Climate Science Glossary

Term Lookup

Enter a term in the search box to find its definition.


Use the controls in the far right panel to increase or decrease the number of terms automatically displayed (or to completely turn that feature off).

Term Lookup


All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

Home Arguments Software Resources Comments The Consensus Project Translations About Support

Twitter Facebook YouTube Pinterest MeWe

RSS Posts RSS Comments Email Subscribe

Climate's changed before
It's the sun
It's not bad
There is no consensus
It's cooling
Models are unreliable
Temp record is unreliable
Animals and plants can adapt
It hasn't warmed since 1998
Antarctica is gaining ice
View All Arguments...

New? Register here
Forgot your password?

Latest Posts


What evidence is there for the hockey stick?

What the science says...

Since the hockey stick paper in 1998, there have been a number of proxy studies analysing a variety of different sources including corals, stalagmites, tree rings, boreholes and ice cores. They all confirm the original hockey stick conclusion: the 20th century is the warmest in the last 1000 years and that warming was most dramatic after 1920.

Climate Myth...

Hockey stick is broken

“In 2003 Professor McKitrick teamed with a Canadian engineer, Steve McIntyre, in attempting to replicate the chart and finally debunked it as statistical nonsense.  They revealed how the chart was derived from "collation errors, unjustified truncation or extrapolation of source data, obsolete data, incorrect principal component calculations, geographical mislocations and other serious defects" -- substantially affecting the temperature index.” (John McLaughlin)

The "hockey stick" describes a reconstruction of past temperature over the past 1000 to 2000 years using tree-rings, ice cores, coral and other records that act as proxies for temperature (Mann 1999). The reconstruction found that global temperature gradually cooled over the last 1000 years with a sharp upturn in the 20th Century. The principal result from the hockey stick is that global temperatures over the last few decades are the warmest in the last 1000 years.

Figure 1: Northern Hemisphere temperature changes estimated from various proxy records shown in blue (Mann 1999). Instrumental data shown in red. Note the large uncertainty (grey area) as you go further back in time.

A critique of the hockey stick was published in 2004 (McIntyre 2004), claiming the hockey stick shape was the inevitable result of the statistical method used (principal components analysis). They also claimed temperatures over the 15th Century were derived from one bristlecone pine proxy record. They concluded that the hockey stick shape was not statistically significant.

An independent assessment of Mann's hockey stick was conducted by the National Center for Atmospheric Research (Wahl 2007). They reconstructed temperatures employing a variety of statistical techniques (with and without principal components analysis). Their results found slightly different temperatures in the early 15th Century. However, they confirmed the principal results of the original hockey stick - that the warming trend and temperatures over the last few decades are unprecedented over at least the last 600 years.

Figure 2: Original hockey stick graph (blue - MBH1998) compared to Wahl & Ammann reconstruction (red). Instrumental record in black (Wahl 2007).

While many continue to fixate on Mann's early work on proxy records, the science of paleoclimatology has moved on. Since 1999, there have been many independent reconstructions of past temperatures, using a variety of proxy data and a number of different methodologies. All find the same result - that the last few decades are the hottest in the last 500 to 2000 years (depending on how far back the reconstruction goes). What are some of the proxies that are used to determine past temperature?

Changes in surface temperature send thermal waves underground, cooling or warming the subterranean rock.  To track these changes, underground temperature measurements were examined from over 350 bore holes in North America, Europe, Southern Africa and Australia (Huang 2000). Borehole reconstructions aren't able to give short term variation, yielding only century-scale trends. What they find is that the 20th century is the warmest of the past five centuries with the strongest warming trend in 500 years.

Figure 3: Global surface temperature change over the last five centuries from boreholes (thick red line). Shading represents uncertainty. Blue line is a five year running average of HadCRUT global surface air temperature (Huang 2000).

Stalagmites (or speleothems) are formed from groundwater within underground caverns. As they're annually banded, the thickness of the layers can be used as climate proxies. A reconstruction of Northern Hemisphere temperature from stalagmites shows that while the uncertainty range (grey area) is significant, the temperature in the latter 20th Century exceeds the maximum estimate over the past 500 years (Smith 2006).

Figure 4: Northern Hemisphere annual temperature reconstruction from speleothem reconstructions shown with 2 standard error (shaded area) (Smith 2006).

Historical records of glacier length can be used as a proxy for temperature. As the number of monitored glaciers diminishes in the past, the uncertainty grows accordingly. Nevertheless, temperatures in recent decades exceed the uncertainty range over the past 400 years (Oerlemans 2005).

Figure 5: Global mean temperature calculated form glaciers. The red vertical lines indicate uncertainty.

