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Is the CO2 effect saturated?

What the science says...

Select a level... Basic Intermediate Advanced

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

Climate Myth...

CO2 effect is saturated

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

At-a-Glance

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

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

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

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

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

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

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

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


Further details

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

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

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

The Electromagnetic Spectrum

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

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

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

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

CO2 heat transfer

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

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

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

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

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

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

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

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

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Further reading

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

Further viewing

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

Comments

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Comments 151 to 175 out of 712:

  1. #146 KR at 08:28 AM on 27 April, 2011 You should, then, be aware that in English "pulled out of thin air" has extremely negative connotations with regard to numbers, namely "manufactured, made up, baseless". English is obviously not my native language, and I am happy to learn. But it was always my impression there was a difference between numbers pulled out of thin air or pulled out of the ass. Anyway, I certainly meant atmospheric IR window radiation flux in Trenberth 2009 is baseless, it is produced seemingly out of nowhere, as if by magic. And Kiehl & Trenberth 1997 does not make it any better. They themselves admit "The estimate of the amount leaving via the atmospheric window is somewhat ad hoc". And indeed it is, by the method they say they've arrived at it. So let's settle at a qualification like it was somewhat ad hoc. Is that OK? I do not believe in a value "that has been known for >80 years", but never measured. Global average IR radiation flux escaping directly from surface to space is an important quantity. If it is not known, average atmospheric IR optical depth can't be calculated and talking about trends in an unknown quantity is just futile. I do not believe either atmospheric transmission can be properly determined as a side product of the line-by-line radiation models. The HITRAN Database is a magnificent product, but with no established cloud (and water vapor distribution and surface emissivity) model it is useless for this purpose. Also, atmospheric transmission is heavily influenced by the gazillion weak absorption lines still missing from the database (because of measurement issues), their far wing shapes and the ill-understood water vapor continuum.
  2. Berényi - The only difference between those two phrases is in which you would use in polite company. Both indicate data made up, manufactured, in order to prop up an argument. Given that Trenberth 2009 is described as an update to Kiehl and Trenberth 1997 (see Trenberth 2009, second paragraph, for the reference), that is the very first location to look for items not discussed in detail in Trenberth 2009. I therefore consider your language here unwarranted. "Somewhat ad hoc" is a reasonable description given the 1997 paper. However, this does not address the underlying issue of using a summary, one that has been adjusted for internal consistency, in place of a GCM. From the 1997 paper, page 10: "The values put forward in Fig. 7 are reasonable but clearly not exact. The purpose of this paper is not so much to present definitive values, but to discuss how they were obtained and give some sense of the uncertainties and issues in determining the numbers. Several quantities in Fig. 7 are not adequately measured to pin them down as much as desirable, and the global climate models are not yet good enough to justify refining the estimates here, which are based on a much simpler but appropriately tuned and observationally constrained radiation model. By putting all the estimates together, however, the fact that the total heat budget at both the surface and