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Calculating the greenhouse effect

Filed under: — gavin @ 21 January 2006

In another forum (on a planet far, far away), the following quote recently came up:

….the combined effect of these greenhouse gases is to warm Earth’s atmosphere by about 33 ºC, from a chilly -18 ºC in their absence to a pleasant +15 ºC in their presence. 95% (31.35 ºC) of this warming is produced by water vapour, which is far and away the most important greenhouse gas. The other trace gases contribute 5% (1.65 ºC) of the greenhouse warming, amongst which carbon dioxide corresponds to 3.65% (1.19 ºC). The human-caused contribution corresponds to about 3% of the total carbon dioxide in the present atmosphere, the great majority of which is derived from natural sources. Therefore, the probable effect of human-injected carbon dioxide is a miniscule 0.12% of the greenhouse warming, that is a temperature rise of 0.036 ºC. Put another way, 99.88% of the greenhouse effect has nothing to do with carbon dioxide emissions from human activity8.

We’ve discussed the magnitude of the greenhouse effect before, but it might be helpful to step through this ‘back-of-the-agenda’ calculation and see what the numbers really give. (Deltoid has also had a go at some of these mis-statements).

The quote comes from a lecture by an Australian climate ‘contrarian’ and frequent contributor to the southern hemisphere op-ed pages. Where did he get this from? One might assume that reference ‘8’ was a scientific text, but one would assume wrong. It was in fact our old friend at Fox News, who may in turn have picked up his (junk)science from here. It is not clear whether this is the original source, but it’s close enough.

So, starting at the top:

  • “33 ºC” is the difference between the mean surface air temperature of the planet and the blackbody radiating temperature (i.e. the temperature a blackbody would need to radiate at to be in equilibrium with the incoming solar radiation given an albedo of about 0.3). So far so good. While that is one way to assess the strength of the basic greenhouse effect, another one is measure the amount of long wave radiation from the surface that is absorbed in the atmosphere (by greenhouse gases (incl. water vapour), clouds, aerosols, etc.). That is currently about 150 W/m2 and would be zero with no greenhouse effect at all.
  • “95% of this warming is caused by water vapour”. This is sourced to a couple of chaps who may have worked for Accu-Weather, but a) is misquoted – their ’90-95%’ is for both water vapour and clouds, and b) just wrong and c) irrelevant anyway.
    Dealing with b) first, if you remove all water vapour and clouds you still absorb about 34% of the long wave radiation, and conversely, if you only have water vapour and clouds you absorb 85% (calculations here). Thus the effect of water vapour and clouds is between 66 and 85% – the range being due to the spectral overlaps with the other absorbers. These calculations were done with the GISS GCM radiation code, which matches line-by-line codes to about 10% – but the numbers are very similar to Ramanathan and Coakley (1978), and so probably aren’t too far off what you would get with any decent radiation code. I’ll get to ‘c)’ below….
  • “The other trace gases contribute 5% … amongst which carbon dioxide corresponds to 3.65%”. That is just 100 minus 95% of course, but really it should be 15 to 34% – of which CO2 on its own is between 9 and 26% (op cit). If you were to naively estimate the total temperature contribution of the CO2 it would be between 3 and 9 ºC – but see below.
  • “The human-caused contribution corresponds to about 3% of the total carbon dioxide in the present atmosphere,”. This one is blatantly false and is erroneously credited to the US Dept. of Energy in the original source (their Table 1)! The ‘3%’ number actually comes from comparing the human emissions with the gross emissions from natural sources while neglecting to consider the large natural sink. Because of the rapid cycling between the biosphere, the atmosphere and the upper ocean, that is an irrelevant comparison – kind of like comparing the interest on your bank account and your salary and expecting to be able to say something about your savings without thinking about your spending. The correct statement is that CO2 is around 30% higher than it was in the pre-industrial period, and all of that rise is due to human emissions (fossil fuel use and deforestation principally).
  • “Therefore, the probable effect of human-injected carbon dioxide is a miniscule 0.12% of the greenhouse warming”. That’s just 0.03*0.0365 of course – but even that is calculated wrong (it should be 0.11% by my calculator). But from our numbers, it would be between 3 and 8%.
  • “a temperature rise of 0.036 ºC”. More like 1-2.6 ºC actually, but although this gives numbers that are in the ballpark of the IPCC estimates (0.6 to 1.7 ºC warming for an increase of 30% in CO2 at equilibirum) this is not a sensible way to calculate climate sensitivty.

Why do I claim this is an irrelevant and not very sensible calculation? Firstly, it assumes linearity – all of the gases contributing according to their effects today when it is obvious that overlaps and saturation effects are large and important, and more importantly, it ignores feedbacks. The calculation above gives the impression that what you are calculating is the change of temperature that would result if you remove all the CO2. But since water vapour concentration is a feedback not a forcing, it can’t be assumed to remain constant as the planet cools. Water vapour does in fact change (roughly keeping relative humidity, as opposed to specific humidity, constant) and this has been shown in the real world as a function of volcanic cooling (Soden et al, 2002) and for longer term trends (Soden et al, 2005, discussed here), and is well reproduced in climate models.

What then is an appropriate calculation? Well, it’s simply the estimate of climate sensitivity for the present climate – how much would you expect the planet to warm if you doubled CO2? We’ve discussed this numerous times before, and in my opinion the best answer so far comes from looking at the difference between the last glacial period and the modern era – this gives a number around 3 +/- 1 ºC at doubling.

