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What the IPCC models really say

Filed under: — gavin @ 11 May 2008 - (Español) (Italian)

Over the last couple of months there has been much blog-viating about what the models used in the IPCC 4th Assessment Report (AR4) do and do not predict about natural variability in the presence of a long-term greenhouse gas related trend. Unfortunately, much of the discussion has been based on graphics, energy-balance models and descriptions of what the forced component is, rather than the full ensemble from the coupled models. That has lead to some rather excitable but ill-informed buzz about very short time scale tendencies. We have already discussed how short term analysis of the data can be misleading, and we have previously commented on the use of the uncertainty in the ensemble mean being confused with the envelope of possible trajectories (here). The actual model outputs have been available for a long time, and it is somewhat surprising that no-one has looked specifically at it given the attention the subject has garnered. So in this post we will examine directly what the individual model simulations actually show.

First, what does the spread of simulations look like? The following figure plots the global mean temperature anomaly for 55 individual realizations of the 20th Century and their continuation for the 21st Century following the SRES A1B scenario. For our purposes this scenario is close enough to the actual forcings over recent years for it to be a valid approximation to the simulations up to the present and probable future. The equal weighted ensemble mean is plotted on top. This isn’t quite what IPCC plots (since they average over single model ensembles before averaging across models) but in this case the difference is minor.

It should be clear from the above the plot that the long term trend (the global warming signal) is robust, but it is equally obvious that the short term behaviour of any individual realisation is not. This is the impact of the uncorrelated stochastic variability (weather!) in the models that is associated with interannual and interdecadal modes in the models – these can be associated with tropical Pacific variability or fluctuations in the ocean circulation for instance. Different models have different magnitudes of this variability that spans what can be inferred from the observations and in a more sophisticated analysis you would want to adjust for that. For this post however, it suffices to just use them ‘as is’.

We can characterise the variability very easily by looking at the range of regressions (linear least squares) over various time segments and plotting the distribution. This figure shows the results for the period 2000 to 2007 and for 1995 to 2014 (inclusive) along with a Gaussian fit to the distributions. These two periods were chosen since they correspond with some previous analyses. The mean trend (and mode) in both cases is around 0.2ºC/decade (as has been widely discussed) and there is no significant difference between the trends over the two periods. There is of course a big difference in the standard deviation – which depends strongly on the length of the segment.

Over the short 8 year period, the regressions range from -0.23ºC/dec to 0.61ºC/dec. Note that this is over a period with no volcanoes, and so the variation is predominantly internal (some models have solar cycle variability included which will make a small difference). The model with the largest trend has a range of -0.21 to 0.61ºC/dec in 4 different realisations, confirming the role of internal variability. 9 simulations out of 55 have negative trends over the period.

Over the longer period, the distribution becomes tighter, and the range is reduced to -0.04 to 0.42ºC/dec. Note that even for a 20 year period, there is one realisation that has a negative trend. For that model, the 5 different realisations give a range of trends of -0.04 to 0.19ºC/dec.


  • Claims that GCMs project monotonic rises in temperature with increasing greenhouse gases are not valid. Natural variability does not disappear because there is a long term trend. The ensemble mean is monotonically increasing in the absence of large volcanoes, but this is the forced component of climate change, not a single realisation or anything that could happen in the real world.
  • Claims that a negative observed trend over the last 8 years would be inconsistent with the models cannot be supported. Similar claims that the IPCC projection of about 0.2ºC/dec over the next few decades would be falsified with such an observation are equally bogus.
  • Over a twenty year period, you would be on stronger ground in arguing that a negative trend would be outside the 95% confidence limits of the expected trend (the one model run in the above ensemble suggests that would only happen ~2% of the time).

A related question that comes up is how often we should expect a global mean temperature record to be broken. This too is a function of the natural variability (the smaller it is, the sooner you expect a new record). We can examine the individual model runs to look at the distribution. There is one wrinkle here though which relates to the uncertainty in the observations. For instance, while the GISTEMP series has 2005 being slightly warmer than 1998, that is not the case in the HadCRU data. So what we are really interested in is the waiting time to the next unambiguous record i.e. a record that is at least 0.1ºC warmer than the previous one (so that it would be clear in all observational datasets). That is obviously going to take a longer time.

This figure shows the cumulative distribution of waiting times for new records in the models starting from 1990 and going to 2030. The curves should be read as the percentage of new records that you would see if you waited X years. The two curves are for a new record of any size (black) and for an unambiguous record (> 0.1ºC above the previous, red). The main result is that 95% of the time, a new record will be seen within 8 years, but that for an unambiguous record, you need to wait for 18 years to have a similar confidence. As I mentioned above, this result is dependent on the magnitude of natural variability which varies over the different models. Thus the real world expectation would not be exactly what is seen here, but this is probably reasonably indicative.

We can also look at how the Keenlyside et al results compare to the natural variability in the standard (un-initiallised) simulations. In their experiments, the decadal mean of the period 2001-2010 and 2006-2015 are cooler than 1995-2004 (using the closest approximation to their results with only annual data). In the IPCC runs, this only happens in one simulation, and then only for the first decadal mean, not the second. This implies that there may be more going on than just the tapping into the internal variability in their model. We can specifically look at the same model in the un-initiallised runs. There, the differences between first decadal means spans the range 0.09 to 0.19ºC – significantly above zero. For the second period, the range is 0.16 to 0.32 ºC. One could speculate that there is actually a cooling that is implicit to their initialisation process itself. It would be instructive to try some similar ‘perfect model’ experiments (where you try and replicate another model run rather than the real world) to investigate this further though.

Finally, I would just like to emphasize that for many of these examples, claims have circulated about the spectrum of the IPCC model responses without anyone actually looking at what those responses are. Given that the archive of these models exists and is publicly available, there is no longer any excuse for this. Therefore, if you want to make a claim about the IPCC model results, download them first!

Much thanks to Sonya Miller for producing these means from the IPCC archive.

