Key Global Warming Study Found Flawed
November 5, 2003
One of the most influential scientific studies supporting the case for man-made global warming has just been publicly condemned for “poor data handling, selective use of sources, reliance on obsolete versions of source data and erroneous statistical calculations.”
The disputed study’s authors, led by Dr. Michael Mann of the University of Virginia, claimed the historically documented Medieval Climate Warming and Little Ice Age never happened. Mann’s temperature history for the Northern Hemisphere (reconstructed mainly from tree rings) shows readings trending down very slightly and constantly from 1000 AD to 1900-and then zooming upward in the 20th century so sharply that the study became famous as “the hockey stick.”
The Mann study’s conclusion, that today’s temperatures are the warmest in 1000 years, was published prominently in the 2001 report of the UN Intergovernmental Panel on Climate Change, and in the Clinton Administration’s National Assessment of the Potential Consequences of Climate Variability and Change. It was also cited by the Canadian government in a national voter mailing supporting Canada’s signing of the Kyoto treaty to control greenhouse gas emissions.
Now, two Canadians say they’ve found a host of errors in the research. When the errors are corrected, they say Mann’s own methodology and intended data sources show Medieval temperatures warmer than today’s and the modern climate looking unexceptional.
The Canadians’ critique has just been published the peer-reviewed journal Energy and Environment, refereed by the World Data Center for Paleoclimatology.
Mann’s original study, “Global-Scale Temperature Patterns and Climate Forcing Over the Past Six Centuries,” was published in the journal Nature in 1998. Mann and his team used tree rings, ice cores, and a variety of other temperature proxies to reconstruct Northern Hemisphere temperatures back to the year 1400 (and later, back to the year 1000).
The critique of the Mann paper is authored by a Canadian economist, Dr. Ross McKittrick of the University of Guelph (and the Fraser Institute); along with Steven McIntyre, a businessman with a background in mathematics and accounting. The two say they had no outside funding for their analysis, and that they have created an audit trail allowing third parties to verify their findings for themselves.
McIntyre says the recent corporate accounting scandals taught him that “when big investments are at stake, due diligence requires relentless testing and independent verification of the data by all parties. Since governments around the world (including Canada) are making some of the most expensive policy decisions ever, based on the uncritical acceptance of the IPCC report, an independent review seemed in order.”
The two Canadians say that Mann and his team members had so much difficulty producing the data that they doubt anyone else had ever asked to see it. The journal Nature does its own vetting of papers, and has said nothing about its Mann reviewers. However, Mann was a principle chapter author for the IPCC report, and may not have done any “due diligence” review of his own study.
As an example of selective data use, McKittrick and McIntyre point out that Mann’s Central England Temperature series is cut off at the year 1730, although the data go back to 1659. The cutoff removed a major late-17th century cold period. The Central Europe temperature series was cut off at 1550, rather than going back to the available 1525, removing the warmest temperatures in the series.
McKittrick and McIntyre say the Mann team also extrapolated, interpolated, or copied values into data sets that were neither required nor statistically justified, and made major calculation errors.
McKittrick and McIntyre’s critique of the Mann “hockey stick” paper is a global policy bombshell. The IPCC has touted a “consensus” among scientists on global warming. However, if the Mann paper was the best evidence the IPCC and the Clinton White House could marshal to support the theory of man-made planetary warming, then its deconstruction throws the global warming debate wide open again.
This, again, pits real-world data showing past global warming/cooling cycles (historic manuscripts, tree rings, ice cores, iceberg debris on the floor of the Atlantic, etc.) against a computer-modeled theory that mankind’s auto exhausts and smokestack are somehow more powerful than the sun.
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