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Climate Hustle

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!

Basic rebuttal written by dana1981


Update July 2015:

Here is a related lecture-video from Denial101x - Making Sense of Climate Science Denial

 

Last updated on 7 July 2015 by pattimer. View Archives

Printable Version  |  Offline PDF Version  |  Link to this page

Related Arguments

Further reading

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

Comments

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Comments 151 to 200 out of 454:

  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.)
  26. For the past six days I have seen a few denialists on alt.global-warming insisting atmospheric CO2 has reached saturation point 12 years ago. At least one denialist has shown signs of hysteria over the issue, when his cherished "smoking gun" assertion gets corrected and evidence is given to him that his assertion is false. (It's like a Scientology customer learning L. Ron Hubbard's real biography; or like a Christian Scientist, who believes his legs don't really exist, trying to walk on a broken ankle.)

    Is there any scientist out there who believes Earth's atmosphere is CO2 saturated?
  27. 176, desertphile,
    Is there any scientist out there who believes Earth's atmosphere is CO2 saturated?
    Climate scientist?

    No.

    I'm sure you'll be able to find some physicists and such, even ones of great stature in their own fields, who will subscribe to such insanity, but not any climate scientists. Not even the likes of Roy Spencer, Richard Lindzen or Roger Pielke, Sr.

    [I won't link to discussions proving that Lindzen or Pielke believe in the greenhouse effect, because [snip] Suffice to say, no, not even serious deniers like Spencer, Lindzen or Pielke will destroy their own reputations that completely by ascribing to "CO2 is saturated"[snip] People who buy into lame points of view like that are either in serious denial or so thoroughly lost in the depth of the science that you can't possibly educate them.]
    Response: TC: Inflammatory snipped.
  28. Question here from a physicist educator.

    I have looked at these satellite comparisons between time frames. I particularly like the last in the series by Chen, et al. They look at the difference between spectra taken in two different satellites between, 1970 and 2006. But, if one were to look at outgoing IR as a function of height, does not the degree of saturation and therefore the details of the spectrum depend on the height you are measuring from? Do we care how precisely these two satellites are at the same height, here? Or perhaps all satellites are so high that the effect I am concerned about is not an issue? This is my first effort to try to understand one of these satellite papers in detail. Therefore I realize my question is probably naive to the expert.
  29. There's a very useful description of the theory, design and operational principles of the AIRS instrumentation at JPL, curiousd.

    How AIRS Works

    I'm certainly no expert but it appears the height of the instruments in this context is insignificant in the same way the distance to a star is not important when obtaining information via spectroscopy.
  30. curiousd @178, I recently created a radiative model of the atmosphere on a spreadsheet to analyze related questions. The result is that essentially all Outgoing Longwave Radiation (OLR) has its last point of emission before being radiated to space in the lower 30 km of the atmosphere, ie, from the surface, troposphere or stratosphere. Above the stratosphere, atmospheric density is so low that emissions from those altitudes are negligible.

    My model was too simple to include additional factors (pressure broadening of emission bands; declining CO2 content of the atmosphere above the tropopause) that would reinforce the result.

    Consequently any satellite, and even sufficiently high flying aircraft, will show essentially the same spectrum.

    You can experiment with the effect of altitude (up to 70 km) using the modtran model placed in the net by David Archer. Just compare different Iout values for different look down altitudes without changing other settings. With default settings, I obtained the following results:

    70 km - 287.844 W/m^2
    35 km - 287.027 W/m^2
    20 km - 287.593 W/m^2
    15 km - 291.863 W/m^2
    10 km - 306.433 W/m^2
    5 km - 348.54 W/m^2
    2 km - 387.79 W/m^2
  31. Thank you, Doug Bostrom and Tom Curtis.

