The hockey stick theory refers to a study conducted by Dr. Michael Mann of the Department of Geosciences at the University of Massachusetts and his associates Raymond S. Bradley and Malcolm K. Hughes. Using tree-ring proxy data, he reconstructed global climate for the past 1,000 years. The resulting graph resembles a hockey stick: The majority of the time period represents little change in temperature and would-be the "shaft" of the stick: a sharp upward rise in the 20th-century portion of the graph illustrates sudden temperature rise and constitutes the stick's "blade." When constructing the graph, Mann used tree-ring data for the pre-1900 portion of the graph and used surface temperature records for the 20th-century portion. The visual effect was very dramatic, illustrating the fact that the 20th century's climate was rising out of control. The year 1998 was especially problematic. This year—which also suffered an extreme El Niño event—was noted as the "warmest year of the millennium." A problem with this, pointed out later, was that data collected via satellite did not exactly correlate to Mann's. In the meantime, this single paleoclimate study became the "foundation" of the global warming theory. The hockey stick graph was adopted by the Intergovernmental Panel on Climate Change (IPCC) and used as a strong basis for evidence as to the urgency of recognizing global warming and the need to take action immediately.
In 2003, Stephen Mclntyre, a Canadian mineral exploration consultant, and Ross McKitrick, an economist at the University of Guelph, in Ontario, challenged Mann's theory, accusing him of using inappropriate data, methodology, and statistical methods. McIntyre and McKit-rick charged Mann with creating the hockey stick with a "collation of errors, incorrect calculation, and other quality control defects." They claimed that the wrong places, the wrong dates, and the wrong numbers were jumbled together to produce the results Mann wanted: proof that the Industrial Revolution had started global warming. Further, they accused Mann of using only 12 sets of proxy data, obtained only from the Northern Hemisphere. He then extrapolated that data to reach the conclusion that global temperatures remained stable and then dramatically increased in the 20th century.
Shortly thereafter, Mann and his associates recognized some slight data preparation errors that had been made and printed a correction. The hockey stick graph still existed, however, so even with minor errors in the original statistical tests, it was not off far enough to change the trend of the upswing in temperature. But the controversy over global warming science had only just begun.
The dispute led to an investigation by the U.S. Congress at the request of Representative Joe Barton of Texas. A panel of scientists convened by the National Research Council (NRC) of the National Academy of Sciences and chaired by Edward Wegman, a statistician, stirred up the scientific community and the issue became embroiled in hot debate.
After many studies and most people's minds made up, there is still a lot of controversy around global warming. The basic results currently stand that although McIntyre and McKitrick raised many sensitive issues, their claims have been rebutted in detail by many other independent climatologists around the world. Meanwhile, Mclntyre and McKitrick are still objecting. The majority of climate scientists worldwide support the hockey stick theory.
Hans von Storch, the director of the Institute for Coastal Research of the GKSS Research Center in Germany, agrees with McIntyre and McKitrick that Mann's methodology was not completely sound, but he also added that correcting it would not alter the overall results: The 20th century was still warmer, as the hockey stick showed.
The bottom line with this study, however, is that the controversy is based on a single paleoclimatic study that took place eight years ago. Since then, dozens of temperature reconstructions have been created in order to better understand climate change worldwide. Although many of these studies do not show the shaft part of the hockey stick as straight (there are a few ups and down in it), the same message is very clear: The 20th century is noticeably warmer than the rest of the millennium, and the 1990s were likely warmer than any other time in that period. This falls in line with exactly what Mann has said all along, as well as the IPCC and thousands of scientists worldwide.
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