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Global Warming and Chaos Theory

  1. Oct 20, 2008 #1
    There has been much controversy concerning Global Warming: sun spot activity, only heat radiation at 15 microns being trapped by CO2, vast amounts of greenhouse gases going intot he atmosphere from exploding volcanos and the general cyclical nature of climate change have attempted to explain the insignificance on human interaction on the environment as having a significant effect on GM.

    I came across documentary which made reference to how 'Chaos Theory' explained the significant effect of human interaction on climate change. Can someone give some elaboration on this?
  2. jcsd
  3. Oct 20, 2008 #2
    I don't think that there has been much controversy concerning global warming from within the scientific community.

    Sunspot activity does affect the climate but variations in solar irradiance are probably less than 10% of the change in radiative forcing due to the anthropogenic part of the greenhouse effect.

    There are a few absorption bands of CO2 that make it a greenhouse gas.

    Volcanoes produce a very small fraction of the CO2 compared to anthropogenic sources.

    The since the middle of last century this warming is mostly (or entirely) anthropogenic. It is not cyclic.

    However, I imagine that chaos theory wrt climate change is because the climate system exhibits sensitive dependence on initial condition. This means that if someone in Australia paints their house roof dark green, then the thermal eddies created there can have a significant effect on the Atlantic Hurricanes two years later. Impossible to predict, and although it probably is a change in climate, it is not really "climate change" by which is generally meant the effect on climate of anthropogenic global warming and its effects.
  4. Oct 21, 2008 #3
    And I don't think that this is a very accurate representation of the reality. For instance the Assessment Reports of the IPCC have not been peer reviewed in the classical way, because the editors were free to accept or reject comments from the reviewers. The summaries for policy makers was not reviewed by the specialists but only by government representatives and showed a somewhat different picture than the chapters.

    Therefore the specialists decided to write their own Independent Summary for Policy Makers, which was reviewed by peers:


    Having somewhat different conclusions than the general party lines:

    Last edited: Oct 21, 2008
  5. Oct 21, 2008 #4
    On the other hand, in the scientific literature there is very little denialism.

    The American Meteorological Society (6), the American Geophysical Union (7), and the American Association for the Advancement of Science (AAAS) all have issued statements in recent years concluding that the evidence for human modification of climate is compelling (8).

    The drafting of such reports and statements involves many opportunities for comment, criticism, and revision, and it is not likely that they would diverge greatly from the opinions of the societies' members. Nevertheless, they might downplay legitimate dissenting opinions. That hypothesis was tested by analyzing 928 abstracts, published in refereed scientific journals between 1993 and 2003, and listed in the ISI database with the keywords "climate change" (9).

    The 928 papers were divided into six categories: explicit endorsement of the consensus position, evaluation of impacts, mitigation proposals, methods, paleoclimate analysis, and rejection of the consensus position. Of all the papers, 75% fell into the first three categories, either explicitly or implicitly accepting the consensus view; 25% dealt with methods or paleoclimate, taking no position on current anthropogenic climate change. Remarkably, none of the papers disagreed with the consensus position.
    (http://www.sciencemag.org/cgi/content/full/306/5702/1686" [Broken], Oreskes, Science (2004)

    Actually there has been a comprehensive list of scientific societies of international standing, including the Joint Science Academies of Australia, Belgium, Brazil, Canada, the Caribbean, China, France, Germany, India, Indonesia, Ireland, Italy, Malaysia, Mexico, New Zealand, Sweden, and the United Kingdom.

