Mann on BBC4

A few comments on Mann’s interview on BBC4 in which Ross McKitrick and I were discussed.

Given the seeming efforts to backpedal on the role of the hockey stick in promoting Kyoto, it was interesting to hear the BBC reporter state that it was "hard to over-estimate how influential that study [MBH98] and that image [the hockey stick] has been".

Question 1: What do you make of the criticisms? Mann stated that the criticisms of the hockey stick graph were "spurious", "not real science", were "politically motivated" and were "ad hominem and somewhat vitriolic in nature". I have tried to avoid ad hominem comments and believe that I have done so for the most part; I would have thought that an evenhanded survey of Mann’s comments and our comments would not conclude that our comments were "ad hominem and somewhat vitriolic in nature".

Question 2: The questioner cited from the abstract of MM03, rather than MM05, and so the question was not a particularly good one. Mann said that every one of our claims had been "discredited". Given that, for example, von Storch, Zorita, Zweiers, Muller, the GRL referees, Mia Hubbert and others have endorsed our criticism of the MBH98 principal components methodology, it is certainly incorrect to state that every one of our claims has been discredited. Mann has argued at realclimate that the PC error doesn’t "matter" – a point which does not actually refute the problem (as opposed to arguing about the damages caused by the problem). We strongly disagree with the argument anyway, see comments at Errors Matter #1, Errors Matter #2, Errors Matter #3 and Was Preisendorfer’s Rule N used in MBH98?.

I have seen no response which even begins to deal with our criticisms of the incorrect benchmark for RE significance, the lack of statistical significance of the MBH98 reconstruction, the lack of robustness to the presence/absence of bristlecone pines – which are the focus of MM05, which reflects additional archival information made available in response to MM03. However, even for MM03, I recently took a look at how the specific criticisms of MM03- see Scorecard for MM03 – have borne up and I don’t see that they have been "discredited". Mann went on to say that we "got a hold of a corrupted datafile" even though the correct data was available at their site. Here Mann is re-hashing a dispute that has nothing to do with MM05 (and little to do with MM03). The "corrupted datafile" was located at Mann’s FTP site and was the dataset to which we were directed in response to our request for the FTP location of MBH98 data. When we noticed problems in this datafile, we asked Mann to specifically verify that this was the dataset used in MBH98. Rather than suggesting that this dataset was flawed, he said that he was too busy to respond to this or any other request. We were not asking for any hand-holding here, just for confirmation that this was the correct dataset. Given that this dataset was at Mann’s FTP site and we were directed to it, it seems disingenuous to say that "we got a hold of a corrupted datafile".

After publication of MM03, this dataset was deleted and another data directory suddenly materialized – see discussion here. Because we noticed problems with the dataset, we totally reconstructed the dataset and carried out fresh principal components calculations. In Scorecard, I acknowledge that 2 of 10 criticisms in MM03 may in fact apply to the now deleted dataset, but also point out that there is some evidence that Rutherford at least used the now deleted and "corrupted" file pcproxy. Mann then said that we "haven’t explained" why we "deleted proxy data". Our calculations in MM05 (and in MM03) are based on the complete proxy network. We point out that quite different results are obtained depending on whether the PC4 from a correct PC calculation is included or excluded in the regression calculations – this is a perfectly valid sensitivity analysis. We also point out that quite different results are obtained depending on whether the bristlecone pines – acknowledged to be a flawed proxy – are included or excluded in the calculations.

Mann has done calculations to show that you get high 15th century values if you don’t include U.S. tree ring data in the 15th century; this is simply because, a fortiori, the bristlecones are excluded. Given that he has claimed that their calculations are "robust" to the presence/absence of dendroclimatic indicators, I don’t see how he can have it both ways – how can it be robust to the presence/absence of dendroclimatic indicators and require the inclusion of the bristlecone pines to get a cold 15th century?

Question 3 and 4: The questioner asked about refusing to disclose workings and methods. Mann denied this. His answer here was rather at odds with his statement reported in the WSJ, where he said disclosing the code would be giving in to "intimidation", but the questioner did not notice this. Mann said that he had provided a "detailed description" of the algorithm. In July 2004, Mann provided an archive which (for the first time) was sufficient to determine which series were used in which calculation step.

There is source code for the tree ring principal components calculation at his FTP site (which was how we were able to detect the problem). However, there is no source code for the steps going from the proxy network to the NH temperature calculation. There is no digital version of the 15th century step through to the calibration and verification period. While we are able to substantially replicate the main features of his reconstruction, the description of the algorithm is insufficient to replicate MBH98 sufficiently to (for example) replicate an RE statistic of 0.51 for the 15th century step. Given that substantial inaccuracies in his description of methodology have already been identified (e.g. the inaccurate characterization of the PC method) and the broad reliance on MBH98, we see no reason why the source code should not be disclosed. In any event, it is a matter of fact that source code for steps after the PC calculations for tree ring networks have not been disclosed.

