO2 at the surface level will result in a higher T-O-A where the sufficiently-large intermolecular distances are achieved to allow infra-red photons to escape the planet.   And that TOA height (and thus temperature) will be different for different types of greenhouse gas (but making some allowance for any infra-red spectrum overlap).

    In short, an increase in CO2 at ground level must result in more warming effect.  And the effect is very far from negligible.

  20. OldHIckory @ 643:

    You have made some very vague, non-specific, non-quantitative statements.

    As Eclectic points out, "saturation" can mean many things. You need to explicitly say exactly what you mean by that term, preferably with a mathematical expression.

    "Enough CO2" is meaningless. With enough power, you can make a bathtub fly.

    "So easy" is also meaningless.

    "Would not cause much more warming" is a vague generality. How much is "much"? Bigger than a house? Smaller than a mouse?

    People that actually do the math have shown that the global mean surface temperature will continue to warm for increasing amounts of CO2 untl CO2 reaches levels at least several times higher than they are now.

    Your last sentence, where you say "more warming, either at the surface, high in the atmosphere, or anywhere in between" demonstrates a severe lack of understanding of the effects of CO2. Increasing CO2 leads to surface warming, but there is less warming the higher you go in the troposphere. At the tropopause, warming is negligible. In the stratosphere, increasing CO2 causes cooling. This was well understood as far back as the 1960s, in such papers as this one:

    Manabe and Wetherald, 1967

    I refer you to figure 16 from that paper:

    Manabe and Wetherald 1967 Figure 16

  21. After reviewing several papers on the topic, I can only conclude that the water vapor feedback loop (from Climate Myth 36) is not possible due to saturation of the CO2 greenhouse effect.  As noted in The Irrelevance of Saturation: Why Carbon Dioxide Matters, the saturation length for the (most important) 14.99 micron CO2 absorption line at a partial pressure of 0.0004 atm is about 18 meters.  Also, the author dana1981 of the rebuttals for this Is the CO2 effect saturated? forum stated the claim is true that adding more CO2 won't absorb much more IR radiation at the surface.

    Now I realize that the bottom layer of the atmosphere (near the surface) will warm the layers above it, but that is irrelevant regarding the water vapor feedback loop.  In this case, we are only interested in what warming occurs at altitudes where there is still liquid or solid state H2O available in order to complete the loop.

    In general, we can expect that adding more CO2 to the atmosphere will increase the CO2 greenhouse warming, but at altitudes well above that which would result in a CO2 "control knob" or disruptions to the weather or climate.  Therefore, atmospheric H2O is in fact the dominant and controlling GHG and Climate Myth 36 actually isn't a myth.

  22. My apologies, OldHickory @646 and prior ~ but I am having difficulty understanding exactly where you think the climate scientists are wrong about the physics of climate.  And it's likely that other readers are sharing my difficulty.

    Please explain yourself more clearly.  You seem to be ignoring the effect of the atmospheric Lapse Rate, which is so crucial to the mechanism of "greenhouse".

    And infra-red photons from the planetary surface can only go a short distance before being absorbed by a CO2 or H2O molecule.  Most of those photons would not even reach the rooftop of your house.  So in that sense you can say that the lower atmosphere is "saturated" for CO2 , H2O etcetera ~ and it would be "saturated" whether the CO2 level were 200ppm or 400ppm or 800ppm or 1600ppm.

    But the concentration level of greenhouse gasses at the bottom of our atmosphere will directly affect the concentration level near the TOA, and the TOA (for each specific gas) is the level where the infra-red is radiated out into space.  The lower levels of air have a colossal re-cycling of IR photon energy . . . but what ultimately matters is the temperature of the TOA level.  Because that is the level from which our planet loses (to space) the heat energy being gained from the sun.  (Here I am disregarding the directly reflected sunlight from Earth's surface; and also the small portion being the IR "window" where IR of that wavelength that can pass directly through the air & clouds).

    And the TOA temperature is dependent on the Lapse Rate.  Conversely, the Lapse Rate determines the surface temperature, if you care to think about it in that way.

  23. Where I believe the climate scientists are wrong is in their common response to climate change skeptics about why we need to be concerned about atmospheric CO2 when it is H2O vapor that is the much stronger GHG.  Their answer to this question is the claim of a water vapor feedback (also called a CO2 "control knob") as explained in the rebuttal of Climate Myth 36.  This only works, however, if the CO2 greenhouse effect isn't already saturated, and more CO2 actually does give a rise in temperature.  Eventually, after adding enough CO2, the rise in temperature starts to decline when adding more CO2, and in fact approaches zero.  At this point, we say the CO2 greenhouse effect is saturated.  Well, it turns out that near the surface of the earth, this effect is highly saturated, and even doubling the CO2 concentration would not result in any signficant temperature change.  This, of course, means that the "control knob" fails, and we need not worry about CO2 emissions, anthropogenic or otherwise.

  24. OldHickory @648 : thank you for expanding on the matter ~ but there is still a major shortfall in your comment.  Not only miscommunication - which may partly be a verbal/semantic problem - but it appears even more certain that you have not grasped the essence of how "greenhouse" warms the lower atmosphere.

    Once you have truly grasped how H2O , CO2 , etcetera operate in the atmosphere, you will see why all the climate scientists (including the famous contrarian Professor Lindzen) are in agreement on the actual mechanism of planetary "greenhouse".   It seems you have confused yourself about the question of "near the surface of the earth ... is highly saturated".  [your quote]

    As I mentioned earlier, the "saturation" question is not really relevant.  It is not the "saturation" which is important, but the concentration (as in greenhouse gas molecules per cubic millimeter . . . or cubic meter . . . or what-have-you ).  Any level of concentration will produce some greenhouse, and as you increase the concentration, there comes an increase in warming effect.   The effective increase is not exactly logarithmic, but for (just) CO2 in the recorded range of recent times [say 180 - 420ppm] the surface warming effect works out to be approx 1.2 degreesC for a doubling of CO2 concentration.   On top of that, must be added the feedback warming from the consequent rise in atmospheric H2O vapor (a figure somewhat greater than 1.2C) .

    OldHickory, you will understand that I am not wishing to write a large number of paragraphs to explain all this in greater detail personally to you. This SkS website exists for the express purpose of providing a wealth of climate science information.   It is your duty to yourself, to go and really read the original article at the head of this thread, at the Basic & Intermediate & Advanced levels.  And to read other related articles here at SkS and elsewhere.  When you have done that, it will become obvious why all the scientists are right.

  25. OldHickory @646&648,
    You say @646 "I realize that the bottom layer of the atmosphere (near the surface) will warm the layers above it" and also "adding more CO2 to the atmosphere will increase the CO2 greenhouse warming, but at altitudes well above..." So if you realize the lower atmosphere warming will heat the upper atmosphere and adding atmospheric CO2 will warm the upper atmosphere, why do you think that high-up CO2 warming will have no warming effect near the surface?

    Troposphere circulations
    CO2 warming occurs in the troposphere. The troposphere contains atmospheric cells (as illustrated above) in which downward air increases in temperature because it is being pressurised as it decends. There is no energy transfer in this warming, just pressurisation. So any warming will transfer top-to-bottom, just as it does botom-to-top. It does not matter if the warming is high or low, it will warm the entire troposphere. And warming at the surface will then increase atmospheric water vapour providing the feedback warming.

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