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The temperature record of the past 1000 years describes the reconstruction of temperature for the last 1000 years on the Northern Hemisphere. A reconstruction is needed because a reliable surface temperature record exists only since about 1850. Studying past climate is of interest for scientists in order to improve the understanding of current climate variability and, relatedly, providing a better basis for future climate projections. In particular, if the nature and magnitude of natural climate variability can be established, scientists will be better positioned to identify and quantify human generated climate variability (commonly referred to as 'anthropogenic global warming' (AGW)). Northern Hemisphere highlighted in yellow. ...
1850 was a common year starting on Tuesday (see link for calendar). ...
The reconstructions of temperature of the last 1000 years vary between:
- ones with significant variability prior to the current century with particular warmth during the Medieval Warm Period and particular coolness during the 19th-century Little Ice Age; and,
- ones with minimal variability prior to the current century, generally involving a slight cooling until the 20th century.
 Reconstructions of Northern Hemisphere temperatures for the last 1000 years according to various older articles (bluish lines), newer articles (redish lines), and instrumental record (black line). In all cases, the increase in temperature in the 20th century is the largest of any century during the record. The Medieval Warm Period (MWP) or Medieval Climate Optimum was an unusually warm period during the European Medieval period, lasting from about the 10th century to about the 14th century. ...
The Little Ice Age (LIA) was a period of cooling lasting approximately from the 14th to the mid-19th centuries, although there is no generally agreed start or end date: some confine the period to 1550-1850. ...
Image File history File links // Description Expansion of the Instrumental Record Last 2000 years This image is a comparison of 10 different published reconstructions of mean temperature changes during the last 1000 years. ...
Image File history File links // Description Expansion of the Instrumental Record Last 2000 years This image is a comparison of 10 different published reconstructions of mean temperature changes during the last 1000 years. ...
Northern Hemisphere highlighted in yellow. ...
Instrumental temperature record
The recent instrumental temperature record extends to approximately 1850. These records of thermometer readings show a general warming in global temperatures. This image shows the instrumental record of global average temperatures as compiled by the Climatic Research Unit of the University of East Anglia and the Hadley Centre of the UK Meteorological Office. ...
This image shows the instrumental record of global average temperatures as compiled by the Climatic Research Unit of the University of East Anglia and the Hadley Centre of the UK Meteorological Office. ...
The instrumental temperature record shows the fluctuations of the temperature of the atmosphere and the oceans since the invention of thermomenters. ...
The instrumental temperature record shows the fluctuations of the temperature of the atmosphere and the oceans since the invention of thermomenters. ...
1850 was a common year starting on Tuesday (see link for calendar). ...
A thermometer is a device used to measure temperatures or temperature changes. ...
For general information about temperature records see the main article: Temperature record The temperature record shows the fluctuations of the temperature of the atmosphere and the oceans through various spans of time. ...
General techniques Reconstructions of temperature rely on 'proxy' records. For example, the width of tree rings is related to temperature as is the amount of snowfall over many glacial sites. Further, the isotopic composition of snow, corals, and stalactites can also record temperature changes. Other techniques which have been used include examining the time of crop harvests, the treeline in various locations and other historical records to make inferences about the temperature. In climate research, a proxy variable is something that is probably not in itself of any great interest, but from which a variable of interest can be obtained. ...
Isotopes are forms of an element whose nuclei have the same atomic number–-the number of protons in the nucleus--but different atomic masses because they contain different numbers of neutrons. ...
In general, the recent history of the proxy records is calibrated against local temperature records to estimate the relationship between temperature and the proxy. The longer history of the proxy is then used to reconstruct temperature from earlier periods.
An important distinction is between so-called 'multi-proxy' reconstructions, which attempt to obtain a global temperature reconstructions by using multiple proxy records distributed over the globe and more regional reconstructions.
Reconstructions with minimal variability Several reconstructions that suggested there was minimal variability in temperatures prior to the past century were generated by Mann and his co-authors. (See, for example, Mann, Jones and Briffa, Pollack et al. [1] [2].) More recently, they have extended their reconstructions to cover the last 2000 years (Mann and Jones, GRL, 2003 [3]). Michael Mann Michael Mann is a well-known climatologist, author of more than 80 peer-reviewed journal publications. ...
The Mann, Bradley and Hughes (1998) version of the temperature record has an unofficial name, the "Hockey Stick" graph, first coined by Jerry Mahlman, a colleague of Mann's.
The work of Mann et al., Jones et al., Briffa and others [4] [5] forms a major part of the IPCC's conclusion that "the rate and magnitude of global or hemispheric surface 20th century warming is likely to have been the largest of the millennium, with the 1990s and 1998 likely to have been the warmest decade and year" [6]. For a comparison of the common temperature plots, see [7].
Reconstructions with greater variability In the 22 October 2004 issue of Science, Hans von Storch and his colleagues claimed that the particular method of Mann et al. probably underestimates the temperature fluctuations in the past by a factor of two or more. Anders Moberg and his Swedish and Russian collaborators who published their results in Nature on February 10, 2005 [8] [9] have also generated reconstructions with significantly more variablity than the reconstructions of Mann et al. Science is the journal of the American Association for the Advancement of Science (AAAS). ...
Hans von Storch [1] is a German climate scientist. ...
The Nature Conservancy - a charitable organization devoted to preserving natural diversity worldwide English Nature UK government organization devoted to preserving natural diversity in the UK Nature Detectives An online research and education project for under 18s in the UK A Guide to Nature and Wildlife Conservation Philosophy Quick Topic Guide...
