Two millennial-length hydroclimatic proxy records from close to the centers of action of the winter North Atlantic Oscillation (NAO) indicate that the Medieval Climate Anomaly (MCA) was characterized by a pervasive positive phase of the NAO. Supplementary Proxy Surrogate reconstructions based on climate model results and proxy data indicate a clear shift to weaker NAO conditions into the Little Ice Age (LIA). Multidecadal NAO variability results in synoptic-scale shifts in surface pressure, wind fields, and precipitation.