Of course, these examples only go back around 500 years - this doesn't even cover the Medieval Warm Period. When you combine all the various proxies, including ice cores, coral, lake sediments, glaciers, boreholes & stalagmites, it's possible to reconstruct Northern Hemisphere temperatures without tree-ring proxies going back 1,300 years (Mann 2008). The result is that temperatures in recent decades exceed the maximum proxy estimate (including uncertainty range) for the past 1,300 years. When you include tree-ring data, the same result holds for the past 1,700 years.

Figure 6: Composite Northern Hemisphere land and land plus ocean temperature reconstructions and estimated 95% confidence intervals. Shown for comparison are published Northern Hemisphere reconstructions (Mann 2008).

Paleoclimatology draws upon a range of proxies and methodologies to calculate past temperatures. This allows independent confirmation of the basic hockey stick result: that the past few decades are the hottest in the past 1,300 years.

Intermediate rebuttal written by John Cook

Update July 2015:

Here is a related lecture-video from Denial101x - Making Sense of Climate Science Denial


Additional video from the MOOC

Interviews with  various experts


Last updated on 12 October 2016 by pattimer. View Archives

Printable Version  |  Offline PDF Version  |  Link to this page

Argument Feedback

Please use this form to let us know about suggested updates to this rebuttal.

Further reading

The National Academy of Science's summation of the various temperature proxies are available online at Surface Temperature Reconstructions for the Last 2,000 Years.

Tamino has an interesting blog post Not Alike where he compares the Moberg temperature reconstruction (one of the least hockey stick like reconstructions with a distinct Medieval Warm Period and Little Ice Age) to modern temperature trends. He finds modern temperatures are 0.53 deg.C hotter than medieval times and the modern warming rate is 64% greater than the fastest rate in medieval times.

The NOAA Paleoclimatology Reconstructions Network has made available paleo data for download including 92 high-resolution temperature records over the past 2+ millennia.


Prev  1  2  3  4  Next

Comments 101 to 150 out of 167:

