Question on whether climate is chaotic or not

  1. Hi Guys,

    Okay I have a question i was wondering if anyone can enlighten me on this discrepancy.

    I asked Gavin Schmidt on RC whether he thought the climate was a chaotic system. He said he did not know (seriously).

    What i fail to understand is how can anyone be confident about the results of a computer model for which the underlying nature of the fundamental science is unknown?

    Their argument is more or less that because climate changes over longer periods they dont need to treat it like a chaotic system (with all the inherent unpredictability that comes with a chaotic system).

    But then on the other hand, they claim that a moderate increase in Co2 will cause this "tipping point" to occur causing run-away global warming.

    Put that all together and we see a monstrous logical contradiction because they claim in equal measure that a) system is not chaotic and sensitive to initial conditions b) Co2 (which is an initial condition in the model) will push climate into new run-away warming configuration within decades.

    Thats makes no sense at all. They are denying the chaotic nature of climate while using charcteristics of chaotic systems to scare the hellp out of us re the Co2 (initial condition).

    I'm all ears for anyone who can explain this unambiguous contradiction.
     
  2. jcsd
    Earth sciences news on Phys.org
  3. Re: CRU hack

    That's crazy. As far as i can tell no-one in the agw community will explain the obvious contradiction.

    In fact I've looked up the RC archives and various chaos experts have questioned Gavin on this issue and his answers are at best misleading.

    So this issue is not about this or that graph but actually goes to the heart of the foundational science involved.
     
  4. well for starters, if you look at the long term ice core "temperatures", like fore instance here in EPICA dome C and NGRIP there is a distinct autocorrelation.

    [​IMG]

    So if the temperature interpretation is correct then the climate is bi-stable, as an oversteered positive feedback system (flip flop) hence in that case climate is not chaotic.

    However this is under the assumption that ice core 'water' isotope ratios (dD and d18O) is equivalent to temperature and when zooming in on macro level on multiple other proxies, the excrements start impacting the rotating wind generator. Hence that should not be challenged.
     
  5. Hi Andre,

    Okay but i dont get how that answers my question re climate and chaos, and the fact that there appears a need for agw to argue that climate is not chaotic (hence predictable), but then they claim that a little more Co2 (initial condition) will cause tipping point leading to run-away gw.
     
  6. Because CO2 corrolate with that temperature graph, inducing the second* fallacy (correlation is causation). However it is also perceived that the CO2 lags the isotopes a few hundred years, this could be explained if the CO2 acts as a strong positive feedback, pushing the temperature to either of the system limits.

    [​IMG]

    However there is a lot more to feedback and this interpretation could be challenged, if it was legal to do so here.

    Note that the sealevel graph is derived directly from the isotope ratios and hence is not an independent corrolating factor.



    * the first was in the previous post, affirming the consequent, if the temperature is high the isotopes are heavy, the isotopes are heavy, hence it was warm)
     
  7. D H

    Staff: Mentor

    Whoa! You appear to have a (somewhat common) misperception of what chaotic means. Chaotic systems are not inherently unpredictable. The solar system is chaotic. That does not mean we cannot predict the locations of the planets over the course of a year or even millennia. The weather is chaotic. Weather forecasts are pretty accurate over the span of a week or so.
     
  8. Hepth

    Hepth 483
    Gold Member

    Re: CRU hack

    No, he is just a scientist. You asked for a definite response to a system that obviously isn't 100% known, and its a pointless question anyway. Of course we don't know if it is chaotic or not. What do you mean by chaotic? If we have a period of relative predictability in an otherwise chaotic system, is it still "chaotic" in your sense? In our scientific sense it is, but if we can model the current state, and predictions tend to be nearly right (not necessarily in this case, but in general), and the predictability holds for say a hundred years or so before some unknowns change it drastically, then what should his response have been?
    That's a very loaded question. Its like asking a scientist "Are you 100% sure you're right? no? Then how can you assert that its right at all!?"
     
  9. Andre,

    I think i get what you are getting at above, and i agree it needs way more invetsigation before anything can be called settled.

    My point is focused on the physics on which the climate models are based. My issue is that gavin schmidt at RC says he doesnt know if climate is chaotic :-) I am 99% sure it is chaotic
    because it has all the hallmarks of a bonafide chaotic system.

    What i find odd is WHY Gavin and other agw scientists seem so keen on suggesting the climate is not chaotic. They dont say its not, but as they wont answer the question, that is the impression they want to make.