For the 30% rise in CO2 there has been so far, that would imply that would represent around 3% of the natural greenhouse effect – a good order of magnitude bigger than that suggested above. Of course, this is at equilibrium and not applicable to a transient change. If one takes into account the human-induced changes in the other GHGs (CH4, N2O, CFCs), you’d get something like double that. Given that even a 5 or 6 ºC cooling was associated with the huge ice sheets 20,000 years ago, and that 33 ºC cooling would reduce our planet to a near-snowball-like state, a potential increase of 5 to 6% of the natural greenhouse effect is not to be sniffed at… nor dismissed as irrelevent with highly misleading arithmetic.

One could make the point that my calculations are ‘just another web page’ no more and no less authoritative than the links above. In some sense that is correct (though I’d argue my sourcing is a little better!). But you will never find a peer-reviewed rebuttal of such a bizarre line of reasoning as we are dealing with here – basically because such a line of reasoning is highly unlikely to make it past peer-review itself. There are innumerable ‘proper’ references to estimates of the climate sensitivity though, and one should indeed hesitate to accept calculations like this example over the mass of peer reviewed studies.

240 Responses to “Calculating the greenhouse effect”

  1. 1
    Coby says:

    Thanks very much for this one, Gavin. It comes up all the time on sci.environment and I have written arguments similar but without as good calculations and without the authority you bring to it! This will save alot of time.

    One frustration I have is a lack of references for CO2’s and H2O’s share of the GH effect. I use your “Feedback or Forcing” article and this quote of a quote of an offline text book here.

    Is there not some canonical reference (online) that presents a table such as yours out there? Is the table you did and the method you used as good as it gets? When people come to sci.environment with their 95% (sometimes 99%) I like to ask for a reference but don’t feel like I have a very solid offering of my own.

  2. 2
    Brian Forbes says:

    If H2O is not forcing it could not be a feedback.It must be a major contributor to the Greenhouse effect since its concentration in air on average is at least an order of magnitude greater than that of CO2 and it has similar spectral characteristics.

  3. 3
    Andre says:

    So let’s try to calculate the effect of doubling CO2 using David Archers Modtran 4 model here:

    To do that we need to look up from ground surface to see the increase of radiation flux (W/m2). So we do two runs as function of pCO2 sensor looking up at 0 km in the 1976 US standard atmosphere. We also use constant Relative Humidity to imply water vapor feedback. leaving the other parameters on the default. A pre-industrial pCO2 of 280 ppmv gives us an output of 257.323 W/m2, the double value 560 ppmv yields 260,526. hence doubling CO2 gives an increase of greenhouse effect / radiation flux of 3,2 W/m2.

    Now let’s get Stefan Boltman’s law out:

    expression 5:
    G = sigma Te^4 = (1-A) S / 4

    We can rewrite that as

    Te= ( (1-A) S / 4 sigma)^ ¼

    Substituting A (albedo) = 0,3 and S (solar flux) = 1367.6 and sigma=5.67E-8 we get the well known black body temperature 254.9 K or -18C.

    Since the average temperature is supposed to be 288K or 15,0C we increase the pure flux with Greenhouse flux (GHF), assuming albedo is zero for IR flux, and hence adjusting the relationship as

    Te= ( GHF/ sigma + (1-A) S / 4 sigma) ¼

    To get the 288K, 15.00 C degrees we see that we have to give GHF the value of 150.75 W/m2. So what would the new temperature be when we add that 3,2 W/m2 (GHF=153.95) for doubling CO2 from 280 to 560 W/m2?

    The answer is 15.589C..

    Hence according to your own MODTRAN4 tell us that doubling CO2 under constant relative humidity (positive forcing) gives us a temperature increase of 0.589 C.

    Hans Erren got a similar result:
    dT=0.6833 centigrade for a doubling of CO2

    Now some more about the positive feedback of water vapor. Soden et al developed their idea based on the eruption of aerosol giant Pinatubo and it’s apparent effect on MSU4 (stratosphere temperature) and MSU2LT (lower troposphere). However they failed to test their hypothesis to the other documented (radio sondes) aerosol eruptions of Agung 1963 and El Chinon 1982. That would have shown that stratosphere reaction would fit perfectly but the lower troposphere did not, which does no good to the credibility.

    Alternative calculations of feedback are here also not supporting the positive feedback ideas:

  4. 4
    Tom Brogle says:

    The contrarian seems well qualified to do the calculation he didn’t need Fox news.
    Bob Carter is a Research Professor at James Cook University (Queensland) and the University of Adelaide (South Australia). He is a palaeontologist, stratigrapher, marine geologist and environmental scientist with more than thirty years professional experience, and holds degrees from the University of Otago (New Zealand) and the University of Cambridge (England). He has held tenured academic staff positions at the University of Otago (Dunedin) and James Cook University (Townsville), where he was Professor and Head of School of Earth Sciences between 1981 and 1999.

    [Response:You’d think so…. -gavin]

  5. 5
    Andre says:

    A few more calculations.

    Playing a bit more with our spreadsheet and see the difference between then (280 ppmv CO2) and now (375 ppmv CO2). The modtran run says: 258.673 W/m3, hence a difference of 1,35 W/m2 with the 280 value (257.323). We run it in the equation increasing the GH factor to 152.1 to find a temperature increase of 0,25 degrees.