  1. Jonathan - Not one of your references supports your assertions. The Ljungqvist data directly contradicts you, see the New temperature reconstruction thread. Current temperatures are higher than anything in the last millenium. From your second link, Oppo 2009, the abstract states - "Reconstructed SST was, however, within error of modern values from about ad 1000 to ad 1250, towards the end of the Medieval Warm Period. SSTs during the Little Ice Age (approximately ad 1550–1850) were variable, and approx 0.5 to 1 °C colder than modern values during the coldest intervals." (emphasis added) The Greenland GISP2 data is interesting, and very limited. See the entire discussion at Crux of a Core, multiple parts. Primarily, that is not a global record. Please - read the works you link to. Currently you appear to just be making stuff up.
  2. An error on my part in my last posting - the Oppo 2009 article states that SST's in the Indo-Pacific warm pool were similar to modern values. But please note that, as Rob Painting pointed out, the MWP was not uniform spatially: Portions of the world were fairly warm during the MWP, portions were much cooler. The global temperature was not as warm as present, and you are cherry-picking spot measurements.
  3. KR, All proxies could be considered cherry-picks, as we do not have a uniform global coverage. I do not know how you could possible make that statment recarding the Lundqvist paper, as it clearly states, "The highest average temperatures in the reconstruction are encountered in the mid to late tenth century," and "The temperature of the last two decades, however, is possibly higher than during any previous time in the past two millennia, although this is only seen in the instrumental temperature data and not in the multi-proxy reconstruction itself." Portions of the globe have cooled during the twentieth century, but that does not mean that global temperatures have decreased.
  4. Jonathon, the proxies in the Lundqvist paper do not include the last few decades. That the highest temperatures in the reconstruction are found in the 10th century does not mean that those were the highest temperatures over the last 2,000 years.
  5. Jonathan - There's a huge difference between single proxies (as you have presented) and looking at groups of proxies from multiple locations, as Ljungqvist and Mann have done. In the Ljungqvist paper he is speaking about the proxies, which don't extend directly to the present. So your argument about the last few decades amounts to claiming that proxy and instrumental data cannot be joined, despite overlap periods where they can be calibrated. I don't believe that's even remotely justifiable. Also note that, as stated in Ljungqvist 2010: "Our temperature reconstruction agrees well with the reconstructions by Moberg et al. (2005) and Mann et al. (2008) with regard to the amplitude of the variability as well as the timing of warm and cold periods, except for the period c. ad 300–800, despite significant differences in both data coverage and methodology." So - you're trying to use Ljungqvist, who agrees with Mann and Moberg, to argue against Mann and Moberg regarding the MWP??? That argument simply doesn't hold up.
  6. KR, The Lundqvist paper covers the period up to 1999, so it includes the warmest year in the instrument record. You need to read the paper (and your quotes) carefully. You are stating that timing and variability agree. However, the paper shows similar proxy temperatures at both the end of the 10th and 20th centuries. You also seem to contradict yourself in your first sentence about the Lundqvist paper to which I presented.
  7. Jonathon, #106 "The Lundqvist paper covers the period up to 1999, so it includes the warmest year in the instrument record." In some instrumental data sets you mean. And it doesn't however include the warmest decade (the last ten years). Also, the paper states, "The proxy reconstruction itself does not show such an unprecedented warming but we must consider that only a few records used in the reconstruction extend into the 1990s." The proxy data for the last decades of the study are weaker than the for the rest of it. The instrumental data trumps the proxy data for that time frame. Again, they concluded (with qualifications) that the decades since 1990 seem to be warmer than at any time during the last 2,000 years for the NH. The "highest temperature in the reconstruction" does not mean the highest temperature in the last 2,000 years. They are quite clear about that.
  8. "I think you have highlighted one of the difficulties in using proxy data. Roh234 showed that even recent proxies can result in opposite conclusions." No I didn't Jonathon (@ 95). I've highlighted how easy it is for those that wish to misrepresent the science to do so by selecting individual proxies that support a particular preconceived interpretation. Happily proper scientists continue to make considerable efforts to include as many verified proxies as possible to maximise the spatial coverage to allow assessment of at least hemispheric paleotemperature evolution on the millenial timescale. I'm sure you'd agree that it would be dumb to try to infer something about global or hemispheric temperatures from a single site in the Sargasso sea, particulalry when we have some rather good information that this is rather senstive to changes in the Meridonal overturning circulation that have no necessary relationship to global scale temperatures....
  9. 103, Jonathan,
    Portions of the globe have cooled during the twentieth century...
    Very, very false.
  10. 103, Jonathan, Oh, wait, if you go by Mann 2010 you're right. That teeny tiny little sliver of western South America has cooled fractionally, along with ocean off the coast of Antarctica. You're right. Any proxy would be a cherry pick if it doesn't include those two critical spots on the globe.
  11. Sphaerica, Over a longer time period, there are more areas. However, I do not think anyone would use just the data from the southern U.S. to from the conclusion that the globe has cooled. I echo your sentiments Chris about using a single site.