    International Council of Academies of Engineering and Technological Sciences
    European Academy of Sciences and Arts
    Network of African Science Academies
    National Research Council (US)
    European Science Foundation
    American Association for the Advancement of Science
    Federation of American Scientists
    World Meteorological Organization
    American Meteorological Society
    Royal Meteorological Society (UK)
    Australian Meteorological and Oceanographic Society
    Canadian Meteorological and Oceanographic Society
    Canadian Foundation for Climate and Atmospheric Sciences
    International Union for Quaternary Research
    American Quaternary Association
    Stratigraphy Commission of the Geological Society of London
    International Union of Geodesy and Geophysics
    International Union of Geological Sciences
    European Geosciences Union
    Canadian Federation of Earth Sciences
    Geological Society of America
    American Geophysical Union
    American Astronomical Society
    American Institute of Physics
    American Physical Society
    American Chemical Society
    Engineers Australia (The Institution of Engineers Australia)
    Federal Climate Change Science Program (US)
    American Statistical Association

    And as with the published papers:

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

    (from http://en.wikipedia.org/wiki/Scient...hange#Statements_by_dissenting_organizations")

    That's been true of the last two assessment reports ... a concession made to time.
    The first two the wording was slogged out at open meetings, with S Fred Singer standing up in the public gallery at every sentence and giving a long speech that everyone there knew was rubbish. (Presumably including himself).

    That's not quite true. The second draft is the one that the government representatives get to review. By that time is has already been reviewed reasonably exhaustively by specialists.

    However that is true. Government delegations always attempt to water down the danger, and the necessity for action. The most vociferous government delegations at the IPCC have traditionally been USA, China, Saudi Arabia and Kuwait. The worlds biggest consumer of fossil fuels per capita, the world's biggest consumer of fossil fuels, the world's biggest exporter of fossil fuels, and another economy dependent fully on the export of fossil fuels.

    And so there is a valid criticism of the IPCC that the reports are too weak. And it is true that anything that is not very clearly true, and with all the research coming down with similar findings, are generally left out at the political review stage. Or not included because of the awareness that they will be chucked by the political review.

    But as long as the are read with the understanding that they describe a best case scenario, the IPCC reports are informative to the intended audience ... laymen and politicians. Experts already know from the published research what is going on, and that there is little doubt.

    Ross McKitrick is an economist with known contrarian views on Global Warming, and a particularly enduring bee in his bonnet about northern hemisphere temperature reconstructions.

    If he and nine of hid cronies wrote a document to challenge the one written by the IPCC's hundreds of authors and thousands of reviewers, I am not surprised that it has received less attention than the IPCC's one.
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  6. Oct 22, 2008 #5


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    In Chaos Therory, the Butterfly Effect states that very small intputs to a system can have disproportionately large effects. This is a way of trying to explain how the tiny influence of man can change the enitre atmosphere of Earth.

    BTW; most of the surveys I've seen show the scientific community split about 60/40.
  7. Oct 22, 2008 #6
    The denialist community are pretty effective at stacking surveys, especially after the damage to their credibility that the Oreskes literature review made plain.

    If the split is over whether the current warming is likely to be mostly anthropogenic, and the scientific community is the climate science community, if the split is not about 99.9/0.1, then there's a selection bias, or a crap survey bias.

    Because that's about the proportions of the published work.

    And there's no disagreement from scientific organisations of any standing.
  8. Oct 22, 2008 #7


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    I suggest you read the EPA's official stance on Climate Change.

    The official US EPA stance on what "is likely" is

    Also, I hope that you are aware that the IPCC hid the first part of their "report" from the public. The final report was not a consensus and they blocked any scientist that questioned what they were doing or provided evidence to the contrary.

    IPCC Fourth Assessment Report Papers: Working Group I, The Physical Science Basis of Climate Change, 2005-2007; Expert Review Comments on First-Order Draft, Chapter 1. ESPP IPCCAR4WG1, which was previously withheld from the public until they were sued for the information under the "Freedom of Information Act".

    The previously withheld report can be viewed here - http://pds.lib.harvard.edu/pds/view/7794905?n=2&imagesize=1200&jp2Res=.25 Where you can see how the IPCC "picked" the data they wished to present.

