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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)


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:


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Comments 501 to 525 out of 684:

  1. Thanks all. Continues to be really informative, and I think I now have a good handle on the different possible ways in which increasing co2 could increase troposphere temperatures. What isn't so clear is how significant those effects are at marginal increases from 400 ppmv, but to br honest I could probsbly spend the next 6 months studying the topic in detail and not be that much more certain given the myriad complexities.

    MA: The Zhong and Haigh paper is really interesting, but I'm not quote following figures 5a and b, top row, which seem to show minimal change in radiative flux (when averaged across the spectrum) even up to 32x co2. I'm not convinced they have taken into account all those phenomena when working out thr logarithmic relationship - they say

    "our calculations assume no change in the surface or atmosphere, do not consider the climate response to the RF, or any issues related to climate sensitivity"

    But perhaps there's something intrinsic to the models that goes without saying. My point was more that it be *more* of a factor going forward, as the proportion of time when thr altitude of emission is in a scenario where increasing altitude does not mean decreasing temperatures is presumably increasing with increasing co2.

    Given the point has been made to me repeatedly that the science is apparently so settled no one's even really looking at it anymore, i thought it might be useful to go back and look at past predictions to see how they measure up against present day. This might not be the right page to discuss such matters, but I came across this analysis of a Hansen 1988 paper, in which apparently actual temperatures are matching up in line with his 'zero co2 increase after 2000' scenario Thoughts?

  2. @eclectic: it appears that is the case. the point wasn't about a single altitide; rather it's about where the altitude of emission is in an area where increasing altitude no longer leads to decreasing temperatures

  3. LTO @501 ,

    A/  Please note that you have duplicated your post #501as #502 and #503. Do not be too embarrassed ~ a Moderator will correct that reduplication.   Likewise with your other duplication !

    B/  On #504 [soon to be #502, I expect] , you will need to explain what you mean by your first and second sentences.   What is the case?   What is the misunderstood point?   There seems to be considerable confusion of communication here.

    Take a look at the atmospheric temperature versus altitude graphs.   For most of the troposphere, the temperature reduces with height.   Above that, the temperature holds steady for a short distance ~ and above that, temperature increases with altitude through the stratosphere.   You need to integrate that information with the decreasing air density ~ because both factors are important in comprehending the (15um) radiative loss to space.   The low density in stratosphere is the reason the tropospheric (15um) loss is vastly more important (and why the weighted average "emission height" is generally in the troposphere, affected by the lapse rate there).

    Things get more complex, if we consider other radiative output from CO2 ~ and also other radiative properties of H2O and all molecules of 3 or more atoms.   But for our mutual purposes, it is enough to consider the 15um band, here in this thread.

  4. LTO , you have mentioned the "realclimatescience" website.

    Perhaps you are not yet aware ~ but that is not a science website, it is a propaganda website.   "Fake News".   As a pointer, one should always be on the alert for disinformation, on any site prominently quoting Feynman, Popper, or Galileo.   [ Feynman, Popper and Galileo are of course very worthy gentlemen in their own right ~ but their philosophies are seriously abused by propagandists hoping to drape themselves with reflected glory . . . propagandists hoping to mislead the uninformed/unthinking reader. ]

    As to your question on Hansen etcetera ~ the propagandists are diverting your attention onto some old predictions/projections of 30+ years ago, in the early days of such assessments.   Worse by far, they are deceiving you by comparing to more recent high-altitude data, not the planetary surface temperatures.   That is classic bait-and-switch deception.

    Also, note that site's reference to "the 52% consensus" ~ based on some very unrigorous survey of members of some meteorological society.  No detailed explanation.   Quite shameless propaganda.

    LTO , please get your information from an honest scientific website.   For instance : RealClimate.  (You can see how the anti-science propagandists are trying to piggy-back, by using a similar sounding name such as realclimatescience, to mislead the careless into their own site.)

  5. Erp . . . I have committed an unfortunate ambiguity, in the second post above this one.   "the temperature reduces with height" should read "the temperature reduces with increased height" ~ which is much clearer !   My apologies for that initial statement, which might well pass in colloquial conversation, but which was very open to misinterpretation (in written form).

  6. LTO:

    A scientific discussion of Hansen's 1988 paper is here Realclimate discussion .  Note that this is the website the denier site "realclimatescience" is attempting to hijack. 

    Hansen's projections were skillful but the release of greenhouse gasses was not what he forecast. While he forecast lower CO2 emissions, he forecast higher cloroflurocarbon emissions.  Simplistic evaluations of only CO2, like the one at realclimatescience, ignore these important greenhouse gasses. 