    My interest in these measurements has a different motivation than most. I am interested in presentations of the overwheming evidence for AGW and also in effective rebuttals to denialist questions. Here is a common denialist objection with which I have been blindsided.....in effect "The revolutionary treatment of CO2 and the greenhouse effect by Professor X (there exists more than one X) shows that the entire edifice of the present science is wrong. You cannot say that log 2 (Conc2/Conc1) is roughly proportional to temp increase, even for the CO2 contribution alone without feedbacks, because of the discovery of X"

    Rather than go to the argument that Proffessor X is not published in a standard peer reviewed jounal (will not hack it for lay audience person) or is rebutted by so and so or worse.....getting involved in real time haggling over the physics on the fly, I would prefer an experimental rebuttal. Perhaps there is such an experimental rebuttal in these papers to wit:

    1. The veracity of log base two (conc2/conc1) prop to delta temp comes out of line by line computer caculations of the total CO2 absorption in the atmosphere.
    2. Particularly in the article by Chen, Harries, et al the difference spectrum for CO2 between 1970 and 2006 is shown to be completely consistent with such line by line computer calculations.

    Therefore, All such professor X's are experimentally disproven in one stroke.

    Do you folks think this argument is valid?
  32. Tom Curtis 174:

    That is a spectacular graphic you post showing concrete environmental consequences related to climate sensitivity. But I am having trouble figuring out how to interpret this graphic, and I suspect my audience, therefore, would have more trouble.

    Lets see..Left hand part of the silver section..corresponds to 450 ppm with C.S. of 1.5, right? Then delta t since 1750 is about 1 degree C. The CO2 concentration is really about 380 ppm at present time with BEST showing 1.5 degrees increase at present time since 1750. Therefore BEST shows 3 degrees C.S. with 3 degrees increase since 1750 once one reaches 450 ppm. O.K. so far, since short term c.s. is now experimentally roughly 3 degrees C from many such data sets.

    But the viewer almost gets the quick, "sound bite take home message" that the lowest 1.5 degree C.S. case is worse than the higher C.S. cases. This I think is because the threshold temperature for the horizontal disaster line at 1000 ppm is, by this graphic, an increase of about 2.8 degrees for the 1.5 C.S. curve but the threshold temperature for the disaster line is higher for the higher C.S. curves. Which, in some sense, cannot be the case.

    But perhaps the key to the graph is the vertical bands of color? Then different classes of disasters are differentiated. Does bright yellow mean "hundreds of millions exposed to increased water stress"? Then by the graphic, at 380 ppm with 3 degree C.S.we should be there already.....well if you look at the American Midwest Plains these days...could be.

    Maybe I have that graph figured out now? Took me an hour of study, but there is a wealth of information to digest from the graph so this was study well spent,if I indeed do now understand. Then I wonder if there is away to tweak that graph toward a more rapid comprehension of the reader. If I have now interpreted the graph correctly, I will try to think of a way to do this.
  33. curiousd @182, the way to read the graph is to take a projected increase in CO2 in the lower section, and draw a line across till it intersects with a particular climate sensitivity. From that point you take a vertical line upwards to read of the expected temperature increase and environmental consequences. The graph shows an example of that procedure for the central climate sensitivity estimate at 450 ppmv (dashed lines), showing also the 95% confidence interval on climate sensitivity.

    The graph needs two important caveats.

    First, it shows only CO2 increases, but CO2 is not the only anthropogenic forcing in the atmosphere. As it happens, CO2 represents about two thirds of all anthropogenic greenhouse gas forcings, and the negative anthropogenic forcing from aerosols approximately balances the forcings from anthropogenic GHG other than CO2. Therefore, for now, the total anthropogenic forcing is approximated by that of CO2 alone. However, aerosols have a short lifetime in the atmosphere, and it is expected that as China and India develop their economy, they will follow the West in limiting the emissions of aerosol. This will increase the expected anthropogenic forcing by up to 50% above the CO2 approximation by the end of this century.

