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Model-data-comparison, Lesson 2

Filed under: — stefan @ 10 April 2008

In January, we presented Lesson 1 in model-data comparison: if you are comparing noisy data to a model trend, make sure you have enough data for them to show a statistically significant trend. This was in response to a graph by Roger Pielke Jr. presented in the New York Times Tierney Lab Blog that compared observations to IPCC projections over an 8-year period. We showed that this period is too short for a meaningful trend comparison.

This week, the story has taken a curious new twist. In a letter published in Nature Geoscience, Pielke presents such a comparison for a longer period, 1990-2007 (see Figure). Lesson 1 learned – 17 years is sufficient. In fact, the very first figure of last year’s IPCC report presents almost the same comparison (see second Figure).

Pielke’s comparison of temperature scenarios of the four IPCC reports with data

There is a crucial difference, though, and this brings us to Lesson 2. The IPCC has always published ranges of future scenarios, rather than a single one, to cover uncertainties both in future climate forcing and in climate response. This is reflected in the IPCC graph below, and likewise in the earlier comparison by Rahmstorf et al. 2007 in Science.

IPCC Figure 1.1 – comparison of temperature scenarios of three IPCC reports with data

Any meaningful validation of a model with data must account for this stated uncertainty. If a theoretical model predicts that the acceleration of gravity in a given location should be 9.84 +- 0.05 m/s2, then the observed value of g = 9.81 m/s2 would support this model. However, a model predicting g = 9.84+-0.01 would be falsified by the observation. The difference is all in the stated uncertainty. A model predicting g = 9.84, without any stated uncertainty, could neither be supported nor falsified by the observation, and the comparison would not be meaningful.

Pielke compares single scenarios of IPCC, without mentioning the uncertainty range. He describes the scenarios he selected as IPCC’s “best estimate for the realised emissions scenario”. However, even given a particular emission scenario, IPCC has always allowed for a wide uncertainty range. Likewise for sea level (not shown here), Pielke just shows a single line for each scenario, as if there wasn’t a large uncertainty in sea level projections. Over the short time scales considered, the model uncertainty is larger than the uncertainty coming from the choice of emission scenario; for sea level it completely dominates the uncertainty (see e.g. the graphs in our Science paper). A comparison just with the “best estimate” without uncertainty range is not useful for “forecast verification”, the stated goal of Pielke’s letter. This is Lesson 2.

In addition, it is unclear what Pielke means by “realised emissions scenario” for the first IPCC report, which included only greenhouse gases and not aerosols in the forcing. Is such a “greenhouse gas only” scenario one that has been “realised” in the real world, and thus can be compared to data? A scenario only illustrates the climatic effect of the specified forcing – this is why it is called a scenario, not a forecast. To be sure, the first IPCC report did talk about “prediction” – in many respects the first report was not nearly as sophisticated as the more recent ones, including in its terminology. But this is no excuse for Pielke, almost twenty years down the track, to talk about “forecast” and “prediction” when he is referring to scenarios. A scenario tells us something like: “emitting this much CO2 would cause that much warming by 2050”. If in the 2040s the Earth gets hit by a meteorite shower and dramatically cools, or if humanity has installed mirrors in space to prevent the warming, then the above scenario was not wrong (the calculations may have been perfectly accurate). It has merely become obsolete, and it cannot be verified or falsified by observed data, because the observed data have become dominated by other effects not included in the scenario. In the same way, a “greenhouse gas only” scenario cannot be verified by observed data, because the real climate system has evolved under both greenhouse gas and aerosol forcing.

Pielke concludes: “Once published, projections should not be forgotten but should be rigorously compared with evolving observations.” We fully agree with that, and IPCC last year presented a more convincing (though not perfect) comparison than Pielke.

To sum up the three main points of this post:

1. IPCC already showed a very similar comparison as Pielke does, but including uncertainty ranges.

2. If a model-data comparison is done, it has to account for the uncertainty ranges – both in the data (that was Lesson 1 re noisy data) and in the model (that’s Lesson 2).

3. One should not mix up a scenario with a forecast – I cannot easily compare a scenario for the effects of greenhouse gases alone with observed data, because I cannot easily isolate the effect of the greenhouse gases in these data, given that other forcings are also at play in the real world.

363 Responses to “Model-data-comparison, Lesson 2”

  1. 51

    Re #37 where Lynn Vincentnathan Says:

    “RE the IPCC, my sense is that even with various scenarios and confidence intervals it might be underestimating CC. That’s just a gut feeling, …”

    Your gut feeling was confirmed only three posts later in #40 where Dave Blair Says:

    “Here is another new study that the current CO2 based models don’t fit historical temperatures.

    The study by Lee Kump and David Pollard is into why the models are under estimating the warmth during the Eocene and the Cretaceous. It follows that they will underestimate the warming caused by anthropogenic CO2 as well.

    Lynn, you also wrote “I know we aren’t going into a permanent runaway scenario, …”

    But there is not such thing as a permanent runaway in a finite universe. Eventually the runaway will end. It is generally believed than on Venus the runaway ended when all the carbon had been converted to CO2. An alternative proposal is that it ended when the surface became so hot that it melted, producing clouds of sulphur dioxide which reflect much of the sunlight away.

    If the later is the case, then on Earth a runaway would end when the oceans become warm enough to produce enough water clouds to reflect away the sunlight arriving here, and so re-establish a global energy balance. That is what happens during abrupt climate change. The energy balance is disrupted by the sudden loss of the albedo from sea ice. The temperature then runs away until the climate system produces enough clouds to compensate for that loss of albedo.

    So, you are correct. We don’t need to worry about the Earth becoming as hot as Venus, only as hot as during the PETM when there was a minor mass extinction

    Cheers, Alastair.

  2. 52
    pete best says:

    Re #42, Adapting to climate change or mitigating it will change over as the world warms and timelines become more and more constrained to fend off its impact.

