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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

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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)

The mistaken idea that the Greenhouse Effect is 'saturated', that adding more CO2 will have virtually no effect, is based on a simple misunderstanding of how the Greenhouse Effect works.

The myth goes something like this:

  • CO2 absorbs nearly all the Infrared (heat) radiation leaving the Earth's surface that it can absorb. True!
  • Therefore adding more CO2 won't absorb much more IR radiation at the surface. True!
  • Therefore adding more CO2 can't cause more warming. FALSE!!!

Here's why; it ignores the very simplest arithmetic.

If the air is only absorbing heat from the surface then the air should just keep getting hotter and hotter. By now the Earth should be a cinder from all that absorbed heat. But not too surprisingly, it isn't! What are we missing?

The air doesn't just absorb heat, it also loses it as well! The atmosphere isn't just absorbing IR Radiation (heat) from the surface. It is also radiating IR Radiation (heat) to Space. If these two heat flows are in balance, the atmosphere doesn't warm or cool - it stays the same.

Lets think about a simple analogy:

We have a water tank. A pump is adding water to the tank at, perhaps, 100 litres per minute. And an outlet pipe is letting water drain out of the tank at 100 litres per minute. What is happening to the water level in the tank? It is remaining steady because the flows into and out of the tank are the same. In our analogy the pump adding water is the absorption of heat by the atmosphere; the water flowing from the outlet pipe is the heat being radiated out to space. And the volume of water inside the tank is the amount of heat in the atmosphere.

What might we do to increase the water level in the tank?

We might increase the speed of the pump that is adding water to the tank. That would raise the water level. But if the pump is already running at nearly its top speed, I can't add water any faster. That would fit the 'It's Saturated' claim: the pump can't run much faster just as the atmosphere can't absorb the Sun's heat any faster

But what if we restricted the outlet, so that it was harder for water to get out of the tank? The same amount of water is flowing in but less is flowing out. So the water level in the tank will rise. We can change the water level in our tank without changing how much water is flowing in, by changing how much water is flowing out.

water tank

Similarly we can change how much heat there is in the atmosphere by restricting how much heat leaves the atmosphere rather than by increasing how much is being absorbed by the atmosphere.

This is how the Greenhouse Effect works. The Greenhouse gases such as carbon dioxide and water vapour absorb most of the heat radiation leaving the Earth's surface. Then their concentration determines how much heat escapes from the top of the atmosphere to space. It is the change in what happens at the top of the atmosphere that matters, not what happens down here near the surface.

So how does changing the concentration of a Greenhouse gas change how much heat escapes from the upper atmosphere? As we climb higher in the atmosphere the air gets thinner. There is less of all gases, including the greenhouse gases. Eventually the air becomes thin enough that any heat radiated by the air can escape all the way to Space. How much heat escapes to space from this altitude then depends on how cold the air is at that height. The colder the air, the less heat it radiates.

atmosphere
(OK, I'm Australian so this image appeals to me)

So if we add more greenhouse gases the air needs to be thinner before heat radiation is able to escape to space. So this can only happen higher in the atmosphere. Where it is colder. So the amount of heat escaping is reduced.

By adding greenhouse gases, we force the radiation to space to come from higher, colder air, reducing the flow of radiation to space. And there is still a lot of scope for more greenhouse gases to push 'the action' higher and higher, into colder and colder air, restricting the rate of radiation to space even further.

The Greenhouse Effect isn't even remotely Saturated. Myth Busted!

Last updated on 13 February 2014 by dana1981. View Archives

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Related Arguments

Further reading

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

Comments

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Comments 51 to 100 out of 174:

  1. Riccardo - a better link I think is Dessler & Davis 2010 ?
  2. Thank you scaddenp :)
  3. #48 Albatross at 05:50 AM on 11 November, 2010
    Berényi Péter,

    Please clarify. Do you believe that the CO2 effect is saturated?


    Of course it is, in most of the 14 μm - 16 μm (wavenumber 625 cm-1 - 710 cm-1) absorption band. In this frequency range effective height of the photosphere (the region from where photons have a reasonable chance to escape to space) is above 20 km, well in the stratosphere. As there is a thermal inversion there (the higher one goes the hotter it gets), with increasing CO2 levels outgoing thermal radiation increases (this is why it is not shown in Harris 2001).

    There are two narrow bands on both sides of this range which belong to the wings of multiple absorption lines there. In these bands CO2 IR optical depth is close to unity and this is where effective height of photosphere is still below the tropopause. In the troposphere temperature usually decreases with increasing height, so at a specific wavelength more CO2 means less outgoing radiation.

    On the low wavenumber (long wave) side there are strong H2O absorption lines as well, so the effect only works in an extremely dry troposphere (mostly in the polar regions where low level dry-freezing occurs).

    Therefore stuff usually happens only at the upper edge of the 8-14 μm main atmospheric thermal IR window (lower edge of wavenumber 710 - 1250 cm-1).

    In this frequency region there are no major absorption lines (except O3 lines around 1040 cm-1), just the somewhat mysterious water vapor continuum.

    Partial pressure of water vapor decreases more rapidly with increasing height than that of carbon dioxide, so at frequency bands dominated by H2O absorption effective thickness of photosphere is much smaller. Therefore outgoing thermal IR radiation in these regions is extremely sensitive to minor variations of water vapor distribution.

    As atmospheric H2O distribution is fractal-like on a scale spanning many orders of magnitude, this effect is neither modeled nor measured sufficiently.
  4. #50 scaddenp

    The actual wording in the IPCC report is "Note that for shorter recent periods, the slope is greater,indicating accelerated warming."

    Link to source:

    IPCC page used in the Climate4you section.