    Now how about the irradiation of the sun. What was that again. Look here:

    “…The new study shows that the TSI (Total Solar Irradiance) has increased by about 0.1 percent over 24 years. That is not enough to cause notable climate change, Willson and his colleagues say, unless the rate of change were maintained for a century or more…..”

    Really? now what if we increase the solar irradiance with 0,1 percent in our little formula? Hence S = 1381.3 and hence in the equation (G = 150.75) Te=15,44 C Hmmm A 0,44 degree increase.

    Let’s take G =152,1 again and S =1381.3. Then we get: T = 15,69 or a 0.69 increase. Isn’t it getting rather close with GISS temp and Jones et al?

  6. 6
    Leonard Evens says:

    Let me repeat the last sentence of the article.

    “There are innumerable ‘proper’ references to estimates of the climate sensitivity though, and one should indeed hesitate to accept calculations like this example over the mass of peer reviewed studies.”

    Lots of highly qualified people have looked at the issue of climate sensitivity. Their estimates, appearing in peer reviewed literature, fall within a relatively narrow range. One has to be credulous indeed to believe that a random geologist, not specially knowledgeable about the area, or someone making comments in response to this article is going to find something that all these smart people have missed. I know that this sounds like an appeal to authority, but do we really have a choice about that? My experience with research in my own field has taught me that whenever I enter a new field, I have to make all the standard mistakes before I even begin to understand the real issues. Even with a good background in physics and mathematics, it would take me a minimum of three to five years to even get to the point where I could start making mistakes in this field. That is what we have graduate schools for.

  7. 7

    Re #6

    I shouldn’t say that climate sensitivity of current models is in a “narrow” range, as the effect of a CO2 doubling is calculated between 1.5 and 4.5 K. Or 1:3. Or the difference between a benign warming and a probable disaster…

    The issue of climate sensitivity was already discussed on RealClimate: different climate models use different sensitivities for the different main forcings. Thus there are questions enough left for discussion.

    [Response: Not so fast. Different models produce slightly different sensitivities for different forcings, mainly related to the forcings’ spatial and altitudinal distribution. For instance, solar and CO2 have opposite effects in the stratosphere, black carbon in the tropics from biomass burning has a different effect from anthropogenic black carbon in the mid-latitudes where it interacts more with snow albedo etc. But these are all results, not assumptions – and the differences are not huge. See Hansen et al, 2005 for more details. -gavin]

  8. 8
    Hans Erren says:

    Given that even a 5 or 6 ºC cooling was associated with the huge ice sheets 20,000 years ago, and that 33 ºC cooling would reduce our planet to a near-snowball-like state, a potential increase of 5 to 6% of the natural greenhouse effect is not to be sniffed at… nor dismissed as irrelevent with highly misleading arithmetic.

    That’s Svante’s back of envelope, which is too much. Hansen makes it only 2.7. But this is an eqilibrium sensitivity which has a relaxation period of more than a century. Transient sensitivities (modeled and observed) point to 1 K/2xCO2 or 0.282 K/Wm-2

    (this entry is logged in ukweatherworld)

  9. 9
    Tom Brogle says:

    The experts have to find keep faith with the conjecture that CO2 causes Global Warming in order to preserve government grants and keep their jobs.
    No wonder they all agree.
    There are lots of illogicalities cited to support the conjecture on this web site and also in many of the refereed articles that appear in scientific journals.
    Read them with an open mind and you might also be enlightened
    I used to be a convinced believer in antroprogenic GW but the more I’ve studied the more skeptical I have become.

  10. 10
    Steve Bloom says:

    Re #7: This last statement reminds me of Bjorn Lomborg’s claim that he used to be an environmentalist until his study of various environmental problems caused him to see the light. It turned out later that the only evidence Lomborg could produce of his claimed environmentalism was that he had once made a modest cash contribution (of which there was no record) to Greenpeace. In other words, the more likely explanation is that he made up the environmentalist bit since it would be an effective ploy to promote his book.

  11. 11
    Stewart Argo says:

    Re. #9
    Strange, that. My experience is the opposite – the more I’ve studied the more convinced I have become.

  12. 12
    Coby says:

    re #9

    Given that the current largest funding source of climate science is also the most antagonistic to evidence of AGW (ie the US gov’t), one would expect that any political pressure would be in the opposite direction of what you suggest.

  13. 13
    Armand MacMurray says:

    Re #12:
    I think most of us would be quite surprised if the scientists reviewing US grant applications for climate science research (those who decide which proposals are funded) were really “…the most antagonistic to evidence of AGW…”.

  14. 14
    Armand MacMurray says:

    Re: #10
    OK, Steve, I’ll bite: which statement in #7 do you feel is self-serving, and most likely untrue?

  15. 15

    Re #7, Gavin’s comment:

    Gavin, indeed I have a tendency to jump to conclusions too fast to follow for other readers. In this case, the difference in general sensitivity for different models is mainly the result of how models treat cloud feedback.

