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Tree-ring proxies and the divergence problem

What the science says...

The divergence problem is a physical phenomenon - tree growth has slowed or declined in the last few decades, mostly in high northern latitudes. The divergence problem is unprecedented, unique to the last few decades, indicating its cause may be anthropogenic. The cause is likely to be a combination of local and global factors such as warming-induced drought and global dimming. Tree-ring proxy reconstructions are reliable before 1960, tracking closely with the instrumental record and other independent proxies.

Climate Myth...

Tree-rings diverge from temperature after 1960
Actual reconstructions "diverge" from the instrumental series in the last part of 20th century. For instance, in the original hockey stick (ending 1980) the last 30-40 years of data points slightly downwards. In order to smooth those time series one needs to "pad" the series beyond the end time, and no matter what method one uses, this leads to a smoothed graph pointing downwards in the end whereas the smoothed instrumental series is pointing upwards — a divergence (Climate Audit).

Tree growth is sensitive to temperature. Consequently, tree-ring width and tree-ring density, both indicators of tree growth, serve as useful proxies for temperature. By measuring tree growth in ancient trees, scientists can reconstruct temperature records going back over 1000 years. Comparisons with direct temperature measurements back to 1880 show a high correlation with tree growth. However, in high latitude sites, the correlation breaks down after 1960. At this point, while temperatures rise, tree-ring width shows a falling trend. This divergence between temperature and tree growth is called, imaginatively, the divergence problem.

The divergence problem has been discussed in the peer reviewed literature since the mid 1990s when it was noticed that Alaskan trees were showing a weakened temperature signal in recent decades (Jacoby 1995). This work was broadened in 1998 using a network of over 300 tree-ring records across high northern latitudes (Briffa 1998). From 1880 to 1960, there is a high correlation between the instrumental record and tree growth. Over this period, tree-rings are an accurate proxy for climate. However, the correlation drops sharply after 1960. At high latitudes, there has been a major, wide-scale change in tree-growth over the past few decades.


Figure 1: Twenty-year smoothed plots of tree-ring width (dashed line) and tree-ring density (thick solid line), averaged across a network of mid-northern latitude boreal forest sites and compared with equivalent-area averages of mean April to September temperature anomalies (thin solid line). (Briffa 1998)

Has this phenomenon happened before? In other words, can we rely on tree-ring growth as a proxy for temperature? Briffa 1998 shows that tree-ring width and density show close agreement with temperature back to 1880. To examine earlier periods, one study split a network of tree sites into northern and southern groups (Cook 2004). While the northern group showed significant divergence after the 1960s, the southern group was consistent with recent warming trends. This has been a general trend with the divergence problem - trees from high northern latitudes show divergence while low latitude trees show little to no divergence. The important result from Cook 2004 was that before the 1960s, the groups tracked each other reasonably well back to the Medieval Warm Period. Thus, the study suggests that the current divergence problem is unique over the past thousand years and is restricted to recent decades.

This suggests the decline in tree growth may have an anthropogenic cause. A thorough review of the many peer reviewed studies investigating possible contributing factors can be found in On the ’divergence problem’ in northern forests: A review of the tree-ring evidence and possible causes (D’Arrigo 2008). Some of the findings:

  • Various studies have noted the drop in Alaskan tree-growth coincides with warming-induced drought. By combining temperature and rainfall records, growth declines were found to be more common in the warmer, drier locations.
  • Studies in Japan and Bavaria suggest increasing sulfur dioxide emissions were responsible.
  • As the divergence is widespread across high northern latitudes, Briffa 1998 suggests there may be a large scale explanation, possibly related to air pollution effects. A later study by Briffa proposed that falling stratospheric ozone concentration is a possible cause of the divergence, since this observed ozone decline has been linked to an increased incidence of ultraviolet (UV-B) radiation at the ground (Briffa 2004).
  • Connected to this is global dimming (a drop in solar radiation reaching the ground). The average amount of sunlight reaching the ground has declined by around 4 to 6% from 1961 to 1990.
  • One study suggests that microsite factors are an influence on whether individual trees are vulnerable to drought stress. Eg - the slope where the tree is located, the depth to permafrost and other localised factors (Wilmking 2008). This paper amusingly refers to the divergence problem as the "divergence effect" so as "to not convey any judgement by the wording" (you wouldn't want to offend those overly sensitive Alaskan trees).

There is evidence for both local and regional causes (e.g. drought stress) as well as global scale causes (e.g. global dimming). It's unlikely there's a single smoking gun to explain the divergence problem. More likely, it's a complex combination of various contributing factors, often unique to different regions and even individual trees.

One erroneous characterization is that scientists have been hiding the divergence problem. In fact, tree-ring divergence has been openly discussed in the peer-reviewed literarure since 1995. A perusal of the many peer reviewed papers (conveniently summarised in D’Arrigo 2008) reveal the following:

  • The divergence problem is a physical phenomenon - tree growth has slowed or declined in the last few decades, mostly in high northern latitudes.
  • The divergence problem is unprecedented, unique to the last few decades, indicating its cause may be anthropogenic.
  • The cause is likely to be a combination of local and global factors such as warming-induced drought and global dimming.
  • Tree-ring proxy reconstructions are reliable before 1960, tracking closely with the instrumental record and other independent proxies.

Last updated on 26 June 2010 by John Cook.

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Comments

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Comments 1 to 50 out of 77:

  1. I'm guessing that acid rain had a *lot* to do with the sudden decline in tree-ring width post-1960. It certainly doesn't prove any kind of global cooling post 1950. It does, however, highlight the need to use more than a single proxy for determining climate in the absence of direct temperature measurements
  2. Mr Cook:

    Regarding: "The divergence problem is unprecedented, unique to the last few decades, indicating its cause is anthropogenic."

    One thing I don't understand is this assumption that if we don't know what causes something in the climate system to happen, it must be us.

    I think the best way to explain this is the study on the links between telephone poles and cancer, where scientists found that in areas with high per-capita telephone poles, there were higher rates of cancer. Thus, telephone poles must be causing cancer!

