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Medieval Warm Period

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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. It has been argued a better name would be the Medieval Climatic Anomaly.

Initial research on the MWP and 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. However, this view has been questioned by some scientists, amongst them Bradley and Jones, 1993; Hughes and Diaz, 1994; Crowley and Lowery, 2000. The 2001 IPCC report summarises this research, saying: "…current evidence does not support globally synchronous periods of anomalous cold or warmth over this timeframe, 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" [1] (http://www.grida.no/climate/ipcc_tar/wg1/070.htm).

During this time wine grapes were grown in Europe and southern Britain [2] (http://www.english-wine.com/history.html#domesday) [3] (http://www.geog.ox.ac.uk/~knicoll/rsch/Geotimes%20-%20August%202004%20-%20Making%20Wine%20in%20a%20Changing%20Climate.htm) although less extensively than they are today [4] (http://www.english-wine.com/vineyards.html) (however, factors other than climate strongly influence the commercial success of vineyards; and the time of greatest extent of mediaeval vineyards falls outside the MWP). The Vikings took advantage of ice-free seas to colonize Greenland and other outlying lands of the far north. The period was followed by the Little Ice Age (LIA), a period of cooling that lasted until the 19th century when the current period of global warming began.

It has been note that most paleoclimatologists developing regionally specific climate reconstructions of past centuries conventionally label their coldest interval as "LIA" and their warmest interval as the "MWP".Template:RefTemplate:Ref 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, particularly in central Antarctica where climate patterns opposite to the North Atlantic area have been noticed.

Contents

Climate events

The Medieval Warm Period partially coincides in time with the peak in solar activity named the Medieval Maximum (AD 11001250).

In Chesapeake Bay, Maryland, researchers found large temperature excursions during the Little Ice Age (~1400-1900 AD) and the Medieval Warm Period (~800-1300 AD) possibly related to changes in the strength of North Atlantic thermohaline circulation [5] (http://geology.er.usgs.gov/eespteam/Atlantic/GPCabs.htm).

Prolonged droughts affected many parts of the western United States and especially eastern California and the western Great Basin. Template:Ref Alaska experienced three time intervals of comparable warmth: 0-300, 850-1200, and post-1800 AD. Template:Ref

A radiocarbon-dated box core in the Sargasso Sea shows that sea surface temperature was approximately 1°C 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] (http://www.sciencemag.org/cgi/content/abstract/274/5292/1503?rbfvrToken=b3527f8140d1ddfd7f0fdac765ac49b01f52eacb).

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) [7] (http://earthobservatory.nasa.gov/Newsroom/MediaAlerts/2004/2004100717709.html).

An ice core from the eastern Bransfield Basin, Antarctic Peninsula clearly identifies events of the Little Ice Age and Medieval Warm Period [8] (http://www.ingentaconnect.com/content/ap/qr/2002/00000058/00000003/art02371). The core clearly shows a distinctly cold period about 1000-1100 AD, nicely 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 Niņa-like configuration of the ENSO patterns [9] (http://www.pac.ne.jp/IUGG2003/EN/program.asp?session_id=MC12&program_id=022025-1).

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

It is fairly common to see occurrence of famines cited during the Little Ice Age. This is not always correct; for example, the famine in 1315, which killed 1.5 million people, is sometimes cited in connection with the LIA despite it having occurred during the MWP.


See also

References

External links and references

  • Vikings during the Medieval Warm Period (http://www2.sunysuffolk.edu/mandias/lia/vikings_during_mwp.html)
  • The Little Ice Age and Medieval Warm Period (http://earth.agu.org/revgeophys/mayews01/node5.html)
  • American Heritage Dictionary (http://bartleby.com/61/34/M0193425.html)- "The period from about 1000 to 1400 in which global temperatures are thought to have been a few degrees above those of the preceding and following periods. The climatic effects of this period were confined primarily to Europe and North America. Also called Medieval Warm Epoch.". (American Heritage Dictionary)
  • The "Medieval Warm Period" (http://greenpeace.org/~climate/database/records/zgpz0231.html)- Greenpeace article citing journal article: (M.K. Hughes and H.F. Diaz, "Was there a 'Medieval Warm Period?", Climatic Change 26: 109-142, March 1994).
  • John L. Daly's graphs (http://www.john-daly.com/hockey/hockey.htm) - claims that the Medieval Warm Period may have been global in character
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