Editing IPCC Third Assessment Report (section)

===Discussion of the "hockey stick" graph===
{{Main|Hockey stick graph (global temperature)}}

[[File:T comp 61-90.pdf|thumb|right|The original northern hemisphere hockey stick graph of {{harvnb|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 {{harvnb|PAGES 2k Consortium|2013}} reconstruction. The red curve shows measured global mean temperature, according to [[HadCRUT]]4 data from 1850 to 2013.]]
[[File:IPCC 1996 SAR Figure 3.20.png|thumb|right|'''Figure 3.20''' on p. 175 of the [[IPCC Second Assessment Report]]]]
[[File:Ipcc7.1-mann-moberg-manley.png|thumb|right|Comparison of MBH99 40-year average from proxy records, as used in IPCC TAR 2001 (blue), with [[IPCC First Assessment Report|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).<ref name="Jones 09">{{Cite journal|last1=Jones|first1=P. D.|last2=Briffa|first2=K. R.|last3=Osborn|first3=T. J.|last4=Lough|first4=J. M.|last5=Van Ommen|first5=T. D.|last6=Vinther|first6=B. M.|last7=Luterbacher|first7=J.|last8=Wahl|first8=E. R.|last9=Zwiers|first9=F. W.|last10=Mann|first10=M. E.|last11=Schmidt|first11=G. A.|year=2009|title=High-resolution palaeoclimatology of the last millennium: a review of current status and future prospects|url=http://shadow.eas.gatech.edu/~kcobb/jones09.pdf|journal=The Holocene|volume=19|issue=1|pages=3–49|bibcode=2009Holoc..19....3J|doi=10.1177/0959683608098952|first30=E.|last30=Xoplaki|first29=E.|last29=Wolff|last24=Riedwyl|first28=H.|last28=Wanner|first27=R.|last27=Villalba|first26=A. W.|last26=Tudhope|first25=M.|last25=Schulz|first24=N.|first18=E.|first23=J. T.|first16=H.|last12=Ammann|first12=C. M.|last13=Buckley|first13=B. M.|last14=Cobb|first14=K. M.|last15=Esper|first15=J.|last16=Goosse|last17=Graham|last23=Overpeck|first17=N.|last18=Jansen|last19=Kiefer|first19=T.|last20=Kull|first20=C.|last21=Kuttel|first21=M.|last22=Mosley-Thompson|first22=E.|s2cid=129606908|access-date=2021-08-12|archive-date=2015-10-14|archive-url=https://web.archive.org/web/20151014073536/http://shadow.eas.gatech.edu/%7Ekcobb/jones09.pdf|url-status=dead}} p. 36</ref> Also shown, Moberg ''et al.'' 2005 low frequency signal (black).]]

The third assessment report (TAR) prominently featured<ref>{{cite web|title=Climate Change 2001: The Scientific Basis|url=http://www.grida.no/climate/ipcc_tar/wg1/pdf/WG1_TAR-FRONT.pdf|access-date=2021-08-12|archive-date=2013-01-13|archive-url=https://web.archive.org/web/20130113142303/http://www.grida.no/climate/ipcc_tar/wg1/pdf/WG1_TAR-FRONT.pdf|url-status=dead}}</ref> a graph labeled "Millennial Northern Hemisphere temperature reconstruction" based on a 1999 paper by [[Michael E. Mann]], [[Raymond S. Bradley]] and Malcolm K. Hughes (MBH99), which has been referred to as the "[[hockey stick graph (global temperature)|hockey stick graph]]". This graph extended the similar graph in [[:File:IPCC 1996 SAR Figure 3.20.png|Figure 3.20]] from the [[IPCC Second Assessment Report]] of 1995, and differed from a schematic in the [[MWP and LIA in IPCC reports|first assessment report]] that lacked temperature units, but appeared to depict larger global temperature variations over the past 1000 years, and higher temperatures during the [[Medieval Warm Period]] than the mid 20th century. The schematic was not an actual plot of data, and was based on a diagram of temperatures in central England, with temperatures increased on the basis of documentary evidence of medieval [[Wine from the United Kingdom|vineyards in England]]. Even with this increase, the maximum it showed for the Medieval Warm Period did not reach temperatures recorded in central England in 2007.<ref name="Jones 09" /> The MBH99 finding was supported by cited reconstructions by {{harvnb|Jones|Briffa|Barnett|Tett|1998}}, {{harvnb|Pollack|Huang|Shen|1998}}, {{harvnb|Crowley|Lowery|2000}} and {{harvnb|Briffa|2000}}, using differing data and methods. The Jones et al. and Briffa reconstructions were overlaid with the MBH99 reconstruction in Figure 2.21 of the IPCC report.<ref name="TAR 2.3.2.2">{{cite book|last1=Houghton|url=http://www.grida.no/publications/other/ipcc_tar/?src=/climate/ipcc_tar/wg1/069.htm#fig220|title=Climate change 2001: the scientific basis|last2=Ding|last3=Griggs|last4=Noguer|last5=van der Linden|last6=Dai|last7=Maskell|last8=Johnson|date=2001|chapter=2.3.2.2 Multi-proxy synthesis of recent temperature change|archive-url=https://web.archive.org/web/20110604072514/http://www.grida.no/publications/other/ipcc_tar/?src=%2Fclimate%2Fipcc_tar%2Fwg1%2F069.htm|archive-date=4 June 2011|url-status=dead}}</ref>

