“…the hockey stick graph became an icon and [climate change] deniers reckoned if they could smash the icon, the whole concept of global warming would be destroyed…” Michael E. Mann
In 2012 Michael E. Mann, one of America’s leading climate scientists, sued several individuals and organizations for making public accusations that he had manipulated climate data in the course of conducting his research. The defendants included the National Review, a conservative magazine, and the Competitive Enterprise Institute, a Libertarian “think tank” whose founder, Fred L. Smith, has stated that climate change is a positive development, leading to milder weather and enhanced agricultural productivity.
A central issue in the suit was the veracity of the so-called “hockey stick” climate graph published by Mann and several colleagues in the prestigious scientific journal Nature in 1998. The graph showed changes in the northern hemisphere’s mean temperature record over the past 600 years. Because we have no thermometer readings from most of those years, Mann’s team analyzed “proxies” such as tree rings, ice cores and sediment records that provided indirect information about the range of temperatures during any given time period.
What the graph showed is that despite periodic variations, overall temperatures for the initial period, roughly the years 1400 to 1900, remained basically flat, actually trending slightly downward, until the twentieth century, when they began to trend steeply upward. The graph resembles a hockey stick lying on its edge, with its long shaft representing the five centuries preceding the twentieth century, and its blade, representing the twentieth century, sticking almost straight up in the air.
Although Mann’s team didn’t liken their graph to a hockey stick, the term was popularized by the climatologist Jerry Mahiman and quickly became an easily remembered visualization representing complicated climate-change data to non-specialist policymakers and the general public.
Soon copies of the hockey stick started appearing in popular magazines and on newscasts. Then, in 2001, an enhanced version of the graph, extending back to the year 1,000, and containing essentially the same profile, appeared in the Intergovernmental Panel on Climate Change’s third climate assessment report’s highly influential Summary for Policymakers.
And that — a simple, effective visual showing global temperatures rising quickly and dramatically toward dangerous levels — got the fossil fuel industry and the groups and publications it supported riled up. The hockey stick was too potent a symbol to be ignored.
Although the graph and data behind the graph were widely accepted in the scientific community, there were, as there should be, some scientific questions raised about the Mann team’s temperature proxy interpretations and therefore some of its conclusions. When some of these questions, or challenges to the graph, appeared in scientific journals, “climate skeptics” pounced, and an endless stream of baseless articles with titles like The Hockey Stick Illusion and Michael Mann’s “Hockey Stick” Hypocrisy appeared in assorted publications. While scientific inquiry eventually confirmed Mann’s methods and conclusions, a certain amount of damage had been done to the credibility of climate science and the idea that we urgently need to cut greenhouse gas emissions if we are to avoid potentially catastrophic damage to the biosphere and civilization.
So, where does this bit of climatology history leave us today? It turns out that Mann’s graph from 25 years ago indeed served as a model for our current situation, with today’s temperature rise headed almost straight up, relative to recent historical trends. It took two centuries, from 1800 until about 2017, for greenhouse gas emissions to raise global temperature 1ºC. But it has taken less than ten years to rise an additional two-tenths of a degree to our current 1.2ºC.
Oh, and Mann’s case is still working its way through the courts. While some have wondered about the source of his tenacity, it seems his ardent desire that the truth be told for the sake of the common good is tantamount.
Editor’s Note: A version of this article appeared previously in other publications as part of an ongoing series called “Your Ecological House,” written by Philip S. Wenz, the publisher of Firebird Journal.
Books by Michael E. Mann
Note: I have no financial incentive for recommending these books. I list them because I think they present critical information for those who want to fight for a better planet. Therefore, I do not provide links to commercial sites where the books can be purchased. Readers can easily find the titles online, or, better, order them through their local independent bookstore. —PSW
The Hockey Stick and the Climate Wars: Dispatches from the Front Lines, Columbia University Press, 2012
The New Climate War: The fight to take back our planet, Public Affairs Books, 2021
Our Fragile Moment: How Lessons from the Earth’s Past Can Help Us Survive the Climate Crisis, Public Affairs Books, 2022
Michael E. Mann’s Website: https://michaelmann.net/