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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.
In the study of past climates ("paleoclimatology"), climate proxies are preserved physical characteristics of the past that stand in for direct meteorological measurements and enable scientists to reconstruct the climatic conditions over a longer fraction of the Earth's history. Reliable global records of climate only began in the 1880s, and proxies provide the only means for scientists to determine climatic patterns before record-keeping began.
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 best known as the founder and editor of Climate Audit, a blog devoted to the analysis and discussion of climate data. He is most prominent as a critic of the temperature record of the past 1000 years and the data quality of NASA's Goddard Institute for Space Studies. He is known in particular for his statistical critique, 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.
Hans von Storch is a German climate scientist. He is a 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. He is a member of the advisory boards of the journals Journal of Climate and Annals of Geophysics. He worked at the Max Planck Institute for Meteorology from 1986 to 1995 and headed the Statistical Analysis and Modelling research group there.
The description of the Medieval Warm Period and Little Ice Age in IPCC reports has changed since the first report in 1990 as scientific understanding of the temperature record of the past 1000 years has improved. The Medieval Warm Period (MWP) and Little Ice Age (LIA) are the best-known temperature fluctuations in the last millennium.
The global temperature record shows the fluctuations of the temperature of the atmosphere and the oceans through various spans of time. There are numerous estimates of temperatures since the end of the Pleistocene glaciation, particularly during the current Holocene epoch. Some temperature information is available through geologic evidence, going back millions of years. More recently, information from ice cores covers the period from 800,000 years before the present time until now. A study of the paleoclimate covers the time period from 12,000 years ago to the present. Tree rings and measurements from ice cores can give evidence about the global temperature from 1,000-2,000 years before the present until now. The most detailed information exists since 1850, when methodical thermometer-based records began. Modifications on the Stevenson-type screen were made for uniform instrument measurements around 1880.
The Atlantic meridional overturning circulation (AMOC) is part of a global thermohaline circulation in the oceans and is the zonally integrated component of surface and deep currents in the Atlantic Ocean. It is characterized by a northward flow of warm, salty water in the upper layers of the Atlantic, and a southward flow of colder, deep waters. These "limbs" are linked by regions of overturning in the Nordic and Labrador Seas and the Southern Ocean, although the extent of overturning in the Labrador Sea is disputed. The AMOC is an important component of the Earth's climate system, and is a result of both atmospheric and thermohaline drivers.
Hockey stick graphs present the global or hemispherical mean temperature record of the past 500 to 2000 years as shown by quantitative climate reconstructions based on climate proxy records. These reconstructions have consistently shown a slow long term cooling trend changing into relatively rapid warming in the 20th century, with the instrumental temperature record by 2000 exceeding earlier temperatures.
The Antarctica cooling controversy was the result of an apparent contradiction in the observed cooling behavior of Antarctica between 1966 and 2000, which became part of the public debate in the global warming controversy, particularly between advocacy groups of both sides in the public arena including politicians, as well as the popular media. In his novel State of Fear, Michael Crichton asserted that the Antarctic data contradicted global warming. The few scientists who have commented on the supposed controversy state that there is no contradiction, while the author of the paper whose work inspired Crichton's remarks has said that Crichton misused his results. There is no similar controversy within the scientific community, as the small observed changes in Antarctica are consistent with the small changes predicted by climate models, and because the overall trend since comprehensive observations began is now known to be one of warming.
Malcolm K. Hughes is a meso-climatologist and Regents' Professor of Dendrochronology in the Laboratory for Tree-Ring Research at the University of Arizona.
The Soon and Baliunas controversy involved the publication in 2003 of a review study written by the aerospace engineer Willie Soon and astronomer Sallie Baliunas in the journal Climate Research, which 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 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.
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.
Cyclonic Niño is a climatological phenomenon that has been observed in climate models where tropical cyclone activity is increased. Increased tropical cyclone activity mixes ocean waters, introducing cooling in the upper layer of the ocean that quickly dissipates and warming in deeper layers that lasts considerably more, resulting in a net warming of the ocean.
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.
References
- ↑ Mann 2012 , pp. 104–105; Mann & Rutherford 2002
- Mann, M. E.; Rutherford, S. (31 May 2002), "Climate reconstruction using 'Pseudoproxies'", Geophysical Research Letters, 29 (10): 139–1–139–4, Bibcode:2002GeoRL..29.1501M, doi: 10.1029/2001GL014554 .
- Mann, Michael E. (2012), The Hockey Stick and the Climate Wars: Dispatches from the Front Lines, Columbia University Press, ISBN 978-0-231-15254-9 .