    Now, this sounds silly, because there are other factors which may cause an increase in both factors (something to do with industrialization/urbanization, etc.), but it is quite comparable to current climate science.

    We assume that because we can't find any other natural factor that could cause the current warming (or tree ring divergence), it is automatically us. But we can't assume that. We have to assume it is natural until it is proven to be caused by us.
    Response: It's not definitely proven that the divergence problem is caused by us but the fact that over the last 1000+ years, it's only occured in the last 40 years is highly suggestive, particularly when likely causes like global dimming are anthropogenic. However, the key point is not that divergence is anthropogenic but that the evidence indicates divergence has not occured before recent decades so tree ring proxies are reliable before 1960.
  3. I am confused. THere seems to be a logic problem here. If the proxies are incorrect post 1960 or there is a divergence at one time and you don't really KNOW the cause for that divergence then how can anybody conclude that there weren't other divergences you didn't understand in the past? Just because we don't see divergence between north and south there could be something which affected tree ring data over any period of time in the past either depressing or increasing temperatures that actually ocurred. You really can't have any confidence in this proxy until you understand the cause. What if the cause is caused by droughts? What if there was a large drought over the areas north and south covered by these trees? What if there was a huge flood or volcanoes or some other co-incidence like a increase in acidification due to some bacterial or animal or plant extinction or proliferation? The point is not the specifc thing but the logic being used here which is flawed by you guys. The fact is that the "science" is still very nascent and major things like what is affecting tree ring densities and widths is not really understoof even TODAY let alone 1,000 years ago.

    It is hard to have confidence in you "scientist" proclamations when a simple computer scientist from MIT can see the logical flaws in your arguments.

    Maybe because I was trained in math and physics my expectations as to logic and proof are much more stringent. For instance, the idea you can use these proxies and eliminate trees so easily, use so few and not have a well understood rigorous process for these things leaves me totally skeptical. This doesn't seem to qualift as science but more like "social science" which is based on surveys and self-reported data. A lot of the climate science stuff strikes me as having these logical errors. For instance, the models are built and calibrated, initialized to match historical data, then "scientists" say they match history good and predict the future. That's just falacious reasoning. I can construct many milllions of models which match history but which fail immediately to predict the future. In fact that looks to be exactly the case. Modelers admit (from what I've read) that they cannot explain current 10 year trends, whether down or flat or even up a little they don't correspond to any models output. WHereas these models are more accurate in past temperature predictions. Of course they are, they are not used UNLESS they fit past temperature records. But that does not give them ANY credibility in saying they "predict" the future. That would have to wait for confirmation that they actually DO predict temperatures and so far they aren't. Doesn't that pretty much say the models are flawed?

    Even if you say the models represent almost all relevant factors the errors introduced by their mathematical nature means that the ability to say with any assurance the predictions have a numerical preciseness is almost impossible. The temperatures could be -10 or +30 and still be in the models error bars. So there is no predictive power possible even if the models were correct. We would all be better reverting to a simplification and look at the earth as one giant thermodynamic entity than trying to break it into pieces and understand interelationships in the pieces at a micro level. THis just seems numerically implausible to return any level of accuracy useful over even a few iterations.
  4. I think some of the statements in this article are worded overly strongly. Tree rings can also be sensitive to moisture or other constraints on growth. This article makes it sound like tree rings are only ever sensitive to temperature, but they aren't. If I understand it, the trick is to find those trees that are primarily reporting temperature.

    Also, you don't know what's unprecedented in the time before the thermometer record picks up around 1850-1880. Maybe divergence has happened before; you'd only know by checking against other proxies. But other proxies come with their own uncertainties.

    So I'd suggest softening some of the language a bit.
  5. This is the most comprehensive explanation I've seen anywhere on this topic, and it's not too strongly worded.

    I have been looking into tree sensitivity to pollution ever since I realized that the trees are not only growing more slowly, they are actually dying at a rapidly accelerating rate. This is being reported from all over the world, not just around my farm in New Jersey. Every species of every age is in decline, as is the understory of the woods.

    Ozone interferes with the ability of vegetation to photosynthesize by damaging the stomata of foliage and needles. Last year, even annual plants showed the unmistakeable symptoms of exposure to toxic greenhouse gases, which is a stippling of the leaves and loss of chlorophyll, in extreme cases turning leaves into brown webs. Crop losses were disguised by the USDA and blamed on weather, but if we do not recognize this problem, famine will be the result.

    Photographs and links to research are posted at www.witsendnj.blogspot.com
  6. I don't think this is good enough. The "divergence" is evidence, surely, of some severe environmental stress, one that could at any moment start to impact on our food supplies.

    If this was any other branch of regular science, an expermiment would be rigged up, 6 or 16 greenhouses in a row, one with increased CO2, one with reduced CO2, one with artificial acid rain, one with extra ultra-violet and so on and so forth. We'd have at least parts of the answer in 12 months.

    Why is nobody treating this problem as a matter of urgency, surely we need to know what's going on?
  7. MalcolmMcDonald,
    "surely we need to know what's going on?"
    i agree but it's not up to climate scientists. I'd be tempted to ask for more research funds, but you know, people would think it's just the standard complaint from scientists.
  8. Malcolm, the research you wish for is very much in play.

    Simply bounce over to Google Scholar, try searching on "plant metabolism anthropogenic C02" or "plant metabolism acid rain" and you'll see what I mean. The first term produces some 7,000 results, the second (being the subject of earlier interest) over 45,000.

    Plugging in better terminology for search terms will yield more and better results.
  9. How's this for a simple explanation.

    Certain high latitude trees are adapted to ice age conditions-ie most of the last million years or so. They will respond to slightly warmer condtions and follow a warmer temperature record to a point, but with too much warmth, accompanied by a decrease in moisture and rainfall, these trees reach a 'threshold', and start to diverge from the temperature record, as in the last few decades. Once this threshold is passed growth rates and tree rings start to diverge from temperatures.