  12. #93, CBDunkerson, we appear to be talking about two different things. In my post 91 I demonstrated that the analogy that the "Yamal 12" (referring to 12 cores post 1988) are analogous to crack cocaine by pointing out the other data sets that were available with 30 or more cores during the same period. Divergence is a discrete phenomenon that causes some trees in some places to show slow growth due to non-temperature factors. But it is certainly not valid to claim that trees that don't show divergence (i.e. are not overtly impacted by those unknown factors) are sufficient for reconstructions "because we all know it has gotten warmer". The last part in quotes is ture, but the first part does not follow. It is equally possible that those faster growing trees are impacted positively by another unknown factor. The crux of the problemn with Briffa 2000 is not divergence but inadequate numbers of cores.
  13. Eric, Please follow this link. Note the date and time. Some of us prefer to live in the present, but to plan for the future, not just for ourselves but also for future generations. I'm disgusted that you chose to defend McIntyre's vitriolic and hateful comments-- and now seem to be trying to use them as a reason or "in" to challenge the dendro plaeo records. It seems to me that you agree with his propaganda on this file? Have you applied, as your moniker suggests, skepticism, or just one-sided skepticism like Pielke et al. do? Surely you aware of the multiple, paleo hockey sticks out there?
  14. 111, Jonathon, From your paper (emphasis mine):
    A notable feature of the observed trend map for the past century (Fig. 7a) is the pervasiveness of the warm- ing on the regional scale: almost all areas of the globe analyzed appeared to have warmed over the twentieth century. A few relatively small areas of cooling are seen, including a region south of Greenland and an- other covering the southeastern United States. The cooling trends in these regions generally do not appear to be statistically significant according to comparison with the control run 100-yr trends (Fig. 7b). On the other hand, the warming trends over much of the globe are statistically significant (compared to internal cli- mate variability) according to these tests.
  15. May I presume that you share my sentiments that no one would conclude that the Earth has cooled based on these areas?
  16. Albatross, I came to this thread to defend one McIntyre comment (singular). The other one brought up in the other thread was undefendable (Hansen refusing to debate Christy = Jihad). If you don't agree, then address my post 91 and explain why crack cocaine is not a good analogy for Briffa Yamal. Please explain why two other series in the peer reviewed literature that cover the same location were always passed up and Briffa Yamal was used in reconstructions instead.
  17. Eric, You did not look at the date and time did you? :) If you think it is OK for McIntyre liken paleo climate scientists to crack cocaine addicts, then by all means go ahead. You honestly think that it is perfectly OK for someone to use that kind of language in a scientific discussion. Got it. Maybe you ought to direct your questions to Dr. Briffa, but I would caution you that you are operating under the dangerous assumption that the information that you have been fed by Mr. McIntyre is accurate.
  18. Eric, no we're talking about the same thing. McIntyre's nonsensical argument about the '12 proxies' has been around for a few years. Seriously. 'Crack cocaine'? For PROXY temperature values since 1988? You do realize that we have these things called thermometers, right?
  19. Eric #112: Why do you waste your time with ancient, disproven arguments from McIntyre? I'll pick on one of your statements: "It is equally possible that those faster growing trees are impacted positively by another unknown factor." Sounds a lot like "unknown unknowns" to me. You're arguing that these trees agree with the instrumental/proxy record both recently and farther into the past millennium, yet you think there's a 50/50 chance that the trees are measuring the wrong thing but accidentally coming out with the right result? For that to be true, you need to believe two things: 1) that the trees measured past climate proxies well, yet broke down in the past 50 years, like the trees of the divergence problem. 2) that the trees which agree with the recent instrumental record have, within the last 50 years, picked up a new signal, not present in their palaeo records which drives their temperature record up very like the instrumental series. Or you could simply agree that these trees are succeeding in picking up the recent temperature series as they did with pre-1950 temperatures. In that way, the trees agree with many other independent proxy records as well as instrumental temperatures. It's hardly 'equally probable', that the trees have these two suspiciously coincident unknowns. It shows what you get if you take your information from McIntyre...
  20. Albatross the issue is not what Dr Briffa thinks or says now, the issue very narrow: whether anyone should have used the Briffa-Yamal series in building reconstructions between 2000 and 2009 when he finally released the raw data, when there were other series created with more data. CB, is there a thermometer in Yamal? Briffa used the HadCrut grid cell which is not remotely similar to most local instrument measurements (mostly flat in the last part of the 20th century). Even for that grid cell temperature, there are other better-correlated series. Skywatcher, "ancient" only because Briffa did not release his data for almost 10 years. A handful of trees matching up to a coarse grid cell is not a sign of agreement particularly when other series have a better match to local temperatures (not gridded) temperatures. My first two links in #91 both show that.
  21. Eric @120, "Skywatcher, "ancient" only because Briffa did not release his data for almost 10 years" SImply not true. You are, again, believing uncritically what Mr. McIntyre is feeding you. I could show you why you are wrong, but I would prefer that you be a true skeptic and discover the truth on this matter yourself. I'm saddened by this Eric, I used to consider you one of the more informed and reasonable "skeptics", but your actions of late have soured that.
  22. Albatross, looking at it has the series result only without any supporting data or metadata (e.g. # of trees). Here's the data released roughly 10 years later: Please let me know if I've missed something, but it seems cut and dry to me.
  23. Muon, it was Doug Cotton again. What's that his 6th or 7th fake identity?