    At the moment we have no post kyoto agreement, no laws in place and not real global mandate for everyone who releases significant amounts of GHG to do there bit to the levels necessary to impact AGW. If you look around you will seee various opinions from both engineers, scientists, environmental groups, politicians and esteemed agents of doom as to what to do about it.

    No single technology for each sector, transport, electricity and heating/cooling is currently in the frame to replace fossil fuels burning as at present they do not exist and are in the R&D/Prototyping stage and time to market is not known and hence mass consumption/uptae of a magnitide to impacr GHG emissions is not known at the present time. If something really concrete does not appear and has not started to impact GH emissions then we are looking more and more at adaption rather than mitigation.

    At the present time we hear of several conflicting technologies that will worsen GHG emissions that are already in production due to the power that fossil fuels have over us. These include, GTL/CTL, Heavy oils, Super critical gas/IGCC coal and the like. These technologies worsen GHG emissions and are either in production or will be soon.

    Technologies working to mitigate GHG emissions are all over the place at the present time and the ones that have been backed smell of desperation including Biofuel from corn and destroying rain forest to plant up palm oil etc. This is a bad idea. Therefore we await second generation algae or switch grass biofuels to assist in mitigating high oil prices on the existing infrastructure but only aglae based fuels can actually yield the amounts of oil necessary to grow th global economy whilst at the same time preserving global food stocks.

    Nuclear power, CCS coal, Wind, wave, solar, solar thermal, photo voltaic, we are going to need them all but no one knows quite sure just how. Can our current infrastructure cope with it all for one.

    Its a bit of a mess to be fair. Coherence is required and it aint coming until 2012 is it and not guarantees even then.

  3. 53
    Matthew Brunker says:

    Somehow the “arrogance” discussion strand was triggered by my comment #7 (see #9 referring to it), so I should better come clean that I am not a climatologist, I work in a completely different field of science – before you blame the wrong group. But what actually did you find arrogant about my comment? I just know how hard it is to get into Nature, you usually have to have something really new and interesting. Given that Pielke’s letter contains apparently nothing that was not already said in the IPCC report, I was wondering why Nature published it, and the best explanation I can see so far is that they just didn’t know about the IPCC graph and accompanying text.

  4. 54
    Manu D says:

    Given the arrogance I have seen over the years coming from Universities, and which I am afraid I see regularly on this blog only tends to confirm the mild, but increasing scepticism I have developed towards Climate Change – aka global warming.#9

    This comment reminds me of a great presentation at the AGU 2006 fall meeting regarding communicating about GW. One part of the presentation (I forgot the name of the author, apologies to him ;-) ) was illustrating the ‘bad way’ to present the case. It was illustrated by a video regarding the evolution vs intelligent design ‘debate’. The video was a fictitious debate between a proponent of each ‘side’. The pro-ID proponent was exposing calmly and kindly his arguments. The more he was using pseudo-scientific evidences, the more the pro-evolution scientist was getting agitated, trying to rectify the inaccuracies, getting more and more upset, he was boiling to the point of explosion. He ended up insulting his opponent. Needless to say who ‘won’ the debate with a test panel who watched the video, and this totally independently of the quality and scientific accuracy of the various arguments exposed. Then a video of a real debate was shown … though the attitude of the two proponents was not as extreme as in the act, similarities were striking.

    Coming back to the post to which you reacted to: where do you see arrogance in the statement that a study that has already been done, moreover with a more exhaustive analysis, probably should have not been published by Nature?

  5. 55
    tom watson says:

    I found the link to this page on It’s currently at the top of the pro, I also read latest con. I found it rather amusing.

    I am an EE with 4 decades of work about how electromagnetic radiation and matter interact. I have spent thousands of hours trying to understand how CO2 has some property that allows for the storage of the trillions and trillions of BTU required to globally warm the earth. I have concluded that if e=MC^2, then CO2 driving climate temperatures is a hoax.

    This goes a some way in confirming I am correct.

    Has the lead author of the IPCC chapter on feedback has written to Spencer agreeing that he is right as written…..

    From the con at climate debate daily….

    ” This has struck the alarmists like a thunderbolt, especially as the lead author of the IPCC chapter on feedback has written to Spencer agreeing that he is right!”

  6. 56
    Chris Dudley says:

    Roger has posted again though not to respond to questions. Again, I reiterate that this a Correspondence, not a Letter and thus may not have been peer reviewed. The guide for authors which shows the difference is here:

    If the IPCC feels that their work has been misrepresented they can reply. Given the discrepencies in the figures shown here, this may well be the case. Should the reply not be (automatically) accepted, then critisism of the editors would seem to be well founded.

    The original Real Climate article should be corrected to use the proper term: Correspondence not Letter. This is the basis for critisism of the lack of originality of Roger’s work, but originality is not a requirement for a Correspondence.

  7. 57
    Geoff Wexler says:

    Stefan’s article, Tamino’s web site and #26

    According to Lawrence Brown (#26) “the warming has been accelerating”

    But, according to Tamino’s* later articles (but not his comment here on an earlier thread) there is a substantial correlation between successive yearly residuals (difference between the data and the least squares linear fit to it). The effect is to widen the error bars considerably and make it very hard to detect any non-linearity in the observations. This leads me to the following questions:

    1. Is there and significant evidence from the temperature data (on its own) that global warming is accelerating? If I understand Tamino (after a brief glance ), you might as well assume a zero value. That would also rule out all the recent suggestions about global warming having slowed or ceased (which crept into BBC2’s Newsnight last week).

    2. If that is the case , could some of the discussion be simplified, the observed results since 1975 could be summarised by a single number i.e the rate of warming say + error estimates representing the noise. Likewise the trend in the observational evidence would consist of only three parallel straight lines (as displayed by Tamino). The smoothed black line in Stefan’s fig.1.1, which is not straight, would therefore still contain too much insignificant noise to be very useful.

