Helama, S., Merilainen, J. and Tuomenvirta, H. 2009. Multicentennial megadrought in northern Europe coincided with a global El Niño-Southern Oscillation drought pattern during the Medieval Climate Anomaly. Geology 37: 175-178.
Helama et al. developed what they describe as "the first European dendroclimatic precipitation reconstruction," based on data obtained from hundreds of moisture-sensitive Scots pine tree-ring records originating in southern Finland (61-62°N, 28-29°E), using regional curve standardization (RCS) procedures. This work revealed, as they describe it, a "distinct and persistent drought, from the early ninth century AD to the early thirteenth century AD," which interval, in their words, "precisely overlaps the period commonly referred to as the Medieval Climate Anomaly, due to its geographically widespread climatic anomalies both in temperature and moisture [our italics]."