Climatologist Michael E. Mann is most famous for what he calls one of the “least interesting” aspects of his work. In the 1990s he used data from tree rings, coral growth bands and ice cores as proxies for ancient temperatures, combining them with modern thermometer readings. This annual record of temperature variations over the past millennium offered insights into natural climate cycles. As an “afterthought,” he included a graph of average temperatures in the Northern Hemisphere going back to the 1400s in a 1998 paper (he later extended it to A.D. 1000). That “hockey stick” graph, which shows temperatures bouncing up and down before rapidly rising more recently, became an icon of climate change.
It was also a focus of controversy. Although the U.S. National Research Council reviewed the hockey stick and endorsed its conclusions in 2006, Mann and his research came under often hostile public scrutiny, culminating in “Climategate”—the theft and publication of his and his colleagues’ personal e-mails in 2009. Mann’s employer, Pennsylvania State University, subsequently investigated him for research misconduct (and cleared him in 2010). And Virginia Attorney General Ken Cuccinelli has filed suit against the University of Virginia, Mann’s former employer, to investigate his work there (at press time, the case is still pending). His detractors, Mann says, “never stop.”