Hockey stick controversy

Hockey stick controversy

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The hockey stick controversy refers to debates over the technical correctness and implications for global warming
Global warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...

 of graphs showing reconstructed estimates of the temperature record of the past 1000 years
Temperature record of the past 1000 years
The temperature record of the 2nd millennium describes the reconstruction of temperatures since 1000 CE on the Northern Hemisphere, later extended back to 1 CE and also to cover the southern hemisphere. A reconstruction is needed because a reliable surface temperature record exists only since about...

. At a political level, the debate is about the use of these graphs to convey complex science to the public, and the question of the robustness of the assessment presented by the Intergovernmental Panel on Climate Change
Intergovernmental Panel on Climate Change
The Intergovernmental Panel on Climate Change is a scientific intergovernmental body which provides comprehensive assessments of current scientific, technical and socio-economic information worldwide about the risk of climate change caused by human activity, its potential environmental and...

 (IPCC).

By the late 1990s a number of competing teams were using proxy
Proxy (climate)
In the study of past climates is known as paleoclimatology, climate proxies are preserved physical characteristics of the past that stand in for direct measurements , to enable scientists to reconstruct the climatic conditions that prevailed during much of the Earth's history...

 indicators to estimate the temperature record
Temperature record
The temperature record shows the fluctuations of the temperature of the atmosphere and the oceans through various spans of time. The most detailed information exists since 1850, when methodical thermometer-based records began. There are numerous estimates of temperatures since the end of the...

 of past centuries, and finding suggestions that recent warming was exceptional. In 1998 Michael E. Mann, Raymond S. Bradley and Malcolm K. Hughes
Malcolm K. Hughes
Malcolm K. Hughes is a meso-climatologist and Regents' Professor of Dendrochronology in the Laboratory for Tree-Ring Research at the University of Arizona. He was born in Matlock, Derbyshire, England, and earned a Ph.D in ecology from the University of Durham. Since 1998, he is a fellow of the...

 produced the first quantitative hemispheric-scale reconstruction, from an analysis of a variety of measures, which they summarised in a graph going back to 1400 showing recent measured temperatures increasing sharply. Their 1999 paper extended this study back to 1000, and included a graph which was featured prominently in the 2001 United Nations
United Nations
The United Nations is an international organization whose stated aims are facilitating cooperation in international law, international security, economic development, social progress, human rights, and achievement of world peace...

 Intergovernmental Panel on Climate Change
Intergovernmental Panel on Climate Change
The Intergovernmental Panel on Climate Change is a scientific intergovernmental body which provides comprehensive assessments of current scientific, technical and socio-economic information worldwide about the risk of climate change caused by human activity, its potential environmental and...

 (IPCC) Third Assessment Report (TAR) as supporting the mainstream view of climate scientists that there had been a relatively sharp rise in temperatures during the second half of the 20th century. It became a focus of dispute for those opposed to this strengthening scientific consensus
Scientific consensus
Scientific consensus is the collective judgment, position, and opinion of the community of scientists in a particular field of study. Consensus implies general agreement, though not necessarily unanimity. Scientific consensus is not by itself a scientific argument, and it is not part of the...

. The term hockey stick
Ice hockey stick
An ice hockey stick is a piece of equipment used in ice hockey to shoot, pass, and carry the puck. Ice hockey sticks are approximately 150–200 cm long, composed of a long, slender shaft with a flat extension at one end called the blade. The blade is the part of the stick used to contact the...

was coined by the climatologist Jerry Mahlman
Jerry Mahlman
-Biography:Mahlman received his undergraduate degree from Chadron State College in 1962 and his Ph.D. from Colorado State University in 1967. From 1970 until 2000 he worked at the Geophysical Fluid Dynamics Laboratory of the National Oceanic and Atmospheric Administration at Princeton, serving as...

, to describe the pattern, envisaging a graph that is relatively flat to 1900 as forming the hockey stick's "shaft", followed by a sharp increase corresponding to the "blade".

In 2003, Willie Soon
Willie Soon
Willie Wei-Hock Soon is an astrophysicist at the Solar and Stellar Physics Division of the Harvard-Smithsonian Center for Astrophysics. Soon has testified before Congress on the issue of climate change He is known for his views that most global warming is caused by solar variation...

 and Sallie Baliunas
Sallie Baliunas
Sallie Baliunas is an astrophysicist at the Harvard-Smithsonian Center for Astrophysics in the Solar, Stellar, and Planetary Sciences Division and formerly Deputy Director of the Mount Wilson Observatory. She serves as Senior Scientist at the George C. Marshall Institute in Washington, DC, and...

 argued against this pattern in a paper which was quickly dismissed as faulty in the Soon and Baliunas controversy
Soon and Baliunas controversy
The Soon and Baliunas controversy involved the publication of a paper written by Willie Soon and Sallie Baliunas in the journal Climate Research, which prompted concerns about the peer review process of the paper and resulted in the resignation of several other editors and the eventual repudiation...

. In the United States there was already a hot political dispute over action on global warming following lobbying regarding the 1997 Kyoto Protocol
Kyoto Protocol
The Kyoto Protocol is a protocol to the United Nations Framework Convention on Climate Change , aimed at fighting global warming...

, and on July 28, Republican Jim Inhofe
Jim Inhofe
James Mountain "Jim" Inhofe is the senior Senator from Oklahoma and a member of the Republican Party. First elected to the Senate in 1994, he is the ranking member of the United States Senate Committee on Environment and Public Works and was its chairman from 2003 to 2007. Inhofe served eight...

 made a Senate speech citing Soon and Baliunas to support his view "that man-made global warming is the greatest hoax ever perpetrated on the American people". Also in 2003, Stephen McIntyre
Stephen McIntyre
Stephen McIntyre is a Canadian mathematician, former minerals prospector, and semi-retired mining consultant who is best known as the founder and editor of Climate Audit, a blog devoted to the analysis and discussion of climate data...

 and Ross McKitrick
Ross McKitrick
Ross McKitrick is a Canadian economist specializing in environmental economics and policy analysis. He is professor of economics at the University of Guelph; a senior fellow of the Fraser Institute, a Canadian free-market public policy think tank; and a member of the academic advisory boards of the...

 published a paper questioning the statistical methods used in the Mann et al. paper, and there was continued debate on these issues. Hans von Storch
Hans von Storch
Hans von Storch is a German climate scientist. He is Professor at the Meteorological Institute of the University of Hamburg, and Director of the Institute for Coastal Research at the Helmholtz Research Centre in Geesthacht, Germany...

 regards that paper as of little consequence, and believes his paper of 2004 to be the first significant criticism. At the request of Congress, a panel of scientists convened by the National Research Council
United States National Research Council
The National Research Council of the USA is the working arm of the United States National Academies, carrying out most of the studies done in their names.The National Academies include:* National Academy of Sciences...

 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. U.S. Rep. Joe Barton
Joe Barton
Joseph Linus "Joe" Barton is a Republican politician, representing in the U.S. House of Representatives since 1985, and a member of the Tea Party Caucus...

 and U.S. Rep. Ed Whitfield
Ed Whitfield
Wayne Edward "Ed" Whitfield is the U.S. Representative of , serving since 1995. He is a member of the Republican Party.The district covers much of the western part of the state, including Hopkinsville, Paducah, Henderson and Kentucky's share of Fort Campbell.-Early life, education and...

 requested Edward Wegman
Edward Wegman
Edward Wegman is a statistician, a statistics professor at George Mason University, and past chair of the National Research Council’s Committee on Applied and Theoretical Statistics. He holds a Ph.D. in mathematical statistics and is a Fellow of the American Statistical Association and a Senior...

 to set up a team of statisticians to investigate, and they supported the view that there were statistical failings, although their report has itself been criticized on several grounds.

More than twelve subsequent scientific papers, using various statistical methods and combinations of proxy records, produced reconstructions broadly similar to the original MBH hockey-stick graph, with variations in how flat the pre-20th century "shaft" appears. Almost all of them supported the IPCC conclusion that the warmest decade in 1000 years was probably that at the end of the 20th century.

Origins


Paleoclimatology
Paleoclimatology
Paleoclimatology is the study of changes in climate taken on the scale of the entire history of Earth. It uses a variety of proxy methods from the Earth and life sciences to obtain data previously preserved within rocks, sediments, ice sheets, tree rings, corals, shells and microfossils; it then...

 influenced the 19th century physicists John Tyndall
John Tyndall
John Tyndall FRS was a prominent Irish 19th century physicist. His initial scientific fame arose in the 1850s from his study of diamagnetism. Later he studied thermal radiation, and produced a number of discoveries about processes in the atmosphere...

 and Svante Arrhenius
Svante Arrhenius
Svante August Arrhenius was a Swedish scientist, originally a physicist, but often referred to as a chemist, and one of the founders of the science of physical chemistry...

 who found the greenhouse gas
Greenhouse gas
A greenhouse gas is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The primary greenhouse gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone...

 effect of carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

  in the atmosphere to explain how past ice age
Ice age
An ice age or, more precisely, glacial age, is a generic geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental ice sheets, polar ice sheets and alpine glaciers...

s had ended. In 1965 Hubert Lamb
Hubert Lamb
Hubert Horace Lamb was an English climatologist who founded the Climatic Research Unit in 1972 in the School of Environmental Sciences at the University of East Anglia.-Career:...

, a pioneer of historical climatology
Historical climatology
Historical climatology is the study of historical changes in climate and their effect on human history and development. This differs from paleoclimatology which encompasses climate change over the entire history of the earth. The study seeks to define periods in human history where temperature or...

, generalised from temperature records of central England by using historical, botanical and archeological evidence to popularise the idea of a Medieval Warm Period
Medieval Warm Period
The Medieval Warm Period , Medieval Climate Optimum, or Medieval Climatic Anomaly was a time of warm climate in the North Atlantic region, that may also have been related to other climate events around the world during that time, including in China, New Zealand, and other countries lasting from...

 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
Climatic Research Unit
The Climatic Research Unit is a component of the University of East Anglia and is one of the leading institutions concerned with the study of natural and anthropogenic climate change....

 (CRU) in the University of East Anglia
University of East Anglia
The University of East Anglia is a public research university based in Norwich, United Kingdom. It was established in 1963, and is a founder-member of the 1994 Group of research-intensive universities.-History:...

 (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
Global warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...

 "by about A.D. 2000".
There was increasing public and political interest, and in 1987 the World Meteorological Organization
World Meteorological Organization
The World Meteorological Organization is an intergovernmental organization with a membership of 189 Member States and Territories. It originated from the International Meteorological Organization , which was founded in 1873...

 pressed for an international scientific panel to assess global warming. The United States Reagan administration, concerned about political influence of scientists, successfully lobbied for the 1988 formation of the Intergovernmental Panel on Climate Change
Intergovernmental Panel on Climate Change
The Intergovernmental Panel on Climate Change is a scientific intergovernmental body which provides comprehensive assessments of current scientific, technical and socio-economic information worldwide about the risk of climate change caused by human activity, its potential environmental and...

 having reports subject to detailed approval by government delegates. The IPCC First Assessment Report
IPCC First Assessment Report
The Intergovernmental Panel on Climate Change first assessment report was completed in 1990, and served as the basis of the United Nations Framework Convention on Climate Change ....

 in 1990 noted evidence that the Holocene climatic optimum
Holocene climatic optimum
The Holocene Climate Optimum was a warm period during roughly the interval 9,000 to 5,000 years B.P.. This event has also been known by many other names, including: Hypsithermal, Altithermal, Climatic Optimum, Holocene Optimum, Holocene Thermal Maximum, and Holocene Megathermal.This warm period...

 around 5,000-6,000 years ago had been warmer than the present (at least in summer) and that in some areas there had been exceptional warmth during "a shorter Medieval Warm Period (which may not have been global)" about AD 950-1250, followed by a cooler period of the Little Ice Age
Little Ice Age
The Little Ice Age was a period of cooling that occurred after the Medieval Warm Period . While not a true ice age, the term was introduced into the scientific literature by François E. Matthes in 1939...

 which ended only in the middle to late nineteenth century. A "schematic diagram" of global temperature variations over the last thousand years has been traced to a graph based loosely on Lamb's 1965 paper, nominally representing central England. Mike Hulme
Mike Hulme
Mike Hulme is a professor of Climate Change in the School of Environmental Sciences at the University of East Anglia . He was educated at Madras College, St.Andrews, and at the universities of Durham and Wales...

 describes this schematic diagram as "Lamb's sketch on the back of an envelope", a "rather dodgy bit of hand-waving".

