Medieval Warm Period

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The Medieval Warm Period (MWP) or Medieval Climate Optimum was a time of warm climate in the North Atlantic region, lasting from about the tenth century to about the fourteenth century. It followed the Migration Period Pessimum or Dark Ages Cold Period and was followed by the Little Ice Age. The MWP is often invoked in discussions of global warming. Some refer to the event as the Medieval Climatic Anomaly as this term emphasizes that effects other than temperature were important.[1]

Northern Hemisphere temperature reconstructions for the past 2000 years.

Contents

[edit] Initial research

The Medieval Warm Period was a time of warm weather around 800-1300 AD during the European Medieval period. Initial research on the MWP and the following Little Ice Age (LIA) was largely done in Europe, where the phenomenon was most obvious and clearly documented.

It was initially believed that the temperature changes were global [2]. However, this view has been questioned; the 2001 IPCC report summarises this research, saying "…current evidence does not support globally synchronous periods of anomalous cold or warmth over this time frame, and the conventional terms of 'Little Ice Age' and 'Medieval Warm Period' appear to have limited utility in describing trends in hemispheric or global mean temperature changes in past centuries".[3] The National Oceanic and Atmospheric Administration (NOAA) states that the "idea of a global or hemispheric "Medieval Warm Period" that was warmer than today however, has turned out to be incorrect" and that what those "records that do exist show is that there was no multi-century periods when global or hemispheric temperatures were the same or warmer than in the 20th century".[2] Indeed, global temperature records taken from ice cores, tree rings, and lake deposits, have shown that, taken globally, the Earth actually averaged slightly cooler (by 0.03 degrees Celsius) during the 'Medieval Warm Period' than in the early- and mid-20th century.[4]

Palaeoclimatologists developing region-specific climate reconstructions of past centuries conventionally label their coldest interval as "LIA" and their warmest interval as the "MWP".[5][4] Others follow the convention and when a significant climate event is found in the "LIA" or "MWP" time frames, associate their events to the period. Some "MWP" events are thus wet events or cold events rather than strictly warm events, particularly in central Antarctica where climate patterns opposite to the North Atlantic area have been noticed.

[edit] By world region

[edit] North Atlantic

The last written records of the Norse Greenlanders are from a 1408 marriage in the church of Hvalsey — today the best-preserved of the Norse ruins.

A radiocarbon-dated box core in the Sargasso Sea shows that the sea surface temperature was approximately 1 °C (1.8 °F) cooler than today approximately 400 years ago (the Little Ice Age) and 1700 years ago, and approximately 1 °C warmer than today 1000 years ago (the Medieval Warm Period).[6]

During the MWP wine grapes were grown in Europe as far north as southern Britain.[7][8][9][10]

[edit] North America

The Vikings took advantage of ice-free seas to colonize Greenland and other outlying lands of the far north.[11] The MWP was followed by the Little Ice Age, a period of cooling that lasted until the 19th century, and the Viking settlements eventually died out. In the Chesapeake Bay, researchers found large temperature excursions during the Medieval Warm Period (about 800–1300) and the Little Ice Age (about 1400–1850), possibly related to changes in the strength of North Atlantic thermohaline circulation.[12] Sediments in Piermont Marsh of the lower Hudson Valley show a dry Medieval Warm period from AD 800–1300.[13]

Prolonged droughts affected many parts of the western United States and especially eastern California and the western Great Basin.[14][4] Alaska experienced three time intervals of comparable warmth: A.D. 1–300, 850–1200, and post-1800.[15] Knowledge of the North American Medieval Warm Period has been useful in dating occupancy periods of certain Native American habitation sites, especially in arid parts of the western U.S.[16] Review of more recent archaeological research shows that as the search for signs of unusual cultural changes during the MCA has broadened, some of these early patterns (e.g. violence and health problems) have been found to be more complicated and regionally varied than previously thought while others (e.g., settlement disruption, deterioration of long distance trade, and population movements) have been further corroborated.[17]

[edit] Other regions

The climate in equatorial east Africa has alternated between drier than today, and relatively wet. The drier climate took place during the Medieval Warm Period (~AD 1000–1270).[18]

An ice core from the eastern Bransfield Basin, Antarctic Peninsula, clearly identifies events of the Little Ice Age and Medieval Warm Period.[19] The core clearly shows a distinctly cold period about AD 1000–1100, neatly illustrating the fact that "MWP" is a moveable term, and that during the "warm" period there were, regionally, periods of both warmth and cold.

Corals in the tropical Pacific Ocean suggest that relatively cool, dry conditions may have persisted early in the millennium, consistent with a La Niña-like configuration of the El Niño-Southern Oscillation patterns.[20] Although there is an extreme scarcity of data from Australia (for both the Medieval Warm Period and Little Ice Age) evidence from wave-built shingle terraces for a permanently full Lake Eyre[21] during the ninth and tenth centuries is consistent with this La Niña-like configuration, though of itself inadequate to show how lake levels varied from year to year or what climatic conditions elsewhere in Australia were like.

Adhikari and Kumon (2001), whilst investigating sediments in Lake Nakatsuna in central Japan, verified the existence there of both the Medieval Warm Period and the Little Ice Age.[22]

For further discussion of regional and global temperature variations see: Temperature record.