    Because the last several hundred years, prior to the late 20th century, has been below this threshold, tree rings closely follow measured temperatures (eg back to ~1800s), and also various other proxy temperatures back to the ~end of the Medieval Warm Period. At about 1960 the 'threshold' was passed and these tree rings diverged from the temperature record, unique in the last several hundred years at least.

    If this simple explanation is the case, there is no way you can use tree rings to ascertain temperatures on longer time scales (eg past the end of the Medieval Warm Period) because they will diverge from any warm enough period once the threshold, mentioned above, is passed; obviously any warm temperatures beyond such a threshold wont show up in the tree ring data, you will get a flat line regardless of warmer temperatures, as in Manns 1998 hockeystick, which lacks a Medieval Warm Period.

    Furthermore, it is not enough to show that tree rings are consistent with other proxies, because it depends on which proxies you pick. Trees ring proxies are consistent with some, and not consistent with others.

    It is also not much use to 'average' out the various proxies to get an 'average' trend, because any inherant bias in the proxies wil simply become enhanced.

    For example, if 30% proxies dont pick up warmer temperatures well, coupled with a decrease in both measurable response the further back you go and a reduction in quality of data the further back you go, then 'averaging' out the proxies will produce a flattened/cool bias in the data, as in Mann's more recent papers. It's similar to the averaging out the 'gaps' in the fossil record, you simply get more 'gaps', and the further back in time you go, the more 'gaps' you get. This is a reflection of the imperfection in the fossil record, and not a reflection of the constant evolution of life. It is a preservation/measurability problem, and averaging out the imperfection of proxies over time also gives unreliable/distorted results.
  10. Trees adapting to changing conditions more likely would happen over generations of trees rather than a single generation being able to adapt. Certain individual trees will flourish as they handle conditions whilst others do poorly, so natural selection would create a bias as the improved growth of succeeding generations becomes perhaps a measurement of the ability of the trees to adapt better to existing conditions rather than the conditions themselves necessarily changing.
  11. I think that this is the real reason for the decline in tree-ring data. An increasing amount of CO2

    http://scienceblogs.com/pharyngula/2009/12/why_climatologists_used_the_tr.php
  12. Here are links to every article I've been able to find so far about ozone, CO2 and vegetation:

    http://witsendnj.blogspot.com/p/basic-premise.html
  13. With regard to tree ring growth diverging from warming. I understand from other sections here that solar activity and cosmic radiation have also declined while temperatures have increased over the past few decades.

    Is there a possible causal effect due to this correlation?
  14. @ Philip Shehan (13)

    Welcome to Skeptical Science! There is an immense amount of reference material discussed here and it can be a bit difficult at first to find an answer to your questions. That's why we recommend that Newcomers, Start Here and then learn The Big Picture.

    I also recommend watching this video on why CO2 is the biggest climate control knob in Earth's history.

    Further general questions can usually be be answered by first using the Search function in the upper left of every Skeptical Science page to see if there is already a post on it (odds are, there is). Or you can search by Taxonomy.

    Forcings, except for CO2, have been flat for nearly 40 years. Temperatures continue to climb, and that rate of climb is still increasing (as are CO2 levels).

    Hope that helps,

    The Yooper
  15. Thank you Daniel for the welcome. My original post may have been ambiguous. I was specifically wondering if ther was any causal link between reduced solar (or cosmic) radiation and reduced tree ring growth.
  16. @ Philip Shehan @ 15

    Tree rings are not my area of expertise, but a re-read of the post above makes it clear there is still significant uncertainty (see the linked summary above for details).

    I suspect the cause is indeed multi-factorial (with the other factors mentioned in play, tree growth response to the rising temps [we are now at temps equal to that of the Holocene Maximum of 8,000 years ago] of the latter half of the 20th Century may be discontinuous to established response).

    Certainly the experts in this field are continuing to look at all possible factors (a scientific "race to glory" for bragging rights).

    My two cents.

    The Yooper
  17. #15: "any causal link between reduced solar (or cosmic) radiation and reduced tree ring growth."

    This was suggested by Suess 1980, who was the author of one of the greatest one-liners in all of science:

    "The line was not drawn by computer - I drew the line by `cosmic schwung'.

    More recently, Kulmala et al 2009 and Dengel et al 2009 provided some fuel for an uptick of chatter in the deniersphere. The usual crowd made the usual misrepresentations of an otherwise valid study (you can find this by googling 'cosmic rays tree ring growth'; I don't link to sources of disinformation).

    The basis of the argument is that increased cosmic ray flux stimulates cloud formation (that's not proven) and clouds control tree growth rates (somewhat), so that cosmic ray flux helps explain tree ring anomalies (indirect, uncertain, unsettled). There are some vague resemblances of tree ring cycles to the solar cycle (see Dengel), but that's hardly a smoking gun for cosmic rays as a cause. But with evidence like the figure shown below (Kulmala), it will take more than cosmic schwung to draw a line.



    The larger subject of cosmic ray flux is discussed in the thread It's cosmic rays.
    Response: [Daniel Bailey] Fixed broken linked image URL.
  18. John, either your inability or choice not to respond to JMath (1/31/10) does not instill confidence. He makes a very valid point of criticism; one I have voiced myself on various forums. The utility of Dr. Mann’s temperature reconstruction is entirely dependent upon an assumption that is neither provable nor disprovable; thus is unscientific. The assumption is, as JMath pointed out, that the tree ring divergence problem only pertains to recent years. Since there are no recorded temperatures throughout most of the time span of the hockey stick graph, there is no way to verify the correctness of this assumption. This in turn casts grave doubts upon the accuracy of the entire reconstruction.
  19. Don Schneider, start by reading Hockey Stick or Hockey League, then look at this RealClimate Wiki, then look at this RealClimate Thread.