    On the plus side, the graph above shows the Charney (or Equilibrium) Climate Sensitivity, ie, the climate sensitivity after equilibrium is achieved with no changes to slow feedbacks like albedo from ice sheets. (Note that albedo change from changes in snow cover and sea ice are considered fast feedbacks.) The Equilibrium Climate Sensitivity takes time to be achieved. The immediate challenge is from the Transient Climate Response, which is the approximate immediate temperature impact of a slowly increasing CO2 level. It is about two thirds of the Equilibrium Climate Sensitivity (though estimates vary). This means that the estimate of current temperature increase since the pre-industrial for a 380 ppmv CO2 increase is approximately two thirds of the 1.3 C ECS, or about 0.8 C - which is a reasonably accurate prediction. That is just shy of the point where major impacts are going to be felt, according to the chart, but means there is another 0.4 to 0.5 degrees C "in the pipeline" even with no further increase in CO2.

    "In the pipeline", however, is an uncertain consequence. It turns out that in the short term (one to two centuries), and with no further emissions, CO2 levels fall at about the rate that the pipeline increase comes through. That means that under ideal conditions the effective increase in temperature could be limited to approximately the transient climate response. Of course, that assumes no further emissions, including from agriculture and construction, or from feedbacks such as methane release from tundra; and ignores the expected increase from reduced aerosol load. It does give us some hope of undershooting the full Equilibrium Climate Response if we genuinely initiate a zero carbon economy.

    Finally, the BEST temperature indice is a land only temperture, and overstates global temperature increase as a result. You should use (in order of probable accuracy) HadCRUT4, NCDC, or GISTEMP LOTI instead.
  34. Thanks again, Tom Curtis. Especially new to me is that at present, aerosols are close to offsetting the GHG effect other than CO2. Also, the good news that presently, were there to be no more CO2 emissions, CO2 should decrease enough to about cancel the rate at which the "other shoe" warming takes place.

    I presume - since you did not comment - that you agree with my post 181 that the results of Chen et al experimentally prove that the standard science of the CO2 greenhouse effect is correct and therefore indeed roughly every doubling of CO2 creates the same increase in temperature (about 1.2 degrees C), due to CO2 alone, with no feedbacks included?
  35. Modtran questions

    Thanks to info here I think Modtran on the David Archer website would be good for me to learn about. Some questions:

    1. What does the water vapor parameter mean?

    2. I am trying to compute the "flux weighted mean altitude of the OLR" by looking "down" from various altitudes. So with the default parameters, then at 1 Km, upward OLR flux is 406 W/m squared and so 1 Km x 406 W/m sqd is 406 Km W/m sqd

    And at 10 Km, upward flux is 306 w/m squared and 10 Km x 306 W/m sqd is 3060 Km W/m sqd

    If I keep doing this I dont think the "flux weighted mean altitude of emission to space' is well defined. It keeps getting bigger and bigger all the way up to 70 km.


    What am I doing wrong, here? Obviously something,or have the whole idea wrong?
  36. curiousd @185:

    1) Switching between Pressure and Relative Humidity changes the way H2O concentrations are calculated with altitude. Essentially, with Pressure, H2O is a function of pressure for the standard atmosphere. As such, it will not rise nor fall if you offset the surface temperature. In contrast, with the water vapour factor set to Relative Humidity, using the surface temperature offset to increase temperature will increase the H2O concentration, while decreasing temperature will decrease it. You can explore the exact effects in greater detail by looking at the output file under atmospheric profile for H2O.

    2) The method you describe will not calculate the flux weighted mean altitude of OLR. Essentially, at each altitude, z, the value recorded is the OLR from z-1 minus absorption at z, plus emissions at z. What you require is the sum of ((emissions at z - absorption of emissions from z between z and space)*z) for all z, divided by / the sum of (emissions at z - absorption of emissions from z between z and space) for all z.

    I strongly suspect that Modtran will not provide you with that information. If it does, it will only be by careful perusal of the output file.