Archives of climate proxies
Proxy (climate)
In the study of past climates is known as paleoclimatology, climate proxies are preserved physical characteristics of the past that stand in for direct measurements , to enable scientists to reconstruct the climatic conditions that prevailed during much of the Earth's history...

 were developed and the first hemispheric reconstructions were published: in 1993 Raymond S. Bradley and Phil Jones
Phil Jones
Philip D. Jones is a climatologist at the University of East Anglia, where he works as a Professor in the School of Environmental Sciences. Jones holds a BA in Environmental Sciences from the University of Lancaster, and an MSc and PhD from the University of Newcastle upon Tyne...

 used historical records, tree-rings and ice cores for the Northern Hemisphere from 1400 up to the 1970s, to come up with findings similar to later "hockey stick" studies. The IPCC Second Assessment Report
IPCC Second Assessment Report
The Second Assessment Report of the Intergovernmental Panel on Climate Change , published in 1996, is an assessment of the then available scientific and socio-economic information on climate change...

 (SAR) of 1996 featured a graph of this reconstruction which included a separate curve plotting instrumental thermometer data from the 1850s onwards. The section proposed that "The data from the last 1000 years are the most useful for determining the scales of natural climate variability", and noted the 1994 reconstruction by Hughes
Malcolm K. Hughes
Malcolm K. Hughes is a meso-climatologist and Regents' Professor of Dendrochronology in the Laboratory for Tree-Ring Research at the University of Arizona. He was born in Matlock, Derbyshire, England, and earned a Ph.D in ecology from the University of Durham. Since 1998, he is a fellow of the...

 and Diaz questioning how widespread the Medieval Warm Period been at any one time. It concluded, "it appears that the 20th century has been at least as warm as any century since at least 1400 AD. In at least some areas, the recent period appears to be warmer than has been the case for a thousand or more years".

Among other large-scale palaeoclimate reconstructions, a November 1995 study by Mann, Park and Bradley also went back to 1400. Tree ring specialist Keith Briffa
Keith Briffa
Professor Keith R. Briffa is a climatologist employed since 1977 by the Climatic Research Unit at the University of East Anglia, of which he is currently deputy director. In his professional work, he focuses on the climate change in late Holocene, with a special focus on northern portions of...

's February 1998 study reporting a divergence problem
Divergence problem
The divergence problem is an anomaly from the field of dendroclimatology, the study of past climate through observations of old trees, primarily the properties of their annual growth rings...

 affecting some tree ring proxies after 1960 warned that this had to be taken into account to avoid overestimating past temperatures. Working towards the next IPCC assessment, Tim Barnett
Tim Barnett
Timothy Andrew Barnett was the member of the New Zealand Parliament for Christchurch Central from 1996 to 2008, representing the Labour Party. He was a British immigrant to New Zealand and New Zealand's second openly gay politician.-Early life:...

 told Jones "What we hope is that the current patterns of temperature change prove distinctive, quite different from the patterns of natural variability in the past". Political pressures increased as the Kyoto Protocol
Kyoto Protocol
The Kyoto Protocol is a protocol to the United Nations Framework Convention on Climate Change , aimed at fighting global warming...

 was opposed by lobbyists such as the American Petroleum Institute
American Petroleum Institute
The American Petroleum Institute, commonly referred to as API, is the largest U.S trade association for the oil and natural gas industry...

 who sought climatologists to dissent and undermine its scientific credibility.

Hockey stick graphs published


On 23 April 1998, the journal Nature
Nature (journal)
Nature, first published on 4 November 1869, is ranked the world's most cited interdisciplinary scientific journal by the Science Edition of the 2010 Journal Citation Reports...

published the Mann, Bradley and Hughes
Malcolm K. Hughes
Malcolm K. Hughes is a meso-climatologist and Regents' Professor of Dendrochronology in the Laboratory for Tree-Ring Research at the University of Arizona. He was born in Matlock, Derbyshire, England, and earned a Ph.D in ecology from the University of Durham. Since 1998, he is a fellow of the...

 multiproxy study on "Global-scale temperature patterns and climate forcing over the past six centuries" (MBH98) which used a new statistical approach to find patterns of climate change in both time and global distribution, building on previous multiproxy reconstructions. They concluded that "Northern Hemisphere mean annual temperatures for three of the past eight years are warmer than any other year since (at least) AD1400", and estimated empirically that greenhouse gases had become the dominant climate forcing
Radiative forcing
In climate science, radiative forcing is generally defined as the change in net irradiance between different layers of the atmosphere. Typically, radiative forcing is quantified at the tropopause in units of watts per square meter. A positive forcing tends to warm the system, while a negative...

 during the 20th century.

The New York Times highlighted their finding that the 20th century had been the warmest century in 600 years, quoting Mann saying that "Our conclusion was that the warming of the past few decades appears to be closely tied to emission of greenhouse gases by humans and not any of the natural factors". Most proxy data are inherently imprecise, and Mann said "We do have error bars. They are somewhat sizable as one gets farther back in time, and there is reasonable uncertainty in any given year. There is quite a bit of work to be done in reducing these uncertainties." Climatologist Tom Wigley
Tom Wigley
Tom Wigley is a climate scientist at the University Corporation for Atmospheric Research . He was named a fellow of the American Association for the Advancement of Science for his major contributions to climate and carbon-cycle modeling and to climate data analysis, and because he is "one of the...

 had high regard for the progress the study made, but doubted if proxy data could ever be wholly convincing in detecting the human contribution to changing climate. Phil Jones
Phil Jones
Philip D. Jones is a climatologist at the University of East Anglia, where he works as a Professor in the School of Environmental Sciences. Jones holds a BA in Environmental Sciences from the University of Lancaster, and an MSc and PhD from the University of Newcastle upon Tyne...

 of the UEA Climatic Research Unit
Climatic Research Unit
The Climatic Research Unit is a component of the University of East Anglia and is one of the leading institutions concerned with the study of natural and anthropogenic climate change....

 was doubtful about adding the 150-year thermometer record to extend the proxy reconstruction, and compared this with putting together apples and oranges; Mann et al. said they used a comparison with the thermometer record to check that recent proxy data were valid. Jones thought the study would provide important comparisons with the findings of climate model
Climate model
Climate models use quantitative methods to simulate the interactions of the atmosphere, oceans, land surface, and ice. They are used for a variety of purposes from study of the dynamics of the climate system to projections of future climate...

ing, which showed a "pretty reasonable" fit to proxy evidence.

In May 1998, Jones, Keith Briffa
Keith Briffa
Professor Keith R. Briffa is a climatologist employed since 1977 by the Climatic Research Unit at the University of East Anglia, of which he is currently deputy director. In his professional work, he focuses on the climate change in late Holocene, with a special focus on northern portions of...

, Tim P. Barnett and Simon Tett
Simon Tett
Simon Tett is a climatologist working at the University of Edinburgh. He used to work at the Hadley Centre.His most-cited paper, is "Climate response to increasing levels of greenhouse gases and sulphate aerosols," Simon Tett is a climatologist working at the University of Edinburgh. He used to...

 published their own analysis, comparing tree ring, coral layer, and glacial proxy records, extending their reconstruction back for a thousand years but not specifically estimating uncertainties. As Bradley recalls, Mann's initial view was that there was too little information and too much uncertainty to go back so far, but Bradley said "Why don't we try to use the same approach we used in Nature, and see if we could push it back a bit further?" Within a few weeks, Mann responded that to his surprise, "There is a certain amount of skill. We can actually say something, although there are large uncertainties."

Mann, Bradley and Hughes 1999


Despite the uncertainties, Mann, Bradley and Hughes found they were able to extend their approach to 1,000 years ago. Their paper (MBH99) was published in March 1999 with the cautious title Northern Hemisphere temperatures during the past millennium: inferences, uncertainties, and limitations to emphasise the increasing uncertainty involved in reconstructions of the period before 1400 when fewer proxies were available. A University of Massachusetts
University of Massachusetts
This article relates to the statewide university system. For the flagship campus often referred to as "UMass", see University of Massachusetts Amherst...

 news release dated 3 March 1999 announced publication in the 15 March issue of Geophysical Research Letters
Geophysical Research Letters
Geophysical Research Letters is a semi-monthly peer reviewed scientific journal published by the American Geophysical Union that was established in 1974...

, "strongly suggesting that the 1990s were the warmest decade of the millennium, with 1998 the warmest year so far." Bradley was quoted as saying "Temperatures in the latter half of the 20th century were unprecedented", while Mann said "As you go back farther in time, the data becomes sketchier. One can’t quite pin things down as well, but, our results do reveal that significant changes have occurred, and temperatures in the latter 20th century have been exceptionally warm compared to the preceding 900 years. Though substantial uncertainties exist in the estimates, these are nonetheless startling revelations." While the reconstruction supported theories of a relatively warm medieval period, Hughes said "even the warmer intervals in the reconstruction pale in comparison with mid-to-late 20th-century temperatures." The New York Times report had a colored version of the graph, distinguishing the instrumental record from the proxy evidence and emphasising the increasing range of possible error in earlier times, which MBH said would "preclude, as yet, any definitive conclusions" about climate before 1400.

Contrary to a long-term cooling trend expected from orbital forcing
Orbital forcing
Orbital forcing is the effect on climate of slow changes in the tilt of the Earth's axis and shape of the orbit . These orbital changes change the total amount of sunlight reaching the Earth by up to 25% at mid-latitudes...

, 20th century warming stood out from the whole period, with the 1990s "the warmest decade, and 1998 the warmest year, at moderately high levels of confidence." The time series
Time series
In statistics, signal processing, econometrics and mathematical finance, a time series is a sequence of data points, measured typically at successive times spaced at uniform time intervals. Examples of time series are the daily closing value of the Dow Jones index or the annual flow volume of the...

 line graph
Line chart
A line chart or line graph is a type of graph, which displays information as a series of data points connected by straight line segments. It is a basic type of chart common in many fields. It is an extension of a scatter graph, and is created by connecting a series of points that represent...

 Figure 2(a) showed their reconstruction from AD 1000 to 1980 as a thin line, wavering around a thicker dark 40-year smoothed line. This curve followed a downward trend (shown as a thin dot-dashed line) from a Medieval Warm Period
Medieval Warm Period
The Medieval Warm Period , Medieval Climate Optimum, or Medieval Climatic Anomaly was a time of warm climate in the North Atlantic region, that may also have been related to other climate events around the world during that time, including in China, New Zealand, and other countries lasting from...

 (about as warm as the 1950s) down to a cooler Little Ice Age
Little Ice Age
The Little Ice Age was a period of cooling that occurred after the Medieval Warm Period . While not a true ice age, the term was introduced into the scientific literature by François E. Matthes in 1939...

 before rising sharply in the 20th century. Thermometer data shown with a dotted line overlapped the reconstruction for a calibration period from 1902 to 1980, then continued sharply up to 1998. A shaded area showed uncertainties to two standard error limits, in medieval times rising almost as high as recent temperatures. When Mann gave a talk about the study to the National Oceanic and Atmospheric Administration
National Oceanic and Atmospheric Administration
The National Oceanic and Atmospheric Administration , pronounced , like "noah", is a scientific agency within the United States Department of Commerce focused on the conditions of the oceans and the atmosphere...

's Geophysical Fluid Dynamics Laboratory
Geophysical Fluid Dynamics Laboratory
The Geophysical Fluid Dynamics Laboratory is a laboratory in the National Oceanic and Atmospheric Administration /Office of Oceanic and Atmospheric Research . The current director is Dr. V...

, Jerry Mahlman
Jerry Mahlman
-Biography:Mahlman received his undergraduate degree from Chadron State College in 1962 and his Ph.D. from Colorado State University in 1967. From 1970 until 2000 he worked at the Geophysical Fluid Dynamics Laboratory of the National Oceanic and Atmospheric Administration at Princeton, serving as...

 nicknamed the graph the "hockey stick", with the slow cooling trend the "stick", and the anomalous 20th century warming the "blade".

