NCPA - National Center for Policy Analysis


July 12, 2004

The United Nations' Intergovernmental Panel on Climate Change (IPCC) claims that human activities are responsible for nearly all earth's recorded warming during the past two centuries. A widely circulated image that dramatically depicts these temperature trends resembles a hockey stick with three distinct parts: a flat "shaft" extending from A.D. 200 to 1900, a "blade" shooting up from A.D. 1900 to 2002, and a range of uncertainty in temperature estimates that envelops the shaft like a "sheath."

Michael Mann of the University of Virginia and Phil Jones of the University of East Anglia updated the influential reconstruction of (Geophysical Research Letters, 2003) used in the IPCC's third assessment of climate change. However, researchers are calling into question all three components of the "hockey stick," says David R. Legates is Director of the Center for Climatic Research at the University of Delaware. For instance:

  • In such widely disparate regions as Argentina, Chile, southern Peru, southern Africa and northern China, records indicate a marked warming at the beginning of the last millennium followed by extreme cold during the middle centuries.
  • Historical proxies for temperature -- such as tree rings, ice cores and bore holes -- in New Zealand, Australia and California also confirm widespread, significant warming and cooling trends.
  • According to the IPCC (2001) and many other published sources, the earth warmed only 0.6°C (1°F) during the 20th century; however, that contrasts sharply with Mann and Jones' most recent reconstruction, which shows warming over the last century of 0.95°C (1.5°F) -- a temperature rise more than 50 percent larger than the IPCC claims.

Mann's research does not fit with the overwhelming evidence of widespread global warming and cooling within the previous two millennia, making his assertions -- and, consequently, the IPCC -- open to question, says Legates.

Source: David R. Legates, "Breaking the Hockey Stick," Brief Analysis No. 478, July 12, 2004

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