    The writers at realclimatescience have had the opportunity to read the correct science at Realclimate and continue to push their incorrect ideas.  In my book that is a deliberate lie.  I recommend you stop wasting your time (and ours looking up the correct analysis) reading denier web sites.

    There is an easy way to find out how increasing CO2 affects temperature: read the IPCC summary and figure they are correct!!  It is a waste of time to attempt to calcualte or completely understand the atmosphere yourself, it is too complex. 

  7. LTO @501: "i thought it might be useful to go back and look at past predictions to see how they measure up against present day."

    You can easily do that right here on SkS. Scroll up to the "thermometer" in the left-side banner. Under that are some rectangular "buttons". Click on the "Lessons from Predictions" button. That will take you to a page listing blog posts dealing with past predictions/projections and how they have measured up.

  8. LTO @501,

    Concerning Zhong & Haigh (2013), you ask about the meaning of "our calculations assume no change in the surface or atmosphere, do not consider the climate response to the RF, or any issues related to climate sensitivity." This is simply saying that they calculate the climate forcing due to these changes in CO2 levels. Such forcings would increase global temperature and the resulting changes to other GHG levels, cloud, surface albedo, etc, which would result from that forcing are not being considered. This is solely about the direct effect of the CO2 and not any feedbacks.

    And the top row of their Fig 5a/b is simply the traces within all the other rows plotted together. The one rather confusing part of this Fig 5 is that Fig5a plots the zero CO2 alongside all the other CO2 levels while Fig5b plots the difference between each different level and a current level (as was) of 389ppm. Thus the second row of Fig5a shows both zero (lt blue) and 1.5ppm (green) but the difference between 389ppm & 1.5ppm (green) appears down in the fourth row of Fig5b.

    Note I still intend to tap out a screed as I promised @492.

  9. LTO - Responding to your earlier questions about energy exchange via collisions, and the relative energies of emitting GHGs and the rest of the atmosphere (sorry this is weeks later, just got back to this thread after a while):

    At sea level each molecule in the atmosphere collides with others at about 10^9 times per second. The time for an excited CO2 molecule to emit IR is about 10^-6 seconds. Therefore (comparing relative numbers) each CO2 molecule collides ~1000 times before emitting. Thus the CO2 molecules emit at a rate tied directly to the gas temperature. 

    The tropopause (where the break-even point of CO2 emission lies, ending convection) ranges from about 7 to 20 km, poles to equator. Air pressure at 15km is roughly 100mb, 1/10 sea level, meaning that at that altitude each CO2 molecule collides 100 times with other atmospheric molecules before emitting. So again, CO2 molecules emit at rates tied directly to atmospheric temperature. 

    One side point, since I've seen this a particular error occur repeatedly - emitting CO2 molecules are by no means tied to absorbing CO2 molecules, and neither are the absorption energies directly tied to emission energies on a photon by photon basis. The gases warm due to convection and IR absorption, that temperature gets shared, and the emissions from any particular gas volume are statistical expressions of the GHG emission spectra from GHGs at that temperature. There's no immediate one-to-one connection. 

  10. michael sweet @506, instructing readers to blindly accept the IPCC summary and not "waste" time trying to understand the atmosphere is not wise if you are trying to gain consensus. There is no scientific method that ends in "trust me". 

    I'm focused on mathematics and, to a lesser extent, the physics of the arguments and most of the posts on this science seem reasonable and well-intentioned. I've been studying the IPCC reports and find it difficult to opine without more research. This site is typically useful although I find the proponents of ACG less reasonable than the skeptics. 

    On the topic of CO2 saturation, the math is not necessarily flawed, but the assumptions are immense and I'm not at all comfortable with the magnitude of error analysis required to reach some of the conclusions. For example, identifying the factors that support a convective heating model with CO2 are statistically impossible. Anthropogenic CO2 is approximately 0.0012% of the atmosphere. But the anthropogenic concentration would have to be increasing dramatically to support the 400ppm if the natural portion were to be static. Of course, we know that the natural portion of the CO2 concentration has increased in recent decades as the planet has been greening. This is the first of many assumptions that do not have much scientific basis. We know the current concentration and its fluctuations through a 12-month cycle. We know natural CO2 has increased although we don't know entirely from where. We know anthropogenic concentrations have increased although we don't know how much is being contributed from each continent. We know that reflective heating has almost peaked. So the assumption is convection but we don't know how much of the convective heating is due to other molecules. So scientists guess at what might be happening and how much heat might be involved in different transfer models without knowing exactly which molecule is involved and to what degree each molecule is contributing to convection. Mathematically speaking we've already reached a level of uncertainty with only the points I've mentioned to make the entire convection from CO2 theory basically worthless. The error rates are exceeding 50% in some models. In any other field of study, such a large error rate would be considered a SWAG and not worthy of publishing. Since the climate argument has gone tribal, the science is not being mathematically supported as long as the conclusion is that the result supports the bias of the publisher. 