    After that, you should find that Mann's reconstruction is not at all the only reconstruction that gives those results.
    If you don't like Mann's, what's your problem with all the rest ?
  20. JMurphy, thanks for your response and the links. It is seldom that I have such a quick turnaround in thought, so I find this astonishing. While driving somewhere just a few minutes ago, and mulling over the point I just made on this forum, I had an epiphany of sorts. How ironic I found it to be that the very first comment posted at the first link you provided—a comment made by one ProfMandia—was exactly the thought that hit me!

    How strange it would seem that if the tree ring proxies were somehow wrong in the prerecorded temperature times of the Mann chart that they should be both wrong and so closely correlated with other reconstructions using various other proxies as opposed to tree rings. As ProfMandia points out, what are the odds of that? What are the odds that they should all be not just inaccurate, but so closely so in the same way?

    Therefore, unless the skeptics can somehow prove collusion on the part of all these researchers who have presented temperature reconstructions based upon various proxies, then at least the part of the theory that we are living in an anomalously warm period has been proven to my satisfaction. Being convinced that we are responsible for this, and that the result will be necessarily deleterious to a significant extent, might take me some more time Perhaps I shall mull over these latter points while shoveling out of yet our next snowstorm! (G)

    By the way, I realize it is hard to sell this theory while so many people in the Northern Hemisphere have been enduring two brutal winters in a row; thus the falling poll numbers as to how many take the theory seriously right now. However, adherents do have a point about warmer air causing more evaporation from lakes and such and thus more snow.

    It hasn’t been, by and large, the temperatures that have been so brutal, just the snow and sometimes ice. When I was a teenager and young man in the 70s here in Philadelphia, I can recall it was not at all uncommon for the temperature in the winter to frequently dip to single digits and even hit zero (F) occasionally. We haven’t experienced too much of that for many years and the ponderous amount of snow we have been getting has largely been (backbreaking!) wet snow as the temperatures unfortunately have a penchant to remain just below freezing. So you might be right on this point as well, as odd as it might seem to others and me. If AGW is true and we must endure it and its potential consequences, I just wish it could at least get us over 32 here! I wasn’t expecting the 70s in January.
  21. Don Schneider, there are plenty more pages on here that will give further information as to the cause of our current warming. Try these two for a start :

    Newcomers Start Here

    The Big Picture

    Also, while I understand that parts of America are experiencing lots of snow and cold temperatures, that isn't the case for the rest of the Northern Hemisphere - as far as I'm aware. Temperatures in Europe, at least, are normal for the time of year, although they are going up and down all the time. And, the last I heard, Canada and the Arctic were pretty mild, comparatively ?

    All that snow digging will keep you fit !
  22. About the only thing anthropogenic about the divergence "problem" are the thermometers.
  23. Hello,

    Concerning the divergence problem, I suggest you should be more cautious in the formulation you choose. Two examples from d’Arrigo 2008, whose review is your main source :

    D’Arrigo 2008 : « Although limited evidence suggests that the divergence may be anthropogenic in nature and restricted to the recent decades of the 20th century, more research is needed to confirm these observations »

    Your choice : « The divergence problem is unprecedented, unique to the last few decades, indicating its cause may be anthropogenic. The cause is likely to be a combination of local and global factors such as warming-induced drought and global dimming. »

    You are quite more affirmative than your source.

    D’Arrigo 2008 : « However, the relative scarcity of ring width and density records from the lower mid latitudes, tropics and Southern Hemisphere precludes making definitive conclusions about the spatial extent of this phenomenon, and more research is needed to more fully evaluate the extent of the divergence problem worldwide »

    So clearly, it’s impossible to say for the moment that DP is limited to circumpolar forest (your « mostly high tlatitude »). For example a well-known scientist of the field observes that mid-latitude tree-rings are also of concern, and that the phenomenon is quite widespread except for low-latitude :

    « Evidence for reduced sensitivity of tree growth to temperature has been reported from multiple forest sites along the mid to high northern latitudes and from some locations at higher elevation. This alleged large-scale phenomenon reflects the inability of temperature sensitive tree-ring width and density chronologies to track increasing temperature trends in instrumental measurements since around the mid-20th century. »
    http://www.st-andrews.ac.uk/~rjsw/papers/Buentgenetal2009.pdf

    Hereafter, another example at mid latitude with a very recent analysis showing a divergence in Alpin Larch (since 1990) and rising some problems for temperature-calibration in order to reconstruct past climate variations.
    http://www.sciencedirect.com/science/article/pii/S0012821X11004109

    IPCC AR4 also mentions : "Others, however, argue for a breakdown in the assumed linear tree growth response to continued warming, invoking a possible threshold exceedance beyond which moisture stress now limits further growth (D’Arrigo et al., 2004). If true, this would imply a similar limit on the potential to reconstruct possible warm periods in earlier times at such sites. At this time there is no consensus on these issues (for further references see NRC, 2006) and the possibility of investigating them further is restricted by the lack of recent tree ring data at most of the sites from which tree ring data discussed in this chapter were acquired."
    http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch6s6-6.html#6-6-1

    It means that if some trees are affected by such a non-linear treshold related to temperature/humidity pressure (no specifically anthropogenic-induced factors), the DP is not necessarily limited to modern era and that tree-growth may have been affected in some locally warmer period in the past.

    So I suggest you're a bit overconfident and selective in some preliminary conclusions of this very active field of research.

    Best
  24. I noticed that in early December, McIntyre was again/still attempting to sow doubt about reconstructions. In this case, it was the Briffa et al 2001 line in Figure 1 of Mann et al (2003). In short, that line of the plot appears to end around 1940.

