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Hot Air and Hockey Sticks: What We Don't Know About Global Warming And What It Doesn’t Mean

By Russell Chibe | 5.21.07

The problem is not one of good science versus bad, or “sound” science versus “junk” science. The problem is that nature can be viewed through many analytical lenses, and the resulting perspectives do not add up to a single, uniform image, but a spectrum that can illuminate a range of subjective positions.

-Dr. Daniel Sarewitz
Director of the Consortium for Science, Policy and Outcomes
Arizona State University

Facts are meaningless; you can use facts to prove anything that’s remotely true!  Facts, schmacts.

-Homer J. Simpson
Nuclear Safety Technician
Springfield Nuclear Power Plant

Imagine you are selected for jury duty. You arrive at the courtroom and learn the basic facts of the case: the plaintiff alleges that the defendant sold his product at below cost in an attempt to illegally drive out the competition. The case hinges on the testimony of two expert witnesses, one testifying on behalf of the plaintiff and the other on behalf of the defendant. Each is a forensic accountant, each has impressive credentials, and each is absolutely positive that the other is wrong. You suddenly find yourself in the jury room, trying to decide who is liable. How are you to make a decision?

On May 4, 2007, the Intergovernmental Panel on Climate Change (“IPCC”) released the final section of its Fourth Assessment Report entitled Climate Change 2007 The first two sections of its Fourth Assessment Report were released throughout the past year, and not surprisingly, pundits were quick to weigh in. On the Left, John Kerry used the Report as an opportunity to plug his proposed anti-emissions legislation and his Al Gore-esque book. On the Right, Sen. James Inhofe (R-OK) looked into his crystal ball and predicted that “the latest IPCC summary will surely spawn another round of media alarmism and hype.”

We’ve come to expect such polarizing responses from the Left and the Right, even when politicians claim their positions are based on science. Consider the infamous and controversial “hockey stick” graph. Published in a 1998 paper by Mann et al., the figure shows an unprecedented upward slope in mean global temperatures during the last century of the past millennium. Mann’s research was challenged by McIntyre and McKitrick, who argued in their 2003 paper that the iconic graph was the result of technical errors in Mann’s statistical methodology. Recently the National Research Council's Board on Atmospheric Sciences and Climate published its own study at the request of Congress, finding that Mann’s original paper was generally scientifically sound.

A Google search of the terms “hockey stick global warming” reveals scientific justifications for the graph from liberal websites and scientific refutations from conservative websites. This leads to one of two conclusions: 1) political pundits are incredibly adept statisticians, and by sheer coincidence their conclusions seem correlated to their political leanings; or 2) they are simply using the studies for their own political ends. If you chose conclusion 2, give yourself a gold star.

Those who read the IPCC Report and understand all the climatological and statistical nuances themselves (and who doesn’t understand the positive and negative feedbacks involved in global warming’s impact on hurricane formation and strength?) don’t need other experts to tell them which argument is right. But if you are one of the roughly 6.5 billion people on this planet who isn’t comfortable discussing the effects of water vapor feedback or the ocean’s role as a carbon sink—in other words, if you’re not a climate scientist—how are you supposed to reach an opinion one way or the other? To go back to the jury analogy, the experts have spoken and it’s time for us as a society to reach a verdict. How the hell are we supposed to do that?

The issue of science in policy is one that has been addressed, and continues to be addressed, by individuals infinitely more qualified than I. One such individual is Daniel Sarewitz of Arizona State University. In examining the role of science in environmental policy, Dr. Sarewitz observed: “Rather than resolving political debate, science often becomes ammunition in partisan squabbling, mobilized selectively by contending sides to bolster their position.”1 Roger Pielke, Jr., of the University of Colorado, has described such fights as “the core dynamic of the climate debate in which political opponents pick a scientific sandbox to fight in, with little connection to policy, and fight things out in a public manner under a pretense that the debate has significance beyond science.”2

Thus we have our hockey stick debate. After all, Sen. Inhofe’s position isn’t really based on a belief that Dr. McIntyre’s research methodology is more scientifically sound than that of Dr. Mann, is it? According to his own web bio, Inhofe has a degree in economics and worked in aviation, real estate, and insurance for over 30 years before entering politics—credentials unlikely to land him on the editorial board of the Journal of Climate.

Inhofe is not alone in his skepticism; late in 2006, U.S. Representative Joe Barton (R-TX) commissioned Edward Wegman, a statistician at George Mason University, to challenge Mann’s findings. Much to Rep. Barton’s delight, Dr. Wegman reported that Mann’s assertions that the 1990s and 1998 were the hottest decade and year of the past millennium “cannot be supported by their analysis.” Less exciting for Rep. Barton was Dr. Wegman’s concession that most climate scientists believe global warming is being influenced by human activity.3 So we see the common pattern of politicians selectively reporting their own arbitrary sandbox victories while often ignoring the relevance of the full data to the broader issue of global warming policy.