    That you would recommend we "trust" the IPCC summaries when the details have so many mathematical SWAGs is intellectually disingenuous. I will fully admit to not understanding the chemistry enough to know how much error is introduced with each atmospheric assumption (not to mention the ocean carbon sink assumptions), but I can say with some authority that the mathematics is not tight enough to support any engineering application. And since we're talking about taking trillions of dollars away from more present and tangible efforts such as disease, I think it is fair to question the outcome of these models that carry such broad ranges of uncertainty.

    Recent temperatures have not followed recent CO2 measurements. It appears that CO2 concentrations might be less convective than the IPCC asserts. And if that is the case, we're pretty much back to guessing on why there appears to be a temperature correlation with CO2 emissions in the first place. I don't think the public or the lawmakers realize how important this CO2 convection issue is to the broader argument of CO2 related climate change. 

    So, my response is, NO! Do not trust the IPCC summary on the topic of heat transfer related to atmospheric CO2 convection since the math is weak. Use the scientific method, question every assertion, and come up with a better explanation for the heat fluctuations in the atmosphere. If somebody doesn't understand the science, learn the science, don't ignore it.

    I would encourage the readers of this site to ignore any advice that suggests a conclusion should be assumed valid if even a single assumption is left untested.


    [PS] This is offtopic. This thread is about myth that adding more CO2 would not increase temperature. If you can do the maths, then Michael Sweet comment does not apply, but you would be better off delving into atmospheric physics text book for starter (eg this one). For a paper start with Ramanathan & Coakley 1978. The Radiative Transfer Equations are key to numerous technologies other than climate science (USAF is source of main database) and the maths has been checked against observation at top of atmosphere or from ground in numerous papers. A very direct observation can be found here. The full IPCC report is massively cross-referenced with the papers. If you dont like their summary of the research, read the papers. You certainly cannot discuss it sensibly with a comic-book view of what the science actually says. Do not discuss offtopic here - they will be deleted. Try Search or Arguments | by taxomony to find for relevant threads. CO2 is just a trace gas, human CO2 is tiny. I cannot understand your "convective" assertion at all.

  11. Jjworld, most of your post is off-topic. This thread is about the argument that additional CO2 is not going to have an effect, as quoted from Marc Morano at the top of the page. That argument is ignorant and worthless. For more detail, see the Real Climate threads named "A saturated gassy argument." I'm sure they are referenced here somewhere and they are easy to find with RC' search function. The additional effect is in the wings of the spectrum. The rest of your objections belong in other threads. I have seen skeptics arguing that CO2 could fall as carbonic snow in Antarctica, that waste heat was the real cause of warming or that MODTRAN was just a computer model without basis in reality so, to me, the idea that skeptics are more reasonable is laughable beyond description.

  12. Your post is full of very confusing pieces. The following need clarification

    "convective heating model with CO2." What exactly is that?

    'the anthropogenic concentration would have to be increasing dramatically to support the 400ppm if the natural portion were to be static." What does that mean? Anthropogenic contribution is approximately 100 times that of volcanic activity, it has increased immensely in the recent past, a blink of an eye in geological scales. What does natural mean? Geological, biological, both? Most living creatures are carbon neutral since they get their carbon, directly or indirectly, from the atmosphere. Plants that fix carbon are in fact carbon negative if they are not burned. You need to be more specific.

    'we know that the natural portion of the CO2 concentration has increased in recent decades as the planet has been greening." This does not follow. The greening suggest plant biomass increases in some regions, not increased contribution to atmospheric CO2 from natural sources.

    "Recent temperatures have not followed recent CO2 measurement." Actually, they have, with the normal wiggles of variability, the trend continues, in all datasets.

    "CO2 concentrations might be less convective than the IPCC asserts" Say what? This requires a detailed explanation, starting with the Trenberth schematic so you can explain where exactly the concentration of a radiatively active gas has convective properties. Perhaps you should tell everyone what you think is "convective."

    "heat transfer related to atmospheric CO2 convection." Once again, you need to clarify what that means. 

