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The AGW climate feedback discussion

  1. Dec 6, 2009 #1
    As promised in the now closed CRU-hack thread, this is intended to show why I am convinced that the cause for global warming is overstated and that changes in use of fossil fuel and CO2 production will have little effect on climate. I will try and stick to the scientific method, no room for politics and groupthink. This would include the basic Popperian falsification principle. Maybe in a bit more fuzzy way. If something doesn’t work nearly as strong as advertised, it can’t be held responsible being the main cause for rising temperatures, melting glaciers, rising sea levels, etc.

    So we can look at perceived climate changes in the past, geologic records, temperature graphs, oceanic behavior, tree ring, ice cores, anything but correlation is not equal to correlation. You’d still need a physically valid mechanism to explain it, as part of the scientific method.

    So doesn’t greenhouse effect exist? You bet it does. However the point is, in what extend? And the whole thing can be regressed to two simple questions:

    A: What is the basic climate sensitivity (Planck response) of doubling the CO2 concentration?
    B: How is that modified by possible feedbacks?
    The “IPCC-answer” to the first question seems to be around one degree Celsius. Sylas explains:

    I’m perfectly happy with that. And the main dispute is not about A but about B: How is that modified by possible feedbacks? That’s the key. If the overall feedback is positive the sensitivity value would get “amplified”, whereas negative feedback would reduce the sensivity value. This is what the scientific climate dispute boils down to. In this thread I will show why I think that negative feedback prevails.
     
    Last edited: Dec 6, 2009
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  3. Dec 6, 2009 #2

    sylas

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    This may be a really useful thread. I personally think there's a lot more to climate science to this but that's a detail. The matter of feedbacks is a huge open question of major importance.

    I look forward to seeing what Andre will offer on the subject. Thanks for a nice tightly focused statement of the problem, Andre! Can I request everyone else help us all keep this as the focus of the thread?

    Cheers -- sylas
     
  4. Dec 6, 2009 #3

    vanesch

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    Just to say that I'm also very interested in learning more about the feedback mechanisms.
     
  5. Dec 6, 2009 #4

    Integral

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    IIRC James Lovelock addresses the feedback mechanisms in his book Gaia. Searching on Amazon I see he has published a number of updated editions so I am not sure where to start reading now, I read the original work sometime in the '70s. I know that this theory has gained a reputation as new age goobly gook but this came more from the noise made by new age nonscientist who adapted the work. Lovelock is a scientist, his works provide a basis of understanding some of the relationships between the chemical composition of our atmosphere and the salinity of the ocean and lifeforms. This is not a simple connection, and he does attempt to answer every question.

    One thing that is certain is that the feedback mechanisms are complex and poorly understood.

    The question that keeps running through my mind is that given that we have a feedback based control system; what happens if you introduce a step function change in a basic controlled parameter, ie concentration of CO2. This is a completely separate issue from any temperature change that may occur.

    Here is a very reasonable wiki article on http://en.wikipedia.org/wiki/Gaia_hypothesis"
     
    Last edited by a moderator: May 4, 2017
  6. Dec 6, 2009 #5
    Thanks Andre :smile:
     
  7. Dec 6, 2009 #6
    Isn't this the theory that forms the basis for movies such as The Day After Tomorrow? Where the Earths climate goes beserk trying to correct itself?

    I find it to be an interesting theory, I don't know much about it but I tend to overlook it I guess. I just think that life formed around original conditions and that spewed life for the conditions the first forms of life took. I do not think that it was 'intentional' in the sense that the organisms all maintain a particular enviroment to continue life... (Unless of course I misunderstood everything.) I think another thread would be needed to discuss that though
     
    Last edited by a moderator: May 4, 2017
  8. Dec 6, 2009 #7
    Yes Gaia is all about feedbacks but I seem to recall in an idealized hypothetical situation. I'd like to stick to directly identified mechanisms in climate.

    And happy to proceed. But most if not all is already in these threads. It's just a compilation. Also it may seen that I'm dumbing down things, but the intention is make a vague attempt to have everybody understand it.

