title: Persistent positive North Atlantic oscillation mode dominated the Medieval Climate Anomaly.
abstract: The Medieval Climate Anomaly (MCA) was the most recent pre-industrial era warm interval of European climate, yet its driving mechanisms remain uncertain. We present here a 947-year-long multidecadal North Atlantic Oscillation (NAO) reconstruction and find a persistent positive NAO during the MCA. Supplementary reconstructions based on climate model results and proxy data indicate a clear shift to weaker NAO conditions into the Little Ice Age (LIA). Globally distributed proxy data suggest that this NAO shift is one aspect of a global MCA-LIA climate transition that probably was coupled to prevailing La Niña-like conditions amplified by an intensified Atlantic meridional overturning circulation during the MCA.
authors.affiliation: Swiss Federal Institute for Forest, Snow, and Landscape Research (WSL), Zürcherstrasse 111, 8903 Birmensdorf, Switzerland. trouet@wsl.ch
authors.forename: Valérie
authors.initials: V
authors.lastname: Trouet
authors.forename: Jan
authors.initials: J
authors.lastname: Esper
authors.forename: Nicholas E
authors.initials: NE
authors.lastname: Graham
authors.forename: Andy
authors.initials: A
authors.lastname: Baker
authors.forename: James D
authors.initials: JD
authors.lastname: Scourse
authors.forename: David C
authors.initials: DC
authors.lastname: Frank