    3. What does the theory (i.e. the models) have to say about estimates of the acceleration?

    4. Tamino estimates that we may have to wait till 2015 before being able to detect that “global warming since 2000 has stopped” . Is it agreed that positively accelerated warming might not show up until then ? or is this long wait unecessary if we start with 1975 instead of 2000?

    (Tamino is a statistician).

    [Response: Answering all this properly would need a scientific paper, but here is what I can say in five minutes. As we argued in “Lesson 1”, you need something around 15-year averaging to determine a robust trend given the interannual “noise” in the data. If you want to see whether the trend is changing (accelerating), you’d need to look at a much longer interval still. IPCC has done something like that in Figure TS6 on page 37 of the technical summary. This graph shows that warming has progressively accelerated, i.e. over the last 25 years warming was faster than over the past 50 years, etc.. Trend over the past:
    25 years = 0.18
    50 years = 0.13
    100 years = 0.07
    150 years = 0.05
    (all in degrees C per decade, more digits and error bars are given in the link). -stefan]

  8. 58
    Chuck Booth says:

    Re # 55 tom watson

    So, despite your education and work experience in your field, you rely on The National Business Review for scientific information? I hope you had higher standards when seeking information related to your job.

  9. 59
    Martin Vermeer says:

    Tom Watson #55:

    I am an EE with 4 decades of work about how
    electromagnetic radiation and matter interact. I
    have spent thousands of hours trying to understand
    how CO2 has some property that allows for the
    storage of the trillions and trillions of BTU
    required to globally warm the earth.

    It would have been better use of your time to first figure out that CO2 has a property affecting the transport of heat rather than its storage :-)

  10. 60
    Hank Roberts says:

    > the lead author of the IPCC chapter

    Says who?
    Which author?
    Which chapter?
    Which IPCC report?

    Show me a more recent source than this one for that statement:

    Publication Date: June 1, 2001
    Publisher: The Heartland Institute

    The Third Assessment Report (TAR) of the United Nations’ Intergovernmental Panel on Climate Change (IPCC), expected to be released sometime in 2001, is already coming under heavy criticism from various directions. But none has been more devastating than the one delivered on March 1 by one of the report’s lead authors.

    Please check your calendar.

  11. 61
    Hank Roberts says:

    > Correspondence …. not a Letter

    Good point. Has anyone asked the Editors there how they reviewed this? Quoting from the link Chris provides:

    “Correspondence provides readers with a forum for comment on papers published in a previous issue of the journal or to discuss issues relevant to the geosciences. … Titles for correspondence are supplied by the editors.
    In cases where a correspondence is critical of a previous research paper, the authors of the criticized paper are given the opportunity to publish a brief reply. Criticism of opinions or other secondary matter does not involve an automatic right of reply.
    Refutations are always peer reviewed. Other types of Correspondence may be peer-reviewed at the editors’ discretion.”

  12. 62
    David B. Benson says:

    Jamie (50) wrote “It may be true that I will never understand the science in all its intricacies.” Probably not. Nobody understands earth’s climate in all its intricacies.

    tom watson (55) — A better use of your time is to explaore and read the following links:

  13. 63
    Richard Ordway says:

    #9 Joc

    “but increasing scepticism I have developed towards Climate Change – aka global warming.”

    Well Joc, you’re in good company! Only 130 countries out of 130 agreed unanimously and signed on paper in 2007-2008 that “it is unambigious that the Earth is warming” and that it is “highly likely that humans are causing it.”

    Included are the oil countries of Saudi Arabia and Venuzuela (that stand to lose big time) as well as Australia, the USA, europe, Russia, China, etc, etc, etc.

    Further, “With the July 2007 release of the revised statement by the American Association of Petroleum Geologists, no remaining scientific body of national or international standing is known to reject the basic findings of human influence on recent climate.”
    Wikipedia 2008

    So I am impressed Joc, that you disagree! I am talking to a real expert here!

  14. 64
    John OConnor (aka joc) says:

    [not sure if this posted correctly the first time – if so please ignore this copy]

    I have decided to post under my full name rather than just joc.

    My apologies for the delay in responding to some of the comments on my possibly intemperate remark #9 earlier. Thank you to those who responded considerately to it and particularly Matthew Brunker (#53) in detailing exactly what he meant in #7. The sarcasm in #63 is best ignored – 130 out 130 countries agree – by that do you mean political leaders signing a document. There are many things leaders do that don’t have the full backing of their countries……

    Right now I have a fairly busy day job + family and other commitments, hence the delay in replying. I am unable to peruse and comment while at work for various reasons (not least that I am paid to work at IT, not browse).

    I should clarify first – my scepticism is more to the alarmism that is raised regarding the potential effects of climate change rather than climate change itself. It is obvious that the climate is changing, and always has. I don’t have a huge problem either with the proposition that man has a significant effect.

    However, I do have issues with the magnitude of the effect, and also how we deal with it – preferring to concentrate on adaption and wise development etc., rather than an outright drive to reduce carbon emissions. That is not to say pollution reduction is important – that itself is crucial to make our environment liveable in. It also makes a lot sense to reduce our energy consumption for a lot of other reasons. For example, we have changed some our energy practices at home (e.g. use of low-energy light-bulbs at key locations in the house) to reduce our electricity bill – simply because our energy bill was way too high.

    However (and I think this is one of Lomborg’s main views), I think it makes far more sense to invest wisely and strategically in our future by trying to avoid catastrophes and loss of life. This to me, means not building in flood plains and also taking note of why the loss of life in countries in Bangladesh is so much greater in the face of floods rather than in say New Orleans. It is facile to simply blame this on global warming and not to look into the development and infrastructure issues. Likewise, there was a lot of silly hysteria in England last year over the floods – maybe it was due to climate change (though a recent report seems to deny this). What was obvious though (and has been for some time) was that floods do occur from time to time there, and it is plain daft to continue building on flood plains and covering the run-off areas with concrete and ashphalt.

