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The Medieval Warm Period in the Alpine Regions of Europe
Reference
Kress, A., Hangartner, S., Bugmann, H., Buntgen, U., Frank, D.C., Leuenberger, M., Siegwolf, R.T.W. and Saurer, M. 2014. Swiss tree rings reveal warm and wet summers during medieval times. Geophysical Research Letters 41: 1732-1737.

Background
The authors write that the Medieval Warm Period - which they refer to as the Medieval Climate Anomaly (MCA) - was characterized by "a prevalence of 'La Niņa-like' situations in the Pacific and positive modes of the North Atlantic Oscillation (Trouet et al., 2009)," but they say that "our knowledge on precipitation and drought in general, and particularly back to medieval times, is still quite patchy and new records are urgently needed," citing Seager et al. (2007).

What was done
In a study that they designed to meet this need, Kress et al. developed "a 1200-year drought reconstruction for the European Alpine region based on carbon isotope variations of tree rings from living larch trees and historic timber," which they combined with "maximum latewood density-derived summer temperature."

What was learned
The eight researchers - representing Switzerland, Germany and the Czech Republic - report they found that after an initial high occurrence of drought events in the ninth century, there was "a pronounced period (A.D. 900-1200) with few dry extremes." And they say that "this absence of droughts, in combination with a slightly enhanced number of wet extremes, suggests a relatively wet/warm period, roughly coinciding with the MCA," which they note "is broadly consistent with Marcott et al. (2013), who concluded that greater warmth was often associated with greater wetness during the Holocene in the extra-tropical Northern Hemisphere (>30°N)."

What it means
In concluding the abstract of their paper, Kress et al. state that their findings point to "beneficial conditions for agriculture and human well-being during the MCA in this region."

References
Marcott, S.A., Shakun, J.D., Clark, P.U. and Mix, A.C. 2013. A reconstruction of regional and global temperature for the past 11,300 years. Science 339: 1198-1201.

Seager, R., Graham, N. and Herweijer, C. Gordon, A.L., Kushnir, Y. and Cook, E. 2007. Blueprints for medieval hydroclimate. Quaternary Science Reviews 26: 2322-2336.

Trouet, V., Esper, J., Graham, N.E., Baker, A., Scourse, J.D. and Frank, D.C. 2009. Persistent positive North Atlantic Oscillation mode dominated the Medieval Climate Anomaly. Science 324: 78-80.

Reviewed 16 July 2014