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Modeller vs. modeller

Filed under: — gavin @ 20 October 2005







  3. What are the dominant external forcing functions?


  4. What are the sources of intrinsic variability?

















52 Responses to “Modeller vs. modeller”

  1. 1

    A very good summary, but in listing the greenhouse agents and aerosols you never mentioned clouds! Clouds are an important part of the climate system; they provide greenhouse warming through infrared absorption (clouds are often blackbodies past 4 microns or so), and cooling through albedo effects. You did mention cumulus convection, so I’m sure this was just an oversight. I’m crazy about clouds, what can I tell you.

    [Response: The listing, I think, was of those things you have to impose. The model generates its own clouds. Of course you do have to get the cloud scheme right - William]

  2. 2
    Tom Fiddaman says:

    The sequence of questions (if it means anything) is quite interesting. In rough order are numerics, forcings, intrinsic variability, fit to data, prediction, and quality control. Extreme conditions tests for robustness aren’t mentioned, though in my experience with policy models they are the most efficient way to detect many flaws. To what extent is this done with climate models, and what does it show? For example, if you suck all the water out of the atmosphere, do the models blow up because you get outside plausible bounds for parameterized relationships, or do they return to some reasonable state?

    [Response: I did that one already: see here - gavin]

    In the policy space, the order of questioning is quite different. People tend to rely on fit to data to the exclusion of all else, even though it’s a weak test. The next question usually concerns forcings (which are routinely tweaked to yield desired results). Predictive performance is seldom tracked, documentation and replication are spotty, and numerics aren’t on the radar. It’s no wonder that people are skeptical of models when the world is polluted with bad ones; too bad their skepticism isn’t better directed.

  3. 3

    Re: #1

    There is a nice article on why here.

  4. 4

    Re #3,

    The previous discussion is about water vapour feedback, not directly clouds. While the two are connected, there are variations in cloud cover directly connected to the solar cycle (+/- 2% over a cycle, see the Kristjansson e.a. paper). Global figures for humidity changes during a sun cycle are more difficult to find (precipitation is available, but that is not only the result of humidity), would be interesting to see if they correlate.

    Clouds indeed are the main problem in current GCM’s and are responsible for most of the wide range projected for a CO2 doubling.

  5. 5
    Lynn Vincentnathan says:

    The good old days of simple science was about doing experiments on isolated variables in clean laboratories & finding (for example) X causes Y. That was the Enlightenment’s analytical (cut up) world, where reality was sliced down into parts — sort of like my brother-in-law taking the old clock apart to see how it works — until it is no longer living reality, but sort of a corpse on which autopsies are done.

    In the real world there are a myriad of variables impacting both X and Y (if one dares to ferret out variables from the living, moving world). I think if it were not for the seriousness of AGW, science would not be so bold in rushing to understand almost the entire real, living world “as is” (r/t a more manageable few isolated variables).

    I see modeling as an attempt to break through from the Enlightenment project (of getting down to the subatomic particle) into a higher level of, shall I say, “holistic” understanding. Contrarians (& perhaps we all) who are back there disputing the number of angels on the head of a pin are unable to grasp either this new project, or the seriousness of AGW — which words and science fail to express adequately.

    The point is we really won’t be able to put the clock back together again or bring the body back to life if we fudge this experiment, so we should tread lightly and try not to destroy our life-support systems.

  6. 6
    Lawrence Coleman says:

    Nice article…but I was really brought up short by the ending:

    OK, I can accept that the models are not the WHOLE case for AGW but I would certainly have given them – and have given them – a bigger role than you seem to. But they do seem “fundamental” to me. Without the models how can one figure out what is human-caused and what is natural warming/climate change? On virtually a daily basis one sees news stories of receding glaciers, melting permafrost, greater hurricane intensities, warmest century in the past millennium, and on and on, but I have always put those in the “anecdote” category as far as AGW is concerned: they raise the question but do not answer it. Further, as a theoretical physicist I am eager to believe that theoretical physics has something to say but I am unable to see how it can do more than make qualitative arguments (in the absence of models) regarding global warming or climate change. I do believe that adding greenhouse gases to the atmosphere will increase the global temperature just as adding another blanket layer on the bed will make one warmer, but this statement has almost zero worthwhile content. While not a AGW skeptic, I am sensitive to the use of anecdotes in lieu of good, hard scientific analysis. While not suggesting that you are guilty of that, I am very interested in knowing what the thinking behind your “final note” was?

    [Response: Well, I am talking about the role of the full climate models, and since I work on these full time, I obviously feel that there is an important role that they can play in make quantative sense of climate change. I don't mean to imply that the role of 'models' in a more generic sense isn't necessary for understanding AGW. Radiative transfer is obviously a good example that helps quantify the role of the different greenhouse gases and aerosols. Those 'models' exist separately from the large GCMs. The bigger point I was making was that criticism of GCMs is often taken as being a major argument against AGW, and I am trying to point out that doesn't really follow. -gavin]

    [Response: Perhaps I should answer this, because it was me who suggested to Gavin to include that final note. So, what does the case for anthropogenic warming rest on?

    (1) The fact that humans are increasing the CO2 concentration. This increase is measured in the atmosphere, and the ice core data show that current levels far exceed those of any time during the past 650,000 years. That humans are responsible for this rise is clear, as the observed rise represents only 56% of our cumulative fossil fuel emissions - that means that the natural system (oceans and biosphere) have taken up some of the CO2 we have added to the atmosphere. (In the oceans this is also a measured fact.) So, no model needed at all for proving point 1.

    (2) CO2 is a greenhouse gas that will warm the climate, with a sensitivity of about 2-4 ºC for a doubling of CO2. The fact that CO2 is a greenhouse gas absorbing long-wave radiation is based on lab measurements and was recognised in the 19th Century. Many data from climate history confirm this, e.g., in high-CO2 climates such as the Cretaceous the planet tends to be free of ice, and after a major carbon release to the atmosphere (the Paleocene-Eocene Thermal Maximum 55 Million years ago) the climate warmed by several degrees. The crux is of course to quantify the effect - this is where models are most useful. But remember that Arrhenius first did it in 1896, without computer, arriving at 4-6 ºC warming for CO2 doubling. A bit high as we now think, but our understanding of the physics has advanced during the intervening hundred years. What is required is an estimate of the major feedbacks, i.e. water vapour, cloud and albedo, the variation of which can be measured during the seasonal cycle. Another way to do it is by multivariate regression analysis of past climate data, as the Vostok ice core team has done (Lorius et al., Nature 1990), arriving at 3-4 ºC for CO2 doubling. So if we had no computers, we would still have arrived at a very similar estimate of climate sensitivity, albeit less certain.

    The two points above lead to the conclusion that further CO2 emissions and consequently a further increase in atmospheric CO2 concentration would lead to warming of the magnitude shown in the well-known IPCC scenarios. All you need to do there is include the ocean's thermal inertia to get the timing right, but this can be estimated in a simple analytical calculation, based on our knowledge about ocean thermal structure obtained from measurements, again no computer required.

