IPCC Third Assessment Report

[6][7] "Robust findings" of the Synthesis Report include: The IPCC was established in 1988 by the United Nations Environment Programme (UNEP) and the UN's World Meteorological Organization (WMO) "... to assess scientific, technical and socio-economic information relevant for the understanding of climate change, its potential impacts and options for adaptation and mitigation.

[24] For example, a joint statement of support was issued in May 2001 by the science academies of Australia, Belgium, Brazil, Canada, the Caribbean, China, France, Germany, India, Indonesia, Ireland, Italy, Malaysia, New Zealand, Sweden and the UK.

It states: "We recognise the IPCC as the world's most reliable source of information on climate change and its causes, and we endorse its method of achieving consensus.

"[24] In 2001, the executive branch of the US federal government asked the US National Research Council (US NRC, 2001)[25] to produce an assessment of climate change science.

US NRC (2001)[28] also state: The most valuable contribution U.S. scientists can make is to continually question basic assumptions and conclusions, promote clear and careful appraisal and presentation of the uncertainties about climate change as well as those areas in which science is leading to robust conclusions, and work toward a significant improvement in the ability to project the future.In 2001, 16 national science academies issued a joint statement on climate change.

In 2001, the US National Research Council (US NRC)[34] produced a report that assessed Working Group I's (WGI) contribution to the TAR.

[40] Trenberth has stated that during the drafting of the WGI SPM, some government delegations attempted to "blunt, and perhaps obfuscate, the messages in the report".

A report by the UK Parliament's House of Lords Economic Affairs Select Committee (EAC, 2005)[44] contains criticisms of the IPCC's work, including the "SRES" greenhouse gas emissions scenarios,[45] which are used in the TAR.

The Economic Affairs Select Committee is made up of members of the House of Lords, which scrutinizes and votes on government legislation.

[50] The MBH99 finding was supported by cited reconstructions by Jones et al. 1998, Pollack, Huang & Shen 1998, Crowley & Lowery 2000 and Briffa 2000, using differing data and methods.

[52] These studies were widely presented as demonstrating that the current warming period is exceptional in comparison to temperatures between 1000 and 1900, and the MBH99 based graph featured in publicity.

Even at the draft stage, this finding was disputed by contrarians: in May 2000 Fred Singer's Science and Environmental Policy Project held a press event on Capitol Hill, Washington, D.C., featuring comments on the graph Wibjörn Karlén and Singer argued against the graph at a United States Senate Committee on Commerce, Science and Transportation hearing on 18 July 2000.

[55] On 23 June 2005, Rep. Joe Barton, chairman of the House Committee on Energy and Commerce, wrote joint letters with Ed Whitfield, chairman of the Subcommittee on Oversight and Investigations, demanding full records on climate research, as well as personal information about their finances and careers, from Mann, Bradley and Hughes.

[citation needed] The National Research Council's report agreed that there were some statistical failings, but these had little effect on the graph, which was generally correct.

[57] An example of scientific research which suggests that previous estimates by the IPCC, far from overstating dangers and risks, have actually understated them is a study on projected rises in sea levels.

[58][59] Greg Holland from the National Center for Atmospheric Research, who reviewed a multi-meter sea level rise study by Jim Hansen, noted "There is no doubt that the sea level rise, within the IPCC, is a very conservative number, so the truth lies somewhere between IPCC and Jim.

IPCC WG1 co-chair Sir John T. Houghton showing the IPCC fig. 2.20 hockey stick graph at a climate conference in 2005
The original northern hemisphere hockey stick graph of Mann, Bradley & Hughes 1999 , smoothed curve shown in blue with its uncertainty range in light blue, overlaid with green dots showing the 30-year global average of the PAGES 2k Consortium 2013 reconstruction. The red curve shows measured global mean temperature, according to HadCRUT 4 data from 1850 to 2013.
Figure 3.20 on p. 175 of the IPCC Second Assessment Report
Comparison of MBH99 40-year average from proxy records, as used in IPCC TAR 2001 (blue), with IPCC 1990 schematic Figure 7.1.c (red) [based on Lamb 1965 extrapolating from central England temperatures and other historical records]; central England temperatures to 2007 shown from Jones et al. 2009 (green dashed line). [ 50 ] Also shown, Moberg et al. 2005 low frequency signal (black).