Briffa and Tim Osborn critically examined MBH99 in a May 1999 detailed study of the uncertainties of various proxies. They raised questions later adopted by critics of Mann's work, including the point that bristlecone pine
Bristlecone pine
The bristlecone pines are a small group of pine trees that are thought to reach an age far greater than that of any other single living organism known, up to nearly 5,000 years....

s from the Western U.S. could have been affected by pollution such as rising levels as well as temperature. The temperature curve was supported by other studies, but most of these shared the limited well dated proxy evidence then available, and so few were truly independent. The uncertainties in earlier times rose as high as those in the reconstruction at 1980, but did not reach the temperatures of later thermometer data. They concluded that although the 20th century was almost certainly the warmest of the millennium, the amount of anthropogenic warming remains uncertain."

With work progressing on the next IPCC report, Chris Folland told researchers on 22 September 1999 that a figure showing temperature changes over the millennium "is a clear favourite for the policy makers' summary". Two graphs competed: Jones et al. (1998) and MBH99. In November, Jones produced a simplified figure for the cover of the short annual World Meteorological Organization
World Meteorological Organization
The World Meteorological Organization is an intergovernmental organization with a membership of 189 Member States and Territories. It originated from the International Meteorological Organization , which was founded in 1873...

 report, which lacks the status of the more important IPCC reports. Two fifty-year smoothed curves going back to 1000 were shown, from MBH99 and Jones et al. (1998), with a third curve to 1400 from Briffa's new paper, combined with modern temperature data bringing the lines up to 1999: the lack of a clarity about this change of data has been criticised as misleading.
Briffa's paper as published in the January 2000 issue of Quaternary Science Reviews showed the unusual warmth of the last century, but cautioned that the impact of human activities on tree growth made it subtly difficult to isolate a clear climate message. In February Thomas J. Crowley and Thomas S. Lowery's paper said that peak Medieval warmth only occurred during two or three short periods of 20 to 30 years, with temperatures around 1950s levels, refuting claims that 20th century warming was not unusual.

Reviewing twenty years of progress in palaeoclimatology, Jones noted the reconstructions by Jones (1998), MBH99, Briffa (2000) and Crowley (2000) showing good agreement using different methods, but cautioned that use of many of the same proxy series meant that they were not independent, and more work was needed.

IPCC Third Assessment Report, 2001



The Working Group 1 (WG1) section of the IPCC Third Assessment Report
IPCC Third Assessment Report
The IPCC Third Assessment Report, Climate Change 2001, is an assessment of available scientific and socio-economic information on climate change by the IPCC. The IPCC was established in 1988 by the United Nations Environment Programme and the UN's World Meteorological Organization ".....

 (TAR) included a section on multi-proxy synthesis of recent temperature change, which emphasised the contribution of earlier studies and the uncertainties highlighted in MBH99. It noted that Jones et al. (1998) using different data and methods as well as Crowley and Lowery (2000) gave support to the MBH conclusion that the 1990s were likely to have been the warmest decade, and 1998 the warmest year, of the past millennium in the Northern Hemisphere. It defined "likely" as "66-90% chance". Its Figure 2.21 showed smoothed curves from the MBH99, Jones et al. and Briffa reconstructions, together with modern thermometer data as a red line and the grey shaded 95% confidence range from MBH99. Above it, figure 2.20 was adapted from MBH99, Figure 5 in WG1 Technical Summary B (as shown to the right) repeated this figure without the linear trend line declining from AD 1000 to 1850. This iconic graph was featured prominently in the WG1 Summary for Policymakers under a graph of the instrumental temperature record for the past 140 years. Versions of these graphs also featured less prominently in the short Synthesis Report Summary for Policymakers, which included a sentence stating that "The increase in surface temperature over the 20th century for the Northern Hemisphere is likely to have been greater than that for any other century in the last thousand years", and the Synthesis Report - Questions.

A large poster of the IPCC illustration based on the MBH99 graph formed the backdrop when Sir John T. Houghton
John T. Houghton
As co-chair of the IPCC, he defends the IPCC process, in particular against charges of failure to consider non-CO2 explanations of climate change. In evidence to, the Select Committee on Science and Technology in 2000 he said:...

, Co-Chair of Working Group 1, presented the scientific basis report in an announcement shown on television, leading to wide publicity.

A suggestion that the graph underestimated the Medieval Warm Period appeared in a March 2002 paper by Jan Esper
Jan Esper
Jan Esper is the head of the dendro sciences division at the WSL division of the Swiss Federal Institute of Technology...

 et al., but in Mann's view this did not contradict MBH as it dealt only with extratropical land areas, and stopped before the late 20th century. Edward R. Cook, a co-author on the paper, agreed with Mann, and later reconsidered the paper's conclusions.

Lonnie Thompson
Lonnie Thompson
Lonnie Thompson , is an American paleoclimatologist and Distinguished University Professor in the School of Earth Sciences at The Ohio State University. He has achieved global recognition for his drilling and analysis of ice cores from mountain glaciers and ice caps in the tropical and sub-tropical...

 published a paper on "Tropical Glacier and Ice Core Evidence of Climate Change" in January 2003, featuring Figure 7 showing graphs based on ice cores closely resembling a graph based on the MBH99 reconstruction combined with thermometer readings from Jones et al. 1999.

IPCC graph enters political controversy


Rather than displaying all of the long term temperature reconstructions, the opening figure of the Working Group 1 Summary for Policymakers in the IPCC Third Assessment Report
IPCC Third Assessment Report
The IPCC Third Assessment Report, Climate Change 2001, is an assessment of available scientific and socio-economic information on climate change by the IPCC. The IPCC was established in 1988 by the United Nations Environment Programme and the UN's World Meteorological Organization ".....

 highlighted an IPCC illustration based only on the MBH99 paper, and a poster of the hockey stick graph was the backdrop when the report was announced on television. The graph was seen by mass media and the public as central to the IPCC case for global warming, which had actually been based on other unrelated evidence. Jerry Mahlman
Jerry Mahlman
-Biography:Mahlman received his undergraduate degree from Chadron State College in 1962 and his Ph.D. from Colorado State University in 1967. From 1970 until 2000 he worked at the Geophysical Fluid Dynamics Laboratory of the National Oceanic and Atmospheric Administration at Princeton, serving as...

, who had coined the "hockey stick" nickname, described this emphasis on the graph as "a colossal mistake, just as it was a mistake for the climate-science-writing press to amplify it." He added that it was "not the smoking gun. That's the data we've had for the past 150 years, which is quite consistent with the expectation that the climate is continuing to warm." From an expert viewpoint the graph was, like all newly published science, preliminary and uncertain, but it was widely used to publicise the issue of global warming. The 1999 study had been a pioneering work in progress, and had emphasised the uncertainties, but publicity often played this down. Mann later said "The label was always a caricature and it became a stick to beat us with".

Controversy over the graph now extended outside the scientific community
Scientific community
The scientific community consists of the total body of scientists, its relationships and interactions. It is normally divided into "sub-communities" each working on a particular field within science. Objectivity is expected to be achieved by the scientific method...

, with accusations from political opponents of climate science. As science historian Spencer Weart said, "The dedicated minority who denied that there was any global warming problem promptly attacked the calculations." The graph was targeted by those opposing ratification of the Kyoto Protocol
Kyoto Protocol
The Kyoto Protocol is a protocol to the United Nations Framework Convention on Climate Change , aimed at fighting global warming...

 on global warming. As Mann said, "Advocates on both sides of the climate-change debate at various times have misrepresented the results for their own purposes". Environmental groups presented the graph flatteringly, and the caution about uncertainty in the original graph tended to be understated or removed: a "hockey stick" graph without error bars featured in a 2001 report by the U.S. National Assessment on Climate Change
National Assessment on Climate Change
The National Climate Assessment is a large-scale national project that is conducted under the auspices of the Global Change Research Act of 1990, and is one of the many activities of the US Global Change Research Program , a program which coordinates and integrates federal research on changes in...

. Similar graphs were used by those disputing the findings with the claim that the graph was inaccurate. When a later Wall Street Journal editorial used a graph without error bars in this way, Gerald North
Gerald North
Gerald R. North is Distinguished Professor and Holder of the Harold J. Haynes Endowed Chair in Geosciences at Texas A&M University, and previous Head of the Department of Atmospheric Sciences. His interests include climate change using simplified climate models.North was born in Sweetwater,...

 described this as "very misleading, in fact downright dishonest". Funding was provided by the American Petroleum Institute
American Petroleum Institute
The American Petroleum Institute, commonly referred to as API, is the largest U.S trade association for the oil and natural gas industry...

 for research critical of the graph. A paper by Chris de Freitas
Chris de Freitas
Chris de Freitas is an Associate Professor in the School of Environment at the University of Auckland in New Zealand.-Education and professional career:...

 published by the Canadian Society of Petroleum Geologists
Canadian Society of Petroleum Geologists
The Canadian Society of Petroleum Geologists is a professional geological society in Canada. The CSPG works to advance the science of geology, foster professional development of members and promote community awareness of the profession...

 in June 2002 argued against the IPCC findings and the Kyoto Protocol, claiming that global warming posed no danger and was innocuous. A section disputing the "hockey stick" curve concluded it was merely a mathematical construct promoted by the IPCC to support the "notion" that recent temperatures were unprecedented. Towards the end of 2002, the book Taken By Storm
Taken By Storm
Taken By Storm is a book about the global warming controversyby Christopher Essex and Ross McKitrick.The authors argue that politicians and others claim far more certainty than is justified by the science:...

 : the troubled science, policy, and politics of global warming
by Christopher Essex and Ross McKitrick
Ross McKitrick
Ross McKitrick is a Canadian economist specializing in environmental economics and policy analysis. He is professor of economics at the University of Guelph; a senior fellow of the Fraser Institute, a Canadian free-market public policy think tank; and a member of the academic advisory boards of the...

, published with assistance from the Fraser Institute
Fraser Institute
The Fraser Institute is a Canadian think tank. It has been described as politically conservative and right-wing libertarian and espouses free market principles...

, included a chapter about the graph titled "T-Rex Plays Hockey".

Iconic use of the IPCC graph came to symbolise conflict in which mainstream climate scientists were criticised, with some sceptics focussing on the hockey stick graph in the hope that they could damage the credence given to climate scientists.

Soon & Baliunas and Inhofe's hoax accusation



An early attempt to refute the hockey stick graph appeared in a joint paper by Willie Soon
Willie Soon
Willie Wei-Hock Soon is an astrophysicist at the Solar and Stellar Physics Division of the Harvard-Smithsonian Center for Astrophysics. Soon has testified before Congress on the issue of climate change He is known for his views that most global warming is caused by solar variation...

, who had already argued that climate change was primarily due to solar variation
Solar variation
Solar variation is the change in the amount of radiation emitted by the Sun and in its spectral distribution over years to millennia. These variations have periodic components, the main one being the approximately 11-year solar cycle . The changes also have aperiodic fluctuations...

, and Sallie Baliunas
Sallie Baliunas
Sallie Baliunas is an astrophysicist at the Harvard-Smithsonian Center for Astrophysics in the Solar, Stellar, and Planetary Sciences Division and formerly Deputy Director of the Mount Wilson Observatory. She serves as Senior Scientist at the George C. Marshall Institute in Washington, DC, and...

 who had contested whether ozone depletion
Ozone depletion
Ozone depletion describes two distinct but related phenomena observed since the late 1970s: a steady decline of about 4% per decade in the total volume of ozone in Earth's stratosphere , and a much larger springtime decrease in stratospheric ozone over Earth's polar regions. The latter phenomenon...

 was due to man-made chemicals. The Soon and Baliunas literature review
Literature review
A literature review is a body of text that aims to review the critical points of current knowledge including substantive findings as well as theoretical and methodological contributions to a particular topic...

 used data from previous papers to argue that the Medieval Warm Period had been warmer than the 20th century, and that recent warming was not unusual. They sent their paper to the editor Chris de Freitas
Chris de Freitas
Chris de Freitas is an Associate Professor in the School of Environment at the University of Auckland in New Zealand.-Education and professional career:...

 who opposed action to curb carbon dioxide emissions, and held that human actions did not cause climatic dangers. He approved the paper for publication in the relatively obscure journal Climate Research
Climate Research (journal)
Climate Research is a peer-reviewed scientific journal published by the Inter-Research Science Center that was established in 1990. Its founder was Otto Kinne. Three volumes are published each year...