    Concerning the consequences of this warming, just one example of many. The data analysis of Kerry Emanuel on hurricane energy shows (a) a strong correlation of hurricane energy and SST, and (b) an increase of both during the past decades, where the SST in the tropics in the hurricane season increases roughly as much as the global mean temperature. These observations would strongly suggest there is a connection of global warming and hurricanes, again without using a computer model.
    - stefan]

  7. 7
    Sashka says:

    I agree that it was a very good Q&A session even though I find (9) too optimistic. But we kind of touched on it in the other thread.


    The latter seems alarming. Could you provide more details? I couldn’t find anything on that in the linked paper. What is degrading and why (if known)?

    [Response: Parameterisations are designed to work at particular resolutions, and so if the resolution changes it's likely that some of the parameterisations would no longer be optimally tuned. Thus simply increasing the resolution does not automatically improve the simulation. However, that isn't to say that we can't eventually get the higher resolution model to be better than the low resolution version, but it takes work and we aren't there yet. -gavin]

  8. 8
    Keith Moulton says:

    About the GISS model, what is the maximum hypothetical global warmth and cooling it can reasonably project? (If all existing fossil fuels were somehow released into the atmosphere within a century, for example.) And can the GISS model project the kind of CO2 declines seen at the beginning of every ice age? David Archer’s comment in this post (#32: “Surprises that could change this [the natural dissipation of CO2] include going into a glacial climate state, which had the mysterious ability to draw down CO2 in the past…”) suggests not.

    [Response:Well in tests we've managed to make the GCM glaciate to the equator (by mistake), or increase the temperature by a fair bit, but we've not yet turned everything up so far that the code breaks. Note that the carbon cycle isn't yet included in most GCMs, and so internally calculating CO2 levels isn't part of the model. It's something we are working on though. -gavin]

  9. 9

    General question in re: models. Can anyone point to any link(s) that show the climate model(s) as block diagrams revealing their internal causative connections?

    [Response: There is a general lack of this kind of info (as far as I'm aware) - William]

  10. 10

    There is some discrepancy between the global temperature data series by Hansen in his response to Crichton and the NASA/GISS data. The latter trend is app. 0.5 C for the period 1960-2004, while Hansen gives 0.6 C for the same period. Until 1988, the year of his testimony, the trend in both graphs is about the same (~0.3 C).

    May we conclude that the Hansen’s projection in 1988 (even for the lowest scenario C) was some 50% over reality, 15 years later?

    [Response: No. The data you link to are two different indices (as you are well aware). The data plotted in the Hansen plot is the global mean anomaly estimated from the met. station network, and the second data is the index that includes SST anomaly data as well over the oceans. All of these data are available from the GISS website. The first data set was the one used in the original papers, and so it makes sense to continue the data using the same index. The difference from 1988 to 2004 in both datasets is the same (around 0.2 deg C) as it is in the model run. There is no way you can get a 50% error from that. -gavin]

  11. 11
    Arun says:

    I take answer #2 to mean that the butterfly effect is not yet decided.

    Can’t you take out many variables and model Mars?

    [Response:#2 has nothing to do with the butterfly effect (but let's not get into that here). To model Mars you need to take out all the water-related physics, and add in dust and CO2 sublimination physics. It has been done before, but not (yet) with our latest GCM. I don't suppose you are looking for an open-source climate modelling problem? -gavin]

  12. 12
    Sashka says:

    Re: 7

    I was asking specifically what was degrading…

    [Response: The matches to surface air temperature, precip and stratospheric temperatures are all a little worse (Table 5 in Schmidt et al linked above). It's nothing dramatic, but you might have expected better. -gavin]

  13. 13
    Brooks Hurd says:


    It appears that you are saying that even though the models are imperfect, that you can take functions from theorectical physics and historical data to support the projections of the models. I would have thought that theoretical physics and historical data would have been used in part to construct the models.

    Am I missing something?

    [Response: I think you've missed the point, which is: that many people seem to think that concern is *entirely* generated because of model output. This is wrong. The models are merely trying to quantify the warming that theory and observation tell you to expect anyway - William]

  14. 14
    Tom Rees says:

    Re #8 – about the maximum warmth possible in the GISS model. You might like to know that an older version of the GISS model has been put in a nice, graphic ‘wrapper’ to make it easy to run on PCs. It’s lower resolution than the modern models, but otherwise fully functional (in fact, it’s the same model that Hansen used in 1988 to make his famous prediction). You can plug in new values of CO2 (and solar, methane, CFCs) and see what happens for yourself. The website is

  15. 15
    Mark A. York says:

    Here’s what your average naysayer is using as proof this whole thing isn’t real.

    Dr. Gray What would you say to him personally about his views?

    [Response: Dear Mark, thanks for pointing out this article. Dr. Gray there says



    I've spent the past 15 years studying the effect of ocean circulation on climate, in past, future and present, and I have many publications on this (see my website). A change in ocean circulation redistributes heat in the climate system, but has only a small effect on the global mean temperature. E.g., an increase in Atlantic thermohaline circulation would have warmed the North Atlantic region but cooled the Southern Hemisphere, because there is simply more heat transported from the Southern Hemisphere into the North Atlantic then. I would ask Dr. Gray to point me to a single scientific paper which shows how 20th Century global warming could be explained by "ocean circulation changes". If there is no such peer-reviewed paper (and I certainly do not know any), then I would ask him to refrain from making such public claims about it. I would ask Dr. Gray how the ocean circulation has changed, and what the evidence for this is. I would also ask him to specify what the "other factors" are that explain the recent global warming, and point me to peer-reviewed papers demonstrating this. And finally, I'd ask him how he knows that "it is not human-induced" - this sounds like a very definite statement, so I would like to know what the supporting scientific evidence is - given that it is well-established physics that the amount of greenhouse gases which we released to the atmosphere has a radiative effect that can easily explain all the observed global warming. Would not any sober and unbiased analyst of the scientific evidence conclude that at least it is quite possible that the warming is human-induced? It makes me highly suspicious if someone claims absolute certainty that it's not, without giving any rational argument as to why he believes this. (And strange the interviewer let him get away with such a claim without asking: what makes you conclude that?)

