RealClimate logo


Technical Note: Sorry for any recent performance issues. We are working on it.

On attribution

Filed under: — gavin @ 26 May 2010

How do we know what caused climate to change – or even if anything did?

This is a central question with respect to recent temperature trends, but of course it is much more general and applies to a whole range of climate changes over all time scales. Judging from comments we receive here and discussions elsewhere on the web, there is a fair amount of confusion about how this process works and what can (and cannot) be said with confidence. For instance, many people appear to (incorrectly) think that attribution is just based on a naive correlation of the global mean temperature, or that it is impossible to do unless a change is ‘unprecedented’ or that the answers are based on our lack of imagination about other causes.

In fact the process is more sophisticated than these misconceptions imply and I’ll go over the main issues below. But the executive summary is this:

  • You can’t do attribution based only on statistics
  • Attribution has nothing to do with something being “unprecedented”
  • You always need a model of some sort
  • The more distinct the fingerprint of a particular cause is, the easier it is to detect

Note that it helps enormously to think about attribution in contexts that don’t have anything to do with anthropogenic causes. For some reason that allows people to think a little bit more clearly about the problem.

First off, think about the difference between attribution in an observational science like climatology (or cosmology etc.) compared to a lab-based science (microbiology or materials science). In a laboratory, it’s relatively easy to demonstrate cause and effect: you set up the experiments – and if what you expect is a real phenomenon, you should be able to replicate it over and over again and get enough examples to demonstrate convincingly that a particular cause has a particular effect. Note that you can’t demonstrate that a particular effect can have only that cause, but should you see that effect in the real world and suspect that your cause is also present, then you can make a pretty good (though not 100%) case that a specific cause is to blame.

Why do you need a laboratory to do this? It is because the real world is always noisy – there is always something else going on that makes our (reductionist) theories less applicable than we’d like. Outside, we don’t get to perfectly stabilise the temperature and pressure, we don’t control the turbulence in the initial state, and we can’t shield the apparatus from cosmic rays etc. In the lab, we can do all of those things and ensure that (hopefully) we can boil the experiment down to its essentials. There is of course still ‘noise’ – imprecision in measuring instruments etc. and so you need to do it many times under slightly different conditions to be sure that your cause really does give the effect you are looking for.

The key to this kind of attribution is repetition, and this is where it should become obvious that for observational sciences, you are generally going to have to find a different way forward, since we don’t generally get to rerun the Holocene, or the Big Bang or the 20th Century (thankfully).

Repetition can be useful when you have repeating events in Nature – the ice age cycles, tides, volcanic eruptions, the seasons etc. These give you a chance to integrate over any unrelated confounding effects to get at the signal. For the impacts of volcanic eruptions in general, this has definitely been a useful technique (from Robock and Mao (1992) to Shindell et al (2004)). But many of the events that have occurred in geologic history are singular, or perhaps they’ve occurred more frequently but we only have good observations from one manifestation – the Paleocene-Eocene Thermal Maximum, the KT impact event, the 8.2 kyr event, the Little Ice Age etc. – and so another approach is required.

In the real world we attribute singular events all the time – in court cases for instance – and so we do have practical experience of this. If the evidence linking specific bank-robbers to a robbery is strong, prosecutors can get a conviction without the crimes needing to have been ‘unprecedented’, and without having to specifically prove that everyone else was innocent. What happens instead is that prosecutors (ideally) create a narrative for what they think happened (lets call that a ‘model’ for want of a better word), work out the consequences of that narrative (the suspect should have been seen by that camera at that moment, the DNA at the scene will match a suspect’s sample, the money will be found in the freezer etc.), and they then try and find those consequences in the evidence. It’s obviously important to make sure that the narrative isn’t simply a ‘just-so’ story, in which circumstances are strung together to suggest guilt, but which no further evidence is found to back up that particular story. Indeed these narratives are much more convincing when there is ‘out of sample’ confirmation.

We can generalise this: what is a required is a model of some sort that makes predictions for what should and should not have happened depending on some specific cause, combined with ‘out of sample’ validation of the model of events or phenomena that were not known about or used in the construction of the model.

Models come in many shapes and sizes. They can be statistical, empirical, physical, numerical or conceptual. Their utility is predicated on how specific they are, how clearly they distinguish their predictions from those of other models, and the avoidance of unnecessary complications (“Occam’s Razor”). If all else is equal, a more parsimonious explanation is generally preferred as a working hypothesis.

The overriding requirement however is that the model must be predictive. It can’t just be a fit to the observations. For instance, one can fit a Fourier series to a data set that is purely random, but however accurate the fit is, it won’t give good predictions. Similarly a linear or quadratic fit to a time series can be useful form of descriptive statistics, but without any reason to think that there is an underlying basis for such a trend, it has very little predictive value. In fact, any statistical fit to the data is necessarily trying to match observations using a mathematical constraint (ie. trying to minimise the mean square residual, or the gradient, using sinusoids, or wavelets, etc.) and since there is no physical reason to assume that any of these constraints apply to the real world, no purely statistical approach is going to be that useful in attribution (despite it being attempted all the time).

To be clear, defining any externally forced climate signal as simply the linear, quadratic, polynomial or spline fit to the data is not sufficient. The corollary which defines ‘internal climate variability’ as the residual from that fit doesn’t work either.

So what can you do? The first thing to do is to get away from the idea that you can only be using single-valued metrics like the global temperature. We have much more information than that – patterns of changes across the surface, through the vertical extent of the atmosphere, and in the oceans. Complex spatial fingerprints of change can do a much better job at discriminating between competing hypotheses than simple multiple linear regression with a single time-series. For instance, a big difference between solar forced changes compared to those driven by CO2 is that the stratosphere changes in tandem with the lower atmosphere for solar changes, but they are opposed for CO2-driven change. Aerosol changes often have specific regional patterns change that can be distinguished from changes from well-mixed greenhouse gases.