Update: Since some people have asked, the test for consistency (at 95% confidence) between the ranges seen in the models in figure 2 and real world trends is that the difference in means must be less than the twice the pooled standard deviation (and since the pooled s.d. is always larger than the s.d. in the models alone, it is trivially true that if the observed mean trend is within the 95% range of the models, it is consistent). See Lanzante 2005 for more info. All observational global SAT trends pass that test. Under no reasonable circumstances is an 8 year trend of -10 deg C/decade (that is 48 s.d. away from the mean) or even -1 deg C/decade going to be consistent with the models. For 7 year trends (beginning of 2001 to end of 2007), the model spread is approximately N(0.2,0.24) in deg C/dec – a little wider than the 8 year trends seen in the figure and there are 10 model simulations with negative trends.

473 Responses to “What the IPCC models really say”

  1. 151
    Ray Ladbury says:

    Gerald Browning, No, the climate models have been misunderstood by you, by Frank and by many others. Climate science is progressing while “skeptics” are spinning their wheels claiming it can’t progress.
    You and your ilk would simply have us throw up our hands when confronted with complex systems. That is an unscientific attitude. I am willing to believe you and Frank when you say you don’t understand climate, but the field seems to progressing nicely.

  2. 152
    Gerald Browning says:

    Well I adressed Anthony Kendall’s comment (#127) and appeared to be answered.
    by Gavin. A rather interesting set if circumstances. Now let us see why the responder refused to answer the direct questions with a yes or no as asked.

    Is the simple linear equation that Pat Frank used
    to predict future climate statistically a better fit than the ensemble of climate models? Yes or no.

    [Response: No. There is no lag to the forcing and it would only look good in the one case he picked. It would get the wrong answer for the 20th Century, the las glacial period or any other experiment. – gavin]

    So in fact the answer is yes in the case that Pat Frank addressed as clearly shown by the statistical analysis in Pat’s manuscript.

    Are the physical components of that linear equation based on
    arguments from highly reputable authors in peer reviewed journals?
    Yes or no.

    [Response: No. ]

    The references that Pat cited in deriving the linear equation are from well known authors and they published their studies in reputable scientific journals.
    So again the correct answer should have been yes.

    Is Pat Frank’s fit better because it contains the essence of what is driving the climate models? Yes or no.

    [Response: If you give a linear model a linear forcing, it will have a linear response which will match a period of roughly linear warming in the real models. Since it doesn’t have any weather or interannual variability it is bound to be a better fit to the ensemble mean than any of the real models. – gavin]

    Again the correct answer should have been yes. If the linear equation has the essence of the cause of the linear forcing shown by the ensemble of models
    and is a better statistical fit, the science is clear.

    Are the models a true representation of the real climate given their unphysically large dissipation and subsequent necessarily inaccurate parameterizations? Yes or no.

    [Response: Models aren’t ‘true’. They are always approximations. – gavin]

    The correct answer is no.A simple mathematical proof on Climate Audit shows that if a model uses a unphysically large dissipation, then the physical forcings are necessarily wrong. This should come as no surprise because the nonlinear cascade of the vorticity is not physical. Williamson et al.
    have clearly demonstrated that the parameterizations used in the NCAR atmospheric portion of the NCAR climate model are inaccurate and
    that the use of the incorrect dissipation leads to the wrong cascade.

    Does boundedness of a numerical model imply accuracy relative to the dynamical system with the true physical Reynold’s number?
    Yes or no.

    [Response: No. Accuracy is determined by analysis of the solutions compared to the real world, not by a priori claims of uselessness. – gavin]

    The answer should have been no, but the caveat is misleading given Dave Williamson’s published results and the simple mathematical proof cited.

    Given that the climate models do not accurately approximate the correct dynamics or physics, are they more accurate than Pat Frank’s linear equation? Yes or no?

    [Response: Yes. Stratospheric cooling, response to Pinatubo, dynamical response to solar forcing, water vapour feedback, ocean heat content change… etc.]

    The correct answer is obviously no. All of those supposed bells and whistles in the presence of inappropriate dissipation and inaccurate parameterizations were no more accurate than a simple linear equation.

    What is the error equation for the propagation of errors for the climate or a climate model?

    [Response: In a complex system with multiple feedbacks the only way to assess the affect of uncertainties in parameters on the output is to do a Monte Carlo exploration of the ‘perturbed physics’ phase space and use independently derived models. Look up or indeed the robustness of many outputs in the IPCC AR4 archive. Even in a simple equation with a feedback and a heat capacity (which is already more realistic than Frank’s cartoon), it’s easy to show that error growth is bounded. So it is in climate models. – gavin]

    The problem is that Monte Carlo techniques assume random errors. Pat Frank has shown that the errors are not random and in fact highly biased. If you run a bunch of incorrect models, you will not obtain the correct answer.
    Locally errors can be determined by the error equation derived from errors in the dissipation and parameterizations. Given that these are both incorrect,
    one cannot claim anything about the results from the models.

    I continue to wait for your proof that the initial-boundary value for
    the hydrostatic system is well posed, especially given the exponential growth shown by NCAR’s Clark-HAll and Wrf models.


  3. 153
    Jeffrey Davis says:


    Look at 100 years of data. Temps go up and down. Temps since 1940 have mostly gone up, but there have been some years down. Even consecutively. The long term trend is up.

    What did you expect?

  4. 154
    Gerald Browning says:

    Gavin (#147),

    Or that the dissipation in the models in unphysically large and is hiding
    the problem. Why do you answer for the people that are addressed?


    [Response: If you want to have a private conversation do it over email. If you are not interested in my answers, then ignore them. – gavin]

  5. 155
    Hank Roberts says:

    > Why do you answer for the people that are addressed?

    The Contributors can often answer questions that the rest of us, who are amateur readers, can’t easily do, may fumble, or may go on at exhaustive length about. In fact if you really want to disable the thread, pick any of several hobbyhorses and bring out the saddle and bridle, and it will be ridden.

    Particularly when someone’s asking loaded or hobbyhorse questions, the Contribs often can save an awful lot of recreational typing time wasted by giving answers that keep the thread on topic.

    Of course that’s only _my_ opinion as an amateur bystander reader of the site (grin). Gavin may put it more bluntly.

