Late 20th Century Warming not unusual, unnatural nor unprecedented

CO2 Science reports  of a new peer-reviewed paper published in Climate of the Past 8: 227-249

Citation: Ljungqvist, F. C., Krusic, P. J., Brattström, G., and Sundqvist, H. S.: Northern Hemisphere temperature patterns in the last 12 centuries, Clim. Past, 8, 227-249 

What was done
As Ljungqvist et al. describe it, they developed "a new reconstruction of the spatio-temporal patterns of centennial temperature variability over the NH land areas for the last twelve centuries based on 120 proxy records," which were "retrieved from a wide range of archives including, but not limited to, ice-cores, pollen, marine sediments, lake sediments, tree-rings, speleothems and historical documentary data." And with respect to how big an improvement their data base makes compared to prior studies of this type, in terms of the amount and distribution of data employed, they present a list of antecedent analyses where the number of proxy records used ranged from only 3 to 46 (compared to their 120), and where the number of records with annual resolution ranged from only 3 to 30, whereas their study included 49 such annual-resolution records.

What it means
As we have often remarked after reviewing the results of literally hundreds of paleo-temperature reconstructions stretching back over a millennium or more, there is nothing unusual, unnatural or unprecedented about earth's current level of warmth when compared to that of the Medieval Warm Period, when there was way less CO2 in the air than there is currently (~280 ppm then vs. ~390 ppm now). And this fact suggests that there is no compelling reason to necessarily attribute any of the post-Little Ice Age warming to this miniscule trace gas of the atmosphere.

Read more at CO2 Science and Climates of the Past.