    [DB] Sorry guys.  Just fingered him & took action.

  24. Readers should note that Doug Cotton has been banned from commenting at SkS for repeated and deliberate violations of the comments policy. He continues violate the policy by posting under pseudonyms and has, I believe, his comments deleted as a result without any regard to their particular content. He is now claiming on his website that his posts are being deleted because we cannot refute his arguments. That is a lie. His arguments where considered fully and resoundingly rebutted previously on SkS as they also have on Science of Doom (where he has also been banned for repeated violation of comments policy). I note that there is no posting permitted on his website. By his logic that lack of permission to post an argument means the argument cannot be refuted, his refusal to allow comments is sufficient proof that his arguments have been refuted. Less facetiously, if anyone believes there is any credibility to Doug Cotton's arguments, by all means present them on an appropriate thread, and in compliance with the comments policy. I enjoy shooting sitting ducks.
  25. Ian Joliffe considers MBH98 to contain 'dubious statistics' and says of the use of decentred PCA: It is possible that there are good reasons for decentred PCA to be the technique of choice for some types of analyses and that it has some virtues that I have so far failed to grasp, but I remain sceptical. Is using a decentred PCA the norm in paleo reconstructions or was it just MBH98?
    Response: [JH] Please define "PCA". Thank you. [Sph] John, PCA is Principle Components Analysis, a statistical technique whereby components are isolated and prioritized.
  26. Tristan - Do you have a reference to what Joliffe wrote? Decentered means are frequently used in Principle Component Analysis (PCA), and have been for a number of different analysis areas. See a quick look at Google Scholar. The various arguments I have seen about decentering have failed to show that use of decentered means invalidates MBH98, or even significantly changes the results. See Wahl 2007 as linked in the original post. While McIntyre 2004 was able to generate some 'hockey-sticks' from red noise, analysis of the eigenvalues for those shows that McIntyre was looking at noise (low correlation, lots of fairly low value components), while the MBH98 data components have only a couple of very large eigenvalues. That's how you determine whether you are looking at actual correlations (MBH98) or just noise (McIntyre). I will note that MBH98 was a pioneering paper in terms of the reconstructions - much work has followed on in both reconstruction techniques, additional and improved proxies, etc. See Mann 2007 for a partial review. All of the work supports the late 20th century being as warm or warmer than anything in the last 1200 years, and warming faster than anything we have data for. There may well be statistical arguments for/against decentered means in this field, but again - none of them invalidate the multiply confirmed results. --- What's really stunning (IMO) about this entire discussion is the 'skeptic' focus on a paper published over a decade ago, while a dozen later works using several different methods (with what should be refined techniques), are getting the same results. It's the equivalent of someone in an active field of professional research criticizing what somebody did in grade school - even though all work done since then agrees...
  27. KR I completely agree with your comment. That said, I'm still interested in the whole MM03 vs MBH debacle. I can't find the original reference, I think it may be one of Tamino's vaporised posts, but here's the context from everyone's favourite website.

    [DB] Links to the once-lost Tamino/Open Mind posts can be found in this post here:

    The post you seek is located here:

    The specific portion of the thread in question begins here:

  28. Sorry JH Principal Component Analysis.
  29. DB - Thanks for the links. Tristan - From that discussion: "It appears [Jolliffe] now discredits decentering, and he's entitled to his opinion. But the hockey stick remains when using centered PCA, and when using no PCA at all. The claim that it's nothing but "utterly bogus artifacts" is what's really bogus." - Tamino For those who are interested in the subject, Tamino has a fairly extensive discussion of Principal Component Analysis (PCA) which is still on the intertubes here: Part 1 and Part 2

    [DB] Tamino also deals with the PCA/non-PCA kerfluffle in this post at RealClimate:

  30. KR and DB You guys are champs. Thanks a lot.
  31. It seems that the link to the reconstruction data is broken (third link in the 'Further Reading' section). Current Link (broken): Suggested Link:
  32. There is a recent paper by Gergis et. al., discussed yesterday in a post on RealClimate site, that covers proxies for Australia and Oceania and results in a hockey stick. it would be interesting to see this SH Australasia hockey stick from Gergis(2012) compared to the Mann(2008) hockey stick, on the same timescale, displayed one above the other. I used the Gergis image from RealClimate, and the Mann image from the SkS site, and there seems to be some interesting agreement periods. For example, the sharp drops in proxy temperatures around 1350 and 1460 are present in both records, as near as I could see. From what I understand, sometimes the NH and SH temperatures will march together, and other times be out of phase. Perhaps SkS could discuss the two proxy records, comparing the temperature swings, written by someone knowledgeable of likely temperature swings over the last 1200 years.
  33. The link for the 'NOAA Paleoclimatology Reconstructions Network' returns a 'forbidden' message.

  34. The Tamino 'Not Alike' link also goes nowhere (not found).

  35. There is an awesome new post on RealClimate about tree rings, soundly refuting McIntyre and other critics.

  36. Hi all. The framing of this page is erroneous. The "skeptic argument" and "what the science says" do not refer to the same issue.

    McIntyre and McKitrick purported to refute/debunk a specific paper -- the Mann 1998 paper. That is all. Their debunking (if it was truly a debunking, which it appears to be) stands. It's not refuted by all the other, later research that reaches similar conlcusions as Mann.

    If the point here is to say that the hockey-stick-is-bogus argument is wrong because of all the other evidence, that's fine. But as far as I can tell, McIntyre and McKitrick were right in their criticism of that particular Mann paper, on various methodological grounds.

  37. Phronesis,

    Are you talking about science or public relations?  I will grant you than Mann and McIntyre disagreed about how to do the analysis.  Mann thinks he was correct and McIntyre thinks Mann was incorrect.  This issue has been resolved by collecting more data and redoing the analysis in a way that everyone agrees is correct.  When that was done it was found that Mann was correct in his interpretation of the data.  How does the noise that McIntyre continues to make relate to the data proving that Mann was correct all along?  When extensive reanalysis and massive amounts of new data confirm the original finding that means Mann was right and McIntyre was incorrect all along.