  6. 156
    Ray Ladbury says:

    Jerry Browning, given that I’ve seen no evidence that either you or Pat Frank have made any effort to actually understand the climate models as they really are, your criticisms only apply in your own little straw-man universe. So, in our Universe, the climate scientists can continue to make progress and in your universe, you can continue to say it’s impossible. In any case, one need not resort to modeling at all. All one need do is decide whether CO2 is a greenhouse gas and whether those properties continue on past concentrations of 280 ppmv or whether they magically stop. On planet Earth, CO2 is definitely a greenhouse gas and it continues to be to much higher concentrations than 280 ppmv. How about your planet?

  7. 157
    Jared says:


    There were many examples of people who have used the 1990s temperature rise and the year 1998 in particular as specific examples of AGW.

    Here is one example from 1999:

    Reuters – Washington – March 10, 1999 “The 1990s were the warmest decade of the millennium, with 1998 the warmest year so far, researchers said Wednesday. The study adds to a growing body of evidence that the global climate has been getting steadily warmer, especially the last half of the 20th century.”

    How about this news from last year?

    “Global warming is accelerating three times more quickly than feared, a series of startling, authoritative studies has revealed.

    They have found that emissions of carbon dioxide have been rising at thrice the rate in the 1990s. The Arctic ice cap is melting three times as fast – and the seas are rising twice as rapidly – as had been predicted.”

    Once again, drawing conclusions about climate from a very short period of time.

    And this from James Hansen:

    “Hansen notes that most previous annual global record temperatures were only a few hundredths of a degree warmer than the previous record, “but in 1998 the temperature was three-tenths of a degree warmer.” He adds, “It has become very difficult for anyone to argue that observed global warming is natural variability. We have good reason for being able to say that the world will be warmer by about a quarter of a degree in the next decade. It’s the same reason we had 10 years ago when we said that the 1990s would be warmer than the 1980s: The planet is out of equilibrium.”

    Note how he uses both 1998 and the 1990s as proof of AGW.

  8. 158
    Jared says:


    Yes, I agree, there is fluctuation in the longer term and temps have trended upwards since 1850. What I fail to see, however, is proof positive that this warming is due primarily to GHG/man-made warming. The fact is, there have been other rises and falls in global temperature before…science is always looking for an explanation, and in this case, GHG makes sense to a lot of people as an explanation as to why we have been warming.

    However, it never hurts to remember that correlation does not equal causation…just because C02 levels have been rising the past 100 years does not mean that the past century of warming was due to them. CO2 concentrations are increasing at a faster rate than ever before (as they were during the 1945-75 cooling period), so it would stand to reason that global temps would follow. So far this decade, they haven’t.

    [Response: As an aside, I have generally found that whenever the phrase ‘it stands to reason’ is used, it very rarely ever does. – gavin]

  9. 159
    Ray Ladbury says:

    Jared, Yes, correlation does not equal causation, but correlation of an event that would be unlikely in the absence of a given cause along with a cause that is well understood in terms of physics and is known to be coincident–that is strong evidence. Why do denialists insist on ignoring physics?

  10. 160
    Jared says:


    Lol, thanks for that, Gavin. Regardless my choice of phrase though, wouldn’t you agree that greater rates of C02 input into the atmosphere should result in greater rates of warming, at least as a general rule?


    Ray, I am not a denialist, though I suppose you can label me as you see fit. I am just looking at all the evidence that I can and trying to come to the best conclusion I can…if that disagrees with your conclusion (and I haven’t fully reached mine yet, that may take some time), that doesn’t mean I am in denial of anything.

    Question for you: what makes you so sure that the warming of the past 150 years would be “unlikely” without CO2?

  11. 161
    Gerald Browning says:

    Ray Ladbury (#156),

    Spare me the verbiage. Heinz Kreiss and I have done more mathematical theory to understand atmospheric and ocenographic models than any climate modelers will ever do.

    As a simple example of my understanding of your games, can you tell me how you treat the upper boundary of your climate model, i.e. is there a sponge layer? Is that physics or a numerical gimmick to damp the upward propagation of gravity waves? What impact does that have on the real solution over time? How does that impact information propagating from above the top of your model? Does your model use the plasma equations at higher altitudes?

    I am well aware of the numerical gimmicks in the models.


  12. 162
    dhogaza says:

    “The 1990s were the warmest decade of the millennium, with 1998 the warmest year so far, researchers said Wednesday. The study adds to a growing body of evidence that the global climate has been getting steadily warmer, especially the last half of the 20th century.”

    Jared, did you perhaps miss that little phrase ADDS TO a growing body of evidence?

    The claim is not being made that the 1990s decade by itself is sufficient evidence, but rather a longer period of time, to which the 1990s are appended.

    Note how he uses both 1998 and the 1990s as proof of AGW.

    And again, Hansen’s not using that ALONE. He’s claiming it’s part of a body of evidence, not all the evidence.

  13. 163
    Hank Roberts says:


    You know, you’re FUNNY.
    That’s hysterical.

  14. 164
    tamino says:

    Re: #157 (Jared)

    I asked you to show us where AGW proponents use a trend from a 10-year time span to show warming. You reply by pointing to the statement that the 1990s was the warmest decade of the millenium. Comparing the 1990s to the last millenium is not even close to using a 10-year period to establish warming; it’s using a 1000-year period. Then you talk about the emissions of carbon dioxide and melting of the arctic ice cap, when the subject at hand is the global temperature. Finally you talk about a comparison of the 1990s to the 1980s as though that’s “using the 1990s.” It’s not using a single decade; it’s comparing one decade to another.

    You tried to use a trend over a 10-year time span to show a lack of warming. When it was pointed out that this is not valid, you accused “AGW proponents” of doing the same thing. Clearly your accusation was wrong, and your attempts to support it are pathetic.

  15. 165
    Dan says:

    re: 158. “What I fail to see, however, is proof positive…”

    Oh brother. How many times must it be said that “proof” is a *mathematical* concept before skeptics and denialists get it? That is not what is accomplished through the scientific method and peer review. Skeptics and denialists simply repeating “there is no proof!” over and over again like a child throwing a tantrum does not make the statement carry any more validity.

