New Book "SuperFreakonomics" Mischaracterizes Climate Science

A follow-up to the bestselling book "Freakonomics" features a chapter that grossly mischaracterizes climate science, according to the Union of Concerned Scientists.

The book, "SuperFreakonomics" by Steven D. Levitt and Stephen J. Dubner, was released in late 2009. Experts at UCS found that the fifth chapter of the book, "Global Cooling," repeats a large number of easily discredited arguments regarding climate science, energy production, and geoengineering.

The authors appear to have taken a purposefully contrarian position on climate change science and economics. While such a position may help draw attention to their book, their reliance on faulty arguments and distorted statistics does a disservice to their readers.

In chapter five, the authors:

Repeat tired global cooling myths

First, the chapter rehashes 1970s global cooling myths (pages 165 and 166). In fact, the 1970s "cooling scare" is largely an invention of the opponents of addressing climate change. Only a few news organizations reported on a handful of scientific papers regarding cooling in the 1970s. What was going on? Scientists noted that sulfur-dioxide production and other particulates that reflect sunlight were on the rise, outstripping the effect of heat-trapping gases such as carbon dioxide and methane. Over time, industry reduced emissions of these cooling pollutants, which also cause acid rain. Meanwhile, fossil fuel emissions and deforestation have exploded, leading to an over-abundance of warming gases in our atmosphere. The scientific research on global warming is orders of magnitude larger and more robust than the science underpinning a handful of cooling articles in the 1970s.

Unfairly trash climate models

The authors claim climate models have a very wide range of future temperature projections (page 168). This is true, but it misses the point. Climate models have a wide range because scientists don't know how much more heat-trapping emissions human activity will put into the atmosphere. Models project that a decrease in production of heat-trapping emissions would lead to less warming—around 2 degrees F by the end of the century—while continued high emissions would lead to greater warming—closer to 10 degrees F. The authors gloss over the fact that reducing heat-trapping gases will lower warming. This simple fact undercuts most of the authors' discussion regarding whether or not reducing emissions is an effective tool for reducing global warming. According to climate models, it is the method for doing so.

The authors emphasize the fact that climate models don't account for relatively small-scale phenomena such as hurricanes (pages 181 and 182). Climate models by their nature focus on the macro-, not the micro-scale. The authors' complaint is akin to criticizing a desk stand globe because it doesn't display the street where they live. Climate models all agree that on the large scale, land and ocean areas worldwide will experience warming as heat-trapping emissions continue to rise.

Highlight irrelevant statistics about carbon dioxide without context

The authors note that carbon dioxide concentrations in the atmosphere were higher 80 million years ago (pages 181 and 182). This is true, but largely irrelevant to the question of whether or not we should do anything to address global warming today. Carbon dioxide and temperature fluctuate naturally on well-understood cycles that take place over tens of thousands of years. Current warming, brought about by human-induced emissions, has been happening over a condensed period of time. To flourish, our civilization has relied on the relatively stable climate of the past few thousand years. Rapid change to that climate is a serious threat.

Extol the virtues of excess carbon dioxide while ignoring the downsides

The authors point out that many plants benefit from higher carbon dioxide concentrations (page 184). While this is true, they ignore how plants suffer when the planet warms. A warmer world would disrupt agricultural production, shift the areas suitable for many tree species, and increase the range of pests and pathogens. And while beneficial plants may grow faster with increased carbon dioxide, so do weeds, allergens and invasive species. Overall, a higher rate of growth for some plants is a minor benefit compared with the major disruptions for human society scientists project under an extreme warming scenario.

Ignore a major source of sea level rise

The authors maintain that sea levels can rise only 1.5 feet by 2100 (page 186). How did they arrive at that statistic? It seems they only considered sea level rise due to a warming (and expanding) ocean, but failed to include additional sea level rise from melting ice sheets.

Over the last few years scientists have gained greater understanding of how land-based glacial ice responds to warming and how much it may contribute to sea level rise. A new study using the latest climate science suggests sea levels may rise 2.6 to 6.6 feet by the end of this century depending on our emissions over the coming century. In addition, unchecked warming may at some time in the future cause the Greenland and West Antarctic ice sheets to melt completely, leading to catastrophic sea-level rise.

