The Hockey Stick and the Climate Wars: Dispatches from the Front Lines

league” of studies now tell the same story as the hockey stick: the earth has warmed signifi cantly in the last 1000–1400 years, humans are the cause, and we have an increasing number of droughts, heat waves, superstorms, and fl oods to show for it. Yet even among those who accept the scientifi c conclusions derived from the hockey stick, there are critics, including those who suggest that the observed warming trends are natural. Mann addressed this questionable claim in a 2017 article in Geophysical Research Letters2 in which he and his colleagues demonstrated that the years 2014, 2015, and 2016 were the warmest years on record (in ascending order) and estimated that it is highly unlikely that this trend was not due to human behavior. If you had approached Michael Mann while he was double majoring in applied mathematics and physics at the University of California, Berkeley, and told him he would one day be one of the most prominent public fi gures in the fi ght against climate change, he likely would have laughed in your face. A mild-mannered scientist at the center of one of the most politically contentious debates in the history of human civilization? It simply wasn’t the plan. Yet there he was in New Orleans, delivering an inspiring keynote address in which he recounted the “evolution of a science nerd” who became a conduit for conveying the science of climate change to the general public—and how he ultimately came to embrace this role. Mann was thrust into the spotlight in 1998 when he and his colleagues published the now-famous “hockey stick curve,” a graph illustrating the increasing global warming trends over the last 1000 years in which the curve is not so much a curve as it is an obtuse angle that resembles its namesake.1 The hockey stick curve became an icon of the climate change debate virtually overnight, and Mann just as quickly found himself at the center of efforts to discredit the graph—and discredit him—as a means of dismissing the case for human-caused climate change altogether. He eventually came to realize that such efforts are rooted in a cynical belief that if the science behind the hockey stick curve is dismissed, the whole climate change debate will collapse like a house of cards. Such attempts seem irrational in light of the evidence, particularly given Mann’s assertion that the science of humancaused climate change is neither new nor scientifi cally controversial (thanks largely to Joseph Fourier, the 18thcentury physicist credited with identifying the greenhouse effect). Furthermore, Mann suggested these attempts are more fallacious than ever given the myriad other lines of evidence for human-caused climate change that have surfaced since the hockey stick’s debut. A “veritable hockey SPEAKER: Michael E Mann Distinguished Professor of Atmospheric Science The Pennsylvania State University State College, Pennsylvania REPORTER: Peter J Olson Senior Copyediting Coordinator Sheridan Journal Services Waterbury, Vermont