, where it appeared on 31 January 2003. In March Soon and Baliunas published an extended paper in Energy & Environment. Scientists cited in the papers said that their work was misrepresented. The Climate Research paper was criticised by many other scientists, including several of the journal's editors. On 8 July Eos
Eos (journal)
Eos, Transactions, American Geophysical Union, a publication of the American Geophysical Union, is a weekly newspaper of geophysics that carries refereed articles on current research and on the relationship of geophysics to social and political questions, news, book reviews, AGU journal and meeting...

featured a detailed rebuttal of both papers by 13 scientists including Mann and Jones, presenting strong evidence that Soon and Baliunas had used improper statistical methods. Responding to the controversy, the publisher of Climate Research upgraded Hans von Storch
Hans von Storch
Hans von Storch is a German climate scientist. He is Professor at the Meteorological Institute of the University of Hamburg, and Director of the Institute for Coastal Research at the Helmholtz Research Centre in Geesthacht, Germany...

 from editor to editor in chief as of 1 August 2003. After seeing a preprint of the Eos rebuttal, von Storch decided that the Soon and Baliunas paper was seriously flawed and should not have been published as it was. He proposed a new editorial system, and an editorial saying that the review process had failed.

When the McCain-Lieberman bill
Climate Stewardship Acts
The Climate Stewardship Acts are a series of three acts introduced to the United States Senate by Senator John McCain and Senator Joseph Lieberman , with a number of other co-sponsors. Their aim was to introduce a mandatory cap and trade system for greenhouse gases, as a response to the threat of...

 proposing restrictions on greenhouse gases was being debated in the Senate on 28 July 2003, Senator James M. Inhofe
Jim Inhofe
James Mountain "Jim" Inhofe is the senior Senator from Oklahoma and a member of the Republican Party. First elected to the Senate in 1994, he is the ranking member of the United States Senate Committee on Environment and Public Works and was its chairman from 2003 to 2007. Inhofe served eight...

 made a two-hour speech in opposition. He cited a study by the Center for Energy and Economic Development and the Soon and Baliunas paper in supporting his conclusion: "With all of the hysteria, all of the fear, all of the phony science, could it be that man-made global warming is the greatest hoax ever perpetrated on the American people? It sure sounds like it." Inhofe convened a hearing of the United States Senate Committee on Environment and Public Works
United States Senate Committee on Environment and Public Works
The United States Senate Committee on Environment and Public Works is responsible for dealing with matters related to the environment and infrastructure.-Members, 112th Congress:...

 held on 29 July 2003, examining work by the small group of researchers saying there was no evidence of significant human-caused global warming.
Three scientists were invited, Mann giving testimony supporting the consensus position, opposed by long term skeptics Willie Soon and David Legates
David Legates
David Russell Legates is a Professor of Geography at the University of Delaware. He is the former Director of the Center for Climatic Research at the same university, and a former Delaware State Climatologist....

. The Soon and Baliunas paper was discussed. Senator Jeffords read out an email in which von Storch stated his view "that the review of the Soon et al. paper failed to detect significant methodological flaws in the paper. The critique published in the Eos journal by Mann et al. is valid." In reply, Mann testified "I believe it is the mainstream view of just about every scientist in my field that I have talked to that there is little that is valid in that paper. They got just about everything wrong." He later recalled that he "left that meeting having demonstrated what the mainstream views on climate science are."

The publisher of Climate Research agreed that the flawed Soon and Baliunas paper should not have been published uncorrected, but von Storch's proposals to improve the editorial process were rejected, and von Storch with three other board members resigned. News of his resignation was discussed at the senate committee hearing.

McIntyre and McKitrick 2003


In October 2003, a paper by Stephen McIntyre
Stephen McIntyre
Stephen McIntyre is a Canadian mathematician, former minerals prospector, and semi-retired mining consultant who is best known as the founder and editor of Climate Audit, a blog devoted to the analysis and discussion of climate data...

 and Ross McKitrick
Ross McKitrick
Ross McKitrick is a Canadian economist specializing in environmental economics and policy analysis. He is professor of economics at the University of Guelph; a senior fellow of the Fraser Institute, a Canadian free-market public policy think tank; and a member of the academic advisory boards of the...

 on "Corrections to the Mann et al. (1998) Proxy Data Base and Northern Hemisphere Average Temperature Series" was published in Energy & Environment (MM03). At a November 2003 event at the George C. Marshall Institute
George C. Marshall Institute
The George C. Marshall Institute is a politically conservative think tank established in 1984 in Washington, D.C. with a focus on scientific issues and public policy. In the 1980s, the Institute was engaged primarily in lobbying in support of the Strategic Defense Initiative...

, co-hosted by Myron Ebell
Myron Ebell
Myron Ebell is an American climate change skeptic. He is the Director of Global Warming and International Environmental Policy at the Competitive Enterprise Institute , a non-profit public policy organization founded in 1984 by Fred L. Smith, Jr. Ebell directs and oversees all aspects of energy...

 of the Cooler Heads Coalition
Cooler Heads Coalition
The Cooler Heads Coalition was originally a project of the National Consumer Coalition in the United States, a project of the nonprofit organization Consumer Alert. The Cooler Heads Coalition is now financed and operated by the Competitive Enterprise Institute. Its objective is described as...

, McIntyre said that he had become interested in the paper in April 2002 when the Kyoto Protocol
Kyoto Protocol
The Kyoto Protocol is a protocol to the United Nations Framework Convention on Climate Change , aimed at fighting global warming...

 was a major political issue in Canada, and had contacted Mann for the data set but found problems in replicating the curves of the graph due to missing or wrong data. He first met McKitrick, for "lunch at the exact hour that Hurricane Isabel hit Toronto" (September 19, 2003
Effects of Hurricane Isabel in Canada
The effects of Hurricane Isabel in Canada were fairly minor due to Isabel transitioning into an extratropical cyclone before affecting the area. Hurricane Isabel formed from a tropical wave on September 6, 2003 in the tropical Atlantic Ocean...

). They prepared their corrections in a proxy data set using 1999 data, and using publicly disclosed methods produced a reconstruction which differed from MBH98 in showing high peaks of temperature in the 15th century. They were not saying that these temperatures had occurred, but that Mann's results were incorrect. When they published their paper, it attracted attention, with David Appell being the first reporter to take an interest. After Appell's article was published with comments from Mann, they had followed links to Mann's FTP
File Transfer Protocol
File Transfer Protocol is a standard network protocol used to transfer files from one host to another host over a TCP-based network, such as the Internet. FTP is built on a client-server architecture and utilizes separate control and data connections between the client and server...

 site and on October 29 copied data files which were subsequently deleted from the site.
In 2007 the IPCC AR4
IPCC Fourth Assessment Report
Climate Change 2007, the Fourth Assessment Report of the United Nations Intergovernmental Panel on Climate Change , is the fourth in a series of reports intended to assess scientific, technical and socio-economic information concerning climate change, its potential effects, and options for...

 noted the claim that MBH98 could not be replicated, and reported that "Wahl and Ammann (2007) showed that this was a consequence of differences in the way McIntyre and McKitrick (2003) had implemented the method of Mann et al. (1998) and that the original reconstruction could be closely duplicated using the original proxy data."

In a corrigendum
Erratum
An erratum or corrigendum is a correction of a book. An erratum is most commonly issued shortly after its original text is published. Patches to security issues in a computer program are also sometimes called errata. As a general rule, publishers issue an erratum for a production error An erratum...

 published on 1 July 2004, Mann, Bradley and Hughes acknowledged that McIntyre and McKitrick had pointed out errors in proxy data that had been included as supplementary information to MBH98, and supplied a full corrected listing of the data. They included an archive of all the data used in MBH98, and expanded details of their methods. They stated that "None of these errors affect our previously published results."

von Storch and Zorita 2004; Cook et al. 2004; Moberg et al. 2005


The statistical methods used in the MBH reconstruction were questioned in a 2004 paper by Hans von Storch
Hans von Storch
Hans von Storch is a German climate scientist. He is Professor at the Meteorological Institute of the University of Hamburg, and Director of the Institute for Coastal Research at the Helmholtz Research Centre in Geesthacht, Germany...

 with a team including Eduardo Zorita
Eduardo Zorita
Eduardo Zorita is a Spanish paleoclimatologist. He is presently a Senior Scientist at the Institute for Coastal Research , GKSS Research Centre in Geesthacht, Germany, where he has worked since 1996...

, which said that the methodology used to average the data and the wide uncertainties might have hidden abrupt climate changes, possibly as large as the 20th century spike in measured temperatures. Tim Osborn and Keith Briffa
Keith Briffa
Professor Keith R. Briffa is a climatologist employed since 1977 by the Climatic Research Unit at the University of East Anglia, of which he is currently deputy director. In his professional work, he focuses on the climate change in late Holocene, with a special focus on northern portions of...

 responded, highlighting this conclusion. Zorita and von Storch later claimed this was a breakthrough in moving the question from "the reality of the blade of the hockey stick" to focus on "the real problems, namely the ‘wobbliness’ of the shaft of the hockey-stick, and the suppressing of valid scientific questions by gate keeping." The von Storch et al. view that the graph was defective overall was later refuted by Wahl, Ritson and Ammann (2006),
who pointed to incorrect implementation of the reconstruction procedure.

Later in 2004, Edward R. Cook, Jan Esper
Jan Esper
Jan Esper is the head of the dendro sciences division at the WSL division of the Swiss Federal Institute of Technology...

 and Rosanne D'arrigo re-examined their 2002 paper, and now supported MBH. They concluded that "annual temperatures up to AD 2000 over extra-tropical NH land areas have probably exceeded by about 0.3 °C the warmest previous interval over the past 1162 years". In December Mann and Gavin Schmidt
Gavin Schmidt
Gavin A. Schmidt is a climatologist and climate modeler at the NASA Goddard Institute for Space Studies in New York. He works on the variability of the ocean circulation and climate, using general circulation models . He has also worked on ways to reconcile paleo-data with models...

 launched the RealClimate
RealClimate
RealClimate is a commentary site on climatology. The site's contributors are a group of climate scientists whose goal is to provide a quick response to developing stories and providing the context sometimes missing in mainstream commentary. The discussion is intended to be restricted to scientific...

 website as "a resource where the public can go to see what actual scientists working in the field have to say about the latest issues."

In a Senate speech on 4 January 2005, Inhofe
Jim Inhofe
James Mountain "Jim" Inhofe is the senior Senator from Oklahoma and a member of the Republican Party. First elected to the Senate in 1994, he is the ranking member of the United States Senate Committee on Environment and Public Works and was its chairman from 2003 to 2007. Inhofe served eight...

 repeated his assertion that "the threat of catastrophic global warming" was the "greatest hoax ever perpetrated on the American people". He singled out the hockey stick graph and Mann for criticism, accusing Mann of having "effectively erased the well-known phenomena of the Medieval Warming Period-when, by the way, it was warmer than it is today-and the Little Ice Age". He quoted von Storch as criticising the graph. In a CBS News
CBS News
CBS News is the news division of American television and radio network CBS. The current chairman is Jeff Fager who is also the executive producer of 60 Minutes, while the current president of CBS News is David Rhodes. CBS News' flagship program is the CBS Evening News, hosted by the network's main...

 opinion piece, Chris Mooney said that Inhofe had extensively cited Michael Crichton
Michael Crichton
John Michael Crichton , best known as Michael Crichton, was an American best-selling author, producer, director, and screenwriter, best known for his work in the science fiction, medical fiction, and thriller genres. His books have sold over 200 million copies worldwide, and many have been adapted...

's fictional thriller, State of Fear
State of Fear
State of Fear is a 2004 techno-thriller novel by Michael Crichton concerning eco-terrorists who attempt mass murder to support their views. The novel had an initial print run of 1.5 million copies and reached the #1 bestseller position at Amazon.com and #2 on the New York Times Best Seller list for...

, mistakenly describing Crichton as a "scientist", and had misrepresented three scientists as disputing the "hockey stick" when they had been challenging a completely different paper which Mann had co-authored.

