David Legates, the director of the Center for Climatic Research at the University of Delaware, in an article published by the libertarian-leaning policy group National Center for Policy Analysis, casts doubt on one of the favorite proofs of human-induced global warming. Excerpts from the press release:
At issue is what is commonly referred to as the "hockey stick"—a widely circulated image that depicts a 700-year period where temperatures remained relatively constant followed by the last 100-plus years where temperatures have shot upwards. The "hockey stick," created by researchers Michael Mann of the University of Virginia and Phil Jones of the University of East Anglia, is used by the IPCC [United Nations' Intergovernmental Panel on Climate Change ]and environmental activists as proof of human-induced global warming.
The NCPA report cites findings from five independent research groups that have uncovered serious problems with Mann and Jones' methodology and calculations, which call into question any of its conclusions. For example:
— Several researchers found Mann and Jones made errors in the collection and use of varying data from multiple sources, used obsolete data, made incorrect calculations, associated data sets with incorrect geographical locations, inappropriately eliminated specific proxy records that they felt were inaccurate and employed statistical methods that removed long time period trends, such as the widely recognized Medieval Warm Period (about A.D. 800 to 1400) and the Little Ice Age (A.D. 1600 to 1850).
— Mann published a retraction in the June 2004 issue of Geophysical Research, in which he admits underestimating the temperature variations indicated by the proxy data by more than one-third since 1400, which accounts for why he missed the Little Ice Age. Strangely, Mann still argues this considerable error doesn't impact his conclusions.
— Further, Legates found the "blade" (or sudden rise in temperature) of Mann's hockey stick could not be reproduced using common statistical techniques, or even employing the same techniques as Mann and Jones.
Legates' complete essay here.