The temperature record of the past 1,000 years is reconstructed using data from climate proxy records in conjunction with the modern instrumental temperature record which only covers the last 150 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 in

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  • The temperature record of the past 1,000 years is reconstructed using data from climate proxy records in conjunction with the modern instrumental temperature record which only covers the last 150 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. Individual proxy records, such as tree ring widths and densities used in dendroclimatology, are calibrated against the instrumental record for the period of overlap. Networks of such records are used to reconstruct past temperatures for regions: tree ring proxies have been used to reconstruct Northern Hemisphere extratropical temperatures (within the tropics trees do not form rings) but are confined to land areas and are scarce in the Southern Hemisphere which is largely ocean. Wider coverage is provided by multiproxy reconstructions, incorporating proxies such as lake sediments, ice cores and corals which are found in different regions, and using statistical methods to relate these sparser proxies to the greater numbers of tree ring records. The "Composite Plus Scaling" (CPS) method is widely used for large-scale multiproxy reconstructions of hemispheric or global average temperatures, this is complemented by Climate Field Reconstruction (CFR) methods which show how climate patterns have developed over large spatial areas, making the reconstruction useful for investigating natural variability and long term oscillations as well as for comparisons with patterns produced by climate models. During the 1,900 years before the 20th century, it is likely that the next warmest period was from 950 to 1100, with peaks at different times in different regions. This has been called the Medieval Warm Period, and some evidence suggests widespread cooler conditions during a period around the 17th century known as the Little Ice Age. In the hockey stick controversy, contrarians have asserted that the Medieval Warm Period was warmer than at present, and have disputed the data and methods of climate reconstructions. (en)
  • El registro de temperaturas en el II milenio describe la reconstrucción de Tª desde el año 1000 en el Hemisferio Norte, y posteriormente extendido hasta el año 1, y luego también cubriendo el hemisferio sur. Es necesaria una reconstrucción debido a contar con un registro confiable de la Tª superficial, sólo desde 1850. Estudiar el clima del pasado es de interés para los científicos, pues mejora la comprensión de la variabilidad climática actual y, relacionado con lo anterior, proporciona una mejor base para las proyecciones futuras del clima. En particular, si la naturaleza y la magnitud de la variabilidad natural del clima puede ser establecida, los científicos serán capaces de detectar en mejor manera las contribuciones antropogénicas calentamiento global. Cabe aclarar que, no obstante, a pesar de que la reconstrucción de las temperaturas obtenidas desde los datos que brindan los proxis nos ayudan a entender las características de la variación del clima natural, esto se basa en una amplia variedad de metodologías en las que las reconstrucciones de proxi son sólo una pequeña parte. De acuerdo con todas las reconstrucciones de temperatura importantes publicados en revistas revisadas por pares (ver gráfico), el incremento en la temperatura en el siglo XX y la temperatura a finales de este siglo es la más alta en los registros. La atención ha tendido a centrarse en los primeros trabajos de Michael E. Mann, Bradley and Hughes (1998), cuyo "palo de hockey" gráfico fue presentado en el 2001 en el reporte de la United Nations Intergovernmental Panel on Climate Change. La metodología y los conjuntos de datos usados para la creación del the Mann et al. (1998) versión del gráfico del palo de hockey están en controversia con Stephen McIntyre y Ross McKitrick, aunque el gráfico está en general aceptado por la comunidad científica. (es)
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  • The temperature record of the past 1,000 years is reconstructed using data from climate proxy records in conjunction with the modern instrumental temperature record which only covers the last 150 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 in (en)
  • El registro de temperaturas en el II milenio describe la reconstrucción de Tª desde el año 1000 en el Hemisferio Norte, y posteriormente extendido hasta el año 1, y luego también cubriendo el hemisferio sur. Es necesaria una reconstrucción debido a contar con un registro confiable de la Tª superficial, sólo desde 1850. Estudiar el clima del pasado es de interés para los científicos, pues mejora la comprensión de la variabilidad climática actual y, relacionado con lo anterior, proporciona una mejor base para las proyecciones futuras del clima. En particular, si la naturaleza y la magnitud de la variabilidad natural del clima puede ser establecida, los científicos serán capaces de detectar en mejor manera las contribuciones antropogénicas calentamiento global. Cabe aclarar que, no obstante, (es)
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  • Temperature record of the past 1000 years (en)
  • Registro de temperatura del último milenio (es)
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