    Someone asked about this over at RealClimate and I think it might be useful to provide a link to the question and Gavin's response

    Dr. Schmidt's key points are -
    It's interesting to add that in Briffa et al, 1998, they state:

    "Over the hemisphere, the divergence between tree growth and mean summer temperatures began perhaps as early as the 1930s;".

    and
    The divergence issue as a recognised problem predates this paper by years (Briffa et al, 1998), and was discussed in the almost contemporaneous Jones and Mann (2004) paper. That paper was a little clearer about what was done and why (i.e. fig 5):

    The various other (smoothed) NH reconstructions shown in the enlargement to Figure 5a have been scaled by linear regression against the smoothed instrumental NH series over the common interval 1856–1980, with the exception of the ‘‘Briffa et al.’’ series, which has been scaled over the shorter 1856–1940 interval owing to a decline in temperature response in the underlying data discussed elsewhere [Briffa et al., 1998a].
  25. Dawsonjg,
    Who says including those data sets was in error? Mann uses specific criteria to exclude problematic data sets. Deniers then add data sets they like and claim Mann is in error for including ones that they do not like. Mann responds by showing that deleting the supposed problematic sets does not affect the result. You are confusing unsupported blog criticism with actual peer reviewed criticism. Keep in mind that the Mann hockey stick has been reproduced by numerous other peer reviewed studies. Can you provide a reference to a peer reviewed study that does not show a hockey stick? If everyone gets a hockey stick, how can you claim that Mann is in error?
  26. Thanks michael

    Mann responds by deleting problematic sets from his 2008 paper one at a time, not by deleting them all at once. I'd like to know where he deletes both bristlecone and Tiljander sets at the same time.

    You have a very malleable definition of a hockey stick. No one anymore defends a millenium graph with a straight handle and 20th century blade such as appeared in the IPCC's 2001 report to (-Snip-). Why can't you just admit that Mann and the IPCC got it wrong?
    Response:

    [DB] perhaps you missed this warning about needed compliance with the Comments Policy.  This site is about the science of climate change, not about scoring rhetorical points.

    Inflammatory rhetoric snipped.

  27. dawsonjg,

    You obviously have not actually bothered to *read* the Mann 2008 paper or the associated SI (and the online update at Mann's personal website). Mann did a reconstruction, reported in the main paper, which excluded all of the dendro proxies. He got essentially the same answer although it was not statistically significant as far back in time as the full recon. In the SI, he tested the results of leaving out the problematic proxies (Tiljander and a couple of others) to test the sensitivity of the main recon to these proxies. No big differences.

    As a result of complaints in the blogosphere Mann reported in the updated SI the result of tests which left out the Tiljander data and the dendro data. The result of this was reduced significance in the earliest part of the no dendro/no Tiljander part of the reconstruction, mostly due to the fact that Tiljander represented a significant part of the earliest data.

    So did Mann 2008 get it wrong? I would say no. He showed that dendro evidence is a valid proxy, in spite of the attacks mounted on it by the denialists. There are almost certainly not enough non dendro proxies with sufficient resolution to do a long recon with nothing but non dendro evidence. The fact that Mann 2008 agrees broadly with other reconstructions despite differences in proxy selection and analytical methodology would seem to indicate that he is in the ballpark. We'll never know with any certainty what the exact history of global temperature is over the last couple of millennia but I think that it is possible to get a pretty good idea of what happened by using the multiproxy methods which Mann pioneered.
    Response:

    [DB] In addition to your sage advice, and also the reading of the OP and the other comments above, this post at RC by Tamino is relevant:

    http://www.realclimate.org/index.php/archives/2010/07/the-montford-delusion/

  28. dawsonjg... "Why can't you just admit that Mann and the IPCC got it wrong? "

    You're describing science at it's best. Mann's work in 1998-99 was new and different. Why would you expect it to be correct by today's standards? Do we expect Darwin's work to be correct by today's standards? No. But what I would say about Mann's work (as with Darwin) is that it has stood up to intensive, hostile scrutiny and has lead to a better understanding of the subject matter today.

    What more could you want from science?
  29. dawsonjg... Peter Hadfield (Potholer54) has a youtube video I've always enjoyed titled "The Scientific Method Made Easy." I'm not trying to be patronizing here but there is an element that he brings up in the video that I always find interesting. He says (paraphrasing), "Whether other researchers think John (the "evil" scientist in his example) cheated or just got things wrong doesn't matter because his work won't be consistent with other research and will eventually be discarded."

    Ultimately what all scientists want is to get things right because that will mean their work will stand the test of time. Even if Mann was (as deniers suggest) trying to push fraudulent work it doesn't matter because if he was it wouldn't fit the broader body of research. What has happened though is Mann's work has fit quite well. Other researchers have been able to reproduce his results with other methods. In fact, there are now almost a dozen multi-proxies that are pretty well consistent with Mann's earlier work. That work has improved on what he did and even Mann's own work has improved on his earlier work.

    All a case of science doing what it's supposed to do.
  30. Thanks Rob - I know what science is suposed to do. What Mann does is not it at its best.

    Thanks DB, I've read Tamino's review. I guess comments would be deemed 'beating a dead horse'

    Thanks jmsuly, I've read some of what you suggested. Might I suggest further reading at http://climateaudit.org/2011/07/06/dirty-laundry-ii-contaminated-sediments/ ?

    When you eliminate all the 'problematic' Tiljander and bristlecone data together rather than one at a time, you eliminate Mann 2008's claim to fame. But why their persistent inclusion when it has been acknowledged that they are 'problematic'?
  31. Dawsonjg,
    Where is your evidence that "When you eliminate all the 'problematic' Tiljander and bristlecone data together rather than one at a time, you eliminate Mann 2008's claim to fame"? here you claim to ask if Mann performed these analysis. here you claim that you have not seen the analysis done. You now claim that the analysis shows Mann was wrong. You are not arguing in good faith.You have been given the information that Mann has done that analysis and it makes no difference in the result, except lowering the statistics. You are now claiming, without any evidence, that Mann is wrong. Please produce some evidence to support your frantic handwaving.
  32. Dawsonjg is referring to this chart reproduced from a chart which I believe to be from the supplementary material of Mann 2009:



    The original Mann 2008 EIV reconstruction is in red, the no tree ring reconstruction is in blue, the reconstruction with seven series with higher uncertainties (including tiljander) removed is in brown, and the reconstruction with neither tree rings nor the seven series with higher uncertainties is in green.