A study by Anders Moberg et al. published on 10 February 2005 used a wavelet transform technique to reconstruct Northern Hemisphere temperatures over the last 2,000 years, combining low-resolution proxy data such as lake and ocean sediments for century-scale or longer changes, with tree ring proxies only used for annual to decadal resolution. They found there had been a peak of temperatures around AD 1000 to 1100 similar to those reached in the years before 1990, and supported the basic conclusion of MBH99 by stating "We find no evidence for any earlier periods in the last two millennia with warmer conditions than the post-1990 period".

McIntyre and McKitrick 2005


In 2004 Stephen McIntyre
Stephen McIntyre
Stephen McIntyre is a Canadian mathematician, former minerals prospector, and semi-retired mining consultant who is best known as the founder and editor of Climate Audit, a blog devoted to the analysis and discussion of climate data...

 blogged on his website climate2003.com about his efforts to get an extended analysis of the hockey stick into the journal Nature
Nature (journal)
Nature, first published on 4 November 1869, is ranked the world's most cited interdisciplinary scientific journal by the Science Edition of the 2010 Journal Citation Reports...

, but he was unsuccessful and it was not until 2005 that he and Ross McKitrick
Ross McKitrick
Ross McKitrick is a Canadian economist specializing in environmental economics and policy analysis. He is professor of economics at the University of Guelph; a senior fellow of the Fraser Institute, a Canadian free-market public policy think tank; and a member of the academic advisory boards of the...

 got their paper into the less prestigious Geophysical Research Letters
Geophysical Research Letters
Geophysical Research Letters is a semi-monthly peer reviewed scientific journal published by the American Geophysical Union that was established in 1974...

. In their renewed criticism of MBH98, McIntyre and McKitrick's 2005 paper (MMO5), published in Geophysical Research Letters reported a technical statistical error. The authors wrote that the "Hockey Stick" shape was the result of an invalid principal component method, and that "the MBH98 method effectively selects only one species (bristlecone pine)" to produce the hockey-stick shape. McIntyre and McKitrick said that using the same steps as Mann et al., they were able to obtain a hockey stick shape as the first principal component in 99 percent of cases (counting both upwards and downwards-pointing "blades") even if simulated red noise without any inherent trends was used as input. The paper was nominated as a journal highlight by the American Geophysical Union
American Geophysical Union
The American Geophysical Union is a nonprofit organization of geophysicists, consisting of over 50,000 members from over 135 countries. AGU's activities are focused on the organization and dissemination of scientific information in the interdisciplinary and international field of geophysics...

, which publishes GRL.

In an immediate public relations
Public relations
Public relations is the actions of a corporation, store, government, individual, etc., in promoting goodwill between itself and the public, the community, employees, customers, etc....

 campaign, the Canadian National Post for 27 January carried a front page article alleging that "A pivotal global warming study central to the Kyoto Protocol contains serious flaws." The Bush administration had already decided to disregard the Kyoto Protocol
Kyoto Protocol
The Kyoto Protocol is a protocol to the United Nations Framework Convention on Climate Change , aimed at fighting global warming...

 which was to come into effect later that month, and this enabled them to say that the protocol was discredited. On 14 February a lead article in the Wall Street Journal said that McIntyre's new paper was "circulating inside energy companies and government agencies. Canada's environment ministry has ordered a review", and though McIntyre did not take strong position on whether or not fossil-fuel use was causing global warming, "He just says he has found a flaw in a main leg supporting the global-warming consensus, the consensus that led to an international initiative taking effect this week: Kyoto."

Others later found the issues raised by McIntyre and McKitrick were minor and did not affect the main conclusions of MBH. Technical issues were discussed in RealClimate
RealClimate
RealClimate is a commentary site on climatology. The site's contributors are a group of climate scientists whose goal is to provide a quick response to developing stories and providing the context sometimes missing in mainstream commentary. The discussion is intended to be restricted to scientific...

 on 18 February in a blog entry by Gavin Schmidt
Gavin Schmidt
Gavin A. Schmidt is a climatologist and climate modeler at the NASA Goddard Institute for Space Studies in New York. He works on the variability of the ocean circulation and climate, using general circulation models . He has also worked on ways to reconcile paleo-data with models...

 and Caspar Amman, and in a BBC News
BBC News
BBC News is the department of the British Broadcasting Corporation responsible for the gathering and broadcasting of news and current affairs. The department is the world's largest broadcast news organisation and generates about 120 hours of radio and television output each day, as well as online...

 interview Schmidt said that by using a different convention but not altering subsequent steps in the analysis accordingly, McIntyre and McKitrick had removed significant data which would have given the same result as the MBH papers.

In a presentation to the Asia-Pacific Economic Cooperation
Asia-Pacific Economic Cooperation
Asia-Pacific Economic Cooperation is a forum for 21 Pacific Rim countries that seeks to promote free trade and economic cooperation throughout the Asia-Pacific region...

 Study Centre on 4 April 2005, McKitrick said that the prominence given to the hockey stick graph in the TAR "was deliberate editorial sleight-of-hand" to trick readers into thinking it was more important than the graph of satellite-measured tropospheric data by Christy
John Christy
John R. Christy is a climate scientist at the University of Alabama in Huntsville whose chief interests are satellite remote sensing of global climate and global climate change. He is best known, jointly with Roy Spencer, for the first successful development of a satellite temperature...

 and Spencer. He said that "The Government of Canada subsequently sent the hockey stick (but not the satellite data) to schools across the country, and its famous conclusion about the 1990s being the warmest decade of the millennium was the opening line of a pamphlet sent to every household in Canada to promote the Kyoto Protocol." Having outlined the arguments about the MBH methodology as detailed in the McIntyre and McKitrick papers, he proposed that an "audit report" by non-climatologists should assess IPCC reports and be published by the IPCC, and that as part of the IPCC process a "counter-weight panel" should critique the Working Group 1 science report on both economic and scientific aspects.

In May the University Corporation for Atmospheric Research
University Corporation for Atmospheric Research
The University Corporation for Atmospheric Research is a nonprofit consortium of more than 75 universities offering Ph.D.s in the atmospheric and related sciences. UCAR manages the National Center for Atmospheric Research and provides additional services to strengthen and support research and...

 advised media about a detailed analysis by Eugene Wahl and Caspar Ammann, first presented at the American Geophysical Union
American Geophysical Union
The American Geophysical Union is a nonprofit organization of geophysicists, consisting of over 50,000 members from over 135 countries. AGU's activities are focused on the organization and dissemination of scientific information in the interdisciplinary and international field of geophysics...

’s December 2004 meeting in San Francisco, which used their own code to replicate the MBH results, and found the MBH method to be robust even with modifications. Their work contradicted the claims by McIntyre and McKitrick about high 15th century global temperatures and allegations of methodological bias towards a hockey stick outcomes, and they concluded that the criticisms of the hockey stick graph were groundless.

Congressional investigations


The increasing politicisation of the issue was demonstrated when, on 23 June 2005, Rep. Joe Barton
Joe Barton
Joseph Linus "Joe" Barton is a Republican politician, representing in the U.S. House of Representatives since 1985, and a member of the Tea Party Caucus...

, chairman of the House Committee on Energy and Commerce
United States House Committee on Energy and Commerce
The Committee on Energy and Commerce is one of the oldest standing committees of the United States House of Representatives. Established in 1795, it has operated continuously—with various name changes and jurisdictional changes—for more than 200 years...

 wrote joint letters with Ed Whitfield
Ed Whitfield
Wayne Edward "Ed" Whitfield is the U.S. Representative of , serving since 1995. He is a member of the Republican Party.The district covers much of the western part of the state, including Hopkinsville, Paducah, Henderson and Kentucky's share of Fort Campbell.-Early life, education and...

, Chairman of the Subcommittee on Oversight and Investigations
United States House Energy Subcommittee on Oversight and Investigations
The U.S. House Energy Subcommittee on Oversight and Investigations is a subcommittee within the House Committee on Energy and Commerce.-Jurisdiction:...

, referring to issues raised by the 14 February 2005 article in the Wall Street Journal and demanding full records on climate research. The letters were sent to the IPCC
IPCC
IPCC may refer to:*Intergovernmental Panel on Climate Change, of the United Nations*Independent Police Complaints Commission, of England and Wales*Irish Peatland Conservation Council...

 Chairman Rajendra Pachauri, National Science Foundation
National Science Foundation
The National Science Foundation is a United States government agency that supports fundamental research and education in all the non-medical fields of science and engineering. Its medical counterpart is the National Institutes of Health...

 Director Arden Bement, and to the three scientists Mann, Bradley and Hughes
Malcolm K. Hughes
Malcolm K. Hughes is a meso-climatologist and Regents' Professor of Dendrochronology in the Laboratory for Tree-Ring Research at the University of Arizona. He was born in Matlock, Derbyshire, England, and earned a Ph.D in ecology from the University of Durham. Since 1998, he is a fellow of the...

.
The letters told the scientist to provide not just data and methods, but also personal information about their finances and careers, information about grants provided to the institutions they had worked for, and the exact computer codes used to generate their results.

Sherwood Boehlert
Sherwood Boehlert
Sherwood "Sherry" Louis Boehlert is a retired American politician from New York. He represented upstate New York in the United States House of Representatives from 1983 until 2007. Boehlert, a Republican, was considered to be a member of the party's moderate wing. In 2003, Utica Union Station was...

, chairman of the House Science Committee, told his fellow Republican Joe Barton it was a "misguided and illegitimate investigation" into something that was the under the jurisdiction of the Science Committee, and "My primary concern about your investigation is that its purpose seems to be to intimidate scientists rather than to learn from them, and to substitute congressional political review for scientific review." Barton's committee spokesman sent a sarcastic response to this and to Democrat Henry A. Waxman's letter asking Barton to withdraw the letters and saying he had "failed to hold a single hearing on the subject of global warming" during eleven years as chairman, and had "vociferously opposed all legislative efforts in the Committee to address global warming .... These letters do not appear to be a serious attempt to understand the science of global warming. Some might interpret them as a transparent effort to bully and harass climate change experts who have reached conclusions with which you disagree." The U.S. National Academy of Sciences
United States National Academy of Sciences
The National Academy of Sciences is a corporation in the United States whose members serve pro bono as "advisers to the nation on science, engineering, and medicine." As a national academy, new members of the organization are elected annually by current members, based on their distinguished and...

 (NAS) president Ralph J. Cicerone wrote to Barton that "A congressional investigation, based on the authority of the House Commerce Committee, is probably not the best way to resolve a scientific issue, and a focus on individual scientists can be intimidating", and proposed that the NAS should appoint an independent panel to investigate. Barton dismissed this offer.

On 15 July, Mann wrote giving his detailed response to Barton and Whitfield. He emphasised that the full data and necessary methods information was already publicly available in full accordance with National Science Foundation
National Science Foundation
The National Science Foundation is a United States government agency that supports fundamental research and education in all the non-medical fields of science and engineering. Its medical counterpart is the National Institutes of Health...

 (NSF) requirements, so that other scientists had been able to reproduce their work. NSF policy was that computer codes "are considered the intellectual property of researchers and are not subject to disclosure", as the NSF had advised McIntyre and McKitrick in 2003, but notwithstanding these property rights, the program used to generate the original MBH98 temperature reconstructions had been made available at the Mann et al. public ftp site.
Following receipt of responses to the letters, Barton and Whitfield had their committee staff contact statistician Edward J. Wegman for advice on the validity of McIntyre and McKitrick's complaints, and Wegman formed an ad-hoc committee consisting of himself, David W. Scott and Yasmin H. Said.