    If you want to read some good posts on Climate Change, I suggest you search on Vanesch's posts and read them and you can respond to them here. If you don't, I will be glad to post them all here for you.
    Last edited: Oct 22, 2008
  9. Oct 22, 2008 #8


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    There are two kinds of "denialists": there are those who think that they can prove that there is no AGW, and then there are those that think that the scientific certainty displayed about AGW is exaggerated as of now. I belong to the second category, because I adhere to Feynman's statement concerning scientific research (paraphrased quote): "If you don't do everything which is in your power to prove yourself wrong, if you don't take every idea that could show you wrong seriously, then you are fooling yourself in science".

    Well, if it does "damage to your credibility" to try to point out some weak points in the argument (and believe me, there are several of them!), then you are infringing on Feynman's statement.

    Now, I know that the typical answer to that one is: yes, but someone who questions, say, relativity, or Newtonian mechanics, that's a crackpot, no ? Or someone questioning evolution, that's a religious fool, no ? That is because theories like relativity or Newtonian mechanics or evolution have a huge amount of unquestionable data behind them. You can take down tens or hundreds of those, and you still have solid proof, gathered over time. This is simply not (yet) true for the scientific case of AGW. There are elements, true. Each of those elements has however, some weakness to it. It is not overwhelming. It takes time to turn a speculative theory in a scientific certainty, and during this time, one should adhere to Feynman's advice.
    The "solid AGW proof" of a few years ago turned out to have to be modified in such a way that it lost its convincing power (say, hockeystick, say, temperature/CO2 delay in paleodata,...). Refusing to take Feynman's advice, refusing to consider seriously the questioning of the solidity of the proof (you say it yourself, 99,9% of publications are not critical towards the AGW theory) at this point, is falling into the trap Feynman is pointing out, and is btw a sociological phenomenon known as groupthink. It happened in other domains (say, string theory :-).

    Of course, nature doesn't care about how people do their science. AGW could well be there. I'm only pointing out that the scientific attitude towards it isn't healthy. One has the idea that one is "scientific" if one endorses the credo, and that one "damages one's credibility" if one asks critical questions. Once this happens, one has left the domain of scientific inquiry, and one is entering the domain of "building a case". I really wonder whether most climate scientists pushing AGW are "trying to prove themselves wrong" or are rather trying to "prove AGW".

    That's exactly what Feynman warned about.
  10. Oct 23, 2008 #9
    No, that's exactly what I was saying, only a bit stronger.

    They say that it is very likely that "Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations".

    I know that it is not certain that most of the warming is anthropogenic, but they the EPA does say that it is certain that CO2 is a greenhouse gas, and that it's concentrations have been increased by human activity.

    The only question that remains is what is the climate sensitivity to a rise in CO2 from 280ppm to 385ppm?

    Well to a doubling it is about 3°C, so it's about 1.4°C for that rise. It may be a lot less, but there is a greater chance that it is a lot more. (If you look at the posterior probability density function for climate sensitivity from this paper: Robust Bayesian Uncertainty Analysis of Climate System Properties Using Markov Chain Monte Carlo Methods)

    I think even outside minimal estimates of climates sensitivity are 1.5°C per doubling, which is still 0.7°C, which is still most of the warming, but it may not yet be all manifest, so possibly half of the warming is natural. We are talking not very likely though.

    A perusal of the first few pages of comments and responses didn't indicate a bias to me. Did it to you?

    It looks as though the IPCC position could have been much stronger, but for space constraints. The first comment in particular, that it should be included that we are returning the CO2 levels to ones that occurred when there was no ice sheet on Antarctica would have been pretty hard hitting in some quarters.
  11. Oct 23, 2008 #10
    There are a lot more than one climatologist in the world. Even if there are a few who you claim are "fooling themselves in science", then there are plenty who would happliy take a Nobel prise by showing that the greenhouse effect doesn't actually work or that the warming that is temporally and spatially distributed in a way that is highly suggestive of the greenhouse effect, is from some other source.