the top of the atmosphere has to balance and all the components add up is a considerable constraint and lends some confidence to the values assigned. Regardless of the errors assigned to each component, the fact that the components sum to zero means some errors must cancel." (emphasis added) The 2009 paper has improved data, fewer uncertainties, but this is still a constrained summary and overview, not in itself a GCM. The biggest, most powerful constraint is that everything has to add up, and that "...some errors must cancel". Now back to the subject matter of this thread. There are definitely uncertainties in cloud absorption, much smaller uncertainties in water vapor distribution. But there is no uncertainty in the fact that CO2 is not saturated at current concentrations.
  3. #152 KR at 00:37 AM on 28 April, 2011 But there is no uncertainty in the fact that CO2 is not saturated at current concentrations. Here is later study applying an improved algorithm. Journal of Quantitative Spectroscopy and Radiative Transfer Volume 85, Issues 3-4, 15 May 2004, Pages 367-383 doi:10.1016/S0022-4073(03)00232-2 Absolute, spectrally-resolved, thermal radiance: a benchmark for climate monitoring from space J. G. Anderson, J. A. Dykema, R. M. Goody, H. Hu & D. B. Kirk-Davidoff Compare it to the obsolete one referenced in the article above from Harries 2001 Anderson et al. say the best estimate is the red curve (dof-wtd cells). Pay careful attention to the differences. Measured CO2 effect can be seen close to the left edge of both figures. The difference between the wavenumber 750-900 cm-1 range and wavenumber 710 cm-1 is about 1.5 K in both figures, but in the improved analysis it turns out only 0.4 K is due to decreased OLR intensity in the CO2 wing, while there is a 1.1 K increase in the low frequency (most transparent) part of the atmospheric window. As surface temperature between 1970 and 1996 increased less than that (and temperature in the mid-troposphere even less), it can only mean photosphere height in this spectral range decreased during this period. It is consistent with balloon radiosonde data, which show decreasing atmospheric specific humidity above the 700 mbar level (while it was increasing closer to the surface). There is an even more striking difference between the two analyses above the O3 absorption line, in the high frequency part of the atmospheric window. According to Anderson at al. brightness temperature anomaly here is 1-1.5 K less than at lower frequencies (while Harries puts them about to the same level). The same is true for the relative depths of the CO2 and CH4 notches. All this boils down to the conclusion that while the CO2 effect may not be fully saturated at the wings, it is almost negligible compared to methane (which is not saturated) and is counteracted to a considerable degree by water vapor (negative feedback).
  4. For your convenience I have merged Fig. 1. Harris 2001 into Fig. 8 (a) Anderson 2004. It is easier to compare them this way (click to enlarge). Between 1970 and 1996 atmospheric CO2 concentration as measured at the Mauna Loa Observatory has increased from 325.68 ppmv to 362.35 ppmv.
  5. Berényi - Several points from those two papers. - From Anderson 2004, final comments: "...there is an increase of greenhousegases from 1970 to 1996 that gives rise to recognizable bands in the observed spectrum." - Anderson makes no claims about invalidating Harries, and in fact notes/thanks him in the Acknowledgements. - Most importantly; Anderson's spectra are not corrected for global warming, to the equivalent black body temperatures. Anderson is showing the raw differences between the two satellite spectra with some fairly impressive corrections added. But this is not corrected for the equivalent black-body spectra (Brightness Temperature) as Harries did, and hence does not show what you claim it does. It would be stunning if there was no difference in IR spectra over 25 years given warming. But your superimposition of Harries black-body corrected spectra over raw differencing is invalid. The elephant has put on weight - but you can't compare that directly to a chart of how it's proportions have changed.
  6. Berényi - I will also note that incorrectly using a graph from Anderson 2004 does not invalidate either Griggs 2004 or Chen 2007 (referenced in the original post), which fully support Harries 2001. The changes in TOA spectra over the satellite era from increasing CO2 are detectable, as predicted by modeling, and indicate that CO2 is not saturated.
