Irreproducible Results in Thompson Et Al., “Abrupt Tropical Climate Change: Past and Present†(PNAS 2006)

In a prestigious and influential article in the Proceedings of the National Academy of Sciences ( PNAS ), Thompson et al. [1] put forward a Tropical Composite Z-score series ( TCZ ), purportedly computed from ice core d 18 O ratios, as evidence of tropical warming over the past 2000 years. This note demonstrates that it bears no replicable linear relationship to the seven series on which they claim it is based, as archived by the authors themselves on the PNAS website. Although TCZ does equal the average of the two Himalayan and Andean component series ( HCZ and ACZ ) to within rounding error, HCZ cannot be constructed linearly from the four Himalayan isotope ratio series with an error less than 100 times the expected rounding error, and ACZ cannot be constructed from the three Andean isotope ratio series with an error less than 30 times the expected rounding error. The authors should provide PNAS with corrected and internally consistent data sets and figures for these series.