Thus far in this series of posts, we’ve established Michael Mann’s original hockey stick was dependent entirely upon a small amount of data. We’ve also established Mann knew this. The obvious question is, why didn’t anyone else? Shouldn’t basic tests have caught this problem?

The answer is, they did. Mann just covered it up.



Mann performed several statistical tests to check the validity of his temperature reconstruction. His tests gave scores between -1 and 1. The higher the value, the better the score. The better the score, the better his reconstruction did on the test.

You can view it like a test in school. A score of .76 is equal to a 76%. On a difficult test, that could be a good score. On the other hand, a score of .00003 (.003%) could never be a good score. And if you got a negative score, that would probably indicate a problem.

Now then, you’ll recall Michael Mann did his reconstruction in steps because different data was available for different periods. He did tests for each of those steps. These are the results of some of those tests:

You’ll notice the values in the left column are respectable. Those are the scores done for the calibration period. Obviously, scores during calibration mean little. The scores that matter are the next ones, the verification scores. They tell us whether or not Mann’s tests verify his work’s quality.

They don’t. Prior to 1750, Mann’s reconstruction doesn’t score above a 2%. That’s terrible. Anyone who heard about that result would have been troubled. That’s why Mann didn’t publish it. He didn’t mention it in his paper, and while he published the results of many tests he perfomed, he intentionally left that test out.

Pretty bad, right? It gets worse. Michael Mann was made a lead author on the paleoclimatology (study of past climates) chapter in the Intergovernmental Panel on Climate Change’s 2001 report on global warming. This report was the most important publication on global warming, being seen by every government and media organization in the world. The chapter Mann was responsible for says:

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 his reconstruction failed a cross-validation test he performed. He hid that fact. He then described his work as having “significant skill in independent cross-validation tests” in a major, intergovernmental report, which gave his work prominent display and made him known worldwide.

Had he not covered up the unfavorable results of his tests, that likely wouldn’t have been possible. It’s likely he’d never have become remotely famous, become a central figure to the global warming debate or been able to write a popular book and make lots of money off it. In short, if he had disclosed all the results of the tests he performed, he’d have probably been a nobody for the rest of his life.

Stay tuned for the next post. In it, I’ll discuss how the attempts to cover this up continued for over a decade.