Magazine article Issues in Science and Technology , Vol. 23, No. 1
Continuing challenges to studies by climate scientist Michael Mann and colleagues by climate change skeptics in the House, led by Rep. Joe Barton (R-TX), chairman of the House Energy and Commerce Committee, appear to have fizzled after the release of a June 22 National Research Council (NRC) report that supported Mann's conclusions. Barton, however, has vowed to keep his committee actively involved in the climate change debate and has requested two new studies on research practices in the field.
Despite the NRC report, which concluded that Mann's statistical procedures, although not optimal, did not unduly distort his conclusions, the Energy and Commerce Committee's Subcommittee on Oversight and Investigations held two hearings in July, each lasting more than four hours. They focused on the statistical methods used in the 1998 and 1999 studies by Mann, Raymond Bradley, and Malcolm Hughes. Barton argued that the use of the studies in the 2001 Intergovernmental Panel on Climate Change report justified a detailed examination of the methods involved. "A lot of people basically used that report to come to the conclusion that global warming was a fact," he said.
Mann, Bradley, and Hughes reconstructed temperatures of the past 1,000 years. Because direct temperature measurements date back only 150 years, the researchers used proxy measurements, including tree ring growth, coral reef growth, and ice core samples. They produced a graph that looked like a hockey stick: a long period of relatively stable temperatures, then a dramatic spike upward in recent decades. Critics of the research, however, argued that the hockey stick shape could simply be the artifact of incorrect statistical techniques, and climate change skeptics seized on the graph as a proxy for everything they believe is wrong about climate change research.
During the a July 19 hearing, Edward Wegman, a George Mason University statistician, testified on behalf of the mathematicians who reviewed the Mann papers at the request of Rep. Barton. He stated, "The controversy of the [Mann] methods lies in that the proxies are incorrectly centered on the mean of the period 1902-1995, rather than on the whole time period." He explained that these statistical procedures were capable of incorrectly creating a hockey stick shaped graph. …