    What may be of more interest, however, is the effective altitude of radiation, defined as the lowest altitude such that, black body radiation with an emissivity of one at the temperature of that altitude equals the total power of the OLR at TOA. The formula for the relevant temperature is, from the Stefan-Boltzman law:

    T= (Iout/(5.67*10^-8))^0.25
  37. Thank you. There are unexplained things in these models. Next question. If you run the "NCAR visible + IR Rad Code" for the default parameters,the first upper left hand graph shows no increase in temperature with altitude once you get to the height of the tropopause. In other words the temperature just stays constant with height after the tropopause. Is this peculiarity because there is no stratospheric ozone in the model?
  38. Never mind! Sorry. I now realize I was fooled by a cartoon drawing of the tropopause.....for an appreciable change in altitude in a realistic drawing the temp almost stays constant. Maybe that is why it is called a "pause".
  39. Question: If I run Modtran, the number given as "ground temperature" is, in the tropical atmosphere setting, the same whether I turn off all the greenhouse gases (CO2, water vapor, methane, ozone) or leave defaults. The ground temperature in the tropics is 299.7 K with or without GHG.

    I don't think this can be right? Help?
  40. curiousd @189, the modtran model is a Line by Line (LBL) model. That means, for a given specified set of atmospheric conditions it will calculate the IR radiation up or down at any given layer of the atmosphere from 0-70 km altitude; but it will not by itself adjust the atmospheric conditions to adjust for any change in radiative forcing.

    You, however, can perform the operation manually to determine the effect of a change in well mixed GHG concentration. To do so:

    1) Open the model in two separate windows.

    2) In the first window, set up your initial conditions. In my example this will be the default conditions of 375 ppmv CO2 and a clear sky tropical atmosphere. Note the Iout for those conditions.

    3) In the second window, set "hold water vapor" to "rel hum" if you want to include the water vapour feedback, or to "pressure" if you want no feedbacks.

    4) Set the change in CO2 or CH4 levels for the experiment. For my example I will double CO2 to 750 ppmv but hold CH4 constant.

    5) Set the temperature offset until Iout matches that in the first window. In my example, with a water vapour feedback, that requires an offset of 1.48 C; or 0.89 C with no feedbacks.

    Other base settings will require different offsets. For example, for the experiment above except for mid-latitude winters, an offset of 0.77 C is required to maintain radiative equilibrium with no feedbacks; and 1 degree C with a water vapour feedback.

    It may seem that if you calculated the values for a number of conditions and determined area weighted values based on the area in which those conditions apply across the Earth, you could determine the the net radiative effect with an LBL model. That is not so, firstly because it only incorporates one of many feedbacks; and secondly because in the real atmosphere a change in radiative forcing will also result in changes in lateral energy transfers, so that radiative equilibrium need not be held at each location but only across the whole planet.

    Of course, it is easy to show with an LBL model that temperatures increases are required under all conditions with an increase in CO2 level to maintain radiative equilibrium so that the planatary Mean Surface Temperature must increase to maintain global radiative equilibrium - but that only tells you that there is an effect, not its precise magnitude.

    Global Circulation Models fill the gap by automatically changing atmospheric conditions at each location based on change in radiative forcing, changes in temperature, and changes in lateral energy transfer. Unfortunately, I know of no GCM with a convenient web interface like that of ModTran.
  41. Tom Curtis you have made my day!!

    So I shut off all the other GHG and ran Modtran with 375 PPM CO2. Wrote down outgoing flux. Kept everything the same except went to 750 ppm CO2. Adusted the temp offset to give same out going flux as before. Doubling CO2 then gives radiative energy balance for this location, if CO2 the only GHG, with a 1.1 degree C increase offset.

    Probably lucky but cool (pardon the expression).

    ( FYI Hansen says in his book that "Any physicist worth his salt can show doubling CO2 with no feedbacks gives 1.2 degree increase".)
  42. curiousd @191, the agreement is, of course, largely coincidence. One reason the model will not produce an accurate estimate of instantaneous forcing is that, unlike in the real atmosphere, increased CO2 will not result in a cooling above the tropopause. The temperature offset is relayed to all higher levels resulting in a warmer stratosphere, not a cooler stratosphere as would actually occur. Professor Brian Fiedler recommends calculating radiative forcing from 20 km look down to allow for this, which will no doubt yield better, but still imperfect results.

