by  Don J. Easterbrook,  2011 in ScienceDirect

The Medieval Warm Period (MWP) was a time of warm climate from about 900 A.D. to 1300 A.D. when global temperatures were apparently somewhat warmer than at present. Its effects were evident in Europe where grain crops flourished, alpine tree lines rose, many new cities arose, and the population more than doubled. The Vikings took advantage of the climatic amelioration to colonize Greenland, and wine grapes were grown as far north as England where growing grapes is now not feasible and about 500 km north of present vineyards in France and Germany. Grapes are presently grown in Germany up to elevations of about 560 m, but from about 1100 A.D. to 1300 A.D., vineyards extended up to 780 m, implying temperatures warmer by about 1.0–1.4 °C (Oliver, 1973).

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