    Quote from the Climate4you web page: "From the text above the period 1981-2005 is identified by IPCC as being unique, representing a new trend characterised by an accelerated temperature rise. The accelerated temperature increase is suggested to be caused by atmospheric increases in carbon dioxide and other greenhouse gases, assumed to dominate the observed warming after the mid-1970s.
  5. #37 Daniel Bailey at 07:28 AM on 10 November, 2010
    Re: Climate4you stuff

    Went to Norman's website source for his graph & poked around a bit. On this page I noted that:

    1. All data is in absolute temps, not anomalies
    2. They establish the post-industrial runup in the temperature trend and use that trend to de-trend the signal in the data. I.e., they "hide the incline" in the 20th Century temperature data.
    3. They attribute 100% of CO2's effects on temperatures when comparing the CO2 rise to temps, showing that since temps don't rise in lockstep with CO2 levels it can't be the CO2 affecting temps
    4. They use a paper by Dr. Syun-Ichi Akasofu as a basis to say that any warming since the LIA is just a reflection of the Earth returning to "normal" and that it's a natural cycle.

    Trenberth demolished Akasofu here.

    The whole site is a bait-trap for the unwary.

    The Yooper

    Not sure what page you looked at. They have several graphs using anomalies.

    He did not claim CO2 did not effect temp...Direct quote from the page. "Consequently, the complex nature of the relation between global temperature and atmospheric CO2 since at least 1958 therefore represents an example of empirical falsification of the hypothesis ascribing dominance on the global temperature by the amount of atmospheric CO2. Clearly, the potential influence of CO2 must be subordinate to one or several other phenomena influencing global temperature. Presumably, it is more correct to characterize CO2 as a contributing factor for global temperature changes, rather than a dominant factor."
  6. #44 Tom Dayton

    Thanks for the link to the posts concerning Outgoing Longwave Radiation. I am reading through the posts working to understand the content. I do love learning.
  7. Norman, thank for that. Now to why I wanted it. Firstly, the claim that 1981-2005 represents a unique new trend is Climate4you, not IPCC. The text never uses the word unique. There is no argument easier to demolish than a strawman. Note how John does it here? He quotes the skeptic claim verbatum with pointer to source of origin.
    What DOES the IPCC paragraph claim.
    1/ The earth is warming, stratosphere cooling in accordance with models.
    2/ It details the nature of the warming.
    3/ It outlines the basis of the measurement
    4/ It notes the consilience of measurements with sea-level rise, glacial melt etc.

    It also claims that the temperature rise is consistant with modelling of known forcings (GHG, aerosol).


    As to climate4you's claim that he/she has shown CO2 is not the dominant factor since 1975, as noted above in posts, he/she has only shown a misunderstanding of the actual climate predictions - trying to demolish what the physics doesnt claim.
  8. Re: Norman (55)

    This page.

    By taking the underlying signal (Figure C) out of the data, you homogenize (Figure D) the data. When you take the pits out of the cherries, is what is left really a cherry?

    Let me ask you this, Norman: Post-1976, what forcings other than CO2 have had any significance on global temperatures?

    Simple question, right?

    The Yooper
  9. #57 scaddenp

    The person who runs Climate4you, has a lot of peer-reviewed publications.
  10. #58 Daniel Bailey,

    "Let me ask you this, Norman: Post-1976, what forcings other than CO2 have had any significance on global temperatures?

    Simple question, right?"

    Yes and Climate4you does have an alternative forcing. If I am successful I will Post the graph.

    Alternate forcing that can affect Global temps.

    Quote from the page on Climate4you that had this graph (from the Homepage click the Climate & Clouds tab):

    "Within the still short period of satellite cloud cover observations, the total global cloud cover reached a maximum of about 69 percent in 1987 and a minimum of about 64 percent in 2000 (see diagram above), a decrease of about 5 percent. This decrease roughly corresponds to a radiative net change of about 0.9 W/m2 within a period of only 13 years, which may be compared with the total net change from 1750 to 2006 of 1.6 W/m2 of all climatic drivers as estimated in the IPCC 2007 report, including release of greenhouse gasses from the burning of fossil fuels. These observations leave little doubt that cloud cover variations may have a profound effect on global climate and meteorology on almost any time scale considered"
  11. Norman - so? So do various fossil fuel shills. Does he have any expertise in climate science, radiative physics etc? Has he published his critique in peer-reviewed journal?

    If you don't have enough expertise in an area to be able to evaluate competing claims, (I'm assuming you havent been able to follow the critiques above) then unfortunately you have either got to acquire the expertise yourself, preferably from textbooks and papers, or you have to rely on expert opinion from people actively working in the field with appropriate domain knowledge. Now where in physical geography do they teach thermodynamics and radiative physics? Not my idea of expert opinion.

    In my opinion, if you are interested in climate science, then you start with IPCC WG1. This reflects the published science and gives you an almighty index into it. You can see what is actually claimed rather than the zillions of strawmen that denialists like to doubt. You dont have to agree with the assessment but at least you get it one place. If you are looking a "skeptic" claims, then only bother with what's been published for reasons I stated earlier.
  12. Norman
    somewhat offtopic here. Disproving the real science is not as easy as you (and many others) apper to think. Look here for some problems related to ISCCP cloud data. Be carefull and, if in doubt, rely on the published litterature.
  13. Berényi Péter @53,

    "Well of course it is", referring to my question as to whether or not the CO2 effect is saturated.

    Let us put aside the rest of your post for now, because your statement raises some relevant questions.

    1) Could you please tell us at what CO2 concentration you believe the CO2 effect became saturated in all bands and at all altitudes.
    2) Perhaps a moot question in view of your belief that the CO2 effect is saturated, but what is your understanding of expected warming arising from doubling CO2 (without feedbacks).
    3) What is your understanding of warming arising from doubling CO2 (with Charney and slow feedbacks).
  14. #57 scaddenp

    "The text never uses the word unique. There is no argument easier to demolish than a strawman."

