The temperature record of the last 2,000 years is reconstructed using data from climate proxy records in conjunction with the modern instrumental temperature record which only covers the last 170 years at a global scale. Large-scale reconstructions covering part or all of the 1st millennium and 2nd millennium have shown that recent temperatures are exceptional: the Intergovernmental Panel on Climate Change Fourth Assessment Report of 2007 concluded that "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 1,300 years." The curve shown in graphs of these reconstructions is widely known as the hockey stick graph because of the sharp increase in temperatures during the last century. As of 2010 this broad pattern was supported by more than two dozen reconstructions, using various statistical methods and combinations of proxy records, with variations in how flat the pre-20th-century "shaft" appears. Sparseness of proxy records results in considerable uncertainty for earlier periods.
Michael Evan Mann is an American climatologist and geophysicist. He is the director of the Center for Science, Sustainability & the Media at the University of Pennsylvania. Mann has contributed to the scientific understanding of historic climate change based on the temperature record of the past thousand years. He has pioneered techniques to find patterns in past climate change and to isolate climate signals from noisy data.
Ross McKitrick is a Canadian economist specializing in environmental economics and policy analysis. He is a professor of economics at the University of Guelph, and a senior fellow of the Fraser Institute.
Stephen McIntyre is a Canadian mining exploration company director, a former minerals prospector and semi-retired mining consultant whose work has included statistical analysis. He is the founder and editor of Climate Audit, a blog which analyses and discusses climate data. He is a critic of the temperature record of the past 1000 years and the data quality of NASA's Goddard Institute for Space Studies. He has made statistical critiques, with economist Ross McKitrick, of the hockey stick graph which shows that the increase in late 20th century global temperatures is unprecedented in the past 1,000 years.
The IPCC Third Assessment Report (TAR), Climate Change 2001, is an assessment of available scientific and socio-economic information on climate change by the IPCC. Statements of the IPCC or information from the TAR were often used as a reference showing a scientific consensus on the subject of global warming. The Third Assessment Report (TAR) was completed in 2001 and consists of four reports, three of them from its Working Groups: Working Group I: The Scientific Basis; Working Group II: Impacts, Adaptation and Vulnerability; Working Group III: Mitigation; Synthesis Report. A number of the TAR's conclusions are given quantitative estimates of how probable it is that they are correct, e.g., greater than 66% probability of being correct. These are "Bayesian" probabilities, which are based on an expert assessment of all the available evidence.
Climate Audit is a blog founded in 2005 by Steve McIntyre.
Hockey stick graphs present the global or hemispherical mean temperature record of the past 500 to 2000 years as shown by quantitative climate reconstructions based on climate proxy records. These reconstructions have consistently shown a slow long term cooling trend changing into relatively rapid warming in the 20th century, with the instrumental temperature record by 2000 exceeding earlier temperatures.
Willard Anthony Watts is an American blogger who runs Watts Up With That?, a climate change denial blog that opposes the scientific consensus on climate change. A former television meteorologist and current radio meteorologist, he is also founder of the Surface Stations project, a volunteer initiative to document the condition of U.S. weather stations. The Heartland Institute helped fund some of Watts' projects, including publishing a report on the Surface Stations project, and invited him to be a paid speaker at its International Conference on Climate Change from 2008 to 2014.
The Soon and Baliunas controversy involved the publication in 2003 of a review study titled Proxy climatic and environmental changes of the past 1000 years, written by aerospace engineer Willie Soon and astronomer Sallie Baliunas and published in the journal Climate Research. In the review, the authors expressed disagreement with the hockey stick graph and argued that historical temperature changes were related to solar variation rather than greenhouse gas emissions as was the position of the Intergovernmental Panel on Climate Change and other researchers. The publication was quickly taken up by the George W. Bush administration as a basis for amending the first Environmental Protection Agency's Report on the Environment.