Question 5: The questioner asked about "being forced to retract" certain claims, which Mann denied. [I’ll finish this later…]

John writes: the link to the interview doesn’t appear to work and I’m trying to get the website support for the "Today programme" to recognize that there’s a fault.


  1. David H
    Posted Feb 24, 2005 at 3:10 PM | Permalink

    Note that Sarah Montague asked if Prof. Mann had disclosed the “maths”. Prof. Mann said he had published the algorithm.

    Show us the computer programme!

  2. N. Joseph Potts
    Posted Feb 24, 2005 at 9:56 PM | Permalink

    DO finish this account! What a tangled web we weave, when first we practice to deceive.

  3. Sonja Boehmer-Christiansen
    Posted Feb 25, 2005 at 9:08 AM | Permalink

    I have forwarded this page to the BBC,following a lengthy request for the Canadian auhtors also to be interviewed at prime time. Mann was even allowed to publicise the ‘working climate scientists’ web site in the interview,outrageous but in line with BBC’s politically correct line of global warming. Note that the BBC is engaged in a difficult battle with government over funding and licence fee. If public broadcasting goes….

  4. Jim
    Posted Feb 25, 2005 at 2:43 PM | Permalink

    Kyoto predates “the hockey stick”.

  5. Ross McKitrick
    Posted Feb 28, 2005 at 12:36 PM | Permalink

    Kyoto doesn’t really predate the hockey stick. It was signed in Dec 1997 but it was by no means clear any countries would ratify it. The debates about ratification got going in 2001-2002 in most western countries (the US excepted). Here in Canada the government engaged in heavy promotional activity during that time, leaning on the hockey stick to sell the deal. I expect it was the same in other countries, and ratification decisions by countries facing emission reduction obligations only took place after the TAR came out in 2001.

  6. David H
    Posted Feb 28, 2005 at 5:04 PM | Permalink

    The importance of the hockey stick in UK politics which largely drove the Kyoto process can not be overstated. In the ongoing House of Lords enquiry into aspects of the economics of climate change Lord Lawson who had been a key member of the government that took us into Kyoto said this in his questions to Professor Robinson on 11 jan 2005 (see and please note these are draft uncorrected transcripts).

    “Q16 Lord Lawson of Blaby: Professor Robinson, you mentioned the Government’s White Paper UK National Priorities in the Energy Strategy. In the climate change section of that, the first page presents in a very prominent position a graph which is used a great deal to demonstrate that there is likely to be warming, which shows from the year 1000 AD to the present, and indeed projections into the future, that the world temperature remained pretty well static until about the early 20th century when it started to rise, and this is projected to continue. You said, quite rightly, that one of your concerns was that the rise that there has been over the past 100 years may be something that should be projected in the future or it may be a cyclical phenomenon. If you look at this graph it does not look like a cyclical phenomenon. Have you made any studies of the reliability of this particular graph, which has had a very, very prominent place not merely in the Government’s White Paper but in most of the climate change literature?

    “Professor Robinson: I think a large part of the graph to which you are referring is a projection and consequently it would not be possible to spot any kind of cyclical effect because it is a projection that shoots up.

    “Lord Lawson of Blaby: Yes, from the year 2000 to 2100 you are absolutely right it is a projection, but from the year 1000, shortly before the Battle of Hastings, to the present day, whatever else it is, that is clearly not a projection. ……. (Q17) Are you aware that this, which has had a very profound influence on thinking, is explicitly stated in the Government’s White Paper to be based on proxy data, whatever proxy data may be, because there are no instrumental observations, they did not begin until the late 19th century, and that for these proxy data, which it says in small writing at the bottom, that the IPCC relies entirely on a study by a Professor Mann in 1998 and this has subsequently been examined and it was found that that Mr Mann got it all wrong in a rather fundamental way. Professor McKitrick, for example, has gone into this in great detail and so I believe have others. Is this something you have studied?

    “Professor Robinson: I have not studied in any detail this question about whether we are in a trend or in a cycle but if you simply cover the projection part at the end of that graph with your hand you can see (it is not all that clear) what is happening. I am merely raising the question because I think it is an important issue because if we were in the warming phase going to a cooling phase and the Government takes action on the assumption it is warming then we are doing precisely the wrong thing presumably, so it is quite an important issue and I was really raising it as a question that might be addressed to the scientists – what confidence they have that this is a genuine trend.”

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