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Persistent Positive North Atlantic Oscillation Mode Dominated the Medieval Climate Anomaly


North Atlantic Sea Surface Temperature image.

Persistent Positive North Atlantic Oscillation Mode Dominated the Medieval Climate Anomaly
Science Vol. 324, No. 5923, pp. 78-80, 3 April 2009.

Valérie Trouet1, Jan Esper1,2, Nicholas E. Graham3,4, Andy Baker5, James D. Scourse6, David C. Frank1
1Swiss Federal Institute for Forest, Snow, and Landscape Research (WSL), Zürcherstrasse 111, 8903 Birmensdorf, Switzerland. 2Oeschger Centre for Climate Change Research, Erlachstrasse 9a, 3012 Bern, Switzerland. 3Hydrologic Research Center, 12780 High Bluff Drive, Suite 250, San Diego, CA 92130-2069, USA. 4Scripps Institution of Oceanography, 9500 Gilman Drive, La Jolla, CA 92093- 0225, USA. 5School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, B15 2TT, UK. 6School of Ocean Sciences, University of Wales Bangor, Menai Bridge, Anglesey, LL59 5AB, UK.
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.
Download data from the WDC Paleo archive:
Multi-decadal Winter North Atlantic Oscillation Reconstruction, Text or Excel format.

To read or view the full study, please visit the Science website.
It was published in Science, Vol. 324, No. 5923, pp. 78-80, 3 April 2009.
doi: 10.1126/science.1166349
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