Looking Back at the Hockey Stick Thesis: The Bishop Hill Account

Because a big part of the scientific misconduct in ClimateGate involves Michael Mann’s now discredited “Hockey Stick” thesis, I thought it might be good to review a couple of the better posts outlining some of the misbehavior. The first is a long post from 16 months ago at the Bishop Hill blog (tip to Andrew Bolt).

The Bishop Hill post goes into great detail to show how the UN’s IPCC was complicit in the conspiracy of scientists to keep the Hockey Stick thesis alive and to retain it as sound science in the IPCC Report.

Here is an excerpt dealing with data manipulation and the initial refusal to share data:

We have seen above that one of the chief criticisms of the hockey stick was the fact that its author, Michael Mann, had withheld the validation statistics so that it was impossible for anyone to gauge the reliability of the reconstruction. These validation statistics were to be key to the subsequent story. At the time of their press release Wahl and Amman (colleagues of Mann) had made public the computer code that they’d used in their papers. By the time their paper was submitted to Climatic Change, McIntyre (the statistician at Climate Audit) had reconciled their work with his own so that he understood every difference. And he therefore now knew that Wahl and Amman’s work suffered from exactly the same problem as the hockey stick itself: the R2 number was so low as to suggest that the hockey stick had no meaning at all, although another statistic, the reduction of error statistic (or RE) was relatively high. It was only this latter figure that had been mentioned in the paper. In other words, far from confirming the scientific integrity of the hockey stick, Wahl and Amman’s work confirmed McIntyre’s criticisms of it! McIntyre’s first action as a peer reviewer was therefore to request from Wahl and Amman the verification statistics for their replication of the stick. Confirmation that the R2 was close to zero would strike a serious blow at Wahl and Amman’s work.

Wahl and Amman’s response was to refuse any access to the verification numbers, a clear flouting of the journal’s rules. As a justification of this extraordinary action, they claimed that they had shown that McIntyre’s criticisms had been rebutted in their forthcoming GRL paper, despite the fact that the paper had been rejected by the journal some days earlier. At the start of July, with his review of the CC paper complete, McIntyre took the opportunity to probe this point, by asking the journal to find out the anticipated publication date of the GRL paper. Wahl and Amman were forced to admit the rejection, but they declared that it was unjustified and that they would seek publication elsewhere.

With the replication of the hockey stick in tatters, reasonable people might have expected some sort of pause in the political momentum. Seasoned observers of the climate scene, however, will be unsurprised to hear that global warming eminences grises like Sir John Houghton and Michael Mann continued to cite the Wahl and Amman papers . . . .

While the AGU (American Geophysical Union) was meeting in San Francisco, Climate Change had provisionally accepted Wahl and Amman’s CC paper, any objections which might have been raised by McIntyre swept aside by simple means of not inviting him to review the second draft. The resubmitted version of the paper turned out to be almost identical to the old one, except that a new section on the statistical treaments had been added, presumably as a condition of acceptance. And here there was an upside because, buried deep within the paper, Amman and Wahl had quietly revealed their verification R2 figures, which were, just as McIntyre had predicted, close to zero for most of the reconstruction, strongly suggesting that the hockey stick had little predictive power. . . .

However, the [RE] figure of 0.52 was insufficient for W & A’s purposes. Their problem was that the key component of the hockey stick had a verification RE of 0.48, leaving it tantalisingly just below the calculated benchmark. They needed it to be in the top rank and getting it there was going to be tricky. For each simulation, a thousand runs through the statistical sausage machine were perfomed and the RE number, the correlation with the temperature record, was recorded. Then all the runs were sorted in order of RE value, the best runs having the highest RE and the worst the lowest. W & A needed to show that the hockey stick RE was right up there with the best simulations — in the top one percent. While its RE was high, it wasn’t good enough. And it was no good simply removing runs which had a higher score than the hockey stick, since this would not increase its position enough — they would have been reducing the total number of runs as well as the number of runs which were scoring better than the hockey stick. To get the answer they needed, the higher scoring runs had to be made to be lower than the hockey stick, but left in the calculation.

To do this, Wahl and Amman came up with a value which they called a calibration/verification RE ratio. As the name suggests, this was the ratio of the two RE numbers for calibration and verification. This ratio is however, entirely unknown to statistics, or to any other branch of science. But it was not plucked out of the air. The ratio and the threshold value which was set for it by Wahl and Amman was carefully calculated. They argued that any run with a ratio less than 0.75 should be assigned a score of -9999. Since the hockey stick had a score of 0.813, 0.75 was pretty much the highest level you could go to without rejecting the hockey stick itself. However if you set your ratio threshold too low, not enough runs would be rejected and the hockey stick would no longer be “99% significant”. Some of the results of this ratio were entirely perverse — it was possible for a run that had scored a reasonably good RE in the calibration (there was a good correlation between it and the actual temperatures) to be thrown out of the final assessment on the grounds that it had done very well in the verification – the correlation with actual temperatures was considered too good!

With this new, and pretty much entirely arbitrary hurdle in place, Wahl and Amman were able to reject several of the runs which stood between the hockey stick and what they saw as its rightful place as the gold standard for climate reconstructions. That the statistical foundations on which they had built this paleoclimate castle were a swamp of misrepresentation, deceit and malfeasance was, to Wahl and Amman, an irrelevance. For political and public consumption, the hockey stick still lived, ready to guide political decision-making for years to come.

One quick test for telling whether a UN or US government climate report is based on solid science and whether a climate scientist is both honest and informed is whether they present Mann’s Hockey Stick thesis as if it is true and established by solid scientific evidence.

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