    From the IPCC page: "Palaeoclimatic information
    supports the interpretation
    that the warmth of the last half century
    is unusual in at least the previous 1,300 years.
    The last time the polar regions were signifi cantly
    warmer than present for an extended period (about
    125,000 years ago), reductions in polar ice volume
    led to 4 to 6 m of sea level rise. {6.4, 6.6}"

    IPCC source of above quote.

    Look at the Thesaurus for the word unusual...do you see unique in that list?
  15. #62 Riccardo

    I read through your link. It does not make the claim that the cloud cover percentage has not changed. They just warn against using this data to form any conclusion about climate because of problems with how the cloud cover is measured. As far as this article goes, Cloud cover could still be the dominant driver. There argument is don't use the cloud cover data at this time.
  16. Norman, in general the IPCC tend to be very cautious in their use of words. I would not recommend reading "unusual" and substituting the word "unique".
  17. I need help from someone more knowledgeable, but it seems to me that BP is incorrect in assuming a 2 degrees increase in brightness temperature equivalent to blackbody temperature in the narrow band of 750 cm-1 and 900 cm-1 requires a layer of atmosphere having increased its measured "temperature" by 2 degrees.
  18. Norman, Ned is understating his case. "Unique" really means one of a kind, not merely unusual. In everyday conversation, "unique" is used casually as a synonym for "unusual," but the IPCC has gone out of its way to be careful in its choice of words, due to certain people jumping to conclusions based on the IPCC's more casual usage in the past.
  19. Norman - so we are having "unusual" weather at the moment. Does that make it unique? A unique event would by unusual but not the other way round.

    But instead of playing word games, look at the sentence that you quoted from the IPCC. Has climate4You refuted this statement? No.
  20. Norman
    indeed. It's exactly what wanted to say, we have no evidence of a significant change in cloud cover, let alone take it as an alternative explanation of current warming trend. This is one more reason why the site you link is unreliable.
  21. #70 Riccardo

    Climate4you is a work in progress as are most climate sites. There is a vast amount of information concerning Global Warming and new information growing daily. I believe he leaves an email address on his site. I can send him the link you posted and see if he does anything with it.
  22. Tom Dayton #67
    there's no need to dig into the well known difference between brightness temperature and temperature. I can't tell if Berényi Péter didn't actually read the paper, deliberately ignored what the authors say or has well founded reasons to believe they're wrong. A few relevant quotes from the paper.

    "the difference in the 800-1,000 cm-1 region is positive, and lies between about 1 and 2K. It is important not to over-interpret the observations to an accuracy that is not justifed by the errors (see below), nor to lose sight of our principal result, which is the observation of the sharp spectral features discussed in the preceding paragraph."

    "we do conclude that the observed window difference spectra strongly indicate an effect involving residual small ice crystal effects, incompletely cleared from the data."

    "we must also take into account inter-annual variability as a possible cause of the observed difference spectra. In the window region, the brightness temperature difference is strongly modulated by short-term fluctuations, such as inter-annual variability (specific concern involves the 1997 warm El Nino/Southern Oscillation, ENSO, event)."
  23. I see the skeptics argument differently. What I see they are preaching is not that GHGs are saturated with energy, but are at or near peak absorption for the energy available. This is quite different from saying the molecules themselves are saturated. They are not.
    Why increases in GHGs do little to add to atmospheric warming is due to the fact that there is no additional energy available, it has already been used up. With this argument, the skeptics say any increase in any or all GHGs will cause little meaningful warming by citing the example when the Earth had 10x to 15x the amount of CO2. No runaway warming!
    Since CO2 is a GHG, increases in any GHG will not increase global warming. Humph! Because the GHG are at
    maximum warmth already. Finally, they state that the energy in the GHGs are in a sort of equilibrium with the
    atmospheric humidity. So, if more CO2 is added, the atmosphere rains out the moisture and re-equilibrates by noting an observed drop in upper atmospheric humidity.
  24. In an argument about this article a friend sent me this. Can someone help me with a layman's language rebuttal?

    ****************************************************
    "Water, a 3-atom dipolar molecule has several ways of rotating and several ways of vibrating, so it interacts with and absorbs electromagnetic radiation in many parts of the spectrum. It is a strong "greenhouse gas".

    Carbon dioxide is linear and symmetrical, so it has no resultant dipole and it therefore cannot absorb in the rotational frequency region. Its symmetrical stretching vibration is also infrared inactive. Its asymmetrical stretching vibration however produces a constantly reversing dipole, so it absorbs in a narrow band of frequencies around 2350 wavenumbers. Likewise the bending vibrations, around 670 wavenumbers.

    So in most of the infrared and microwave spectrum the molecule behaves just like N2 and O2. It doesn't absorb at all. It does absorb in two narrow frequency bands, and absorbs so strongly there that the present concentration of CO2 (about 340 parts per million by volume) achieves almost complete absorption. Increasing the concentration can cause only a little more absorption. The high extinction coefficients are known, the concentration is known, the calculation is not difficult abstruse or speculative, and I think you will agree that it is relevant to anyone who wants to write informatively about the greenhouse effect."
    ****************************************************
  25. Re: Colin Bridge (74)

    Hey, welcome to Skeptical Science! Thanks for posting your first question on an appropriate thread!