    You start your post by saying "the math is not necessarily flawed" and then concludes with "the math is weak." Which is it? What math are you refering to? Demonstrate how it is weak or provide references to peer-reviewed publications that do so. As it stands, you post is a gish gallop of confusing language without a single reference, full of advice that you do not seem to follow yourself.


    [PS] Thank you. The poster does not appear the understand the science he/she is criticizing but hopefully will do some more research. Please respond to any further comments in an appropriate thread.

  13. I re-read my post to make sure I didn't misstate anything and you've proven one of my points regarding proponents being less reasonable. In your third sentence of a two post response you call my comments ignorant and worthless. So you didn't even bother to follow my statements to the conclusion. That makes you unreasonable.

    My initial response was to the statement from michael sweet that readers should not "waste" time trying to "understand" the science. Seriously? What about that premise is not directly on topic with this or any thread? And what part of my critique about using the scientific method are you calling ignorant and worthless?

    My second portion is precise and accurate if you were willing to process it before calling my efforts ignorant and worthless. The math can be accurate and weak. Those adjectives are not mutually exclusive. Taking time to explain the language to you is far more off topic than my original post. For example, if f(x) = ax + bx and both a and b are assumptions derived from estimates, the math is potentially correct but definitely weak. Before you attack someone who is trying to learn and instruct, perhaps you should be more REASONABLE and consider the position first. My advice is to research, be skeptical and prove each point. I was responding to another poster's advice to ignore the science and trust a group of people that are still learning and evolving their positions as much as any other research group. I don't need any examples to recommend that readers not follow bad advice.

    This post relates to saturation. The argument in this post is that saturation is not the issue since heat is being transferred to CO2 by convection. I'm not making up the topic, the 11 pages of comments brought up the topic as it relates to saturation. I'm directly on the topic if you cared enough to process my comments. 

    Since there is no mention of convection in the IPCC summary, I had to try and explain some of the details from the supporting references, all of which are already mentioned in this and other posts. So, I don't need to re-reference material here. I tried to be pithy since the post was getting long and you picked apart the abbreviated supporting points while leaving the premise untouched. 

    Thus far, this response is completely off topic since I'm having to defend my language which you chose to attack rather than consider. In an effort to get back on topic and honor the spirit of this site, I'll summarize as follows:

    This topic suggests that the ONLY reason that the saturation argument doesn't hold is because of CO2 heat transfer via convection. For reference, read the post and the comments. I'm not arguing the math or the physics related to CO2 convection. I'm familiar with the calculations in a controlled environment. And despite your incorrect statement, the last several decades DO NOT correlate temperature and CO2. CO2 has steadily increased while the temperature spiked, leveled, and spiked again. Convection does not exhibit this pattern and cannot explain the temperature changes. In order for the convection argument to trump the saturation argument, the convection would need to involve something OTHER THAN CO2. Since the anthropogenic portion of CO2 in the atmosphere is less than 20ppm, there is no way CO2 can explain the temperature. I'm not arguing about the totality of climate change. I'm simply stating the physical limitations with the argument that CO2 convection can adequately explain the storage of IR heat in the atmosphere. The theory (and it is still a theory since the scientific method has not proven it), is that other GHGs are also contributing to convective heating. That discussion is off-topic for this post. But the IPCC math makes huge assumptions regarding the contribution of CO2 in the convective process. Are you suggesting that isn't true? And since the anthropogenic portion of CO2 is extremely small it cannot explain the totality of the temperature anomaly. The IPCC reports do cover this topic, but it goes beyond this thread's subject.

    In summary, the convection story does NOT invalidate the saturation argument. This is the statement I was trying to make and encourage readers to research the topic and NOT trust the IPCC report just because one poster recommended it. Convection only explains the heat differential with one or more of the following:

    1) Non CO2 GHGs are contributing more heat via convection than CO2. If this is true, than what are the ratios of those GHGs? The question remains unanswered without using a model to guesstimate the ratios. I'm a mathemetician and don't support guesstimates as scientific. (the non CO2 GHG question is beyond the scope of this thread)

    2) More CO2 is coming from natural sources or indirectly caused by temperature change (thawing tundra, etc). If this is true, the CO2 is coming from temperature changes and not causing temperature changes. (the CO2 is leading or following temperature change is beyond the scope of this thread)

    Regardless, the IPCC reports support my statements. My conclusion is simple. Since the source of the heat cannot be explained without assumptions on CO2 sources that cannot yet be proven, the math is unable to accurately predict future temperatures with any reasonable accuracy. From a mathematical scenario, a range of 1.5C to 4.5C is not reasonable accuracy. In the lower range, we have little change to worry about. If the upper range, we have dramatic regional climate changes. The math has a 50% error range and cannot be relied upon to divert trillions of dollars. 

