Technical Comments

Comment on “The Spatial Extent of 20th-Century Warmth in the Context of the Past 1200 Years”

Science  29 Jun 2007:
Vol. 316, Issue 5833, pp. 1844a
DOI: 10.1126/science.1140982

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Osborn and Briffa (Reports, 10 February 2006, p. 841) identified anomalous periods of warmth or cold in the Northern Hemisphere that were synchronous across 14 temperature-sensitive proxies. However, their finding that the spatial extent of 20th-century warming is exceptional ignores the effect of proxy screening on the corresponding significance levels. After appropriate correction, the significance of the 20th-century warming anomaly disappears.

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