Question: What is the Hockey Stick?
Michael E. Mann: The “Hockey Stick” is a graph that my colleagues and I published in the late 1990s depicting estimated changes in the average temperature of the Northern Hemisphere over the past thousand years. The graph shows a long-term decline from relatively warm conditions during Medieval time into the colder conditions of the Little Ice Age (the “handle”), followed by the abrupt warming of the past century (the “blade”). The Hockey Stick was featured in the 2001 IPCC (Intergovernmental Panel on Climate Change) report Summary for Policy Makers, which helped to establish it as an icon in the debate over human-caused climate change. The graph told a simple story: that a sharp and highly unusual rise in atmospheric warming was occurring on Earth. Furthermore, that rise seemed to coincide with human-caused increases in greenhouse gas levels due to the burning of fossil fuels.
Q: Why has it generated so much controversy?
MEM: The controversy that the hockey stick ultimately generated had little to do with the depicted temperature rise in and of itself. Rather, it was the beginning of what became a pattern. Vested interests, including a handful of companies in the fossil fuel industry, perceived this graph as a threat because it was easy to understand and clearly showed through the rapid rise of temperatures in the last 100 years that our climate is changing due to human interference. It’s understandable that the fossil fuel industry, which is among the largest and most deeply embedded industries in history, would seek to discredit science it perceived as a threat to its short-term interests. But the dishonest attacks on science and scientists are unacceptable. Oil and coal have been very good to us--they have enabled dramatic economic growth in our country and around the world. But now we know that continued reliance on fossil fuels will come at the price of a changing climate. To their credit, some energy and fossil fuel companies understand this and have backed away from attacks on climate science. But others have stepped in to take their place. And the ideological groups and politicians they fund who are opposed to action on climate change have continued to attack me and my research.
Q: What is it like as a scientist to find yourself embroiled at the center of the debate over human-caused climate change?
MEM: It is somewhat surreal. As an aspiring scientist, one never imagines that he or she will eventually find themselves at the center of a raging storm of controversy. Unfortunately, it is a fact of modern life that science, like so much else in our culture, has become increasingly politicized. Scientific findings that prove inconvenient to vested interests are often viciously attacked, in a very public and personal way. And thus it was with our “hockey stick” graph. As a scientist subject to such attacks, I have learned to develop a thick skin. I understand that the attacks are not really about me, but instead about the threat that our findings represent to fossil fuel industry special interests. One scientist who was a real role model for me, the late Stephen Schneider, took me aside a decade ago when the attacks were beginning to ramp up. He explained to me that I should wear these attacks as a badge of honor, that they were really a testament to the importance of my scientific work
Q: What have you learned from the experiences you've been through? What is it like as a scientist to be in the public eye?
MEM: I was a reluctant public figure, thrust into the spotlight by circumstances beyond my control. But I have ultimately embraced that role. I can think of nothing more important as a scientist working on a societally important problem to be doing all I can to inform the public discourse, to make sure that the actions we choose to take as a society to confront global environmental threats are informed by the best possible science and an honest discussion of our options and their implications. In this sense, my experiences have transformed me into a different person--I like to think for the better.
Q: Why is the science of climate change under attack? Who is at the center of the attacks?
MEM: Human-caused climate change is an inopportune fact for those who profit greatly from the unfettered burning of fossil fuels. A combination of major fossil fuel interest groups such as ExxonMobil and the American Petroleum Institute, and--increasingly--powerful private interests allied with the fossil fuel industry such as Koch Industries and the Scaife Foundations, have spent millions of dollars funding a propaganda campaign aimed at convincing the public that the underlying science is fatally flawed and uncertain, and that taking action to combat climate change will bankrupt our economy. Neither is true, but a well-known lesson of politics is that a lie repeated often enough is often accepted as truth. Thus, by funding an elaborate echo chamber for trumpeting their claims, these groups have successfully clouded the public’s understanding of the problem and the threat.
Q: What can we do about climate change? What should we do?
MEM: Scientists who study climate change impacts generally believe that the overall warming of the globe should be limited to no more than about 2 degrees C (3.5 degrees F) relative to the pre-industrial (i.e., early 19th century) if we are to avoid what might reasonably be described as “dangerous human impacts” on our climate. We have already warmed about 1C, and another 0.5C is already in the pipeline due to the lagging response of the climate to historical emissions. That total warming of 1.5C (about 3F) is thus called the “committed warming”—we will have to deal with it no matter what, which means we already have to take steps to adapt to some amount of overall climate change, which involves protecting coastlines from inundation from rising seas, shifting farming patterns to adjust crops, rotation patterns, etc. to warming temperatures and shifting rainfall patterns, among other things.
To avoid breaching 2C there obviously isn’t much wiggle room. We likely must avoid exceeding 450 parts per million of CO2 in the atmosphere, and we’re already at about 390 ppm and increasing at 2-3 ppm per year. So avoiding “dangerous” warming of 2C (3.5F) means bringing fossil fuel emissions to a peak within less than the next decade, and ramping emissions down to near zero by the end of the century.
How we choose to achieve these reductions is of course a matter of policy--which is not my expertise. But it must be informed by science--and the science tells us that we are in the process of creating profound changes in our climate that are likely to be detrimental to civilization and indeed the planet, if we continue on our current course. As a father of a six-year-old daughter, I feel we are ethically bound to not pass that legacy along to her and her children.