    Dr. Gray further states:


    This simply insinuates hidden and egotistical motives in a lot of scientists, including myself. I have little respect for people who resort to such ad-hominem attacks rather than using factual arguments. Besides, what most climatologists (including myself) are saying actually is: we know enough to act (or, as California governor Schwarzenegger put it: the science is settled, the time for action is now). We are not saying: we are still uncertain about the greenhouse effect, please give us more money to study it. I come from a country where the government listens to what science has to say (I am a member of the Advisory Council on Global Change of the German government), and the result is that funding for basic climate research (like my own work) is being reduced, and money is invested to work on solving the problem (e.g. renewable energy research). Hence, the advice that scientists like myself are giving is actually against our own funding interests - but, in contrast to what Dr. Gray seems to believe, there are actually many people in this world, including scientists, who are not corrupt and who put the public good above their own vested interests. -Stefan]

  16. 16
    John Dodds says:

    Re #6 Response by Stefan:
    (1) is undeniable. Man is increasing the CO2 in the air.
    “(2) CO2 is a greenhouse gas that will warm the climate, …. The fact that CO2 is a greenhouse gas absorbing long-wave radiation is based on lab measurements and was recognized in the 19th Century. …. But remember that Arrhenius first did it in 1896, without computer, arriving at 4-6 ÂºC warming for CO2 doubling. … So if we had no computers, we would still have arrived at a very similar estimate of climate sensitivity, albeit less certain.”

    OK, yes, CO2 absorbs some of the IR energy that is generated by the air @288K. Now what happens to that CO2 molecule?
    Try this: after absorbing the photon or energy, the CO2 is @~900K. It is so hot that it bumps into a whole passel of air molecule neighbors who are at 288K or less. In fact at ground level it hits the first one in about 8 millionths of a centimeter apparently. The absorbed energy is so rapidly returned to the air molecules that the air and the CO2 returns to its original 288K in microseconds. Any CO2 molecule that is warmer than its surroundings will ALWAYS bump into a cooler neighbor & they will all adopt the same equilibrium temperature, (unless it reemits the photon to the air or space and returns the CO2 to its original temperature) Because there are more air molecules than CO2, the energy return by collision is the faster, more dominant process. Conservation of energy requires that the air @288K first give up energy to radiate it, the energy is absorbed by the CO2, the energy is returned to the air by collisions. Net result NO CHANGE IN THE SYSTEM due to the CO2 absorption.

    Sorry to say but Arrhenius was wrong. (can I have a Noble Prize for daring to say this?

    [Response: Try publishing your theory in the scientific literature first - will be hard to get a Nobel prize without that.]

    or is denouncing a Swede automatic denial for the Swedish Nobel Prize?) His analysis did not go far enough. He only considered CO2 absorption. (as do the current computer models!) and ignored the return of the same amount of energy by molecular collisions. The actual net result by high school physics, of adding energy to GHGs is NOTHING. The energy is always returned to the air from which it came (because the air is the source of the Stefan-Boltzman radiated energy). – simple pure conservation of energy. GHGs do NOT trap and retain energy, they use the environmentally sound trap and release philosophy, they pass the energy through from ground level eventually to space. and they do a much better job of it than convection or conduction.

    OK Gavin/Stefan where is this wrong?- it is so extremely obviously simple! (when you think it through rather than accepting the 100+ year old idea that a greenhouse gas traps energy.)

    [Response: It is amazing how often lay-people write letters claiming that the experts have overlooked the "extremely obviously simple" for over a hundred years. Not so likely, right? Every scientist coming fresh into this field has looked at and understood this again (rather than sheepishly accepting what Arrhenius said), and remember many of us teach this to university students every year - they do ask the critical questions until they have understood the energy balance! I'm afraid you simpy have not understood the basics of how the greenhouse effect works. You're wrong in two points. First, only some of the energy is absorbed (i.e., goes into molecular collisions), while some is re-radiated, in all directions. Some of that is re-radiated back towards the ground, where it increases the incoming radiation - you can look up the exact numbers in any textbook or the radiation budget graph in the IPCC report. That extra radiation coming from the CO2 molecules aloft warms the surface. Second, the energy absorbed by the CO2 leads to warming of the surrounding air: molecular motion = heat. Arrhenius knew this, and all models take this into account, of course. - Stefan]

    This is also the same mechanism used in a glass greenhouse. The longwave energy emitted from the solar radiation absorbed by the ground is absorbed by the CO2 and water vapor (the GHGs) and then transferred to the air inside the greenhouse by collisions. However, the GLASS of the greenhouse confines the air and heat to the inside, glass being non-transparent to longwave or IR energy and air molecules, thus allowing it to get hotter than the outside air – ie the true greenhouse effect. Opening a window will allow the heat to escape by convection, or movement of the air. The amount of GHGs, CO2 or water vapor, is irrelevant, since it acts only as a transfer mechanism heating up all the air, which includes the GHGs. If the GHGs were not in the greenhouse air then normal convection and conduction would STILL transfer the sun’s heat energy from the ground to the air (but not as efficiently), in the same or reverse way that conduction of heat through the ground or glass will cool a greenhouse down overnight when there is no continuing solar radiation heat source, and regardless of the GHG concentration.

    For the IPCC “enhanced greenhouse effect”, in the current atmosphere where mankind IS increasing the amount of GHGs/CO2, there is no glass to confine the heated air, so the heat energy is distributed globally. The GHGs still act as a transfer agent, absorbing the ground radiated longwave or IR energy, and then transferring it to the air, until the energy reaches the upper atmosphere where it is radiated to space. Both convection (hot air rising) and conduction (hot air heats up cool air by collisions) contribute to the transfer of the ground heat/energy to the air, and WOULD DO SO even more if the GHGs did not exist. (see the IPCC figure The greenhouse effect, ie ground level temperature is warmer than the 255K equilibrium temperature, would still be there even without the GHGs ( another argument for why the quantity of GHGs is irrelevant). The decreasing air temperature gradient from the ground ~288K (15C) to the effective mean radiative equilibrium level @~10KM and~255K where the incoming solar energy balances the outgoing earth radiated energy, is basically dictated by the decreasing energy flux and the corresponding decrease in air density, both of which are dictated by the inverse square law- ie bigger volumes at larger heights, means less energy per square or cubic meter (flux), or less matter per cubic meter (density). The amount of GHG transfer agents does not significantly influence the temperature because the GHGs “instantly” lose any absorbed energy by colliding with the other air molecules. The GHGs do not retain any more energy than the overall air, because if they were hotter then collisions would soon (within microseconds) cool them down to the air temperature. Also since the source of the radiated energy that is resulting in the “increased” flux and absorption, is actually the air and GHGs itself, then just how can the air heat itself up to a temperature than what it started at?

    Sorry people I am not an activist trying to disrupt the world, or a paid consultant to the oil companies. I simply do NOT understand the high school physics basis for the greenhouse effect where a GHG is supposed to absorb and retain energy. My understanding says it doesn’t exist. & if it doesn’t exist then there is no basis for GHGs causing global warming. If someone can explain it please do. but do it in simple single molecule and energy terms. In my global warming education I have at least accepted that the hockey stick exists, and the world IS warming, and that when you emit CO2 you remove twice as much O2 for a net loss of air density, so I can accept sound logic. BUT the Arrhenius CO2 warming the world concept doesn’t meet the common sense or basic physics test.