    Your friend's article is incorrect in many respects:

    1. Even if the absorption band of carbon dioxide would be fully saturated in the lower parts of atmosphere, it is not saturated in higher atmosphere and the addition of carbon dioxide (CO2) will cause more absorption of thermal radiation (extra CO2 has extra effect for a multitude of reasons). Nice-to-know: CO2 exerts its effects primarily though bending mode (you can see visualizations of the various modes of CO2 here). As shown there, CO2 is infrared (IR) active due to a transient dipole: bending results in charge being asymmetrically distributed with net positive near the carbon atom and negative near the two oxygen atoms.

    2. Water vapor is a condensible GHG. Short-term increases in concentrations of it condense out and equalize in about 9 days time. CO2 stays aloft for centuries-to-millennia. Like the Energizer Bunny, it keeps on doing its thing.

    3. The Earth currently takes in more energy than it emits. We can physically measure this. This emission takes place at the Top Of Atmosphere (TOA), well above where water vapor has anything but a minimal effect (it is found in only trace amounts there). Only the increasing concentrations of CO2, which we can isotopically tell come from fossil-fuel emissions, explain the imbalance. And they explain it quite well. Turning up the CO2 control knob is like cranking up the thermostat to max...and breaking it:



    The NOTES section at the bottom of this page contain much useful material. Also see here for background on the greenhouse effect and the 2nd Law of Thermodynamics, which usually comes in the next contrarian article. :)

    BTW: The introduction of N2 and O2 is a complete red herring, as they are unaffected by infrared.

    Hope that helps.

    The Yooper
  26. Thank you Daniel Bailey, it certainly helps my understanding. If no more warming was available with increased CO2, it is hard to see how Snowball Earth could have ended where my reading is that a trigger was reached sending earth into a transient super-greenhouse.
  27. I know I am coming to this discussion late, but I wanted to discuss the statement from the advanced tab that states:
    "We can see that although the absorption dip cannot fall below the 220 K curve, it becomes wider and the absorbed energy increases accordingly."

    I have an alternate/additional hypothesis that I am trying to explore:
    * Raising the CO2 concentration should raise the effective altitude of the "last layer", since you need to go higher to get to a place where CO2 is thin enough to "let the IR escape".
    * Raising the altitude of the new "last layer" take us to a layer with a lower average temperature.
    * That cooler layer will radiate less energy.
    * To return to equilibrium, that new "last layer" must warm up, which will in turn warm all the layers below it.

    This mechanism is in addition to the effects of line broadening that have already been discussed.


    This fall apart a bit if that "last layer" is already at or above the tropopause. The temperatures in the model suggest that the "last layer" is still a little below the tropopause.

    Does any one here
    1) have any links to the level of the effective "last layer"?
    2) comments or corrections to what I am hypothesizing?
  28. tjfolkerts, you are correct. In that same Advanced tabbed page, look for the paragraph "There's one more subtle effect related to increased absorption. Upon increasing CO2 concentration, the layer at which the absorption coefficient at each wavelength is low enough to let the IR light escape will be found higher in the atmosphere. The emitting layer will then have a lower temperature, at least until the tropopause is reached, and hence a lower emitting power."

    A good source of more info are the RealClimate posts A Saturated Gassy Argument and the followup Part II: What Angstrom Didn't Know.
  29. Tom,

    Thanks for the info and the link to the other discussions - they were quite informative. I should have guessed that if a relative novice like me can think of it, then others would have already explored the idea in more depth. :-)
  30. tjfolkerts, regarding lapse rate, you'll be interested to read Eli Rabbett's post about a skeptic named Hermann Harde, who used a climate model so simple that it had only two layers of atmosphere--too few layers to adequately represent the strength of the effect of higher layers being cooler.
  31. My take on the science is this:
    1. The undisputed absorption figures for CO2 mean that an increase in concentration cannot directly greatly (I mean by more than 0.5W/m^2) increase the absorption of surface energy by the atmosphere.
    2. The increased absorption of sunlight by the upper atmosphere means a drop in insolation at the Surface of about 1W/m^2. The increased back radiation due to the decreased average altitude of the CO2 surface-bound emissions is about 0.5W/m^2, so the NET direct effect of doubled CO2 on the Surface is a cooling forcing of 0.5W/m^2.
    3. At the other boundary, it is clear from the outgoing spectra that CO2 is responsible for between 15 and 18W/m^2 of the emissions to space. It is also very clear that the emissions at the stronger wavenumber 670 are stronger than the rest of the CO2 band. Because emissions to space have to get through the overlying gas, it is also clear that the more strongly absorbed wavenumber 670 emissions are coming from higher in the atmosphere than say the wavenumber 650 emissions. So in this case, Higher = hotter, ie the wavenumber 670 emissions are definitely coming from the stratosphere.
    4. All very well, but what about the rest of the CO2 band? At STP 50% of wavenumber 650 emissions are absorbed in the first 25m of atmosphere. At say 17km the same number of CO2 molecules occupy about 250m. The pressure decrease over these 250m means only a small narrowing of the emission/absorption lines, so absorption rate will not be greatly affected: at 17km just under half the wavenumber 650 photons are absorbed within 250m.
    5. I calculate that the published absorption data for CO2 means that the great majority of emissions from CO2 must be coming from above the Tropopause.
    6. If so, then we would expect a doubling of CO2 to have a COOLING effect on the planet.
  32. novandilcosid takes on basic physics on the CO2 lag thread. He writes:

    "1. The undisputed absorption figures for CO2 mean that an increase in concentration cannot directly greatly (I mean by more than 0.5W/m^2) increase the absorption of surface energy by the atmosphere."


    novan calculates this by calculating the change in brightness temperature of the back radiation assuming the atmospheric temperature profile remains constant, and that the increased CO2 concentration reduces the average altitude from which the back radiation is emitted. The problem with this is not that it is in error, but what it ignores. Specifically, what heats the surface is not the back radiation but the sun. The way the back radiation effects the surface temperature is only by modulating the rate at which heat escapes, but it is a minor player in that role. Far more important is convection, which carries heat rapidly to the upper atmosphere. In the event that the upper troposphere warms, as for example, because of reduced IR radiation because of increased CO2 concentrations, that will slow the rate of convective heat transfer, and because heat is being carried away from the surface slower, the surface will warm until equilibrium is reestablished. This will result in an increase in back radiation, but because the lower atmosphere has warmed, not because of the lower effective altitude of emission of back radiation.