  7. #155 KR at 08:44 AM on 28 April, 2011 - Most importantly; Anderson's spectra are not corrected for global warming, to the equivalent black body temperatures. You are right. However, I would use a different wording: Anderson's spectra are not adjusted until they confess. The reason I am saying that is because Harries at al. do not simply correct for equivalent black body temperatures, they perform a vastly more sophisticated transformation. Unfortunately there is no open access copy of Harries 2001 online, so I will use a conference abstract by the same authors which discusses their adjustments at some length. 11th Conference on Satellite Meteorology and Oceanography Session 2, Climatology and Long-Term Satellite Studies (Continued) Monday, 15 October 2001, 4:00 PM-5:00 PM 2.2 Changes in the Earth's resolved outgoing longwave radiation field as seen from the IRIS and IMG instruments (Invited Presentation) Helen E. Brindley, P. J. Sagoo, R. J. Bantges & J. E. Harries First of all let's compare their raw difference spectrum with the one given in Anderson 2004. The match is reasonably good considering Anderson processed many more spectra, attained finer spectral resolution, smaller error bars and also covers a larger area. And Brindley et al. show even less decrease in brightness temperature in the CO2 wing (at the left edge) than Anderson et al. do. Practically none at all, while both analyses show increase in the window and decrease in the methane band (the curve is above or below zero, respectively). So. How does Fig. 1. Harries 2001 come about? It is the difference between the spectrum above and a theoretical spectrum where radiative effects of changes in water vapor distribution along with sea surface and atmospheric temperatures are taken into account, but GHG concentrations (other than H2O, and only for radiance calculation purposes) are kept constant. Therefore their finding is not "direct experimental evidence" in any reasonable sense of the word. It can't be better than their theoretically derived spectrum used for adjustment. I quote the full passage dealing with this theoretical derivation from the extended abstract, because it is essential. "3. SIMULATION METHODOLOGY Pentad mean global temperatures and specific humidity fields representative of two twenty-seven month intervals centred on the operational periods of the two instruments, running from April 1969 to June 1971, and April 1996 to June 1998 were generated using the HadleyCentre Atmospheric Model version 3 (HADAM3). HADAM3 comprises the atmospheric portion of the Hadley Centre Coupled Climate Model, with 19 levels in the vertical, and a horizontal resolution of 2.5° latitude x 3.75° longitude. The model was forced by observed sea surface temperatures taken from the Global Sea Ice and Sea Surface Temperature (GISST) data set, and also included the effects of changes in trace gases, and a parameterisation of volcanic and solar forcing over the period considered. In order to quantify the impact of model uncertainties, four realizations of the atmospheric state were provided. Using the model geophysical fields along with representative values of trace gas concentrations for each period, radiance spectra were calculated for each grid point and month at 1 cm-1 resolution over the wavenumber range 600-1400 cm-1 by the MODTRAN3.7 radiative transfer code. These 1 cm-1 radiances were then degraded to 2.8 cm-1 resolution using the IRIS instrument function and converted to the equivalent BT". The take home message is they have used various data sources for their theoretical calculations, but neither atmospheric temperatures nor specific humidity fields were measured, they were derived by running HADAM3 (four times). They do not verify if HADAM3 is correct or not, they assume it. See: "Assuming that HADAM3 correctly captures etc., etc." It means their result is neither measured nor verified. It is assumed. Have a careful look at Fig. 3 (a) in Brindley 2001 please. This is the theoretical spectrum to be subtracted from the measured one to arrive at Fig. 1. Harries 2001. You will notice H2O forcing is the decisive factor. Influence "SST only" (measured) is neutral, "T only" (not measured) overfills the CO2 notch in measured spectrum, while "H2 only" (not measured) is an exaggerated mirror image of it, if subtracted, re-creates the notch. Therefore what you see in Fig. 1. Harries 2001 is the result of HADAM3 computations and has only extremely weak relation to IRIS or IMG data. As we do not have actual specific humidity measurements along the entire air column over the East Pacific for the IRIS period and there is no way to go back in time and recover it, their result is utterly unverifiable. When I was young, inherently unverifiable propositions used to belong to other realms of the human endeavor, not science.
    Response: [DB] This goes no farther without links to proof of malfeasance. No more insinuations, no more implications. Further remarks not complying with the Comments Policy will be simply deleted.
  8. Berényi, You are comparing against the wrong Harries graph. The comparable graph showing measured brightness difference is item b in Fig 1., not item c. You will notice it is similar to the other graphs you have provided. Here is the full figure: And caption: "a, Observed IRIS and IMG clear sky brightness temperature spectra for the central Pacific (10° N–10° S, 130° W–180° W). b, Top, observed difference spectrum taken from a; middle, simulated central Pacific difference spectrum, displaced by -5 K; bottom, observed difference spectrum for 'near-global' case (60° N–60° S), displaced by –10 K. c, Component of simulated spectrum due to trace-gas changes only. 'Brightness temperature' on the ordinate indicates equivalent blackbody brightness temperature." Since you are not comparing equivalent data, your analysis and conclusions are moot.