Climatic Research Unit documents including thousands of e-mails and other computer files were stolen from a server at the Climatic Research Unit of the University of East Anglia in a hacking incident in November 2009. The documents were redistributed first through several blogs of global warming deniers, who alleged that the documents indicated misconduct by leading climate scientists. A series of investigations rejected these allegations, while concluding that CRU scientists should have been more open with distributing data and methods on request. Precisely six committees investigated the allegations and published reports, finding no evidence of fraud or scientific misconduct. The scientific consensus that global warming is occurring as a result of human activity remained unchanged by the end of the investigations.
Watts Up With That? (WUWT) is a blog promoting climate change denial that was created by Anthony Watts in 2006.
Andrew William Montford is a British writer and editor who is the owner of the Bishop Hill blog. He is the author of The Hockey Stick Illusion (2010).
The Hockey Stick Illusion: Climategate and the Corruption of Science is a book written by Andrew Montford and published by Stacey International in 2010, which promotes climate change denial.
Eduardo Zorita is a Spanish paleoclimatologist. As of 2010, he is a Senior Scientist at the Institute for Coastal Research, GKSS Research Centre in Geesthacht, Germany, where he has worked since 1996. Zorita is review editor of the journal Climate Research.
Berkeley Earth is a Berkeley, California-based independent 501(c)(3) non-profit focused on land temperature data analysis for climate science. Berkeley Earth was founded in early 2010 to address the major concerns from outside the scientific community regarding global warming and the instrumental temperature record. The project's stated aim was a "transparent approach, based on data analysis." In February 2013, Berkeley Earth became an independent non-profit. In August 2013, Berkeley Earth was granted 501(c)(3) tax-exempt status by the US government. The primary product is air temperatures over land, but they also produce a global dataset resulting from a merge of their land data with HadSST.
The Roman Warm Period, or Roman Climatic Optimum, was a period of unusually-warm weather in Europe and the North Atlantic that ran from approximately 250 BC to AD 400. Theophrastus wrote that date trees could grow in Greece if they were planted but that they could not set fruit there. That is still the case today, which implies that South Aegean mean summer temperatures in the 4th and the 5th centuries BC were within a degree of modern ones. That and other literary fragments from the time confirm that the Greek climate was basically the same then as around 2000. Tree rings from the Italian Peninsula in the late 3rd century BC indicate a time of mild conditions there around the time of Hannibal's crossing of the Alps with imported elephants in 218 BC.
The Hockey Stick and the Climate Wars: Dispatches from the Front Lines is a 2012 book about climate change by the American climatologist and geophysicist Michael E. Mann. In the book Mann describes how he became a researcher investigating the temperature record of the past 1000 years and was lead author, with Raymond S. Bradley and Malcolm K. Hughes, on the 1999 reconstruction that was the first to be dubbed the hockey stick graph. He concisely explains the basics of climate science including statistical methodology dealing with paleoclimate proxy data, and examines the tactics which opponents of action on climate change use to distort the science and attack the reputations of climate scientists. The book describes both this controversy and the broader context of skepticism in science and contrarians rejecting evidence of human influence on climate.
Novim is a non-profit group at the University of California, Santa Barbara that organizes teams for objective scientific study of global issues and identification options for addressing the concerns, based upon a collaborative problem-solving approach used in the field of physics.
The Wegman Report was prepared in 2006 by three statisticians led by Edward Wegman at the request of Rep. Joe Barton of the United States House Committee on Energy and Commerce to validate criticisms made by Stephen McIntyre and Ross McKitrick of reconstructions of the temperature record of the past 1000 years, in particular the reconstructions by Mann, Bradley and Hughes of what had been dubbed the hockey stick graph.
The North Report was a 2006 report evaluating reconstructions of the temperature record of the past two millennia, providing an overview of the state of the science and the implications for understanding of global warming. It was produced by a National Research Council committee, chaired by Gerald North, at the request of Representative Sherwood Boehlert as chairman of the U.S. House of Representatives Committee on Science.