    The difference in individual sensitivities by Hansen is based on different radiative responses in latitude and altitude. But even if this is a result of the GISS model, this largely depends on the assumptions made in the model for e.g. amounts and radiative effect of aerosols, which are far from settled. A recent study by Heald ea. shows that natural VOC induced aerosols above the boundary layer are mostly of natural origin (7:1), and comprise a 2:1 up to >10:1 amount, compared to SOx (SO2+sulfate) aerosols in the 0.5-10 km free troposphere, or 10% of the total aerosol optical depth measured by satellites… Add to that the effect below the boundary layer and the effect of other natural aerosols (natural fires, sea salt, sand dust, DMS, NOx), good for some 38% of the < 1 micron fraction of total aerosols (according to IPCC estimates)…

    Further, Hansen concludes that solar sensitivity efficacy is around 0.92 the efficacy of CO2, while the Hadcm3 model only uses 0.5. I am interested to know what other models use as individual sensitivities…

    [Response: They don’t use, they produce… PS. do not use a raw < symbol in comments, it is interpreted as html. Use “& l t ;” instead. -gavin]

  16. 16

    Re #10&14:

    I suppose that this is a reaction on comment #7 which is deleted?

    I still am an environmentalist, be it less active than end 1960’s when being an environmentalist was very necessary and costed a lot of individual money (compared to the not so bad wages of some rich NGO’s today…). See my short cv here

  17. 17
    Brian Jackson says:

    Re #1 Coby, One possibility is this paper by Kiehl and Trenberth.

  18. 18
    Hans says:

    Re#9: The funding/ ad hominum argument is wearing a bit thin.
    The people who are involved in climate research are intelligent and highly qualified. If they wanted to they could get good jobs in the commercial world. Science does not pay very well. If a scientist would want more money (s)he would change jobs, not manipulate the research.

  19. 19
    Stephen Berg says:

    Re: #2, “If H2O is not forcing it could not be a feedback.It must be a major contributor to the Greenhouse effect since its concentration in air on average is at least an order of magnitude greater than that of CO2 and it has similar spectral characteristics.”

    The first sentence is dead wrong. As a result of climate warming, water vapour increases, which is a feedback loop. This is caused by the increased moisture capacity of the atmosphere with increased temperature, as well as warmer oceans, seas, and rivers, which leads to increased evaporation rates.

    Water vapour is a major contributor to the greenhouse effect. That is correct. However, it is a result of the feedback described above which increases water vapour in the atmosphere.

    What is the principal cause of this feedback over the last century-and-a-half? Human activities which produce greenhouse gases, such as CO2, methane, and others!

    What must we do to minimise this feedback loop and prevent long-term catastrophic events in the very near future? Reduce greatly our GHG emissions!

  20. 20
    Dragons flight says:

    I’ve never really understood why people like to talk about the world without water vapor, because I surely wouldn’t want to live there.

    It seems to me that if one wants to make an apples to apples comparison about the relative importance of different climate forcing factors, then one ought to be looking at their differential impact under modern conditions. In other words, if I increase substance X by 1% in the atmosphere, what is the effective change in radiative forcing (or temperature), either with or without water vapor feedbacks? I’ve never really seen anyone put it in these terms for the modern atmosphere, and I don’t really know why not, though some results on long-term forcing changes do allow one to ball-park the differential effect.

    Is anyone here familiar with literature that compares the effectiveness of various forcing factors in the modern atmosphere under small perturbations?

  21. 21
    Hank Roberts says:

    > compares the effectiveness of various forcing factors …

    Lots. Also depends on whether you measure at the source or after mixing. (mention) (PDF)

  22. 22
    Steve Bloom says:

    Re #s 10, 14 and 16: Just to clarify, what is now comment 9 was comment 7 at the time I submitted my response. This re-ordering happens sometimes when comments come in almost simultaneously. Just to clarify, generally I feel that someone’s background is irrelevant to the validity of their views on climate *except* when this particular conversion is claimed. Normally, as with Lomborg, there is little evidence to back up such claims.

  23. 23
    Lynn Vincentnathan says:

    I think I could make an argument why there’s no gravity on earth. For one thing universal gavity (according to my high school physics course) has to to with mass – the more mass the greater the gravity. Well, dah, the sun has a lot more mass than the earth and would be counterbalancing all of earth’s gavity many times over. Ergo, earth doesn’t have any measurable gavity that would affect us humans. But because we are suffering under the delusion that it does, we obstinantly cling to earth.

    Then, of course, there are birds & airplanes that prove beyond any doubt that earth’s gavity just doesn’t exist, at least not in any significant amount that would affect any of us.

    As for things that come back down to earth when we throw them up in the air, well that’s a matter to them bumping into all those natural & human-emitted GHGs up there & bouncing back.

  24. 24
    Dave Nicosia says:


    The confusing thing for me is radiatively CO2 has its greatest absorption of IR radiation from about 14 microns to 20 microns wavelength….(which corresponds to -50C and below by wien’s displacement law). The Water vapor bands totally overwhelm the CO2 contribution above -50C….is that correct? So increased CO2 should have it greatest leverage on the climate system in places where the mean temperatures are -50C…which is Antarctica for example. There has been basically no trend there in the last 50 years as CO2 builds up. What gives here?

    Also, in the ice core data, CO2 appears to passively follow the inferred temperature trends through the millenia suggesting
    its concentration follows the glacial to interglacial periods and the increased solubility of the oceans at lower temperatures.

    We all have to remember it is a trace gas….and it has increases 100 ppm in 140 years. Yes that is significant, but enough
    to throw the earth’s climate out of whack?

    Also, has anyone proven the increased absorption of IR radiation from increased CO2? Aren’t there satellites that measure outgoing long wave radiation? Shouldn’t we see less OLR for a given temperature at the surface. If you look at these curves….the higher the temperature in a region, the more OLR. Has anyone actually proven that CO2 is reducing OLR from the surface or lower troposphere for the same temperature? I have never seen this in the literature.
    That would be a smoking gun!