  9. #158 e at 03:49 AM on 29 April, 2011 Since you are not comparing equivalent data Since you have not read the paper I was talking about
  10. Berényi, Moderators (Emphasis as in originals) KR: "- Most importantly; Anderson's spectra are not corrected for global warming, to the equivalent black body temperatures. Anderson is showing the raw differences between the two satellite spectra with some fairly impressive corrections added. But this is not corrected for the equivalent black-body spectra (Brightness Temperature) as Harries did, and hence does not show what you claim it does." (hence overlaying these two different graphs is incorrect) Berényi: "You are right. However, I would use a different wording: Anderson's spectra are not adjusted until they confess. The reason I am saying that is because Harries at al. do not simply correct for equivalent black body temperatures, they perform a vastly more sophisticated transformation." -- Confess? What does Anderson have to confess to? Having written a rather clear paper on comparing data from two different platforms, that you have misinterpreted? Moderators, I think this is going entirely too far. These constant unjustified insinuations and accusations of bad science and data manipulation are clearly outside the Comments Policy limits. Berényi, unless you have proof of malfeasance, I would suggest you drop the accusations. If you disagree with a paper, point out the issue you disagree with. But attributing bad practice and data manufacture (as you have done at least twice in this thread alone) is a completely unjustified, insulting, and repetitive ad hominem fallacy.
    Response: [DB] Agreed. This goes no farther without links to proof of malfeasance. No more insinuations, no more implications. Further remarks not complying with the Comments Policy will be simply deleted.
  11. #160 KR at 07:33 AM on 29 April, 2011 Confess? What does Anderson have to confess to? Having written a rather clear paper on comparing data from two different platforms, that you have misinterpreted? Nothing. He himself does not have to confess anything. What I have written is even his spectra are not adjusted until they confess, which means exactly what you say: his paper is rather clear and extracts information by straightforward methods from measurements which were actually performed. It is a good paper. However, his data do not "confess" about the radiative effect of trace greenhouse gases, most notably about the relative importance of saturated vs. unsaturated ones. By "saturated" I mean saturated in a spectral interval around the absorption line center (like CO2 around 15 μm). In spectral regions like this the photosphere (the layer of atmosphere from where thermal IR photons have a reasonable chance to escape to space) is high up in the stratosphere, where the lapse rate is zero or even negative. It means the more stuff you put in, the higher the photosphere gets, that is, to a warmer level in the stratosphere (where thermal inversion prevails). Of course it is not saturated in the wings of the absorption band, where absorption gradually decreases to zero. For your convenience: 14 μm is wavenumber 710 cm-1, the lower frequency limit in the Harries graph. The 160 mbar level is above 13 km altitude. The really important question is the relation between radiative effects of a saturated absorber (like CO2) and an unsaturated one like CH4 which has a strong absorption line centered near wavenumber 1300 cm-1 (7.7 μm) with its own wings, but is not saturated at the line center, that is, thermal IR radiation has some chance to escape to space from the surface even there. Anderson's difference spectra (and raw difference spectra of Harries as well) show a much more pronounced decrease of brightness temperature in the methane band compared to the almost negligible one in the carbon dioxide wing. To bring them to comparable levels, one needs to assume unmeasured quantities like changes in atmospheric moisture and temperature fields behave in a certain way and adjust difference spectra accordingly. That step is not measurement, that's theoretical derivation using an extremely convoluted and basically unpublished, intrinsically unverifiable theory called CRUTEM3, embodied in thousands of lines of low quality computer code. So. We of course know (from first principles) that the CO2 effect is not saturated (in the wings of the absorption band centered at 667 cm-1). The same way we do know Earth is not a sphere. But would it follow from this proposition it must be flat?
