The Wegman Report (officially called the Ad Hoc Committee Report on the 'Hockey Stick' Global Climate Reconstruction) was prepared in 2006 by three statisticians led by Edward Wegman at the request of Rep. Joe Barton of the United States House Committee on Energy and Commerce to validate criticisms made by Stephen McIntyre and Ross McKitrick of reconstructions of the temperature record of the past 1000 years, in particular the reconstructions by Mann, Bradley and Hughes of what had been dubbed the hockey stick graph.
Background
Investigations of paleoclimate date back to the 1930s, but quantitative methods were slow to come into use. In the 1960s, Hubert Lamb generalised from historical documents and temperature records of central England to propose a Medieval Warm Period from around 900 to 1300, followed by Little Ice Age. This was the basis of a "schematic diagram" featured in the IPCC First Assessment Report beside cautions that the medieval warming might not have been global. The use of proxy indicators to get quantitative estimates of the temperature record of past centuries was developed, and introduced the "Composite Plus Scaling" (CPS) method used by most later large scale reconstructions. Their study was featured in the IPCC Second Assessment Report, and in the United States House Committee on Science its findings were disputed by Pat Michaels.
In 1998 Michael E. Mann, Raymond S. Bradley and Malcolm K. Hughes developed new statistical techniques to produce (MBH98), which showed global patterns of annual surface temperature, and included a graph of average hemispheric temperatures back to 1400 with shading emphasising that uncertainties (to two standard error limits) were much greater in earlier centuries. independently produced a CPS reconstruction extending back for a thousand years, and (MBH99) used the MBH98 methodology to extend their study back to 1000. The term hockey stick was used by the climatologist Jerry Mahlman to describe the pattern this showed, envisaging a graph that is relatively flat to 1900 as forming an ice hockey stick's "shaft", followed by a sharp increase corresponding to the "blade". A version of this graph was featured prominently in the 2001 IPCC Third Assessment Report (TAR), which also drew on Jones et al. 1998 and three other reconstructions to support the conclusion that, in the Northern Hemisphere, the 1990s was likely to have been the warmest decade and 1998 the warmest year during the past 1,000 years. The graph was featured in publicity, and became a focus of dispute for those opposed to the strengthening scientific consensus that late 20th century warmth was exceptional.
In 2003, as lobbying over the 1997 Kyoto Protocol intensified, Soon and Baliunas published a paper claiming greater medieval warmth, and on this basis the Bush administration chief of staff Philip Cooney deleted references to climate reconstructions from the first Environmental Protection Agency Report on the Environment. The paper was quickly dismissed by scientists in the Soon and Baliunas controversy, but on July 28, Republican Jim Inhofe spoke in the Senate speech citing Soon and Baliunas to claim "that man-made global warming is the greatest hoax ever perpetrated on the American people".