First off, Mann's own data refutes his work. The reason he had to do the "trick" was to ignore that temperatures since 1960 have been going the wrong way according to his tree ring data:
Message 26335773
Tree-ring anomaly mystifies scientists
By Eloise Gibson
4:00 AM Monday Feb 22, 2010
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Scientists are chipping away at a glitch in the climate records, hoping to explain why tree-rings that track temperature changes successfully until the 1950s suddenly veer off.
Researchers believe global warming or other man-made changes may be to blame for an unexplained slowdown in growth of some of the ancient trees used to track temperatures back more than 1000 years.
Although tree-rings records appear to be a good measure of temperature changes most of the time, nobody knows why the usual techniques used with them fail from the 1960s.
The divergence between tree-rings and real, thermometer measurements in the past 50 years has been used to attack temperature reconstructions used by the International Panel on Climate Change and others - particularly since emails from the University of East Anglia's climatic research unit revealed unit head Phil Jones discussing "hiding the decline" in tree-ring temperatures.
It turned out the email referred to a common technique of replacing tree-ring records with direct thermometer measurements from 1961, when tree-rings show temperature declining while real measurements from thermometers do not.
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Message 26380716
.... There may be something unprecedented going on in temperature, but the only piece of empirical evidence that actually says so—yes, the only one—is the hockey stick.
And the hockey stick is wrong. The emails that were leaked from the University of East Anglia late last year are not proof of this; they are merely the icing on the lake, proof that some of the scientists closest to the hockey stick knew all along that it was problematic. Andrew Montford’s book, despite its subtitle, is not about the emails, which are tagged on as a last chapter. It is instead built around the long, lonely struggle of one man— Stephen McIntyre—to understand how the hockey stick was made, with what data and what programs.
A retired mining entrepreneur with a mathematical bent, McIntyre asked the senior author of the hockey stick graph, Michael Mann, for the data and the programs in 2003, so he could check it himself. This was five years after the graph had been published, but Mann had never been asked for them before. McIntyre quickly found errors: mislocated series, infilled gaps, truncated records, old data extrapolated forwards where new was available, and so on.
Not all the data showed a 20th century uptick either. In fact just 20 series out of 159 did, and these were nearly all based on tree rings. In some cases, the same tree ring sets had been used in different series. In the end the entire graph got its shape from a few bristlecone and foxtail pines in the western United States; a messy tree-ring data set from the Gaspé Peninsula in Canada; another Canadian set that had been truncated 17 years too early called, splendidly, Twisted Tree Heartrot Hill; and a superseded series from Siberian larch trees. There were problems with all these series: for example, the bristlecone pines were probably growing faster in the 20th century because of more carbon dioxide in the air, or recovery after “strip bark” damage, not because of temperature change.
This was bad enough; worse was to come. Mann soon stopped cooperating, yet, after a long struggle, McIntyre found out enough about Mann’s programs to work out what he had done. The result was shocking. He had standardised the data by “short-centering” them—essentially subtracting them from a 20th century average rather than an average of the whole period. This meant that the principal component analysis “mined” the data for anything with a 20th century uptick, and gave it vastly more weight than data indicating, say, a medieval warm spell.
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If this had been a drug trial done by a pharmaceutical company, the scientific journals, the learned academies and the press would have soon have rushed to discredit it—and rightly so. Instead, they did not want to know. Nature magazine, which had published the original study, went out of its way to close its ears to McIntyre’s criticisms, even though they were upheld by the reviewers it appointed. So did the National Academy of Sciences in the US, even when two reports commissioned by Congress upheld McIntyre. So, of course, did the IPCC, which tied itself in knots changing its deadlines so it could include flawed references to refutations of McIntyre while ignoring complaints that it had misquoted him.
The IPCC has taken refuge in saying that other recent studies confirm the hockey stick but, if you take those studies apart, the same old bad data sets keep popping out: bristlecone pines and all. A new Siberian data series from a place called Yamal showed a lovely hockey stick but, after ten years of asking, McIntyre finally got hold of the data last autumn and found that it relied heavily on just one of just twelve trees, when far larger samples from the same area were available showing no uptick. Another series from Finnish lake sediments also showed a gorgeous hockey stick, but only if used upside down. McIntyre just keeps on exposing scandal after scandal in the way these data were analysed and presented.
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Lots more has been posted on this thread showing Mann's conclusion that today's temperatures are higher than the last 1000 years and that the medieval warm period didn't really exist is wrong. Here's merely one of them:
Message 26518418
Trees of Medieval Warming Period Found Under Swiss Glacier: Scientists Conclude MWP Warmer Than Present
Read here. Map here. Studying the fossil remains of trees located under a Swiss glacier, scientists verify that the treeline was some 200 meters higher than the current one. This indicates that Medieval Warming Period (MWP) was not only warmer, but lasted an extended period.
"Based on radiocarbon dating of the fossil wood remains of eight larch fragments found one meter beneath the surface of the ground at the base of the front of the Piancabella rock glacier,... the authors determined that the wood was formed somewhere between AD 1040 and 1280 ...Then, based on this information and "geomorphological, climatological and geophysical observations," they inferred that "the treeline in the Medieval Warm Period was about 200 meters higher than in the middle of the 20th century, which corresponds to a mean summer temperature as much as 1.2°C warmer than in AD 1950."...adjusting for warming between 1950 and the present, we calculate that the MWP was about 0.5°C warmer than the peak warmth of the CWP."
c3headlines.com
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