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How sensitive is our climate?

What the science says...

Select a level... Basic Intermediate Advanced

Net positive feedback is confirmed by many different lines of evidence.

Climate Myth...

Climate sensitivity is low
"His [Dr Spencer's] latest research demonstrates that – in the short term, at any rate – the temperature feedbacks that the IPCC imagines will greatly amplify any initial warming caused by CO2 are net-negative, attenuating the warming they are supposed to enhance. His best estimate is that the warming in response to a doubling of CO2 concentration, which may happen this century unless the usual suspects get away with shutting down the economies of the West, will be a harmless 1 Fahrenheit degree, not the 6 F predicted by the IPCC." (Christopher Monckton)

 

Climate sensitivity is the estimate of how much the earth's climate will warm in response to the increased greenhouse effect if we double the amount of carbon dioxide in the atmosphere.  This includes feedbacks which can either amplify or dampen that warming.  This is very important because if it is low, as some climate 'skeptics' argue, then the planet will warm slowly and we will have more time to react and adapt.  If sensitivity is high, then we could be in for a very bad time indeed.

There are two ways of working out what climate sensitivity is. The first method is by modelling:

Climate models have predicted the least temperature rise would be on average 1.65°C (2.97°F) , but upper estimates vary a lot, averaging 5.2°C (9.36°F). Current best estimates are for a rise of around 3°C (5.4°F), with a likely maximum of 4.5°C (8.1°F).

The second method calculates climate sensitivity directly from physical evidence, by looking at climate changes in the distant past:

adapted fig 3a

Various paleoclimate-based equilibrium climate sensitivity estimates from a range of geologic eras.  Adapted from PALEOSENS (2012) Figure 3a by John Cook.

These calculations use data from sources like ice cores to work out how much additional heat the doubling of greenhouse gases will produce.  These estimates are very consistent, finding between 2 and 4.5°C global surface warming in response to doubled carbon dioxide.

It’s all a matter of degree

All the models and evidence confirm a minimum warming close to 2°C for a doubling of atmospheric CO2 with a most likely value of 3°C and the potential to warm 4.5°C or even more. Even such a small rise would signal many damaging and highly disruptive changes to the environment. In this light, the arguments against reducing greenhouse gas emissions because of climate sensitivity are a form of gambling. A minority claim the climate is less sensitive than we think, the implication being we don’t need to do anything much about it. Others suggest that because we can't tell for sure, we should wait and see.

In truth, nobody knows for sure quite how much the temperature will rise, but rise it will. Inaction or complacency heightens risk, gambling with the entire ecology of the planet, and the welfare of everyone on it.

Basic rebuttal written by GPWayne

Last updated on 1 August 2013 by gpwayne. View Archives

Printable Version  |  Offline PDF Version  |  Link to this page

Related Arguments

Further reading

Tamino posts a useful article Uncertain Sensitivity that looks at how positive feedbacks are calculated, explaining why the probability distribution of climate sensitivity has such a long tail.

There have been a number of critiques of Schwartz' paper:

Comments

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Comments 151 to 200 out of 307:

  1. Actually the Archer model you reference seems to be consistent with White's numbers:

    385 W/m^2 x .566 (% absorbed clear sky) = 217.9; 217.9 W/m^2 x 0.333 (% clear sky) = 72.6 W/m^2

    385 x .857 (% absorbed cloudy sky) = 329.9; 329.9 W/m^2 x 0.666 (% cloudy sky) = 219.7 W/m^2

    219.7 W/m^2 + 72.6 W/m^2 = 292.3 W/m^2; Archer = 287.8 W/m^2, which is awfully close.
  2. http://www.google.com/search?q=top+of+atmosphere+255K

    First hit:
    meteo04.chpc.utah.edu/class/1020/Lecture2.201009.pdf
    Start around slide 31.
  3. RW1 @150, if you care to look at the settings, Modtran is run for specific typical locations, with the default being the tropics. It does not produce a globally averaged result. Because the tropics is warmer than the global average, OLR at the tropics is warmer than the global average of approx 240 w/m^2. As set for default, it also does not include the effect of clouds.

    Further, and for the umpteenth time (as this is just your same question in a different guise) the OLR from the atmospheric window is included in the calculation. This can clearly be seen in the graph of the emissions for each model run. It can also be seen with line by line detailed data by viewing the whole output file.

    If you want a closer approximation to the global average, use the 1976 US Standard atmosphere (effective brightness temperature = 259 K). Alternatively, use the ground temperature offset to either set the surface temperature at 288 K (effective brightness temperature = 257 K), or adjust it to match an output of 240 w/m^2, and then run the doubling of CO2 experiment.