    Well, if it does "damage to your credibility" to try to point out some weak points in the argument (and believe me, there are several of them!), then you are infringing on Feynman's statement.

    The impression one gets from the IPCC reports is that the case for AGW is in fact much stronger than it was in the late 90s.

    And your two examples make me wonder what you've been reading. Not peer reviewed scholarly research, I suspect.

    There have been a dozen northern hemisphere temperature reconstructions since Mann et al. 1998. And they are all "hockey sticks":
    ipcc_6_1_large.jpg (from figure 6.10 of the IPCC 2007 working group I report).

    The temperature/CO2 delay in paleodata is not at all problematic for AGW. It is known that the ice ages are regular, so they had to be set off by Malankovic cycles, or at least something regular. That an ice age gives way rapidly to a interglacial shows that CO2 is positively feeding back into the global temperature.

    In fact careful analysis of paleoclimatic reconstructions of temperature and CO2 concentrations lead to historical climate sensitivity estimates to a doubling of CO2 not unlike current estimates. (which shows how much the behaviour is in line with expectations). Here are four examples of such papers off the top of my head; I'm sure a full literature review would confirm that paeloclimatic reconstructions are not problematic to AGW.

    1) Efficiently[/PLAIN] [Broken] Constraining Climate Sensitivity with Ensembles
    of Paleoclimate Simulations
    Annan et al. SOLA (2005)
    We attempt to validate the resulting
    ensembles against out-of-sample data by comparing
    their hindcasts of the Last Glacial Maximum (LGM) to
    paleoclimate proxy data, and demonstrate through this
    that our ensembles of simulations are probably biased
    towards too high a sensitivity. Within the framework of
    our single-model ensemble experiment, we show that
    climate sensitivity of much greater than 6°C is hard to
    reconcile with the paleoclimate record, and that of
    greater than 8°C seems virtually impossible. Our
    estimate for the most likely climate sensitivity is in the
    region of 4.5°C.

    2) Climate sensitivity estimated from ensemble simulations of glacial climate Schneider von Deimling et al. Climate Dynamics (2006)
    Based on our inferred close
    relationship between past and future temperature evolution,
    our study suggests that paleo-climatic data can
    help to reduce uncertainty in future climate projections.
    Our inferred uncertainty range for climate sensitivity,
    constrained by paleo-data, is 1.2–4.3°C and thus almost
    identical to the IPCC estimate.

    3) Climate sensitivity constrained by temperature reconstructions over the past seven centuries Hegerl et al. Nature (2006)
    Here we demonstrate that such
    observational estimates of climate sensitivity can be tightened if
    reconstructions of Northern Hemisphere temperature over the
    past several centuries are considered. We use large-ensemble
    energy balance modelling and simulate the temperature
    response to past solar, volcanic and greenhouse gas forcing to
    determine which climate sensitivities yield simulations that are
    in agreement with proxy reconstructions. After accounting for
    the uncertainty in reconstructions and estimates of past external
    forcing, we find an independent estimate of climate sensitivity
    that is very similar to those from instrumental data. If the latter
    are combined with the result from all proxy reconstructions,
    then the 5–95 per cent range shrinks to 1.5–6.2 K, thus substantially
    reducing the probability of very high climate

    4) Climate sensitivity constrained by CO2 concentrations over the past 420 million years Royer et al. Nature (2007)
    We conclude that a climate sensitivity greater than
    1.5 6C has probably been a robust feature of the Earth’s climate
    system over the past 420 million years, regardless of temporal

    I don't see that that is happening. Investigations into climate sensitivity are common, follow a wide range to methods, and estimates way outside the accepted range have been published in high profile journals.

    The fact that CO2 is a greenhouse gas and that human activity has increased its concentration are not questioned, but there are known.
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  12. Oct 23, 2008 #11


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    Let us concentrate exactly (we're using indeed the same data :-) on this "hockey stick".