    We should adress the following:
    1: We need a bit of understanding of the pecularities of feedback first (time delay, persistency etc).
    2: identify possible feedback mechanims (hypothesis) identified either by textbooks (Pierehumbert) or in IPCC selected literature or any other logical effect that is not mentioned there.
    3: Go over any possible evidence of feedback (lagging CO2 in ice cores, temperature drop after the Pinatubo eruption - Soden and Held, persistency in data series, model calculations etc).

    That's for tomorrow.
     
  9. Dec 6, 2009 #8
    I may need some sort of definition for feedback. Are yall talking about a biological like feedback?
     
  10. Dec 6, 2009 #9
    wordnetweb.princeton.edu/perl/webwn

    http://www.enviroyellowpages.com/Resources/GlobalWarming/globalwarming_glossary.htm

    There are generally two types of feedback Positive and Negative... anything elsee :smile:
     
  11. Dec 6, 2009 #10

    Integral

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    Andre,
    Have you actually read Gaia or just read about it?

    He talks pretty specifically about the chemistry's involved. It has been 30+ yrs since I read it so I cannot get very specific.

    More recently he created a model of a very simple ecosystem which behaved as he predicted called http://gingerbooth.com/courseware/daisy.html" [Broken] article about it.

    But again that simple simulation is NOT discussed in the book. The book is short but dense. It may be an easy read for someone with a good chemistry background, mine is weak so I had to slog through a lot of it.

    This may be one of the better sources for good information on the current knowledge of feedback mechanisms some what independent of the Global warming group.
    You'd love it, lots of graphs!
     
    Last edited by a moderator: May 4, 2017
  12. Dec 6, 2009 #11

    Xnn

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    Sylas is a great guy, but last I check he has not been put in charge of the IPCC.:smile:

    Anyhow, the IPCC's value for climate sensitivity for CO2 doubling is somewhere between 2 to 4.5 C.
    One of the reason why the range is as large as it is, is that there is also uncertainty about the Oceans response time to the warming.
    The oceans being as large as they do not respond conterminously to warming.
    There is also the influence of aerosols on the climate (cooling), that needs to be accounted for.

    So, it is not just about feedbacks.

    In the meantime, I'll check the math for Planck response.
     
  13. Dec 6, 2009 #12

    sylas

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    Aw, shucks. :blushing:

    But back to the point at issue; Andre is quite right; and I am simply reporting values in the research used by the IPCC. The value we are talking about is not "climate sensitivity", but "non-feedback response", a theoretical value which is useful for breaking down the details of the actual response we experience, and understanding it as a physical theory.

    Andre, and I, and the IPCC, all use a value of a little bit over 1K per doubling of CO2. Andre says "around 1 degree". That's correct, as a reasonable approximate value in discussion. I gave 1.12 to 1.16, which is a range of values from various papers. The IPCC says "around 1.2", on page 631 of the IPCC 4AR WG1 report, in chapter 8. You can think of a value somewhere between 1.1 and 1.2 K/2xCO2.

    Bear in mind that this is not what we actually experience. It's a mathematical approximation corresponding to the unphysical assumption that as temperature changes, nothing else changes that could impact energy balance. The real sensitivity (which is what Xnn is quoting) is much harder to estimate. Most research indicates sensitivity is significantly greater than 1.2 K/2xCO2, with a strong net positive feedback (that is, what Xnn has given). Some research argues for a net negative feedback, which would give very small sensitivity values less than 1.1.

    I've had a fair bit to say about this research in the past, in a number of threads; but on this occasion I think it only fair to leave the floor to Andre, who will be presenting some published investigations or analysis proposing net negative feedback and very low climate sensitivity. I do not want to anticipate that or preempt the discussion by jumping in with my own view again; and I confirm that the number he has given for the non-feedback response is correct and consistent with what is published by the IPCC.

    In my opinion it is a very positive thing to have tight topic focus in a thread. Andre is not proposing to solve climate science entirely, but to take a focused look at one aspect. Let's not diverge into another sweeping look at all the issues of climate!

    Cheers -- sylas
     
    Last edited: Dec 6, 2009
  14. Dec 7, 2009 #13

    vanesch

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    Just to recall what "feedback" is: it is, as Sylas said, an "artificial" way of chopping up the system response of a system, where one has defined an external input signal, and where one is looking at an "output" signal. What actually counts is the input-output relationship.