  16. 166
    David B. Benson says:

    Jared (160) wrote “what makes you so sure that the warming of the past 150 years would be “unlikely” without CO2?” One way is to look at the temperature rises during the entire Holocene. There appears to be only one (other) large temperature rise in such a short time in the past 10,000+ years. That was during the recovery from the 8.2 kya event and so it started from a much colder temperature.

  17. 167
    Geoff Beacon says:


    You get much argument from the Skeptics so I don’t want to raise your ire by an attack from the other side but I am concerned that there may be positive feedbacks that have not really kicked in yet – at least to any great extent.

    I was concerned when I received a reply from the Hadley Centre last year which included “The CH4 (and CO2) permafrost feedback isn’t included in current EarthSystemModels and it is potentially large but no-one really knows. I think the community has been a bit slow to take up on this feedback because of the lack of data.”

    That may not be the only “missing” feedback – failing sinks, burning forests & etc. I have a friend who worries about air-conditioning in developing countries as a form of positive feedback.

    I think I’m prone to panic but should I loose sleep over the latest increase in methane after last year’s arctic warming?

    [Response: The methane budget has significant uncertainties because of the widely distributed sources, poor reporting and significant naturally variable wetland components. There is some indication that a number of anthropogenic sources may be starting to pick up again, but the change last year is still small. People are quite concerned about the permafrost sources, but as yet, it doesn’t appear to be large. So don’t lose sleep, but maybe keep a closer eye on things. – gavin]

  18. 168
    Jared says:


    Yes, I realize they are not claiming the warming in the 1990s as the main evidence of AGW, but they are still using the data from ONE DECADE as evidence (and one year – 1998). Tamino’s assertion was that one decade is not a long enough to be evidence one way or the other (but 20 years apparently is).

    And Hansen’s comments strongly implied that the temperature rise seen in ONE decade, the 1990s, and the high temps from ONE year, 1998, was clear evidence of AGW. No, he’s not claiming that as the only evidence, but he is clearly pointing to short periods of time as significant indicators.


    What does the website have to do with it? That was directly from a Reuter’s news article from 1999…


    Timino, you are arguing semantics. You know just as well as I do that people point to the warming over a very short period of time on earth (10, 20, or 30 years) as evidence of AGW. Haven’t you watched An Incovenient Truth? How many of Gore’s examples of global warming are things that have happened in recent years?

    All I did was show that over the past 10 years (or if you don’t like to include 1998, 2001-2008), there has not been the continued rise in temperatures that was seen in the 1980s and 1990s. I didn’t accuse AGW proponents of doing anything, except also pointing to the 10 year trends that occured in the 1980s and 1990s.

    How about this article?

    The author uses such facts as “2006 was also the hottest year on record in the United Kingdom” and “New Jersey recorded the hottest temperatures ever seen in that state” and “Because of the warmer U.S. temperatures from October through December, energy use for residential heating was 13.5 percent below average for those three months” to eventually build to the statement: The Global Warming Debate is Over.

    And honestly, you see stuff like this all of the time. People use all sorts of time periods and facts to shout their warnings about AGW, and ignore the trends or facts or time periods that don’t back up their beliefs.

    Now, could you show me another 10 year period since 1977 that shows a flat trend? Blocking out 1992-93, of course, since there has not been a major volcanic eruption in the past 10 years. In other words, since many of you are so convinced I am cherry picking to arrive at a certain result, prove me wrong by showing how 1978-1988 had a flat trend…ok, that one didn’t, how about 1981-1991? Try 1984-1996 (eliminating 92-93)? Maybe 1995-2005?

  19. 169
    Jared says:


    I don’t know David, there is a lot of conflicting information out there when it comes to past climate. I know that several global reconstructions I have seen showed a .5C increase from about 200 AD to 350 AD. Also, a jump of .4C from 780 to 850 AD. Or a jump of .5C from about 1200 to 1270 AD. Even more recently, some graphs show a spike of about .6C from 1700 to 1800. Those are all comparable to what we’ve seen the past century.

  20. 170
    David B. Benson says:

    Jared (169) — It depends upon the required precision. I take the last 100 years of warming as 0.7 K. Others put it as 0.6 K. Either of these might be taken as comparable to your 1700 to 1800 CE jump.

    I didn’t see those jumps in the GISP2 temperature data, but perhaps my program wasn’t set up properly for that purpose. I may have time over the weekend to attempt a closer look.

    But even so, such jumps certainly appear to be rare events, yes?

  21. 171
    Hank Roberts says:

    > What does the website have to do with it? That was directly from
    > a Reuter’s news article from 1999…

    No, it was a partial excerpt from a second hand copy of a U. Mass press release.

    And it’s about one of the most discussed papers on the subject, discussed in great detail here and elsewhere. You’re stuck on one sentence from the press release. That’s not the paper.

    Do you know which paper you’re talking about?

    Have you read the discussion here about press releases?

  22. 172
    Hank Roberts says:

    Just sayin’ — we amateur readers here often won’t recognize names, til given a clue to follow.

  23. 173
    Ray Ladbury says:

    Jared, you ask why I am sure the warming in the current epoch is related to anthropogenic CO2. Basically, it comes down to physics. CO2 has to play a central role in supplying the 33 degrees of greenhouse warming we know are normally part of Earth’s energy balance. As I have said many times, I know of no reason why that should magically stop at the pre-industrial value of 280 ppmv. CO2 is central to understanding paleoclimate, response of climate to perturbations and on and on.
    Equally important, nobody is publishing any alternatives in scientific journals. You will have the occasional contrarian idea (e.g. cosmic rays), but after it is published, it goes nowhere. That doesn’t happen in science unless the way forward is pretty narrow. Scientists are always trying to break from the pack–it’s how they make careers for themselves. Climate science is over 150 years old and a mature field. We still have much to learn, but the uncertainty on the role of CO2 is small. If that is wrong, then everything we know about climate is wrong–and that is not plausible any more than everything we know about speciation or gravity being wrong.