    Compare it to the initial hockey stick on p 3 of

    the summary for policy makers in 2001.

    Now, admit that there is a world of difference in the convincing power that we are *on an exceptional and dramatic temperature rise* which was the aim of that plot (with well-choosen coloring too) in the last century - a rise that was OBVIOUSLY an order of magnitude larger than what had happened in the last 1000 year.

    When you look at the data of the proxies in the 2007 plot, no such *obvious* dramatic rise is present. Nor the values, nor the rise is an order of magnitude above what "seems normal". If this plot had been there in the 2001 report, it wouldn't have alarmed many people. I know that there has been a statistical analysis (you use "torturing the data until they confess" if the data aren't obviously indicating what you want - I know this, I do this sometimes too) that shows that the null hypothesis "the rise in the last 100 years is not greater than any rise in the previous 1000 years" can be rejected with a limited confidence, but admit that it is far from being as dramatic and obvious as it was in the "proof beyond doubt" in the 2001 report.
    There is another error in the presentation of the 2007 plot. That is the visual confusion (using well-chosen coloring) of the proxy data and the actual measurements. Clearly, the proxy data are not 100% the same as the actual measurements (the solid black curve doesn't coincide perfectly with the proxies). That means that there is a dynamical system in between both, which can be for instance, a low pass filter. Well, you shouldn't compare data with different dynamical properties if the aim is to show a difference in dynamics (rise in this case). You shouldn't compare actual measurements which show a quick rise, with proxies which don't show such a quick rise, not now, and probably not in the past. Because if those proxies temper quick rise NOW, (low pass filtering), then they might have done so too in the past. So you cannot conclude then that the rise is faster now than back then.

    Even better: shift the instrument data and the smooth grey curve back about 1000 years. You'd find about equal agreement. Was there an accute climate catastrophy around the year 1000 ?

    Now, tell me, where is this critical analysis present in the current report ?

    Leave away the current data (which are not the same as the proxies), and show only the proxies. Do you think that this still has the "hockey stick" conviction power ? You only see a smooth rising before 1000 AD, then a dip and indeed a slightly stronger rise in the last century. NOTHING TO DO with the dramatic effect displayed in the 2001 report. Where is the scientific honesty here ?
    Last edited: Oct 23, 2008
  13. Oct 23, 2008 #12
    Important is the observation that the blade of these hockeystick is glued upon it and that the proxies are not following which basically already refutes the robustness of these proxies.

    But there is more, Mann et al 2008 admit that the adbundantly used and recycled tree ring proxies are basically flawed by showing the difference in skill in fig 2:

    See also here the glued on blade, not following the proxies (still containing tree rings) and hence refuting the same.


    See also that the CRU temperatures is a distinct outlier, temperatures were not al all through the roof at the end of the former century; on the contrary.

    This is what it should have looked like:


    So indeed one might challenge scientific honesty.
  14. Oct 23, 2008 #13


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    Well, again, there is no tight proof (although there is suggestive evidence) for this. What is usually taken as the evidence that the rise in CO2 is human-caused ?

    1) there is the correlation between the human consumption of fossil fuels and of its concentration in the atmosphere

    2) there is the correlation between the decrease of oxygen in the atmosphere and the rise in CO2

    3) there is the isotopic composition of CO2 in the atmosphere, which shows that it has a rising component that most probably comes from fossil fuels (lower C-14 content).

    However, although this is of course suggestive evidence, this is no proof at all. In order to show this, let us take on a purely imaginary situation. Imagine that the cause-effect relation is different: that a rise in temperature CAUSES a rise in equilibrium atmospheric CO2. I'm not saying that this is the case, or that I have the slightest bit of evidence for this. I'm just indicating a working hypothesis to show the PROOF false. Imagine, as a gedanken experiment, that it is temperature that sets CO2 levels, and not vice versa. Also, one can acknowledge that humanity did indeed produce a lot of CO2 from fossil fuels.