The expected patterns for any particular driver (the ‘fingerprints’) can be estimated from a climate model, or even a suite of climate models with the differences between them serving as an estimate of the structural uncertainty. If these patterns are robust, then one can have confidence that they are a good reflection of the underlying assumptions that went into building the models. Given these fingerprints for multiple hypothesised drivers (solar, aerosols, land-use/land cover change, greenhouse gases etc.), we can than examine the real world to see if the changes we see can be explained by a combination of them. One important point to note is that it is easy to account for some model imperfections – for instance, if the solar pattern is underestimated in strength we can test for whether a multiplicative factor would improve the match. We can also apply some independent tests on the models to try and make sure that only the ‘good’ ones are used, or at least demonstrate that the conclusions are not sensitive to those choices.

These techniques of course, make some assumptions. Firstly, that the spatio-temporal pattern associated with a particular forcing is reasonably accurate (though the magnitude of the pattern can be too large or small without causing a problem). To a large extent this is the case – the stratospheric cooling/tropospheric warming pattern associated with CO2 increases is well understood, as are the qualitative land vs ocean/Northern vs. southern/Arctic amplification features. The exact value of polar amplification though is quite uncertain, though this affects all the response patterns and so is not a crucial factor. More problematic are results that indicate that specific forcings might impact existing regional patterns of variability, like the Arctic Oscillation or El Niño. In those cases, clearly distinguishing internal natural variability from the forced change is more difficult.

In all of the above, estimates are required of the magnitude and patterns of internal variability. These can be derived from model simulations (for instance in their pre-industrial control runs with no forcings), or estimated from the observational record. The latter is problematic because there is no ‘clean’ period where there was only internal variability occurring – volcanoes, solar variability etc. have been affecting the record even prior to the 20th Century. Thus the most straightforward estimates come from the GCMs. Each model has a different expression of the internal variability – some have too much ENSO activity for instance while some have too little, or, the timescale for multi-decadal variability in the North Atlantic might vary from 20 to 60 years for instance. Conclusions about the magnitude of the forced changes need to be robust to these different estimates.

So how might this work in practice? Take the impact of the Pinatubo eruption in 1991. Examination of the temperature record over this period shows a slight cooling, peaking in 1992-1993, but these temperatures were certainly not ‘unprecedented’, nor did they exceed the bounds of observed variability, yet it is well accepted that the cooling was attributable to the eruption. Why? First off, there was a well-observed change in the atmospheric composition (a layer of sulphate aerosols in the lower stratosphere). Models ranging from 1-dimensional radiative transfer models to full GCMs all suggest that these aerosols were sufficient to alter the planetary energy balance and cause global cooling in the annual mean surface temperatures. They also suggest that there would be complex spatial patterns of response – local warming in the lower stratosphere, increases in reflected solar radiation, decreases in outgoing longwave radiation, dynamical changes in the northern hemisphere winter circulation, decreases in tropical precipitation etc. These changes were observed in the real world too, and with very similar magnitudes to those predicted. Indeed many of these changes were predicted by GCMs before they were observed.

I’ll leave it as an exercise for the reader to apply the same reasoning to the changes related to increasing greenhouse gases, but for those interested the relevant chapter in the IPCC report is well worth reading, as are a couple of recent papers by Santer and colleagues.


559 Responses to “On attribution”

  1. 151
    dhogaza says:

    Lichanos:

    #127 Neither the temperature record nor GCMs (or the computers on which they run) were around when the foundations of greenhouse gas warming of the climate were laid down

    A lot of people make arguments like this. Oreskes proposes a similar non sequitur. In the 19th century, Arrhenius proposed the “green house” effect deriving from burning fossil fuel. This was based on knowledge of the physical characteristics of CO2. Nobody disputes the nature of CO2.

    You’ve correctly identified the foundation, and it’s nice to see that you agree that GCMs and the temperature record aren’t the “foundations of AGW”.

    That’s not what’s at issue. If it were all so simple and straightforward, why the heck would you need to spend hundreds of millions of dollars on computer models? Obviously, the system is complicated.

    Don’t break your back moving those goalposts, dude.

    And this is the kind of dishonest debating technique that leads to people saying unkind things about you.

    #128 I bet my life on science and technology every time I step on an airplane.

    That’s like saying you take a bet everytime you flush the toilet that the water will go down and not up. Some odds! Just for laughs let me ask you, would you bet your life on something that actually makes for a wager as it’s usually understood, like whether or not the BP “top kill” will work…today…this week?

    No, I wouldn’t bet my life on something that BP itself has only a 60%-70% probability of success.

    Would you bet your life on a 30%-40% probability of failure?

    Are you going to bet your life on the exceedingly small chance that most of what we know about atmospheric physics, planetary atmospheric physics, paleoclimate, etc etc are wrong?

    Remember, for climate science to be wrong about the effect of injecting massive amounts of CO2 into the atmosphere today to be wrong, it also has to be wrong about the other 99% of what has been learned about atmospheric physics that deals with the past on earth, why Venus is so hot, etc etc etc.

    Denialists like yourself seem to have little or no understanding of how much science has to collapse for their denialist hopes to come true.

  2. 152
    John E. Pearson says:

    140: Lichanos sez: “Nobody disputes the nature of CO2.”

    You’re either ignorant or you’re lying which is it. denialists dispute the nature of CO2 on this site and many others everyday. We’re been treated to gobs and gobs of nonsense. Some lawyer somewhere is explaining the climate of Venus based on his ignorance of the ideal gas law and adiabatic processes. So. Which is it. Are you lying or are you unaware of the vast amount of pure bull shit spewed by blog “scientists”?

  3. 153
    Doug Bostrom says:

    John E. Pearson says: 27 May 2010 at 7:33 PM

    Some lawyer somewhere is explaining the climate of Venus based on his ignorance of the ideal gas law and adiabatic processes…

    Goddard explains, meanwhile CEI’s Senior Fellow of Sewer Inspections Chris Horner is trying to have a subpoena served on the Venera 9 lander. The robot’s stubborn silence is taken as an admission of guilt.