    Some things are immediately obvious:

    1) The green reconstruction is still a Hockey Stick;

    2) The highest temperatures in the MWP in the green reconstruction is still less than current temperatures;

    3) The highest temperature in the green reconstruction still lies withing the error bars of the original reconstruction (shaded yellow); and

    4) The green reconstruction is still closer to Mann 2008 than to Lamb 1966.


    These four facts show clearly, according to the deniers, that Mann committed fraud; that Mann's reconstructions of MWP temperatures are entirely in error regardless of how many independent confirmations show the same thing; and that Lamb's 1966 guesstimate was much more accurate than Mann's 2008 reconstruction.

    More reasonable people might consider these facts to show that Mann's reconstructions are essentially confirmed by this sparse network. They might also conclude that the increased variability is more likely to be due to the restricted number of the remaining data sets rather than because Mann 2008 got anything wrong.
  33. dawsonjg... "Why can't you just admit that Mann and the IPCC got it wrong?"
    and "Thanks Rob - I know what science is suposed to do"


    Do you really know - or are you just using the words for rhetorical effect?

    Why do you fall into the common trap laid by incorrigible denialists of pretending that new science can ever be about presenting 100% perfect papers? That is an impossible standard which has never been achieved or has never been presented (by scientists) as achievable. It is absolutely not how science works. Only the ignorant, or those wishing to twist ordinary people's minds with propaganda, would ever claim that.

    What you are doing is this. You are misrepresenting the situation by trying to suggest that Mann, by presenting 13 years ago a "first of a kind" paper that was not 100.00% "perfect", was "wrong". Clearly, you do NOT know what science is supposed to do.

    You, along with all the others like you, are clearly trying a well worn propaganda technique by creating a blizzard of misdirection that because the paper was not 100.00% perfect it must, in the weird, difficult, nit-picky, obstructive way that too many think, be wholly worthless and evidence of incompetence at best and fraud at worst. Deny you are doing that that, dawsonjg. I dare you.

    The all too familiar use of such innuendo was the reason for my "mole-on-the-face-of-the-supermodel analogy. She remains incredibly beautiful and any minute nit-picky perceived flaws (most of which are misperceived camera artefacts anyway) doesn't in any way take away from that. Similarly, small perceived flaws, even if a few of them are real, in otherwise sound science are only "evidence" that climate science is "wrong" in tinfoil hat land, not in the real world.
  34. This page contains the supplementary material for Mann 2009 (direct link to pdf). The figure provided in post 32 above has been altered from the original (Figure S8, p31). Specifically, the green line before 1500AD is dashed in the original. This is because it does not pass the validation tests. These tests are described in the section titles "Validation Exercises" on p4. To pass the test the reconstruction must rule out a 'red noise' null hypothesis at the 5% significance level. Care should therefore be taken when interpreting the green line.
    To quote from the "Sensitivity Tests" section, p9:

    "This additional test reveals that with the resulting extremely sparse proxy network in earlier centuries, a skillful reconstruction is no longer possible prior to AD 1500. Nonetheless, even in this case, the resulting (unskillful) early reconstruction remains almost entirely within the estimated error bounds of the original reconstruction."

    I think it would have been nice to show uncertainty bands for the green line alone. However, presumably that would require significant CPU time and not add much information.
  35. Michel

    I have read thoroughly convincing analyses that the hockey stick is 'problematic' (to put it in terms that I hope won't get snipped). But knowledgable people on sites such as this ridicule such analysis as il-motivated nonsense (Mann has been doing this very noisily for nearly a decade, before tacitly backing down very quietly on issue after issue). So who am I to believe? All I can do is read the pro and con arguments and pose a few questions to see if I get credible answers. But accusations that my questions amount to 'frantic handwaving' or 'crafted disinformation' for an industry funded defamation campaign are not very informative. I can't give you evidence re the 2001 graph because that's deemed dead horse territory, I've given some evidence re the 2008 graph above.
  36. @dawsonjg

    As I understand it; if those "thoroughly convincing analyses that the hockey stick is 'problematic'" have any merit, then they'll be submitted to a credible journal and peer reviewed. If the reviewers feel the 'analyses' have any merit, then they'll be approved for publication and will appear in the next available issue of the journal. Then the scientific community will read and consider the 'analyses', and those with an interest will undertake further work and submit further papers, following the same procedure. That's the scientific process. Whether we like it or not, what is said in blogs is largely irrelevant to the consensus view of the science at any particular moment.

    What Mann wrote a decade or more ago can really never be 'wrong', as it represented the best understanding of the science at the time it was written. If subsequently someone can show that a paper is flawed in some way, then, more often than not, the original author is likely to write another paper correcting any flaws and incorporating the new ideas. That's how knowledge of climate science develops. It's what Steven Schneider did in the 70's when he realised that the paper he'd written predicting forthcoming cooling was based on an over-simple model, and the fact was we were actually warming.

    As a layman, I find this quite easy to understand. It's a logical procedure that works well. Don't you think so?
  37. dawsonjg @37, if you cut of the "snake" at 1000 AD (the duration of the MBH 99 hockey stick) then it isn't a snake. Still less so if you cut it of of at 1600 AD to compare it with MBH 98.

    This ignores the fact that by drastically restricting the data available for the reconstruction, it was inevitable that the green line above should show more variability.

    The simple fact is that through all your inuendo you have carefully kept the data of stage, and the reason is obvious. When the data is placed front and center your case transparently evaporates, and all you are left doing is playing word games.