    The other issue is that i find it laughable that they claim not to be able to define the sort of physics operating in a climate system. If they cant define the physics underlying their model then what good is their model?
     
  10. pretty accurate is not the sort of accurate we need for the type of certain predictions being spouted from agw computer models.

    I think you dont understand the nuance between a system one can predict with certainty and one which one cannot predict with certainty.

    Chaotic systems are not predictable with any level of certainty at which one can rule out surprise behaviour.

    You've also missed the central point in your rather sloppy attempt to disrupt the main focus of my question. The point being that gavin wont commit to an answer on this question at all, so until he commits himself to stating the basis of the underlying science of agw models, then there can be no confidence in the predictions of those models.

    I suggest you read up on the n-body problem because it is unsolvable (from any practical perspective) and it is far simpler non-linear system than the climate.

    But let me ask you : is climate a chaotic system?
     
  11. Re: CRU hack

    Hepth,

    "No, he is just a scientist. You asked for a definite response to a system that obviously isn't 100% known, and its a pointless question anyway"

    Its not 100% known? Then if they dont fully understand the underlying physics of a climate system then they can say nothing for certain about the predictions of those models based on this unknown system.

    Its like if i were to make up a bunch of bs and say: "our solar system does not obey the laws of relativity as does the rest of the universe, so the same rules which normally apply should not be applied to my solar system model". Now most people would rightly laugh at that.

    Thats exactly the same as is being said by Gavin about climate. he is trying to imply it works on some law of physics of whcih we have no history or description, hence it cannot be criticised on fundamental scientific grounds.

    "That's a very loaded question. Its like asking a scientist "Are you 100% sure you're right? no? Then how can you assert that its right at all!?"

    Its a simple question asking a scientists to explain the underlying physics of his model. There is nothing loaded about it other than the bs answer claiming he does not know.

    You cant have it both ways. Either he admits that climate is a chaotic system and then he has real problems because the certainty they claim to predict goes out the window, or they formulate a whole new science for the climate.
     
  12. vanesch

    vanesch 6,236
    Staff Emeritus
    Science Advisor
    Gold Member

    I'm no specialist, but I do see a lot of misconceptions here.

    We know that the weather is chaotic, which means that close initial conditions can/will evolve in widely different systems on a certain, finite time scale. So that means that predictability is possible within that time scale, and hopeless beyond. That's why we have weather forecasts on the level of a few days, but we will never have day-by-day weather forecasts for 6 months in a row.

    Now, climate is average weather over 30 years or so. In other words, climate is the statistical description of weather. Now, chaotic systems can have completely well-defined statistical descriptions. This statistical description can itself have a (slow) dynamics. This is what one is after in climate models: the slow dynamics of the statistical description of weather.

    The question of whether this dynamics of the statistical system is chaotic itself is entirely different from weather the original system is chaotic. It could be that this dynamics is relatively "simple". It also depends what kind of dynamics one includes in "climate". Is El Nino part of the "climate dynamics" or is this still part of the "weather dynamics" ? Is there a long enough time scale beyond which the average weather is determined in a rather simple way ?

    Also, it depends on what one considers to be "boundary conditions" and what are to be "internal variables". For instance, all "outer space" influences, like solar irradiation, cosmic rays,.... are to be considered as boundary conditions. Not that we can predict them, and not that they may not alter randomly, but they are most definitely not part of the climate dynamics itself. They are external inputs. Probably one should say the same for geological events, such as volcanic eruptions or the like.
    This doesn't mean that one knows how to predict them, but they are not part of the climate itself, they just "steer" it.

    However, people building climate models should at least know whether their MODELS are chaotic or not - at least over time scales where one is interested in them (a few centuries/millennia). That shouldn't be too difficult to find out !

    BTW, no sensible scientist would tell you that there will be a run-away climate. And in fact, a run-away climate would not be chaotic! We would know exactly where it would go.

    Also, "chaotic" doesn't mean "it will sometimes do surprising things you didn't expect". Chaotic means that small changes in initial conditions will give you widely different outcomes after a certain time of evolution.
     
  13. Is that the main -important- question or is the main question if carbon dioxide is the main forcing function for global temperature?
     
  14. Andre,

    I agree with you that there are various weaknesses in the agw theory. I dont know enough about certain areas to comment, and i try to stick with a topic i am comfortable on.

    You are right and determining once and for all the link between Co2 and temperature is part of coming to a conclusion.

    But i rather hammer away at the fundamental nature of the physics underlying their models because i believe there is a major weakness in this question about defining climate as chaotic or not.

