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.
There is a nearly unanimous scientific consensus that the Earth has been consistently warming since the start of the Industrial Revolution, that the rate of recent warming is largely unprecedented, and that this warming is mainly the result of a rapid increase in atmospheric carbon dioxide (CO2) caused by human activities. The human activities causing this warming include fossil fuel combustion, cement production, and land use changes such as deforestation, with a significant supporting role from the other greenhouse gases such as methane and nitrous oxide. This human role in climate change is considered "unequivocal" and "incontrovertible".
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.
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.
Philip Douglas Jones is a former director of the Climatic Research Unit (CRU) and a professor in the School of Environmental Sciences at the University of East Anglia (UEA) from 1998, having begun his career at the unit in 1976. He retired from these positions at the end of 2016, and was replaced as CRU director by Tim Osborn. Jones then took up a position as a Professorial Fellow at the UEA from January 2017.
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.
David Russell Legates is a former 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. In September 2020, the Trump administration appointed him as deputy assistant secretary of commerce for observation and prediction at the National Oceanic and Atmospheric Administration.
Downscaling is any procedure to infer high-resolution information from low-resolution variables. This technique is based on dynamical or statistical approaches commonly used in several disciplines, especially meteorology, climatology and remote sensing. The term downscaling usually refers to an increase in spatial resolution, but it is often also used for temporal resolution. This is not to be confused with image downscaling which is a process of reducing an image from a higher resolution to a lower resolution.
Jan Esper studied geography at the University of Bonn, where he later earned his doctorate. After a postdoc position at Columbia University in New York City, he continued his work on dendrochronology at the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), and qualified as a professor at the University of Bern. In 2018, Esper became a member of the Academy of Sciences and Literature. Since 2010, he has been a professor at the Department of Geography at Johannes Gutenberg University Mainz.
Climate Research is a peer-reviewed scientific journal published by the Inter-Research Science Center and best known to the general public for its 2003 publication of a controversial paper. The journal was established in 1990 and covers all aspects of the interactions of climate with organisms, ecosystems, and human societies. Its founder and long time publisher was marine biologist Otto Kinne.
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.
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.
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.
Gabriele Clarissa Hegerl is a German climatologist. She is a professor of climate system science at the University of Edinburgh School of GeoSciences. Prior to 2007 she held research positions at Texas A&M University and at Duke University's Nicholas School of the Environment, during which time she was a co-ordinating lead author for the Intergovernmental Panel on Climate Change (IPCC) Fourth and Fifth Assessment Report.
The Medieval Warm Period (MWP), also known as the Medieval Climate Optimum or the Medieval Climatic Anomaly, was a time of warm climate in the North Atlantic region that lasted from c. 950 to c. 1250. Climate proxy records show peak warmth occurred at different times for different regions, which indicate that the MWP was not a globally uniform event. Some refer to the MWP as the Medieval Climatic Anomaly to emphasize that climatic effects other than temperature were also important.
Heinz Wanner is a Swiss geographer and climate researcher. He is a professor emeritus and works at the Oeschger Centre for Climate Change Research of the University of Bern.