Cherry-pick short-term climate fluctuations while missing the bigger picture

The authors briefly repeat the false claim that global temperatures have decreased over the last decade (page 186). This is an indefensible way of looking at the Earth's temperature record. Warming is a long-term trend and temperatures continue to increase over time, though they do fluctuate year-to-year. Counting only a few years in the global temperature record is akin to trying to determine who is winning a baseball game by only counting runs scored in the 7th and 8th innings. It ignores the broader, longer-term picture. In reality, the eight warmest years on record for the globe have all occurred since 1998, and the 14 warmest years in the record have all occurred since 1990. Global mean temperatures every year this century (to the end of 2007) were all above the average of the 20th century.

10/27/09 UPDATE: Levitt has clarified what the authors meant when they wrote this passage in an Associated Press article debunking "global cooling" claims.

A line in the book says: "Then there's this little-discussed fact about global warming: While the drumbeat of doom has grown louder over the past several years, the average global temperature during that time has in fact decreased."

That led to a sharp rebuke from the Union of Concerned Scientists, which said the book mischaracterizes climate science with "distorted statistics."

Levitt, a University of Chicago economist, said he does not believe there is a cooling trend. He said the line was just an attempt to note the irony of a cool couple of years at a time of intense discussion of global warming. Levitt said he did not do any statistical analysis of temperatures, but "eyeballed" the numbers and noticed 2005 was hotter than the last couple of years. Levitt said the "cooling" reference in the book title refers more to ideas about trying to cool the Earth artificially.

Use faulty statistics to trash renewable energy

The authors criticize renewable electricity sources, notably solar power (page 187). Energy expert Joe Romm does an excellent job debunking their claims on his blog.

Advocate rolling the dice on unproven technology

The authors discuss the idea of using geoengineering to address global warming (beginning on page 193) as if it is a panacea to the global warming problem. But according to climate scientists, such technologies are unproven and the possibility that they might work is no excuse for failing to curb emissions now. While geoengineering deserves research, the authors' implication that it could be a substitute for reducing heat-trapping emissions is unfortunate. It is also worth noting that in addition to warming the climate, carbon dioxide is also acidifying the oceans, making it less able to support marine life. Geoengineering the climate would not stop that.

10/26/09 UPDATE: On WAMU and National Public Radio's Diane Rehm Show, the authors conducted an interview with UCS scientist Dr. Peter Frumhoff. In the interview, Levitt seems to indicate that he believes geoengineering is not a substitute for reducing emissions. At about 19 minutes into the interview, Peter Frumhoff says we "need research" on geoengineering, but says it's "not a substitute" for reducing emissions. Levitt responds, saying "We don't really fundamentally disagree on those points..." He then notes that is has been said that geoengineering is a solution to global warming like "methadone is to a heroin addiction." He also notes that sulfur dioxide sprays would not address ocean acidification. He adds, "You won't be able to stop this if you don't deal with the carbon issue."

At a book signing talk and event later that evening, Levitt and Dubner did not object to this characterization of their argument and Dubner said they would respond to scientific criticisms of the book in more detail.

10/27/09 UPDATE: A USA Today opinion piece from Levitt and Dubner presents geoengineering as an "alternative" to reducing emissions, although they do acknowledge that sulfur dioxide sprays would not address ocean acidification.

Use a silly analogy to attack plans to reduce emissions

The chapter concludes with a story about doctors failing to wash their hands. The authors say this example shows how hard it is to change human behavior. This argument is a red herring. Energy efficiency, renewable electricity production, and cars that maintain performance with better fuel efficiency are all examples of technologies that reduce emissions without forcing people to change their behavior. While individual choices are incredibly important when it comes to addressing climate change, the authors' implication that it is the only way the problem can be addressed is fundamentally wrong.


  • On Friday, October 16, the Huffington Post published a review of SuperFreakonomics by UCS climate scientist Dr. Melanie Fitzpatrick.
  • On Saturday, October 17, Steven Levitt appeared on National Public Radio's Weekend Edition. At the end of the segment, host Scott Simon read from UCS's response to the global warming chapter. On that same day, Levitt posted an initial response to the book's critics on his blog. In his post, he fails to recognize that critics have read the chapter in question and that criticisms are coming from scientists. Further, he said UCS "pressured" NPR into reading a statement. In reality, UCS communications staff merely passed on the criticism to Weekend Edition's producers, who readily recognized its value. UCS responded accordingly on Levitt's blog.
  • On Sunday, October 18, Stephen Dubner posted a response to the claim that he and Levitt misrepresented the views of one scientist, Ken Caldiera. UCS posted a response urging Dubner to publish a more thorough response to the many scientific misrepresentations the book makes. Meanwhile, Joe Romm responds to this particular claim on his blog.
  • NASA climate scientist Gavin Schmidt has published a thorough response to the book's geoengineering claims.
  • On October 20, Nathan Myhrvold responded to criticisms of the book and his quotes in it. UCS responded, pointing out that Myhrvold's blog post, in which he states, "Geoengineering is proposed only as a last resort to try to reduce or cope with the even greater harms of global warming!" directly contradicts the main premise of the book's chapter and his quotes in it.
  • Also on October 20, Bloomberg News published Eric Pooley's review of the book. In the review, Pooley explains how the book says the opposite of what scientist Ken Caldiera believes about the role of geoengineering:

One of the injured parties is Ken Caldeira, a climate scientist at Stanford University who is quoted (accurately) as saying that “we are being incredibly foolish emitting carbon dioxide.” Then Dubner and Levitt add this astonishing claim: “His research tells him that carbon dioxide is not the right villain in this fight.”

Provocative, Untrue

That’s provocative, but alas, it isn’t true. Caldeira, like the vast majority of climate scientists, believes cutting carbon dioxide and other greenhouse-gas emissions is our only real chance to avoid runaway climate change.

“Carbon dioxide is the right villain,” Caldeira wrote on his Web site in reply. He told Joe Romm, the respected climate blogger who broke the story, that he had objected to the “wrong villain” line but Dubner and Levitt didn’t correct it; instead, they added the “incredibly foolish” quote, a half step in the right direction. Caldeira gave the same account to me.

Levitt and Dubner do say that the book “overstates” Caldeira’s position. That’s a weasel word: The book claims the opposite of what Caldeira believes. Caldeira told me the book contains “many errors” in addition to the “major error” of misstating his scientific opinion on carbon dioxide’s role.

  • On October 23, Good Morning America's George Stephanopoulos read a portion of UCS's criticism of the global warming chapter to Stephen Dubner. Unfortunately, Dubner did not respond directly to UCS's criticism, but instead tried to mischaracterize the scientists who are criticizing the book:

Stephanopoulos: But a lot of scientists who have studied this for an awful long time say you're not just simplifying, you're over simplifying. And here's what the Union of Concerned Scientists said about this book. They said, "The chapter on global warming is riddled with misrepresentations. The 'Superfreakonomics' authors appear to have taken a purposely contrarian position on climate change, science and economics." They basically say you're being contrary for the sake of being contrary so you can sell books.

Dubner: I think what we don't represent at all are the entrenched political and financial incentives of the global warming activist movement. So I would hate this book, too, if I were the global warming activist movement. But what we're saying is we need to look at the problem... 

Stephanopoulos: But what's in it for them? They're saying they're trying to save the planet.

Dubner: As are we...

  • On October 23, Steven Levitt published a response to the chapter's critics that failed to address the many scientific objections UCS has presented to the book. UCS initially submitted the text below as a response, but the editors of the Freakonomics blog did not publish it. Instead, UCS submitted a different, shorter comment that simply asked the authors to respond to UCS's scientific objections. That comment was published, but later removed from the blog. Here is the original comment that was not published:

Scientists are objecting to the chapter because it misrepresents climate science. Levitt and Dubner have still not accounted for the Union of Concerned Scientists’ objections to the book, including repeating the 1970s global cooling myth and narrowly citing facts about carbon dioxide out of scientific context to make excess carbon dioxide seem like less of a problem than it is.

In Levitt’s first response post, he linked to my organization’s criticism of the chapter. This post fails to respond to UCS’s objections.

Levitt invites us to look at the footnotes. I have, and I found further evidence that the book misrepresents climate science. Overall, the footnotes support the narrow facts that Levitt and Dubner cite, but they do not support their broader claims about carbon dioxide and climate science.

Here is an illustrative example: On page 253, in the book’s footnotes, Levitt and Dubner cite an article that says the opposite of what they claim in the chapter.

They cite a Real Climate article “What does the lag of CO2 behind temperature in ice cores tell us about global warming?” to support a claim on page 183 that “carbon dioxide levels have risen after a rise in temperature, not the other way around.”

The full sentence in the book reads, “Nor does atmospheric carbon dioxide necessarily warm the earth: ice-cap evidence shows that over the past several hundred thousand years carbon dioxide levels have risen after a rise in temperature, not the other way around.”

In fact, the Real Climate article says that atmospheric carbon dioxide does warm the Earth. It says:

“At least three careful ice core studies have shown that CO2 starts to rise about 800 years (600-1000 years) after Antarctic temperature during glacial terminations. These terminations are pronounced warming periods that mark the ends of the ice ages that happen every 100,000 years or so.

