Friday, April 03, 2009

The North Atlantic Oscillation and Medieval Climate

Persistent Positive North Atlantic Oscillation Mode Dominated the Medieval Climate Anomaly in Science.
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 NiƱa–like conditions amplified by an intensified Atlantic meridional overturning circulation during the MCA.

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