    As previously indicated, this is an obsolete model. And as implemented on the net, it does not even allow us to control all parameters so that you cannot set up a globally averaged surface temperature plus cloud cover. It's use is to show you quite clearly that the 3.7 w/m^2 is the difference in total OLR from doubling CO2. If you want a more up to date model, you'll have to pay the licensing fees.
  4. RW1 @151, it is no surprise that the figures are close to George White's in that GW used a hi-tran model to get his figures. He then misinterpreted the Outgoing Long-wave Radiation as being the the total energy emitted from the top most layer of the atmosphere, and divided it by two to get what he believes to be the OLR.

    Looking at the Modtran model you can clearly see that that is a mistake. That model calculates the IR radiance at a given location that is either out going, or incoming. You can set the altitude to 0 and Look Up to calculate the back radiation. Or you can use the default to set the altitude to 70 km and look down to model what a satelite at 70 km altitude would detect. Clearly that satellite is not going to detect the radiation that is returning to the Earth, it will only detect the OLR. So, the I(out) of the model with that setting is the OLR. There is no need to divide it by two, and doing so shows complete incompetence on this subject. (Not a problem in somebody who is trying to learn, but a huge problem in someone like George White who purports to lecture.)
  5. "Looking at the Modtran model you can clearly see that that is a mistake."

    I've spent the last hour or more looking at the detailed line by line output and don't see the 'mistake' you're referring to. I do see that the atmospheric window is included in the data though (more on that in my next post).

    Also, I know this model is out of date, but for the purposes of understanding what these numbers mean, let's break them down as they are.

    Here are the inputs I'm using:

    CO2 (ppm) 375 & 750
    CH4 (ppm) 1.7
    Trop. Ozone (ppb) 28
    Strat. Ozone scale 1

    Ground T offset, C -1
    hold water vapor pressure
    Water Vapor Scale 1

    Locality 1976 US Standard Atmosphere
    No clouds or rain

    Sensor Altitude km 70
    Looking Down

    This is the data output I'm looking at.
  6. You did not show the data output. However, with settings as indicated and 375 ppm CO2, the base output is:


    I, W / m2 = 255.565
    Ground T, K = 287.20

    For 750 ppm, the output is:

    I, W / m2 = 252.801
    Ground T, K = 287.20

    The difference in I is 2.764 w/m^2.

    That is the difference, according to this model, between the IR leaving the atmosphere with 350 ppm and with 750 ppm. Plainly, if that is the IR leaving the atmosphere, it is incorrect to divide it by two to determine the difference in the IR energy leaving the planet in the two cases. But that is exactly what George White does with his equivalent calculation.
  7. "he then misinterpreted ... that is a mistake."

    The misinterpretation.
  8. The first thing I notice in the data is that at 375 ppm, the average transmittance is 0.2526, and the average transmittance at 750 ppm is 0.2465 (a reduction of 0.0061 or about 2.4%).

    At temperature of 287.2K, the earth's surface emits about 385 W/m^2. 385 W/m^2 x .2526 = 97.251 W/m^2 passing through the atmospheric window at 375 ppm, and 385 W/m^2 x .2465 = 94.903 passing through at 750 ppm for (a reduction of 2.348 W/m^2).

    385 W/m^2 - 97.251 W/m^2 = 287.749 W/m^2 absorbed by the atmosphere at 375 ppm. 385 W/m^2 - 94.903 W/m^2 = 290.907 W/m^2 absorbed at 750 ppm.

    Here is what I can't figure out: The output of the data is showing 255.565 W/m^2 leaving at 375 ppm and 252.801 W/m^2 leaving at 750 ppm (a reduction of 2.764 W/m^2).

    If I divide 287.749 W/m^2 (375 ppm) by 2, I get 143.8745 W/m^2. 143.8745 + 97.251 = 241.1255 W/m^2 leaving (255.565 W/m^2 needed to match the data?).

    If I divide 290.907 W/m^2 (750 ppm) by 2, I get 145.0485 W/m^2. 145.0485 W/m^2 + 94.903 = 239.9515 W/m^2 leaving (252.801 W/m^2 needed to match the data?).

    145.0485 W/m^2 - 143.8745 W/m^2 = 1.174 W/m^2, which is exactly half of the 2.348 W/m^2 reduction in the atmospheric window.

