Volume 26, Issue 6 p. 759-762
Free Access

Northern hemisphere temperatures during the past millennium: Inferences, uncertainties, and limitations

Michael E. Mann

Michael E. Mann

Department of Geosciences, University of Massachusetts, Amherst Massachusetts

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Raymond S. Bradley

Raymond S. Bradley

Department of Geosciences, University of Massachusetts, Amherst Massachusetts

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Malcolm K. Hughes

Malcolm K. Hughes

Laboratory of Tree-Ring Research, University of Arizona, Tucson, Arizona

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First published: 15 March 1999
Citations: 1,248

Abstract

Building on recent studies, we attempt hemispheric temperature reconstructions with proxy data networks for the past millennium. We focus not just on the reconstructions, but the uncertainties therein, and important caveats. Though expanded uncertainties prevent decisive conclusions for the period prior to AD 1400, our results suggest that the latter 20th century is anomalous in the context of at least the past millennium. The 1990s was the warmest decade, and 1998 the warmest year, at moderately high levels of confidence. The 20th century warming counters a millennial-scale cooling trend which is consistent with long-term astronomical forcing.