  17. 17
    Dan Allan says:


    The greenhouse effect does not depend on the heat staying permanently trapped in the atmosphere. It just depends on the average photon’s heat staying in the atmosphere a little longer than it would have without the co2.

    What if there were just one co2 particle in the atmosphere, that continuously absorbed and then transferred heat? Wouldn’t the atmosphere be miscroscopically warmer for this than if there was no co2? Don’t forget that as soon as it transfers it’s heat, it’s ready for the next photon, so at any point in time, there is more absorbed heat in the atmosphere than without it.

  18. 18
    John Dodds says:

    Re 17:
    You are missing the point. The photon comes from the AIR, is absorbed by the CO2 IN THE AIR, & is returned TO THE AIR by molecular collision. The energy NEVER leaves the air. There is NO energy added to the system by the CO2. & if no energy is added then it can’t warm up. Arrhenius ignored the return of the energy to the air – He was wrong.

    Even if you add CO2, since the energy from the solar-in sunlight is fixed, and is continuously being radiated from the earth so that at equilibrium energy in equals energy out, then ADDING CO2 can NOT absorb more of the energy in because there is NO MORE energy in to absorb, It was ALL already being radiated out by the preexisting CO2, before the extra CO2 was added. The CO2 can NOT absorb extra energy if there is none to absorb. Hence NO WARMING (unless the sun does it)
    Where does the warming energy come from? I think it was created out of nothing in the computer or on Arrhenius’ paper.

  19. 19
    John Dodds says:

    Add another question to #16 & 18. If you accept that the GHG Forcing is created by the energy that is added by the absorbtion by the added CO2 (sounds fine to me) AND you accept that the absorbed energy is returned to the air by molecular collisions (I do not see much CO2 at 900K from the absorbed photon out there!), then WHERE is the Forcing that accounts for the energy that was returned to the air? It will be equal and opposite of the GHG forcing that supposedly accounts for the global warming. If it is ignored then Arrhenius and the Computer Models are WRONG.

  20. 20


  21. 21
    Theo Kurten says:

    (Re 16, 18):

    John, I think you are missing a central point. The IR photons in the lowest part of the atmosphere are not “generated by the air @288K”, but by the Earth’s surface. Without GHGs, these photons would pass straight through the atmosphere. Due to GHGs, they are absorbed and, as you quite rightly point out, quickly re-emitted, multiple times. As a result, the lower part of the atmosphere is warmed. (Indeed, without the collisional energy transfer the greenhouse effect wouldn’t even work, or at least not so effectively.)

    This is analogous to passing a beam of EM radiation of some suitable wavelength through a container with some gas inside. If the gas mixture contains molecules that are able to absorb at that wavelength, then the gas warms up. If not, it doesn’t.

    Another analogue would be a microwave oven. According to your reasoning, a microwave oven should not be able to heat up anything, since the molecules that absorb MW photons “ALWAYS bump into a cooler neighbor & they will all adopt the same equilibrium temperature”.

  22. 22
    Timothy says:

    Re; #16 John: The energy is in your photon. The photon [travelling at the spped of light] will exit the atmosphere very quickly if not interrupted by an atom/molecule that can absorb its energy. The energy of the photon can not be said to be “in” the atmosphere in the sense that it does not contribute to the temperature of the atmosphere. Once the photon is absorbed you are right that this energy is quickly distributed amongst large number of molecules by collision. Surely this would raise the overall average temperature slightly?

    If I understand your argument correctly you are arguing that the global mean surface temperature is unaffected by the molecular composition of the atmosphere. Therefore if there were no CO2 or 10XCO2 would have no affect on the energy balance. This simply isn’t the case. We know this because we have the example of the Moon, without an atmosphere, but with the same amount of incident solar radiation, to compare to. If you increase the quantity of something that is keeping you warm [in this case CO2] you will get warmer [two blankets instead of one].

  23. 23
    Timothy says:

    Re: #20 Wayne: I haven’t heard about NOAA’s forecast but I have heard about the Met Office forecast for a colder than “normal” winter for the UK. The key part of the Met Office forecast is an NAO forecast that predicts a strongly negative NAO => less cyclonic activity over the UK => less heat transported north by the cyclones => colder than “normal” UK. This heat has to be somewhere else, which will therefore be warmer than “normal”.

    Incidentally the seasonal forecast model doesn’t show this signal convincingly. This might be because it isn’t able to generate sufficient blocking [anti-cyclonic activity] as many GCMs suffer from this failure. It [the seasonal forecast model] would therefore not be picking up the strong negative NAO that is being forecast.

    I believe the NAO forecast is made simply by a statistical relationship between a North Atlantic SST anomaly pattern in the summer and the following winters NAO index. It is, however, quite a strong relationship as it has been used quite succesfully as a hindcast for the historical record of the NAO.

  24. 24
    Tom Fiddaman says:

    Re 16 etc.

    By this line of reasoning water vapor would also have no greenhouse effect. It may be hard to detect .2 degreeC decadal trends, but I think a 30 degree absolute difference between theory and reality might be noticeable, especially when the oceans froze over.

  25. 25
    Andrew Dodds says:

    Re: 16, 18, 19:

    John – Please stop dragging the family name down..

  26. 26

    Re #16. Correct me if I’m wrong but I thought that any CO2 intercepts infrared radiation arising from the sun-heated EARTH’S SURFACE, and bounces it around before it is finally lost to outer space. More CO2 bounces it around more, before it is finally lost to space. More bouncing equals higher temperature.

  27. 27
    John Dodds says:

    Rebuttal to 21 etc relating to 16 & 18

    YES I am claiming that there is no such thing as a Greenhouse effect CAUSED by GHGs which includes CO2 AND Water vapor…

    [Response: In that case, we can stop there. Find yourself some web space, or a newsgroup, but don't spam your pet theories here please. A brief link to your exciting new reseach should suffice for those interested - William]

  28. 28
    John Dodds says:

    Re #26.
    The radiation is radiated from any material depending upon its temperature. (Stafan Boltzman law) both the ground and the air radiate.

    The concept of MORE CO2 means more bounces means more temperature is wrong. The limiting factor is the radiated energy, not the amount of CO2. You can only transmit the amount of energy that is radiated. The sun solar-in energy dictates how much energy comes in, gets absorbed by the air and ground, and is then radiated out to be absorbed by the GHGs and returned to the air or space. Regardless of how many GHGs you have the total energy transmittal is limited by what the sun puts in. You can NOT absorb more energy if there is no more energy to be absorbed. AND if the GHGs return the energy to the air by collisions in microseconds , with no addition or loss of energy, then it doesn’t matter how many GHGs there are. They are a neutral transfer agent. Conservation of energy means that any absorbtion took energy out of somewhere, (in our case from the ground and air) and since the GHGs return the energy to the air (which warms the ground), there is a net NO change in the energy of the air and the temperature regardless of what you do to the GHGs, and NO global warming by changing the GHGs. BUT global warming still exists.

