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The 'Medieval Warm Period (MWP)' or 'Medieval Climate Optimum' was a time of unusually warm climate in the North Atlantic region, lasting from about the tenth century to about the fourteenth century.
The MWP is often invoked in contentious 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]

Contents

Initial research

Climate events

North Atlantic and North American regions

Other regions

Criticism

See also

References

External links

Initial research

The 'Medieval Warm Period' was a time of unusually 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. 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".^[2]
Palaeoclimatologists developing regionally specific climate reconstructions of past centuries conventionally label their coldest interval as "LIA" and their warmest interval as the "MWP".^[3][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.

Climate events

North Atlantic and North American regions

During the MWP wine grapes were grown in Europe as far north as southern Britain^[5][6][7], similar in extent to vineyards today^[8] (however, factors other than climate strongly influence the commercial success of vineyards). The Vikings took advantage of ice-free seas to colonize Greenland and other outlying lands of the far north. The MWP was followed by the Little Ice Age, a period of cooling that lasted until the 19th century. 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.^[9] Sediments in Piermont Marsh of the lower Hudson Valley show a dry Medieval Warm period from AD 800–1300.^[10]
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: A.D. 1–300, 850–1200, and post-1800.^[11]
A radiocarbon-dated box core in the Sargasso Sea shows that the 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).^[12]

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).^[13]
An ice core from the eastern Bransfield Basin, Antarctic Peninsula, clearly identifies events of the Little Ice Age and Medieval Warm Period.^[14] 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.^[15] 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^[16] 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.^[17]
For further discussion of regional and global temperature variations see: Temperature record.

Criticism

The National Oceanic and Atmospheric Administration (NOAA) has conducted research claiming that there is a lack of data supporting that the Medieval Warming Period ever took place. Instead, they state that there were no multi-century periods when global or hemispheric temperatures were the same or warmer than in the 20th century. Summarily, it "appears that the 20th century, and in particular the late 20th century, is likely the warmest the Earth has seen in at least 1200 years."^[18] This might indicate that claims from global warming critics that regions of the North Atlantic (such as Greenland) were once capable of sustaining temperate wildlife and plantlife is unfounded. ^[19]

See also

★ Holocene Climatic Optimum

★ MWP and LIA in IPCC reports

★ Historical climatology

★ Little Ice Age

References

1. Bradley, Raymond S. Climate System Research Center. "Climate of the Last Millenium." 2003. February 23, 2007. [1]
2. Climate Change 2001: Working Group I: The Scientific Basis 2.3.3 Was there a “Little Ice Age” and a “Medieval Warm Period”? Intergovernmental Panel on Climate Change
3.
4. (''links to pdf file'')
5. The History of English Wine: Domesday & Middle Ages
6. Making Wine in a Changing Climate
7. Medieval warmth and English wine
8. The Vineyards of England and Wales
9. Medieval Warm Period, Little Ice Age and 20th Century Temperature Variability from Chesapeake Bay
10. Marshes Tell Story Of Medieval Drought, Little Ice Age, And European Settlers Near New York City
11.
12.
13. Drought In West Linked To Warmer Temperatures
14. Unstable Climate Oscillations during the Late Holocene in the Eastern Bransfield Basin, Antarctic Peninsula, , B-K, Khim, Quaternary Research, 2002
15. The Medieval Cool Period And The Little Warm Age In The Central Tropical Pacific? Fossil Coral Climate Records Of The Last Millennium
16. 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
17.
18. Paleoclimatology Global Warming - The Data
19. The Medieval Warm Period was just as warm as today



★ 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