  24. 174

    I hope you don’t mind if I ask an ignorant question. From reading an article about the GISS measurements on the Earth Observatory site, assuming I understood correctly (always a good question), then the urban heat island temps are thrown out if they are far off from the temps of the surrounding countryside. But, my question is: why shouldn’t some of that heat be included? We have lots of urban sprawl that is hot, don’t we? I understand that when a thermometer is located in an area that absorbs an inordinate amount of heat, that that might be an anomaly that could be kicked out, but is most of the heat of the urban centers accounted for?

    This is from the EO article:

    “Weather stations are screened for potential bias from urban heat islands by comparing station locations with maps of urbanization. Measurements from nearby stations in rural areas are used to correct urban station data for warming due to the heat island effect. If no rural neighbors are available for comparison, data from urban and peri-urban stations are left out of the global average calculation.”

    I guess what I am asking is if there is a downward bias in the data collection method. On the other hand, maybe the EO explanation was written in such a way that they had to leave out really technical stuff that laypersons like me would not have understood anyway.

  25. 175
    Hank Roberts says:

    Tenney, this is the kind of reading I’ve found helpful on that question, for whatever use it may be:

  26. 176
    Martin Vermeer says:

    Tenney Naumer #174: I guess the authoritative answers are in the original articles linked from the GIStemp site, but having read up a little on this myself, I will give it a try.

    Indeed it would make sense to include urban heating into the definition of global surface heating, but only if the station geometry would allow that. I.e., it would have to be areally random (think throwing darts at a map) and it clearly isn’t in relation to city locations. This makes removing urbanization-related trends as well you can the only possibility.

    About a downward bias: no. The trend adjustment is always done, independent of the algebraic sign of the urban trend relative to surrounding rural stations. The only info used here is the urban/rural flags.

    Note that not all anomalous trends are due to the UHI effect; there can be many reasons. Removing only the up trends would indeed introduce bias and is therefore a big no-no. Same applies to the cross-validation done on all stations against their rural neighbours, using the redundancy caused by the long-range correlations to remove outliers from the data.

    (PS your question was not ignorant. You have no idea what real ignorance looks like ;-) )

  27. 177

    J posts:

    Do you know whether anyone has done this (archived a globally averaged time series version, with annual or monthly steps, somewhere where it would be publicly available)?

    Type “NASA GISTEMP” into Google and click on the first link that comes up.

  28. 178
    Ray Ladbury says:

    Hank, I’m aware of Browning, and what he has cannot be correctly characterized as understanding. I notice that he scrupulously avoided the issue of whether CO2 is a greenhouse gas–and all the other physics. The issue is not whether the models work–their success speaks for itself. The thing that bothers me about Browning et al. is that they completely lose sight of the physics by getting lost in the details of the models.
    If you are a “skeptic,” the models are your best friends–they’re really the only way we have of limiting the risk we face. That the planet is warming is indisputable. That CO2 is behind that warming is virtually beyond doubt. What is open to dispute is how much harm will come of that. If we were to limit ourselves to the worst-case from paleoclimate, the damage to human society is effectively unlimited. The models tell us where to worry. They give us ideas of how much we have to limit emissions and how long we have to do it. They make it possible to go from alarm to cost-effective mitigation. If the models were to be demonstrated unreliable, they are more likely to err on the conservative side. We still have large risks, but now they are unquantifiable. Ask Warren Buffet if he’d prefer a risk that is imperfectly bounded to one that is unbounded and see which one he’ll take.
    I’m sorry, but I don’t attach a lot of value to technical prowess when it is divorced from the context (physical and societal) of what is being modeled.

  29. 179
    Ray Ladbury says:

    Tenney, Yes, land use does have an effect, but we have to look at long term trends, and if what we’re interested in is the effect of CO2, we have to get rid of confounding effects so we are comparing apples to apples.
    Actually, they don’t completely throw out the data. They may analyze it separately, or downweight it. The question has been treated here:

  30. 180

    Thanks, guys, I will go and read further.

    (Re: “no-man-is-an-urban-heat-island — hahahaha)

  31. 181
    Ron Taylor says:

    Jared, I agree that you cannot use a regional data point to support a global conclusion. But as long as one is comparing apples to apples (global point in relation to a global trend), then it seems to me that the established trend is important in interpreting a new data point.

    So, if a new global temperature is recorded that falls well below the trend, it may be noise, or it may represent a drop in the warming trend, but it is impossible to know which for many more years.

    If a temperature on or well above the trend is recorded, however, it can only support a continuation or strengthening of the established warming trend. Statistically, it cannot support a decline in the warming trend. So it is perfectly legitimate to say that it is consistent with the global warming trend.

    I am not a statistician, but this seems like common sense to me.

  32. 182
    Gerald Browning says:


    I would like to comment on Ray’s lack of understanding of mathematics
    in his comment 174. [edit – please link rather than repeat]

    It is well known in mathematics that if an initial-boundary value problem for a time dependent partial differential equation is not properly posed, i.e. it is ill posed, then there is no hope to compute the solution in the continuum and certainly not with any numerical method. The reasons that the ill posedness of the hydrostatic system that is the basis of all the atmospheric components of the current climate models has not yet been seen are as follows.

    The climate models are only resolving features greater than 100 km in size, i.e. they are not resolving mesoscale storms, hurricanes, fronts, etc. These are certainly important to any climate. How is it possible that the climate models are able to run when not resolving these features. The answer is by using unphysically large dissipation that prevents the small scale features from forming. Thus the model is not physically realistic as claimed by Ray and the forcing terms are necessarily inaccurate in order to overcome the unphysically large dissipation (energy removal). Runs by Dave Williamson at NCAR have shown the inaccuracy of the spatial spectrum when using unphysically large dissipation and have also shown that the forcing terms (parameterizations )are not physically accurate (references available on request [edit – please give references directly]). Thus the models are not accurately describing the continuum dynamics or physics (forcing), i.e. the numerical solutions are not close to the continuum solution of the hydrostatic system.

