The Hockey Stick and the Climate Wars: a book review

Published: 12:48 PM GMT on May 16, 2012

No climate scientist has been subject to more attacks on their science and character than Penn State's Michael Mann, originator of the famed "hockey stick" graph of Earth's temperature history. Dr. Mann has an excellent new book called "The Hockey Stick and the Climate Wars: Dispatches from the Front Lines" that takes the reader on a fascinating journey to the front lines the high-stakes battles between climate scientists and their detractors. It's a must-read for every serious student of Earth's climate. Along the way, you'll learn about tree rings, the IPCC process, the fossil fuel industry's savvy PR campaigns to discredit climate change science, and get an insider's view of the notorious stolen emails of "climategate."

For those unfamiliar with the "hockey stick", the shape of the graph showing Earth's temperature has a long, relatively flat portion representing the period 1000 AD - 1800 AD--the shaft of the hockey stick--followed by a sharp upward rise that began in the late 1800s and continues to this day--the blade of the hockey stick. When Dr. Mann first published the hockey stick graph in papers he wrote in 1998 and 1999, it quickly became a central icon in the climate change debate. As he writes in "The Hockey Stick and the Climate Wars," the hockey stick graph "told an easily understood story with a simple picture: that a sharp and highly unusual rise in atmospheric warming was occurring on Earth." Contrarians bent on discrediting the science of climate change have fiercely attacked the hockey stick, attempting to portray it as the key piece of evidence upon which all of climate change science depends (which is not correct, since many different data sets unrelated to the tree ring studies under attack show a hockey stick-like shape.) The contrarians have adopted "the Serengeti strategy" towards Dr. Mann--"a tried-and-true tactic of the climate change denial campaign...isolate individual scientists just as predators on the Serengeti Plain of Africa hunt their prey: picking off vulnerable individuals from the rest of the herd."

The history of the hockey stick
The book starts with some interesting background on Dr. Mann's career. He got into climate science by accident--while working on his Ph.D. in physics at Yale, funding got tight, and he elected to switch to the Department of Geology and Geophysics, where funding to perform research on natural climate cycles was available. In the mid-1990s, while working on his Ph.D., he helped discover the decades-long natural cycle of alternating warm and cool ocean temperatures in the Atlantic Ocean thought to be responsible for the active hurricane period that began in 1995. He gave the phenomenon the now widely-used name, the Atlantic Multidecadal Oscillation (AMO), during an impromptu interview with science writer Dick Kerr. After receiving his Ph.D. in 1996, Dr. Mann moved on into using statistical methods to study past climate, as gleaned from tree ring studies. He takes the reader on a 5-page college-level discussion of the main technique used, Principal Component Analysis (PCA), and shows how his famed "hockey stick" graph came about. It's one of the best descriptions I've seen on how PCA works (though it will be too technical for some.) His inaugural PCA work showing that the 1990s were likely the warmest decade in at least the past 600 years was published in 1998. Since the paper coincidentally happened to be published on Earth Day during the warmest year in Earth's history, the paper received a huge amount of media attention. His follow-up 1999 paper went further, suggesting that the 1990s were the warmest decade in the past 1,000 years, and 1998 was the warmest year. Dr. Mann was appointed as one of the lead authors of the 2001 Intergovernmental Panel on Climate Change (IPCC) report, the massive United Nations summary of climate change science that comes out every six years. We learn some interesting details about the approval process for the 2001 IPCC report, like the fact for two days, the scientists haggled with the Saudi Arabian delegation about one word in the Summary for Policy Makers. The IPCC report's summary requires unanimous approval by all nations, and the Saudis objected to the language that said, "the balance of evidence suggests an appreciable human influence on climate." They debated 30 different alternatives before finally settling on the language, "the balance of evidence suggests a discernible human influence on climate."

Figure 1. The hockey stick graph as it appeared in the IPCC Third Assessment Report WG1 (2001) summary, Figure 2.20, Northern Hemisphere temperature reconstruction. Tree rings, corals, ice cores, and historical records are shown in blue, and instrumental data in red, from AD 1000 to 1999. The grey shaded region indicates the uncertainty in the annual temperature estimates (there is a 95% certainty that the temperature for any given year lies in the gray shaded region.) The thick black line is a smoothed version which highlights the long-term variations. A similar version of this graph appeared in Dr. Mann's original 1999 paper. Climate scientist Dr. Jerry Mahlman was responsible for giving this graph the nickname, the "hockey stick".