    I also have issues those to try and label everyone who is sceptical as being either a denialist, or somehow or other connected with “Big Oil”. This does not help your argument, or any campaign related to it. I’m not connected and never have been connected with big oil or power companies. In fact the company I work for stands has bought into carbon trading in a big way and possibly stands to make a lot of money out of it.

    Although I trained in EE, I haven’t actually worked for it, though I retain a strong interest in it (e.g. I am an IEEE member, and would agree that “Spectrum” does give a very good case for AGW and various mitigating technologies). There have incidentally being some very interesting essays on the effectiveness of the whole peer review process in it’s sister publication “Computer” in the last year or two, that would go against Gavin’s apparent “faith” in it.

    I agree to a point with Ray Ladbury (#13) regarding ignorance, but I would also note that sometimes you (RC and other “scientists”) have a habit of making “science” sound like a High Priesthood, that unless you are admitted to it, you don’t have a clue, and therefore, your argument can’t be taken seriously. Ok – as I noted earlier – my initial comment was a bit inflammatory too – I hope it won’t be taken as simply trolling.

    Meltwater (#22) and BPL (#23) are correct – scepticism based on a reaction to people isn’t very logical. However, I do have a problem with L Brown (#26), and the whole “acceleration” of warming. The reality here is that we have been doing “real” temperature measurements over a relatively short period of time – an astonishingly short period of time. The remainder of the measurements are by using proxies (e.g. ice cores). Even Gavin has admitted recently that the proxy analysis keeps throwing up surprises. I have no doubt that the calibration of the proxy data in comparison to the “real” current measurements are improving, but I still have my doubts about it.

    I also have a lot of doubts about how much we should depend and believe in computer models to help us evaluate future climates. This is based on the practical realities of the complexity of programming. My specialty is Release and Configuration Management – a constant battle to ensure that very bright and able developers actually deliver reliable software to a demanding production environment. It is also based on the little matter of the actual stability of the atmosphere and the daily demonstrated inability of the current Met Office systems to predict the actual weather beyond 3-5 days. OK – I know that this is weather, not climate, as RC, but “climate” is an equally complex and chaotic system.

    Finally, as regards “arrogance in Universities” – it has been my personal experience that while there have been some wonderful academics – I was privileged to study under two in particular – there is also a lot of self-serving arrogance. Unfortunately this also does come across sometimes in some of the articles here and some of the put-downs. It is always worthwhile to remember that a little courtesy can go a very long way in convincing someone. Manu D (#54) makes this point very well.

    I could write a lot more, and would like to, but other work beckons.

  15. 65
    David B. Benson says:

    John OConnor (aka joc) (64) — Here are two links to explore and read as time allows:

    and here is a graph of global temperatures since 1850 CE:

    While reading (and noticing the temperature has risen noticably for the past 50 years or so), keep in mind that agriculture depends upon the remarkably steady climate of the Holocene. Since we are rapidly headed out of that optimum temperature and precipitation pattern range, there is quite a serious danger that we will leave agriculture behind…

  16. 66
    Lawrence Brown says:

    In comment #42, Ike Solem refers to the term “clean coal”. Sounds like the PR people in the coal industry are earning their keep. Coal contains sulfur,and mercury,can contaminate surface and groundwater resources through acid mine drainage, and can cause black lung disease to name a few of its drawbacks. The term clean coal is an oxymoron(no offense to anyone :) ).No matter how you slice it(or sequester its burned biproducts) coal is very dirty.

  17. 67
    tamino says:

    Re: #57 (Geoff Wexler)

    The temperature time series since 1975 don’t support acceleration of global warming. They’re consistent with a constant warming rate plus “red noise” (bearing in mind that “noise” can include physical processes which are essentially unpredictable, like volcanic eruptions and el Nino).

    But while there’s no statistical reason to deny a strictly linear warming, the physical likelihood of a strictly linear progression is vanishingly small. The true signal is almost certainly nonlinear, but the data so far don’t enable us to confirm or quantify its nonliner behavior. A straight line is perfectly consistent with the data, but the thick black “smoothed” line shown by Stefan is also perfectly consistent with the data. We simply don’t yet have enough data to discriminate between these plausible alternatives.

    On my website I addressed a comparison between the alternative hypotheses of “continued warming at an unchanged rate” and “global warming stopped in 2001” (which seems to have superceded its predecessor, “global warming stopped in 1998”). There’s no reason to believe that global warming stopped in 2001, any more than there’s valid reason to believe that global warming stopped last Thursday. But the data since 2001 are so sparse, and the time span so short, that of course it can’t be disproved statistically. In my opinion, it’s foolish of the statistically ignorant, and unethical of the statistically savvy, to exploit the naivete of the common person with such a claim. It’s rooted in the fact that most people have no real idea of the unavoidability of noise, or its likely effect. I also posted about what conditions would disprove this claim statistically; by 2015 that will probably have happened, but it depends on the data.

  18. 68
    Geoff Wexler says:

    re #64

    I think it is both important to try to be both rigorous and non-rigorous on different occasions and to know the difference.

    We should thank our lucky stars that the most alarming papers are rather controversial, otherwise we might become too depressed especially as there is political paralysis.
    But there is a difference between arguing that the climate sensitivity (GW caused by doubling of CO2) is unlikely to be as high as 6 degs.C and to ignoring that possibility altogether. I think that the debate about this kind of issue is one of the most important of all. The stronger the argument against this kind of estimate the better provided the arguments are valid. In so far as 6 degs. remains a reasonable but unlikely possibility I think it should certainly not be ignored. Would an engineer be allowed to design a bridge or a nuclear reactor on the basis of a complete disregard of low probability outcomes? (The USSR did it with their nuclear reactors and according to a colleague of Gorbachov it may have contributed to the downfall of communism).

    Finally I note that you raised a similar topic to that of my previous comment i.e. the acceleration of warming. But my views are quite different from yours in the following ways:

    1. I don’t agree about the need to invoke ice cores. That may be an academic problem of interest to the professionals but it involves much longer time scales and no human influence. The question I asked has nothing to do with the physics and just refers to the statistical analysis of the recent data. It may well be possible to isolate the acceleration, if not yet, then soon because of the accumulation of more data.