    To match output of the data exactly, at 375 ppm there needs to be 158.314 W/m^2 from the atmosphere (158.314 + 97.251 = 255.565 W/m^2). For 750 ppm there needs to be 157.898 W/m^2 from the atmosphere (157.898 + 94.903 = 252.801 W/m^2).

    The difference between 158.314 W/m^2 and 157.898 W/m^2 is 0.416 W/m^2, which is the exact difference between 2.348 W/m^2 reduction in the window and the reduction in the data output of 2.764 W/m^2).

    What accounts for the missing 0.416 W/m^2???
  9. RW1 - Why are you dividing by 2? Seriously, why? What Modtrans outputs is the total outgoing IR, and hence the 2.764 change on doubling CO2 is the entire, whole, complete difference between outgoing IR. Not half the amount, not twice the amount, but the whole amount.

    Dividing by 2 is wholly unphysical and wrong. This is the basic mistake that GW makes, and that you have repeated. It is wrong.
  10. KR,

    Then why does the 2.764 W/m^2 difference outputed NOT match up to the difference in the transmittance data outputed? Are you saying it shouldn't? Explain why. What accounts for the difference?

    All I've done is run some calculations showing what the numbers would be dividing by 2. Those calculations using the exact transmittance data provided at least yield about 240 W/m^2 (255K) leaving.
  11. RW1 @158:

    1) You did not account for the emissivity of 0.98 for the Earth's surface. That means Surface Radiation (SR) = 385.8 * 0.98 = approx 378 w/m^2

    2) The average transmittance, ie, the sum of each line's transmittance divided by the number of lines, cannot be used as you have done it. The energy emitted at each line is not constant, so the distribution in variation in transmittance relative to the distribution in emitted energy can make very large differences in the net transmission. Therefore using a simple average of transmission will give invalid results.

    3) Total radiance obviously includes values for emissions by the atmosphere, as for example at line 400:

    Surface Transmission: 3.18E-29
    Total Radiance: 1.42E-03
    Transmittance: 0.00000

    Clearly with a transmittance of 0, Total Radiance would be 0 if radiation emitted from the atmosphere was excluded.

    To conduct the analysis you wish to make, you need to go through line by line, and sum the total of surface radiation * transmittance to get the amount of radiation from the surface that escapes to space unabsorbed. You then need to go through line by line and sum (total radiance - (surface radiation * transmittance)) to get the amount of radiation emitted from the atmosphere to space. You will then be in a position to do what you are trying to do in 158.

    Have fun.
  12. Tom,

    The average transmittance for '100 TO 1500 CM-1' is given at the bottom.

    Also, I tried using an emissivity of .98 and it didn't make much difference (2.3058 W/m^2 instead of 2.348 W/m^2).
  13. Addendum to 161:

    Looking at the values, it appears quite probable that "Surface transmittance" is the surface radiation that escapes to space at each line, with transmittance rounded to five significant figures, thus showing 0 in this case.

    In that case, to get the transmittance you would have to calculate independently the surface radiance at the surface for each line. However, it would save you a step in integrating determining the total emissions from the atmosphere.

    You may need to find a manual to clarify this.

    Of course, the sensible thing to do would probably be to assume that no fundamental errors slipped into the programing based on the fact that a large number of independently programed models yield essentially the same result.
  14. @162, I know the average is given at the bottom. That does not mean you can use it as you are doing.
  15. Tom,

    'INTEGRATED ABSORPTION FROM 100 TO 1500 CM-1 = 1054.84 CM-1
    AVERAGE TRANSMITTANCE =0.2465'

    You're saying this doesn't account for the differences in energy emitted at each line? How do you know this?
  16. Tom,

    "I know the average is given at the bottom. That does not mean you can use it as you are doing."

    How do you know? Have you added all the lines up and divided?
  17. Tom Curtis, RW1 - do you have a link to the Modtran model you are using? I'm not seeing the same freedom of parameters you seem to have discussed at the model here.
  18. Tom,

    Most of the radiance is in the window, so if anything that would seem like it would make the number much higher than only about 0.25?
  19. Tom,

    Should I add up all individual transmittance lines and divide?
  20. RE: my 168

    Actually most of the energy is not really in the window.
  21. KR @167, that is the model. If you run it there will be a link to "View the whole output file" which shows a large number of additional values.

    RW1 @168, as can be seen in this image, the peak of the surface transmission is in the 400 to 800 wavenumber band, ie, in the band with a deep trough due to CO2 and a number of troughs due to H2O. The peak radiance is at wavenumber 592, inside the left hand side of the CO2 trough. Therefore if the average transmittance is the mean, it would definitely underestimate the reduction in outgoing IR from the surface.