    The water vapor feedback is hard for me to understand. More water vapor eventually will equal more clouds and precipitation which is a sink of water vapor and a therefore primary greenhouse gas. Are we certain that the RH will remain the same? I saw your Mount Pinatubo stuff…interesting but it don’t feel conclusive to me. Also if there is a strong water vapor feedback, then when the CO2 concentrations rose 100 ppm between glacial and interglacial periods, why wasn’t the climate system thrown out of whack? Based on the modelling what is the “breaking mechansim” to keep the earth from becoming like venus?
    I believe this is the precipitation, snowfall and ice accumulations.
    The oceans also are a huge storage house for heat to stablize the climate system and restore balance. I would like to see some proof that CO2 increases are causing less long wave radiation to escape given a certain temperature. That would be neat.

    What about solar forcing? The 20th century has had the highest solar activity in a long time (1000 years?)after a period of a quiet sun during the little ice age. Can’t this recent warming be natural from changes in solar activity?

    Yes I believe the earth has warmed since the 1960s…but before that I think the records are questionable. The satellite record finally is showing some small warming. So i do believe we are on an upswing. It could end abruptly….I wouldn’t be surprised. Can we really say its from anthropogenic causes though? I am not convinced but open to learning more.

    Thanks. Look forward to your reply. I am really curious about this stuff and find your blog very informative!!!

  25. 25
    Eli Rabett says:

    Re: #2, “If H2O is not forcing it could not be a feedback.It must be a major contributor to the Greenhouse effect since its concentration in air on average is at least an order of magnitude greater than that of CO2 and it has similar spectral characteristics.”

    The second part is also wrong. The IR absorption spectrum of water is very different from CO2. To see this go to

    CO2 has two allowed IR absorptions, only one of which is very important for atmospheric processes (the bend at ~650 cm^-1). That is the big absorption you see if you run the calculation at the web site. (Wavenumbers are cm-1) The absorption bands of CO2 are compact, extending ~50 cm-1 on each side for atmospheric conditions. There is no allowed rotational absorption at lower frequencies.

    Now set the CO2 concentration to zero and run the calculation again. Water vapor has an allowed rotational spectrum that extends from ~100 cm-1 to 700 cm-1 or so. That is the hash that you see in the figure. The lines are widely separated, unlike the case for CO2. The hash to the right of the figure at ~1200 cm-1 is the IR spectrum of the H2O bending mode.

    The compact peak at ~1100 cm-1 is from ozone. You can see this by zeroing out the trop and strat ozone.

    Rerun the calculation at ~ 1,2,3,4 km altitude with full O3 and CO2. The reason you see little net absorption at 1 km is that the emission from the relatively warm CO2 and H2O balances the absorption.

  26. 26
    Eli Rabett says:

    Oh yes, one other thing about, that I think Andre misses. The surface temperature is fixed for the calculation, thus just holding relative humidity constant does not capture the full effect of any water vapor feedback. To do so, in a quick and dirty way, you have to raise the temperature in the “Ground T Offset Box” This makes quite a difference. If you raise the ground temperature 3 C, the intensity is 269.6 W/m2, an additional ~9 W/m2.

    I REALLY like that site. Thanks again to the Chicago crew for maintaining it.

  27. 27
    Chris O'Neill says:

    Re #3

    Doubling the CO2 in Modtran 4 creates an atmosphere that radiates more IR to the ground but that atmosphere also radiates LESS IR into space. e.g. looking down at 70km, a doubling of CO2 from 280ppmv to 560ppmv causes the radiation to drop from 260.023W/m2 to 257.197W/m2. The problem now is that the earth is no longer in thermal equilibrium, so even if the earth’s surface did only warm up by 0.589C initially, it is going to keep warming up until it achieves thermal equilibrium. I invite everyone to try Modtran to find what the surface temperature would be that achieves thermal equilibrium.

  28. 28
    RON MANZI says:



    [Response: Please avoid all caps comments in future. They are inappropriately visually loud. Thanks. -Moderator]

  29. 29

    I wrote a very crude, semi-gray RCM for Earth using a fixed convective adjustment of 6.5 K/km and accounting for 19 spectral bands for H2O, CO2, O3 and clouds. I used the Kiehl and Trenberth (1997) cloud scheme. The model ended when dT/dt for all layers becamse less than 0.001 K. The time step was 1 day, cutting in half after every 500 cycles to ensure convergence. :)

    The first run, with 380 ppmv of CO2, gave a surface temperature of 288.3 K after 525.5 simulated days, with surface illumination 0.489 of incoming visual light, and wound up with a TOA discrepancy of 8.0%.

    The second run, with 760 ppmv of CO2, gave Ts = 294.9 K, 349 days, 0.460 surface illumination and 9.3% I/O discrepancy at TOA. So my surface temperature increase by doubling CO2 alone (no H2O or other feedbacks) is 5.6 K. This is very much on the high side; Houghton (2004) makes it 1.2 K for doubling CO2 alone.

    But if you represent the physics even close to accurately, you get a much huger effect from doubling CO2 than from the (contrarian) calculations above.