  12. Berényi - Thank you, that does clarify matters. - You were not insinuating data manipulation by Anderson, but rather accusing Harries of overprocessing their data and reaching unwarranted conclusions. Which by implication is also an accusation against Griggs 2004 and Chen 2007, as their results agree with Harries. - Secondly, the Anderson data was indeed inappropriate to compare directly to Harries, as you did earlier. Finally, I will note that Anderson has stated that he cannot make conclusions about moisture from the data points. I don't have a copy of Harries readily available, I don't know what they wrote on that subject. But, quite frankly, we have plenty of data on relative and absolute humidity from other sources over the last 50-70 years, and adjust accordingly. The conclusion from all these papers? That CO2 is not saturated, and that the last quarter century of satellite data shows increasing effects at the GHG frequencies expected from GHG concentrations and the spectroscopic physics.
  13. #162 KR at 07:06 AM on 2 May, 2011 But, quite frankly, we have plenty of data on relative and absolute humidity from other sources over the last 50-70 years Really? Other than balloon radiosonde data? Because on face value those show decreasing specific humidity above the 700 hPa level (between 1973 and 2007). If you have other data, please show us. The conclusion from all these papers? That CO2 is not saturated, and that the last quarter century of satellite data shows increasing effects at the GHG frequencies expected from GHG concentrations and the spectroscopic physics. If you look at the raw brightness temperature data, you can see that average brightness temperature change in the high frequency wing of the main CO2 emission band (wavenumber 710 - 760 cm-1) between 1970 and 1996 is negligible. You can suppose there is a large decrease masked by changes in atmospheric temperature and moisture fields and you can assume those fields behaved just like that, but that is not measurement. If average specific humidity in fact shows a decreasing trend above 700 hPa (as measured), that is inconsistent with masking. If a computational climate model like CRUTEM3 indicates otherwise, it is still not measurement, but a theoretical result contradicted by measurement. If average brightness temperature decreased by 1°C in said band, that would decrease OLR (Outgoing Longwave Radiation) by about 0.2 W/m2. However, raw brightness temperature data show it was less than 1°C (and possibly zero). The low frequency wing was not measured, but that's already outside the main atmospheric window and overlaps with pretty strong H2O absorption lines, so its effect is probably even less pronounced. The question is not whether the CO2 effect is saturated or not, but if it is saturated enough to exclude a strong effect. The same way as in the case when one has to choose between a spherical vs. flat Earth model. Then the differences between a sphere and the geoid are surely negligible.
  14. Are you seriously unaware of problems with the Paltridge paper? (The re-analysis is not up to doing trends - this is widely reported).
  15. BTW. Science of Doom has just done interesting article question of how much absorbance is in the weak lines versus the "far wings" of individual lines. Illuminating.
  16. Berényi - From the Griggs 2004 conclusions: "Calibration has been performed so that the three datasets of spectrally resolved OLR recorded in 1970, 1997, and 2003 can be directly compared... which show features in the absorption bands of the major greenhouse gases in the atmosphere. ... Simulations created using profiles merged from a number of datasets show that we can explain the differences seen in the CO2 and ozone bands by the known changes in those gases over the last 34 years." Water vapor indications in early datasets did not match well, which they conclude upon analysis of the OLR data is due to poorly understood temperature profiles for those early datasets - the 2003 dataset profiles are obviously more accurate. Results? Measured changes in CO2 and H2O spectra match observed concentration changes, and match the theory. Again. I cannot speak to the "weak lines" versus "far wings" issue directly, not having run line-by-line spectra (have you, Berényi?) - but the total CO2 focing is right along that predicted. This, I will note, discounts/disproves your rather vague questions of whether CO2 has a strong effect. Increasing CO2 concentrations are doing just what we expect them to do from the physics. --- scaddenp - Do you have links to any discussions on the Paltridge paper?
  17. KR, Dessler and Davis 2010 for starters looks closely at it, but also Sherwood et al notes "However, this result had already been reported by Chen et al.[2008], who also noted nearly opposite results in the ERA‐40 reanalysis. Numerous studies have concluded that reanalysis data are easily corrupted by time‐varying biases and are therefore not useful for trend analysis [see U.S. ClimateChange Science Program, 2006]." Not to mention blog commentaries.