    [Response: Cue press release on Venusian 'stalling' on 1, 2, 3.... - gavin]

  4. 154
    Hank Roberts says:

    > assume he’s serious about learning.

    That’s what we’re here to do.

  5. 155
    Ray Ladbury says:

    Lichanos,
    Have you noticed which side has the evidence in this “debate”? I will give you a hint. It is not pudknockers like you.

    You say that nobody disputes the nature of CO2–from which I presume you acknowledge that CO2 is a greenhouse gas. Do you dispute that CO2 sensitivity is around 3 degrees per doubling–a value supported by about a dozen seperate lines of evidence. If so, where is your evidence. Put up or shut up time.

  6. 156
    Ray Ladbury says:

    Kevin King: “You don’t have to
    have a phd in physics to grasp this very simple(emphasis simple) point.”

    Yet, isn’t it funny that the vast majority of PhDs in physics (myself included) do see that the evidence is quite strong–as well as PhDs in chemistry, metorology… Indeed, no professional society or honorific society of scientists that has looked at the issue dissents from the consensus.

    No, the dissenters are mostly proud ignoramuses like you. Odd, that, isn’t?

  7. 157
    Lichanos says:

    #151 dhogaza:

    Remember, for climate science to be wrong about the effect of injecting massive amounts of CO2 into the atmosphere today to be wrong, it also has to be wrong about the other 99% of what has been learned about atmospheric physics that deals with the past on earth, why Venus is so hot, etc etc etc.

    I don’t see why this is true at all! If it were, it would be a serious argument. Just try a thought experiment. It’s 2030. The global temperature anomaly, however it comes to be measured, has bopped around a bit and is only slightly higher than it is now, or was 15 years ago. Just imagine this happens. No volcanoes have gone off. Are you telling me that you would feel it necessary to jettison 99% of what is known? No. Scientists would say, “Hmmm…we were wrong. I guess we didn’t understand all the interactions probably. Our models were too sensitive to the biases of the input data…etc. etc.”

    I’m not certain this will happen, but that’s what I’m betting on. Is it really so improbable a scenario?

    Obviously, I’m damned if I do, damned if I don’t, as look as I don’t toe the line. By recognizing the physics of CO2 I am somehow a liar because some kooks don’t. Also, by refusing to dispute it, I have somehow “moved the goal posts.” The physics of CO2 are not an issue for any skeptic that cares about science. If you think only the unconvinced have ignorant yahoos in their ranks, you haven’t been reading the stuff your own supporters put out on the web.

    Regarding the recent turn of the comments –
    One of the reasons I like to debate in threads like this, besides the chance that someone might actually deign to construct a rational argument, is that I enjoy the spectacle of seeing the professed high minded guardians of truth descend into a mob of insulting, yapping, schoolboys. Responding to my comments by calling me ignorant, psychotic, a liar, etc. seems to be preferred rejoinder now. Not a very fine reflection on the quality of your minds…

    [Response: While it is no doubt very satisfying to feel that everyone else is a fool and that people arguing with you automatically implies the correctness of your position, you might just want to consider that imagining futures that confirm your beliefs is not evidence of anything. What if it warmed twice as fast as ipcc expects? Surely that is just as likely? (see how unconvincing proof by imaginary assertion is?). This is a thread about attribution, and your contribution has been singularly devoid of anything resembling evidence, logic, or actual information content. A feeling that you are not convinced is not any kind if evidence. So, please either up your game (cites, refs, actual issues) or take it elsewhere. Thanks. -gavin]

  8. 158
    Rod B says:

    Nice non ad hominem there (109) Doug Bostrom….

  9. 159
    Jacob Mack says:

    Hank, thanks for the reference from Springer Link regarding reversing Global Warming. I will access the full article later in the week and try and find others like it. If you find similar ones, please post them here.

    Very much appreciated.

  10. 160

    “Lichanos, blah, blah, blah, Lichanos. . .”

    (Apologies to Gary Larson.)

  11. 161
    Edward Greisch says:

    60 RalphieGM: “I don’t see the alarm.” I have listed the kill mechanisms of GW too many times already. Suffice to say that AGW has many way to make humans EXTINCT and the process isn’t pleasant. The first kill mechanism, disruption of agriculture, is already kicking in.

    Lichanos many: It all started in 1859 when John Tyndall measured the infrared optical properties of N2, O2 and CO2. N2 and O2 are transparent. CO2 is opaque in the infrared. That is the physical mechanism.
    “NRC?”: About [or is it at least?] 10 independent groups of climatologists have come to the same conclusions. NASA-GISS, NOAA, The British MET office and CRU to name 4.
    “You should” get a degree in physics and along the way study the optical properties of gasses. From your blog at http://iamyouasheisme.wordpress.com/
    you appear to be an humanitologist, untrained in science and math.
    And you seem to change your mind. “You should” not “should” those who “should” be your professors.

    111 John: “YOU MEAN THE MASSIVE SHORT TERM EXTREME OF LESS THAN A DEGREE?”
    No john. We mean the extreme hunger you are going to experience at at a few more degrees, if not sooner. The 1.4 degree F we already have is impacting agriculture here and around the world. I guess you will understand when you go to the grocery store and there is no food. We will surely be extinct by the time it gets to 11 degrees F.

  12. 162
    mike roddy says:

    Thanks for the lesson, Gavin, I am rusty and needed the refresher course.

    It’s especially bracing to read something written by someone who is really smart, certainly a lot smarter than I am. We are really going to need you in the coming decades.

  13. 163
  14. 164
    Completely Fed Up says:

    “But calling a man a liar and diagnosing me as subject to psychosis is…polite?”

    It is, however, supported by the evidence.

    Would I bet my life on you NOT being nuts?

    No.