    [Response: Its fairly easy to demonstrate this is wrong. Consider a simple situation in which (short wave, SW) radiation R (W/m2) comes in to an infinite planar black body. Then the temperature at equilibrium is given by R=eT^4 and T=(R/e)^1/4. Now consider the situation where an absorber is present, transparent to SW but opaque to long-wave (IR), above the surface. The absorber and the surface warm, to Ta and Ts. The absorber radiates, in IR, Ra up and down, Ra=eTa^4; the surface radiates, in IR, Rs=eTs^4 (all at equilibrium). Now the radiations must balance, hence Rs=R+Ra and 2Ra=Rs; hence Ra=R, and hence Rs=2R, hence 2R=eTs^4, so Ts=(2R/e)^(1/4) which is 2^1/4 bigger than without the absorber. You can generalise this to multiple levels and to make the absorber only partially opaque, and you find that Ts increases with opaqueness - William]

  29. 29

    #23, Thanks Timothy

    Met office projections you’ve stated look sound, there is a lack of “clashing” hence movement between cold and warm air masses because it is extremely warmer in the Polar region.
    It will take a wide spanning quasi-static massive high North of Alaska, clearing clouds just to bring down temperatures a great deal say to “normal” winter temperatures around here. I measure the absolute density of Arctic Ocean atmosphere, and it is quite thinner than previous warm years at about the same dates. The official North American statements I have heard from the radio were perplexing, the heat is here, radiance rates are constant, I don’t see a cold winter coming at all.

  30. 30
    John Dodds says:

    [Response: Very long exposition deleted. This is *not* the place to dump your pet theories. Get your own website, or post to a newsgroup: please don't spam us - William]

  31. 31
    John Dodds says:

    Very sorry William. 26 & 30 crossed in internet space.

    The full explanation of why I believe Arrhenius is wrong, and why global warming is caused by the sun is available at

    John Dodds

    [Response: URL corrected. Now, thats all jolly good, please don't post again on this - William]

  32. 32
    Blair Dowden says:

    This discussion gives me a chance to ask a few basic questions. When a greenhouse gas molecule absorbs infrared energy, what portion is translated into molecular motion (thus increased temperature – sorry John) compared to that re-radiated? Is there any pattern to the wavelength of the re-radiated energy (ie. usually longer or shorter)? And how much re-radiated energy is absorbed by the ground, directly causing surface warming?

  33. 33
    John Dodds says:

    Re #21.

    The microwave analogy is confusing the issue. I would prefer to please stick to GHGs and energy.

    BUT since you brought it up. The MW analogy is wrong, in that the food ONLY heats up because the MW generator adds energy from the outside just like the sun. The energy in the air in the MW Oven, will not heat the food above ambient. In fact, lets take some GHGs (a bowl of water and a volume of CO2 in a plastic container) and add it to a microwave oven (that emits energy in the frequencies that water & CO2 absorb). The GHG concentrations increase inside the microwave. Does the temperature of the water (or CO2) increase? Will it come to a temperature that is higher than the equilibrium of the air in the MW before you add the two containers? Answer: NOT until you push the button to add extra energy from the external microwave generator. Why not, you just added enough of the extra CO2 to absorb all those 900K photons to heat it to way past boiling? Could it be that it is the energy that comes into the system (ie the sun) is that dictates the temperature, and the if the air density doesn’t change then the type of constituents in the air can NOT change the temperature , regardless of their ability to absorb & return energy.

    John Dodds

  34. 34
    John Dodds says:

    Re #31 I suggest you read comment #26 @ from Eli Rabett, who seems to be the local expert in this area.

    This MAY help. (or confuse even more- I found it very informative)

    As for the -sorry John comment. I do not dispute that adding energy will increase the temperature (obviously it does- this is what collisions are all about) What I dispute is that there is any extra energy available to be absorbed by the added CO2. Where does it come from? All the suns energy was previously being absorbed by the preexisting CO2 at the preexisting equilibrium. By adding CO2 we do NOT add energy to the system.

  35. 35
    John Dodds says:

    Re # 34, which is trying to respond to what is now #32 Blair Dowden request.
    Whoops, Sorry wrong address to go to.
    Please try Eli Rabett comment #26 at where he discusses the whole absorbtion energy return subject. (the discussion subject was “Climate Sensitivity & aerosol forcing”

  36. 36
    Blair Dowden says:

    None of the sun’s energy is absorbed by carbon dioxide. Some of the infrared energy radiated by the Earth is absorbed by CO2 and other greenhouse gases, the rest escapes into space. Each greenhouse gas absorbs energy in a few wavelength bands, and only a part of the energy in those bands, generally proportional to the logarithm of the gas’s concentration (at the concentrations found on Earth).

    For example, Venus actually receives less solar energy than the Earth, because its albedo is twice as high. Yet its average temperature is 470o C compared to the Earth’s 15o C. The carbon dioxide is adding energy to the Venus system by preventing the escape of infrared radiation from the surface of Venus.

    This is basic physics established long ago, and not even questioned by any of the scientifically literate skeptics. I am hoping someone more expert in this area can answer the questions I asked a few comments ago.

    [Response: Exactly right and very clear. Thanks for this! We don't have time to get into discussions of all the non-issues that are occasionally brought up in the comments. -Stefan]

  37. 37
    John Dodds says:

    Regarding William’s Response (below) to Comment #28 ( and 16 and 6) in the blog . (Modeller vs Modeller)

    JOHN DODDS Response:
    The William response to 28 is the standard (Arrhenius based) proof that adding CO2/GHGs causes warming or the greenhouse effect. It is available in most high school or college courses and text books. (eg )
    I claim that this mathematical model of GHGs causing global warming is INCORRECT. The model fails to conserve energy.

    First, an infinite planar black body in reality does NOT represent the earth, it should be a spherical black body of earth radius. (Did Arrhenius believe in a flat earth?)
    The flaw is the statement ..” Now the radiations must balance, hence Rs=R+Ra and 2Ra=Rs; hence Ra=R, and hence Rs=2R,…” The Conservation of Energy Law requires that ENERGY must balance, not the fluxes (R, Ra etc…) or energy per unit area. You MUST include the total area of the fluxes at the surface, or at the absorbing layer etc. If you do this then you get the standard R-squared dependence of the flux, that everyone knows about. The flux at the ground is larger than the flux at the “energy-in equals energy-out” equilibrium point @ ~10,000m. Gravity also forces the density of the air to comply with the R-squared dependence. Since all the GHG absorbed energy is transmitted to the air by the molecular collision mechanism (ie all air molecules are at the same global annual averaged energy/temperature at a given elevation) then you get a higher air temperature at the ground (288K,15C, 59F) than at an elevated point (255K @10,000m). This works even if there are NO GHGs, and the energy transport mechanism from the ground up is convection or conduction. This works underground in gold mines or at the center of the earth, where the temperature is higher due to the decreased radius but there are no GHGs. This works on the surface of Venus where the atmospheric pressure (& density) is 90 times that of earth.