    Runs by Lu et al of the NCAR Clark-Hall and WRF models have also shown that as soon as finer numerical meshes that resolve the smaller scale features are used, fast exponential growth appears even in the well posed nonhydrostatic models (reference available on request – [edit – as above, please give references]). In the case of the hydrostatic system, meshes of this size will show the unbounded exponential growth typical of ill posedness (see numerical runs on Climate Audit under the thread Exponential Growth in Physical Systems).

    Thus hydrostatic climate models are currently so far from the real solution of the hydrostatic system that they are not showing the unbounded exponential growth. And the numerical gimmick that is used to run the models unphysically removes energy from solution at too fast of rate, i.e. it is not physically accurate.

    So CO2 has increased, but climate models are not close to reality so adding forcing terms (physics) at this stage or later when the unbounded exponential growth appears is nonsense.

    Climate audit has shown that the global measurement stations are questionable (to say the least) and the numerical climate models are inaccurate and always will be. So the arguments for AGW are not scientific, but hand waving. I have nothing to gain in this argument (I am retired), but RC has lots to lose in terms of funding.


    [Response: The argument for AGW is based on energy balance, not turbulence. The argument existed before GCMs were invented, and the addition of dynamical components has not provided any reason to adjust the basic picture. As resolution increases more and finer spatial scale processes get included, and improved approximations to the governing equations get used (such as moving to non-hydrostatic solvers for instance). Yet while many features of the models improve at higher resolution, there is no substantial change to the ‘big issue’ – the sensitivity to radiative forcing. It should also be pointed out (again) that if you were correct, then why do models show any skill at anything? If they are all noise, why do you get a systematic cooling of the right size after Pinatubo? Why do you get a match to the global water vapour amounts during an El Niño? Why do you get a shift north of the rainfall at the mid-Holocene that matches the paleo record? If you were correct, none of these things could occur. Yet they do. You keep posting your claim that the models are ill-posed yet you never address the issue of their demonstrated skill. In fact, you are wrong about what the models solve in any case. Without even addressing the merits of your fundamental point, the fact that the models are solving a well posed system is attested to by their stability and lack of ‘exponential unbounded growth’. Now this system is not the exact system that one would ideally want – approximations are indeed made to deal with sub-gridscale processes and numerical artifacts – but the test of whether this is useful lies in the comparisons to the real world – not in some a priori claim that the models can’t work because they are not exact. So, here’s my challenge to you – explain why the models work in the three examples I give here and tell me why that still means that they can’t be used for the CO2 issue. Further repetition of already made points is not requested. – gavin]

  33. 183
    David B. Benson says:

    Jared (169) wrote “Also, a jump of .4C from 780 to 850 AD.” That is the only time period which shows up as a ‘large temperature increase’ in my analysis of the GISP2 central Greenalnd ice core temperature data. Using that as a normalizer, the only times in the Holocene with temperature increases comperable to those of the last 100 years are, indeed, during the recovery from the 8.2 kya event and the subsequent run-up to the Holocene maximum there. That is two such runs.

    Using a less stringent notion for ‘large, fast run-up’, there are a total of nine. The only one in the GISP2 record in the last (almost) four thousand years is associated with the event quoted above.

  34. 184
  35. 185
    Hank Roberts says:

    (PS, the first link starts with Judith Curry’s review, worth reading)

  36. 186
    Ron Taylor says:

    Re Gerald Browning in 182.

    Gavin, thank you for your lengthy rebutal of this…(stuff). I do not know anything about Browning, but his post reeks of denialist strategy. First, by the inaccuracy of his statements, as you have exposed them, he seems to have begun with a conclusion (“…the ill posedness of the hydrostatic system that is the basis of all the atmospheric components of the current climate models…”), then constructed a house of cards argument that would support the conclusion, conveniently ignoring contrary evidence. It would appear that “ill posedness” is the latest sound bite mantra of denialists who have the knowledge to sound at least scientifically plausible.

    If you can’t refute the physics, try a mathematical argument. What next?

  37. 187
    Ray Ladbury says:

    Gerald Browning, I am sure you know the quotation by George Box:

    “All models are wrong; some models are useful.” The goal of a physical model is not to reproduce every feature of a physical system down to the last molecule, but rather to yield insight into the system. GCM have amply fulfilled this criterion–yielding insight into such phenomena as ocean circulation, feedbacks, etc. As I said before, the issue is whether CO2 is a greenhouse gas and whether that contribution continues above 280 ppmv or whether it magically stops there. I’ll take physics over magic.
    You seem to hear only the first part of what George Box said–rejecting any model that does not reach your exacting standards of fidelity. You offer no way forward, or rather the only way forward in your eyes would be to wait until computer power advances sufficiently that modeling becomes easy. Fortunately, science finds ways to advance even through difficult problems. You can scream that it is impossible, but the climate models will continue to advance.
    Moreover, even if we abandoned modeling entirely, one doesn’t need much of a model to see that the problem of anthropogenic warming is real and won’t go away from our ignoring it.
    Science celebrates those who solve problems–not those who say that can’t be solved.

  38. 188
    Hank Roberts says:

    Seriously, folks, read Dr. Curry on this question, over at the Other Place.

  39. 189
    Jared says:


    It’s true, Ray, that C02 and other GHG are certainly necessary to maintain the warmth on earth. However, just because their presence is required for a warm earth does not necessarily mean that C02 levels are always directly proportionate to earth’s temperature, or that there cannot be negative feedbacks to them. There are negative feedbacks to almost everything else in climate…it’s the earth’s way of balancing things out (to a certain extent). Possible negative feedbacks to increased C02 are not fully understood. There are theories on positive feedbacks, mostly involving water vapor, that have not been fully supported by observation. Therefore, I would think it be possible for some negative feedbacks to exist that we don’t understand yet.


    So Ron, if I understand correctly, you are saying that as long as temperatures are not falling, the global warming trend is still ongoing? Hmmm…well, if global warming was continuing at the same rate as before (and according to AGW theory, barring a major volcanic eruption it shouldn’t stall for more than a year or two – after all, that C02 is continually rising – which is why NASA predicted that a consensus record warm year will occur in the next 2-3 years), then every decade should show warmer temps by the end than the beginning. In other words, the warming should be evident through the decade. This occurred in the 1980s, it occurred in the 1990s, and it was predicted to occur in the 2000s. If it does not happen this decade, then global warming will have apparently stalled. Which would not add up, according to AGW theory.

