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Hockey stick graphs present the global or hemispherical mean temperature record of the past 500 to 2000 years as shown by quantitative climate reconstructions based on climate proxy records. These reconstructions have consistently shown a slow long term cooling trend changing into relatively rapid warming in the 20th century, with the instrumental temperature record by 2000 exceeding earlier temperatures. The term "hockey stick graph" was coined by the climatologist Jerry Mahlman, to describe the pattern shown by the (MBH99) reconstruction, envisaging a graph that is relatively flat with a downward trend to 1900 as forming an ice hockey stick's "shaft" followed by a sharp, steady increase corresponding to the "blade" portion.〔〔 The reconstructions have featured in Intergovernmental Panel on Climate Change (IPCC) reports as evidence of global warming. Arguments over the reconstructions have been taken up by fossil fuel industry funded lobbying groups attempting to cast doubt on climate science.〔, 〕 Paleoclimatology dates back to the 19th century, and the concept of examining varves in lake beds and tree rings to track local climatic changes was suggested in the 1930s. In the 1960s, Hubert Lamb generalised from historical documents and temperature records of central England to propose a Medieval Warm Period from around 900 to 1300, followed by Little Ice Age.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 of 1990 beside cautions that the medieval warming might not have been global. The use of indicators to get quantitative estimates of the temperature record of past centuries was developed, and by the late 1990s a number of competing teams of climatologists found indications that recent warming was exceptional. introduced the "Composite Plus Scaling" (CPS) method used by most later large scale reconstructions.〔.〕 Their study was featured in the IPCC Second Assessment Report of 1995. In 1998 Michael E. Mann, Raymond S. Bradley and Malcolm K. Hughes developed new statistical techniques to produce (MBH98), the first eigenvector-based climate field reconstruction (CFR). This 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.〔〔 A version of the MBH99 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 became a focus of dispute for those opposed to the strengthening scientific consensus that late 20th century warmth was exceptional.〔 ("Part three: Hockey stick graph took pride of place in IPCC report, despite doubts" ).〕 In 2003, as lobbying over the 1997 Kyoto Protocol intensified, a paper claiming greater medieval warmth was quickly dismissed by scientists in the Soon and Baliunas controversy.〔 Later in 2003, Stephen McIntyre and Ross McKitrick published disputing the data used in MBH98 paper. 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.〔(The Decay of the Hockey Stick ), Nature "Climate Feedback" blog post by von Storch. "... we do not think that McIntyre has substantially contributed in the published peer-reviewed literature to the debate about the statistical merits of the MBH and related method." (comment by von Storch & Zorita, May 7, 2007 07:35 PM, in response to multiple comments on their failure to acknowledge McIntyre and McKitrick's contributions)〕 In 2005 McIntyre and McKitrick published criticisms of the principal components analysis methodology as used in MBH98 and MBH99. Their analysis in was subsequently disputed by published papers including and which pointed to errors in the McIntyre and McKitrick methodology. Political disputes led to the formation of a panel of scientists convened by the National Research Council, their North Report in 2006 supported Mann's findings with some qualifications, including agreeing that there were some statistical failings but these had little effect on the result.〔, ("Part four: Climate change debate overheated after sceptics grasped 'hockey stick'" ).〕 More than two dozen reconstructions, using various statistical methods and combinations of proxy records, support the broad consensus shown in the original 1998 hockey-stick graph, with variations in how flat the pre-20th century "shaft" appears.〔〔.〕 The 2007 IPCC Fourth Assessment Report cited 14 reconstructions, 10 of which covered 1,000 years or longer, to support its strengthened conclusion that it was likely that Northern Hemisphere temperatures during the 20th century were the highest in at least the past 1,300 years.〔 Further reconstructions, including Mann et al. 2008 and , have supported these general conclusions. ==Origins: the first paleoclimate reconstructions== Paleoclimatology influenced the 19th century physicists John Tyndall and Svante Arrhenius who found the greenhouse gas effect of carbon dioxide () in the atmosphere to explain how past ice ages had ended.〔 From 1919 to 1923, Alfred Wegener did pioneering work on reconstructing the climate of past eras in collaboration with Milutin Milanković,〔(introduction to the English edition ), ''The Climates of the Geological Past,'' (2015), retrieved August 28, 2015〕 publishing ''Die Klimate der geologischen Vorzeit'' (“The Climates of the Geological Past”) together with Wladimir Köppen, in 1924.〔Köppen, W. & Wegener, A. (1924): ''Die Klimate der geologischen Vorzeit'', Borntraeger Science Publishers. In English as ''The Climates of the Geological Past'' (2015).〕 In the 1930s Guy Stewart Callendar compiled temperature records to look for changes. Wilmot H. Bradley showed that annual varves in lake beds showed climate cycles, and A. E. Douglass found that tree rings could track past climatic changes but these were thought to only show random variations in the local region. It was only in the 1960s that accurate use of tree rings as climate proxies for reconstructions was pioneered by Harold C. Fritts. In 1965 Hubert Lamb, a pioneer of historical climatology, generalised from temperature records of central England by using historical, botanical and archeological evidence to popularise the idea of a Medieval Warm Period from around 900 to 1300, followed by a cold epoch culminating between 1550 and 1700.〔.〕〔; 〕 In 1972 he became the founding director of the Climatic Research Unit (CRU) in the University of East Anglia (UEA), which aimed to improve knowledge of climate history in both the recent and far distant past, monitor current changes in global climate, identify processes causing changes at different timescales, and review the possibility of advising about future trends in climate. During the cold years of the 1960s, Lamb had anticipated that natural cycles were likely to lead over thousands of years to a future ice age, but after 1976 he supported the emerging view that greenhouse gas emissions caused by humanity would cause detectable global warming "by about A.D. 2000".〔 The first quantitative reconstruction of Northern Hemisphere (NH) annual mean temperatures was published in 1979 by Brian Groveman and Helmut Landsberg. They used "a short-cut method" based on their earlier paper which showed that 9 instrumental stations could adequately represent an extensive gridded instrumental series, and reconstructed temperatures from 1579 to 1880 on the basis of their compilation of 20 time-series. These records were largely instrumental but also included some proxy records including two tree-ring series. Their method used nested multiple regression to allow for records covering different periods, and produced measures of uncertainty. The reconstruction showed a cool period extending beyond the Maunder Minimum, and warmer temperatures in the 20th century.〔〔, 〕 After this around a decade elapsed before Gordon Jacoby and Rosanne D'Arrigo produced the next quantitative NH reconstruction, published in 1989. This was the first based entirely on non-instrumental records, and used tree rings.〔 They reconstructed northern hemisphere annual temperatures since 1671 on the basis of boreal North American tree ring data from 11 distinct regions. From this, they concluded that recent warming was anomalous over the 300-year period, and went as far as speculating that these results supported the hypothesis that recent warming had human causes.〔. .〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「hockey stick graph」の詳細全文を読む スポンサード リンク
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