  30. 30
    Tom Brogle says:

    If H2O wasn’t forcing at a low concentration (Estimated to be between 0.7% and 1.0% at 15 degrees)It woulld not be forcing at higher concentration ( between 0.91 and 1.3% at 19 degrees) You cannot say that CO2 is causing the water vapour to rise. Temperature rises increase both CO2 (released from a warmer sea) and H2O {evaporated from same).
    Water vapour must be the major temperature forcer because it present in air at a much higher concentration than CO2.
    We could theorise that H2O has fed back on itself and but for clouds the earth would have overheated long ago
    Increasing H2O in the air would produce more clouds producing perhaps a negative feedback.

  31. 31
    Pat Neuman says:

    Stewart wrote (#11.) : “Strange, that. My experience is the opposite – the more I’ve studied the more convinced I have become”.

    Same with me, Stewart… although I became convinced six years ago… but I’m still learning. For instance,

    Tom Brogle wrote (#9.) : “The experts have to find keep faith with the conjecture that CO2 causes Global Warming in order to preserve government grants and keep their jobs”. …

    I learned quite a bit in reading at the links and article posted to RC Jan 2, 2006 titled Polar Amplification.

    Reading Polar Amplification motivated me to create spread sheet temperature plots with data at climate stations in Alaska, SD_ND MN_WI MI_IND and WA_OR … (1888-2005).

    After doing all that, and in actually seeing the high latitude warming amplification, the only kind of global warming that could be happening is greenhouse gas driven, in order to explain the amplified warm overnight low temperature observations shown in the data as occurring in higher latitude areas… where low humidity air is transitioning into air with higher humidity levels (H2O GHG). If we were to have global warming from a more intense period of solar radiation, the high latitude warming amplification would not be taking place in that manner.

    The obvious explanation for the GHG driven global warming is the heavy CO2 accumulation in the atmosphere which is being observed and monitored by NOAA CMDL CO2, showing rapid accumulation of CO2 in the atmosphere at sampling points at many measuring sites throughout the world. From my perspective, the case is closed… the primary cause of the rapid global warming in progress is the billions? of tons of CO2 which have been emitted into the atmosphere by our burning of fossil fuels for power generation.

    My surface climate station average temperature plots for AK, the Upper Midwest and the U.S. Northwest are at:

  32. 32
    Stephen Berg says:

    Re: #30, “Temperature rises increase both CO2 (released from a warmer sea) and H2O {evaporated from same).”

    CO2 increases are, therefore, both a forcing and a feedback. CO2 is emitted due to human activities, forcing the temperature to rise. As the temperature rises, CO2 is emitted from the oceans, forests, etc., which is a feedback.

    Increasing water vapour concentrations does increase clouds, but only in the situation of temperature increases, the current situation of which is primarily the result of human activities. This may help the Earth keep itself from burning up for the short term. However, clouds also increase incoming longwave radiation, which keeps the heat inside the troposphere, yielding warmer temperatures.

  33. 33

    Re #3, specifically to the references to work by the Estonian statistician, O. Karner.

    Karner has been taking single time series of diurnal temperature differences and showing that they act as if they are constrained to return to a fixed value. The statistical properties of this time series are “antipersistent” and may be associated with a feedback in a simple lumped parameter model. This is a purely statistical rather than physical model, and it shows there is a homeostatic process, with a number that can be considered “the feedback”.

    Unfortunately, it appears to me that Karner confuses this mathematical property with the H2O amplification of radiative forcing, a physical quantity with which Karner’s feedback constant has only a distant relationship.

    Indeed, there is an antipersistence in temperature anomalies on Earth, and the mechanism is well-known: radiative equilibration. In this phenomenon, water vapor plays an important role but it isn;t a soliloquy. Thus, when Karner says things like (see )

    The revealed antipersistence in the lower tropospheric temperature increments does not support the science of global warming developed by IPCC [1996]. Negative long-range correlation of the increments during last 22 years means that negative feedback has been dominating in the Earth climate system during that period. The result is opposite to suggestion of Mitchell [1989] about domination of a positive cumulative feedback after a forced temperature change

    to my reading he is confused. (I am surprised this text passed review at JGR-A.)

    His subsequent paper ( ) seems to show increased awareness on the matter:

    Using the H estimates to ascertain the cumulative feedback sign dominating in the Earth climate system for the particular variable. In the present study the term feed-back is used in the sense of total reaction of the variable to customary forcing in the Earth climate system. Such an understanding is unavoidable in statistical analysis of meteorological time series because, as a rule, they are affected by many forcing types including the seasonal and daily cycles in solar radiation. In climatology the term feedback is usually connected to the corresponding feedback loop, e.g ice-albedo feedback [13]. For the whole climate system this means that one has to consider many feedbacks at the same time.

    Karner’s methodology does not separate out specific physical mechanisms but is simply a way of characterizing a time series. It in some sense includes but (as I understand it) in no sense measures the impact of water vapor feedback on radiative equilibrium.

  34. 34
    Stephen Berg says:

    “2005 Was the Warmest Year in a Century”:

    “The year 2005 may have been the warmest year in a century, according to NASA scientists studying temperature data from around the world.

    Climatologists at NASA’s Goddard Institute for Space Studies (GISS) in New York City noted that the highest global annual average surface temperature in more than a century was recorded in their analysis for the 2005 calendar year.”