    2. Even if the observed acceleration turned out to be effectively zero ‘now’, it may well rise later depending on the emissions scenario or the onset of new positive feedbacks.

    3. The only good result would be the onset of negative acceleration. A continuation of the linear trend of about 2 degs/century would still be of extreme concern.

  19. 69
    Alex Burton says:

    I am an electrical engineer too !
    I work in research on solar thermal energy systems.

    The control systems knowledge that being an electrical engineer gives me, makes me very worried about GW.

    We have a control system with seemingly slow responses (governmental, society, mob psychology), being asked to control the worlds climate system which apparently has nonlinearities, and quite a fast response in comparison to that of the control system.
    Add to that a delay of the order of 10 years between observed consequences (melting warming etc) and emissions, and you have yourself a system that any student of control systems will tell you is most likely to go unstable.

    Given this basic information I am surprised that electrical engineers (the field most associated with control systems) aren’t jumping up and down about GW more than anybody else.


  20. 70
    Steve Latham says:

    I know that some work has been done modeling changes in oceanic acidity as carbon emissions increase. I’ve never seen a comparison of these models with those of temperature changes. Presumably they are simpler or have much more ‘certainty’ associated with them. I imagine that changes in acidity would be relatively monotonic (if that term can be applied) in it’s relationship to atmospheric CO2.

    I mention this for two reasons. First, with relevance to the current thread, I’m curious to learn about how tight the relation is (over time) between atmospheric CO2 measures and ocean acidity. Second, since the negative effect on the oceans of increasing acidity is (?) uncontroversial, why does there seem to be so much more focus on temperature? Is it because it’s so obvious or bland that the media don’t pick up on it and nobody (of any occupation) denies it? Or is it because the science of this issue is relatively young?

  21. 71
    Jim Eager says:

    Re Tom Watson @ 55

    Tom, as others have pointed out, CO2 does not absorb heat and store it, very quickly it either radiates that energy back out in any direction as new IR photons, and those photons in turn strike and excite other greenhouse gas molecules, or it transfers the energy to other gas molecules–IR inert gas or greenhouse gas–as kinetic energy through collision. Either way, the energy remains active in the atmosphere for longer than it otherwise would before reaching space, thus warming the entire atmosphere, not just CO2.

    In addition, it’s not just CO2 that is at work here. Ordinary water vapour is also a greenhouse gas, as is methane, nitrous oxide, chlorofluorocarbons, and a number of lesser trace gasses. Water vapour is many times more abundant than CO2 and thus has a much greater capacity to intercept IR photons, but unlike with CO2, human activity does not add more water vapour to the atmosphere because of relative humidity–it will just condense and precipitate out. The only way to add more water vapour is to increase temperature, which will happen as increasing CO2 continues to add more warmth to the atmosphere. In fact, this is already happening at the poles, where the current warming is highest, and polar air is now able to hold more water vapour, thus acting as a feedback adding even more warming.

  22. 72
    tom watson says:

    # Chuck Booth Says:
    12 April 2008 at 10:59 AM

    Re # 55 tom watson

    So, despite your education and work experience in your field, you rely on The National Business Review for scientific information? I hope you had higher standards when seeking information related to your job.

    tom watson replies; Well Chuck, One’s standards are simply a function of one’s methods. I read first, I think about it. I determine if the writer is using logic and sense. I don’t assume any person because of their education or background is to be disregarded because of some phony idea of my own self genius. I also reported how I came to read that article. I also asked, is this true.

    # Martin Vermeer Says: 12 April 2008 at 11:41 AM

    to Tom Watson #55:

    It would have been better use of your time to first figure out that CO2 has a property affecting the transport of heat rather than its storage :-)

    tom watson replies: I find it interesting that you made that statement. I believe it is a silly miss-interpretation of the point of my original post.
    And in that you don’t seem to know how to be specific. I will point out that even CO2 has a property called it’s specific heat and plants by the way fix hydrogen to CO2 to create hydrocarbons, the O2 from the water is what goes back into the air. So you say CO2 has a property affecting the transport of heat rather than its storage :-)

    I am working on my what the hell is air page, but this is very very rough and not peer reviewed.

  23. 73
    Ken Coffman says:

    Excellent, a rarified gas does not store energy, it transports it. Thanks for the clarification.

  24. 74
    Holly Stick says:

    #69 Alex Burton’s comment on control systems is fascinating because it’s from an unfamiliar professional viewpoint yet clear enough for me (nonengineer, nonscientist with some understanding of ecosystems) to understand what he means (I think!)

    Maybe someone should make a blog or a wiki on how to explain the likely effects of global warming to various professionals in terms that they will understand. How to explain AGW to an electrical engineer, an economist, a city planner, etc.

  25. 75
    Timothy Chase says:


    Al Gore has a new slide-show:

    Al Gore: New thinking on the climate crisis

  26. 76
    Miss Priss says:

    In response to comment 66, I think you’re splitting hairs a bit, Mr. Brown: “clean coal” is a term that simply refers to a specific method of refining — via chemicals, steam, and gasification — so as to better rid coal of its sulfur dioxide. I actually grew up in the mining industry, soft rock and hard, and even worked for a time in the coal industry; indeed “clean coal” is cleaner — at least in the sense that the carbon dioxide and the flue are recouped.

    About coal, however, and the widespread use thereof, your point is well taken. And it’s the anti-nuclear groups we have to thank for that preponderating use. In fact, uranium generates gigantic amounts of energy in a very small space, which wind and solar combined cannot come close to, and yet those who say otherwise — those who are anti-nuclear, in other words — have brought the world 400 million more tons of coal used per year, because for thirty years now, since 1979, following the Three Mile Island accident, we’ve been using more and ever more coal. In fact, the meltdown of the uranium core in 1979 at Three Mile Island was so overblown by anti-nuclear groups that it went virtually unnoticed how the containment vessel at Three Mile Island had done its job and prevented any significant release of radioactivity.