    If the temperature were constant and it drives the CO2 equilibrium value, then the equilibrium values of CO2 would remain constant. That means then that there is somewhere a mechanism that takes up or releases CO2 if this amount is changed somehow by an external process. Now, if you burn a lot of fossil fuels, you are going to put much more CO2 in the atmosphere, and the regulatory mechanism will "sink" an equal amount. However, the amount of fossil-fuel related CO2 (tracable with isotope analysis) will then of course rise in the atmosphere: most CO2 will be from fossil-fuel origin, but its LEVEL will be determined by the causal system driven by temperature.
    Also, because burning fossil fuels consumes O2, one would see a decrease in O2 on par with the consumption of fossil fuels, and hence with the immediate production of CO2. If the regulatory mechanism driven by temperature has some inertia, one would indeed see, upon a rise in fossil fuel burning, an immediate CO2 rise, and an immediate O2 decrease ; but the CO2 level would then be steered by the control mechanism to its equilibrium value.

    Now, imagine that the temperature rises for some or other reason. Now the equilibrium set value of CO2 will rise too. And what would we observe then ? We would observe:
    1) a rising equilibrium value of CO2 in the atmosphere
    2) a correlation between the CO2 increase in the atmosphere and the O2 decrease in the atmosphere
    3) an isotopic composition which indicates that an increasing fraction of the CO2 content in the atmosphere is from fossil fuel origin.

    In other words, this gedanken experiment, with its working hypothesis that temperature drives CO2 equilibrium values, is entirely in agreement with observations. That's no proof of course. It is only a proof that these 3 observations DON'T PROVE any causal relationship between rising CO2 levels in the atmosphere and human CO2 production by fossil fuel burning, given that they are also compatible with a model in which this is not assumed.

    Again, don't understand me wrong: I didn't say that I proved that human CO2 production is NOT responsible for the rise in CO2 in the atmosphere. I only indicated that the arguments that are advanced as PROOF of this, are not a proof (although, I admit, suggestive), because they can be compatible with a working hypothesis which is the inverse of the to be proven statement.

    If you want an analogy, consider that you are on the seaside. It is rising tide but you don't know what a rising tide is. You see somebody poor heavy water in the sea, you see the sealevel rise, and you accuse him of rising the level of the sea. For that, you do an isotopic analysis, and you show that there is more heavy water than usual present in the water that is rising at the shore. You also see that when he poors in a lot of water, the water level rises a bit faster, and when he poors in slower, the water rises a bit slower (on a background of steady rising). From this, you conclude that the guy is making the sealevel rise.

    Again, don't understand me wrong. I'm not saying that there is no CO2 rise because of human fossil fuel consumption, that this doesn't lead to AGW, and so on. This is very well possible, and even plausible. But to say that it has been scientifically established requires one to envision ALL POSSIBLE WAYS IN WHICH THIS COULD NOT BE TRUE, and then exclude them one by one, so that only one remains. I DON'T SEE THIS BEING DONE. I rather see a lot of suggestive stuff, but no critical analysis of how all this could not be indicating what it is "supposed to indicate". And that, in my book, is bad science.
  15. Oct 23, 2008 #14
    But the first thing in greenhouse effect is understanding how it works.

    The global warming hypothesis assumes that the difference between basic Earth black body temperature and actual atmospheric temperature is caused by radiative properties of the greenhouse gases, of which water vapor is the most important, basically nullifying all other mechanisms. In reality it is convection and latent heat transport, which heats the atmosphere from the surface at daylight, while there is no comparable mechanism at night to cool it again. So this mechanism is one way only. This can be demonstrated when comparing day and night lapse rates in the atmosphere, where the difference between day and night is greatest at the Earth surface

    http://mtp.jpl.nasa.gov/missions/texaqs/austin_poster/Image11.gif [Broken]

    http://mtp.jpl.nasa.gov/missions/texaqs/austin_poster/MTP_Austin_Paper.htm [Broken]

    Hence the upper levels hardly cool at night as the only cooling mechanism is .... greenhouse effect, radiation out. And at those levels, with strongly reduced water vapor, radiation escapes to outer space much easier. This effect appears to be neglected in the IPCC endorsed literature and if you don't account for it in the models, you're basically stuck to the GIGO principle.