    Anyway, that is not the primary purpose of this comment. Rather, Monash University (in Melbourne, Australia) have just placed online a global energy balance model, which you may enjoy playing with. Unlike LBL models it is globally resolved, and allows for lateral energy transfers. I believe these are handled by parametrization, however, rather than being an emergent property of dynamic and radiative processes as in a GCM. As Domminget and Floter say:

    "In contrast to CGCMs the model assumes a fixed atmospheric circulation, clouds and soil moisture, which are given as boundary conditions. It thus does not simulate internal chaotic climate variability caused by weather fluctuations and also assumes that climate change, due to external forcings such as 2 9 CO2 increase, is a small perturbation, which does not change the atmospheric or ocean circulation, which is clearly a simplification."


    Clearly such a simple model cannot be used to "prove" anything; or indeed to make detailed quantitative predictions. It is potentially a useful tool for instruction (and learning), particularly as key parameters can be left out of the model to judge their influence (with suitable caveates).

    Full documentation of the model can be found in Domminget and Floter (2011) (PDF).
  43. Thank you again. The application of Modtran by Professor Fiedler is most illuminating. I tried the MONASH program and have given feedback to their group.

    Another program on David Archer's website is the NCAR radiation code. The out put table has symbols

    1ev p z T q

    What do these mean? I am certain 1 eV cannot mean one electron volt?
  44. curiousd @193, I am not familiar with that model, so I can't be much help. However:

    lev = Level, numbered from the top of the atmosphere (32 km)
    p = atmospheric pressure at that level
    z = altitude in kilometers
    T = temperature

    Unfortunately I cannot help you with q.
  45. curiousd, Tom:

    q is almost certainly specific humidity (mass of water vapour per unit mass of moist air). Humidity units can be quite confusing - the only one that makes sense to everyone is relative humidity, and it's the one that is most useless for serious work.

    Other common ones:

    e - vapour pressure (partial pressure of water vapour)
    r - mixing ratio (mass of water vapour per unit mass of dry air)
    Td - dew point temperature (temperature at which air would reach saturation if cooled)

    Conversion between various forms is a common torture test subject in undergraduate meteorology courses.
  46. Hi,

    Thanks to the help here, and hours of struggling, I can now demonstrate some cool things with Modtran, which if used with care, is a great teaching tool.

    Potentially that NCAR program on the same website would also be useful. Maybe there is some kind of workshop people hold for users? In my own research field they hold such workshops at synchrotrons to help people hone their software analysis skills. If there were at least a handbook on NCAR with worked examples? Sigh! Just one example of where I go awry here, follows:


    1. I find the temperature corresponding to no GHG for the default incoming solar flux. That should be T earth, which averaged over the globe would be about 255 K.

    2. I go back to default and put in CO2 375 ppm.

    3. The output gives you temperatures associated with various altitudes.

    4. If the T earth for the setting you use were 255 K for no GHG - then go back to 3 above and write down the altitude for 255 K

    5. Now try 750 ppm. The surface temperature goes up but the altitude for 255 K should go up too. It does this, but....

    6. Check against equation: change in this altitude times lapse rate = change in temperature.

    6. I get a much bigger change in temperature using the altitude change method than the actual computed change in temperature.

    I have a feeling I am careening around in a complex vehicle randomly trying to make sense out of tweaking the controls. I probably need to go someplace to learn this one on one?
  47. Never mind, The Archer course web site has many bugs but I am able to at least learn what the parameters do by ignoring the bugs and proceeding as best I can.
  48. Now a specific question: In NACAR from Archer web site I keep everything default except I increase the high cloud fraction from zero. The temperature goes down, not up.

    As an amateur here I have absorbed the "high clouds tend to add to the Greenhouse Effect, low clouds tend to reflect" (over?)generalization. So why does adding high clouds cool in this NACAR program at default settings? I do not think there is a way to ask a question on line with that course.
  49. Never mind. I think I have figured out that NACAR thing pretty much now on my own now, just by persistent putzing around, day after day.
  50. Stealth, see also "A Saturated Gassy Argument" part 1 and part 2.  For more technical depth, check out Science of Doom; there are several places where saturation is discussed, but you might start with Part Five.

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