    As to the threat of closed-minds, your mind seems to be closed to the idea that the IPCC is pointing to solid and acceptable evidence and that AGW is a real effect of human activity on the ecosystem.

    You have no EVIDENCE that they are wrong, but you still say “it’s something else”.

    This is a closed mind.

  15. 165
    Completely Fed Up says:

    “all the datasets we’re working with are more or less imperfect. scientists may reduce this imperfectness by appropriate statistics and reasonable modelling. but although they try this all the time, they sometimes fail.”

    Well, there’s weak-sauce for you.

    Mind you, he’s right: the likes of McIntyre used datasets that are too imperfect to draw the conclusions they have done.

    Lomberg has failed in his modelling of the atmosphere.

  16. 166
    Completely Fed Up says:

    “#132 What other way could it happen?

    Your lack of imagination in the face of nature is astonishing.”

    Either

    1) He can’t think of one either

    or

    2) He wants YOU to do his work for him

    or

    3) All the above.

  17. 167
    ccpo says:

    Gavin, et al.,

    I would like to propose the following:

    1. Assertion: Repetition of a falsehood to explain that falsehood reinforces the falsehood. (Many articles/research on this effect)
    2. Assertion: Oreskes, et al., have demonstrated the following: A. The denial industry is just that, an organized business intended to spread doubt about things known to be true. B. Ideology trumps reason in decision-making. C. As of 2004, there was essentially zero scientific literature that could be construed to rebuke AGW. To my knowledge, none has emerged since.

    3. Given 1 and 2 above, repeating the denialist talking points here is self-destructive. It reinforces their claims, which we know to be without merit.

    4. I propose two approaches be taken to such as Lichanos in the future: 1. Unless their posts have any substantive data that challenges and refutes AGW, en toto, responses to them should be thus

    Ex.: Re: Lichanos – 27 May 2010 @ 11:35 PM

    Please see (link),(link) and (link). We will entertain legitimate, thoughtful questions if you require assistance parsing the information linked, however, further assertions that do not provide links to valid research to back them up will not be published. – gavin

    OR

    2. simply do not publish them at all.

    It’s time to get on to the business of dealing with AGW. We really cannot continue to reinforce dishonest/disingenuous assertions.

    Cheers

  18. 168
    CM says:

    Lichanos,

    You’ve asked us to read Weart as if we were AGW doubters requiring answers that would satisfy us. I ask you to read the science as if you want to know if scientists might have actually thought about and addressed the concerns you are ever so vaguely raising.

    On your (otherwise literate) blog, you say it was “news to you” that urban and rural stations are being paired to check for UHI bias. Well, now you know. What do you do with this news? Does it make you revise, ever so slightly, your impression UHI has not been adequately addressed? This is a fairly obvious control to do, really, when you think about it. Does it occur to you that if you missed this, maybe there’s some more work you ought to learn about before you pontificate?

    On your blog, you go on to talk about bad tree-ring data for recent decades being thrown out, and you speculate this is because it doesn’t match the “projected” uptick in temperatures. Uhm, no, the reason the data is not used is because it doesn’t match the observed uptick in the instrumental record. Isn’t that pretty obvious too? Does that make you think? Could any of your other doubts be similarly based on lazy wild guesses that you could easily have put to rest? (Several people here have given you pointers.)

    Come on, do like scientists do, don’t trust your reasoning, check it against the facts. Be a skeptic.

    (By the way, I enjoyed the pun of Didactylos [Two-Fingered] responding to Lichanos [Index Finger]… Next up: CFU changes his tag to Fákhlos [Middle Finger]?)

  19. 169
    Didactylos says:

    Lichanos said: “$2500 says AGW will be generally regarded as a fad in twenty years.”

    Not enough. Not nearly enough. Do you know the cost of delaying that long? It will be astronomical.

    Of course, this whole discussion is a waste of time. In 20 years, you will say “there’s still not enough evidence. We need to wait longer. Maybe it has started cooling since 2027!”

    I thought you were merely in doubt about the science. Now, I see you are just another delayer.

  20. 170
    Mark says:

    A friend of mine is preparing a paper that matches the temperature curve since 1980 with the derivative of the curve for CO2 levels. When temperatures rise, the rate of CO2 increase rises, and when temperatures fall, the rate of CO2 increase falls. This would seem to suggest that temperature is driving CO2 levels (aside from or outside of the background CO2 level rise attributable to human sources). Are there any papers out there that have matched the curves in this way? Please comment on this comment!

  21. 171
    Mesa says:

    With the limited amount of data that exists, you are never going to be able to “prove” much about future climate projections, or get much traction on hind-casts or attribution. A more interesting question is:

    –in the n-dimensional space of models that con be plausibly constructed to back-fit the data, what % of them predict dramatic (positive feedback) future warming? Or alternatively have a large role for CO2?

    –how honest is the selection of the size of the n-dimensional space of models used above? IE is it not polluted by confirmation bias? This is the real question I think, since I know what the RC answer to the first question is…

    With simpler problems like financial modeling, you can do monte-carlo simulations over the space of all possible models to give you an idea of whether a good back tested fit means anything or not. In other words whether or not the model is over-fit. You do this essentially by seeing if a given model will explain any type of simulated historical data.

    In addition, you will likely insist on bootstrapping the model so that the predictive accuracy is never calculated in-sample.

    The most difficult thing in this process is to avoid fooling yourself. With the more complex models of the climate, I wonder how this type of problem is approached?

  22. 172
    dhogaza says:

    Responding to my comments by calling me ignorant, psychotic, a liar, etc. seems to be preferred rejoinder now. Not a very fine reflection on the quality of your minds…

    Ignorant people exist. Psychotic people exist. Liars exist. Regardless of the quality of my mind.

    CM has pointed out that you’ve made two assertions from ignorance, one regarding work to understand what effect the UHI might have on the instrumental record, and another regarding the handling of the divergence problem.

    What do assertions from ignorance tell us about the quality of your mind?