    Other than my last sentence, I don't think many would disagree with any of my assertions. This thread is titled "Is the CO2 effect saturated?". The response to the question is YES, CO2 is saturated as it relates to radiant heat, but convection provides the difference. 

    To the readers, research the IPCC reports in detail since the IPCC summary does NOT mention convection. Convective heat transfer is a linear temperature model unless pressure or concentrations change. The temperature changes do not follow the path of a convection heat transfer based on the current CO2 concentrations without additional interference. There is plenty of support for this statement on this site. 

    Consider this article:

    In order to explain the current temperature trajectory, assumptions have to be made for time of year, location, and concentration. Those variables create the huge range of error in the climate models that predict 1.5C to 4.5C over a doubling of CO2. In other words, the models that predict these temperature changes still need dramatic improvements since we simply do not know how to treat all these variables under so many different conditions.  

    I say again, the math is not necessarily flawed, but it is weak. It relies on huge assumptions that no applied mathematician would support since each assumption adds more room for error. In other words, we don't know! CO2 does appear to be saturated for radiated IR and trapped convection doesn't explain the temperature anomaly.

    But I'm "ignorant" and my comments are "worthless" according to the "reasonable" Philippe Chantreau. If only we had a scientific method to help us formulate, test, and MODIFY our hypotheses.   

  14. It's you who need to re-read my post. I very specifically mentioned Marc Morano's comment, quoted at the top of the page on this thread. That comment belongs to Morano, and it is demonstrably ignorant and worthless, as can be shown by any examination of the science behind the radiative properties of CO2.

  15. I'm not sure when green boxes appear in this thread as I'm new to the site. So I'll respond to that one here. 

    Why is my comment regarding the math behind the CO2 saturation question off topic but this comment is considered reasonable?

    There is an easy way to find out how increasing CO2 affects temperature: read the IPCC summary and figure they are correct!! It is a waste of time to attempt to calcualte or completely understand the atmosphere yourself, it is too complex.

    If nobody questioned the IPCC reports we'd be stunting our progress. 

  16. It appears that you confuse radiation and convection. Since you seem enclined to stay on topic, let's go back to the topic at hand, namely the saturation argument, as expressed in the Morano quote. That argument is wrong. Do you have any science to demonstrate otherwise? 

  17. Philippe, I don't understand what you gain by calling anyone ignorant or worthless (me, Morano, or anyone). It is why I made my comment about proponents being less reasonable. If you count the name calling on this site you'll find the majority coming from folks like you that try to bully those of us that want to understand the issue fully before giving a blank check to governmental organizations that don't have a history of good stewardship. 

    I believe the CO2 saturation statement is relevant since the heat stored in the atmosphere cannot be explained by anthropogenic CO2 alone. Temperature observations do not support convection via CO2. The IPCC conclusions agree with my statement and introduce other GHGs to fill in the blanks. That's where I believe the math doesn't work without huge assumptions. I don't trust assumptions without tight mathematical tolerances. A previous poster seems we should take all the IPCC assumptions as gospel. That set me off, and here we are. 

  18. And, by the way, the answer is not yes, it is saturated; it is not. As I said earlier, the extra absorbtion happens in the wings of the spectrum. You do not provide any refutation of that. Convection can not add heat to the system, that's nonsense. The only ways to add heat  to the system is by impairing the cooling of the surface or adding solar insolation.

  19. Marc Morano's comment indicates his lack of understanding of the science, showing ignorance. It leads to a conclusions that's entirely wrong, so it is also worthless. These are objective facts. Calling it anything else wouldn't do it justice.

  20. "Convection via CO2" is nonsense. CO2 does not cause by its presence changes to convection. Convection can not act as a forcing. Additional energy in the system can alter convection patterns, different thing altogether. You clearly lack an understanding that would allow you to formulate an cogent, well informed opinion. The article you linked does not support your position at all, read it more carefully. You also need to read the RC posts on the saturated argument.

  21. Well no, I think we are both agreeing that Morano is correct if we are only talking about radiative heat. 

    Perhaps I don't understand the thread, but I think the site is arguing that Morano is not including heat retained by convection. That doesn't make Morano ignorant or worthless. It makes him accurate but incomplete. There's a huge difference to those of us trying to understand the issues. You can't call him wrong when he is actually correct. The rebuttal in the post suggests there is more to the greenhouse effect than just radiative heat. I agree. So Morano's statement is incomplete but it puts a greater burden on other methods of heat retention such as trapped convection. This is a tremendously important concept since most climate change sites don't mention anything about how the heat is stored other than radiative heat captured by CO2 molecules. It's an oversimplification that is repeated on many climate energy budget graphics. 