    It should of course be noted that you have not said anything to impugn any of the many other reconstructions which confirm Mann et al 2008's result. Nor, quite frankly have you presented a single substantive reason to think there is anything wrong with any of the proxies used in Mann et al 2008 to begin with. Your entire case todate has consisted of asking some rhetorical questions on another thread, and asserting on this one without evidence that the proxies where "problematic". That apparently is enough to count as evidence in your mind.
  38. You describe the way the review process should work John Russell, the way it worked for Einstein and the way it still works in some fields such as medicine. But consider who controls the billions of dollars poured into climate research and who influences the peer review process and who has been claiming that the debate is over and anyone who disagrees is an industry funded denier - imagine where we would be if Einstein had politicised the process in that way. And investigate what MM had to go through to get their peer reviewed papers published. And consider whether the graphs presented above would ever have replaced the 2001 hockey stick if McIntyre and a few others had not navigated the obstacles and weathered the vilification to prove it was 'problematic'.
    Response: [muoncounter] Accusation of fraud, conspiracy, etc violate the Comments Policy. Einstein did not go through 'peer review.'
  39. dawsonjg, you should learn about how science works--including funding--before making such extreme claims. It is obvious that you never have been a published scientific researcher who has applied for funding, been accepted and rejected for funding, and has reviewed funding proposals. Nor do you understand the difference between funding of research and peer reviewing of research results that were produced regardless of the funding of the work that produced those results. You can start learning with historian Spencer Weart's account of the history of Keeling's climate research funding and of funding for science in general.
  40. Indeed, Tom D, and dawsonjg could further use some reading on Einstein's life and work--the Isaacson bio is readable enough. Good grief. Dawsonjg, you're working backwards. You're starting with models and trying to disprove physics. Read Weart. Understand the development of the science. There is no multi-generational hoax involving tens of thousands of scientists. I know you will say that you're not making this claim, but your rhetoric strongly implies the claim, and all I know about you and your ability to think comes from the words you string together.
  41. dawsonjg

    You are stuck on this idea that editors and reviewers can somehow be corrupted by those "billions of dollars," whereever they are, to allow a consensus to develop despite all evidence to the contrary. I am a subject editor at a pretty well read journal and I cannot conceive of how such a thing could happen except in the least populated and most arcane corners of science.

    You have to understand that people editing and reviewing papers are actually, at some level, professional competitors of the people they edit/review. In fact, the editors deliberately pick the reviewers to reflect a range of opinion/expertise. Editing and reviewing activities also occur in the public eye of at least some of your quite critical peers. The appearance of favoritism or collusion (or the opposite) is very much looked down upon, and often stigmatized. If anything, lack of critical insight in the reviewing process will hurt, not help your chances at getting funding because of the infuence on your reputation as a critical thinker. Knowing someone is no guarantee of a friendly review, either. I have often had to reject papers by people who I consider friends of mine.

    Given all this, it is really hard for someone truly familiar with the process to comprehend your thinking. Perusing the level of critical discourse even in the "leaked" CRU emails confirms how seriously even those with close working ties interrogate each other about methods etc. If I weren't convinced that you simply didn't have the experience to temper your judgement, I might even find it insulting that you would even intimate that somehow it could as thoroughly corrupted as you suggest.

    Second, If you think climate science has problems due to the amount of money sloshing around, I can think of no worse counter example than medical science, in which the amount of money sloshing around dwarfs that in climate science. Lots of potential conflict of interest there! Still, as you say, they manage a pretty tight ship...although there are several high profile instances of fraud that pop up now and again.
  42. dawsonjg continues his preference for innuendo rather than facts, on this occasion suggesting that there was no proper scientific critique of MBH 98 and 99 prior to McIntyre and McKittrick's interventions. As it happens, following publication and prior to M&M's intervention MBH 98 and 99 where criticized by Jones 1998 (Nature), Huang, Pollock et al 2000 (Nature), Broecker 2001 (Science), and Esper et al 2002 (Science). Mann responded to these criticisms, agreeing with some points and rebutting others. Mann also published a detailed analysis of the virtues of different climate reconstruction methods, developing the RegEM which was later further improved on to become the EIV algorithm. Hans von Storch also published a methodological paper in 2004 performing a detailed analysis of different algorithms for reconstructions.

    So, before M&M had even appeared on the scene, the scientific community was conducting an extensive debate on methods of reconstruction and Michael Mann had already replaced the MBH algorithm with a superior one two years before M&M decided to criticize the by by then six year out of date method of MBH 99.

    Clearly dawsonjg's innuendo of scholarly inaction is a complete fiction and without any basis in fact. What is more, it entirely neglects that no substantive criticism in M&M 2003 or 2005 has stood the test of time, and their most fundamental criticism has been shown repeatedly to be itself flawed far beyond any problems found in Mann's earlier algorithm.

    Given dawsonjg's continued use of innuendo, complete absence of evidence presented in his case, and defamatory comments, perhaps it is time that he be required to fully comply with the comments policy.

    Muoncounter, it is a minor point but Einstein did go through peer review.
  43. Tom C,
    Off-topic here, but Kennefick 2005 showed that peer review (as we know it) did not necessarily apply at Annalen der Physik. As usual, the real story is not as clear as wikipedia would have us believe.

    But an Einstein throwdown in a denier argument is about as valuable as 'Galileo was outvoted.'
  44. dawsonjg @ 35... "I have read thoroughly convincing analyses that the hockey stick is 'problematic'."

    We all know what you've been reading and many here have read that same work. But you might stop to consider this... Why did someone go to so much trouble to try to undermine one piece of science? Normally, if a piece of research is poorly crafted and the results are suspect the course of action is to reproduce similar research using different methods to show that the results are erroneous. The new research would conflict and probably supersede the previous research. There you go. Problem fixed. MBH99 shown wrong. Move on with the research.

    So, why haven't McIntyre or Montford done this? Why do they only operate to try to find flaws without producing any actual research of their own? Why don't we have any multi-proxy reconstructions from them showing a different conclusion? They obviously consider themselves qualified. They obviously have the time and backing to perform such research. But they don't. Why?

    I can tell you for sure that the Idso's (who are well connected with the same folks) have several hundred studies on the MWP that they've collected and posted online. I've poured through them in detail. But they also don't go so far as to try to produce a multi-proxy reconstruction of that data. Why?

    You should really go and watch that Peter Hadfield video on the scientific process. Here is the link.
  45. Dawsonjg says, talking about science "What Mann does is not it at its best."