    I, too, looked at your blog. You appear to have no technical background whatsoever. You’re like a poet trying to tell a cardiac surgeon how to do her job.

  23. 173
    Lichanos says:

    Since Gavin has weighed in with his put up or shut up request for evidence, I feel I must simply explain my position again and sign off.

    #161 EG suggests that I am a “humanitologist” untrained in science and math.
    I do consider myself a “humanist” and I am trained in science and math. I also have a strong interest in the history, logic, and philosophy of scientific explanation. What strikes me about most of the attacks on me here, including Gavin’s, is the total lack of interest on your part in the logical structure of your explanationn. It seems to me that if the logic is bad, “evidence” is beside the point. An explanation must deal in a logically coherent way with the observations.

    So, one of my initial assertions was that the temperature record and GCMs are at the base of the AGW hypothesis. Many assumed that I therefore am a fantasist, uninterested in the characteristics of CO2. I ask you, if the temperature record were flat, would Weart have written his book? No. He would have written an essay speculating on why Arrhenius’ hypothesis didn’t work out as expected, despite the inputs of CO2. Without GCMs, there would be no long-rang predictions. Ergo, those two items are the crucial foundation blocks of evidence for AGW.

    [Response: But when told, and shown, that this is not true, you persist in your error. This might be a great debating tactic, but it's connection to logical thought is tenuous at best. Arrhenius made long term predictions, as did Callendar, and as did Plass - none of them used GCMs, and all did so without knowledge of temperature trends in the last 40 years. If you don't like GCMs for some personal reason, then the predictions are obviously going to be less quantitative, but the predictions are there none-the-less. And, as a point of logic, no prediction of the future is evidence of anything in the present. - gavin]

    Gavin S. remarks:
    While it is no doubt very satisfying to feel that everyone else is a fool and that people arguing with you automatically implies the correctness of your position, you might just want to consider that imagining futures that confirm your beliefs is not evidence of anything.
    Of course, that superior feeling is well in evidence in the comments here, that increasingly veer towards outraged character attack, but nevermind…
    If the imagined future he posits came to be, I would consider myself completely wrong. I don’t claim that my scenario proves anything. I proposed it as a ‘thought experiment’ to try and get through to one commenter. As for warming twice as fast as the IPCC predicts, why is that “surely just as likely?” Regardless, I wasn’t suggesting my scenario was likely, only possible, and useful to consider.

    [Response: How is it useful? If things come to pass that were not predicted obviously people will think about why that might have happened - is the data faulty, was the theory faulty or incomplete, is the comparison appropriate? These questions get asked all the time whenever there is an apparent mismatch. But you can't assume the answer, and so such storylines are absolutely useless in determining what the evidence shows now. Again, a logical fail. - gavin]

    Gavin S. asserts that my response has been devoid of logic. I think I have struggled mightilty to engage you with logic, and I have been given insults and ranting in return for the most part. It’s true that I have presented little evidence! Why should I? I’m questioning your LOGIC! Do you get that? If I can show that your own argument is incoherent, then I don’t need evidence to dismiss your hypothesis. That’s my game. You can claim I have failed, but you can’t claim I need to play by other rules than the ones of science and basic rationality.

    [Response: I don't imagine that many people want to play your game, being more interested in actually working out what is going on. However, your 'game' ' is one where you decide what the opposing theory is (with no support from your opposition) and you proceed to 'logically' show that your caricature is deficient in some way. This is simply a strawman argument, and it is not a valid logical point. Fail. - gavin]

    I just don’t “feel” unconvinced. I have gone from a cautious supporter of AGW to unconvinced by watching over a period of fifteen years how people like Gavin S. Jim Hansen, Oppenheim, et al. deal with critiques of their work. They don’t engage. They make assertions, collect more ‘evidence’, run more models, hurl insults, imply dark conspiracies and voodoo science and talk about ‘multiple lines of evidence’. Nope. Each bit has to be proven independently of the other. Not very convincing.

    [Response: And you respond by making fact-free assertions of your own? Not very convincing either. - gavin]

    #167 cpo and #168 cm made comments that nicely encapsulate this point of view:

    I propose two approaches be taken to such as Lichanos in the future: 1. Unless their posts have any substantive data that challenges and refutes AGW, en toto, responses to them should be thus…

    You’ve asked us to read Weart as if we were AGW doubters requiring answers that would satisfy us.

    Basically, unless you can totally disprove AGW outright, nothing you say matters. And…YOU decide on the results. Of course, the ultimate proof WILL come in a few decades. Perhaps you will be right and I will be wrong…

    And yes, I ask that you read Weart just as you have suggested. Isn’t that appropriate when reviewing a scientific hypothesis?

    Finally, this snippet is indicative of your approach to evidence:

    #168 cm: Uhm, no, the reason the data is not used is because it doesn’t match the observed uptick in the instrumental record. Isn’t that pretty obvious too?

    Sooo, it’s okay to use tree ring data that does appear to match instrumental records, and when it doesn’t match it, we throw it out, but we still have confidence in the vast proxy record of tree ring data because we know it’s basically good…because more recent data [mostly] matches recent instrumental data?

    Wouldn’t you worry, just a little, about that discrepancy between tree ring data and the instrument record? I sure would.

    [Response: Indeed, and perhaps people would write papers about it, and discuss it at conferences, and write more papers about it. Oh, look, they have... - gavin]

  24. 174

    Lichanos (157),

    You say that a major reason you like debates like this is because you “enjoy the spectacle of seeing the professed high minded guardians of truth descend into a mob of insulting, yapping, schoolboys.”

    So it’s not constructive discourse you’re seeking, but rather you’re trying to provoke people into getting (overly) defensive, so that then you say, “See, they’re so mean to me! They must have something to hide!”. If you want to be a serious discussion partner, you should really abandon that rather unconstructive purpose.

  25. 175

    171 (Mesa),

    The most difficult thing in this process is to avoid fooling yourself.

    An interesting comment. Ever consider applying it to your own reasoning process?

