WINTER AIR-TEMPERATURE VARIATIONS IN WESTERN-EUROPE DURING THE EARLY AND HIGH-MIDDLE-AGES (AD 750-1300)

In this paper an attempt is made to reconstruct air temperature variat ions in winter (December, January and February) from 2500 documentary data over the period AD 750-1300 for a region comprising the Benelux c ountries, eastern France, western Germany, Switzerland and northern It aly. Anomalous (warm and cold) winters were classified on the basis of proxy information on frost, freezing of water bodies, duration of sno wcover and untimely activity of vegetation using semiquantitative indi ces. For the most severe winters during the 'Medieval Warm Period' (MW P) as well as for the outstanding warm and dry winter AD 1289/90, poss ible analogue cases from the last 300 years are considered, analysed, synoptically interpreted and compared with each other. It is concluded that severe winters were somewhat less frequent and less extreme duri ng the MWP, AD 900-1300, than in the ninth century and from 1300 to 19 00. Mean air temperatures for 30 year. periods were estimated from lin ear regression models including indices and instrumental measurements. From AD 1090 to 1179 winter temperatures were at the level of the 'Li ttle Ice Age' (LW). From AD 1180 to 1299 they were at that of the twen tieth century. The warm and stable winter climate in the thirteenth ce ntury supported subtropical plants such as olive trees in the Po valle y (northern Italy) and fig trees around Cologne (Germany). The period AD 1300-1329 which marks the transition to the LIA was 1 degrees C col der. It is concluded that the 1961-90 level of winter temperatures in western central Europe is still within the threshold of natural variab ility of the last thousand years, albeit at its upper boundary.