    I don't have evidence refuting or supporting Morano. I do have concerns with the calculations that attempt to explain the amount of heat trapped by convection. As I explained in a prior post, the IPCC math is complicated but not impossible to follow. I just wish sites like this one would give a little on how much we DON'T know. Billions in research and we have little more than guesswork on precisely how much heat is being convected through CO2. 

    So, I put it back to you. I agree that Morano is incomplete. But the only hard evidence that he is incomplete, is a suspicion that heat is being convected which cools the surface but heats the atmosphere. OK, we know some of that is happening because it has to. But we don't actually know that CO2 is the primary convection delivery molecule. Maybe it is, maybe it isn't. CO2 certainly is NOT the most efficient of the GHGs at convecting heat. And water vapor is far more abundant but pretty easy to measure. 

    The premise of this thread is that Morano is wrong because he's leaving out convection. The bulk of the responses focus on CO2 alone. We're being beat over the head that CO2 is the key.

    We all agree that CO2 radiated heat is saturated and not responsible for the temperature increases. The top of the thread states that "... the saturation of the absorption at the central frequency does not preclude the POSSIBILITY to absorb more energy." OK, so is Morano wrong or is he possibly wrong? I don't see the myth here. Morano is correct about part of the story. If CO2 can possibly hold more heat through convection, it can possibly not hold enough heat to explain the temperature anomalies. 

    The thread quotes Hulburt and he hedges his conclusion: "Apparently the uncertainties and omissions have conspired to counteract each other to some extent." I agree entirely. 

    So how does the fact that heat is stored in CO2 across a wider band than previously considered 100 years ago change the fact that CO2 can only hold a certain amount of energy for a limited amount of time? In order for the recent temperature records to be modeled, a tremendous variability has to be answered. I just don't think the math works without assuming too much. Again, I'm not talking about the lab coefficients of CO2. I'm talking about the global scenario Morano explores. When the climate moves the molecules around we have tremendous negative feedback. Heat is absorbed all over the planet and it escapes all over the upper atmosphere. None of this changes the fact that Morano is at least paritally correct and we have no idea where the heat goes. We know where large portions go but when the portions are added together we end up with too much heat or not enough depending on the IPCC model that is chosen.

    I don't know why my questions have produced such ire. We know what I'm saying is correct by nature of the number of climate models that are currently in the works. I'm in California and there are 18 models just in Northern California that attempt to predict precipitation:

    These models are off topic but look at the graphic at the top of the article. Would any mathematician actually agree to consider any of this worth publishing? The error rate is so large that we might as well just stop spending money on models and admit we don't know. 

    That's my only premise: Morano is correct but probably incomplete. We don't know where the heat goes and we don't even know if CO2 molecules are the primary convection vehicle or just a secondary heat transport. They might be, but nobody has proven it yet. And since CO2 concentrations fluctuate so much across the planet and year, we aren't likely to prove or disprove anything soon. 

    I just wish we could be intellectually honest about what we don't know and how much variability that lack of knowledge causes before we slam scientists for being incomplete.


    [PS] Your statements here are causing concern because you are making assertions based on you dont know and assuming that science dont know either. You do not appear to be reading material commentators have pointed you to and continue to postulate an incorrect version of how atmospheric physics work.

    It would not be intellectually honest to say we dont know about that things that are perfectly well understood in theory and confirmed by numerous observations and experiments.

    If you want to continue this argument, asserting science is wrong or incomplete, then first you cite the science statements that you beleive is incorrect (eg from the IPCC report). Then you cite the evidence that you believe contradicts the science. You cannot get anywhere postulating the science is based on your bizarre ideas about the role of CO2 molecules in "convective" heat transport. This is nonsense and if that is what the science did postulate, then you would have a point. Take Phillipe's advice and learn what the actual physics is. I recommend Science of Doom's excellent series for the basics. And throw away your own preconceptions for starters.

  22. jjworld,

    You do spout a lot of nonsense. If you are genuinely hoping to understand the science of the greenhouse effect, you will need to stop spouting and take on board that science being presented to you, but probably in small bits.

    And note that @521 you write "I don't know why my questions have produced such ire." yet you don't actually present any questions; just bold unsupported assertions.