  38. Phronesis - "McIntyre and McKitrick purported to refute/debunk a specific paper -- the Mann 1998 paper... as far as I can tell, McIntyre and McKitrick were right in their criticism of that particular Mann paper" Unfortunately for your argument, they utterly failed to make their case. 

    M&M's several papers on the subject have been at the center of numerous peer-reviewed refutations (five of them listed here), with numerous errors and erroneous claims pointed out at RealClimate, including critical failures to apply PCA selection rules to identify significant components; an error that alone invalidates their work. Similar errors in PCA selection (which would have distinguished invalid noise-generated hockey sticks as insignificant) and a rather amazing amount of cherry-picking in their 'red-noise' model are discussed on Deep Climate, notably with an unconventional 'red-noise' model that actually was derived from the proxies (rather than a theoretic red-noise spectra), and therefore included the 'hockey-stick' - no surprise that they found it in their 'noise'. 

    The M&M critcisms of Mann's work are completely invalid, on various methodological grounds. 

    Is MBH1998 without flaw? Hardly - it's the initial paper in the field applying PCA and machine learning techniques to multi-proxy climate data, and as such is rather rough around the edges. Their centering method is arguably not the best available, additional proxies and further clarification of then-existing proxies have improved the data, and there are reasonable arguments for different combinatorial and statistical techniques. 

    But methodological issues with MBH1998 don't invalidate the general conclusions, that recent temperatures are the warmest in the last 1000 years. And many papers, many reconstructions, looking at the issue come to the same conclusions. 

    Multiple reconstructions

    [Source, data here]

    At this point I see (IMO) unsupported objections raised against MBH1998 to be a clear identifying marker of someone in climate science denial. 

  39. Michael and KR, thanks for the correction. I'll read the material you linked. I'm a social scientist so I know PCA – hopefully I'll be able to understand what I'm reading. I didn't find a published refutation of M&M, and the more bloggy stuff I'd seen were ad hominem attacks on McIntyre for not being a climate scientist. I did not take that as a good sign. I will say that if Mann's methods were invalid (I'm not sure if Michael is conceding or disputing this), but the conclusions turned out to be correct, I'd still cross out Mann's paper and only care about the subsequent, valid work (perhaps including Mann's.)

    I will say that McIntyre was spot on in his debunking of the recent Psych Science paper on belief in conspiracy theories and AGW skepticism -- there I'm in the comfy surrounds of my own field and expertise. His regression diagnostics were solid. There were hardly any participants in the dataset that fit the advertised effects. The paper should not have been published, and it's the first time I've ever seen a social psychologist (the lead author) say that we shouldn't care about outliers (in response to McIntyre) –- we're all trained contrary to that notion (McIntyre showed that a handful of outliers (5?) drove a huge part of the reported correlations.) Maybe McIntyre's skill with the social psychology paper biased my judgment of what he had done with the Mann paper -- well, it's kind of easy to debunk social psychology papers, which says something about the state of social science.


    [DB] All discussions of conspiracies and AGW skepticism shoud take place on a more appropriate thread, like this one:

    Recursive Fury: Facts and misrepresentations

  40. Phronesis - I have replied on the appropriate thread

  41. The link to the Oerlemans paper is dead; consider replacing it with this:

  42. I have been playing around with the top 100 (cherry picked) Hockey Stick Index (HSI) that are all that are supplied by McIntyre and McKitrick in supplementary data for their 2005 paper in GRL.  In doing so, I noticed certain defects in the Hockey Stick index they used.  Of these, the most glaring is that for any straight line with a any slope other than zero (fat) or infinite (vertical), it indicates that the straight line is a hockey stick.  Even with white noise added, so long as the Signal to Noise ratio does not excede one, the line will probably (>50% chance) be given a HSI greater than 1, the conventional benchmark used by McIntyre to indicate something is a hockey stick.  

    Here is an example of a straight line "hockey stick":

    In this case, the HSI is less than that for MBH 98 or 99, but the mean is of the 132 realizations is greater.  That is, according to the M&M05 HSI, a straight line with white noise and a S/N ratio of 1.25 or more is more like a hockey stick than are MBH98 and 99.

    This fact does not depend in any way on the slope (provided it is neither flat nor vertical).  Negative slopes will yield negative HSI's, but M&M05 (correctly) regard negative HSI's as equivalent to positive values in that the MBH98 reconstruction method flips the sign on proxies if that yields a better fit to the temperature data (which is not an error).