    One has to wonder then what M&M do should be called; whatever that may be, Wegman's work should wear a similar name. This is recommended reading for all those who think that Dawsonjg or M&M have any kind of a valid point.

    It reviews the errors in M&M methodology (first identified by David Ritson) and dives deep into the computer code used by M&M, where the explanation lies for their findings. It also clearly demonstrates how Wegman did not truly replicate anything.

    Dawsonjg has rambled about funding and politics.
    This contains a nice timeline summary of the emergence of M&M, readers can decide how much the whole thing was influenced by politics and money sources.

    As usual, with often touted "billions in climate research," fake skeptics make heavy use of the method that consist of accusing others of what they themselves do. It ensures that subsequent denunciation of what is really happening loses all impact, with masses thoroughly confused as to what to believe. They then naturally gravitate toward what they are inclined to believe anyway. All factual information becomes moot.

    Dawsonjg illustrates very well that feeling in the following quote "So who am I to believe?"

    Surely enough, he mixes that with "All I can do is read the pro and con arguments." Reading the pro and con arguments found in the press and blogs is the last thing one should do when considering a scientific issue.

    SkS is a better blog only because it has its roots in the science that has been published. Science publications on the matter considered is what should be read, not arguments from blogs or newspapers. Dawsonjg should know that, as he claims also "I know what science is suposed to do."

    If one knows what sience is supposed to do, then the "arguments" worthy of consideration are the following, listed by Tom Curtis above:
    Jones 1998 (Nature), Huang, Pollock et al 2000 (Nature), Broecker 2001 (Science), and Esper et al 2002 (Science). There has been more, Moeberg has been mentioned, along with numerous other reconstructions, some excluding tree rings.

    All the stuff on blogs and opinions pieces in newspapers are nothing but noise, and, to use some exotic statistical terminology created by M&M, it is not "trendless."
  46. Hey, I have an idea. Lets say Mike Mann is a bumbling researcher who makes mistakes and should be cast into the netherhells with others like him (eg Spenser, Christy, Soon, Baulinus, ... Hansen, Einstein etc). Now lets see what a difference to the science that make.

    Better?

    Whoops, still have hockey sticks, global warming and anthropogenic causes...
    Response: [muoncounter] Perhaps dawson should review 'Its not about the hockey stick' for some much-needed perspective.
  47. dawsonjg:

    What Mann does is not [science] at its best.

    Before this goes any further, let's get one thing clear. You've acknowledged that working with Mann's data is beyond your capabilities. You've also conceded in #35 that you lack the necessary skills to judge which side's arguments are scientifically sound.

    It logically follows that you lack the knowledge to critique Mann's work. And from there, it follows that you have absolutely no right to accuse him of bad scientific practice, let alone anything worse. That being the case, perhaps you should show a bit of humility and tone down your rhetoric.

    Take yourself out of the equation for a moment and think about this in abstract terms. Suppose that on the one hand, lots of respected scientists in a variety of countries and fields have used a variety of methods to arrive at results that basically agree with one another. And suppose that on the other hand, a guy who doesn't understand these disciplines or these methods decides that their conclusions are possibly or probably wrong because he saw a website that attacked one of them.

    Logically speaking, what's more likely: That all these scientists made errors that somehow turned out to agree with each other? That all these scientists put aside their professional rivalries and personal morality in order to falsify mountains of evidence over generations for some unknown purpose? Or that the guy who doesn't understand the science is easy to mislead?

    On the Internet, there are sites explaining that the AIDS virus doesn't exist, that chemotherapy is deadlier than cancer, that the Holocaust never happened, that vaccines don't work and that evolution is mathematically impossible. The arguments sometimes sound plausible, and the authors are sometimes actual experts in the relevant fields. They usually have no problem citing instances of "official suppression" of their work, not least because their followers usually can't appreciate the distinction between "suppressed" and "thoroughly debunked countless times" or "correctly viewed by experts as the work of a crazy person." And they usually have no problem coming up with plausible motives for conspiracy, because money and power are at stake in just about any field you can name.

    I'm sure you know all of this as well as I do, and I'm also willing to bet that you side confidently with the scientific consensus on most or all of these "controversies." So why do you feel justified in throwing that perfectly rational approach out the window here? If you really want to get to the bottom of this argument, that's the first question you need to address, I'd say. Challenging Mann's work before you've even begun to understand it -- let alone all the work done subsequently -- is like showing up for the Tour de France on a plastic tricycle and expecting to win.
  48. dawsonjg wrote:

    But consider who controls the billions of dollars poured into climate research

    Ah, the old they've-been-corrupted-by-the-money line. Desperate hand waving.

    Just for once try looking at the development of climate science. The basic physics were sorted by the 60s, 50 years ago, yet it took until the 80s before the world at large took notice and realised that we could face a very risky future. Only then did the "billions" get ploughed in - after it became clear that we needed a helluva lot more research pronto.

    Yet denialists portray the situation as if the money had been available up front before any conclusions were drawn and they imply or even state that climate scientists decided to make a grab for it by manufacturing fake science. Somebody should sue these nasty minded traducers for libel.
    Response: [Rob P] all caps changed to bold font. No all caps in the future thanks.
  49. If dawson is going to bring up the "corrupted by the money" argument, I'd have to suggest that main stream climate scientists are not real smart on that aspect (no offense). If they want to get on the real gravy train they should publish work vigorously rejecting AGW and land themselves a lucrative FF funded think tank position. The money researchers make doing actual research is a penny ante game.

    I would suggest that nearly all climate researchers are motivated merely by the desire to learn more and get things right.
  50. Thanks for the interesting advice guys.

    Philippe says: 'As usual, with often touted "billions in climate research," fake skeptics make heavy use of the method that consist of accusing others of what they themselves do.'

    Do I take it from that that billions have been funding 'fake skeptics'? I know about the often touted few million from Exon and McIntyre's travelling expenses, but who pays the rest to whom? That FF gravy train sounds interesting Rob, what's that all about?

    No innuendo, I'd really like to know.

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