Q: Why is it important to prevent the politicization of science?
Michael E. Mann: History is replete with all too many examples of the dangers that arise when science becomes politicized, like Lysenkoism and its detrimental impact on Soviet agriculture during the Stalin regime. Science is almost unique among endeavors in terms of the self-correcting machinery that govern its progress. Those findings, theories, and predictions that have merit ultimately prevail because of their explanatory success, while those which do not fall to the wayside. But the success of the process relies on the open, objective, and unfettered give-and-take between scientists. When those with an agenda attempt to game the system, they threaten the integrity of the scientific process.
As I discuss in the book, the attacks against climate science might be even better described as the “scientization of politics” in the sense that the science of climate change, like other disciplines of science (e.g., human health/pharmaceuticals) whose findings prove threatening to some vested interests, is now being used by politicians as just another tool for waging politics, i.e., science itself has become a political football—a very dangerous and, in many ways, chilling development.
Q: Has your defense been similarly politicized? Are only Democrats defending you?
MEM: Not at all. Leaders from both political parties have come to my defense and expressed concern about the politicization of science. As I discuss in the book, prominent Republicans such as former chair of the House Science Committee Sherwood Boehlert (R-NY) and Senator John McCain (R-AZ), both came to our defense, in addition to prominent Democrats such as Henry Waxman (D-CA), when we came under attack by Joe Barton (R-TX) in 2005. Even though Barton was a powerful House Committee Chair, other prominent members of his own party were willing to call him out for what they saw as a politically inspired witch hunt against scientists.
It is unfortunate that climate change, and indeed other areas of science, has become hyper-politicized in recent years, and that denial of science has essentially become a litmus test now for one of the major parties. It was not that long ago when this was not the case. Climate change doesn’t care about your politics. The detrimental impacts will affect the children and grandchildren of Republicans and Democrats alike. It is good to see prominent Republicans like Sherwood Boehlert and Bob Inglis (R-SC) taking on leadership on this issue for their party–because ultimately their party does not want to be on the wrong side of history.
Q: Did Climategate discredit the hockey stick model of global warming? Is the hockey stick model dead . . . or alive and well?
MEM: Let’s remember that the so-called climategate was really a case of hacked and stolen emails–that seems to get lost. Ultimately “Hacked–gate” was yet another tactic in the long-term campaign to sow doubt among the public about the validity of climate change science. The largest science associations in the world issued a statement that reconfirmed the science, the emails not withstanding. There have now been more than a half dozen independent investigations in the U.K. and the U.S. that have all found that there was no evidence of impropriety. The emails were deliberately edited, words and phrases cherry-picked and taken out of context, and emails juxtaposed across a decade to suggest they were a single chain. All in the effort to undermine public confidence in the fact of climate change. Nonetheless, the smear campaign was timed for maximum effect, in the lead up to the 2009 Copenhagen Summit, and it probably set back efforts to deal with the climate change crisis several years, at great potential cost to us and our environment.
As for the Hockey Stick, it is alive and well! More than a decade later, there are now well over a dozen different reconstructions using different methods and different data which all come to the same conclusion: that the large-scale warming of recent decades is anomalous for at least the past millennium. Indeed, the most recent (2007) IPCC report extended the conclusions of our original work, finding that recent warming is likely anomalous for at least the past 1,300 years, now that reconstructions extend even further back in time.
Q: Critics say temperatures haven’t been rising as fast as the UNIPCC predicted. Doesn’t that discredit the hockey stick model?
MEM: The Hockey Stick really only characterizes temperature changes prior to the industrial period. The warming of the past century is actually documented by thermometer records around the globe, and even critics of climate change research like Berkeley astrophysicist Richard Muller now concede that the instrumental record of warming temperatures is robust. While claims are sometimes made by climate change critics that the models overestimate the warming, the actual scientific literature shows that the warming is occurring at the upper end of the changes that have been projected for decades by climate models. Certain phenomena, like declining sea ice in the Arctic, are proceeding at a far greater pace than the models projected. By many measures, the climate model projections have been overly conservative, rather than alarmist!
Q: How have climate models changed?
MEM: When I first got into climate science in the early 1990s, the models were quite crude by modern standards. They were very coarse in their spatial resolution, with (for example) New York City and Pittsburgh both falling within a single “grid box” of the model. The ocean’s currents were not especially well captured. Though these models were able to make successful predictions about future global temperature changes, they were not very credible when it came to making regional predictions about (for example) seasonal temperature and rainfall changes. This deficiency was related, among other things, to the fact that the models failed to reproduce certain key natural phenomena such as the El Niño/Southern Oscillation (ENSO). As the models were improved over time, and the ocean currents and wind patterns were better resolved, the models begin to produce El Niño events that looked a lot like the real world phenomenon. El Niño wasn’t “put into” the model—it arose as what we call an emergent phenomenon; once the physics of the models was sufficiently improved, El Niño events spontaneously began to occur, and increasingly they looked a lot like the real-world El Niño phenomenon. This is just one example of why we have increased confidence that the models are credible, and that their projections are to be taken seriously.