    A hint… man solves problems by making assumptions. It’s an invaluable and very dangerous art. Correct assumptions simplify a problem and lead to a quick and accurate solution. Incorrect assumptions lead to disaster. Too many assumptions (i.e. “thinking inside the box”) lead nowhere — to no solution at all, for lack of options. Too few assumptions similarly lead nowhere, but due to an overwhelming volume of noise.

    So what you have to ask yourself is “what in my post is an incorrect or missing assumption?” What do I fail to properly grasp, or where am I lead astray by complete ignorance, such that I think I can arrogantly proclaim to professional scientists that they are deluding themselves and seemingly have no idea what they are doing, while I myself am above such petty frailties and have a true grasp on the truth about life, the universe, and climate change?

  26. 176
    Completely Fed Up says:

    “This would seem to suggest that temperature is driving CO2 levels”

    That’s an 11, Bob.

    http://www.skepticalscience.com/co2-lags-temperature.htm

  27. 177
    Completely Fed Up says:

    Amphi-Fákhlos, please, CM..!

    ;-P

  28. 178
    Alan Millar says:

    Let us deal with undeniable facts about the Earths climate.

    1. There is a greenhouse effect.

    2. CO2 is a greenhouse gas.

    3. The greenhouse effect is actualy an increase in radiative forcing on the Earths surface.

    3. Radiative forcing is the only significant energy input into the Earths climate.

    4. The Sun is the ultimate source of all direct radiative forcing on the Earth.

    5. The Sun has been increasing its output at 1% per 100 million years. (i.e. radiative forcing has increased by 5% over the last 500 million years for instance)

    6. A five percent increase in this direct radiative forcing is much larger than any hypothesised increase in radiative forcing due to increased CO2 for the forseeable future.

    6, There has been no increase in the Earths average temperature over the last 500 million years. (consensus actually states there has been a fall)

    [Response: Not at all clear - Snowball Earth and the Oridivician glaciation were very cold indeed. There has certainly not been a smooth cooling over that time period.- gavin]

    7. Therefore the Earth has exhibited a negative feedback to this increased radiative forcing over a period of at least half a billion years. (Not positive, not even neutral but negative!)

    [Response: No. You make the mistake of thinking every change on Earth other than the solar input must be a climate feedback. This is not true in the slightest. Tectonic changes (and associated changes in vulcanism and CO2 outgassing) for instance are not connected to the solar input at all and cannot be considered feedbacks. Evolutionary changes - the emergence of land plants, flowers and deciduous trees are not climate feebacks either and yet likely had dramatic effects on the reflectivity, water cycling and atmospheric composition. Climate changes associated with the KT impact are not feedbacks to a solar input change either. To actually do the calculation you are attempting you would need to know all of these things pretty exactly, as well as having a quantitative estimate of the temperature changes. Big decreases in greenhouse gases due to a slowdown in ocean sea floor spreading for instance would dramatically overturn your conclusion. - gavin]

    Now lets look at what the AGW believers hypothesise. They hypothesise that the Earths response to increased radiative forcing is a strongly positive one and what proof do they have?… GCMs!

    [Response: No. A thousand times no. How many times do you need telling this is not true? - gavin]

    So flying in the face of everything we know, about how the Earths climate has been reacting to increased radiative forcing, they prefer models to facts and observation!

    I would like an someone on here to explain, in detail, seeing as climate science is largely settled apparantly, what processes have prevented the Earth warming up over the last 500 million years in the face of the strong increase in radiative forcing. I don’t want hand waving or guesses, I want the actual processes involved and the changes in the various factors with the figures and percentage changes backing up the explanation. Should be no problem in a largely settled science after all.

    I would then like to know if these processes and factors are still present in the Eaths climate system and if not when and how did they disappear.

    Alan

  29. 179
    Ray Ladbury says:

    Mesa, First, you seem to not understand that the models are qualitatively different from the models you are evidently used to–they are physics-based, dynamical models. The way you avoid fooling yourself is by putting in the physics as best you can determine it and letting the model run.

    Having said this, all the models have a significant CO2 sensitivity. This is inevitable given the physics. You simply do not get anything that looks like Earth without a significant role for a long-lived, well mixed greenhouse gas. This is all documented in the resources the Start Here page vectors you to. Why not actually learn what the scientists are doing rather than speculate based on ignorance?

  30. 180
    Thomas says:

    mark 170 (appologies as it is only a partial answer).
    If one takes the rate of increase in CO2 as an indication od emission rate, it might be an imperfect proxy for aerosol emissions. A reasonable physics based simpl model would be that tempterature departure is a linear combination of CO2 concentration (actually the log, but for smallisg changes we can ignore that), and aerosols, which we can use as the derivative of CO2 concentration for. In such a simplistic model, with CO2 warming, and aerosol cooling there is an exponentially increasing rate of CO2 concentration which exactly balances out aerosol cooling. Of course if we were to follow such a curve, someday we would have to stop, as sources of fuel will someday run out, and then we would see the full effect of the increase.

    There is significant short term variation in atmospheric CO2, driven by vegetation growth and decay, which is seasonable, but also variable year to year. In short, taking the derivative of something amplifies the effect of noise.

  31. 181
    Completely Fed Up says:

    “So it’s not constructive discourse you’re seeking, but rather you’re trying to provoke people into getting (overly) defensive, ”

    Bart, there’s already a perfectly cromyulent way of explaining Lichanos:

    http://en.wikipedia.org/wiki/Troll_(Internet)

  32. 182
    Jim Eager says:

    Lichanos: One of the reasons I like to debate in threads like this…

    At last Lichanos lets slip that he’s nothing more than a garden variety troll.

  33. 183
    Tom Pesch says:

    That’s a very good article. The only problem is that the people who should understand its contents, don’t read articles this long. You would have to squeeze that into five sentences, without using commas or other nuisances. Good luck with that.

