In This Issue

Updated surface temperature reconstructions of the past two millennia provide further evidence that the current climate warming in the northern hemisphere is a unique event and that we are now at an all-time high temperature. Michael Mann et al. compiled historical surface temperature data from tree rings, marine sediment, ice cores, and other data sources. The dataset provided temperatures resolved over years and decades, covering the land and sea, mostly in the northern hemisphere. After weighting and averaging the data, the authors found that the past 10 years stand out as the warmest in at least 1,300 years, and perhaps up to 1,700 years if tree ring data are included. Their results accord with previous estimates, while extending the data to before 1000 A.D. Further data are needed from the southern hemisphere before statements can be made regarding the south and the globe as a whole, the authors say. — P.D.