Mann’s Screw Up #3.2 – Rotten Cherry #2

This is a follow-up to the last post. If you haven’t read it yet, you should.

Two cherry-picked proxies were responsible for Michael Mann’s 1998 hockey stick. The last post showed how one of the two (NOAMER PC1) was a bad proxy for temperature reconstructions. This post will show how the second proxy, Gaspe, was also a bad proxy for temperature reconstructions.

As you may recall, the Gaspe data series was used twice. It was used once in the same data set as NOAMER PC1; it was used a second time on its own. That’s never been acknowledged by the authors of the paper much less explained. A similarly unexplained issue is why the series was arbitrarily extended back in time to 1400 AD when used on its own (but not when used as part of the NOAMER network). To make matters worse, Mann et al list the duplicated series as starting at 1400, the extended date (North American Treeline, line 11).

A lack of explanation for those issues is disturbing given they were necessary for Gaspe to be used as one of the two proxies responsible for the hockey stick. However, they are issues about how the data was used. They don’t address the fact the data shouldn’t have been used at all.

The data is attributed to a paper by Gordon C. Jacoby Jr. and Rosanne a’Arrigo (sadly, I don’t know of a freely available copy). Before discussing Gaspe itself, we should take a moment to look at the views of these authors. Their paper says they sampled 36 sites in a region, but they only archived the 10 “judged to provide the best record of temperature-influenced tree growth.” That’s cherry-picking. In case it isn’t obvious enough, when Steve McIntyre tried to get data from those authors, Jacoby said:

We strive to develop and use the best data possible. The criteria are good common low and high-frequency variation, absence of evidence of disturbance (either observed at the site or in the data), and correspondence or correlation with local or regional temperature. If a chronology does not satisfy these criteria, we do not use it. The quality can be evaluated at various steps in the development process. As we are mission oriented, we do not waste time on further analyses if it is apparent that the resulting chronology would be of inferior quality.

If we get a good climatic story from a chronology, we write a paper using it. That is our funded mission. It does not make sense to expend efforts on marginal or poor data and it is a waste of funding agency and taxpayer dollars. The rejected data are set aside and not archived.

As we progress through the years from one computer medium to another, the unused data may be neglected. Some [researchers] feel that if you gather enough data and n approaches infinity, all noise will cancel out and a true signal will come through. That is not true. I maintain that one should not add data without signal. It only increases error bars and obscures signal.

As an ex- marine I refer to the concept of a few good men.

A lesser amount of good data is better without a copious amount of poor data stirred in. Those who feel that somewhere we have the dead sea scrolls or an apocrypha of good dendroclimatic data that they can discover are doomed to disappointment. There is none. Fifteen years is not a delay. It is a time for poorer quality data to be neglected and not archived.

He wasn’t talking about the Gaspe data, but it should give one pause to see this author proudly announce he cherry-picks his data.

Rather than say more at this point, I’ll simply quote from Steve McIntyre’s list about Gaspe (the sixth item shows how cherry-picking matters with Gaspe):

Third, in the early portion of the Gaspé chronology, there is only one tree – a point that was widely publicized back in 2005. Standard chronological methods require a minimum of 5 cores and preferably more. The early portion of the Gaspé chronology did not meet quality control standards.

Fourth, the Gaspé series is a cedar chronology. There is no botanical evidence that cedars respond linearly to warmer temperatures. World experts on cedar are located at the University of Guelph, Ross McKitrick’s university. Ross and I had lengthy discussions with these cedar experts about this chronology – they said that cedars like cool and moist climate.

Fifth, the Gaspé chronology was never published in formal literature. There was an informal description in Natural Areas Journal, where the HS shape was observed – with the caution that this shape would have to be confirmed in other sites, mentioning pending cedar sites in Maine and Michigan. Neither of these sites had a HS shape. There is another long cedar chronology in the ITRDB (Lac Duparquet – cana106). This series was listed in the original SI as being used, but was not used, as later admitted in the Corrigendum. It does not have a HS shape.

Sixth, and this is very troubling: an update to Gaspé was done in the early 1990s – the update did not get a HS shape (shown below). This update was never published. I happened to obtain a copy of the update which was shown at CA here. The updated version of the Gaspé series does not have a HS shape. It has never been shown publicly except here at CA. Jacoby and d’Arrigo refused to provide me with either the updated chronology or with the measurement data. D’Arrigo refused to provide the updated information on the basis that the older version was “probably superior with regards to a NH signal”.

Maybe it’s lazy to quote him so extensively, but I don’t see a point in restating what he’s already said so clearly. Gaspe was not remotely suitable for reconstructing temperatures back to 1400 AD, even if we disregard Mann et al’s arbitrary duplication and extension of the series.


That brings us to the end of our discussion of how Mann’s 1998 hockey stick got its shape. As we’ve seen, its shape is due to two cherry-picked proxies. One proxy was manually cherry-picked and the other proxy was cherry-picked by a faulty implementation of principal component analysis. On top of that, neither of those proxies were remotely suitable for reconstructing temperatures.

Don’t worry though. This isn’t the end of our discussion of Michael Mann. There is still his 1999 paper which extended the 1998 hockey stick back to 1000 AD. There’s also his 2008 paper which offered two new temperature reconstructions. Plus, there are a number of other topics related to his reconstructions that are worth covering even though they aren’t tied to how he got his results.

If we wanted to, we could add to this list for the rest of the year. And that’s without being any more detailed than we’ve been thus far. Can you imagine if I tried to make this discussion exhaustive?

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2 comments

  1. The comment above isn’t necessarily cherry picking. Substitute rural and urban temperature stations, for example.
    Rob Wilson says the comment about ‘picking and choosing to enhance a desired signal’ has been taken out of context.

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