    To the good Mr. Daniel Goodwin in comment 39 above, your hostility toward industrialization — echoed and answered, incidentally, here: — is something you would do well to reconsider. As Thomas Hobbes famously noted, life before industrialization was “solitary, poor, nasty, brutish and short.”

  27. 77

    All scientists should immediately halt whatever they are doing and regard these two charts:

    Global Average Temperature vs Number of Pirates

    All Theories Proven With One Graph by Don Grace of Florence, Alabama.

  28. 78
    John Mashey says:

    re: #64 John O’Connor

    “I also have a lot of doubts about how much we should depend and believe in computer models to help us evaluate future climates. This is based on the practical realities of the complexity of programming. My specialty is Release and Configuration Management”

    1) You are almost certainly over-generalizing from the kind of software with which you are familiar, a common problem. [I’m familiar with it also: many current R&CM tools are remote descendants of work we did 30-35 years ago at Bell Labs to help manage software to meet telephone-company reliability standards. Some of these were 200-300-person projects. Most were smaller, thank goodness.]

    2) We had a similar case in:

    wherein a well-educated scientist was convinced that climate models couldn’t be useful, because he was used to models (protein-folding) where even a slight mismodel of the real world at one step caused final results to diverge wildly … just as a one-byte wrong change in source code can produce broken results.

    See #197 where I explained this to him, and #233 where light dawned, and if you’re a glutton for detail: #66, #75,l #89, #1230, #132, #145, $151, #166 for a sample.

    Climate models aren’t the same as weather models.

  29. 79
    Ian Castles says:

    Re #67 (Tamino):

    I take your point that there’s no reason to believe that global warming stopped in 2001, any more than there’s valid reason to believe that global stopped last Thursday. But, by the same line of argument, doesn’t it follow that there’s no valid reason to assert, as the IPCC did in Chapter 9 of the WGI contribution to AR4, that ‘Six additional years of observations since the TAR … SHOW that temperatures ARE CONTINUING to warm near the surface of the planet” (p. 683, EMPHASES added)? If six years is too short a period from which to conclude that warming has stopped, how can it be a long enough period from which to show conclusively that warming is continuing?

  30. 80
    Geoff Wexler says:

    re: #67

    Thanks for discussing my comment. First a correction. I quoted your starting point as 2000 instead of 2001. This mistake of mine was provoked by Jeremy Paxman on BBC 2’s Newsnight who asked his interviewees whether it was true that there had been no global warming this century (i.e. since 2000)? Leading UK contrarian Nigel Lawson said yes and ex-climatologist Chris Rapley (ex BAS, now Science Museum) also said yes, but then added that there were always short term fluctuations. This suggested that the whole period of eight years was being dismissed as a fluctuation. I thought that Rapley’s answer might have been slightly stronger, and so I checked out your site. I then decided that it was a pity that you had not been on Newsnight to repeat that (a) the least square fit this century was positive in contradiction to Lawson’s suggestion and (b) that it was insignificant anyway as Rapley had argued but rather vaguely.

    I agree about the physics, except that I think that it makes for more clarity to talk about one thing at a time, which is why I liked your approach.

    “unethical of the statistically savvy”

    I wonder how you would classify Nigel Lawson? He was the UK’s chancellor for several years. He and his colleague Nigel Calder (also from Channel 4’s Swindle programme) have been busy writing popular books. Perhaps Realclimate might consider reviewing them?

    [Response: I reviewed Calder’s book here, and we discussed Lawson’s arguments a while ago. If there is something new in his latest book, we might revisit it… – gavin]

  31. 81
    Jim Eager says:

    Re Tom Watson @ 72: Tom, right away I see one problem with your ‘what the hell is air’ page. It appears that you are assuming that water vapour is equally mixed throughout the atmosphere when it is not. As you go higher in the atmosphere, and as temperature drops, the atmosphere holds less and less water vapour as it condenses out. There is relatively little in the upper troposphere and almost none in the stratosphere. CO2, on the other hand is well mixed throughout the entire troposphere and into the stratosphere. In fact, above the mid-troposphere CO2 dominates water vapour as a greenhouse gas.

    It appears that your basic premise is the “there is too little CO2 in the atmosphere to make a difference” argument. If so, you need to do some more homework before you page is ready for prime time.

  32. 82
    Jim Cripwell says:

    Please excuse an off topic item. I have just found the following:, which is the 2008 news from NSIDC on this year’s Arctic ice melt. I believe NSIDC may put out a forecast for the expected amount of ice in the Arctic in September 2008, in the near future.

  33. 83
    tamino says:

    Re: #79 (Ian Castles)

    Whether or not the six additional years indicate further warming, depends on exactly what years they’re talking about. Six years is a very short time, but if the trend *and* the noise both go up, then it’s possible to get statistical significance in spite of the brevity of the time span.

    If they’re referring to 1999.0 to 2005.0, or 2000.0 to 2006.0, then the numbers support their claim; if they’re referring to 2001.0 to 2007.0 then the numbers don’t support the claim. This is true using either GISS or HadCRU data.

    Despite passing or failing significance tests, in a broader sense drawing conclusions from a mere six years of data, given the noise level, is at best “dicey.” There’s also the nontrivial issue of the statistical impact of choosing from a number of *possible* starting and ending points; in this case, passing significance for a mere six years depends on the strong warming observed from 1999 to 2001. In my opinion, whether it’s defensible or not their statement is ill-advised.