  18. scaddenp - Thanks, the Dessler and Davis 2010 is very interesting. Paltridge appears to be analyzing a serious outlier (NCEP/NCAR) in the various analyses, and their finding that long term feedback has a different sign (negative) than short term feedback (positive) without an accompanying model for how that could happen seems to indicate that Paltridge is in error.
  19. If you google "comparison NCEP ERA-40", I think it gives you a good reason to be extremely cautious of conclusions based on NCEP reanalysis without support from other data.
  20. jonicol - instead making a post with your theories, perhaps you are better to put up your paper on arXiv.org in publication format so world can look at it. Post link here. Frankly any amount of non-physical rubbish has been published about influence of cycles etc. Let see the radiative physics first so we can see if there is a real physical basis first.
  21. Following a tip from DB, I am responding to Guigenbresil here. Guigenbresil objects to Harries 2001 because it uses clear sky spectra rather than all sky spectra. The problem with not using clear sky spectra is a problem of interpretation. Consider the spectrum from the thunderstorm anvil in figure C below. The important thing here is not that it obscures the radiation from all Green House Gases below the stratosphere, but that it radiates with an approximately equal brightness temperature across the whole spectrum. That means that if you do not have clear skies, IR radiation from clouds across the spectrum will be significant. They may or may not obscure the absorption band for any particular greenhouse gas. Whether it does or not will depend on the altitude of the cloud and the effective altitude of emission for that particular greenhouse gas,ie, the average altitude from which IR photons emitted from that gas escape to space. But because the emissions from the clouds come from across the spectrum, and in particular the wavelengths at which various GHG emit photons, it will become difficult, or even impossible in the presence of clouds to determine how much of the reduction in emissions at those wavelengths is due to the increased concentration of a Green House Gas, and how much is due to the cloud. The point is that Harries is trying to detect any reduction in emissions due to increase green house gas concentrations, if there are any such reductions. Therefore like any good scientist he uses data that restricts the number of independent variables which might obscure the relationship he is looking for. The problem appears to be that you are looking for some sort of silver bullet approach to science, and that is not how science works. Well, occasionally it is. The graphs above are cast iron proof that Green House Gases effect the Earth's energy balance, and hence that there is a greenhouse effect. They do not by themselves show how strong that greenhouse effect is, and nor do they show that the greenhouse effect will be strengthened by increasing the concentration of Green House Gases. Haries has found proof that increasing the concentration of GHG does increase the strength of the greenhouse effect, ie, the CO2 is not saturated and that their is an enhanced green house effect. You seem to want him to also show exactly the strength of the enhanced greenhouse effect, but he cannot do that with the data provided, and nor does he try to. He is only attempting to show, and does show, one thing - that enhancing GHG concentrations reduces top of atmosphere emissions in the wavelength of absorption/emission by those Green House Gases. You would be astonished at how many denialist arguments are falsified by that simple observation.
  22. Guigenbresil asks a wholes series of questions to show that Harries 2001 is based on localized conditions both temporally and spatially and excludes common meteorological conditions. However, those questions miss the point. Haries 2001 is not trying to determine a global energy balance, or to show the strength of the greenhouse effect. Indeed, if the strength of the greenhouse effect is understood as the climate sensitivity of doubling CO2, the type of observations by Harries even if truly global would not be able to determine that strength. As explained above, what Harries was trying to do is to provide empirical proof that there is an enhanced green house effect. And to show that, all he needs to show is that increasing GHG concentrations results in reduced emissions in the wavelengths of their emission/absorption. As the greenhouse gases are well mixed, ie, their concentrations anywhere on Earth closely approximate each other, if there is an enhance greenhouse effect over the central Pacific, there will also be an enhanced greenhouse effect over the Arctic, or anywhere else. Finally, Guigenbresil writes:
    "So the increasing CO2 changes the OLR spectrum, but since the system is essentially in a quasi-equilibrium when averaged spatially and temporally, the integrated spectrum would have essentially the same total value so you wouldn't expect to see it as a drop in measured total OLR. "