    If you use the “..hence Ra=R..” conclusion from Arrhenius and William above, then the energy-in from the sun (R times the ground surface area) does NOT equal the energy-out (Ra times the absorber surface area, effectively at ~10,000m, the radiation equilibrium point). Because the area of the sphere at the 10,000m level is larger, the total calculated energy out would be larger, and we would NOT conserve energy. THIS IS IMPOSSIBLE. The mathematical derivation has created the energy that is attributed to the GHG absorption and to the GHG Forcing in the computer models. The GHG Forcing, which predicts that GHGs are the most significant cause of global warming, is thus an erroneous and artificial mathematical creation of the Arrhenius et al. modeling of the greenhouse effect.

    Intuitively, if ALL the sun’s energy (less albedo) is assumed to hit the ground, or spherical black body, (ie Energy=R flux times ground surface area), and is then radiated up as long-wave or IR, then, as the height or radius increases, the total energy going out (ie R at the height, times the area at the varying heights) is constant. – Conservation of energy. This means that any Ra down flux that is artificially created by GHG energy absorption MUST have an energy value of ZERO, or else there is no conservation of energy. Besides, if the sun dictates that the Flux energy at the surface is R, then where can we get the extra energy to also make the surface flux or Rs=2R, or twice as much, as indicated in the Arrhenius based derivation above? “You can’t pull the extra energy out of thin air!” GHGs do NOT create or absorb extra energy to warm the planet. They simply transfer the suns energy at ground level to the air to space with 100% efficiency. (no gains, no losses) Arrhenius was wrong. With no CO2/GHG induced warming, there is no need for the Kyoto treaty and any CO2 reduction schemes or CO2 emissions monitoring and trading, or for much of the GHG research.

    See for a more detailed explanation, that also identifies why global warming still exists but is caused by the sun over which we have little control.

    John Dodds
    (c) J Dodds, San Francisco, Ca, USA, 29Oct2005. Reproduction permitted with appropriate reference to the “John Dodds GHG Letter of 29 Oct.”

    [Response:Of course, energy is usually not created from just air (assuming no nuclear reactions), but its level is given by the total solar irradiance from the Sun. Although the sun is bright and looks yellow, the so-called 'black body' theory can sucessfully be applied to it's surface (photosphere) to infer the surface temperature on the Sun (approx. 6000K). The black body radiation gives a so-called 'conituoum spectrum' - a light with a wide range of wave lengths and whose peak is given by Wien's displacement law (l = a/T). This is standard physics. The long-wave radiation from the Earth is also well-documented, and can be found in standard text books on Earth's atmosphere (I can reccommend Fleagle & Businger (1980) , 'An Introduction to Atmospheric Physics' Academic Press; Houghton (1991) 'The Physics of Atmospheres', Cambridge University Press): the long-wave spectrum is consistent with a black body, with some absorbtion at frequency bands consistent with known effects of atmospheric gases. This is well-established, and does not make any assumption of a 'flat earth'. The comment about 'flat earth' is pehaps caused by the very simple concetual model of the greenhouse effect, often used for illustrative purposes, but this simple model is of course not used for serious estimates of the greenhouse effect. It is assumed that the Earth is spherical! When making a volume-integral of the energy fluxes at any atmospheric altitude (eg using Green's theorem), then all fluxes must be taken into account - both short and long waves (including albedo, and downwelling longwave radiation) in order to estimate the total energy. This is implicitly done in climate models (GCMs) with realistic radiation schemes. The fact that the models do a good job describing our climate (e.g. the response to a volcanic eruptions) give confidence in their ability to describe our climate. Furthermore, there is a wealth of empirical evidence corroberating the theoretical aspects of an increased greenhouse effect. Finally, Earth's emision temperature is substantially (~32K) lower than the estimated surface temperature, and Venus surface is hotter than Mercury's, despite being further away from the Sun. It is well-established that the greenhouse effect is real and naturally occuring - as well as being disturbed by increases in GHG. -rasmus]

    [Response: This thread is well past its sell by date. No more please. -gavin]

  38. 38
    Mark A. York says:

    Thanks Stefan. I used your answer in a post. As a biologist myself I try to debunk a lot these political fallacies being spread like wildfire out there. This site is the best defense there is.

  39. 39
    John Dodds says:

    Sorry for the frustration Gavin, The response to 37 is NOT convincing. You guys are failing in the convincing department in spite of being the absolute best available resource.
    I like William’s & everyone else’s simple illustrative model that is taught in most colleges in the world, EXCEPT for the flat vs spherical part. Why can’t that assumption/flaw be fixed then address the results. ie the flux is R-squared dependant as I said? The flux & density radius dependance explains part if not all of the 33 degree temperature difference. (regardless of what CO2 does!) OR is this illustrative model so erroneous that it should never be in any college textbooks?

    You still have not addressed the conservation of energy question. How can a CO2 absorbtion that returns exactly the same amount of energy to the air (conservation of energy) heat the air up? Where does the extra energy come from? If the preexisting CO2 equilibrium took ALL the energy in and exhausted it out, then there is NO extra energy to be absorbed by the added CO2. So where does the energy come from? According to this latest response the solar irradiance dictates the energy levels. Well CO2 does NOT change the solar irradiance.

    The inconsistency is infuriating.

    The technique of invoking it works because we say it works, and volcanos prove it works is not convincing. Volcanic eruptions do NOT test the CO2 part that I am questioning. I do not doubt that the model works for volcanos.

    Your inability to explain away the problems in simple terms is impacting your credibilty.

    John Dodds

    I will be happy to take this off line if you all will still talk to me.

    [Response: John, this is the last time. William gave you the derivation (which clearly does not violate conservation of energy) yet you insist that it does. You refuse to relax your (incorrect) assumption that the flux from the surface is the same as the flux from the top of the atmosphere, which is equivalent to assuming that there is no GHE at all. So you assume the result you wish to prove. All further protestations to the contrary will be removed since it is not adding anything to the discussion. -gavin]

    [Response: Anyone frustrated because their pet theory cannot be discussed endlessly here is invited to take it to a newsgroup, for example sci.environment. Some of us read that. Beware though - people who disagree with you may be far less polite that we are - William]

  40. 40

    In simple terms, correct me if I’m wrong, but there is NO extra energy required for a higher temperature. By addition of greenhouse gas molecules, the chances are increased for the re-radiated energy to be bounced around more, so the system is simply HOLDING ONTO THE ENERGY LONGER, before it is finally lost to outer space. Sort of like wearing a heavier coat in winter, (though of course the cloth is visibly opaque!)

  41. 41
    Dan Allan says:

    John D:

    Here’s a friendly tip for you: don’t go spending that Nobel money just yet.