  34. 184
    CM says:

    Mark #170, try Google Scholar with “temperature” and “interannual CO2″. Here’s one example: http://dx.doi.org/10.1016/j.chemosphere.2005.03.064. Following the references will get you more.

    CFU #174, I think you missed the time scale Mark was talking about, and his qualification “aside from or outside of the background CO2 level rise attributable to human sources.”

  35. 185

    “I would like an someone on here to explain, in detail, seeing as climate science is largely settled apparantly, what processes have prevented the Earth warming up over the last 500 million years in the face of the strong increase in radiative forcing. I don’t want hand waving or guesses, I want the actual processes involved and the changes in the various factors with the figures and percentage changes backing up the explanation. Should be no problem in a largely settled science after all.

    I would then like to know if these processes and factors are still present in the Eaths climate system and if not when and how did they disappear.”

    And you want all that in a blog comment?

    I’d like a million dollars and an end to the threat of climate change, while we’re wishing here.

  36. 186
    Howard says:

    Gavin,

    It would have been much more educational had you used one of the many AGW attributions to explain “how might this work in practice” instead of
    the impact of the Pinatubo eruption.

    For instance how does “attribution in an observational science like climatology” work with Jane Lubchenco’s attributing Oregon’s Ocean Dead Zones to AGW?

    Perhaps her work falls short of attribution and she is merely making a suggestion of possible linkage?

    If that’s the case do you think it is acceptable to infer attribution?

    If so it really doesn’t matter how attribution works. Anyone can make any suggestion they dream up and it’s close enough.

    [Response: Pop attributions are rarely very useful and often wrong - doing it properly takes time and effort. However, I have no knowledge about the Oregon dead zones, not Lubchenco's discussion of the same, but the basic technique would be the same. You need to understand what is happening, you need to have a model of some sort of the system and you need to show that of the possible causes, one or more have fingerprints that fit the observations. Issues that might arise in this particular case, might be the change in stratification as upper waters warm in summer, changes in runoff timing, the addition of nitrate through the rivers causing algal blooms etc. This might well have been tackled in a study, and perhaps someone can point to it. But simply assuming that any attribution must be false because it comes from a politician, while perhaps a good guess, cannot be justified in general. - gavin]

  37. 187
    Completely Fed Up says:

    I don’t think so CM because he goes on with this:

    “This would seem to suggest that temperature is driving CO2 levels”

    If Mark’s first language is not English, or he just got a little sloppy (this is a blog, not a Nature journal) then his confusion between:

    “When temperatures rise, the rate of CO2 increase rises”

    and

    “this would seem to suggest that temperature is driving CO2 levels”

    is merely confusion and he (well, his friend) needs to work out whether it’s levels or increase in levels in CO2 he’s considering being a driver.

    And before that, what he expects to know after having done the work, either in seeing a link or not seeing a link. Without that, you don’t know what the point was and the work is going nowhere.

    E.g. “if d(CO2)/dt2 ~ dT/dt, then this alludes to some temperature dependent sink being a pertinent factor, which we should be able to locate”. Thereby giving a purpose to the work: are there CO2 increase feedbacks that we can see in our data now?

  38. 188
    Doug Bostrom says:

    Rod B says: 27 May 2010 at 9:49 PM

    Nice non ad hominem there (109) Doug Bostrom….

    Honestly, to my regret sometimes I think there’s no other conclusion. If a fellow finds that his inner voice compels him to believe certain things regardless of all evidence to the contrary, no matter what, it really is about the person, not the ideas.

    Here’s a case where public ideas and factual knowledge don’t matter, are not even considered, instead are subordinated to a private belief system which trumps all, entire detachment.

    If it were really a matter of pure doubt I’d not use the term. But it’s not fundamentally about doubt as far as the evidence I see; in this case we see dogged adherence to failed concepts, positive assertions hinging on factual errors that have been demonstrated as incorrect.

    So how does one address ideas, how does one explain this without reference to the person? Any suggestions?

  39. 189
    Hank Roberts says:

    > 170 Mark says: 28 May 2010 at 4:43 AM
    >… This would seem to suggest that temperature is driving CO2 levels

    (apart from the anthropogenic increasing trend). No surprise there.
    Mark (the URL linked to your name is bogus). Suggest your friend look up “primary productivity” and “photosynthesis” and “annual cycle” and “forcing and feedback”;

    This may help: http://www.yaleclimatemediaforum.org/2007/10/common-climate-misconceptions-co2-as-a-feedback-and-forcing-in-the-climate-system/

  40. 190
    Completely Fed Up says:

    “It would have been much more educational had you used one of the many AGW attributions to explain “how might this work in practice” instead of the impact of the Pinatubo eruption.”

    Except that Pinatubo IS an “AGW attribution”. As Ray’s said before, the theory is Climate Theory and AGW is just the result of Climate Theory when humans are burning hydrocarbons. It is the same theory that has Pinatubo cause cooling. It is the “AGW models” as the denialerati put them that Hansen ran in the 1980′s that included a Pinatubo-like eruption and showed the effect. When Pinatubo erupted, the effect was concordant.

    Since that was the same GCM that showed AGW effects, showing Pinatubo effects shows the same model and the same theory: Climate Models and Climate Theories.

  41. 191
    Alan Millar says:

    Gavin 178

    “You make the mistake of thinking every change on Earth other than the solar input must be a climate feedback. This is not true in the slightest”

    I don’t make that mistake at all. My point is that the Earth is a dynamic system and ever since life emerged on the planet a billion years ago or so there has been no warming of the Earth. None, even though there has been a huge increase in radiative forcing during this time. Temperatures have changed significantly at times as the equlibrium is perturbed but the Earth eventually comes back into equilibrium and the overall response trend remains negative.

    Of course there are a huge number of factors other than radiative forcing but it is clearly a fact that when all these changes and processes are factored in, it has caused the Earths climate response to be a negative one over a period of a billion years or so.

    Now that is a heck of a significant trend!

