In the 1960s, Hubert Lamb generalised from historical documents and temperature records of central England to propose a Medieval Warm Period from around 900 to 1300, followed by Little Ice Age.
In 1998 Michael E. Mann, Raymond S. Bradley and Malcolm K. Hughes developed new statistical techniques to produce Mann, Bradley & Hughes 1998 (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.
[8] 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.
In 2004 Hans von Storch published criticism of the statistical techniques as tending to underplay variations in earlier parts of the graph, though this was disputed and he later accepted that the effect was very small.
In June 2005 Rep. Joe Barton launched what Sherwood Boehlert, chairman of the House Science Committee, called a "misguided and illegitimate investigation" into the data, methods and personal information of Mann, Bradley and Hughes.
At Boehlert's request a panel of scientists convened by the National Research Council was set up, which reported in 2006 supporting Mann's findings with some qualifications, including agreeing that there were some statistical failings but these had little effect on the result.
[12] Barton and U.S. Rep. Ed Whitfield requested Edward Wegman to set up a team of statisticians to investigate, and they supported McIntyre and McKitrick's view that there were statistical failings, although they did not quantify whether there was any significant effect.
The letters were sent to the IPCC Chairman Rajendra Pachauri, National Science Foundation Director Arden Bement, and to the three scientists Mann, Bradley and Hughes.
Thomas Crowley argued that the aim was intimidation of climate researchers in general, and Bradley thought the letters were intended to damage confidence in the IPCC during preparation of its next report.
Barton was given support by global warming denier Myron Ebell of the Competitive Enterprise Institute, who said "We've always wanted to get the science on trial ... we would like to figure out a way to get this into a court of law", and "this could work".
[26] The report provided a summary and an overview, followed by 11 technical chapters covering the instrumental and proxy records, statistical procedures, paleoclimate models, and the synthesis of large scale temperature reconstructions with an assessment of the "strengths, limitations, and prospects for improvement" in techniques used.
This conclusion has subsequently been supported by an array of evidence that includes both additional large-scale surface temperature reconstructions and pronounced changes in a variety of local proxy indicators".
It said "Based on the analyses presented in the original papers by Mann et al. and this newer supporting evidence, the committee finds it plausible that the Northern Hemisphere was warmer during the last few decades of the 20th century than during any comparable period over the preceding millennium", though there were substantial uncertainties before about 1600.
"[29][32] Various criticisms of the MBH statistical methods were discussed in Chapter 11 in the context of more recent research which explored ways of addressing these problems, and showed greater amplitude of temperature variations over 1000 to 2000 years.
"[32] Barton dismissed the offer of a joint investigation with an independent panel appointed by the U.S. National Academy of Sciences (NAS),[16] and on 1 September 2005 statistician Edward Wegman was contacted about giving testimony.
Bardon's staffer then met Wegman, and explained that the United States House Energy Subcommittee on Oversight and Investigations wanted expert opinion on the validity of criticisms of the Mann, Bradley & Hughes 1999 reconstruction.
[38] Lacking Barton's agreement, Boehlert's Science Committee independently requested the NAS in November to commission the National Research Council Report.
[39] In an editorial dated 14 July 2006, the Wall Street Journal announced that a report commissioned by the Energy and Commerce Committee was due to be released that day.
They produced a social network analysis to imply problems of peer review not being independent, suggested that climatologists worked in isolation from statisticians, and alleged that there was inadequate sharing of methods and data.
A 250-page study by computer scientist John Mashey, posted on the "Deep Climate" website, claims that 35 of the 91 pages in the Wegman Report were plagiarized, and "often injected with errors, bias and changes of meaning."
[73] Reviews by outside experts contacted by USA Today found plagiarism from textbooks which was obvious and inappropriate; the social network analysis section had also been partly copied from Wikipedia.
"[75] After computer scientist Ted Kirkpatrick of the Simon Fraser University read the "Deep Climate" website allegations of plagiarism, he made a formal complaint to the journal.
Network analysis expert Kathleen Carley described it as an opinion piece which speculated that collaboration between scientists "leads to peer review abuse.
"[38] A Nature editorial commented on the implication that the plagiarised material in the retracted paper was likely to also be present in the earlier "infamous" Wegman Report, including allegations against Mann and his co-authors which had frequently been cited by climate-change deniers.
The George Mason University's policies indicated that its initial inquiry should have been completed within 12 weeks of the original complaint, and although 14 months had passed without this being resolved, there were loopholes for extensions.