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Northern Hemisphere (20-90N)
Reference
D'Arrigo, R., Wilson, R. and Jacoby, G. 2006. On the long-term context for late twentieth century warming. Journal of Geophysical Research 111: 10.1029/2005JD006352.

Description
D'Arrigo et al. (2006) assembled mostly tree-ring width (but some density) data from living and subfossil wood of coniferous tree species found at 66 high-elevation and latitudinal treeline North American and Eurasian sites, after which they analyzed the data via the Regional Curve Standardization detrending technique to reconstruct a history of annual temperature for the Northern Hemisphere between 20 and 90N for the period AD 713-1995. In comparing the temperatures of the Medieval Warm Period (MWP, 950-1100 A.D.) with those of the Current Warm Period (CWP), based on the six longest chronologies they analyzed, they concluded that "the recent period does not look particularly warmer compared to the MWP." However, the mean of the six series did depict a warmer CWP; but they describe this relationship as "a bias/artifact in the full RCS reconstruction where the MWP, because it is expressed at different times in the six long records, is 'averaged out' (i.e., flattened) compared to the recent period which shows a much more globally consistent signal." Nevertheless, the data are what they are; and for the period covered only by the proxy data (so that "apples and oranges" are not compared), they found that peak twentieth century warmth (which occurred between 1937 and 1946) exceeded peak MWP warmth by 0.29C.