    As for the future, well as far as I know all these factors and processes such as bio mass evolution, tectonics, etc etc, are still continuing and for a billion years they have, in combination with a huge increase in radiative forcing, resulted in a negative climate response.

    Now why should I start to believe that these combinations are now suddenly going to result in a positive response trend in the future.

    I need convincing since I see a billion year trend which says different. My request is for someone to explain why this is so and to back it up with figures.

    Alan

  42. 192
    Jim Eager says:

    Re Alan Millar @178: 6, There has been no increase in the Earths average temperature over the last 500 million years. (consensus actually states there has been a fall)

    Have you even bothered to look at the temperature record over the last 500 million years?

    Here, allow me to point it out to you:
    http://www.globalwarmingart.com/images/2/28/Phanerozoic_Climate_Change_Rev.png

    Oh, look, not only have there been multiple long periods of increase in earths average temperature, but multiple long periods of decrease as well, making Alan’s number six a false assertion.

    Perhaps Alan meant to write 50 million years?
    http://www.globalwarmingart.com/images/1/1b/65_Myr_Climate_Change.png

    Oh there it is, a 50 million year period of more or less sustained decrease, with minor upward excursions.

    Gee, I wonder what might have happened 50 mya to have caused that long decline?

    Could it have been the collision of the Indian subcontinent with Asia and the resulting uplift of the Himalaya and Tibetan Plateau, which exposed massive amounts of silicate rock to weathering resulting in a long steady drawdown of atmospheric CO2?

    In other words, Alan has completely overlooked geology as a factor.

    Any surprise, given that his quest is to disprove the strawman that “warmists” assert that CO2 is the only driver of climate.

  43. 193
    Rick Brown says:

    Surely Gavin (inline to # 186) wasn’t referring to Jane Lubchenco, member of the NAS and former president of AAAS, when he used the term “politician.” Heck, she wasn’t even a political appointee when she (and her co-authors) suggested that climate change may have contributed to an expansion of oceanic dead Zones.

    Chan, F., Barth, J.A., Lubchenco, J., Kirincich, A., Weeks, H., Peterson, W.T., Menge, B.A. (2008). Emergence of Anoxia in the California Current Large Marine Ecosystem. Science, 319(5865), 920. | DOI: 10.1126/science.114901

  44. 194
    Hank Roberts says:

    > I’m questioning your LOGIC! Do you get that? If I can show that
    > your own argument is incoherent, then I don’t need evidence to
    > dismiss your hypothesis. That’s my game.

    Just flagging that as cautionary. It’s very tempting bait. Eschew.

  45. 195
    Ray Ladbury says:

    Poor Lichanos. Here he has access to the latest information on Earth’s climate, presented by experts, eager to help us learn… and all he can think to do is “debate”. Pearls before swine.

  46. 196
    Doug Bostrom says:

    Rod B, I might add that the person in question did not actually offer any useful ideas to discuss, really instead directed the conversation to the topic of himself as a phenomenon, inadvertently.

    By the way, what happened to the bet? A wager was offered, though in a strangely qualified way, was accepted and in fact invited to be raised. Silence; are we not even to be treated to an explanation of why words are more powerful than deeds?

  47. 197
    Hank Roberts says:

    Alan, look up: faint young sun oceans
    This has been better explained in the last year or so than before.
    This may also help, it’s mostly pictures:
    http://www.es.ucsc.edu/~pkoch/EART_110A/Lectures/L5_Radiation-FaintSun.pdf

  48. 198
    snorbert zangox says:

    Luboš Motl has posted an excellent analysis of Gavin’s “Attribution” at http://motls.blogspot.com/2010/05/gavin-schmidt-on-attribution.html#more. It is well worth a read.

    [Response: Sure, if you like fantasy. - gavin]

  49. 199
    Lichanos says:

    Gavin’s Response:
    …Arrhenius made long term predictions, as did Callendar, and as did Plass – none of them used GCMs, and all did so without knowledge of temperature trends in the last 40 years. – gavin]

    I get the feeling that you purposely misunderstand my argument. So, Newton did all his calculations of the tides by hand, on paper…does that prove they were correct? No. The tests of his predictions did. If computer models were required to make scientific predictions, we’d be in the days of Pythagoras – that’s absurd and I don’t believe that.

    What’s your point? The AGW view does not REQUIRE computer models? I agree, of course. Moreover, your claims would be far more circumspect if you didn’t have them. Perhaps the science would be better served if you abandoned them and got back to basics.

    Arrhenius didn’t have GCMs or the long temperature record – he didn’t need them to make long-term forecasts. If he were alive today, he would certainly need the temperature record to prove any points he might make about the future if he expected to be believed. Otherwise, where’s the proof?

    [Response: I love this. But one question first - how do you manage to type when you are spinning so fast? - gavin]

  50. 200
    ccpo says:

    Quite a long time ago I identified a style of poster on climate denial that was exceedingly consistent from site to site, user name to user name. It was quite easy to identify denialists, even those attempting the wolf in sheep’s clothing technique, by the style of the argument, the argument itself, and the utter similarity of all the posts. Years of this sort of thing have gone on, which leads to the invariable conclusion that not only is the conspiracy at the higher levels, such as the well-known denialists and the think tanks, but down at the (snake-in-) the grass roots level.

    These people were organized, doubtless, many of them paid. This was revealed by such things as the revelation that Republicans had boiler rooms of people writing fake letters to newspapers to affect the political debate. I cannot conceive of the same not being true with AGW denialism.

    Lichanos is an exemplar of the incarnation that showed up about a year ago. It’s the, “I’m looking for honest debate, gosh, I really want to understand, but I’m so misunderstood” type. They always give themselves away with the accidental pejorative that not only reveals that they are lying their arses off about their intent, but make them hypocrites in the doing.

    Please, can we stop pretending these people are anything approaching honorable, or that allowing them space where real discussion is going on is in any way useful?


Switch to our mobile site