    @164 and 165, I don't know, but that seems the most natural reading to me. You should always take average to mean "mean", not "weighted mean" (or median or mode) unless there are clear contextual reasons to think otherwise. There are no such contextual reasons here; and furthermore, your discreprancy gives weight to that interpretation. Which is more likely, that a program developed by the air force for research and which has been used in various incarnations since 1988 with good correspondence to observational results has an error that produces up to 20% errors in its output? Or that you are simply mistaken in your interpretation of average?

    Regardless, if you disagree with me, you do the LBL integration. I am not the one chasing windmills here.

    @169, no, you just add up the individual lines. Any divisions (if necessary, see 163) shoud be done for each line only.
    Response: Fixed image width.
  22. I'm downloading the manual.
  23. wrong version.
  24. Tom,

    Do we agree that the reduction in the window should be twice the 2.764 w/m^ outputed (or about 5.528 W/m^2)?

    If not, why not? You don't think that all the infrared the atmosphere absorbs is directed toward the surface? Clearly it's not.
  25. RW1 - "Do we agree that the reduction in the window should be twice the 2.764 w/m^ outputed" Ummm, absolutely not.

    It's both a reduction in the atmospheric window and a deepening in the GHG emission bands. As we have said repeatedly. Not just a single effect, but two different ones that make up the total reduction in emissions.
  26. RW1 - Why is it that you cannot accept that it's two effects adding up to the total IR reduction?
  27. "Why is it that you cannot accept that it's two effects adding up to the total IR reduction?"

    Simple. I haven't seen the evidence showing/prooving it, nor do I understand what a "deepening in the GHG emission bands" actually means.
  28. I can't find the manual online. I emailed Ontar to see if they can provide it.
  29. Tom,

    What use would the 'average transmittance' number be if it were NOT how I interpreted it? Maybe you're correct, but then the information is totally useless as far as I can tell.
  30. Tom,

    "Which is more likely, that a program developed by the air force for research and which has been used in various incarnations since 1988 with good correspondence to observational results has an error that produces up to 20% errors in its output? Or that you are simply mistaken in your interpretation of average?"

    Not the program itself, but the web interface integration of the program. Where do you see the 2.764 W/m^2 in the line by line output, either directly or indirectly? I don't see it in there.
  31. Tom,

    Nor do I see the 252.801 W/m^2 or 255.565 W/m^2.
  32. Tom,

    Is it just a coincidence that using the average transmittance numbers and dividing the surface difference by 2 yielded nearly exactly 240 W/m^2 leaving (for 255K)? Maybe, but it certainly warrants further investigation.
  33. RW1, I cannot keep up with your stream of consciousness posting, and nor will I try to. Sit down, think it out, and work our your objections and problems after a little thought.

    As regards the "average transmittance", I have seen a comparison of the Modtran model at David Acher's site with the data from a satellite over Barrow Island, and the match is pretty good. Close enogh that you can't tell the difference by eyeball, although if you overlaid them I'm sure some differences would jump out. The "error" you have found is too large for that to be plausible.

    If you have a further problem with it, work the problem out line by line as I suggest. If you are correct, there will be no difference in the reult. If I am correct, you initial calculation will be shown to be in error.

    As regards the window, the figure above @ 171 shows the radiance for 325 ppm CO2 overlaid on the radiance for 750 ppm CO2 on the right. As you can see, the main difference is on the wings of the trough, where a slight step pattern is deeper with 750 ppm than with 325 ppm. That is not a change in the atmospheric window, because IR radiation at those frequencies were already absorbed, possibly completely absorbed as far as radiation from the surface is concerned. If you look even closer, (closer than the resolution will allow, unfortunately), you will also see that the center of the trough is slightly deeper. You will also see the walls of the trough at the top are slightly wider (which is a reduction of the window). You will also see some of the secondary troughs generated by CO2 are deeper. There is one just to the right of the main CO2 trough where a single spike shows up in the center.

    Here for comparison is a modtran graph for 10,000 ppm CO2 with not H2O or O3:



    You will notice that that small spike noted above has become a deep trough that overlaps with the first trough, with a resulting large reduction in the atmospheric window. But that widening took place step by step, and in each step, it was always the smallest effect.
  34. Tom,

    "As regards the window, the figure above @ 171 shows the radiance for 325 ppm CO2 overlaid on the radiance for 750 ppm CO2 on the right. As you can see, the main difference is on the wings of the trough, where a slight step pattern is deeper with 750 ppm than with 325 ppm. That is not a change in the atmospheric window, because IR radiation at those frequencies were already absorbed, possibly completely absorbed as far as radiation from the surface is concerned. If you look even closer, (closer than the resolution will allow, unfortunately), you will also see that the center of the trough is slightly deeper. You will also see the walls of the trough at the top are slightly wider (which is a reduction of the window). You will also see some of the secondary troughs generated by CO2 are deeper. There is one just to the right of the main CO2 trough where a single spike shows up in the center."

