In 2006, an article appeared in Science magazine reconstructing the temperature of the Northern Hemisphere back to 800 AD based on 14 smoothed and normalized temperature proxies (e.g., tree ring records). Osborn and Briffa proclaimed at the time that “the 20th century is the most anomalous interval in the entire analysis period, with highly significant occurrences of positive anomalies and positive extremes in the proxy records.” Obviously, concluding that the Northern Hemisphere has entered a period of unprecedented warmth is sure to make the news, and indeed, Osborn and Briffa’s work was carried in papers throughout the world and was loudly trumpeted by the American Association for the Advancement of Science (AAAS) that publishes the journal Science.
A recent issue of Science contains an article not likely to receive any press coverage at all. Gerd Bürger of Berlin’s Institut für Meteorologie decided to revisit the work of Osborn and Briffa, and his results raise serious questions about the claim that the 20th century has been unusually warm. Bürger argues that Osborn and Briffa did not apply the appropriate statistical tests that link the proxy records to observational data, and as such, Osborn and Briffa did not properly quantify the statistical uncertainties in their analyses. Bürger repeated all analyses with the appropriate adjustments and concluded “As a result, the ‘highly significant’ occurrences of positive anomalies during the 20th century disappear.” Further, he reports that “The 95th percentile is exceeded mostly in the early 20th century, but also about the year 1000.” Needless to say, Gerd Bürger is not going to win any awards from the champions of global warming – nothing is more sacred than 20th century warming!