  35. 35
    Tom Brogle says:

    Re 31
    That is only a local effect (same as medieval optimum} so cannot be global.
    Some of the highest temperature rises are in places where the population has increased over the last century Did you account for this effect in your calculations.
    Why is Antartica coolng?
    Why is the wjnter ice pack around it as extensive now as it was in 1912 (a bad year for ice)?
    Why was Nansen able to sail his ship right up to 79th parallel above the East Siberian Isles in Nov 1893? I doubt that it will be possible in Nov 2006, it certainly wasn’t in Nov 2005.
    Have a look at the crude Sea Surface Temperatures published in Nature in 1995 and you will see that SSTs in 1860 were as high as the were in 1980.
    History does not agree with the CO2 causes GW conjecture.

  36. 36
    PHEaston says:

    To qualify the claim in No.34:

    NASA states that the reason their result is higher than others is because they use a different method which includes more weight to the Arctic. This includes an extrapolation of temperature estimates to as much as 1200 km from a station. While they have faith in this method, they state; “in some cases this method can increase error by giving undue weight to one isolated station with anomalous temperature.” NASA aknowledges that results from other eminent groups do not rank 2005 as the highest, and state “the ranking of individual years depends upon differences of only a few hundredths of a degree, which is finer than the accuracy that any method can achieve given observational limitations.”

    This is all in the link.

  37. 37
    Coby says:

    Some of the highest temperature rises are in places where the population has increased over the last century Did you account for this effect in your calculations.

    Hi Tom,

    Which places are you thinking of? The most pronounced warming is occuring in the Arctic regions, where there is no urbanization. The Urban Heat Island effect is well studied, very minor and yes, it is accounted for. Check the details of the GISS anaysis here:
    Also look at the global anamoly map and you will see that urbanization is not a good predictor of warming at all. It is pretty clear that UHI can not explain the observed warming trend.

    All that is not even to mention that satellite measurements show similar warming of the troposphere and borehole records also indicate similar surface warming. There is just no credible reason to doubt the surface temperature analysis.

    Whatever website you are reading that is telling you UHI is the cause of a spurious warming trend is either very outdated, very uniformed or very dishonest.

    Why is Antartica coolng?

    I don’t believe this is a correct statement as you have it. What is your source? The continental antarctic AFAIU is showing very little trend, while the peninsula is warming. But as you pointed out regarding someone else’s information, this is regional, the causes will be regional. I believe regional factors in the Antarctic include currents in the Southern ocean and ozone depletion.

    Why was Nansen able to sail his ship right up to 79th parallel above the East Siberian Isles in Nov 1893? I doubt that it will be possible in Nov 2006, it certainly wasn’t in Nov 2005.

    Source? But do you really consider a single anecdote from over 100 years ago to be cause to doubt the millions of temperature measurements we are looking at today? If the “GW alarmists” were telling you such stories with an opposite spin, from long dead Russian sailors, would you find that compelling? The best information about arctic ice is satellite information. Unfortunately we have not had satellites in orbit for long enough to use sea ice extent to confirm the 150 year surface temperature records. But it is notable that for as long as these records exist, they say the same things.

  38. 38
    Coby says:

    To qualify the qualification in 36 to 34 ;)

    NASA also states:

    Record warmth in 2005 is notable, because global temperature has not received any boost from a tropical El Niño this year. The prior record year, 1998, on the contrary, was lifted 0.2°C above the trend line by the strongest El Niño of the past century

    As you say, it’s all in the link! (Though note that my quote came from

  39. 39
    Lynn Vincentnathan says:

    Re#9, okay, skip the science. What’s impressed me is that the ocean has warmed by 1/2 a degree. Now air warming that much doesn’t impress me quite as much as the ocean warming. Do you know how vast all the waters in the oceans are? A half a degree is a really impressive indicator of the earth system absorbing extra heat. I may be wrong, maybe air is a better indicator, but I know in the kitchen, a 12 quart pot of water takes for ever to warm up, much less boil, even while inputting maximum heat from the burner. I think GW denialists should really spend more time in the kitchen.

    As for other arguments–that there is warming, but not from human emitted GHGs–it seems to me all other explanations have been pretty well shot down. At the very least those explanations are no more the likely suspect than A-GHGs. So, it really does behoove us to reduce our GHGs, on the outside chance (as you seem to think) that we are indeed warming our world.

    See, you don’t need to be a rocket scientist or even a climate scientist to figure things out, and what to do about them. And luckily most solutions also save us money! I really think denialists should try a few money-saving solutions, just give them a little try. I assure you you will not regret it. It’ll make you feel good, sort of like you’re cheating Economics 101 – saving money, while doing good to the world.

  40. 40
    Pat Neuman says:

    In 35: Tom wrote… “That is only a local effect” (#31.) .. “cannot be global”.


    Polar amplification isn’t global, the enhancement is in high lat. areas.

    Furthermore, I didn’t do the calculations, cooperative observers with the NWS did, along with Microsoft Excel software. Furthermore again, Antarctica is not cooling. I pay attention to recent articles, data and reports by Will Steger, polar explorer from Minnesota by dogsled.

  41. 41
    Hank Roberts says:

    Tom — references, please? Assuming you know for sure what you’re saying is true, you can give us links or footnotes so we can find exactly the same thing. If you got it from a second-hand source, give us your source.

    If you don’t have a reference, you’re asking us to check for you whether what you’re posting has facts behind it. Probably it does, but everyone’s got a life, don’t ask us to find your facts based on what you say, eh?

  42. 42

    Re #31:

    If we were to have global warming from a more intense period of solar radiation, the high latitude warming amplification would not be taking place in that manner.