  34. 84
    Lawrence Brown says:

    Referring to comments #57 by Geoff Wexler and #64 by John O’ about my comment re that global warming is accelerating, I was referring to a comment in the 2007 IPCC report(IPCC ,2007 Summary for Policy Makers,The Physical Science Basis) It states under the heading Direct Observations of Recent Climate Change: “The linear warming trend over the last 50 years(0.13C[0.10C to 0.16C]per decade) is nearly twice that for the last 100 years.”
    The rate of increase over a longer term than that discussed in the correspondence by Roger Pielke Jr. is increasing.At least according to the latest IPCC report.

  35. 85
    David B. Benson says:

    Miss Priss (79) wrote “As Thomas Hobbes famously noted, life before industrialization was ‘solitary, poor, nasty, brutish and short.'” I believe he was referring to life before govenments. If not, then he was certainly wrong about life during high medieval times; life was communial, wealthy enough to be able to support extensive religious holidays, and the ‘nasty, brutish and short’ bit was reserved for common soldiers.

    Industrialization has not been an un-mixed blessing; somehow there are more poor people in the world with an increasing number of who’s lives have become ‘nasty, brutish and short’.

  36. 86
    David B. Benson says:

    Lawrence Brown (84) — Yes. You can see it yourself here:

    entitled “temperatures since 1850”, although I believe the graph to show 5-year running averages.

  37. 87

    tom watson writes:

    I am an EE

    Saw it coming.

    with 4 decades of work about how electromagnetic radiation and matter interact. I have spent thousands of hours trying to understand how CO2 has some property that allows for the storage of the trillions and trillions of BTU required to globally warm the earth. I have concluded that if e=MC^2, then CO2 driving climate temperatures is a hoax.

    You have concluded wrong. CO2 doesn’t “store” energy other than in the conventional way of having a non-zero Kelvin temperature. It absorbs infrared light, heats up a bit, and radiates, like any hot object, whereupon some of the radiation goes back to the ground, heating the ground up. If you want to understand the process, I recommend reading through a book like John T. Houghton’s The Physics of Atmospheres (3rd ed. 2002), or Grant W. Petty’s A First Course in Atmospheric Radiation (2006), and, of course, working all the problems. Or for a quick precis, try here:

    Greenhouse 101

    It is easy to demonstrate that the radiative equilibrium temperature of the Earth is well below freezing. Earth is habitable at 288 K mean global annual surface temperature instead of 255 K because of the greenhouse effect. If it didn’t exist, we wouldn’t exist either.

  38. 88
    Jim Cripwell says:

    Ref 83. I agree basically with everything Tamino says. However, it seems to me that there are two legitimate questions that can be asked about what is happening to global temperature anomalies. The first question is:- Have temperatures risen in recent history, e.g. over the last 40 years? I think pretty well everyone agrees that the answer to that question is Yes! It is quite legitimate to put a straight line fit through the data points, and measure the average rate of rise of temperature. The second question is:- What is happening to temperatures now, whenever now happens to be? As of this time, now is April 2008. Or in other words, what is the slope of the temperature/time graph as of now? Is it positive or negative? It seems to me that there ought to be statistical methods to answer this question, and they probably only use data for a few recent years. I cannot see why temperatures taken 10 years or more ago tell us very much about what the slope of the temperature/time graph is as of now. My own, very limited analysis convinces me that the current slope of the temperature/time graph is negative.

  39. 89
    Martin Vermeer says:

    Ian Castles #79:

    If six years is too short a period from which to conclude that
    warming has stopped, how can it be a long enough period from which to
    show conclusively that warming is continuing?

    By looking at the big picture and applying Occam’s razor. If a single trend line fits, in a statistically valid way, the whole data from 1975 (say) to today, then don’t use two of them :-)

    Empirical results are always preliminary (though sometimes very strong), never conclusive. They hold up until refuted, which hasn’t happened here. IPCC claims no conclusiveness from what I see.

  40. 90
    Hank Roberts says:

    Jim, intentionally limited analysis is cherrypicking.
    Do a comprehensive analysis, use all the available data.

  41. 91
    Ray Ladbury says:

    Jim Cripwell says: ” The first question is:- Have temperatures risen in recent history, e.g. over the last 40 years? I think pretty well everyone agrees that the answer to that question is Yes! It is quite legitimate to put a straight line fit through the data points, and measure the average rate of rise of temperature. The second question is:- What is happening to temperatures now, whenever now happens to be?”

    Congratulations: You have managed to ask two questions that distinguish between climate and weather. Now bonus round: Can you tell us which question pertains to which?
    Hint It does not make sense to talk about climate on any less than a multidecadal scale.

    He then says “My own, very limited analysis convinces me that the current slope of the temperature/time graph is negative.”

    Buzzzz! Oh, sorry, but thanks for playing. It appears that even the most advanced analysis techniques of wishful thinking are up to the job.

  42. 92
    tamino says:

    Re: #86 (David B. Benson)

    The graph you link to isn’t 5-year averages, it’s 1-year averages. For a graph of 5-year averages (from GISS), see this.

    Re: #88 (Jim Cripwell)

    The fact that linear regression (or other trend analyses) for very brief time spans gives a negative rate, doesn’t mean the trend is negative. One has to estimate the uncertainty in such values. If you analyze data since only 2001, the estimate from GISS data is +0.0024 +/- 0.033 deg.C/yr (2-sigma), while that from HadCRU data is -0.0102 +/- 0.0302 deg.C/yr. Note that the 2-sigma possible errors are much larger than the values themselves, and for both data sets the range includes the rate since 1975. There’s really no evidence at all that the rate today is any different than it has been for 30 years. As for the rate temporarily seeming negative, it’s not just possible for noise to make that happen, it’s inevitable.

  43. 93
    Jonas says:

    Re: 88 Jim Cripwell
    The reason you can not easily determine the current slope is that you do not know the current size of the noise. The exact noise will never be known but by using data over a period of years we can approximately cancel the noise and find the average slope during that period.

    Without knowing the exact noise in a system no statistical method can give an accurate estimate of the behaviour right now. If the noise is small we can take averages over short time periods, but there is always a minimum time period where the expected size of the noise dominates over the actual value we want to estimate.