[edit] See also

[edit] References

  1. ^ Bradley, Raymond S. Climate System Research Center. "Climate of the Last Millennium." 2003. February 23, 2007. [1]; E.L. Ladurie, Times of Feast, Times of Famine: a History of Climate Since the Year 1000 (0(Barbara Bray, tr.) (New York: Doubleday)1971.
  2. ^ a b "Paleoclimatology Global Warming - The Data". NOAA. November 10, 2006. http://www.ncdc.noaa.gov/paleo/globalwarming/medieval.html. Retrieved on 2007-07-11. 
  3. ^ Intergovernmental Panel on Climate Change. "Climate Change 2001: Working Group I: The Scientific Basis 2.3.3 Was there a “Little Ice Age” and a “Medieval Warm Period”?". http://www.grida.no/climate/ipcc_tar/wg1/070.htm. Retrieved on 2006-05-04. 
  4. ^ a b c Raymond S. Bradley, Malcolm K. Hughes, Henry F. Diaz (2003). "Climate in Medieval Time" (PDF). Science 302 (5644): 404–405. doi:10.1126/science.1090372. PMID 14563996. http://www.geo.umass.edu/faculty/bradley/bradley2003d.pdf.  (links to pdf file)
  5. ^ Jones, P. D., and M. E. Mann (2004). "Climate over past millennia". Rev. Geophys. 42 (RG2002): 404–405. doi:10.1029/2003RG000143. 
  6. ^ Keigwin, Lloyd D. (29 November 1996). "The Little Ice Age and Medieval Warm Period in the Sargasso Sea". Science 274 (5292): 1503–1508. doi:10.1126/science.274.5292.1503. 
  7. ^ "The History of English Wine: Domesday & Middle Ages". http://www.english-wine.com/history.html#domesday. Retrieved on 2006-05-04. 
  8. ^ Jones, Gregory (August 2004). "Making Wine in a Changing Climate". Geotimes. http://www.agiweb.org/geotimes/aug04/feature_wineclime.html. Retrieved on 2007-09-04. 
  9. ^ Schmidt, Gavin (2006). "Medieval warmth and English wine". RealClimate. http://www.realclimate.org/index.php/archives/2006/07/medieval-warmth-and-english-wine/. Retrieved on 2006-07-12. 
  10. ^ "The Vineyards of England and Wales". English-Wine.com. http://www.english-wine.com/vineyards.html. Retrieved on 2006-05-04. 
  11. ^ Diamond, Jared (2005). Collapse: How Societies Choose to Fail or Succeed. New York: Penguin Books. ISBN 0143036556. 
  12. ^ "Medieval Warm Period, Little Ice Age and 20th Century Temperature Variability from Chesapeake Bay". USGS. http://geology.er.usgs.gov/eespteam/Atlantic/GPCabs.htm. Retrieved on 2006-05-04. 
  13. ^ "Marshes Tell Story Of Medieval Drought, Little Ice Age, And European Settlers Near New York City". Earth Observatory News. May 19, 2005. http://eobglossary.gsfc.nasa.gov/Newsroom/NasaNews/2005/2005051918986.html. Retrieved on 2006-05-04. 
  14. ^ Stine, Scott (1994). "Extreme and persistent drought in California and Patagonia during mediaeval time". Nature 369 (6481): 546–549. doi:10.1038/369546a0. 
  15. ^ Hu FS, Ito E, Brown TA, Curry BB, Engstrom DR (2001). "Pronounced climatic variations in Alaska during the last two millennia". PNAS 98 (19): 10552–10556. doi:10.1073/pnas.181333798. PMID 11517320. 
  16. ^ C. Michael Hogan (2008) Los Osos Back Bay, Megalithic Portal, editor A. Burnham.
  17. ^ Jones, Terry L.; Schwitalla, Al (2008). "Archaeological perspectives on the effects of medieval drought in prehistoric California". Quaternary International 188 (1): 41–58. doi:10.1016/j.quaint.2007.07.007. 
  18. ^ "Drought In West Linked To Warmer Temperatures". Earth Observatory News. 2004-10-07. http://earthobservatory.nasa.gov/Newsroom/MediaAlerts/2004/2004100717709.html. Retrieved on 2006-05-04. 
  19. ^ Khim, B-K; Yoon H.; Kang C.Y.; Bahk J.J. (November 2002). "Unstable Climate Oscillations during the Late Holocene in the Eastern Bransfield Basin, Antarctic Peninsula". Quaternary Research 58 (3): 234–245(12). doi:10.1006/qres.2002.2371. http://www.ingentaconnect.com/content/ap/qr/2002/00000058/00000003/art02371. Retrieved on 4 May 2006. 
  20. ^ Cobb, Kim M.; Chris Charles, Hai Cheng, R. Lawrence Edwards (July 8, 2003). "The Medieval Cool Period And The Little Warm Age In The Central Tropical Pacific? Fossil Coral Climate Records Of The Last Millennium". The Climate of the Holocene (ICCI) 2003. http://www.pac.ne.jp/IUGG2003/EN/program.asp?session_id=MC12&program_id=022025-1. Retrieved on 2006-05-04. 
  21. ^ Allen, Robert J.; The Australasian Summer Monsoon, Teleconnections, and Flooding in the Lake Eyre Basin; published 1985 by Royal Geographical Society of Australasia, S.A. Branch; ISBN 0909112096
  22. ^ Adhikari DP, Kumon, F. (2001). "Climatic changes during the past 1300 years as deduced from the sediments of Lake Nakatsuna, central Japan.". Limnology 2 (3): 157–168. doi:10.1007/s10201-001-8031-7. 

[edit] Further reading

  • M.K. Hughes and H.F. Diaz, "Was there a 'Medieval Warm Period?", Climatic Change 26: 109-142, March 1994

[edit] External links

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