Medieval Warm Period

The Medieval Warm Period (MWP) or Medieval Climate Optimum was an unusually warm period in history lasting from about the 10th century to about the 14th century.

During this time wine grapes were grown in Europe up to 300 miles north of their present northerly growing limit. 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 19^th century when the current period of global warming began. Since that time, there has been a nearly continuous increase in global temperatures with the exception of a period of several decades in the mid 20^th century when global temperatures fell significantly - then resumed their climb.

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, recently the IPCC has questioned this view. The 2001 IPCC report says: "...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]. It remains to be seen whether the IPCC's views will be endorsed by other organizations or individuals.

For more on the topic of the MWP in various IPCC reports, see MWP and LIA in IPCC reports.

See also the 1000 year temperature reconstruction of Mann et al [2]. The IPCC TAR says of the MWP that the posited Medieval Warm Period appears to have been less distinct, more moderate in amplitude, and somewhat different in timing at the hemispheric scale than is typically inferred for the conventionally-defined European epoch. The Northern Hemisphere mean temperature estimates of Jones et al. (1998), Mann et al. (1999), and Crowley and Lowery (2000) show temperatures from the 11th to 14th centuries to be about 0.2°C warmer than those from the 15th to 19th centuries, but rather below mid-20th century temperatures. However, Mann's conclusions do not support IPCC claims with regard to the LIA as described in the paragraph below.

A paper by Soon and Baliunas disagrees with the IPCC and Mann and states that those warm and cold periods were indeed widespread climatic anomalies while Mann shows a widespread Little Ice Age. However, the Soon and Baliunas report itself has been itself criticised [3]. As a result, there is no definitive answer to this question.

For further discussion of regional and global temperature records based on their reconstruction from climate proxy data, see Temperature record of the past 1000 years.

External links and references

• Vikings During the Medieval Warm Period
• 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)
• The "Medieval Warm Period"- Greenpeace article citing journal article: (M.K. Hughes and H.F. Diaz, "Was there a 'Medieval Warm Period?", Climatic Change, v.26, p.109-142, March 1994).
• John L. Daly's graphs - claims that the Medieval Warm Period may have been global in character