Many scientists protested, with 20 prominent climatologists writing to Barton questioning his approach. Alan I. Leshner
Alan I. Leshner
Alan Leshner is a scientist, educator and public servant from the United States.-Education:Leshner received an undergraduate degree in psychology from Franklin and Marshall College in 1965. He earned an M.S. in physiological psychology from Rutgers University in 1967, and a Ph.D...

 wrote to him on behalf of the American Association for the Advancement of Science
American Association for the Advancement of Science
The American Association for the Advancement of Science is an international non-profit organization with the stated goals of promoting cooperation among scientists, defending scientific freedom, encouraging scientific responsibility, and supporting scientific education and science outreach for the...

 expressing deep concern about the letters, which gave "the impression of a search for some basis on which to discredit these particular scientists and findings, rather than a search for understanding," He stated that MBH had given out their full data and descriptions of methods, and were not the only evidence in the IPCC TAR that recent temperatures were likely the warmest in 1,000 years; "a variety of independent lines of evidence, summarized in a number of peer-reviewed publications, were cited in support". 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
IPCC
IPCC may refer to:*Intergovernmental Panel on Climate Change, of the United Nations*Independent Police Complaints Commission, of England and Wales*Irish Peatland Conservation Council...

 during preparation of its next report.
A Washington Post editorial on 23 July which described the investigation as harassment quoted Bradley as saying it was "intrusive, far-reaching and intimidating", and Alan I. Leshner of the AAAS describing it as unprecedented in in the 22 years he had been a government scientist; he thought it could "have a chilling effect on the willingness of people to work in areas that are politically relevant."

Congressman Boehlert said the investigation was as "at best foolhardy" with the tone of the letters showing the committee's "inexperience" in relation to science. Barton was given support by global warming sceptic Myron Ebell
Myron Ebell
Myron Ebell is an American climate change skeptic. He is the Director of Global Warming and International Environmental Policy at the Competitive Enterprise Institute , a non-profit public policy organization founded in 1984 by Fred L. Smith, Jr. Ebell directs and oversees all aspects of energy...

 of the Competitive Enterprise Institute
Competitive Enterprise Institute
The Competitive Enterprise Institute is a non-profit think tank founded on March 9, 1984 in Washington, D.C. by lobbyist Fred L. Smith, Jr to advance economic liberty and fight over-regulation by big government...

, 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". In in his Junk Science column on Fox News
Fox News Channel
Fox News Channel , often called Fox News, is a cable and satellite television news channel owned by the Fox Entertainment Group, a subsidiary of News Corporation...

, Steven Milloy
Steven Milloy
Steven J. Milloy is a commentator for Fox News and runs the Web site junkscience.com, which is dedicated to "debunking" what Milloy labels "faulty scientific data and analysis." On Fox News Channel he is billed as a "Junk Science commentator." He describes himself as a libertarian.Among the topics...

 said Barton's inquiry was reasonable.

In comments on MM05 made in October, Peter Huybers
Peter Huybers
Peter Huybers is an American climate scientist, and Professor of Earth and Planetary Sciences at Harvard University, in the Department of Earth and Planetary Sciences.-Life and work:...

 showed that McIntyre and McKitrick had omitted a critical step in calculating significance levels, and MBH98 had shown it correctly.
In their comment, Hans von Storch
Hans von Storch
Hans von Storch is a German climate scientist. He is Professor at the Meteorological Institute of the University of Hamburg, and Director of the Institute for Coastal Research at the Helmholtz Research Centre in Geesthacht, Germany...

 and Eduardo Zorita
Eduardo Zorita
Eduardo Zorita is a Spanish paleoclimatologist. He is presently a Senior Scientist at the Institute for Coastal Research , GKSS Research Centre in Geesthacht, Germany, where he has worked since 1996...

 examined McIntyre and McKitrick's claim that normalising data prior to principal component analysis by centering in relation to the calibration period of 1902–1980, instead of the whole period, would nearly always produce hockey stick shaped leading principal components. They found that it caused only very minor deviations which would not have a significant impact on the result. In the same month a paper in the Journal of Climate
Journal of Climate
The Journal of Climate is a scientific journal published by the American Meteorological Society.The journal publishes articles on climate research, in particular those concerned with large-scale atmospheric and oceanic variability, changes in the climate system , and climate simulation and...

, co-authored by Scott Rutherford, Mann, Osborn, Briffa, Jones, Bradley and Hughes, examined the sensitivity of proxy based reconstruction to method, and found that a wide range of alternative statistical approaches gave nearly indistinguishable results. In particular, omitting principal component analysis made no significant difference.

In November 2005, Science Committee chair Sherwood Boehlert requested the National Academy of Science to arrange a review of the matter. The National Research Council
United States National Research Council
The National Research Council of the USA is the working arm of the United States National Academies, carrying out most of the studies done in their names.The National Academies include:* National Academy of Sciences...

 set up a special committee to investigate.

Inconvenient Truth


In February 2006 two more reconstructions were published, using different methodologies and supporting the main conclusions of MBH. Rosanne D'Arrigo, Rob Wilson and Gordon Jacoby suggested that medieval temperatures had been almost 0.7°C cooler than the late 20th century but less homogenous, Osborn and Briffa found the spatial extent of recent warmth more significant than that during the medieval warm period.

Al Gore
Al Gore
Albert Arnold "Al" Gore, Jr. served as the 45th Vice President of the United States , under President Bill Clinton. He was the Democratic Party's nominee for President in the 2000 U.S. presidential election....

's film An Inconvenient Truth
An Inconvenient Truth
An Inconvenient Truth is a 2006 documentary film directed by Davis Guggenheim about former United States Vice President Al Gore's campaign to educate citizens about global warming via a comprehensive slide show that, by his own estimate, he has given more than a thousand times.Premiering at the...

, which premiered in May 2006, included a section on Lonnie Thompson
Lonnie Thompson
Lonnie Thompson , is an American paleoclimatologist and Distinguished University Professor in the School of Earth Sciences at The Ohio State University. He has achieved global recognition for his drilling and analysis of ice cores from mountain glaciers and ice caps in the tropical and sub-tropical...

's ice core
Ice core
An ice core is a core sample that is typically removed from an ice sheet, most commonly from the polar ice caps of Antarctica, Greenland or from high mountain glaciers elsewhere. As the ice forms from the incremental build up of annual layers of snow, lower layers are older than upper, and an ice...

 measurements showing a correlation between levels and temperature going back 650,000 years. Gore showed this "thermometer" graph going back a thousand years for a "couple of reasons", the first being that "so called skeptics" will sometimes say "Oh, this whole thing is cyclical phenomenon. There was a medieval warming period after all", but as shown on the graph, "compared to what is going on now, there is just no comparison".
The book issued at the same time includes a similar statement beside a graph like Figure 7 from Thompson's 2004 paper, and adds that the skeptics "launched a fierce attack against another measurement of the 1,000 year correlation between and temperature known as 'the hockey stick,' a graphic image representing the research of Michael Mann and his colleagues. But in fact, scientists have confirmed the same basic conclusions in multiple ways–with Thompson's ice core record as one of the most definitive."

National Research Council Report


At the request of the U.S. Congress, a special "Committee on Surface Temperature Reconstructions for the Past 2,000 Years" was assembled by the National Research Council's
United States National Research Council
The National Research Council of the USA is the working arm of the United States National Academies, carrying out most of the studies done in their names.The National Academies include:* National Academy of Sciences...

 Board on Atmospheric Sciences and Climate. The Committee consisted of 12 scientists, chaired by Gerald North
Gerald North
Gerald R. North is Distinguished Professor and Holder of the Harold J. Haynes Endowed Chair in Geosciences at Texas A&M University, and previous Head of the Department of Atmospheric Sciences. His interests include climate change using simplified climate models.North was born in Sweetwater,...

, from different disciplines and was tasked with explaining the current scientific information on the temperature record for the past two millennia, and identifying the main areas of uncertainty, the principal methodologies used, any problems with these approaches, and how central the debate is to the state of scientific knowledge on global climate change.

The panel published its report in 2006.
"The basic conclusion of Mann et al. (1998, 1999) was that the late 20th century warmth in the Northern Hemisphere was unprecedented during at least the last 1,000 years. This conclusion has subsequently been supported by an array of evidence that includes ...
    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. The substantial uncertainties currently present in the quantitative assessment of large-scale surface temperature changes before about A.D. 1600 lower our confidence in this conclusion compared to the high level of confidence we place in the Little Ice Age cooling and 20th century warming. Even less confidence can be placed in the original conclusions by Mann et al. (1999) that "the 1990s are likely the warmest decade, and 1998 the warmest year, in at least a millennium" because the uncertainties inherent in temperature reconstructions for individual years and decades are larger than those for longer time periods, and because not all of the available proxies record temperature information on such short timescales."


The report agreed that there were statistical shortcomings in the MBH analysis, but concluded that they were small in effect. The report summarizes its main findings as follows:
  • The instrumentally measured warming of about 0.6 °C (1.1 °F) during the 20th century is also reflected in borehole temperature measurements, the retreat of glaciers
    Retreat of glaciers since 1850
    The retreat of glaciers since 1850 affects the availability of fresh water for irrigation and domestic use, mountain recreation, animals and plants that depend on glacier-melt, and in the longer term, the level of the oceans...

    , and other observational evidence, and can be simulated with climate models.
  • Large-scale surface temperature reconstructions yield a generally consistent picture of temperature trends during the preceding millennium, including relatively warm conditions centered around 1000 (identified by some as the “Medieval Warm Period
    Medieval Warm Period
    The Medieval Warm Period , Medieval Climate Optimum, or Medieval Climatic Anomaly was a time of warm climate in the North Atlantic region, that may also have been related to other climate events around the world during that time, including in China, New Zealand, and other countries lasting from...

    ”) and a relatively cold period (or “Little Ice Age
    Little Ice Age
    The Little Ice Age was a period of cooling that occurred after the Medieval Warm Period . While not a true ice age, the term was introduced into the scientific literature by François E. Matthes in 1939...

    ”) centered around 1700. The existence and extent of a Little Ice Age from roughly 1500 to 1850 is supported by a wide variety of evidence including ice cores, tree rings, borehole temperatures, glacier length records, and historical documents. Evidence for regional warmth during medieval times can be found in a diverse but more limited set of records including ice cores, tree rings, marine sediments, and historical sources from Europe and Asia, but the exact timing and duration of warm periods may have varied from region to region, and the magnitude and geographic extent of the warmth are uncertain.
  • It can be said with a high level of confidence that global mean surface temperature was higher during the last few decades of the 20th century than during any comparable period during the preceding four centuries. This statement is justified by the consistency of the evidence from a wide variety of geographically diverse proxies.
  • Less confidence can be placed in large-scale surface temperature reconstructions for the period from 900 to 1600. Presently available proxy evidence indicates that temperatures at many, but not all, individual locations were higher during the past 25 years than during any period of comparable length since 900. The uncertainties associated with reconstructing hemispheric mean or global mean temperatures from these data increase substantially backward in time through this period and are not yet fully quantified.
  • Very little confidence can be assigned to statements concerning the hemispheric mean or global mean surface temperature before about 900 because of sparse data coverage and because the uncertainties associated with proxy data and the methods used to analyze and combine them are larger than during more recent time periods.


A group-authored post on RealClimate
RealClimate
RealClimate is a commentary site on climatology. The site's contributors are a group of climate scientists whose goal is to provide a quick response to developing stories and providing the context sometimes missing in mainstream commentary. The discussion is intended to be restricted to scientific...

, of which Mann is one of the contributors, said "the panel has found reason to support the key mainstream findings of past research, including points that we have highlighted previously." Similarly, Roger A. Pielke, Jr.
Roger A. Pielke (Jr)
Roger A. Pielke, Jr. is an American professor in the Environmental Studies Program and a Fellow of the Cooperative Institute for Research in Environmental Sciences where he served as Director of the at the University of Colorado at Boulder from 2001 to 2007...

 said that the National Research Council publication constituted a "near-complete vindication for the work of Mann et al."; Nature
Nature (journal)
Nature, first published on 4 November 1869, is ranked the world's most cited interdisciplinary scientific journal by the Science Edition of the 2010 Journal Citation Reports...

reported it as "Academy affirms hockey-stick graph. But it criticizes the way the controversial climate result was used."

North was reported as saying at the press conference announcing the report that the panel had "concluded that systematic uncertainties in climate records from before 1600 were not communicated as clearly as they could have been". In a letter to Nature
Nature (journal)
Nature, first published on 4 November 1869, is ranked the world's most cited interdisciplinary scientific journal by the Science Edition of the 2010 Journal Citation Reports...

on August 10, 2006, Bradley, Hughes and Mann pointed out that the original title of their 1999 paper (MBH99) was "Northern Hemisphere temperatures during the past millennium: inferences, uncertainties, and limitations", and it had concluded that "more widespread high-resolution data are needed before more confident conclusions can be reached". They said that "the uncertainties were the point of the article", and that it was "hard to imagine how much more explicit" they could have been about the uncertainties surrounding their work. They suggested that "poor communication by others" had led to the "subsequent confusion".

