The origin of the European "Medieval Warm Period"
1Institut d’Astronomie et de Géophysique G. Lemaître, Université catholique de Louvain, 2 Chemin du Cyclotron, 1348 Louvain-la-Neuve, Belgium
2Institute of Geography and NCCR Climate, University of Bern, Hallerstrasse 12, 3012 Bern, Switzerland
3Department of Meteorology and Earth and Environmental Systems Institute (EESI), Pennsylvania State University, University Park, PA16 802-5013, USA
4Faculty of Earth and Life Sciences, Vrije Universiteit Amsterdam, De Boelelaan 1085, 1081 HV Amsterdam, The Netherlands
5IPRC, SOEST, University of Hawaii, 2525 Correa Road, Honolulu, HI 96 822, USA
Abstract. Using a combination of proxy records and results of a three dimensional climate model, we show that European summer temperatures roughly a millennium ago were comparable to those of the late 20th century. Those two relatively mild periods are separated by a rather cold era, supporting the existence of a summer ``Medieval Warm Period" in Europe. The long-term temperature history appears to result from the superposition of various anthropogenic forcings, the summer cooling associated with changes in land-use over the last 1000 years having the same magnitude as the net warming due to the combined increase in greenhouse gas concentration and in sulphate aerosols during the last 200 years. Volcanic and solar forcing plays a weaker role in this comparison between the late 20th century and the early second millennium. Evidence for winter is more equivocal. The forced response in the model displays a clear temperature maximum at the end of the 20th century but the uncertainties are too large to state that this period is the warmest of the past millennium in Europe in winter.