    I know all of this. The total atmospheric window is simply the quantity of the whole spectrum of surface emitted infrared that passes through the atmosphere completely unabsorbed and goes straight out to space. Visually, there is a slight widening of the CO2 absorbing bands at 750ppm, which narrows the more overtly visual part of the 'window', but it's a specific quantity - not just a visual reduction. The outputs of these programs are detailed numbers, specifically the transmittance - not just what can be seen overtly in visuals of a graph. The decrease in transmittance directly tells us how much more outgoing surface power, across the entire emitted spectrum, is absorbed by the atmosphere.
  35. Tom,

    "The decrease in transmittance directly tells us how much more outgoing surface power, across the entire emitted spectrum, is absorbed by the atmosphere."

    If 'transmittance' does NOT tell us this, then what does it tell us?
  36. RW1 @184, evidently you do not know all this. You may think you do, but that is another question entirely.

    Consider the "atmospheric window". An "atmospheric window" is any part of the spectrum where transmittance is sufficiently high that you can place a telescope on a mountain, and observe the stars effectively at that frequency. Alternatively, it is a part of the spectrum where the transmittance is sufficiently high that you can use it as a channel for communication to space.

    If you want to see the atmospheric window in the IR spectrum, you should look at the back radiation at the surface:



    Clearly, if you looked up at 680 cm^-1 wave number, all you would see is the thermal radiation of the atmosphere. You would not even be able to see the sun in that portion of the spectrum, from the surface. In contrast, the intervals between 810 and 950 probably have sufficiently high transmittance to be useful for telescopes (and sidewinders). That is a atmospheric window. There is another, smaller one on the other side of the O3 trough.

    With that in mind, closing the window means reducing the IR radiation from the surface that escapes to space, particularly in those parts of the spectrum; and it is a minor effect. Deepening of the CO2 emission band means that in that part of the spectrum outside of the atmospheric window, the amount of IR from the atmosphere itself is reduced because it comes from a higher altitude and hence has a colder temperature.

    These effects are not strictly independent. For example, at the right edge of the CO2 trough, there are transmittances that rise from around 0.2 to 0.8 over a 60 wave number interval. Over this interval, both trough deepening,and narrowing of the atmospheric window occur with rising CO2. On the equivalent left side, however, transmittances peak around 0.2 because of the overlapping effects of H2O. The trough deepening, however, contributes almost as much to the reduced OLR as does the equivalent on the other side.

    Speaking of which, on the graph shown, total area under the line equals the total power (watt's per square meter) radiated to space, so the difference in area is the difference in radiated power. As you can see, the most significant part of this comes from the deepening of the trough on the wings, and that is approximately equal on both sides, even where transmittances are very low. Therefore it is clearly not a narrowing of the atmospheric window.
  37. RW1 @185, sorry, I don't recognize the quote. Could you please cite the source and link to it if on the web. If not on the web, could you please embed the quote in a wider context.
  38. Tom, RW1 185 quotes himself. No other source for it.

    http://www.google.com/search?q=%2Bdecrease+%2Btransmittance+"outgoing+surface+power"+"emitted+spectrum"+"absorbed+by+the+atmosphere"
  39. > total atmospheric window is simply the quantity

    No, it's not a quantity.

    It's a term defined in various ways in papers published in science journals.

    It's never defined as a quantity.
  40. Tom,

    When I use the term "atmospheric window" I mean the total transmittance - the specific amount of emitted surface power that passes through the atmosphere unabsorbed and goes straight out to space. If that is not the technical definition, then I stand corrected, but that's what I mean when I use the term.
  41. Are you claiming that the 3.7 W/m^2 of additional absorption from 2xCO2 does NOT represent a 3.7 W/m^2 reduction in transmittance?