  42. 42
    John Dodds says:

    Re 41 & 25
    The nobel comment in 16 was a joke. An attempt at humor that obviously a lot of people did not get. What do you want? Smiley faces to tell you when to laugh?
    Ususally Nobel Prizes go to people who invent something new. Determinng that one little assumption in a mathematical proof was wrong obviously does not qualify for that.
    Arrhenius was a VERY good Scientist – capital S.( ) He discovered many pieces of what is now common knowledge, such as the dissociation of chemicals into ions etc. I am not a scientist of that caliber.

    The Andrew Dodds humorous comment (#25) about me dragging down the Family name was a piece of humor that I as an amateur genealogist did appreciate. Have you ever heard of a famous Dodds? Best we can do is the “Dodds 5&10″ in South Carolina, or a member of the Australian Supreme Court in 1901.
    My response to Andrew is: What if I am right?

    [Response: You'd want to start looking out for porcine aviators.... gavin]

  43. 43
    David Donovan says:

    John D.

    You seem to be forget that the flow (transfer) of energy is a time dependent process (i.e. Watts vs Joules)…see also post # 40. Also not that the `standard text book models’ are built explicitly on the conservation of total energy.

  44. 44
    John Dodds says:

    Re 40, 43
    Gavin won’t let me comment any further on technical issues that challenge the assumptions of the greenhouse model. So I do not think it FAIR that he allow others to continue to comment on my work.

    But the same logic applies. IF TIME results in more energy being stored in the air due to more collisions due to added CO2 (what happened to the loss of O2 & the fewer collisions that generates?), then the temperature of the air is Higher. If the temperature is higher then by Stefan Boltzman, the energy radiated out to space must be higher. If the energy coming in from the sun is NOT higher then we have an imbalance that will resolve itself by the air radiating energy until it cools down to equal the original temperature that was available at the pre CO2 addition equilibrium.

    In the interest of not infuriating Gavin et al, I will NOT respond to any more comments. That is NOT to say that I consider the discussion resolved.
    They have porcine aviators, also bovine ones, in most any airport novelty store. You can attach them to the ceiling and they fly around in circles.- insert smiley face here!


  45. 45

    I do have a concern that models have a whole bunch of musicians playing beautiful but uncoordinated music, and seem to give conclusions not matching reality, which is found in the future. Could it be that they work in a initial random based starting configuration, instead of having given preset parameters analyzed by another model? I give the example of AGW forcing which subscribes heating, but by how much? Would it be easier for a model to use a reliable estimate, from a good source , like Dr Hansen and al. at NASA, and go from there. If for instance the coming summer is expected to be #1 warmest in history (from one good model), it should be less complicated for a weather model to place the various main meso-systems from that premise instead on relying on placing weather systems landing somewhere by chance and past persistence only to finally give a global and local temperature estimate , which may be not usually very accurate.

    [Response: This seems to me to have a complete misconception of how the coupled AOGCMs used for prediction work. Basically, the premise is to predict climate - not a days or a years weather, but the long-term climate changes - William]

  46. 46

    Hi William,

    For me it could be one and the same, climate and weather for the lay person has no distinction, I do understand the difference though, but scientists like Dr Lindzen at MIT are having fun showing our incapacity to forecast weather beyond 4 days. Not that his point makes any sense on a Global prediction scale, but I guess his contention is that climate models (not unlike weather models) can’t replicate the future. I disagree that they can’t, but they can be made more impressive in a presentation sense, by showing how correct they were, and also with some fine tuning as mentionned above they can be quite accurate . As a basic idea I see potential in limiting probable variances, if we knew, as an example, with great accuracy what the Global average temperature will be for the next 6 months or so (it can be next 10 or 100 years as well), that 4 days range can be stretched out a good deal longer just as much.

  47. 47

    I think John Dodds’s confusion may be because he is confusing temperature with energy. The greenhouse effect doesn’t increase the amount of energy in the climate system, but it does redistribute it. There is no violation of conservation of energy involved. The flux leaving the Earth is exactly the same as the flux coming in, over the long run. (A little more is coming in at the moment, but the system wll reach equilibrium eventually).

    Perhaps this would be clearer if he wrote a simulation to follow a fixed amount of energy, or better yet, a fixed power input, and traced the various fluxes. I agree with the person who recommended Houghton’s book. I have the 1977 edition, and there’s a 3rd edition out there from 2002. “The Physics of Atmospheres.” It’s not just for breakfast any more.

  48. 48
    Tom Cole says:

    Sorry to take so long in posting, but I have been on a a cruise from Monte Carlo to Athens and have given the internet a long needed rest.

    Some responses and follow up questions.

    - “It should be pointed out though, that the dynamics are only a small part of the physics included in the models.”

    I am unsure what you are trying to state here. Are you implying that the dynamics are relatively unimportant compared to the other physics (e.g., equation of state, solar radiation absorption in water, etc.), or what? I would be greatly surprised if the solution of the momentum equations were anything other than the most important “physics” of the global climate models when it comes to sensitivity of the models, but I could be wrong (and oftentimes am :^).


    You’ve lost me in what you are trying to communicate here. I am aware that the type of parameterization used for things like turbulence are greatly dependent upon the scales used in the solutions. However, given the appropriate parameterizations for the time and length scales chosen during model development, there is still a range of computational grid dimensions that you can operate within. Within the appropriate range based on the parameterizations used in the model, have you shown that model results are independent of grid size? This is a fundamental question that needs to be addressed before proceeding further in any numerical model application, be it water quality or global climate. Without showing that model results are independent of scale (within the appropriate range determined by the type of parameterizations used), then all model results need to be taken with a very LARGE grain of salt.

    - “This isn’t much of a test.”

    Actually, this is a HUGE test of any model’s efficacy, in my opinion. One has to be able to simulate the ends of the spectrum they are attempting to model in order for me as a modeler to feel warm and fuzzy with any given model’s results inside the bounds of the spectrum. As you rightly emphasize, you have developed a global climate model, not a weather forecasting tool. Therefore, if one asserts that they have developed a global climate model that can be used to simulate the impacts of global warming, they need to also be able to simulate periods of global cooling, such as the not too long ago last ice age.

    Again, have you shown that your global climate model has been able to simulate ice ages such as have occurred in the earth’s past (and the short term cooling in the last decade)? If so, are they for plausible reasons that can be used to further research on ice age development. If so, this is HUGE in showing that your model is a useful scientific tool. Models shouldn’t just reproduce observed data. They should provide greater insight into natural phenomenon and lead the way to further investigations. When the model in whose development I have been involved in began providing these types of insights was the time when I finally felt like I had something useful for not only myself, but others as well.

    I again assert that, in the context of global climate models, this is a “BIG DEAL” when it comes to showing the usefulness and applicability of said models.