    Not quite, or at least, not true until the equilibrium response to increased GHG concentrations is reached. It takes decades to reach the equilibrium climate sensitivity after increasing the concentration of a greenhouse gas. During those decades, we expect the OLR on average to be slightly less than the incoming short wave radiation, and hence slightly less than the equilibrium OLR. However, during that periods, sometimes the Earth will have hotter years and sometimes colder. In hotter years its OLR will be greater, causing it to cool. In colder years, it will be smaller, causing the Earth to warm. These fluctuations can exceed the disequilibrium between OLR and ISR introduced by increased GHG concentrations. So, if you compare a La Nina year with an El Nino year, you cannot say the OLR has increase and therefore there is no enhanced green house effect. You need to take an average over a reasonable period to eliminate the noise introduced by annual fluctuations in surface temperature.
  23. Tom Curtis: Excellent response! Thanks! My apparent criticism of the spectral work of Harries and others is not that they didn't demonstrate a change in the spectrum of outgoing radiation due to increasing CO2. They clearly did. My objection is in the phrase "and therefore the greenhouse effect..." The change in a spectral component of the OLR does not directly translate into a global temperature change - the total behavior of the OLR must be impacted to affect the energy balance. I would agree if all else remained constant. - athough that is not very physical... For example, you can see that a slight increase in the average frequency, duration, altitude or size of thunderstorms (see your third graph @170 (excellent by the way!)) would easily offset any changes in CO2 - they have a much wider band, much higher brightness temperature at the high end of the variation, very large swing in the effect on the spectrum. Are you aware of any analyses of experimental data that would put this to rest? This is a foundational aspect of AGW theory, and it would be a little weak to rely entirely on assertion or models...
  24. Guinganbresil @173, I'm sorry but you are confusing two issues. The first issue is whether or not there is an enhanced greenhouse effect. The second is will the climate response to an enhanced greenhouse effect result in a net negative or positive feedback. The important point from Haries is that he shows beyond reasonable doubt that there is an enhanced greenhouse effect. Adding more CO2 to the atmosphere will introduce a positive forcing to the temperature, and it is known independently that that forcing is 3.7 W/m^2 for a doubling of CO2 with low uncertainty. Having established that, and this is another of those areas of settled science in climate change; the question becomes, "What is the climate sensitivity?", and we must look to independent evidence for that. Suffice it to say that a range of empirical evidence including recent observations and paleoclimate observations show that the climate sensitivity for a doubling of CO2 is around 3 degrees. Given that you need to look at the likely impacts of such a climate sensitivity. Ignore the impacts for 450 ppm (the current notional limit on CO2 increases for the international community). Rather consider the business as usual (A2) scenario for the end of this century, which will result in over 800 ppm of CO2. At 800 ppm, even with a climate sensitivity of 1.5 degrees C per doubling of CO2, the Earth's temperature will rise over 2 degrees C. At 2 degrees C there is an expected 50/50 chance that the Great Barrier Reef will be destroyed. At 2 degrees C there is an expected 50/50 chance that the Amazon Rainforest will be destroyed. And these are not on/of states. Even if they survive they will survive in severally degraded conditions. That level of ecosystem collapse is not consistent with a flourishing civilization. If our civilization survives that level of ecosystem collapse, it will be a hard, unpleasant skin of our teeth affair. And that is for a climate sensitivity so low that we have a less than 1 in 20 chance of being that lucky. More likly we will be looking at a 4.5 degree increase, an increase of the same order as the difference between glacial and interglacial temperatures, and which will have similarly large impacts on ecosystems and habitability. As an aside, the anvil head thunderstorm does negate the effect of CO2 over the region of the thunderstorm, but only by imposing a much stronger greenhouse effect.
  25. Link given in "Further reading" appears to be broken as of April 2012. A quick scan revealed another link: http://www-ramanathan.ucsd.edu/files/pr78.pdf (Ramanathan, V., 1998: Trace Gas Greenhouse Effect and Global Warming, Underlying Principles and Outstanding Issues. Ambio, 27(3): 187-197.)

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