    What I don't think you understand is that unless the specific wavelengths are saturated, some of the outgoing surface power still passes through them unabsorbed, and this amount is included in the transmittance. Increasing the concentration of CO2, for example, will reducing the amount that passes through at wavelengths NOT already saturated (i.e. widening the band or deepening the trough). The effect of more CO2 at saturated wavelengths will just reduce the height from the surface where 100% absorption occurs.
  42. RW1 @190 &191, given that at many frequencies, the atmosphere has an optical thickness greater than 1 (ie, transmittance is 0 for less than the full thickness of the atmosphere) than much of the IR absorbed by that region of the atmosphere that actually radiates to space does not come from the surface, but only from lower regions of the atmosphere. So an increase of absorption by 3.7 w/m^2 may have absolutely no effect on transmittance, or the atmospheric window (as you have defined it).

    Further, as much of the heat in the atmosphere is carried there by evaporation or transpiration, there is not even a necessary correlation between surface radiation and the thermal radiation of the lower levels of the atmosphere. Certainly that correlation is broken over antarctica in the winter, and may be broken at other places periodically as well. That is why Line By Line models use temperature profiles in developing their predictions, either a simple lapse rate (as in Modtran) or measured (or modelled) values in more sophisticated programs.

    Worse for your interpretation, a decrease in transmittance will automatically mean that a higher proportion of radiation from lower in the atmosphere is absorbed higher in the atmosphere, even with opticat thicknesss less than 1, but greater than 0. Because the higher gas is cooler (in the troposphere) it will radiate less energy, thus reducing the total IR radiation leaving the planet. That means a change in transmittance has more effect than simply reducing surface radiation to space.

    The only way to properly calculate its effect is, as the LBL models do, calulate its effect on each layer of a large number of layers of the atmosphere (in modtran's case, 33).

    The LBL models take account of radiation flows in both directions. That is, for each layer, they determine its emission at each individual wavenumber (or wavenumber couplet for modtran), based on its temperature. They then apply that radiation as both upward and downwelling radiation. For each layer, they also take the total incoming radiation (upward and downward), multiply by the transmittance for that layer, and apply the result as upwelling or down welling radiation from that layer as appropriate.

    Here is a diagram illustrating the process from Science of Doom:



    Although this only indicates transmittance in one direction, be assured it is calculated in both. In the thread from which this comes SoD is developing a simple radiation model, and you can see in the code that he makes the calculations first for upwelling, and then for downwelling radiation.

    (By the way, this illustration also appears in SoD's thread on theory and experiment in atmospheric radiation, from which I got the diagrams which showed the close correlation between the model predictions and observations. That thread has already been linked here. So your claim that all you have received is statements, not evidence, is nonsense.)

    Because the transfers in radiation are calculated for each wavenumber, and for each level independently, there is no single calculation that corresponds to what you are seeking, ie, a level in which all incoming radiation is from the surface, and all upwelling radiation goes to space. But that does not mean that both the upwelling and downwelling emittance from each level is ignored, or that the absorption at any level is ignored which is what is required for George White's adjustment to make any sense.

    Of course, in the LBL models, the total upwelling radiation of the highest level (emitted and transmitted) is just the Outgoing Long-wave Radiation. And the difference between that for 375 ppm and for 750 ppm is the increase of the greenhouse effect for doubling of CO2.

    So, if you want to verify Modtran, and all the other LBL models programed by different teams around the world, and all the energy balance models also programed by different teams around the world, which all come up with essentially the same result; which just happens to match observations almost exactly, you either need to accept the observational match as confirming the models, or you need to go through the models line by line. There is no other short cut.



  43. "given that at many frequencies, the atmosphere has an optical thickness greater than 1 (ie, transmittance is 0 for less than the full thickness of the atmosphere) than much of the IR absorbed by that region of the atmosphere that actually radiates to space does not come from the surface, but only from lower regions of the atmosphere. So an increase of absorption by 3.7 w/m^2 may have absolutely no effect on transmittance, or the atmospheric window (as you have defined it)."

    And where does the radiation from the lower regions of the atmosphere come from?

    So this is what you're claiming? That the 3.7 W/m^2 does NOT represent a reduction in total transmittance, as I have defined it? I just want to be clear.

    "Further, as much of the heat in the atmosphere is carried there by evaporation or transpiration, there is not even a necessary correlation between surface radiation and the thermal radiation of the lower levels of the atmosphere."

    Define what you mean by "correlation". I understand that a good amount of the heat in the atmosphere is carried there by evaporation and transpiration, but those amounts are in addition to emitted surface power and are non-radiative, which means they have to be returned to the surface in equal and opposite amounts, because all the infrared energy leaving at the top of the atmosphere is radiative. It's true that some of the kinetic energy moved into the atmosphere from the surface by evaporation and transpiration can radiate some energy into the atmosphere, but again it has to be offset by the surface radiation in equal and opposite amounts. If some of the surface originating kinetic energy is radiated into the atmosphere and that energy is ultimately radiated out to space, the amount of kinetic energy returned to the surface will be less, having a cooling effect on the surface, effectively reducing the emitted surface power by the opposite amount.
  44. RW1 @193:

    "And where does the radiation from the lower regions of the atmosphere come from?"

