Blowing Hot and Cold

Abstract
Tree-ring records play an important role in reconstructing climate change patterns over the last millenium. In their Perspective, Briffa and Osborn highlight the report by Esper et al. of a largely independent record of widespread tree-growth variations across the extra-tropical Northern Hemisphere. Estimates of past temperature changes based on the record suggest that climate swings in the last 1000 years were greater than has yet been generally accepted.