    According to CRU data, the 1980s average temperature increased .25C from the 1970s, the 1990s increased .14C (lower in part to the Pinatubo eruption), and 2000-2007 period has increased about .17C from the 1990s. Now, if we assume the 1990s would have had a similar rate of increase as the 1980s if it weren’t for Pinatubo, the 2000s rate of warmth from the 1990s would be even lower. And then consider that so far 2008 is considerably colder than 2007, and the rate of increase drops even further for this decade.

    In my opinion, it’s fairly obvious that the 2000s have at the very least not continued the same rate of warming as the 1980s and 1990s. Which doesn’t make sense, since C02 levels have continued to climb.

  40. 190
    tamino says:

    Re: #168 (Jared)

    You used a trend rate over a 10-year time span to claim an absence of warming. Many people tried to educate you to the fact that this is too small a time span to give an accurate trend rate. You retorted that AGW proponents do the same thing.

    So I asked you to show us where anybody used a trend rate from a 10-year time span as evidence of AGW. You haven’t been able to do so. You attempted to do so by mentioning the statement that the 1990s were the warmest decade of the millenium. Apparently you can’t really tell the difference between a 10-year time span and a 1000-year time span.

    Now you dare us to show a 10-year time span (other than the most recent) since 1977 which shows a flat trend. But while you felt entitled to start with 1998 (huge el Nino) and end with 2008 (la Nina) to show a flat trend, you now insist we block out 1992-1993. This is hypocrisy.

    I’ll make one last attempt to educate you. I’ve computed the trend rate for every 10-year period, from Jan.1975-Dec.1984 through Jan.1998-Dec.2007, for both GISS and HadCRUT3v data, *with error ranges* computed using an AR(1) error model. These error ranges are actually too small because the errors are not AR(1), but at least they’re in the ballpark. They’re plotted here. Note that for 10-year time spans, the error range is large, but for the 30+ year time span it’s much smaller.

    It’s the failure to understand the probable error in trend estimates that is the root of foolish claims that global warming has abated.

    Re: #189 (Jared)

    so far 2008 is considerably colder than 2007

    Considering that the trend estimate from a 10-year time span is as uncertain as it is, how accurate is a trend estimated from a year and four months?

  41. 191
    Bryan S says:

    Re #187: Ray, it is my policy to show patience with people who may not yet agree with scientific arguments that I may make, but I am about to violate my own policy. Gerald Browning is a respected scientist with many peer-reviewed papers to his credit. Like it or not, he has the professional experience and reputation to comment on this issue. Parroting uncritically the same old tired line of name-calling (brand them a heretic by calling them the dreaded D word) that so typifies many pushing one particular perspective, does not further the science or your agenda. Several of us who drop by this websight from time to time happen to be scientists in various disciplines who spend our professional lives in the domain of physics. Suggesting that those scientists who dare to critically examine the underlying science behind the current climate claims, somehow do not “believe the physics”, amounts in some ways to a cheap and easy kind of slandor (its really a not-so-subtle propaganda tactic). By the way, no credible scientist doubts that CO2 is a greenhouse gas, so save your simpleton schoolboy lecture. Why don’t you take the time to read the paper by Carl Wunsch that I linked to above? For those who don’t know, he is one of the most renowned oceanographers of our day, and he in fact agrees with many of the same points given by Gerald Browning here. Inadequate sub-grid scale parameterizations, truncated physics, poor initilization, accumulating systematic error, ect, may not end up rendering the GCMs useless for multi-decadal climate predictions, but the burden of proof of their skill certainly lies with the claimant. It is very telling that two of the examples of skill Gavin gives above involve hindcasts of short-term initial value problems regarding certain aspects of a volcanic eruption and El Nino, and not the multi-decadal boundary value problem being sold with so much vigor. One of the hindcast examples involves the shift in mid-Holocene precipitation patterns, and is not yet well established. And then Gavin states that the argument is about energy balance and not turbulence. Well,is not the ocean a turbulent fluid, and does not this turbulent fluid advect heat and vapor into the atmosphere, thereby regulating to some extent (unarguably on at least decadal timescales) the TOA energy balance? So please save us the pitiful line about “believing the physics”.

    And by the way Ray Ladbury, Einstein remained a skeptic of quantum mechanics until his dying day, and he was nonetheless fairly well celebrated. Sorry if this is a little harsh, but you caught me in a particularly bad mood.

  42. 192
    Jared says:


    Thank you for your attempts at “education”, but there is no need to talk down to me.

    In response…

    1) As I already explained, the flat trend can be obtained by looking at the mean between 1998-1999 (strong El Nino to strong La Nina). I believe this is fair, considering that most of the 2000s have been dominated by El Nino. Or, you can look at 2001-2008 and see the same basic flat trend.

    2) The reason I ask that you block out 1992-93 is reasonable: it was a much cooler period due to a volcanic eruption. There was no such cooling due to volcanic eruption in the past 10 years. ENSO variations, however, have been a constant for the past 30 years. (You will note that the authors on this site have a disclaimer regarding volcanic eruptions in their bet with the German scientists, for the same reason).

    3) If you think the ten year trend may be flawed due to error, that is your perogative. It is what it is…you can interpret it however you want. I have already presented other evidence as to why I believe global warming has at the very least slowed the past decade.

  43. 193
    Jared says:

    One more thing, Tamino. I’m not claiming that 2008 being colder than 2007 would prove anything, just that it would lower the average temperature for the 2000s further…which would then contribute to the slowing trend in global warming.

  44. 194
    JCH says:

    Bryan S, I read both of your links for Carl Wunsch when you posted them.

    Do you think Carl Wunsch would agree with your assessment, and correct me if I misunderstood your drift, that these guys have a lousy hypothesis?