    Pat, if the Alaska/Arctic warming was 100% solar driven, this would have the same effect, even more pronounced, as solar has it’s highest effect in the tropics and in the stratosphere (while CO2 effects are more evenly distributed in the troposphere). This causes stratospheric temperature differences which drives planetary waves / jet stream position / rain/clouds more to higher latitudes. And has an effect on the Arctic Oscillation, where warmer/moister air is driven into the Arctic. Thus it is difficult, if not impossible, to say what is attributable to GHG forcing (with feedbacks) and what the part of solar forcing (with feedbacks) in the amplified Arctic warming is.

    The recent warming in the Arctic anyway is not direct from regional CO2, as the observed warming needs a heat/radiation unbalance which is an order of magnitude larger than the direct change in radiation caused by CO2 increases…

  43. 43
    Pat Neuman says:

    Ferdinand, in 42 you wrote: “Thus it is difficult, if not impossible, to say what is attributable to GHG forcing (with feedbacks) and what the part of solar forcing (with feedbacks) in the amplified Arctic warming is”.

    It isn’t that difficult, and certainly not impossible, to see the difference between global warming triggered by GHG emissions and global warming initiated by a solar radiation surge. For example, the hot and dry dust bowl years, early 1930s, cannot be attributed to GHG accumulations. If that were true, warmer and more humid conditions would have lasted for centuries, not years.

  44. 44
    Coby says:

    Re 43,

    Careful here, Pat, you are talking about weather, not climate! There are plenty of predictions of drought in the coming century due to GHG driven warming. On smaller spatial scales and smaller temporal scales (such as ~10 yrs and a portion of the continental US) climatic trends can easily be dominated by regional effects.

  45. 45
    Pat Neuman says:


    I don’t see how you interpreted what I said in #43 to be what you said I said, in #44.

    In saying what I said, in #43, I was thinking about what it says below.

    “One look at the graph below shows some interesting results. The first of which is the minima beginning in 1924 and lasting until 1937. This stretch of lower dew points matches well with the dust bowl era when precipitation was also at a minimum”.

    103 Years of Twin Cities Dew Point Temperature Records: 1902-2005

  46. 46
    Pat Neuman says:


    I read this article on solar variability by Drew Shindell a few years ago, which may help explain what I was trying to say in #43.

    “Through this coupling, however, solar variability affects the lower atmosphere by changing the distribution of the large amount of energy which is already present. The impact on global average temperature seems indeed to be small; however, changing the flow of energy produces large regional impacts”.

    Solar Variability, Ozone, and Climate
    By Drew Shindell – March 1999

    I consider weather to be what happens in the short term, less than 90 days. NOAA’s NWS Climate Prediction Center gives “climate” predictions (outlooks) for the U.S. for periods extending to 90 days, 120 days, etc.

  47. 47
    Coby says:

    Pat, I have always thought climate was much longer term than a few months. I am sure I have seen 30 years thrown around, though I don’t know if there is a consensus definition of this or not. That’s why I thought it was incorrect to infer anything about a climate change, much less what forced it, from a regional drought that was less than a decade.

    I did reread the thread, and I think I still agree with Ferdinand about not being able to seperate solar forcing vs GHG forcing based on regional responses.

  48. 48
    JohnnyBGoode says:

    #43, 45 & 46

    “It isn’t that difficult, and certainly not impossible, to see the difference between global warming triggered by GHG emissions and global warming initiated by a solar radiation surge.”

    You still have not made a case for the above claim. Neither the dust bowl of the 1930’s nor dewpoints in the Twin Cities point to a source of global climate change. If we could look at regional weather or even regional climate and deduce the source of global climate change anyone could be a climate scientist.

  49. 49

    42, Ferdinand, Although RC scientists have patiently debunked this solar effect, I repeat myself through 2 pictures in order to reinforce this debunking in near real time, it is hoped that you will appreciate the meaning of this January’s incredibly warm winter (Moscow appears back to normal temperatures now), and contrast it with 2004-05 winter. Your reasoning is that the signal given by much warmer temperatures may not be attributable to CO2, and only solar forcing generated this winter heat wave, rings wrong. On my website look at the news item on the top of the page, the two sun comparison, the one to the left ( early November 2004) shows a huge sun spot, the summer/ fall of 2004 had several sun spots, in large contrast to the summer fall of 2005, almost none were seen, 2005 was a weak year for sun spots. You would probably agree that solar activity was less in 2005, yet 2005 was #1 warmest in history. Go back to the sun disk comparison , the one to the right devoid of sun spots (October 30 2005) taken at the same astronomical elevation, is almost round compared to 2004 shot. You are looking at sun disks penetrating 200 km of high arctic troposphere, and clearly 2005 disk shows by a refraction analysis a less colder atmosphere than 2004. Despite lesser solar activity, it is warmer. So what triggers this warmth? In less than a year… It is likely as explained a combination of gradual GHG heat build up, (ice melting) finally triggering more specific humidity , a greater water vapor presence, especially due to open water of the more open Arctic Ocean Your solar explanation fails and should be put to rest. You may continue defending this idea, I can’t see how given this sun spot conundrum.

  50. 50
    john mann says:

    re #39 Lynn
    Remember that the ocean is heated from the surface, and that warmer waters would have less tendency to sink. Increases in surface temperatures don’t necessarily mean that the bulk oceans have warmed.

    Wouldn’t this in fact be a very slow process anyway? And to get warm water to sink it would have to be very saline indeed. Has anyone done any detailed work on heating of water columns?