Michael Mann Committed Fraud

I’m not sure there’s any argument to say Michael Mann’s work isn’t fraudulent. I tend not to do it myself because I don’t think it’s necessary, but it’s certainly a defensible position. Consider:

1) When Michael Mann published his 1998 temperature reconstruction, he said:

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.

This statement was untrue. Mann’s results were entirely dependent upon a relatively small amount of tree ring data. Not only do we know this now, we know Michael Mann became aware of it shortly after publishing his paper. On page 51 of his book, Mann tells us 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.

It’s not clear how Mann managed to make the false claim in his original paper, but he was obligated to inform people of its falsity. We could perhaps forgive not correcting an earlier mistake except Mann went on to publish his 1999 paper, extending the 1998 reconstruction back another 400 years. By building upon his 1998 paper while knowing it made false claims about his results, Mann committed fraud.

Anyone reading MBH99 would be directed to MBH98 for information about the reconstruction. MBH98 contained important claims about his results Mann knew to be false (at the time he published MBH99). It is perfectly reasonable to say by directing people to information about his results he knew to be false, Mann committed fraud.

2) Michael Mann was responsible for text in the IPCC TAR which said:

Mann et al. (1998) reconstructed global patterns of annual surface temperature several centuries back in time. They calibrated a combined terrestrial (tree ring, ice core and historical documentary indicator) and marine (coral) multi-proxy climate network against dominant patterns of 20th century global surface temperature. Averaging the reconstructed temperature patterns over the far more data-rich Northern Hemisphere half of the global domain, they estimated the Northern Hemisphere mean temperature back to AD 1400, a reconstruction which had significant skill in independent cross-validation tests.

Mann knew perfectly well his reconstruction failed r2 verification, a test he used multiple times in MBH98. By saying his reconstruction “had significant skill in independent cross-validation tests” while hiding the fact his reconstruction failed one of his own cross-validation tests, Mann committed fraud. That was fraud even if we ignore the fact Mann went on to lie about it and repeatedly try to cover up the fact he did calculate those scores.

We don’t have to call what Michael Mann did fraud if we don’t feel like focusing on the word, but if we are going to focus on the word, what Mann did was fraud.

I originally wrote this as comment at Judith Curry's blog. I thought it made for a good overview so I've decided to post it here as well. It's worth noting the numbered points are both links to previous posts which give more detail.


  1. I agree with everything you say here.

    However, the Mann vs. Steyn trial will recast the issue of fraud into the issue of whether his graph is fraudulent.

    Most of what you say here has direct bearing on the issue of the graph being fraudulent.

    But whether or not Mann is a fraud is not the issue in the defamation trial.

  2. RickA, that's why I titled the post the way I did. I didn't specify the fraud was in the graph, but that's because long titles suck.

    To be clear though, I say Michael Mann is a fraud who committed fraud when he produced a fraudulent graph.

    I just don't say it much because the word "fraud" tends to be a distraction.

  3. Brandon, are you familiar with Mann et al 2000, a re-working of MBH98 https://www.ncdc.noaa.gov/paleo/ei/ei_cover.html. See the section https://www.ncdc.noaa.gov/paleo/ei/ei_nodendro.html where Mann stated:
    "MBH98 found through statistical proxy network sensitivity estimates that skillful NH reconstructions were possible without using any dendroclimatic data, with results that were quite similar to those shown by MBH98 based on the full multiproxy network (with dendroclimatic indicators) if no dendroclimatic indicators were used at all. We show this below for annual-mean reconstructions of Northern Hemisphere mean temperatures....Whether we use all data, exclude tree rings, or base a reconstruction only on tree rings, has no significant effect on the form of the reconstruction for the period in question. This is most probably a result of the combination of our unique reconstruction strategy with the careful selection of the natural archives according to clear a priori criteria. Furthermore, we note that Jones et al. (1998), get similar results for the recent changes using an almost completely different tree-ring network based on wood density from high latitude trees. These comparisons show no evidence that the possible biases inherent to tree-ring (alone) based studies impair in any significant way the multiproxy-based temperature pattern reconstructions discussed here."

    Mann showed an AD1750 where the dendro/nodendro effect was not large, but did not report results for AD1400 step where the effect is very pronounced.

  4. Yup. It's even worse when you realize the link to that section is described with text saying:

    For example, the NH annual mean temperature series appears to exhibit skill back to at least AD 1400 (and has now been extended back to AD 1000 by Mann et al (1999), albeit with expanded uncertainty estimates). We have also verified that possible low-frequency bias due to non-climatic influences on dendroclimatic (tree-ring) indicators is not problematic in our temperature reconstructions.

    Which implies their claims cover their results all the way back to 1000 AD.

  5. By the way, your mention of Mann 2000 reminded me of another paper he (co) authored that year (Delworth and Mann 2000). I remember it because it says:

    Because the paleoreconstruction approach of MBH98 does not build any a priori frequency domain information from the twentieth century calibration period into the pre-1900 century reconstructions, the latter indications of a multidecadal climate signal are truly independent from any inferences from the instrumental record

    This statement always struck me as odd. As I understand it, frequency domain information from the calibration period is effectively removed from the pre-calibration period by the process MBH used. That's the nature of the screening fallacy. The calibration period's variance is kept constant while the pre-calibration period's variance is deflated. The frequency domain information of the calibration period determines (in part) what frequency domain information of the pre-calibration period is lost. That means you are doing what this paper claims doesn't happen, just with an inverse relationship.

    I can't tell if I'm missing some nuance which justifies the paper's claim or if it really is as wrong as it seems.

  6. Brandon, from everything I've read this will never get to trial.
    Mark will end up settling out of court.
    I just can't figure how much money over his attorney fees and other costs
    Mark will need to recover for this interruption to his life.
    My guess is Mikie ain't got that much.

  7. mikerstin, why do you think this would go to settlement? Mark Steyn has said he wants a trial. I can't see any reason he'd settle unless the settlement favored him. It seems more like he'd make Michael Mann settle (dropping his countersuit).

    Steyn has repeatedly said he wants a trial. Michael Mann has barely spoken in public about this, and his legal actions have involved a lot of stalling. I'd guess Mann is the one less anxious for this to ocntinue.

  8. Brandon

    Here is borehole data published by the University of Michigan


    It clearly shows the temperature has been rising since 1700. Presumably certain proxies show different results to other proxies and whether the overall results show a rise or fall will depend on the type of proxies used and their location.

    Certainly my own reconstructions using thousands of actual observed records show results very different to Dr Mann's reconstruction whereby his steady state climate version for the last 1000 years is at odds with the considerable fluctuation the pre instrumental records back to 1100 demonstrate, with several very warm periods roughly equivalent to ours in virtually every century except the 17th and the 15th.


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