    "4. All very well, but what about the rest of the CO2 band? At STP 50% of wavenumber 650 emissions are absorbed in the first 25m of atmosphere. At say 17km the same number of CO2 molecules occupy about 250m. The pressure decrease over these 250m means only a small narrowing of the emission/absorption lines, so absorption rate will not be greatly affected: at 17km just under half the wavenumber 650 photons are absorbed within 250m.
    5. I calculate that the published absorption data for CO2 means that the great majority of emissions from CO2 must be coming from above the Tropopause."


    It is odd that novan concentrates his discussion on the 650 wave number. It is well known that at that wave number, CO2 absorption is at its peak, and that as a result the majority of CO2 emissions to space at that wavenumber come from the stratosphere. However, the CO2 absorption band in the atmosphere is approximately 350 cm^-1 wide, with most of that band being much weaker absorption than at 650^-1. Science of Doom has calculated the change in transmission at the troposphere for a doubling of CO2:



    This is total change in transmittance, and does not take into account the emissions by the CO2, but the effect of the stratosphere and above on transmittance or emissions in the wings (<625cm^-1, >715cm^-1) is negligible. The consequence of including all the line numbers in your calculations (rather than just one, and done by novan) is to show that increasing CO2 concentrations reduces total emissions to space from the upper troposphere, requiring a compensating warming of the surface to restore the energy balance.
    Response: [DB] Closed blockquote tag.
  33. Tom Curtis wrote:
    "novandilcosid takes on basic physics on the CO2 lag thread. He writes:


    "1. The undisputed absorption figures for CO2 mean that an increase in concentration cannot directly greatly (I mean by more than 0.5W/m^2) increase the absorption of surface energy by the atmosphere."


    novan calculates this by calculating the change in brightness temperature of the back radiation assuming the atmospheric temperature profile remains constant, and that the increased CO2 concentration reduces the average altitude from which the back radiation is emitted. The problem with this is not that it is in error, but what it ignores. Specifically, what heats the surface is not the back radiation but the sun. The way the back radiation effects the surface temperature is only by modulating the rate at which heat escapes, but it is a minor player in that role. Far more important is convection, which carries heat rapidly to the upper atmosphere. In the event that the upper troposphere warms, as for example, because of reduced IR radiation because of increased CO2 concentrations, that will slow the rate of convective heat transfer, and because heat is being carried away from the surface slower, the surface will warm until equilibrium is reestablished. This will result in an increase in back radiation, but because the lower atmosphere has warmed, not because of the lower effective altitude of emission of back radiation."

    For a system in equilibrium (ie for the planet integrated over the surface and over a year) the Surface Energy Flow Balance is:
    Absorbed Sunlight + Back-Radiation = Surface Radiation + Evaporated water + Conduction

    For doubled CO2, the Absorbed Sunlight is less by 1W/M^2 because of increased absorption in the upper atmosphere. The Back Radiation is about 0.5W/m^2 more, due to a drop in the average height of CO2 radiation (lower is hotter). So the LHS (the forcing side) is less, and unless there are any other influences the Surface will cool slightly, resulting in slightly less Surface Radiation, and slightly less evaporated water.

    Note there is no mechanism to change the energy balance at the surface other than by varying the absorbed sunlight or the back radiation. The Surface couldn't give two hoots about what is happening in the thin cold and radiatively isolated upper atmosphere. It can only change temperature if the LHS of the equation changes.

    The absorbed sunlight will change if the albedo (clouds, ice) changes, the sun changes or as in this case, the absorption into the atmosphere changes.
    The back radiation will change if the atmospheric window closes, or if the Greenhouse gases heat up.

    So I disagree with Tom in one important detail. He suggests the surface heats up because of slowed atmospheric convection, then back radiation increases because of a heated atmosphere.

    That's not the case. The surface temperature can only increase if the atmosphere heats up first. And I'm not sure that it does.

    [There are some other interesting aspects: The atmospheric window is almost constant, the conduction is almost constant, so the heat transport from the surface into the atmosphere is almost a constant whatever the surface temperature. What happens as the temperature rises is that the Net radiation (surface radiation less radiation through the window less back radiation) DECREASES and this balances the increase in water vapour condensation.

    It is also of interest, as Tom points out, that the surface heat transport into the atmosphere is one fifth Net radiation, one fifth conduction, and three fifths condensation of water vapour.]
    Response: [DB] Please do not quote more than a sentence at a time from someone else's comment. A link to their comment plus the specific point you wish to quote will be sufficient. Thanks!
  34. Tom went on to claim that the 15um CO2 band is very wide. But examination of outgoing spectra suggests that the major CO2 effect is confined to the wavenumber 625-700 region, as does a plot of the absorption lines. In this region, the outgoing spectrum is about 15-18W/m^2.

    Of that around 12-15W/m^2 is being emitted above the tropopause. And that number goes up as the concentration of CO2 goes up, as the emissions come from higher in the Stratosphere (higher = warmer = stronger emission).

    I don't know how much emission is coming from CO2 molecules emitting the very weak lines outside this region, but not very much. I think it may be time to reveal how much energy is believed to be radiated from these weak lines, and what the exact effect of a doubling of CO2 is thought to be.