    Any substance with an emissivity greater will radiate energy with a total energy proportional to its emissivity times the fourth power of its temperature. That is where the radiation comes from, from the gases in the lower atmosphere which radiate in the IR spectrum and have non-zero temperatures (primarily water vapour and CO2).

    The heat that warms that gas comes evapo/transpiration from the surface, radiation from the surface, and atmospheric absorption of incoming solar radiation, although at any given layer, a large part of it will come from thermal radiation from adjacent layers, or convective heat transfer from adjacent layers.

    "So this is what you're claiming? That the 3.7 W/m^2 does NOT represent a reduction in total transmittance, as I have defined it? I just want to be clear."

    If your definition of total transmittance is "... the specific amount of emitted surface power that passes through the atmosphere unabsorbed and goes straight out to space", then no it is not. A small part is reduction of transmittance, but a more significant part is the reduction of thermal radiation from lower levels of the atmosphere to space, as per the diagram @171.

    "Define what you mean by correlation ..."

    The normal statistical sense. What I am pointing out is that because not all energy transfers are radiative, situations can arise in which the atmosphere returns more energy to the surface than it receives from the surface. This will only happen when there is a temperature inversion, as sometimes happens with low lying clouds. In Antarctica in the winter it can happen on a continental scale because Antarctica is receiving no insolation, and there is still an energy transfer from the Antarctic Ocean to the Antarctic interior carries by the atmosphere.

    However, when you say "If some of the surface originating kinetic energy is radiated into the atmosphere and that energy is ultimately radiated out to space, the amount of kinetic energy returned to the surface will be less, having a cooling effect on the surface, effectively reducing the emitted surface power by the opposite amount", you appear to be making an error. Specifically, when energy is transferred to the atmosphere, it makes no distinction in the source of that energy when it radiates. So, the sum total of the energy it receives is radiated away, and half of that energy must be downwelling, and half upwelling. And if the sum of Insolation plus back radiation is less than the sum of Surface radiation plus energy transfer by evapo/transpiration and (a small) energy transfer by by collisions between gas molecules and the surface, then the surface will indeed cool.

    You also may be not making a mistake, and I have simply misunderstood you. It is true that the presence of evapo/transpiration and convection, by making energy transfer more efficient, cool the surface compared to the temperature it would be if all energy transfers in the atmosphere were radiative (about 70 degrees C). So in that respect, the fact that evapo/transpiration carries energy into the atmosphere, a portion of which does eventually escape to space does mean the surface is cooler than it otherwise would have been.

    Having said that, I do not see the relevance to the basic point at issue - is it George White, or all the world's radiative transfer modelers who are correct in their interpretation of the output of radiative transfer models?
  45. "Worse for your interpretation, a decrease in transmittance will automatically mean that a higher proportion of radiation from lower in the atmosphere is absorbed higher in the atmosphere, even with opticat thicknesss less than 1, but greater than 0. Because the higher gas is cooler (in the troposphere) it will radiate less energy, thus reducing the total IR radiation leaving the planet. That means a change in transmittance has more effect than simply reducing surface radiation to space."

    How do you figure? If anything, it seems a decrease in transmittance will shorten the height from the surface where the atmospheric absorption occurs.

    "The only way to properly calculate its effect is, as the LBL models do, calulate its effect on each layer of a large number of layers of the atmosphere (in modtran's case, 33).

    The LBL models take account of radiation flows in both directions. That is, for each layer, they determine its emission at each individual wavenumber (or wavenumber couplet for modtran), based on its temperature. They then apply that radiation as both upward and downwelling radiation. For each layer, they also take the total incoming radiation (upward and downward), multiply by the transmittance for that layer, and apply the result as upwelling or down welling radiation from that layer as appropriate.

    Because the transfers in radiation are calculated for each wavenumber, and for each level independently, there is no single calculation that corresponds to what you are seeking, ie, a level in which all incoming radiation is from the surface, and all upwelling radiation goes to space. But that does not mean that both the upwelling and downwelling emittance from each level is ignored, or that the absorption at any level is ignored which is what is required for George White's adjustment to make any sense."