    My point is not that they are necessarily completely wrong, as agw could be right to some degree. My point is about the level of certainty they project concerning their models and that we are facing catastrophe.

    In fact agw could be partly correct and still not mean any catastrophes, so there are all sorts of shades involved from a scale of right---------wrong.
     
  15. turbo

    turbo 7,365
    Gold Member

    Re: CRU hack

    That's a perfect "gotcha" question because demanding a yes or no answer assumes a dichotomy in a complex situation. It is quite possible that climate is chaotic on small scales, yet more predictable on larger scales or over time, or when observations are averaged, etc, etc. That's what the models are for.
     
  16. Re: CRU hack

    Nevertheless, predictions go nowhere when when it is based on flawed interpretations of proxies of the climate of the past.
     
  17. Exactly, and that's also the big problem. Everybody does. The general picture is lacking if you can only think for your own expertise and have to rely on others like CRU personel for the rest.
     
  18. Hepth

    Hepth 483
    Gold Member

    Re: CRU hack

    What I'm trying to say is asking "Do you think XX is chaotic?" Is a VERY poorly worded question. You can be very strong in your understanding of climate modeling, but nothign can ever be perfect, and noone ever claims it is.

    No, its like saying "our solar system's planetary data does not seem to be obeying the laws of newton, but more closely fits this other model we have. We may be right, wrong, or a little of each. The system may actually be chaotic. There could be a billion things wrong. We understand the majority of the physics behind it, and adding this new method makes it that much more accurate. So if this new method can replicate previous data, then it MAY be able to predict new data."



    THAT is such a poor idea of what science truly is. NO ONE is saying ANYTHING about PREDICTIONS for "certain". They are "certain" only about previous data. There are no certainties for the future. To demand that there are before accepting a working model is ludicrous. That is not what science is about, its about modeling. I hope you're not too stubborn to realize the difference.


    (btw, I am not pushing either political stance. I'm just a scientist and arguing about the question being poor.)
     
  19. Vanesch,

    "We know that the weather is chaotic, which means that close initial conditions can/will evolve in widely different systems on a certain, finite time scale. So that means that predictability is possible within that time scale, and hopeless beyond. That's why we have weather forecasts on the level of a few days, but we will never have day-by-day weather forecasts for 6 months in a row......"

    Agreed.

    "However, people building climate models should at least know whether their MODELS are chaotic or not - at least over time scales where one is interested in them (a few centuries/millennia). That shouldn't be too difficult to find out!"

    Agreed and this is exactly what i am demanding from Gavin or toher agw scientists: a commitment to state categorically whether he believes his models are chaotic or not. He/they will not! You will see that in their literature they ALWAYS resist giving a straight answer to this question. But ironically they have no problem telling us run-away global warming is a certainty or near certainty. Now if they say otherwise in private, its bloody time for them to communicate that to the media who appear to be under the impression its all settled (which to most ordinary folks means CERTAIN).

    So i hope you can agree with me, that there is something fishy going on when these guys are so intent to skip the whole question of whether the climate is a chaotic system or not.

    And i agree with most of your post and understand the nuances of chaotic systems and their properties.

    But the other contradiction and is relevant to your explanation above is that while agw theorists argue that because the changes take place over a long time period (as opposed to the weather) they can question the chaotic nature of the "system", BUT in the same breath they claim that a moderate amount of extra Co2 will have a tipping point effect, hence catastrophe. If the initial condition or call it variable Co2 can have such a dramatic effect on temperatures in a relatively small space of time, then that in itself contradicts the idea that we cant call it chaotic because the tipping points happen on larger time scales.

    Do you see what i mean?
     
  20. Hepth

    Hepth 483
    Gold Member

    Re: CRU hack

    Or when your analysis and models can change faster than the time needed to test predictions. At least the advancements from it (modeling) will benefit us one way or another.
     
  21. I'm certainly no expert on chaos theory and non-linear system, however i am facinated by them from a layman's perspective and have read just about every book on the subject.

    So for me, i have always been sceptical of the level of certainty declared in these climate models as i know that they MUST inherently be based on chaotic physcis as is just about every other natureally occuring system in the universe. I will happily eat humble pie if someone can prove to me that climate systems are not chaotic. I'll feel really stupid but i'll eat the pie :-)

    However i do agree with you, and follow both WUWT and Climate Audit, who have i think been really unfairly labelled as cranks. But I'm not knoweldgable enough on the Co2 - temp link to comment other than i have noted the apparent problems with causality dynamic between the two in the historical record - as best we can make out.
     
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