    It is all in this thread, discussing the Chilingar et al 2008 study.


    In this mechanism the concentration of greenhouse gasses for temperature is strongly reduced. More greenhouse warming simply increases the convection rate, removing the excess heat again from the surface.
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  16. Oct 23, 2008 #15
    If you look at those graphs, you see that the direct measurements of temperatures, and other indirect measurements based on tree rings and all that, agree very well during approximately the time 1850-1980. So if the measurements agree on such long interval, and then the reliable direct measurements show dramatic rise in the latest years near 2000, isn't the whole graph genuinely honest and alarming hockey stick then?
  17. Oct 23, 2008 #16
    But they do not! Look at the big gap between the measured temperatures and the reconstruction, with and without blade of the hockeystick at the very end. Moreovere the red CRU temperatures hitting the roof at >0.9 degrees is very dishonest Just check the real numbers.
  18. Oct 23, 2008 #17
    I see the gap at the very end, near 2000, but I was pointing out that the measurements agree earlier during somewhat long interval 1850-1980. Of course it is puzzling that there seems to be disagreement in the end, but the reconstructions look like reliable for little bit longer intervals. And on the other hand the direct measurements are reliable for short intervals too. So when you put this together, the entire hockey stick looks pretty reliable.
  19. Oct 23, 2008 #18
    The problem with that is if you try for instance albedo and temperature like here, you suddenly find a plausible correlation/causation without any CO2:


    on the other hand if you'd test paleo temperature reconstructions based on CO2 (Van Hoof et al 2008) versus other reconstructions like here the match is rather underwhelming:


    See the problem Jostpuur?

    Attached Files:

  20. Oct 23, 2008 #19


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    The graph (especially the 2001 graph) wanted to display that the dramatic rise in 1990-2000 was exceptional, and wanted to show that never in the last 1000 years, the *level* as well as the *slope* was reached in an obvious and "order of magnitude" way.

    The problem is that if this rise is not reproduced in the proxies, then that means that the proxies (for instance through a low-pass filtering effect) don't follow such quick rises, but smoothen them out. And that means that if there have been such "glitches" in the past, we probably won't see them either. So the very fact that the big rise in 1990-2000 wasn't seen in the proxies means that they don't show such quick rises. It isn't a surprise then that they didn't show them in the past, and hence the fact that they don't show them in the past is no proof anymore that they didn't happen, as we have under our very nose an example of when there was a quick rise in the actual temperature and no obvious signal in the proxies. If there had been a similar glitch around the year 1000, the proxies would have reacted as they are reacting now, and wouldn't have followed the temperature glitch. So we don't see it. That's no proof that there hasn't been any.

    That the proxies correspond on some time scale with the temperature shouldn't surprise us either, as proxies need to be calibrated. So you need to take some patch in time to set equal measured temperatures and proxy data.

    Finally concerning the *level* of the temperatures, contrary to the 2001 plot which indicated a proxy which did show uniform lower temperatures than recently, you clearly see now that different proxies don't agree and that we are completely within the "noise".
  21. Oct 24, 2008 #20
    Certainly the emphasis of the average estimate rather than the range of error does more to create that impression, but the reconstructions are all largely similar.

    An average line on this graph would do the same thing.

    More likely a more limited global coverage.

    Not if you let your eye average the temperatures a little. There are four proxies up by the Mann et al. curve, and only two down by the D’Arrigo et al. curve. You'd guess a 0.2°C of warming occurred then. Whereas now we have four times that.

    I think the data is pretty similar.
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