    - “If there was an analytical solution for climate we wouldn’t need numerical models at all! ”

    Actually, this is wrong. Analytical solutions, almost by definition, are VERY simplified mathematical descriptions of complex dynamic behavior commonly observed in the real world, and are generally totally inappropriate for addressing any given real world phenomena. However, that doesn’t mean they are never useful, just that their usefulness occurs very rarely and in very specific situations.

    That said, one can always simplify the problem such that an analytic solution can be obtained and the results be used to compare with the results of numerical models of the same phenomena in order to determine if a model is capable of reproducing the most simplified/ideal behavior seen in the real world. If not, then it is back to the drawing board for the numerical model. Additionally, you need not test your model against full blown analytical solutions of atmospheric/land/ocean interactions. You can single out specific parts of the set of equations being solved to ensure that each equation is capable of reproducing simplified analytical solutions of the real world.

    Again, have you tested your global climate model against simplified analytical solutions? If so, how did the results compare? If not, then you have bypassed a very significant stage of numerical model development that should be required of all numerical models, regardless of what field they are being used in. If I remember correctly, back in the early ’80′s in the hydrodynamic engineering field an ASCE task force was set up to identify various analytical solutions that the developing field of multidimensional hydrodynamic models could be used as a standard validation test for the new models.

    - “It might be valid if it were true, but it isn’t.” Thanks for pointing this out. I’m surprised I haven’t run across this in any previous responses to Crighton’s criticisms. Have any results of these comparisons been published in peer-reviewed journal articles? If so, what were the findings? Were other researchers able to reproduce the results starting from square one without relying on any of the data developed by the first developers/appliers of the given model? If not, what was the spread of the model results?

    A few more questions to further the discussion.

    1. John Dodds circuitously touched on an important subject – conservation of energy (and mass as well, although he didn’t mention it in his discussion). Have you shown that your model conserves momentum, energy, and mass to machine accuracy? This, in my opinion, is another fundamental question that needs to be addressed before moving on to using global climate models for what they are intended to be used for. As far as I know, my model is the only one in my field that shows that these properties are conserved, so I suspect you have not. This is important, because in the process of showing the model conserves these properties, I found a number of bugs/errors in the code, even though the model had been used for over a decade previously and provided reasonable results. Unfortunately, they were just wrong, some results more wrong than others, if that makes any sense.

    2. Included in a followup to my original correspondence with Gavin was a question involving the fact that numerical models make all sorts of predictions that one can use to determine a given models efficacy. In my field, one can compare model results for water surface elevations, velocities, temperature, ice cover, and various water quality constituents such as dissolved oxygen, phytoplankton, etc.

    What are the available model outputs that can be used to compare GISS results with observed data besides temperature? How many of these available model outputs has the model been compared to? How well has the model done? If available model results have not been compared to observed data, why not? Are any of these results of additional model/data comparisons in the literature?

    3. Averaging over space and time is common when comparing model results to observed data in order to determine the appropriate scales that the model can be used on (contrary to part of Gavin’s original response, oftentimes the appropriate temporal/spatial scales cannot be determined a priori, but have to be sorted/coaxed out of model output). Part of this procedure involves the aforementioned averaging. At what scales are the model/observed data averaged over? How do model results compare when not spatially/temporally averaged?

    4. Finally, and I am embarassed that I did not include this in the original set of questions, how did you set initial conditions? Forcing functions are only part of the picture of a numerical model’s boundary conditions. Initial conditions are the other part of the boundary conditions that have to be accurately set in order to obtain useful model results. The relative importance of these boundary conditions depends upon what, in my field, is termed the residence time of the system. The longer the residence time of the system, the more important a role initial conditions plays, and vice versa. I have a difficult time visualizing how one would accurately set initial conditions in the context of a global climate model.

    How important are initial conditions in global climate modeling? Have sensitivity analyses been conducted to determine the variation in model results given different methods for setting model initial conditions? [Again, this would fall under the heading of independent researchers starting from scratch verifying model results. I understand that this is difficult with hard to find funding sources and this is why it has historically been bypassed in the numerical modeling field. As a result, model results are taken on face value. Unfortunately, this is not what science is about.]

    In summary, the original set of questions I posed to Gavin and these subsequent ones I just posted basically involve trying to determine just how much of what I term “homework” has been done before ever starting to feel warm and fuzzy about a given model’s ability to reproduce the real world for the right reasons.

    Having been in the field of numerical modeling for nearly 30 years, I maintain a healthy skepticism of many numerical modeling claims. Hopefully, this discussion will help address the dispelling/reinforcing of skepticism with regards to global climate models.

  49. 49
    Tim Osborn says:

    Re #28

    It seems to me that John Dodds actually describes the greenhouse effect, but perhaps without realising it?!

    John, you say in #28 that “…Conservation of energy means that any absorbtion took energy out of somewhere, (in our case from the ground and air) and since the GHGs return the energy to the air (which warms the ground), there is a net NO change in the energy of the air and the temperature…”

    Aren’t you describing the greenhouse effect here? Your own description of what happens seems to be consistent with the greenhouse effect!

    I’ll expand on things a bit…

    The key part in what you wrote, John, is that by absorbing the energy that was lost from the ground/air, the GHGs transfer (some of) the energy back to the ground, “which warms the ground”.

    Suppose the climate is in a steady state with some GHGs in the atmosphere. This energy that the GHGs absorb and then transfer back to the ground might indeed simply balance the energy lost from the ground in the first place, but that’s fine because it’s a steady state.

    But now think what happens if the GHGs are removed. The ground will still lose heat by emission of long-wave radiation. But there are no GHGs to absorb it and transfer (some of it) back to the ground. Hence the ground will cool. This will continue until the ground has cooled so much that the reduction in its long-wave radiation equals the energy that was previously being returned to the ground by the GHGs (that are no longer there). When this happens, a new steady state will be reached. This new steady state will have a cooler ground temperature. So… without GHGs the ground will be cooler than with GHGs. Is this not the greenhouse effect?

    I know other comments have already contained similar explanations – I just wanted to point out that the reasoning was already contained in John Dodd’s own description!

  50. 50
    Timothy says:

    There’s an interesting paper recently published by Knight et al in GRL about the Atlantic Multi-Decadal Oscillation [AMO]. The AMO is thought to be an internal mode of variablity which varies the stength of the Atlantic THC. They’ve analysed the AMO in HadCM3 and they’ve concluded that, independent of anthropogenic forcing, they expect the Atlantic THC to weaken over the next few decades, moderating the increase in temperatures expected due to GW in the Northern Hemisphere over that period.

    Interestingly they state that “Southern hemisphere links, in contrast, show generally less significance and lack a clear pattern.” which I take to mean that the heat which is not transported north when the AMO is in a ‘weak’ phase does not go/stay in a particular location in the SH.

    This paper could be important for fine tuning predictions on Arctic Sea Ice melting as it would partially offset the expected acceleration in melting due to the positive ice-albedo feedbacks.

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