    But sometimes the physical construction of the system is such, that one can discern "subsystems" in it, of which we can define also "input" and "output" signals.

    Now, if we discern two subsystems, one which has the same "input" and "output" signals as the overall system, but in which there is also another "backward" subsystem, which seems to take as "input" what we call "output" and which ADDS its output to the overall input, then we have a feedback system.

    The wiki entry is rather good: http://en.wikipedia.org/wiki/Feedback

    680px-Ideal_feedback_model.svg.png

    The "forward" subsystem is A, the "feedback" is B.

    We have that: (X is external input, Y is output, X' is input to A)

    Y = A X' (forward subsystem)

    X" = B Y (feedback)

    X' = X + X"

    From which:

    Y = A (X + B Y)

    (1 - B) Y = A X

    Y = {A / (1 - B)} X

    EDIT: I made a silly mistake here !

    it has to be:
    (1 - A B) Y = A X
     
    Last edited: Dec 8, 2009
  15. Dec 7, 2009 #14
    I think Lovelock's original hypothesis has much going for it, particulalrly if like me, one thinks the climate system and in fact the whole earth is a self-organsing chaotic system.

    However i think he's recently contradicted himself by claiming that humans are going to cause the whole system to go out of whack. As humans we are part of the natural cycle, we evolved on this earth through natural process in line with the larger natural process of climate and biosphere. I think he is wrong to seperate humanity from the overall system.

    If the earth is self-organising as he has implied in GAIA, and there exists an attractor maintaining system stability (and i think 3-4 billion years of climate stability is evidence of that) then it would logically follow that the earth will react with either positive or negative feedbacks depending on what is necessary for that stability to remain.

    If it was so unstable that 100ppm increase in human Co2 emisisons was enough to cause the fabled "tipping point" then it would have happened numerous times in earths history and we would not be here today, as earth would as dead as Mars.

    So the climate models that project a bias only towards positive feedbacks are clearly not representative of how the real climate and earth behaves. Again it shows those models are simplistic idealisations and unlikley to have any bearing on physical reality.
     
  16. Dec 7, 2009 #15
    hear hear!
     
  17. Dec 7, 2009 #16
    Please hold your breath for a few hours, I'm working on a big post.
     
  18. Dec 7, 2009 #17
    Thanks all for the patience and for pointing to the main principles of feedback, so I can take it from there. Vanesch shows how the total gain of a feedback process can be calculated in a steady state but in reality we are looking at constant dynamic transients, as the forcings functions of climate are constantly changing. The process reacts to that with the gain factor A, but with a certain delay, in climate ranging from minutes to centuries perhaps. Feedback uses (part) of the (delayed) output of a process as input and has it's own inertia and gain factor B.

    680px-Ideal_feedback_model.svg.png

    To illustrate what happens when introducing a delay, I have made a very modest little model of the most simplest feedback that uses a step of one to simulate total delay from proces imput to the arrival of the feedback signal to be added or subtracted to the next system input (see attachment). I hoped to be able to use an older version I made a few years ago but I was out of luck so I had to make it again.

    As input we use a one dimensional random walk (column C) and we compare the reaction in a zero feedback process (column D) with a gain A (cell C2) , a positive feedback process (column D) with the factor B (cell C3) and a negative feedback process with the factor -B in column F.

    Let's look at a certain output, the first 100 steps, with A = 1 and B = 0.5 (green cells)

    2v0e2yh.jpg

    We see the average total gain for the feedbacks (in steady state pos:2, neg 0.67) are close (2.13 and 0.62). So that's fine. We also count the number of signal reverses for n=1000. The random walk makes 528 reverses (from a positive to a negative step or vice versa), which is close to the expected average of 0.5n = 500. But we see that the positve feedback process makes less reverses (344) and the negative feedback makes more reverses (640). This is obvious and important, as the added previous positive feedback steps tends to increase the deviation from to zero persistently (instable), whereas the negative feedbacks tends to pull the process back to the zero mark (stable) anti-persistent. Because of that we also see that the red positive feedback process is smoother and the negative feedback process is more jerky.

    Before the all revealing playing with the parameters it's maybe better to see if we didn't lose everybody/anybody. Still here?
     