    Have you verified with GW that this is what he's claiming? Because that's not my interpretation of it. The model simulations he's using are multi-layered through the atmosphere - he's simply showing the aggregate effect through all the layers. Is it just another coincidence that he's getting an incremental absorption or reduction in transmittance of 3.7 W/m^2 for 2xCO@ from his HITRAN based simulations?
  46. "What I am pointing out is that because not all energy transfers are radiative, situations can arise in which the atmosphere returns more energy to the surface than it receives from the surface. This will only happen when there is a temperature inversion, as sometimes happens with low lying clouds. In Antarctica in the winter it can happen on a continental scale because Antarctica is receiving no insolation, and there is still an energy transfer from the Antarctic Ocean to the Antarctic interior carries by the atmosphere.

    However, when you say "If some of the surface originating kinetic energy is radiated into the atmosphere and that energy is ultimately radiated out to space, the amount of kinetic energy returned to the surface will be less, having a cooling effect on the surface, effectively reducing the emitted surface power by the opposite amount", you appear to be making an error. Specifically, when energy is transferred to the atmosphere, it makes no distinction in the source of that energy when it radiates. So, the sum total of the energy it receives is radiated away, and half of that energy must be downwelling, and half upwelling. And if the sum of Insolation plus back radiation is less than the sum of Surface radiation plus energy transfer by evapo/transpiration and (a small) energy transfer by by collisions between gas molecules and the surface, then the surface will indeed cool.

    You also may be not making a mistake, and I have simply misunderstood you. It is true that the presence of evapo/transpiration and convection, by making energy transfer more efficient, cool the surface compared to the temperature it would be if all energy transfers in the atmosphere were radiative (about 70 degrees C). So in that respect, the fact that evapo/transpiration carries energy into the atmosphere, a portion of which does eventually escape to space does mean the surface is cooler than it otherwise would have been."


    Tom,

    All I'm saying is that globally, energy has to be conserved. Any kinetic energy moved from the surface into the atmosphere, some of which ultimately leaves radiatively at the top of the atmosphere, has to reduce the amount of emitted surface power by an equal opposite amount due to less being returned to the surface in kinetic form, which has the effect of reducing the surface temperature; thus reducing surface emitted radiation.

    I know about the Antarctic temperature inversion. It's highly localized.
  47. "Any substance with an emissivity greater will radiate energy with a total energy proportional to its emissivity times the fourth power of its temperature. That is where the radiation comes from, from the gases in the lower atmosphere which radiate in the IR spectrum and have non-zero temperatures (primarily water vapour and CO2).

    The heat that warms that gas comes evapo/transpiration from the surface, radiation from the surface, and atmospheric absorption of incoming solar radiation, although at any given layer, a large part of it will come from thermal radiation from adjacent layers, or convective heat transfer from adjacent layers."


    Agreed, but ultimately what matters here is the net combined effect of all these things relative to surface emitted radiation. Aferall, that's what we're talking about here is it not? That's what determines global average temperatures, right? Heat flows - how much from the surface is coming back from the atmosphere and how much is passing through. This is determining the heat flux or power flux at the surface, which ultimately is determining the temperature.
  48. "Having said that, I do not see the relevance to the basic point at issue - is it George White, or all the world's radiative transfer modelers who are correct in their interpretation of the output of radiative transfer models?"

    Yes this is crux, but if GW is so obviously wrong as you claim, where is the smoking gun? And why haven't you presented it to him? I mean if it's so egregiously wrong, it should be easy to point directly to the specific evidence that disproves it, right?

    I admit I have not yet verified if what he's claiming is correct or not, but you have neither verified what the IPCC is claiming the 3.7 W/m^2 represents from the model simulations. I've looked all through the IPCC 2007 report, I don't find this information - they seem to be really ambiguous about where exactly the 3.7 W/m^2 is derived from. I've also looked all over the internet and cannot find verification either way.

    Regardless, I'm determined to get to bottom of this - even it means I have to get the MODTRAN software and run the simulations myself.
  49. Enjoy!
    http://www.modtran.org/
    http://download.cnet.com/Modo/3000-2054_4-77505.html
  50. "Having said that, I do not see the relevance to the basic point at issue - is it George White, or all the world's radiative transfer modelers who are correct in their interpretation of the output of radiative transfer models?"

    There is yet another possibility too. They assumed or convinced themselves that there was a remote possibility that the full 3.7 W/m^2 of incremental absorption could somehow make it back to the surface through multiple absorptions and re-emissions. I've seen this claim argued before, though ultimately never convincingly. Maybe they used this as a rationalization to count it all as a "just in case" precaution. I don't know.

    Without knowing the detailed specifics of the outputs of these model simulations there's no way to know.

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