Scientists such as astrophysicist Sallie Baliunas have argued that these ups and downs correlate with solar activity and that the number of observed sunspots give us a rough measure of how bright the sun is. Balunias and others believe that periods of decreased solar radiation are responsible for historically recorded periods of cooling such as the Maunder Minimum and the Little Ice Age. Similarly, they say, periods of increase solar radiation contributed to the Medieval Warm Period, when Greenland's icy coastal areas thawed enough to permit farming and colonization. Sallie Baliunas is at the Harvard-Smithsonian Center for Astrophysics in the Solar, Stellar, and Planetary Sciences Division and formerly Deputy Director of the Mount Wilson Institute. ...
20 years of solar irradiance data from satellites Solar variation refers to fluctuation in the amount of energy emitted by the Sun. ...
A sunspot is a region on the Suns surface (photosphere) that is marked by a lower temperature than its surroundings, and intense magnetic activity. ...
The Maunder minimum in a 400 year history of sunspot numbers The Maunder Minimum is the name given to the period roughly from 1645 to 1715 A.D., when sunspots became exceedingly rare, as noted by solar observers of the time. ...
The Little Ice Age (LIA) was a period of cooling lasting approximately from the 14th to the mid-19th centuries, although there is no generally agreed start or end date: some confine the period to 1550-1850. ...
The Medieval Warm Period (MWP) or Medieval Climate Optimum was an unusually warm period during the European Medieval period, lasting from about the 10th century to about the 14th century. ...
Reconciliation of the two approaches The apparent differences between the statistical and historical approaches are not fully reconciled. One possibility is that the fluctuations recorded in the historical records are regional rather than hemispheric in scale.
Criticism The reconstructions mentioned above rely on various assumptions to generate their results. The most fundamental are that the proxy records vary linearly with temperature and that there are no non-temperature factors that confound the results. If these assumptions do not hold, the reconstructions would be unreliable.
The methodology of papers by Mann et al (MBH98 and MBH99) have been criticised by McIntyre and McKitrick on various grounds. In the February 11th, 2005 issue of Science, Richard A. Kerr describes Geophysical Research Letters paper that appeared on February 12th, 2005 [10] by Steven McIntyre and Ross McKitrick. Science is the journal of the American Association for the Advancement of Science (AAAS). ...
Historical temperature estimates For information on the description of the Medieval Warm Period and Little Ice Age in various reports of the United Nations Intergovernmental Panel on Climate Change, see the main article: MWP and LIA in IPCC reports The Medieval Warm Period (MWP) or Medieval Climate Optimum was an unusually warm period during the European Medieval period, lasting from about the 10th century to about the 14th century. ...
The Little Ice Age (LIA) was a period of cooling lasting approximately from the 14th to the mid-19th centuries, although there is no generally agreed start or end date: some confine the period to 1550-1850. ...
This law-related article does not cite its references or sources. ...
IPCC is science authority for the UNFCCC The Intergovernmental Panel on Climate Change (IPCC) was established in 1988 by two United Nations organizations, the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) to assess the risk of human-induced climate change. The Panel is open to all...
This page discusses the description of the Medieval Warm Period and Little Ice Age in various reports of the Intergovernmental Panel on Climate Change. ...
Mann, Bradley and Hughes temperature reconstructions Quantitative hemispheric temperature reconstructions were showing the pattern of slow cooling followed by more rapid warming.
Stephen McIntyre and Ross McKitrick attempted an "audit" of MBH98 [11] in Corrections to the Mann et. al. (1998) Proxy Data Base and Northern Hemispheric Average Temperature Series. This publication claimed various errors, but M&M offered no explanation as to why their analysis also differs from other reconstructions [12]. Stephen McIntyre has worked in mineral exploration for 30 years, much of that time as an officer or director of several public mineral exploration companies. ...
Ross McKitrick is a Canadian environmental economist. ...
In turn, Mann (supported by Tim Osborn, Keith Briffa and Phil Jones of the Climatic Research Unit) has disputed the claims made by McIntyre and McKitrick [13] [14], saying "...MM have made critical errors in their analysis that have the effect of grossly distorting the reconstruction of MBH98...". In 2004 Mann, Bradley, and Hughes published a corrigendum to their Nature 392, 779-787 (1998) article, correcting a number of mistakes in the online supplementary information that accompanied their article but leaving the actual results unchanged. Michael Mann Michael Mann is a well-known climatologist, author of more than 80 peer-reviewed journal publications. ...
The Climatic Research Unit is a component of the University of East Anglia. ...
2004 (MMIV) was a leap year starting on Thursday of the Gregorian calendar. ...
1998 (MCMXCVIII) is a common year starting on Thursday of the Gregorian calendar, and was designated the International Year of the Ocean. ...
M&M have published another Geophysical Research Letters article [15] on February 12th, 2005, claiming that the "Hockey Stick" shape was a result of a flawed principal component analysis, and that using the same steps like Mann et al., they were able to obtain the Hockey Stick graph in 99 percent of cases even if red noise was used as input. Mann and his collaborators have responded to the M&M articles via various means, including posts at the blog RealClimate. There is an ongoing debate about the details of the temperature record and the means of its reconstruction. In statistics, principal components analysis (PCA) is a technique that can be used to simplify a dataset; more formally it is a linear transformation that chooses a new coordinate system for the data set such that the greatest variance by any projection of the data set comes to lie on...
Updates There are ongoing updates and future events related to the MBH work. - RealClimate - Climate scientists blog, including Mann
- ClimateAudit - McIntyre blog
- A processing aliasing artifact in the early Quelccaya ice core record has been found. Original data was rounded to the nearest centimeter and this can cause analysis problems. A 2003 ice core will provide new data when processed. [16]
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