[UPDATE July 1, 2010: Penn State just today issued a final report on their investigation into allegations of misconduct by Dr. Mann. Note their criteria for misconduct were as follows:
(1) fabrication, falsification, plagiarism or other practices that seriously deviate from accepted practices within the academic community for proposing, conducting, or reporting research or other scholarly activities;
(2) callous disregard for requirements that ensure the protection of researchers, human participants, or the public; or for ensuring the welfare of laboratory animals;
(3) failure to disclose significant financial and business interest as defined by Penn State Policy RA20, Individual Conflict of Interest;
(4) failure to comply with other applicable legal requirements governing research or other scholarly activities.
where "research misconduct does not include disputes regarding honest error or honest differences in interpretations or judgments of data, and is not intended to resolve bona fide scientific disagreement or debate."
The report concludes "there is no substance to the allegation against Dr. Michael E. Mann"; the worst they could say was that he was somewhat "careless" in sharing unpublished manuscripts with colleagues. However, this was a pretty high-level review, and seems it did not get into the "Tiljander" issue. So we'll see where that goes here.]
Deep Climate has a new post up concerning the IPCC TAR Figure 2.21 "hockey stick" curves prepared by lead author Michael Mann for the 2001 report. This follows up on my post looking into similar questions regarding the AR4 Figure 6.10b "hockey sticks" in the latest (2007) report. Despite Steven Mosher's claims that the same rather subtle "trick" of padding the Briffa curve with instrumental temperatures was used in both figures, my analysis showed it could not have been in the AR4 case. Deep Climate has now shown that it's possible this padding was used for the Briffa curve in the TAR figure, but it makes essentially no difference (0.01 degrees over about 10 years, almost imperceptible in the full graph). The Mann curve in the TAR figure ("MBH") clearly was padded from 1980 with instrumental temperatures in the end-point smoothing, while the Jones curve in that figure clearly was not. The details of Mosher's (and McIntyre's, in this case) accusations about Mann and Briffa also seem to be contradicted by the actual record as DeepClimate shows, but that's another matter.
In any case, there definitely was an issue with the way Michael Mann was doing end-point smoothing in several of his early published papers, and in at least one of the curves in this IPCC report. As noted in the previous discussion, Mann admitted to this several years ago and indicated it wouldn't happen again, and it doesn't seem to have. So, an error, with minor impact on a couple of curves, since repented of.
In my last post, I called for the best examples of anything close to fraud by climate scientists, in particular Mann. There certainly are a number of cases where he has made similar errors that seem to have not substantially effected the results, but still were indicative of a certain carelessness, and sometimes stubbornness in recognizing the problem. And there are other examples of minor errors by other groups, for example several glitches in the GISS instrumental temperature analysis over the years that caused minor shifts in historical temperature numbers, particularly regionally.
Of course the worst case of unacknowledged errors in climate science was probably the UAH satellite analysis, which for 26 years was substantially under-reporting warming due to an algebra error in the analysis.
People make mistakes; as long as they correct them when the error is detected, it's really not such a big deal. The question I raised in my "Where's the fraud?" post was whether there was any substantive error of some sort that had not been admitted or corrected after exposure.
The strongest case seems to be the Tiljander proxy issue in a 2008 paper, as outlined by AMac in comments on my last post, and reference links there. Since nobody has proposed anything stronger, I plan to look into it in some further detail to make sure I understand the alleged error myself in its proper context. Here's how I understand it from my reading so far of the case (which hasn't yet included looking at any of the scientific papers or data involved, merely reading comments from others):
* Several data series were published by Tiljander et al which they believed could act as a temperature proxy (in ways they described) but only up to about 1720; for more recent years the authors believed the data were contaminated by human influences that masked any temperature signal
* Michael Mann and coauthors included the Tiljander series in a 2008 reconstruction paper. They were apparently aware of the possible contamination issue and made note of it in supplemental material that included a graph comparing the reconstruction with and without the Tiljander (and a few other suspect) series
* What Mann apparently was not aware of, or did not acknowledge, was that the contamination, for at least some of the Tiljander series, was bad enough to reverse the correlation between temperature and their data, so that Mann's calibration method would spuriously turn some of the Tiljander temperature proxies upside down in the pre-1720 period (at least if Tiljander's temperature correlation claims are correct). Mann's calibration method was regression-based and so didn't care whether the input was "upside down" or the right way up, it would determine a linear coefficient of whatever sign made the modern temperature correlation work.
* Kaufman published a similar reconstruction in 2009, using a different calibration method that really did care about sign but didn't use modern-period calibration; since some of the Tiljander proxies in that case were truncated to the earlier period that would have made sense, except that that method depended on having the right sign. A correction was published when this was discovered.
* McIntyre and McKitrick published a comment on Mann 2008 making the "upside down" accusation, but not being clear that the issue was a twisting of the correlation in Tiljander itself
* Mann's reply indicated he didn't understand the twist either.
* There's been a lot of blogosphere discussion of this, but one side seems to keep saying "upside down" while the other side says "it doesn't matter to the reconstruction", ie. the usual people talking past each other. The real problem is the twist in the data, which nobody seems to talk about.
Open questions to me are:
(1) Is the "twist" real - was the original Tiljander paper correct in assignment of certain temperature correlations which reversed in the modern period?
(2) Should Mann and friends have figured out the twist from the blogosphere discussion, the M&M comment, and Kaufman's correction, rather than interpreting "upside down" literally and not understanding it, as their reply and various defenses since suggest?
(3) Is it possible, despite the one figure showing no substantive difference to the reconstruction, that use of Tiljander did make a material difference to some of the conclusions of Mann 2008 (and apparently later papers using the same data)?
If the answer to these 3 questions is "Yes", then that adds up to a somewhat damning allegation against Mann's work on this. Evidently he's made some minor errors in the past, if those are true then I agree this one was a bit worse.
So, I'll spend a bit of time looking into these; references and help welcome in the comments, thanks.