More questions raised about Mann’s hockey stick graph
A new research paper, written by statistical scientists and to be published next month in the Annals of Applied Statistics, has found that Michael Mann’s hockey stick graph, showing a steep increase in global temperature in the last two hundred years, is statistically invalid. Key quote:
Research on multi-proxy temperature reconstructions of the earth’s temperature is now entering its second decade. While the literature is large, there has been very little collaboration with university level, professional statisticians (Wegman et al., 2006; Wegman, 2006). Our paper is an effort to apply some modern statistical methods to these problems. While our results agree with the climate scientists findings in some respects, our methods of estimating model uncertainty and accuracy are in sharp disagreement.
[We] conclude unequivocally that the evidence for a ”long-handled” hockey stick (where the shaft of the hockey stick extends to the year 1000 AD) is lacking in the data. The fundamental problem is that there is a limited amount of proxy data which dates back to 1000 AD; what is available is weakly predictive of global annual temperature. Our backcasting methods, which track quite closely the methods applied most recently in Mann (2008) to the same data, are unable to catch the sharp run up in temperatures recorded in the 1990s, even in-sample. [emphasis mine]
In other words, the temperature data going back to 1000 AD is poor, and cannot be reliably used to prove a sudden increase in global temperature in the last two hundred years. More importantly, according to this paper, Michael Mann tried to use statistics to prove his point, without consulting any statisticians.