    Last edited by a moderator: May 9, 2012
  19. Dec 7, 2009 #18
    Very well explained, thank you.
     
  20. Dec 7, 2009 #19

    Xnn

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    Can't think of any normal climate feedback mechanism that take only a few minutes.
    It's a large planet that takes weeks for weather systems to travel around.
     
  21. Dec 7, 2009 #20
    Few minutes, was to take all option open but in the daily cycle, the forming of low cumulus clouds tempering insolation, which decreases cumulus clouds again (negative feedback) is in the order or magnitude of an hour.
     
  22. Dec 7, 2009 #21

    Xnn

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    A new study just came out in Nature Geoscience.

    Apparently, up to now, mostly short term feedbacks have been included
    in climate models. These are those typically thought of such as
    water vapor, clouds and sea ice.
    However, if longer term feedbacks are included such as vegetation
    cover and land ice then climate sensativity is between 30 to 50% greater.

    Can't find anything currently on the Nature Geoscience site, but
    here is news article about the upcoming study:

    http://www.sciencedaily.com/releases/2009/12/091206162955.htm

     
  23. Dec 7, 2009 #22

    Xnn

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    Here's another article on feedbacks.

    http://www.sciencedaily.com/releases/2006/05/060522150948.htm

    So, "fast" is within a few years while "slow" is up to the millennia length.
    And warming from human CO2 emissions may result in higher natural CO2 emissions.
     
  24. Dec 7, 2009 #23

    Xnn

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    Here's the paragraph from the IPCC Chapter 8 page 631:

    I believe "surface albedo feedback" is referring only to sea ice.

    Next 2 paragraphs:

     
  25. Dec 7, 2009 #24
    Before addressing alleged feedback processes in climate, maybe it is better to return to topic and observe what our very simple basic model does on various gain parameters.

    I also hope that somebody is checking my excel sheet, seeing if it correctly describes the simple zero - order of feedback model with a total delay of one step, (omitting transient behavior) and see if the gain is correctly calculated. I also upload the original version in which the b-column generates a new one dimensional random walk on every calculation cycle.

    We have been looking at proces gain A = 1 and feedback gain B = 0.5 giving this,

    2v0e2yh.jpg

    and we see that positive feedback can change the original signal considerably
    Now if we increase the process gain for instance to A = 1.5, the positive feedback (B=0.5) grows to dominant proportions:

    2dse5wk.jpg

    We notice also that persistency, or reluctance to reverse, has increased considerably

    The reason obviously is that the process gain is bigger than one, hence the amplification can put more energy in the system. However there is no energy source available in climate other than the solar input, that means that attenuation requires that both process gain A and feedback gain B are smaller than one. Sometimes maybe close to one, if the process converts nearly all input energy to the same output energy and dito for the feedback. It can also be much smaller than one if the output is diverted in several other forms and dito of course if feedback is partly positive and partly negative.

    So this is median result with both gains A and B on 0.5:

    2z4ereb.jpg

    We see the role of positive feedback has been reduced considerably, the total practical gain being only 0.69. Now to see which is dominant A or B, We look at a gain A = 0.2 and B = 0.99 to get this:

    2yzhcar.jpg

    Obviously, despite the 'strong' positive feedback factor, the attinuation of A has reduced the effect of feedback considerably and if we reduce the feedback gain B to a 'normal' 0.5, there is not a lot that any feedback does anymore:

    2i6djjt.jpg

    It appears that the process gain A as amplification or attenuation determines whether or not the feedback has a big effect. I expect that in climate the factor A is usually not too large. If my ramblings are vaguely into the right direction, maybe that the effects of feedback in attenuated processes are not too dominant, but we would have needed quite some strong feedback to increase the climate sensitivity (Planck response) of about one degrees to about double values or more in attenuated processes.

    But there is more, the persistency and antipersistency characteristics of the output signal, can we do something with that? That's for tomorrow.
     
    Last edited by a moderator: May 9, 2012
  26. Dec 7, 2009 #25

    Xnn

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    Here's the abstract from the Nature Geoscience article:

    http://www.nature.com/ngeo/journal/vaop/ncurrent/abs/ngeo706.html


    Bottom line; including long term feedbacks results in between 30 to 50% more warming.
     
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