    [I distrust "Transmittance". How is it defined? There needs to be a distance and a concentration specified to make sense of the number. It is far more instructive and useful to use absorption tables, where the percentage remaining after passage through a specified amount of gas is defined.
    "Change in Transmittance" is even worse!]
  35. novandilcosid @83 (A) claims the surface energy balance is given by:

    Absorbed Sunlight + Back-Radiation = Surface Radiation + Evaporated water + Conduction

    Clearly in doing so he is talking about the actual surface - ie the top 1 mm of dirt of water that covers the planets surface. Oddly enough, there are very few thermometers stuck into that top 2 mm, with most thermometers being stuck in the atmosphere 2 meters above that surface. The "Global Mean Surface Temperature" is actually the temperature of the lowest surface layer of the atmosphere, so the proper energy balance equation is:

    Absorbed Sunlight + Back-Radiation = Surface Radiation + Evaporated water (including water from transpiration in plants) + Convection

    Although nonstandard, we can still work with novan's actual surface.

    (B) Novan also claims the only way the temperature can change is if the Left Hand Side of the surface balance equation changes. This is patently false, and refuted by everyday experience. It is standard procedure in cooking to alter the heat flow or temperature of water on the stove by adjusting evaporative heat loss rather than the heating element or flame. I come from Mount Isa where it is standard practice to cool homes by using evaporative air conditioners. Further, in Australia drinking water in the outback is typically stored in canvas bags rather than Jerry Cans so that evaporation will cool the water.

    If, at the surface, conductive heat flow was restricted, say, by raising the temperature of the layer immediately above the surface, and the inputs were left unchanged, the surface temperature would increase. The surface air layer could be warmed by a reduction in convection (and hence also latent heat transfer) by the warming of the air layer above that, and so on till you reach the upper troposphere where the air will be warmed by a reduction in the net outgoing IR radiation from that level by an increase in CO2 levels.

    C) Novan purports to have proved from first principles or empirical research or to just know a priori (I'm not sure which) that conduction between the surface and atmosphere is near constant, which is false. He also claims that the change of evaporative heat loss from a surface will automatically match in magnitude, but with opposite sign the change in radiative loss of heat to the atmosphere. This principle apparently holds true whether the surface in question is rocky desert or ocean, and also to hold independently of wind speed over the surface. That is an astonishing result, and I cannot wait to see the proof. I expect to be disappointed, however, for it sounds more like magical thinking than science.
  36. novandilcosid @84 as the situation stands, a large number of scientists using different programs on different computers have calculated the absorption, emission and transmittance for each wave number across the entire IR spectrum for the surface, plus each of 33 or more layers of atmosphere using observationally based information on temperature levels, and trace gas concentrations. In doing so they have produced spectra that almost exactly match those actually observed from space. Using these diverse models, if they increase the amount of CO2 by a factor of two, they reduce the outgoing IR radiation by approximately 3.7 Watts/meter squared.

    Those scientists and others, using still other computers have used equivalent techniques, but in which they allow the temperature and humidity at each layer to be set by the program based on energy balance equations and produced almost identical results. Deniers almost always ridicule these results as being "only based on models".

    But you want me to believe your claims about the effects of increasing CO2 based on the fact that you have calculated for just two wave numbers and just two poorly defined levels of the atmosphere.

    How about you program your line by line model and see if your results actually hold when you consider the whole atmosphere and all of the radiation. In the mean time, if you click on the picture below, you might get a clue:


    (Atmospheric absorption for 280 and 560 ppm CO2 as calculated by DeWitt Payne using Spectralcalc; difference between values shown in 82 above.)
  37. Tom Curtis @ #85 has fallen into a trap. His claims are all correct. So are mine.

    It will be noted that I prefaced my analysis with the following words:
    "For a system in equilibrium (ie for the planet integrated over the surface and over a year)"

    Essentially this is what is claimed when the IPCC states there is 3.7W/m^2 of Radiative Forcing if CO2 is doubled. Or when a 3 DegC temperature rise is claimed.
    It is not for a specific location but is an average for the whole planet integrated over a year.

    Consider a planet 3 degrees hotter (in the above sense). The likelihood is that the relationship between the Surface and Air is the same (this is implicit in the claim of a constant lapse rate) ie the average temperature difference between the air and surface is THE SAME. So the Conductive term, which is solely driven by temperature difference will be the same.

    We know that a doubling of CO2 has little DIRECT effect on the absorption of surface heat - maybe about 0.5W/m^2 of increase. ie the Window to space only closes fractionally.

    So both these terms are nearly zero change.

    The equation for surface heat absorbed into the atmosphere is:

    Surface Heat Absorbed into the Atmosphere = Surface radiation - the portion escaping through the Window - Back Radiation + Conduction + Evaporated water

    We also know from the surface energy balance that, providing Conduction and absorbed solar don't change,

    Change in Back Radiation = Change in Surface radiation + Change in Evaporation,
    or
    Change in surface radiation - change in backe radiation = -change in Evaporation
    or, if radiation through the window is cobstant,

    Change in NET radiation from the surface into the atmosphere = - Change in Evaporation

    Putting this in words, any increase in evaporation is balanced by an equal and opposite reduction in Net radiation from the surface.

    Hope this helps.
  38. Actually, it isn't just anthropogenic global warming... based on his statements, novandilcosid appears to deny the carbon dioxide greenhouse effect entirely.

    Though how he then explains why the Earth isn't a giant ball of ice, glaciation cycles, the data measuring this 'non-existent' effect in the article above, the disagreement of thousands of scientists (including all the major AGW 'skeptics'), et cetera remains unexplained.
  39. CBDunkerson @88, in fact he goes further. From his 81:

    "6. If so, then we would expect a doubling of CO2 to have a COOLING effect on the planet.