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. Denialist [[John Lawrence Daly]] featured a modified version of the IPCC 1990 schematic, which he mis-identified as appearing in the IPCC 1995 report, and asserted that "Overturning its own previous view in the 1995 report, the IPCC presented the 'Hockey Stick' as the new orthodoxy with hardly an apology or explanation for the abrupt U-turn since its 1995 report".{{cn|date=August 2021}} Criticism of the MBH99 reconstruction in a review paper, which was quickly discredited in the [[Soon and Baliunas controversy]], was picked up by the Bush administration, and a Senate speech by US Republican senator [[James Inhofe]] alleged that "manmade global warming is the greatest hoax ever perpetrated on the American people". The data and methodology used to produce the "hockey stick graph" was criticized in papers by [[Stephen McIntyre]] and [[Ross McKitrick]],<ref name="MM05a">{{Cite journal|last1=McIntyre|first1=Stephen|author1-link=Stephen McIntyre|last2=McKitrick|first2=Ross|author2-link=Ross McKitrick|year=2005|title=Hockey sticks, principal components, and spurious significance|url=http://climateaudit.files.wordpress.com/2009/12/mcintyre-grl-2005.pdf|journal=[[Geophysical Research Letters]]|volume=32|issue=3|page=L03710|bibcode=2005GeoRL..32.3710M|doi=10.1029/2004GL021750|access-date=31 October 2013|doi-access=free|archive-date=19 January 2011|archive-url=https://web.archive.org/web/20110119200854/http://climateaudit.files.wordpress.com/2009/12/mcintyre-grl-2005.pdf|url-status=live}}</ref> and in turn the criticisms in these papers were examined by other studies and comprehensively refuted by {{harvnb|Wahl|Ammann|2007}},<ref name="Weart fn48">{{harvnb|Weart|2011|loc=[http://www.aip.org/history/climate/20ctrend.htm#N_48_ footnote 48]}},(p. 19, n1 in pdf).</ref> which showed errors in the methods used by McIntyre and McKitrick.<ref name="ar4-ch6">{{harvnb|Jansen|Overpeck|2007}}{{rp|466}}</ref>

On 23 June 2005, Rep. [[Joe Barton]], chairman of the [[United States House Committee on Energy and Commerce|House Committee on Energy and Commerce]], wrote joint letters with [[Ed Whitfield]], chairman of the [[United States House Energy Subcommittee on Oversight and Investigations|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.<ref name="wapo Witches">{{cite news|date=22 July 2005|title=Hunting Witches|url=https://www.washingtonpost.com/wp-dyn/content/article/2005/07/22/AR2005072201658.html|access-date=12 August 2021|archive-date=24 July 2008|archive-url=https://web.archive.org/web/20080724050436/http://www.washingtonpost.com/wp-dyn/content/article/2005/07/22/AR2005072201658.html|url-status=live}}</ref> [[Sherwood Boehlert]], chairman of the [[United States House Committee on Science, Space and Technology|House Science Committee]], said this was a "misguided and illegitimate investigation" apparently aimed at intimidating scientists, and at his request the [[United States National Academy of Sciences|U.S. National Academy of Sciences]] arranged for its [[United States National Research Council|National Research Council]] to set up a special investigation.{{cn|date=August 2021}} <!-- This: <ref name="Revkin606">{{Harvnb|Revkin, 22 June|2006}} (NYT).</ref> is not a valid reference. --> 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. In a 2006 letter to ''[[Nature (journal)|Nature]]'', Mann, Bradley, and Hughes pointed out that their original article had said that "more widespread high-resolution data are needed before more confident conclusions can be reached" and that the uncertainties were "the point of the article".<ref>{{Cite journal|last1=Bradley|first1=Raymond S.|author1-link=Raymond S. Bradley|last2=Hughes|first2=Malcolm K.|last3=Mann|first3=Michael E.|author3-link=Michael E. Mann|year=2006|title=Authors were clear about hockey-stick uncertainties|journal=Nature|volume=442|issue=7103|page=627|bibcode=2006Natur.442..627B|doi=10.1038/442627b|pmid=16900179|doi-access=free}}</ref>