Politicians are not the only combatants in this sandbox, as the Fourth Assessment Report has also provoked extreme reactions from people with impressive scientific pedigrees. On one side you have Chris Landsea, who withdrew his participation in the authoring of the Report because he felt the IPCC was making unfounded statements suggesting that global warming would contribute to stronger and more frequent hurricanes. On the other side, you have Joseph Romm, former member of the US Department of Energy, claiming that the Report underestimates positive feedbacks, thereby understating the severity of future warming. Certainly these discussions are highly relevant within the scientific community, but what role should they play in the shaping of public policy? Put another way, how should these discussions effect how you interpret the Report?

It seems counterintuitive to suggest that you should ignore the facts. After all, that’s how human beings think: we observe facts, process those observed facts, and reach a conclusion. Or at least we like to think we do. But let’s go back to our courtroom analogy one last time. The purpose of a court of law is to reach a resolution. The jury can’t come back and say, “You know, your honor, we’re just not sure. The plaintiff’s expert from M.I.T. was convincing, but so was the defendant’s expert from the University of Chicago.” But if we’re the jury in the case of In re Global Warming, who’s to say we can’t do just that?

Dr. Pielke has observed that “the problem of global warming is much more complex than the simple yes or no debate implies.”4 Yet an issue such as the “hockey stick” debate gets blown up as if it’s the lynchpin to understanding climate change. To that extent, the “hockey stick” debate is a red herring: its resolution would have little impact on our current understanding of global warming. Sen. Inhofe is quick to point out studies, such as that by meteorologist Gerald North of Texas A&M, that question the methodology behind Dr. Mann’s “hockey stick” graph. Sen. Inhofe is less likely to recall Dr. North’s ultimate conclusion that “our reservations [regarding the “hockey stick” graph] should not undermine the fact that the climate is warming and will continue to warm under human influence.”5

Another red herring issue is the scientific consensus, or lack thereof, regarding the existence of human-induced warming. In his essay, “Science and Environmental Policy: An Excess of Objectivity,” Dr. Sarewitz gave an example of an exchange among prominent atmospheric scientists in 1997. It started when a group of scientists circulated a “Scientists’ Statement on Global Climate Disruption” which concluded that “effects of the disruption of climate are sufficiently complicated for us to assume that there will be effects not now anticipated.” Tom Wigley, a prominent climate modeler from the National Center for Atmospheric Research, responded by asserting that “phrases like [my emphasis] ‘climate DISRUPTION is under way’ have no scientific basis . . .”6 To non-climate scientists, such an argument may appear to be the scientific equivalent of “it depends on what the meaning of the word of ‘is’ is.” Nonetheless, if scientists can’t agree on the definition of “disruption,” what happens when they argue about something relevant?

While the exchange described by Dr. Sarewitz occurred ten years ago, the lesson is applicable today. After all, global warming is a complex issue involving many different disciplines, each with their own internal debates and methodological limitations. As Dr. Sarewitz points out:

Geologists struggle to piece together a historical record of atmospheric change, but there is little that they can say about causation, because the details of the complex climate system have been erased by time. Atmospheric scientists, on the other hand, are awash in detailed observation and bolstered by theory, but they can never validate their models because climate is an open system, and is therefore unpredictable.7

Accordingly, the very notion of a consensus is at best unrealistic and at worst unattainable. For example, after the Third Assessment Report (2001), IPCC author and M.I.T. professor Richard Lindzen stressed that “there is no consensus, unanimous or otherwise, about long-term climate trends and what causes them.”8 Dr. Landsea’s resignation from the Fourth Assessment likewise demonstrates that there are divergent opinions among the authors of the current Report as well. Be it 1997 or 2007, credible scientists can disagree.

So we don’t need a definitive answer on the global warming debate, which is a good thing because we don’t have, and can’t get, a consensus. And, unless you’re an atmospheric scientist (or otherwise well versed in the science of global warming), the current scientific debate is of little value. What are we supposed to take away from the Fourth Assessment Report then?

While it doesn’t represent scientific certainty beyond a reasonable doubt, the IPCC does represent a comprehensive overview of the current state of global warming research. To that end, the first lesson of the Report is that the earth is indeed warming. Where this fact may have still been open to debate in 1997, the overwhelming majority of current studies support the IPCC’s conclusion that the warming of the climate system is unequivocal. Even critics such as Dr. Wigley have since acknowledged anthropogenic contributions to observed warming.9

The most significant debate at this point is exactly how much warming can be attributed to man-made greenhouse gases, at what rate future warming is likely to occur, and what the impact of that warming will be. It is important to keep in mind that, while the current research is nearly unanimous in its conclusion that the earth is warming, the certainty of future predictions is far less so. For example, the Working Group I Summary for Policymakers, released in February of 2007, notes a >90% certainty that that most of the observed increase in globally averaged temperatures since the mid-20th century is due to observed increases in anthropogenic greenhouse gases.10 However, when predicting the increase in mean temperatures from now until the end of the 21st century under various emissions scenarios (which range from +0.3 to +6.4°C), the certainty offered is only >66%. Naturally, a >66% certainty is significant; for example, if a meteorologist told you there was a 66% chance of rain today, you’d probably take an umbrella. Nonetheless, the probability of this prediction proving accurate is more likely than not, but it is worth distinguishing from the near certainty of what’s going on right now in the atmosphere.