    My emphasis.

    So not only does he need to explain why the Earth isn't a cozy 255K, he needs to explain why it isn't 250K or less. It is however already apparent that he will not mere observation kill his beautiful theories.
  40. novan >Surface Heat Absorbed into the Atmosphere = Surface radiation - the portion escaping through the Window - Back Radiation + Conduction + Evaporated water

    "Portion escaping through the window" should not be part of the equation. It is an output from the surface and so must be included in any energy balance equation for the surface. It's quite simple: take all the inputs on one side and all the outputs on the other. So the real total energy balance equation from the surface would be:

    Absorbed Solar + Back Radiation = Surface radiation + Convection + Evaporated water (latent heat).

    If we take your assumption that convection and absorbed solar didn't change, then that gives us:

    Back Radiation = Surface Radiation + Evaporation.

    or

    Evaporation = Back Radiation - Surface Radiation

    So an increase in evaporation may be balanced out by either decrease in surface radiation or an increase in back radiation. It does not hold (even with your assumptions) that increased evaporation must be balanced by decreased surface radiation.

    Also note that evaporation and surface radiation are tightly related to temperature. It would not make physical sense to have increased evaporation with less surface radiation, as that would imply increased evaporation with lower temperatures.
  41. e's claims at #90 above are erroneous.
    His second equation should read:
    Change in Back Radiation = Change in Surface Radiation + Change in Evaporation.

    The Surface Balance equation can be rewritten:

    Absorbed Solar = Net Surface radiation into the atmosphere + Net Surface Radiation through the window to space + Convection + Evaporated water (latent heat).

    Writing this in terms of change, and making the (only slightly wrong) assumptions that changes to Absorbed Solar, Conduction and Net Surface Radiation through the window to space are zero, then yes indeed

    Net Surface radiation into the atmosphere = -Evaporated water (latent heat).

    This is another way of saying two things:
    1. The energy transported from the surface always equals the insolation. Unless the solar constant or the albedo change, the energy from the surface is a constant.
    2. As the Greenhouse tightens we expect the back-radiation to increase at a greater rate than the surface radiation: the radiative balance between the atmosphere and the surface narrows. At a perfect greenhouse, the retransmission of energy from the GHGs would be from the first layer of molecules - no temperature difference, perfect black body so total balance. The relative increase in back radiation allows the surface temperature to rise. This rise increases the evaporation rate in such a way that the relative increase in back radiation balances the increased evaporation.

    Note that the heat transport into the atmosphere from the surface is approximately
    Conduction one fifth
    Net Radiation one fifth
    Evaporation three fifths

    If the temperature increases, evaporation goes up and net radiation goes down. The rate at which evaporation increases with temperature is in dispute - essentially it is unkown. Measurement suggests 5% per DegC. The modellers use 2.5% or less. Additionally relative humidity is often taken to be constant. Measurement suggests that this may be abrave assumption.
  42. Tom Curtis wrote at #82:
    "It is odd that novan concentrates his discussion on the 650 wave number. It is well known that at that wave number, CO2 absorption is at its peak, and that as a result the majority of CO2 emissions to space at that wavenumber come from the stratosphere."

    Actually my calculations were not for the Wavenumber 670 region (indisputably stratospheric) but used the table values for wavenumber 650.
    [There are two ways to interpret this table, as it lists absorption rates through different gas depths at 50 wavenumber intervals. So either the table value is a spot measurement, or it is an average across the 50 wavenumber band centred on the tabled value. Either way it does not invalidate the conclusions.]
    I took a standard line and decremented it iteratively using the amplitude at each frequency as an attenuation factor, checking at each iteration for the total remaining power. In this way I was able to replicate the table absorptions at STP. I then had the number of iterations per atmcm of CO2. I then repeated the exercise at altitude, altering the shape of the absorption line (it gets peakier but narrower with altitude) to see what happens. I found that at wavenumber 650 (not 670) the emissions to space are mostly from the stratosphere. Emissions from the troposphere are not totally extinct but are only a small fraction of the spacebound photons in that band.

    We should not lose sight of the fact that over 10% of the atmosphere lies ABOVE the Tropopause (8% in the region 35N to 35S, 20% at higher latitudes). In the strong emission/absorption CO2 band from wavenumbers 625 to 725 most emissions are coming from above the Tropopause.
  43. novan,

    I believe I misread your original energy balance comment so you can disregard my subsequent post. I'm not sure what point you're trying to make with post 87 though. I would rather suggest you stick to the topic at hand (CO2 effect saturation and GHG physics) in order to keep your argument clear.
  44. novandilcosid @92, I will not dispute the claim that the majority of emissions to space in the range 630 to 710 cm^-1 come from the stratosphere. (I am not agreeing, I am just not disputing.) Certainly it comes from high enough that, as shown in 82 and 86 above, that increasing CO2 concentrations make no difference to the amount of radiation escaping from the troposphere at those wave numbers, which is all that is relevant to this discussion. But those same figures above clearly show that there is a substantial reduction in radiation to leaving the troposphere outside those that range, but between 500 and 850 cm^-1.

    While you ignore that substantial reduction, your theories are irrelevant. Therefore you need to either accept the values indicated above, in which case we can proceed, or you need to calculate the change in tropospheric radiation at those wave numbers for yourself and show the basis of your dispute with the scientists.
    Response: [DB] Fixed missing bold closing tag.
  45. My apologies to the moderators - I really am giving you a lot of trouble of late.
    Response: [DB] I've been given worse.
  46. DB, if you have been given worse in that sense, I am truly mortified.
    Response:

    [DB] Some days you're the windshield, some days you're the bug. But you can always do this afterwards:

  47. novandilcosid @87, the claim I was responding to is quite specific:

    "There are some other interesting aspects: The atmospheric window is almost constant, the conduction is almost constant, so the heat transport from the surface into the atmosphere is almost a constant whatever the surface temperature. What happens as the temperature rises is that the Net radiation (surface radiation less radiation through the window less back radiation) DECREASES and this balances the increase in water vapour condensation."