    From this it follows that the HSI developed by M&M cannot consistently distinguish between a straight line and a hockey stick shape. I suspect there are other shapes that it cannot distinguish either, but for now we need only consider the straight line. That means that, from the M&M05 HSI, we are unable to determine whether or not half of the 10,000 pseudo proxies are distinguishable from a straight line. Nor, using that index, are we able to distinguish MBH98 from a straight line. That means that as a statistical test of the tendency of short centered PCA to generate shapes similar to that of MBH98, the test is totally without power. It tells you absolutely nothing.

    The total statistical power of the first part of M&M05, it turns out, comes from the visual comparison between MBH98 (fig 2) and the MBH first Principle Component of the North American Tree Ring Network (fig 3).  That's it.  And as everybody should no, eyeball Mark 1 has very little statistical power as well.

    Not being content with finding a flaw with M&M05 statistical test, I looked to see if they could have done better.  In the end I developed five variant Hockey Stick Indexes (vHSI) that were superior as a statistical test of a hockey stick shape (although not necessarilly under all circumstances).  These were,

    1. The ratio of the standard deviation of the calibration period relative to the calibration period (1902-1980) relative to the standard deviation of the non-calibration period.  This tests for flatness in the "handle" vs noisiness or a high relative slope in the "blade".  Like the M&M HSI, it will only work well when the "handle" is flat, but will work better in that circumstance. 
    2. The angle formed by the slope in the calibration period relative to the angle of the slope of the non-calibration period if the two are displaced to intersect at the first year of the calibration period.  This tests merely for the angle between "blade" and "shaft" and will work well regardless of orientation .  It will not tell you how flat the "handle" is, however, and so can be confused by "hockey sticks" with very crooked "handles".
    3. The closeness of the largest inflection point in the period 1850-1900 to the inflection start of the calibration period.  The inflection point is defined as the start year of the largest 50 year trend starting in that period.  The index is defined as the difference between the inflection point and 1850 divided by the square root of the difference beween the start of the calibration period and 1850.  (not shown)
    4. The angle formed by the slope to 1850 and the fifty year trend from the inflection point.  This again works best with a flat "handle".
    5. The inflection point angle weighted by the inflection point index.

    Here are the results, comparing MBH 98 and 99 to the cherry picked top 100 HSI pseudoproxies from M&M05:

    The twelve point mean is the average of the 12 pseudoproxies used by McInyre (and Wegman) in various illustrations M&M's results.  MBH98 PC1 is the first principle component of the reconstruction of 1450-1400 temperatures from MBH98.

    As can be seen, MBH98 and 99 are statistically distinguishable from even the cherry picked top 1% of pseudoproxies, with differences in index values never less than 2 standard deviations above the mean, and for one index nearly 10 standard deviations above the mean.  MBH98 PC1 does not perform as well, but still can be statistically distinguished from the cherry picked top 1%  in 3 out of the five tests.  (The Inflection point vHSI shows MBH98 PC1 to be just over two standard deviations above the mean.)

    This is still a work in progress.  I think I need to improve my vHSIs by making comparisons with the instrumental record rather than the calibration period, and a combination of angle based and standard deviation based vHSI would probably be superior.  Further, I should make comparisons with the first principle component of the North American Tree Ring data base.

    Never the less, even at this stage the results show that you can devise variant Hockey Stick Indexes that are better able to determine a hockey stick shape, and that if you use those vHSIs MBH98 and 99 stand out as easily statistically distinguishable from PC1s generated from red noise using short centered PCA.  Further, those vHSIs are demonstrably superior to that of M&M05 in that at least none of them will mistake a straight line for a hockey stick (except the pure inversion method, which is why it was not shown ;))  So not only did M&M05 use a test with no statistical power, without validating the test; but alternative tests exist which would have refuted their thesis.

    The take home is that the first part of M&M05 is simply scientific garbage.  It has no scientific merit whatsoever.

    When I get around to it, I am going to see if I can develop even better vHSIs, but probably will wait at least till I have a copy of the NOAMER PC1, and ideally until I (or a colaborator) can generate a full set of pseudoproxies without the cherry picks for statistical comparisons.  (Help with either would be appreciated.) 

  43. Unless I am mistaken, the IPCC published Mann's 1995 "Hockey Stick" graph in "Science" magazine.  They also published the graph for roughly the same time frame 5 years earlier in the same "Science" magazine.  In the 1990 graph, the Medieval period showed massive heat for a few hundred years, much hotter than today. Much, much hotter than today. Mann's 1995 graph conveniently changed his later graph by illiminating that great warming period. That specific act is why the world is full of deniers.  (Also because the water levels have not risen at Malibu Beach.

  44. Gumball.  

    No.  The IPCC does not publish original research in journals. It only reviews the original research. IPCC authors may publish their own work in journals like Science, because as experts they do some of the original research being reviewed. Science may have published an IPCC figure from a report, but they are not doing so as the IPCC.  