    This is a basic limitation to all statistical methods.

  44. 94
    Ian Castles says:

    Re #83 (Tamino):
    Thank you. I agree that the IPCC’s statement was ill-advised. The First Order Draft referred to ‘five more years’ and the final report referred to ‘six additional years’ of observations since the TAR – and Chapter 3 refers to temperatures in calendar 2006 as ‘similar to the average of the past 5 years’. So it’s reasonable to interpret the ‘six additional years of observations’ as referring to 2001 to 2006.

    Re #89 (Martin Vermeer):
    The IPCC authors were not attempting to look at the big picture, or to apply Occam’s razor, or to fit a trend line to the ‘whole data’ beginning from some past period. They made a specific assertion that six additional years of observations ‘show’ that temperatures have continued to warm. They don’t ‘show’ that at all, and this is true irrespective of what happened in 2007.

  45. 95
    Aaron Lewis says:

    Re 57
    Global warming includes the accumulation of heat in deep oceans, ice sheets, and the melting of ice.
    Much of the data so artfully addressed by Tamino are various measures of air temperature. As long as areas of solid ice remain as a heat sink, absorbing large amounts of heat at 0C, air temperatures may not fully reflect the rate or impacts of global warming.

    The area of Greenland Ice Sheet melt has been increasing in a noisy but linear function since 1979. However, as the melt area includes thicker and thicker ice, the volume of ice with melt water above it has increased exponentially. Moreover, the number of melt days has increased. Together, these factors make it likely that heat transfer to the GIS is increasing exponentially.

    Given the highly nonlinear behaviors of ice near its melting point, we can expect that the expressed impacts of AGW (sea level rise) will be non-linear in the extreme, and may occur prior to our being able to statistically detect nonlinear effects of global warming from air temperatures.

  46. 96
    tom watson says:

    Re: 81 Jim Eager

    Jim, let’s put H20 in the same units as CO2.
    There is nothing wrong with the what the hell is air page. It is not complete and does not argue any points. Now H20 has concentrations in the air up to and even higher than 30,000 or 30 thousand PPM. Does one have to be in the arctic on a very cold dry day to get anywhere near 1000 ppm.

    What I believe is that H20 that has a higher specific heat than CO2, has a several hundred times heat transporting heat of fusion and the ability to make air lighter as it PPM increase all cause more convention of ground based heat skyward where the hundreds of molecules that are not water or CO2 emit a percentage of black body radiation that is not adsorbed and in less than a blink of the eye is gone from the earth forever.

    More CO2 in the air means a small percent surface emitted black body radiation gets absorbed even closer?? 40 ft vs 45 ft and that would make for an increase in convection properties of the air.

    The suggestion that the current decades increase of several tens of PPM of CO2 slows the rate of radiation cooling makes no sense to me in the current mix of the earth’s atmosphere.

    And to me all the data I’ve seen reported from satellites suggests all supposition of some property or interaction of CO2 to cause some huge global warming is silly.
    I wrote some scripts to capture various sats higher pixel images so I could create longer term HD like movies or animations. Think about what are we looking at when we see large areas of -70C.
    You can see the deserts heat and cool daily. Mexico..

    [Response: The argument from personal incredulity is not a very useful one in scientific discussions. – gavin]

  47. 97
    Jim Cross says:

    Since there seems to be much “to do” about the uncertainty ranges, can some one explain how the ranges are derived for the models?

  48. 98
    Lawrence Brown says:

    Re 86:Thank you for the graph David. It starkly shows that a picture can be worth 1000 words. I should visit Tamino’s Open Mind site more often.

    On Miss Priss’s comments in #76, I didn’t think I was nit picking about the processes used to refine coal, though I do succumb to it at times.
    Nuclear power,of course, is a Faustian bargain. Frankly I’m on the fence as far as fission use for power is concerned. Sure it’s nearly free of greenhouse gas emissions and its energy is concentrated, meaning,for one thing, that amounts of uranium many orders of magnitude less than fossil fuels can be used to provide the same amount of energy. Waste disposal is definitely a problem. But where the aforementioned bargain comes in, is in it’s possible use for nuclear weapons profiferation.

  49. 99

    Ian Castles #79: You can look at whether the additional 6 years confirm the trend, i.e., the moving average is still trending up as you add points. If you take a few years in isolation, you can’t get a better fit than random. Since a few in the denialosphere are alleging no warming since 2001, I fetched the HadCRUT3 data and tried to find a trend from 2001 to now. With linear regression, I found the sort of downward “trend” some like Monckton claimed (though I could not match the exact number he gives) to have found (without specifying his methodology), but couldn’t get an r2 much better than 0.05, which is pretty much random.

    Try it yourself. Get the data and do a correlation. Then do correlations on random data a few times (or better still, look up a stats text to see how to interpret data). You’ll find the 2001-present data doesn’t behave much differently than rand().

    Monckton’s “cooling trend” story appears in various places including here with discussion at another site of how his “trend” can’t easily be replicated on the information he supplied.

    I don’t know how much faith I can put in any of Monckton’s claims if he makes statements like “Given the stability of the climate over the past half billion years” when discussing a graph showing a temperature variance of over 10°C over that period.

  50. 100
    Jim Eager says:

    Re Tom @ 96: I’m sorry, Tom, but I’ve read your last post three times and I just can not understand what you are trying to say. The only thing I got clearly is that it is your opinion that CO2 caused global warming is silly, and we already got something like that in your very first post. The physics of greenhouse gases has nothing what so ever to do with specific heat or heat of fusion, so I can only assume that you don’t understand the radiative physics of greenhouse gases and how they work, be it H2O or CO2. Fortunately there are several physicists among the regular posters here who can help you to figure it out if you want, myself not among them, I’m afraid. But you might want to slow down, think about what you want to say–might be better to ask questions, though–and how to say it clearly, and then type slower. I’m not trying to be rude or snarky, I just can’t understand what you wrote, and I’m probably not alone.