    So according to you for any two temperatures T1 and T2, e1sT14-W-Rback1+E1+C1=e2sT24-W-Rback2+E2+C2, where T stands for temperature, W for energy escaping through the atmospheric window, R for back radiation, E for evaporative energy transport (latent heat), C for conduction, e for the emissivity, and s for the Stefan-Boltzman constant.

    I can allow (as indicated in the notation) that energy escaping the atmospheric window is near constant for small changes in temperature with no changes in GHG concentrations. However, all other factors are variable with temperature. Specifically, you insist that an increase in temperature will result in an increase evaporation. But increased evaporation reduces soil moisture content, thus reducing the emissivity of the soil (factor 1). It also increases the emissivity of the lowest portion of the atmosphere, thus reducing the altitude of emission (factor 2), and at the same time reduces the lapse rate which increases the temperature at any given altitude (factor 3). Factor's (2) and (3) combine to increase back radiation. (The increased humidity will also decreases the size of the atmospheric window, but we will neglect that.) Increasing temperatures also increases wind speed globally, thus increasing conductive heat transfer by increasing the rate of turn over of the layer of atmosphere in immediate contact with the surface (factor 4). Increased humidity will also increase conductive transfer because of the high heat capacity of water vapour.

    So, you have at least four hetergenious factors you need to juggle to gain your equality, and only one term (W) which can be eliminated from the equation. The proof that change in net surface radiation equals the negative change in net evaporative transfer, therefore does not follow, and is highly implausible.
  48. Tom Curtis @#94 wrote: "the range 630 to 710 cm^-1 come from the stratosphere. (I am not agreeing, I am just not disputing.) Certainly it comes from high enough that, as shown in 82 and 86 above, that increasing CO2 concentrations make no difference to the amount of radiation escaping from the troposphere at those wave numbers, which is all that is relevant to this discussion. But those same figures above clearly show that there is a substantial reduction in radiation to leaving the troposphere outside those that range, but between 500 and 850 cm^-1.

    1. I dispute that there is no change in energy radiated from the troposphere. I think the figures in #82,86 are NOT sufficient to estimate what happens: they are disclosing the opacity of the atmosphere as seen from the ground. This is not helpful when trying to determine what the effects are in the region which is already 100% opaque.

    It seems obvious that for the level in the atmosphere at which 20% of the photons make it through the CO2 fog to outer space, a doubling of the thickness of the fog will move the 20% emission layer higher.

    2. The $64 question is where are the photons coming from in the very active 625-700 region with CO2 at 380ppm? My calculations suggest only 10% are coming from below the Tropopause, the remainder from above.

    If that is the case, then for this band a doubling of CO2 will mean emissions from higher in the stratosphere. The net effect in this band will therefore be an INCREASE in power radiated to space.
  49. Tom Curtis @ #94 wrote:
    " But those same figures above clearly show that there is a substantial reduction in radiation to leaving the troposphere outside those that range, but between 500 and 850 cm^-1. "

    The most active region is the band between 625 and 725. (See http://spectralcalc.com/spectral_browser/db_intensity.php) The lines here are around two orders of magnitude greater intensity than the lines in the rest of the band.

    1. The question relevant to saturation is how much additional surface energy is absorbed outside the saturated 625-725 band, ie by how much does the window close, in W/m^2? I have always assumed that this is small - not more than 0.5W/m^2 for a doubling of CO2.

    2. At the top of the atmosphere, what is the emission strength from CO2 in these weak parts of the band? The 625-725 region is emitting about 15-18W/m^2 (see plots of outgoing radiation measured in space eg http://acmg.seas.harvard.edu/people/faculty/djj/book/bookhwk7-1.gif http://www.mathstat.dal.ca/~folkins/Cloud-LWspectrum.jpg . http://climateaudit.org/2008/01/08/sir-john-houghton-on-the-enhanced-greenhouse-effect/ ).

    The much weaker lines outside this region won't be emitting much.

    So I guess I'd like to see some calculation of both these effects in the weak band to see if it is relevant. If the powers are small then this part of the band can be ignored, even though the majority of the emissions from them are plainly from below the Tropopause.
  50. Tom Curtis responded in #97 to my statement that surface energy into the atmosphere is essentially constant.
    "Specifically, you insist that an increase in temperature will result in an increase evaporation"
    Too right!

    We recall that the statement is only true when the energy flows are integrated over the entire surface over an entire year, then averaged. A second stipulation is that the system is in equilibrium - there are no net inflows or outflows. This is essentially what Kiehl & Trenberth say in their 1997 diagram, and is also implied by any statement that "the average temperature of the planet will increase by X degrees."

    While the statement will not be true at specific locations, it is true for the planet as a whole (remembering that 70% is water).

    [Off topic: The amount of increase in evaporation per DegC is disputed (see for example Schneider, Gorman and Levine, 2009, http://arxiv.org/abs/0908.4410 ). It is also unknown if relative humidity changes.

    The modellers assume constant RH (no better estimate), Clausius-Clapeyron water vapour increase (6.5%/DegC) and around 2.5%/DegC for evaporation. Actual measurements suggest that RH has decreased with increasing temperature, and that the rate of evaporation increase is 5%/DegC.

    Essentially the water properties of the atmosphere are unsettled science. Many climate scientists disagree with the assumptions in the models.]

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