    I have a guess as to what you're talking about, but the dates don't match up.  You will have to provide more specific — providing links to these figures etc — before anyone can clear up your confusion about this.

  45. And as an aside, the tide gauge data at Santa Monica does not seem to squate with your assertion of no sealevel rise. But given possibility of local tectonics, dont you think a better guage of sealevel rise would from satellites or analysis of the global tide guage data?

    What is your evidence that a perception of a Mann graph is the reason for climate denial? In my experience, denial is mostly rooted in political values and identity and will jump on any ridiculous excuse to bolster a position. A cool-headed review of all available data seems beyond many people.

  46. Gumball67 @143:

    1)  As Stephen Baines has already noted, the IPCC does not publish original research.  Rather, it reviews original research already published in the peer reviewed literature.

    2) Michael Mann's iconic hockey stick graph, as reproduced by the IPCC in the Third Assessment Report (IPCC TAR, 2001) was published in the Geophysical Research Letters in 1999 (PDF version of paper).

    3) That version was an update and extension of the prior version published in Nature in 1998, which only extended back to 1400 (PDF version of paper).

    4) Those papers were revolutionary in being among the first to use actual temperature proxies from a several cites around the globe to determine NH temperatures, and more importantly, being the very first to assess the error margins of the estimates.  They represented a major step forward in paleoclimate temperature reconstructions for the last few thousand years, but not the last or most recent step by any means.

    5)  The graph used by the IPCC in its First Assessment Report (IPCC FAR, 1990) was a version of a graph devised by Hubert Lamb.  Hubert Lamb's graph was based on the Central England Temperature series, a thermometer based record of temperatures in central England.  That record only extends back to 1659, whereas Lamb's graph extended back prior to 1000 AD.  Astute observers will therefore note that he must have relied on other information for the extension, and that other information was anecdotal historical data, mostly from Europe and Greenland.  Astute observers will further note that Central England is not the World, or even the Northern Hemisphere.  They will even note that Central England plus Greenland is still not the world or the NH and conclude that using strictly regional temperature information (and anecdotal information in the crucial period) is not an adequate methodology, and not to be preffered to using a number of temperature proxies from around the world.

    6) In the IPCC Second Assessment Report (IPCC SAR, 1996), the figure based on Lamb's guesses was replaced by proxy data, primarilly that from Bradley and Jones, 1993, which was a reconstruction based on 16 proxies and hence already a quantum leap in methodology over Lamb's free hand line drawn based on regional anecdotes:

    (Image version from wikipedia)

    The SAR also featured icecore records from around the globe, giving a similar picture.

    So, in summary, every feature of your account of the events relating to the IPCC, Lamb and Mann's graph is wrong.  But that is indeed why the world is full of deniers.  Because it is full of people who seize on convenient "facts" as an excuse to avoid uncomfortable conclusions - never bothering to check their sources.  Consequently it is full of people who confidently assert fictions as the basis of their opinions, and then go on to assert fraud by scientists for disagreeing with those opinions (as the scientist's opinions must, being based on facts).

  47. As Scaddenp seems to have forgotten the link, here is the Santa Monica tide guage data:

    And here is the annual data from that site:

    The trend since 1933 is 1.37 mm per annum.

  48. Hey guys - would anyone be so kind as tell me or point me to the appropriate response to the denialist talking point, "The hockey stick isn't in IPCC AR5!"

  49. dvaytw, AR5 WGI Chapter 5 pages 409, 413, and 419 all show different versions of holocene temperature reconstructions... aka, 'the hockey stick'.

    They may be looking specifically for the work of Michael Mann... which is referenced extensively throughout Chapter 5. Just search on ' Mann' in the text of the chapter. In figure 5.7, the hockey sticks on page 409, the four reconstructions with labels starting with 'Ma' (e.g. 'Ma09rem') are from Mann's work.

    The only way of interpreting the claim to be 'correct' might be that Mann's original 1998 'hockey stick' is not included... having since been superceded by subsequent work by Mann and others. So, to rephrase, 'The original hockey stick isn't in IPCC AR5! Instead, they used several of the newer ones which reach the same conclusions with even more conclusive data.'

  50. Oh man, CBDunkerson, man did you just help me put egg on somebody's face.  Much appreciated.

Prev  1  2  3  4  Next

Post a Comment

Political, off-topic or ad hominem comments will be deleted. Comments Policy...

You need to be logged in to post a comment. Login via the left margin or if you're new, register here.

Link to this page

The Consensus Project Website


(free to republish)

© Copyright 2022 John Cook
Home | Links | Translations | About Us | Privacy | Contact Us