The last item in this series discussed Mann responding to criticisms with (sometimes contradictory) lies. Today's item will show he resorts to dishonesty even when not criticized.
In 1998, Michael Mann and two co-authors published a paper (MBH98) claiming to reconstruct temperatures of the northern hemisphere back to 1400 AD. It claimed modern warmth was unprecedented in 600 years with “roughly a 99.7% level of certainty," and it said this result was robust:
the long-term trend in NH is relatively robust to the inclusion of dendroclimatic indicators in the network, suggesting that potential tree growth trend biases are not influential in the multiproxy climate reconstructions.
Dendroclimatic indicators means tree ring data, the primary source of data for MBH98. That, coupled with the strong statement of certainty, portrayed their results as beyond dispute. This was nonsense. You don't have to take my word for it. Michael Mann himself says so in his book. On page 51, he said after MBH98 was published he performed tests that:
revealed that not all of the records were playing an equal role in our reconstructions. Certain proxy data appeared to be of critical importance in establishing the reliability of the reconstruction–in particular, one set of tree ring records spanning the boreal tree line of North America published by dendroclimatologists Gordon Jacoby and Rosanne D’Arrigo.
If “one set of tree ring records” was “of critical importance in establishing the reliability of the reconstruction,” the reconstruction could not have been “relatively robust to the inclusion of dendroclimatic indicators.” And according to Michael Mann, he knew this shortly after MBH98 was published.
This raises all sorts of questions. Why did he only test his claim of robustness after he published a paper saying his results were robust? Once he found out his results weren't robust, why didn't Mann tell people? Why didn't Mann correct his paper? Most importantly, why did Mann keep silent about this when he published another paper (MBH99) the next year extending his results back to 1000 AD?
We can speculate as to Mann's motives as much as we want, but the reality is simple. He made a bold claim in his paper without testing to see if that claim was true. When he found out his claim was untrue, he made absolutely no effort to correct it. Instead, he continued working on the same project, acting as though his earlier claim was completely true.
After that, Mann spent years defending his work from critics. He argued point after point, even starting a blog with several colleagues to better be able to defend his work. And in all the years and all the arguments, not once did he knew his results weren't robust. Not once did he just come out and say his results were dependent entirely upon “one set of tree ring records.” With that in mind, read this paragraph Mann wrote:
The MBH98 reconstruction is indeed almost completely insensitive to whether the centering convention of MBH98 (data centered over 1902-1980 calibration interval) or MM (data centered over the 1400-1971 interval) is used. Claims by MM to the contrary are based on their failure to apply standard ‘selection rules’ used to determine how many Principal Component (PC) series should be retained in the analysis. Application of the standard selection rule (Preisendorfer’s “Rule N’“) used by MBH98, selects 2 PC series using the MBH98 centering convention, but a larger number (5 PC series) using the MM centering convention. Curiously undisclosed by MM in their criticism is the fact that precisely the same ‘hockey stick’ pattern that appears using the MBH98 convention (as PC series #1) also appears using the MM convention, albeit slightly lower down in rank (PC series #4) (Figure 1). If MM had applied standard selection procedures, they would have retained the first 5 PC series, which includes the important ‘hockey stick’ pattern. The claim by MM that this pattern arises as an artifact of the centering convention used by MBH98 is clearly false.
Your eyes glazed over, right? Who cares about PCA, Preisendorfer’s 972 or whatever this argument is about? Mann could be completely right or completely full of it in this paragraph. Most people wouldn't be able to tell the difference, especially not when there are pages after pages of text like this.
But now that we know Mann tested his results and found “one set of tree ring records” was “of critical importance in establishing the reliability of the reconstruction,” it's easy to see what Mann did. Look at the second to last sentence of that paragrpah:
If MM had applied standard selection procedures, they would have retained the first 5 PC series, which includes the important ‘hockey stick’ pattern.
Ignore the technical issues. Just look at that and remember the reliability of Mann's results depended entirely upon "one set of tree ring records." Mann is saying you get a hockey stick if you keep the right "PC series, which includes the important 'hockey stick' pattern." What that means is, if you you keep that "one set of tree ring records," you get a hockey stick.
Think about that. Years and years of technical discussions and arguments over details all boils down to one simple fact. Mann's results were entirely dependent upon a small amount of tree ring data. Remove it, and you don't get a hockey stick. Remove it, and Michael Mann doesn't get his name heard by millions of people. Remove it, and Michael Mann doesn't get fame and acclaim. Remove it, and Michael Mann is just another nobody toiling away in obscurity.
And he knew that. He knew his results were entirely dependent upon a small amount of tree ring data. That's why he vehemently argued, for years, that we have to include that data. He just coached it in technical jargon because he knew if he ever came out and told people, "Yeah, my results are entirely dependent upon a small amount of tree ring data," he'd have been laughed at.
Or maybe not. Maybe people would have thought it was cool. I mean, maybe Michael Mann just found an area with some magical trees which could tell us the temperature of the entire Northern Hemisphere.
Of course, if those trees really are magical thermometers, shouldn't he have highlighted that so people could investigate them further?