Reference
McCarroll, D., Loader, N.J., Jalkanen, R., Gagen, M.H., Grudd, H., Gunnarson, B.E., Kirchhefer, A.J., Friedrich, M., Linderholm, H.W., Lindholm, M., Boettger, T., Los, S.O., Remmele, S., Kononov, Y.M., Yamazaki, Y.H., Young, G.H.F. and Zorita, E. 2013. A 1200-year multiproxy record of tree growth and summer temperature at the northern pine forest limit of Europe. The Holocene 23: 471-484.
Description
By combining nine tree growth proxies from four sites stretching from the west coast of Norway to the Kola Peninsula of NW Russia along the northern pine tree limit of Europe, McCarroll et al. (2013) developed "a well replicated mean index of tree growth over the last 1200 years that represents growth of much of the northern pine timberline forests of northern Fennoscandia." This index was based on both ring width and late wood maximum density data that were detrended using Regional Curve Standardization to preserve low frequency variability. Their results indicated that (1) the 20th century was the warmest of the last 1200 years, but that it was not significantly different from the 11th century; and that (2) the warmest summer in the regression-based reconstruction was AD 1092 (13.47 ± 1.32°C), followed by AD 1937 (13.29 ± 1.32°C). Hence, the MWP and CWP would appear to have experienced essentially equivalent degrees of elevated warmth to this point in time, and that the MWP (for which the 17 researchers gave no temporal start and end times) should, at the very least, be assigned to the 11th century (AD 1000 - 1100).