According to Hans von Storch
Hans von Storch
Hans von Storch is a German climate scientist. He is Professor at the Meteorological Institute of the University of Hamburg, and Director of the Institute for Coastal Research at the Helmholtz Research Centre in Geesthacht, Germany...

, Eduardo Zorita
Eduardo Zorita
Eduardo Zorita is a Spanish paleoclimatologist. He is presently a Senior Scientist at the Institute for Coastal Research , GKSS Research Centre in Geesthacht, Germany, where he has worked since 1996...

 and Jesus Rouco, reviewing the NAS report on McIntyre's blog Climate Audit
Climate Audit
Climate Audit is a blog which was founded on 31 January 2005 by Steve Mcintyre.The New York Times has called it "a popular skeptics’ blog".The website has won the 2007 Best Science Blog award and was a runner up in the same category in 2008.-Founding:...

, "With respect to methods, the committee is showing reservations concerning the methodology of Mann et al. The committee notes explicitly on pages 91 and 111 that the method has no validation (CE) skill significantly different from zero. In the past, however, it has always been claimed that the method has a significant nonzero validation skill. Methods without a validation skill are usually considered useless." It was noted by their critics, however, that no such statement, explicit or implicit, is present on the two pages cited; the closest the report comes being a statement that "Some recent results reported in Table 1S of Wahl and Ammann (in press) indicate that their reconstruction, which uses the same procedure and full set of proxies used by Mann et al. (1999), gives CE values ranging from 0.103 to −0.215, depending on how far back in time the reconstruction is carried."
However, CE is not the only measure of skill; Mann et al. (1998) used the more traditional "RE" score, which, unlike CE, accounts for the fact that time series change their mean value over time. The statistically significant reconstruction skill in the Mann et al. reconstruction is independently supported in the peer-reviewed literature.

Richard Muller
Richard A. Muller
Richard A. Muller is a noted American professor of physics at the University of California, Berkeley. He is also a faculty senior scientist at the Lawrence Berkeley National Laboratory.-Career:...

 said in his December 2006 book Physics for future presidents that "the strongest statement that could be made was that the present years were the warmest in the last 400 years, not 1,000 as Mann had said" and that "In the end, there was nothing new left in Mann's papers that the National Academy supported, other than the idea that using principal component analysis was, in principle, a good one."

At the American Statistical Association
American Statistical Association
The American Statistical Association , is the main professional US organization for statisticians and related professions. It was founded in Boston, Massachusetts on November 27, 1839, and is the second oldest, continuously operating professional society in the United States...

 2006 Joint Statistical Meetings
Joint Statistical Meetings
The Joint Statistical Meetings is a professional conference/academic conference for statisticians held annually every year since 1840 . Billed as "the largest gathering of statisticians held in North America", JSM has attracted over 5000 participants in recent years...

, John Michael Wallace
John Michael Wallace
John Michael Wallace is a professor of Atmospheric Sciences at the University of Washington, as well as the former director of the Joint Institute for the Study of the Atmosphere and Ocean --a joint research venture between the University of Washington and the National Oceanic and Atmospheric...

 reported that the NRC had found the Mann et al. claim that the last two decades were the warmest of the last 1000 years "entirely plausible", supported by a wide range of evidence. They had reported this cautiously, as "plausible" meaning 2:1 odds in favor.

Committee on Energy and Commerce Report (Wegman Report)


In an editorial dated 14 July 2006, the Wall Street Journal announced that a report commissioned by the House Committee on Energy and Commerce
United States House Committee on Energy and Commerce
The Committee on Energy and Commerce is one of the oldest standing committees of the United States House of Representatives. Established in 1795, it has operated continuously—with various name changes and jurisdictional changes—for more than 200 years...

 was due to be released that day. It gave a preview of the conclusions of the report, which had been prepared by three statisticians: Edward Wegman
Edward Wegman
Edward Wegman is a statistician, a statistics professor at George Mason University, and past chair of the National Research Council’s Committee on Applied and Theoretical Statistics. He holds a Ph.D. in mathematical statistics and is a Fellow of the American Statistical Association and a Senior...

, David W. Scott and Yasmin H. Said. The committee chairman U.S. Rep. Joe Barton
Joe Barton
Joseph Linus "Joe" Barton is a Republican politician, representing in the U.S. House of Representatives since 1985, and a member of the Tea Party Caucus...

 issued a press release giving a summary of the report's findings, with quotations from the report. The report primarily focused on the statistical analysis used in the MBH paper, but also considered the personal and professional relationships between Mann et al. and other members of the paleoclimate community. It became known as the "Wegman Report", and its findings were discussed at hearings of the Energy Subcommittee on Oversight and Investigations
United States House Energy Subcommittee on Oversight and Investigations
The U.S. House Energy Subcommittee on Oversight and Investigations is a subcommittee within the House Committee on Energy and Commerce.-Jurisdiction:...

 under its chairman U.S. Rep. Ed Whitfield
Ed Whitfield
Wayne Edward "Ed" Whitfield is the U.S. Representative of , serving since 1995. He is a member of the Republican Party.The district covers much of the western part of the state, including Hopkinsville, Paducah, Henderson and Kentucky's share of Fort Campbell.-Early life, education and...

.

Allegations and responses

  • "In general, we found MBH98 and MBH99 to be somewhat obscure and incomplete and the criticisms of MM03/05a/05b to be valid and compelling."
    • Mann's immediate response was that the report "uncritically parrots claims by two Canadians (an economist and a mineral-exploration consultant) that have already been refuted by several papers in the peer-reviewed literature inexplicably neglected by Barton's 'panel'. These claims were specifically dismissed by the National Academy in their report just weeks ago."
  • The report stated that the MBH method creates a hockey-stick shape even when supplied with random input data (Figure 4.4), and argues that the MBH method uses weather station data from 1902 to 1995 as a basis for calibrating other input data. "It is not clear that Dr. Mann and his associates even realized that their methodology was faulty at the time of writing the MBH paper. The net effect of the decentering is to preferentially choose the so-called hockey stick shapes." (Section 4)
    • Gerald North
      Gerald North
      Gerald R. North is Distinguished Professor and Holder of the Harold J. Haynes Endowed Chair in Geosciences at Texas A&M University, and previous Head of the Department of Atmospheric Sciences. His interests include climate change using simplified climate models.North was born in Sweetwater,...

       gave testimony that "Dr. Wegman's criticisms of the statistical methodology in the papers by Mann et al. were consistent with our findings", referring to the NRC report which had found that the methodology did not have an undue effect on the graphs. In his view, "none of the statistical criticisms that have been raised by various authors unduly influence the shape of the final reconstruction. This is attested to by the fact that reconstructions performed without using principal components yield similar results."
    • Hans von Storch
      Hans von Storch
      Hans von Storch is a German climate scientist. He is Professor at the Meteorological Institute of the University of Hamburg, and Director of the Institute for Coastal Research at the Helmholtz Research Centre in Geesthacht, Germany...

       testified that the tendency to produce hockey-stick shapes from random data would only apply if there were no other significant signals, and "in very many practical situations it would not show up."
    • RealClimate
      RealClimate
      RealClimate is a commentary site on climatology. The site's contributors are a group of climate scientists whose goal is to provide a quick response to developing stories and providing the context sometimes missing in mainstream commentary. The discussion is intended to be restricted to scientific...

       stated that the result of fixing the alleged errors made no practical difference to the overall reconstruction, and the hockey stick shape remained. Similarly, studies that use completely different methodologies also yield very similar reconstructions.
  • The report said that MBH method creates a PC1 statistic dominated by bristlecone and foxtail pine
    Foxtail Pine
    The Foxtail Pine is a rare pine that is endemic to California, United States, where it is found in two areas with a separate subspecies in each, the typical subsp. balfouriana in the Klamath Mountains, and subsp. austrina in the southern Sierra Nevada.-Description:Foxtail Pine is a tree to tall,...

     tree ring series (closely related species). However there is evidence in the literature, that the use of the bristlecone pine series as a temperature proxy may not be valid (suppressing "warm period" in the hockey stick handle); and that bristlecones do exhibit CO2-fertilized growth over the last 150 years (enhancing warming in the hockey stick blade).
    • The NRC report, according to North's testimony, found that this issue affected trees at some of the places where samples had been taken for the Mann study, and in view of calibration difficulties it was easier not to use them. However, "strip-bark data are considered suspect only after the modern increase in atmospheric carbon dioxide concentrations. This is why other studies that rely on strip-bark pine records only use them to infer past temperatures prior to 1850.
  • A social network of authorships in temperature reconstruction is described of at least 43 authors with direct ties to Mann by virtue of having coauthored papers with him. The findings from this analysis suggest that authors in the area of paleoclimate studies are closely connected and thus ‘independent studies’ may not be as independent as they might appear on the surface. Dr. Wegman stated this was a "hypothesis", and "should be taken with a grain of salt."
    • North criticised aspects of this analysis, which had not been available for the NRC to examine. He "was not impressed by the social network analysis" and differed from "the report's conclusions on this subject".
    • In John Quiggin
      John Quiggin
      John Quiggin is an Australian economist and professor at the University of Queensland. Quiggin studied at the Australian National University, obtaining bachelor's degrees in Arts and Economics in 1978 and 1980 respectively, and completing a master's degree in Economics in 1984. Quiggin was awarded...

      's opinion, the social network analysis was not based on meaningful criteria, did not prove a conflict of interest and did not apply at the time of the 1998 and 1999 publications. Such a network of co-authorship is not unusual in narrowly defined areas of science.
    • When allegations of plagiarism in this section were examined, Wegman said that material in it had been "basically copied and pasted" by a student who was the "most knowledgeable" person about such analyses on his team, as she had taken a one week course on network analysis with Kathleen Carley
      Kathleen Carley
      Kathleen M. Carley is an American social scientist specializing in dynamic network analysis. She is a professor in the School of Computer Science in the Institute for Software Research International at Carnegie Mellon University and also holds appointments in the Tepper School of Business, the...

       of Carnegie Mellon University
      Carnegie Mellon University
      Carnegie Mellon University is a private research university in Pittsburgh, Pennsylvania, United States....

      . Carley described the paper based on this section as "more of an opinion piece", lacking the data needed to support its argument.
  • Many of the same proxies are reused in most of the "independent studies" so these "cannot really claim to be independent verifications."
  • The Wegman Report said that there was no evidence that Mann or any of the other authors in paleoclimatology studies have had significant interactions with mainstream statisticians. The paleoclimate community is relatively isolated; its members rely heavily on statistical methods but do not seem to interact with the statistical community.
    • RealClimate responded that the National Center for Atmospheric Research
      National Center for Atmospheric Research
      The National Center for Atmospheric Research has multiple facilities, including the I. M. Pei-designed Mesa Laboratory headquarters in Boulder, Colorado. NCAR is managed by the nonprofit University Corporation for Atmospheric Research and sponsored by the National Science Foundation...

       Geophysical Statistics Project had provided such expertise for years, and its head Doug Nychka had been directly consulted for the Wahl and Ammann (2006) paper.
  • Sharing of research materials, data, and results was done haphazardly and begrudgingly.
  • Overall, the committee believed that Mann’s assessments, that the decade of the 1990s was the hottest decade of the millennium and that 1998 was the hottest year of the millennium, cannot be supported by his analysis.

Discussion and hearings

  • The report was not subject to formal peer review
    Peer review
    Peer review is a process of self-regulation by a profession or a process of evaluation involving qualified individuals within the relevant field. Peer review methods are employed to maintain standards, improve performance and provide credibility...

     by paleoclimatologists. At the hearing, Wegman listed 6 people that participated in his own informal peer review process via email after the report was finalized and said they had no objection to the subcommittee submitting it. He defined the social network as peer reviewers that had "actively collaborated with him in writing research papers" and answered that none of his peer reviewers had.
  • Gerald North
    Gerald North
    Gerald R. North is Distinguished Professor and Holder of the Harold J. Haynes Endowed Chair in Geosciences at Texas A&M University, and previous Head of the Department of Atmospheric Sciences. His interests include climate change using simplified climate models.North was born in Sweetwater,...

