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Global Signatures and Dynamical Origins of the Little Ice Age and Medieval Climate Anomaly

Fig. 2. Reconstructed surface temperature pattern for MCA (950 to 1250 C.E.) and LIA (1400 to 1700 C.E.).
Fig. 2. Reconstructed surface temperature pattern for MCA (950 to 1250 C.E.) and LIA (1400 to 1700 C.E.).
Global Signatures and Dynamical Origins of the Little Ice Age and Medieval Climate Anomaly

Vol. 326, pp. 1256-1260, 27 November 2009

Michael E. Mann1, Zhihua Zhang1, Scott Rutherford2, Raymond S. Bradley3, Malcolm K. Hughes4, Drew Shindell5, Caspar Ammann6, Greg Faluvegi5, and Fenbiao Ni4
1 Department of Meteorology and Earth and Environmental Systems Institute, Pennsylvania State University, University Park, PA 16802, USA.
2 Department of Environmental Science, Roger Williams University, Bristol, RI 02809, USA
3 Department of Geosciences, University of Massachusetts, Amherst, MA 01003-9298, USA.
4 Laboratory of Tree-Ring Research, University of Arizona, Tucson, AZ 85721, USA.
5 NASA Goddard Institute for Space Studies, New York, NY 10025, USA.
6 Climate Global Dynamics Division, National Center for Atmospheric Research, Boulder, CO 80305, USA.
Global temperatures are known to have varied over the past 1500 years, but the spatial patterns have remained poorly defined. We used a global climate proxy network to reconstruct surface temperature patterns over this interval. The Medieval period is found to display warmth that matches or exceeds that of the past decade in some regions, but which falls well below recent levels globally. This period is marked by a tendency for La Niña-like conditions in the tropical Pacific. The coldest temperatures of the Little Ice Age are observed over the interval 1400 to 1700 C.E., with greatest cooling over the extratropical Northern Hemisphere continents. The patterns of temperature change imply dynamical responses of climate to natural radiative forcing changes involving El Niño and the North Atlantic Oscillation-Arctic Oscillation.

Download data from the WDC Paleo archive:
1000 Year Gridded Climate Reconstructions
Description of Data and Matlab Code

Data from Figure 1:
Each of the following files corresponds to a panel in Figure 1. Files have 4 columns, year, reconstruction, -2sigma and +2sigma. File name ending in "all" are from the "allproxy" or full network reconstruction and file names ending in "scr" are from the "screened" proxy reconstruction. For each series, the years 1850-2006 are the PC-filtered instrumental data. That is, the instrumental data but retaining the first 7 PCs, the number that were retained in the 1800-1849 reconstruction step.
AMO Full
AMO screened
Northern Hemisphere full
Northern Hemisphere screened
NINO3 full
NINO3 screened
PDO full
PDO screened
Global SST full
Global SST screened

The Spatial Reconstruction:
The Spatial Reconstruction is a large file and has been gzipped. Column 1 is year, columns 2-2593 are gridboxes. Years 1850-2006 are the PC-filtered instrumental data (retaining 7 PCs). The RegEM infilled instrumental data can be found in the "allproxy" tarball linked below.
The longitudes and latitudes for each gridbox are listed here.

Code and Data:
The "allproxy" code and data are in a gzipped tarball. After unpacking the tarball, you will have to change the paths in the code to run on your machine. See the "README.txt" in the tarball for more information. The RegEM code is included but is from Tapio Schneider's Web Site. Metadata for the proxies used here and in Mann et al., 2008 are in an Excel file.

All the proxy series are in the directory Mann et al. 2008. Verification data are in this matlab file and the code is here. Included are the gridbox verification scores, the monte carlo, red-noise significant levels and the code to calculate the spatial series RE/CE values. These data have also been utilized in the NOAA Paleoclimatology Reconstructions Network.

To read or view the full study, please visit the Science website.
It was published in Science, Vol. 326, pp. 1256-1260, 27 November 2009
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