The certainty also drops when discussing the impact of future climate change. One example can be found in the Report’s discussion of tropical cyclones, which include hurricanes. The Report is >66% certain that we have observed an increase in tropical storm intensity since 1960, but only >50% certain that human activity is in some way responsible for the observed intensity. It then offers a >66% certainty that human activity will subsequently lead to more frequent and/or stronger tropical storms in the future. Again, a certainty of >66% is certainly worth noting when considering the consequences of future global warming, but it falls far short of the 95% certainty that the climate is warming right now.

Indeed, some of the greatest criticism of the IPCC Report seems to revolve around some of the “doomsday” predictions regarding future climate scenarios. As already mentioned, Dr. Landsea left the IPCC because he felt the impact on tropical storms was being overstated. To some extent, media reports may be to blame. For example, a recent article in the Stanford Daily discussed the dire predictions of IPCC author Stephen Schneider, but never mentioned that most of the predictions were only >50% or >66% certain.11

Benny Peiser of Liverpool John Moores University suggests that “science editors and campaigners have employed strategies to discourage or intimidate reporters from even asking climate skeptics about their assessment.”12 Whether any perceived bias is due to a campaign of intimidation or simply a natural attraction to the sensational is unclear. However, partisan denialists of Sen. Inhofe’s ilk likely share some responsibility for creating the impression that global warming skeptics are members of the Flat Earth Club. Regardless of the reason, it is important to recognize that prediction is far from an exact science. While in the minority, a significant number of scientists subscribe to David Orrell’s belief that “when models about the future climate are in agreement, it says more about the self-regulating group psychology of the modeling community than it does about global warming and the economy.”13 Or, as stated more succinctly by Patrick Swayze’s character in Road House: “Opinions vary.”

So, in the end, the plethora of statistics and studies, facts and opinions available about global warming leave us with some fairly certain conclusions and a whole lot of maybes. It’s a far cry from an absolute “innocent” or “guilty” verdict. But seeking out such a verdict misses the point. As Dr. Sarewitz notes: “Hidden by this discourse are the underlying issues that drive the problem of climate change: the future economic path of the post-industrial world, population growth and distribution, patterns of land use, the distribution of wealth and resources among nations, and the vulnerability of poor nations to natural and anthropogenic hazards.”14

If you favor curbing fossil fuel emissions, there’s nothing wrong with citing the nearly universal view that fossil fuels are currently warming the planet, and the majority view that continued emissions will more likely than not lead to more extreme weather. But you can also acknowledge the fact that these predictions may not come true. On the other hand, you can argue that curbing emissions will be disastrous to developing nations while recognizing that there’s a risk that our inaction will lead to other disasters down the road.

Regardless of your political leanings or your stance on global warming, there’s little to be gained from getting bogged down in the facts of the matter. Resolving the “hockey stick” controversy will do little to determine our energy and environmental policies in the next decade and beyond. The IPCC Report reflects the current state of global warming research, and that research is fairly certain about current warming while less so regarding future warming and its impact. How these findings will impact your actions and your politics is something that science cannot answer.


1. Sarewitz D. 2000. Science and environmental policy: an excess of objectivity. Earth Matters: The Earth Sciences, Philosophy, and the Claims of Community, Robert Frodemen, ed. Prentice Hall, pp. 79-98..

2. Pielke R Jr. 2005. Is the ‘hockey stick’ debate relevant to policy? Prometheus: The Science Policy Blog, May 17, 2005.

3. Kerr RA. 2006. Politicians attack, but evidence for global warming doesn’t wilt. Science 313: 421.

4. Pielke R. Jr. 1997. Asking the right questions: atmospheric sciences research and societal needs. Bulletin of the American Meteorological Society 78(2): 255-64.

5. Kerr 2006.

6. Sarewitz 2000.

7. Ibid.

8. Lindzen RS. 2001. Scientists’ report doesn’t support the Kyoto Treaty. The Wall Street Journal. June 11, 2001.

9. A paper co-authored by Dr. Wigley found that a model forced by a combination of anthropogenic factors and volcanic aerosols yields surface-troposphere temperature trend differences closest to those observed. Santer BD, et al. 2000. Interpreting differential temperature trends at the surface and in the lower troposphere. Science 287(5456): 1227-32.

10. In an effort to contextualize their probabilities, the IPCC refers to >90% as “very likely,” >66% as “likely,” and >50% as “more likely than not.” The author of this article is not referring to such probabilities when using any of these terms.

11. Newman L. 2007. Int’l report: dire warnings on climate. The Stanford Daily. April 19, 2007.

12. Peiser B. 2007. Editorial bias and the prediction of climate disaster: the crisis of science communication (conference paper: Climate Change: Evaluating Appropriate Responses, Brussels), April 18, 2007.

13. Orrell D. 2007. Apollo's Arrow: The science of prediction and the future of everything. HarperCollins.

14. Sarewitz 2000.