    Your assertion that there is some sort of convective effect attached to the greenhouse effect is unsupported by anything anywhere in these threads. Convection is discussed as the mechanisms of heat transfer through the upper troposphere include convection, there being large convective circulations throughout the troposphere. The other mechanism is radiation and for that you need greenhouse gases. 99.95% of the upper troposphere is transparent to radiation. Only 0.05% is radiatively active. These gases are directly responsible for a quarter of the +35ºC greenhouse effect and indirectly responsible for the other three-quarters.

    I hope this reply to your various comments begins to be helpful.

  23. JjWorld :

    As a reader of this thread, permit me to make the observation that your posts present you as highly confused about the physical realities of the Earth's atmosphere.

    Perhaps part of your problem is that you are using neologisms (such as "CO2 convection" ~ a term which is, at face value, meaningless) and you are failing to use the precise terminology of science.   And this failing gives the strong (but perhaps unjustified?) impression that you have not grasped the essential basics of the situation.   Once you attain an understanding of the physics, then you will be able to apply your mathematical skills.

    But to talk of mathematical ideas of error margins etc before you understand the the underlying science of what is happening with the radiation, the molecules, the heat/energy transfers . . . is to put the cart before the horse, and risks you embarrassing yourself even further.

    It might help, if you gave indications of the source of your misinformation ~ for it is clear that you have not used physics textbooks or genuinely scientific formal websites such as the N.A.S., the U.K. Royal Society, the A.A.A.S., or the more informal ones like RealClimate, S.O.D., SkepticalScience, etcetera.


    # FYI, Mr Morano is not a scientist but a propagandist (with a long track record of giving misinformation and disinformation to the general public).   Nor has he redeemed himself, in the matter of CO2 "saturation".

  24. Jjworld,

    You have a severe reading comprehension problem. I did not call you, Morano, or anyone ignorant or worthless. I called Morano's comment ignorant and worthless, and I stand by that statement. There is plenty of scientific literature to justify calling it that, literature that you have declined to discover, despite being repeatedly pointed toward it. Now if you want to have your little feelings all hurt and be a snowflake by proxy of an inanimate thing like a comment, be my guest.

    You say "I think the site is arguing that Morano is not including heat retained by convection." You think wrong. The site does not mention convection a single time. I read it again, the word convection does not appear in the OP. You pulled it out of thin air, showed that you do not understand what it means, then argued about it. That pathetic attempt at spreading the confusion raging i your mind is evident here too: "the convection story does NOT invalidate the saturation argument." There is no convection story othe than what you made up.

    jjworld " I do have concerns with the calculations that attempt to explain the amount of heat trapped by convection." I am not aware of any atmospheric dynamics that can accomplish that, you must cite scientific works including such calculations and expose where you believe the weaknesses are. 

    Further "convection delivery molecule". What in the world is that? How do molecules deliver convection?

    "The thread quotes Hulburt." No, it does not. Where is the quote? Who the heck is Hulburt, why is it relevant? The name, or a quote from the person does not figure anywhere in the OP.

    "The error rate is so large" talking about the diagrams at the top of this page. What is the error rate? Where is the error rate in the diagrams? These diagrams have no other purpose than to explain concepts in a graphic way to a lay audience; as such they do not contain any numbers. They are not graphs of exact data, they are not calculations, they are not from scientific publications, so your attack of "who would want to publish that" is once again BS, completely removed from any reality. Nothing but hot air.

    "When the climate moves the molecules around we have tremendous negative feedback." SO the climate moves molecules around? I would have thought that weather does that. In any case, there is an immense scientific literature on feedbacks, positive and negative. Your arguments seems to be that negative feedbacks prevail; it is again, nothing but hot air if not supported by scientific work, where are the citations?

    "we don't even know if CO2 molecules are the primary convection vehicle or just a secondary heat transport." What in the world could this possibly mean other than that you do not have any grasp of the subject? 

    This funny one " I think we are both agreeing that Morano is correct if we are only talking about radiative heat." So grotesque, it truly falls within the not even wrong category. We do not agree at all, and Morano is so far from being correct that he would need a super fast "vehicle" (of convection or other) to make it back to relelvance within his lifetime.

    This "If CO2 can possibly hold more heat through convection, it can possibly not hold enough heat to explain the temperature anomalies." comes in response to being pointed to the fact that having the central part of the radiation spectrum of CO2 saturated does not preclude the possibility of absorbing more heat, namely in the wings of the spectrum. In a sort of lawyer fashion, you latch on the word possibility and attempt to sow confusion, as if it meant probability, when in this case, it means capability. The gas does absorb more, that can be demonstrated by both experiment and calculation. 