“Does this prove that CO2 doesn’t cause global warming? The answer is no…

“From studying all the available data (not just ice cores), the probable sequence of events at a termination goes something like this. Some (currently unknown) process causes Antarctica and the surrounding ocean to warm. This process also causes CO2 to start rising, about 800 years later. Then CO2 further warms the whole planet, because of its heat-trapping properties. This leads to even further CO2 release. So CO2 during ice ages should be thought of as a “feedback”, much like the feedback that results from putting a microphone too near to a loudspeaker.

“In other words, CO2 does not initiate the warmings, but acts as an amplifier once they are underway. From model estimates, CO2 (along with other greenhouse gases CH4 and N2O) causes about half of the full glacial-to-interglacial warming.”

To put this simply, the Real Climate article supports a narrow fact Levitt and Dubner cite, but actually contradicts their overall claim. In reality, scientists know that excess carbon dioxide from burning fossil fuels and destroying forests is warming the planet rapidly today and carbon dioxide released over longer periods of time due to natural processes has warmed the planet in the past. While other processes have initiated natural warming in the past, it is clear that the rapid release of excess carbon dioxide and other heat-trapping emissions from human activity have initiated today’s warming.

I look forward to a direct response to this criticism as well as UCS’s previous criticism.

For reference, the UCS criticism, with ongoing updates, can be found here:

The Real Climate article cited in the book can be found here:


Aaron Huertas

Union of Concerned Scientists

  • On October 26, On WAMU and National Public Radio's Diane Rehm Show, the authors conducted an interview with UCS scientist Dr. Peter Frumhoff in which they made it clear that they believe geoengineering is not a substitute for reducing emissions. [more detail] However, a USA Today opinion piece from Levitt and Dubner the next day took a step back and again presented geoengineering as an "alternative" to reducing emissions. [more detail]
  • On October 27, Levitt clarified what the authors meant when they wrote about global temperature trends in an Associated Press article debunking "global cooling" claims. [more detail]
  • A November 1 Boston Globe article challenges several assertions in the book, including the authors' miscitation of a Real Climate article. Unfortunately, Levitt fails to acknowledge that the book clearly misrepresents climate science in this case:

“Asserting that CO2 doesn’t cause warming at this point is tantamount to saying cigarette smoking doesn’t cause cancer,” Severinghaus says. “It’s just laughable.”

Asked over e-mail about the use of Severinghaus’s research, Levitt responded, “The sentence may be poorly written, but I do not think it is factually inaccurate.” He also defended the citation on the grounds that, while Severinghaus may not think his finding supports their point, it does not clearly disprove it, either. “Severinghaus says that this is not definitive evidence against CO2 warming the earth; he certainly can’t argue that this is definitive evidence that CO2 does warm the earth,” Levitt wrote.

  • The same Boston Globe article shares Dubner's response to the broader question of why he and Levitt left out so much information that would have helped readers understand their claims in context. The explanation printed here does not indicate that Levitt and Dubner were concerned with whether or not their book would cause readers to misunderstand major aspects of climate science:

...[Joe Romm] argues, climate scientists familiar with the book see Dubner and Levitt as gravely mischaracterizing the state of the science. And even fellow proponents of geoengineering research have piled on, arguing that Dubner and Levitt do the cause few favors by associating it with fringe arguments.

Asked why they didn’t mention any of the rebuttals that others have offered up to the arguments in “SuperFreakonomics,” Dubner says, “I think that’s a very legitimate question. And the reason they’re not rebutted is because they are rebuttals to the conventional wisdom.” The conventional wisdom, in other words, can take care of itself.

“These guys are colluding among each other to a, make their findings be right for their positions but b, even more troubling if you’re a scientist or a fan of science, is keep out the dissenters,” Dubner said. He connected scientists to Al Gore and tax money, completing a typical conspiracy theory trifecta.

Dubner went on to make the dubious claim that scientists “won’t get funding” if they don’t follow the scientific consensus. Even if we accept the incorrect premise that scientists do research primarily for money, his point overlooks the large amount of financial support the oil and coal industry and its allies offer to people with views that contradict the scientific consensus on global warming.

The truth is that the basic hypothesis that human activity is driving climate change remains strong because it has withstood decades of serious scrutiny from scientists around the world. Unfortunately, it also must withstand paranoid conspiracy theories and outright falsehoods in the media and online.

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