  45. 195
    Chris Colose says:

    #191, Bryan

    The TOA energy balance is simply the net incoming radiation (accounting for albedo) and the outgoing longwave radiation. It is the TOA energy balance that regulates climate, and it is the addition of CO2 that inhibits the energy loss to space. In fact our current situation is that the Earth is taking in more radiation than it is emitting back to space. The SURFACE energy budget, however, which essentially regulates the surface-atmosphere gradient involves convective and conductive heat loss, etc. Personally, I have not seen any good evidence that internal variations can alter the TOA energy balance on climate timescales (they certainly do on shorter ones) like ENSO, etc. This seems to go along with Roy Spencer’s argument on “internal radiative forcing” but I don’t know if there is such a thing.

    Now Gerald Browning is talking about mesoscale features that cannot be captured by climate models. I don’t do modelling so I’ll let Gavin or more serious people answer those objections. But I will say that inability to capture hurricanes, fronts, etc will not alter the conclusion that if you take in more radiation than you give off, you’re going to warm? How can it not? How is Gerald Browning going to sidestep energy conservation principles? It sounds like “handwaving” to Ray by asking things on “upward propagation of gravity waves” and “plasma equations.” I think someone is just trying to sound fancy, but ignoring the undergraduate level stuff. If you add CO2, the planet WILL warm, and you actually don’t need GCM’s to tell you that. Svante Arrhenius didn’t have a fancy GCM back in his 1896 paper when he said that doubling CO2 would cause a good deal of warming. What’s more, the paleoclimatic record, as well as what other planets can tell us (say, Venus) only reinforce this knowledge. You’re not going to get “unbounded exponential warming” because the outgoing radiation scales to the fourth power of the temperature. Surface speaking, any cooling due to evaporation is how the surface comes back to equilibrium after being perturbed by the increased radiative heating; that is automatically accounted for in models, and is necessary for them to reach equilibrium, which is a prerequisite for an estimate of the “equilibrium climate sensitivity” to, say, 2x CO2.

  46. 196

    Bryan S writes (in the midst of a long rant):

    Inadequate sub-grid scale parameterizations, truncated physics, poor initilization, accumulating systematic error, ect, may not end up rendering the GCMs useless for multi-decadal climate predictions, but the burden of proof of their skill certainly lies with the claimant.

    What part of “the models successfully predicted a number of things” do you not understand? The skill of the models was proved a long time ago. It was proved when they got the magnitude and duration of the cooling after the Mt. Pinatubo eruption correct. It was proved when they reproduced the water vapor profile during the recent El Ninos and La Ninas. Why do you and Gerald Brown keep babbling about how the modelers have to prove the skill of the models, when the modelers did so a long time ago?

    Arguments about how the models can’t possibly work are out of court from the beginning when we can see the damn things working. Get a clue!

  47. 197

    Jared posts:

    As I already explained, the flat trend can be obtained by looking at the mean between 1998-1999 (strong El Nino to strong La Nina).

    No, the flat trend can’t be obtained that way, because that’s not how you obtain a trend. You obtain a trend by doing a linear regression against elapsed time. This isn’t something on which people can hold different possibly correct views. It’s basic statistics.

  48. 198
    Ray Ladbury says:

    Bryan S., I am aware of Gerald Browning’s C.V. I am also aware that the contributors here at RC have C.V.s that are equally if not more impressive. What is more, the contributors here are gracious–and the same cannot be said of Browning with his snide insinuations. Looking back, some of what I’ve said may sound harsh. I do apologize if what I said seemed to question Browning’s accomplishments and abilities. However, I think that the substance of my criticism stands. I think his criticism is based on a fundamental misjudgment of the science.
    Browning came on here extolling the merits of Pat Frank’s article. I’ve looked at the article–it’s garbage. First, it exaggerates the flaws that are in current climate models. Computational physics always has flaws and kludges. The question is whether these flaws undermine the insight the models provide, and this is demonstrably not the case when it comes to climate models. Second, even if the climate models went away entirely, it would not undermine the case for anthropogenic CO2 as the cause for the current warming epoch. Indeed, I contend that the models are the best friend of those who would have us take a conservative approach to mitigation, as they are the only means we have of limiting risk. There are many other flaws in that article. Perhaps one could chalk them up to rhetorical flourish before a lay audience, but that in my mind does not diminish the sin.
    Bryan, perhaps an illustration would help. I work in applied physics, so I work with a lot of engineers. Some of the qualification methods they use are fundamentally flawed at a formal level–and yet they work. I could go in and rail against these methods–and I would be ignored. Alternatively, I could try to understand why these methods work despite their flaws, and then try to develop new methods on more solid formal ground that are more general and still allow cost-effective qualification. Jerry’s critiques don’t offer a way forward, and since science is about progress, it will progress around him. It progressed around Einstein, after all.
    Jerry doesn’t need you to defend him. My criticism matters to him as much as a fart in a windstorm. It would be more disrespectful of me to withhold my criticism out of some misplaced deference of feelings of intimidation. So, I’ll apologize for the tone. I’ll admit to a tendency to lapse disrespectful when I see someone behave in a disrespectful manner. However, I stand by my criticism that he is ignoring the physics by concentrating too much on perceived shortcomings in the models.

  49. 199
    Ron Taylor says:

    No Jared, I am not saying “that as long as temperatures are not falling, the global warming trend is still ongoing.” I am saying that if the temperature falls on or above the trend line, then it supports continuing warming. Nice try, but please don’t put words in my mouth.

  50. 200
    Ray Ladbury says:

    Jared, I’d like a little more than “might be” when talking about the future of human civilization. At present there is no credible evidence for some magical negative feedback that will save us. There is evidence for positive feedback that is not in the models (e.g. outgassing from thawing permafrost, oceans, etc.). Moreover, it is undeniable that paleoclimate shows significantly higher temperatures persisted for long periods in the past. This suggests that any negative feedback has its limits.
    You claim warming has “paused”. Yet, if you look at the trend line, it has barely budged. I urge you to learn the physics. Look at the evidence. Decide which hypotheses have the most explanatory (and predictive) power. Become familiar with and weigh the risks. Our energy infrastructure will have to change, independent of how it is affecting climate. Climate merely introduces another set of constraints