    This gem is priceless "I just wish we could be intellectually honest about what we don't know" and then a suggestion that Morano is a scientist, and "incomplete." I'll let readers appreciate the supreme irony.

    You have been pointed in the right direction and have refused to engage with that. You have attributed fantasy-like concepts to the OP, and a careful read shows that it is all pure invention on your part. You have been asked repeatedly to support you extremely wide-ranging and bold assertions with references, and the only one you mustered does not accomplish anything close to that.

    You have contributed thousands of words to this thread, and so far they amount to little more than technical sounding word salad.

  25. In the discussion about the effect of CO2 on the climate there are certain images which may be said to incorporate the essential part of the arguments. Such iconic graphs are the driving force in changing one's view of the world. A good example is the sun with the planets rotating around it. This stopped all phantasies about what happens at the edge of the (flat) earth. This iconic image made it possible to sail Westward in 1492 in order to reach India.

    For CO2 the iconic image is the rippled increasing graph of the CO2 concentration as measured at Mauna Loa from 1960 onwards, sometimes extended over the past thousand years by observations from tree rings and ice cores to obtain the "hockey stick". For the influence of CO2 on climate the iconic graph is given in Wikipedia (last updated 23 August 2019)

    Caption: "Atmospheric gases only absorb some wavelengths of energy but are transparent to others. The absorption patterns of water vapor (blue peaks) and carbon dioxide (pink peaks) overlap in some wavelengths. Carbon dioxide is not as strong a greenhouse gas as water vapor, but it absorbs energy in longer wavelengths (12–15 micrometers) that water vapor does not, partially closing the "window" through which heat radiated by the surface would normally escape to space."

    The graph shows that the effect of water vapour, H2O, is much greater than the effect of CO2. It also shows the saturation of the absorption due to CO2. The first argument (about water vapour) is valid. We can't do anything about the concentration of H2O though, except perhaps by increasing the temperature. So we will just have to accept this effect. The second argument (about saturation) is also valid. The absorption at wavelength 4 - 4.4 μm is 100% over most of the region, and so too at 12-15 μm. In comparison with H2O the peaks of CO2 are very steep and the wings have little effect. It is only the thin peaks at 2 μm and at 4.9 μm which will grow significantly if the concentration of CO2 is increased.

    The basic physics is simple: A photon of light at a wavelength of 14 μm is passed from one CO2 molecule to the next performing a kind of random walk until it exits the atmosphere. There are two exits, outer space and the earth. Saturation means that a photon starting from the earth has very little chance of exiting to outer space. It is almost certain to exit the atmosphere to the earth, where like shortwave radiation it will be re-emitted at a different wavelength. Even if the new wavelength with probability a half lies in an absorption band of CO2 or H2O, this only means a stay of execution. In the end the photon will escape to outer space through one of the long wave gaps in our atmosphere.

    The graph in Figure 2 in Zhong & Haigh (2013) is perhaps more precise, but the vertical scale runs over twelve orders of magnitude, (twelve orders of magnitude is from one mm to a million km, or from one gram to a Megaton). The result of this scale is that I am not able to comprehend the significance of the graph. Figure 5b, bottom, gives the difference between the radiative flux for the present level of CO2 (389 ppmv) and a level increased by a factor 32 (12500 ppmv). The total negative impact is almost cancelled by the positive impact around 15 μm. This impression is reinforced by Figure 6a where the graph is practically horizontal beyond 400 ppmv. In Figure 6b we see an increase in the slope beyond ten thousand ppmv. In that graph the horizontal axis is logarithmic and runs up to a million ppmv, which is a pure CO2 atmosphere. These results are based on models and therefore should be taken with a pinch of salt.

    The conclusion is: The direct impact on the temperature of the earth of the increase in CO2 from the present level of around 400 ppmv is relatively small. This is due to saturation at the bands where CO2 absorbs long wave radiation.

    Is the graph above misleading? It is described as "(Illustration adapted from Robert Rohde.)". Clicking on Robert Rohde results in the message: refused to connect.
    If anyone knows a better graph I would be very happy to obtain a link.

    There is a nice course on climate denial presented by the University of Queensland The course is free of charge and contains a huge amount of good information on climate change. Unfortunately the course does not address the topic of the absorption of CO2 at specific wavelengths. Neither does the basic rebuttal by dana 1981.

    The near saturation of CO2 at present levels makes it difficult to convince people to vote for a cut in CO2 emissions or for a tax on such emissions.


    [RH] Your image was breaking the page formatting. I can add it back in but it needs to be smaller than 450 px wide, which for that image was going to render it unreadable.

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