The battle begins
The majority of the book focuses on the battles over the hockey stick that ensued in 1998, as soon as Dr. Mann published his research. He writes: For more than a decade, the scientific community, in its effort to communicate the threat of climate change, has had to fight against the headwind of this industry-funded disinformation effort. The collective battles are what I term the "Climate wars". The battle raged furiously through 2006, when an extensive review of the hockey stick was performed by the National Academy of Sciences (NAS)--an organization founded in 1863 by Abraham Lincoln to "investigate, examine, experiment, and report upon any subject of science" for the purpose of informing government policy. The NAS reaffirmed the validity of the hockey stick, concluding: "based on the analyses presented in the original papers by Mann et al. and this new supporting evidence, the committee finds it plausible that the Northern Hemisphere was warmer during the last few decades of the 20th century than during any comparable period over the preceding millennium." Dr. Mann writes, "One might think that this would have put an end to the accusations once and for all. But one would be wrong."

In November 2009, a few weeks before the December international climate summit in Copenhagen, the website that Dr. Mann contributes to was hacked into, and a file with emails stolen from the University of East Anglia's Climatic Research Unit (CRU) was posted. Dr. Mann explains in detail how these "climategate" emails were taken out context and distorted to appear scandalous by "a massive public relations campaign conducted by major players in the climate change denial movement." To illustrate, he gives the example of Isaac Newton's writings, which can easily be taken out context and distorted to give the impression that he was guilty of "conspiring to avoid public scrutiny," "insulting dissenting scientists," "manipulation of evidence," "knowingly publishing scientific fraud," "suppression of evidence," "abusing the peer review system," and "insulting critics." In the end, no evidence of scientific misconduct was found by any of the five independent reviews of the affair, conducted by the UK Parliament, a CRU commission led by eminent geoscientist Lord Oxburgh, Penn State University, the National Science Foundation Office of the Inspector General, and the University of East Anglia. As a result of "climategate", nothing at all changed in the peer-reviewed scientific literature on climate change. It was a phony scandal.

A fierce advocate of good science
As I read the book, I was impressed by Dr. Mann's tremendous passion for science and knowledge that comes through. He loves figuring out how things work, and stands in fierce opposition to shoddy science and anti-science political attacks. I had the opportunity to sit down over a beer and talk with him at a recent conference, and he had little interest in talking politics. He'd much rather talk about science, and we had a great discussion about hurricanes--he's published several papers that use statistical techniques to estimate how many tropical storms we missed counting in the Atlantic before the advent of satellites. He frequently talks about how science works and the importance of following the scientific method in his book: "The scientific process--left to operate freely--is inherently self-correcting, even if the gears may at times turn more slowly than we would like...Scientists must be allowed to follow the path along which their intellectual inquiries take them, even if their findings and views might appear inconvenient to outside special interests." In the end, Dr. Mann is "cautiously optimistic" that humanity can meet the challenge of climate change, but acknowledges that climate scientists are in a "street fight" against well-funded climate change disinformers bent on obscuring the science.

Conclusion: five stars out of five
The Hockey Stick and the Climate Wars: Dispatches from the Front Lines is a must-read for every serious student of climate change science, and gets my highest rating: five stars out of five. The book is $17.78 at True to its title, the book has spawned its own mini-war in the ratings section of Amazon, where readers either loved it or hated it--75% of the reviews were 4 or 5 stars, while 21% were 1 star reviews. Only 4% of the readers gave it a mediocre 2 or 3 star rating. Some of the 1 star reviews are no doubt there because “Watt’s Up With That,” one of the most prominent climate science confusion sites, put up a post calling on readers to attack Mann’s book and to attack positive reviews.

Besieged by Climate Deniers, A Scientist Decides to Fight Back, an opinion piece by Dr. Mann that appeared on the Yale Environment 360 site on April 12.

Much-vindicated Michael Mann and Hockey Stick get final exoneration from Penn State — time for some major media apologies and retractions. blog post by Joe Romm.

An interview with Dr. Mann about his book, "The Hockey Stick and the Climate Wars", appeared on Andy Revkin's Dot Earth blog in the New York Times on May 3.

My favorite climate science blog is, which Dr. Mann co-founded. You can see one of the latest challenges to the hockey stick answered in a May 11 post discussing tree ring records from Siberia.

I'll have a new post by Friday at the latest.

Jeff Masters

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.