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Science 10 February 2006:
Vol. 311. no. 5762, pp. 841 - 844
DOI: 10.1126/science.1120514
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Reports

The Spatial Extent of 20th-Century Warmth in the Context of the Past 1200 Years

Timothy J. Osborn* and Keith R. Briffa

Periods of widespread warmth or cold are identified by positive or negative deviations that are synchronous across a number of temperature-sensitive proxy records drawn from the Northern Hemisphere. The most significant and longest duration feature during the last 1200 years is the geographical extent of warmth in the middle to late 20th century. Positive anomalies during 890 to 1170 and negative anomalies during 1580 to 1850 are consistent with the concepts of a Medieval Warm Period and a Little Ice Age, but comparison with instrumental temperatures shows the spatial extent of recent warmth to be of greater significance than that during the medieval period.

Climatic Research Unit, School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK.

* To whom correspondence should be addressed. E-mail: t.osborn{at}uea.ac.uk

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Science. ISSN 0036-8075 (print), 1095-9203 (online)