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The Medieval Warm Period (MWP) or Medieval Climate Optimum was a time of unusually warm climate in Europe, lasting from about the 10th century to about the 14th century.
The MWP is often involved in contentious discussions of global warming and the greenhouse effect. Some prefer to refer to the event as the Medieval Climatic Anomaly as this term emphasizes that effects other than temperature were important *.
Initial Research
Medieval Warm Period was a time of unusually warm weather 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. 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 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".
During this time wine grapes were grown in Europe as far north as southern Britain although less extensively than they are today (however, factors other than climate strongly influence the commercial success of vineyards, for example wine is made in Alaska today; and the time of greatest extent of medieval 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, a period of cooling that lasted until the 19th century when the current period of global warming began.
It has been noted 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". }} | url = http://www.geo.umass.edu/faculty/bradley/bradley2003d.pdf }} (links to pdf file) 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.
Climate Events
The Medieval Warm Period partially coincides in time with the peak in solar activity named the Medieval Maximum (AD 1100–1250).
In Chesapeake Bay, Maryland, researchers found large temperature excursions during the Little Ice Age (~AD 1400–1850) and the Medieval Warm Period (~AD 800–1300) possibly related to changes in the strength of North Atlantic thermohaline circulation. Sediments in Piermont Marsh of the lower Hudson Valley show a dry Medieval Warm period from AD 800–1300.
Prolonged droughts affected many parts of the western United States and especially eastern California and the western Great Basin. Alaska experienced three time intervals of comparable warmth: 1–300, 850–1200, and post-1800 AD. }}
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).| title=The Little Ice Age and Medieval Warm Period in the Sargasso Sea| first=Lloyd D.| last=Keigwin| accessdate=2006-05-04}} However, all the reconstructions, as shown above, appear to indicate that it was not.
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).
An ice core from the eastern Bransfield Basin, Antarctic Peninsula, clearly identifies events of the Little Ice Age and Medieval Warm Period. The core clearly shows a distinctly cold period about AD 1000–1100, 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 Niña-like configuration of the ENSO patterns. 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 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) in investigating sediments in Lake Nakatsuna in central Japan have verified there the existence of both the Medieval Warm period and the Little Ice Age.
For further discussion of regional and global temperature variations see: Temperature record.
See also
References
- Bradley and Jones, 1993
- M.K. Hughes and H.F. Diaz, "Was there a 'Medieval Warm Period?", Climatic Change 26: 109-142, March 1994
- Crowley and Lowery, 2000.
External links
- The Little Ice Age and Medieval Warm Period
- American Heritage Dictionary- "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)
History of climate | Middle Ages
Mittelalterliche Warmzeit | 中世の温暖期 | Den varme perioden i middelalderen | Keskiajan lämpökausi
"Medieval Warm Period"