Northern Hemisphere temperature patterns in the last 12 centuries
1Department of History, Stockholm University, 10691 Stockholm, Sweden
2Centre for Medieval Studies, Stockholm University, 10691 Stockholm, Sweden
3Bert Bolin Centre for Climate Research, Stockholm University, 10691 Stockholm, Sweden
4Department of Physical Geography and Quaternary Geology, Stockholm University, 10691 Stockholm, Sweden
5Department of Mathematics, Stockholm University, 10691 Stockholm, Sweden
Abstract. We analyse the spatio-temporal patterns of temperature variability over Northern Hemisphere land areas, on centennial time-scales, for the last 12 centuries using an unprecedentedly large network of temperature-sensitive proxy records. Geographically widespread positive temperature anomalies are observed from the 9th to 11th centuries, similar in extent and magnitude to the 20th century mean. A dominance of widespread negative anomalies is observed from the 16th to 18th centuries. Though we find the amplitude and spatial extent of the 20th century warming is within the range of natural variability over the last 12 centuries, we also find that the rate of warming from the 19th to the 20th century is unprecedented in the context of the last 1200 yr. The positive Northern Hemisphere temperature change from the 19th to the 20th century is clearly the largest between any two consecutive centuries in the past 12 centuries. These results remain robust even after removing a significant number of proxies in various tests of robustness showing that the choice of proxies has no particular influence on the overall conclusions of this study.