    , chairman of the National Research Council panel that studied the hockey-stick issue and produced the report Surface Temperature Reconstructions for the Last 2,000 Years, stated the politicians at the hearing at which the Wegman Report was presented "were twisting the scientific information for their own propaganda purposes. The hearing was not an information gathering operation, but rather a spin machine."
  • As a lot of claims regarding the hockey stick revolve around statistical aspects, the American Statistical Association
    American Statistical Association
    The American Statistical Association , is the main professional US organization for statisticians and related professions. It was founded in Boston, Massachusetts on November 27, 1839, and is the second oldest, continuously operating professional society in the United States...

     held a session at the 2006 Joint Statistical Meetings
    Joint Statistical Meetings
    The Joint Statistical Meetings is a professional conference/academic conference for statisticians held annually every year since 1840 . Billed as "the largest gathering of statisticians held in North America", JSM has attracted over 5000 participants in recent years...

    , on climate change with Edward Wegman
    Edward Wegman
    Edward Wegman is a statistician, a statistics professor at George Mason University, and past chair of the National Research Council’s Committee on Applied and Theoretical Statistics. He holds a Ph.D. in mathematical statistics and is a Fellow of the American Statistical Association and a Senior...

    , John Michael Wallace
    John Michael Wallace
    John Michael Wallace is a professor of Atmospheric Sciences at the University of Washington, as well as the former director of the Joint Institute for the Study of the Atmosphere and Ocean --a joint research venture between the University of Washington and the National Oceanic and Atmospheric...

    , and Richard L. Smith. E. Wegman presented the discussion of the methodological aspects of PC analysis by MBH98, and his response to those saying that the paper had been validated by other studies, Method Wrong + Answer Correct = Bad Science, "in other words, the fact that the answer may have been correct does not justify the use of an incorrect method in the first place." J. M. Wallace outlined the NRC report and the range of evidence which had led to their belief "that the Mann et al. claim that the last two decades were the warmest of the last 1000 years was entirely plausible." Despite this, the NRC report had phrased its conclusions cautiously, describing this as "no more than 'plausible' (2:1 odds in favor)". R. L. Smith (U. of North Carolina, Statistics) analyzed statistical methodology behind the CCSP
    Climate Change Science Program
    The Climate Change Science Program was the program responsible for coordinating and integrating research on global warming by U.S. government agencies from February 2002 to June 2009...

     "Report on Temperature Trends in the Lower Atmosphere” and shared his vision of the role of statisticians in the process. The session was summarized by R. L. Smith in ASA Section on Statistics and the Environment newsletter.

Plagiarism charge


Wegman's institution, George Mason University
George Mason University
George Mason University is a public university based in unincorporated Fairfax County, Virginia, United States, south of and adjacent to the city of Fairfax. Additional campuses are located nearby in Arlington County, Prince William County, and Loudoun County...

, confirmed in October 2010 that they were investigating misconduct charges, following a March 2010 formal complaint by Raymond S. Bradley alleging plagiarism
Plagiarism
Plagiarism is defined in dictionaries as the "wrongful appropriation," "close imitation," or "purloining and publication" of another author's "language, thoughts, ideas, or expressions," and the representation of them as one's own original work, but the notion remains problematic with nebulous...

 and fabrications in the Wegman Report. 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." Wegman responded that he was "very well aware of the report", but at the university's request would not comment further until all issues were settled. Reviews by outside experts contacted by USA Today found the plagiarism obvious and inappropriate, with social network analysis partly copied from Wikipedia. Wegman said there was "speculation and conspiracy theory" in John Mashey's analysis, and said that "[t]hese attacks are unprecedented in my 42 years as an academic and scholar." He stated that the Wegman Report never "intended to take intellectual credit for any aspect of paleoclimate reconstruction science or for any original research aspect of social network analysis." The investigation was still at the preliminary "inquiry" stage rather than being a full investigation, according to a 26 May 2011 clarification from a George Mason University spokesman.

Wegman and Said authored a paper as an extension of the part of the Wegman Report which used social network analysis to suggest that there had been inappropriate close collaboration between some climate scientists. This paper, which omitted the names of the scientists, was published in the journal Computational Statistics and Data Analysis in 2008. After computer scientist Ted Kirkpatrick of the Simon Fraser University
Simon Fraser University
Simon Fraser University is a Canadian public research university in British Columbia with its main campus on Burnaby Mountain in Burnaby, and satellite campuses in Vancouver and Surrey. The main campus in Burnaby, located from downtown Vancouver, was established in 1965 and has more than 34,000...

 read the "Deep Climate" website allegations of plagiarism, he made a formal complaint to the journal. On 16 March 2011, Wegman sent an email to the journal saying that a student "had basically copied and pasted" work by other authors into the Wegman Report, and this text had been used in the journal paper without acknowledgement. He said that "We would never knowingly publish plagiarized material". In May 2011 the journal's editor, Stanley Azen of the University of Southern California
University of Southern California
The University of Southern California is a private, not-for-profit, nonsectarian, research university located in Los Angeles, California, United States. USC was founded in 1880, making it California's oldest private research university...

, announced that the journal was retracting the paper, because it used portions of other authors' writings without sufficient attribution. John Dahlberg of the United States Office of Research Integrity
United States Office of Research Integrity
The Office of Research Integrity is one of the bodies concerned with research integrity in the United States. It was created when the Office of Scientific Integrity in the National Institutes of Health and the Office of Scientific Integrity Review in the Office of the Assistant Secretary for...

 indicated that plagiarism could result in sanctions. A George Mason University spokesman declined to comment and said it was a "personnel matter".

The manuscript of the paper had been submitted on 8 July 2007 and accepted for publication on 14 July 2007. The student issued a statement that she had been "Dr. Wegman's graduate student when I provided him with the overview of social network analysis, at his request. My draft overview was later incorporated by Dr. Wegman and his coauthors into the 2006 report. I was not an author of the report." She had met with a GMU misconduct committee, and said that "My academic integrity is not being questioned."

A Nature
Nature (journal)
Nature, first published on 4 November 1869, is ranked the world's most cited interdisciplinary scientific journal by the Science Edition of the 2010 Journal Citation Reports...

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 sceptics. 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. It said that the university should "take the initiative to move investigations along as speedily as possible while allowing time for due process. Once an investigation is complete, the institution should be as transparent as it can about what happened", especially where public funds were involved.

IPCC Fourth Assessment Report, 2007


Paleoclimate findings by the IPCC before and after the Hockey Stick Controversy:

Before: 2001 (page 2)
" proxy data for the Northern Hemisphere indicate that the increase in temperature in the 20th century is likely to have been the largest of any century during the past 1,000 years. It is also likely that, in the Northern Hemisphere, the 1990s was the warmest decade and 1998 the warmest year."


After:
SPM statement from 2007 (page 10)
"“Average Northern Hemisphere temperatures during the second half of the 20th century were very likely higher than during any other 50-year period in the last 500 years and likely the highest in at least the past 1300 years. Some recent studies indicate greater variability in Northern Hemisphere temperatures than suggested in the TAR, particularly finding that cooler periods existed in the 12 to 14th, 17th, and 19th centuries. Warmer periods before the 20th century are within the uncertainty range given in the TAR.”


In May 2007, Hans von Storch
Hans von Storch
Hans von Storch is a German climate scientist. He is Professor at the Meteorological Institute of the University of Hamburg, and Director of the Institute for Coastal Research at the Helmholtz Research Centre in Geesthacht, Germany...

 reviewed the changes in thought caused by the hockey stick controversy writing:
In October 2004 we were lucky to publish in Science our critique of the ‘hockey-stick’ reconstruction of the temperature of the last 1000 years. Now, two and half years later, it may be worth reviewing what has happened since then.

At the EGU General Assembly a few weeks ago there were no less than three papers from groups in Copenhagen and Bern assessing critically the merits of methods used to reconstruct historical climate variable from proxies; Bürger’s papers in 2005; Moberg’s paper in Nature in 2005; various papers on borehole temperature; The National Academy of Science Report from 2006 – all of which have helped to clarify that the hockey-stick methodologies lead indeed to questionable historical reconstructions. The 4th Assessment Report of the IPCC now presents a whole range of historical reconstructions instead of favoring prematurely just one hypothesis as reliable.


McIntyre was critical of this Nature blog entry because von Storch did not acknowledge the role of McIntyre and McKitrick:
They then proceed to discuss various articles on the Hockey Stick mentioning Bürger, Moberg, borehole papers, the NAS report, but failing to mention McIntyre and McKitrick. Pretty annoying.

However von Storch replied that:
This was on purpose, as 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. They have published one peer-reviewed article on a statistical aspect, and we have published a response – acknowledging that they would have a valid point in principle, but the critique would not matter in the case of the hockey-stick ... we see in principle two scientific inputs of McIntyre into the general debate – one valid point, which is however probably not relevant in this context, and another which has not been properly documented.

Mann et al. 2008 and 2009


In a paper published by PNAS on 9 September 2008, Mann and colleagues produced updated reconstructions of Earth surface temperature for the past two millennia. This reconstruction used a more diverse dataset that was significantly larger than the original tree-ring study, at more than 1,200 proxy records. They used two complementary methods, both of which showed a similar "hockey stick" graph with recent increases in northern hemisphere surface temperature are anomalous relative to at least the past 1300 years. Mann said, "Ten years ago, the availability of data became quite sparse by the time you got back to 1,000 AD, and what we had then was weighted towards tree-ring data; but now you can go back 1,300 years without using tree-ring data at all and still get a verifiable conclusion." In a PNAS response, McIntyre and McKitrick said that they perceived a number of problems, including that Mann et al used some data with the axes upside down. Mann et al. replied that McIntyre and McKitrick "raise no valid issues regarding our paper" and the "claim that 'upside down' data were used is bizarre", as the methods "are insensitive to the sign of predictors." They also said that excluding the contentious datasets has little effect on the result.

A study of the changing climate of the Arctic
Climate of the Arctic
The climate of the Arctic is characterized by long, cold winters and short, cool summers. There is a large amount of variability in climate across the Arctic, but all regions experience extremes of solar radiation in both summer and winter...

 over the last 2,000 years, by an international consortium led by Darrell Kaufman of Northern Arizona University
Northern Arizona University
Northern Arizona University is a public university located in Flagstaff, Arizona, United States. It is accredited by the North Central Association of Colleges and Schools, and has 39 satellite campuses in the state of Arizona. The university offers both undergraduate and graduate degrees.As of...

, was published on 4 September 2009. They examined sediment core records from 14 Arctic lakes, supported by tree ring and ice core records. Their findings showed a long term cooling trend consistent with cycles in the Earth's orbit which would be expected to continue for a further 4,000 years but had been reversed in the 20th century by a sudden rise attributed to greenhouse gas emissions. The decline had continued through the Medieval period and the Little Ice Age. The most recent decade, 1999–2008, was the warmest of the period, and four of the five warmest decades occurred between 1950 and 2000. Scientific American
Scientific American
Scientific American is a popular science magazine. It is notable for its long history of presenting science monthly to an educated but not necessarily scientific public, through its careful attention to the clarity of its text as well as the quality of its specially commissioned color graphics...

 described the graph as largely replicating "the so-called 'hockey stick,' a previous reconstruction".

Further support for the "hockey stick" graph came from a new method of analysis developed by Martin Tingley and Peter Huybers
Peter Huybers
Peter Huybers is an American climate scientist, and Professor of Earth and Planetary Sciences at Harvard University, in the Department of Earth and Planetary Sciences.-Life and work:...

 of Harvard University, which produced the same basic shape, albeit with more variability in the past, and found the 1990s to have been the warmest decade in the 600 year period the study covered.

See also

  • Description of the Medieval Warm Period and Little Ice Age in IPCC reports
  • Global warming controversy
    Global warming controversy
    Global warming controversy refers to a variety of disputes, significantly more pronounced in the popular media than in the scientific literature, regarding the nature, causes, and consequences of global warming...

  • The Hockey Stick Illusion
    The Hockey Stick Illusion
    The Hockey Stick Illusion: Climategate and the Corruption of Science is a book written by Andrew Montford and published by Stacey International in 2010...

    , a book about the controversy