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Hockey stick was debunked

The skeptic argument...

The below graph shows the results of a study of 112 proxy studies: tree rings, isotopes in ice, and other markers of relative temperature. Two Canadian investigators, McKitrick and McIntyre, re-did the study using Mann’s data and methods and found dozens of errors. When they corrected the errors, they came up with sharply differing results.

It turns out that Mann and his associates used a non-standard formula to analyze his data, and this particular formula will turn anything into a hockey stick---including trendless data generated by computer. (Source: The Case for Skepticism on Global Warming by Michael Crichton)

What the science says...

Debates continue even now over the statistical methods used in Mann's initial study. However since 1998, there have been at least ten proxy studies, analysing a variety of different sources including corals, stalagmites, tree rings, boreholes, ice cores, etc. Here is a visual summary (courtesy of Global Warming Art) of the various results (solid black is actual observed temperatures):

The results all confirm the same general conclusion: although each of the temperature reconstructions are different (due to differing calibration methods and data used), they all show some similar patterns of temperature change over the last several centuries. Most striking is the fact that each record reveals that the 20th century is the warmest of the entire record, and that warming was most dramatic after 1920.

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.

AlexLockwood.net writes a good overview of the Hockey Stick controversy with an emphasis on how the media and public have overstated the hockey stick's importance in looking for a potent symbol of climate change.

Comments

  1. Two words of warning about Michael Crichton's science: It's Fiction!

    RealClimate debunk Michael Crichton’s State of Confusion

    A review of the distorted science in Michael Crichton's State of Fear

    Checking Crichton's footnotes: Just how factual are Crichton's claims? How do they stack-up? Do they actually support his claims?
    [ Response: Indeed! For the record, I wasn't quoting his book but an article he'd published on his website - it probably covers much the same ground. Generally, for the skeptic argument, I try to find the most succinct skeptic article to use as an example. If I find a better version than Crichton's, I'll use that instead. ]
  2. I find your site very interesting and it links to some good content. However I have to take you up on the use of this graph , especially the way you present it.

    Firstly as your site clearly demonstrates there is sadly no "the science" to say anything. It's an ever more muddy mix of conflicting vested interests and distorted pseudo science. Sorting the chaff from the wheat is research project itself.

    Secondly you do not accurately represent this graph which I have already examined. It presents 10 , not a dozen sets of results, THREE of which are none other than the largely discredited M.E. Mann including his infamous hockey stick paper.

    I also dispute that the red line shows 20th century hotter than 11th century. Neither can I read anything from the jumbled mess to either agree or disagree with your comment about since 1920 although again the red line clearly does not conform to your statement.

    I don't think the graph is a good choice but if you use it you should probably review your comments about it and make the Mann bias very clear.

    Thanks for your other comments and links I find very informative.
    [ Response: When you say "no 'the science' ", what specific problems do you have with Jones 1998, Crowley 2000, Briffa 2001, Esper 2002, Huang 2004, Moberg 2005 and Oerlamans 2005? As for "ten studies" versus "around a dozen", you could add a recent paper Juckes 2007 which concludes "Instrumental temperatures for two recent years (1998 and 2005) have exceeded the pre-industrial estimated maximum by more than 4 standard deviations of the calibration period residual". Does eleven come close enough to "around a dozen"? But lest it be a stumbling block, I've changed the wording to "at least ten". Thanks for your comments. ]
  3. Will Nitschke (www.capitaloffice.com.au) at 19:04 PM on 19 December, 2007
    I think the main problems are:

    (a)The graph is a jumbled mess and hard to read.

    (b)Most of the proxies appear to terminate before 2000, much less 2005 or 2007.

    (c) At least 5 of the 10 proxies are by Mann or associates (co-authors/researchers who have worked with Mann). These are proxies 1, 2, 4, 6 and 7. (I do not know if the others are connected or not.)

    The evidence here is completely circular: You are arguing that reconstruction X is true because reconstruction X agrees with reconstruction X. Perhaps you should consider rewriting this article and excluding any proxy studies that are the subject of the dispute? If you have to use the studies under dispute to support your argument that there is independent verification of the results, you actually play into the hands of 'deniers.'
    [ Response: I don't see how criticism of a proxy study Mann did in 1998 invalidates all of his subsequent proxy studies. Nor how he would 'taint' any other researcher by mere association. If you dispute the studies by Briffa or Jones or the 5 other proxies that don't involve them, what is it about their processes that you have a problem with? ]
  4. Will Nitschke (www.capitaloffice.com.au) at 19:41 PM on 19 December, 2007
    If the CO2+global warming hypothesis is strong, as asserted here, then why is it unreasonable to ask for independent verification from other scientists? Why must all the 'proof' always come back to the same small group of researchers who all happen to collaborate with each other?

