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 2