    Let me put it this way. Let's say you wanted to release a new cancer drug and the company that designed that drug also tested and certified the drug for safety. Would you feel confident in the quality control of the research? Why isn't this sort of behaviour considered acceptable?

    Specifically with regard to Mann, he has refused to accept any of the criticism of independent statisticians to my knowledge. If he feels he is 'right' and everyone else is wrong, why would I, or anyone else, feel confident that his later research is any better than his research done in 1998?
  5. Will Nitschke (www.capitaloffice.com.au) at 14:14 PM on 21 December, 2007
    "The results all confirm the same general conclusion: although each of the temperature reconstructions are different (due to differing calibration methods and data used)..."

    An appendum to my first post: I found this link:

    http://www.climate2003.com/blog/hockey_team.htm

    It turns out that the proxy reconstructions all done by the same group of scientists and their students are: 1, 2, 3, 4, 5, 6 and 7. So the methods are not independent, as stated incorrectly in this article. Only 8-10 may be independent reconstructions.

    Unfortunately the graph is so hard to read it is not possible to tell if there are still 'hockey sticks' if only the remaining three are used. We would be interesting to see what a graph like that would look like.
  6. Probably the most striking element of your graph is the abscence .4C of warming that is shown by the instrument record, but is simply not present in any of the reconstructions. So if the proxies are unable to represent the level of warming that we have today, why would we believe that they could represent the level of warming in the past. Considering that there are excellent tree ring studies that have been done by people like Linah Ababneh that go up to 2007, the embarassing question is, why haven't those studies been used. Mann uses the Graybill Idso tree ring series and gives it the highest weighting of any of his series. Many of Mann's colleagues use the same Graybill Idso series in their reconstruction. And they use many of the same methods as Mann. To represent the above graph as seperate sources of independent data is simply not true. The independence is partial.

    Getting back to Linah Ababneh's doctoral distertation, she basically went to the same areas as Graybill and Idso, and she took cores from the same kinds of trees. But she took a much larger sample set. She also divided the trees that had gone strip bark from those that had not. She found that strip barking had an effect of showing accelerated growth. The trees that had not gone strip bark did not show such growth. In fact, the non strip bark trees showed virtually no warming for the 20th century.

    Graybill and Idso's purpose in producing their series was to show CO2 feeding of trees. In other words, they were searching for accelerated growth that was due to the presence of more CO2 in the air. Their sample set was about half of what Ababneh took. And it consisted mostly of strip bark trees. Furthermore, they only archived about one third of the trees that they sampled, indicating the possibility of cherry picking. Well Graybill and Idso got the CO2 feeding that they were looking for, but it was actually mostly a strip bark effect. Then Mann and many of his friends decided that Graybills series was perfect for their temperature reconstruction. Mann made it his most heavily weighted series. In fact, he weighted it as being 200 times as important as his most lightly weighted series. His freinds used it similary. Now in his latest reconstruction Mann could have used Ababneh's series to help get himself up to date. But he simply did not want to do this. The avoidance of the truth that the proxies do not follow the instrument record for the last 20 or 30 years is obvious. The same applies for other tree ring series, such as those by Hakken Grudd. His series cover northern European areas and they also show an MWP that is warmer than today.

    http://www.springerlink.com/content/8j71453650116753/?p=fcd6adbe04ff4cc29b7131b5184282ebπ=0

    Mann and his friends will not use that series in their reconstructions either. Beyond, the entries that you have in your graph, there have been non tree ring studies done by people like Craig Lohele that also show MWP temperatures that are warmer than today.

    Going back a little further and leaving proxy studies behind, there is increasing evidence of periods that were much warmer than today. Here is one such example.

    http://www.ngu.no/en-gb/Aktuelt/2008/Less-ice-in-the-Arctic-Ocean-6000-7000-years-ago/

    Furthermore, in reference to Tamino's comment about Moberg's reconstruction, Moberg states in his Abstract that that the temperatures of the 20th century are not at all exceptional.

    One last thing. Earlier this year Steve McIntyre went to some of the exact same trees that Graybill took cores from in Colorado, cored them again, and had the cores read. The updated cores did not show recent warming.

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