[Update Oct 19: My (concluding?) thoughts here.]

This may not be terribly interesting, but here is an email correspondence I had with Steven Levitt this morning:

From: Yoram Bauman
To: Steven Levitt

Hi Steve: This email is a hard one for me to write because it may void your kind offer to mention my forthcoming cartoon book on your blog, but I’m going to follow the dictates of my conscience and leave the rest to you:

I have just seen a PDF of the Superfreakonomics chapter on climate change, and it makes basic mistakes when it says things like “When Al Gore urges the citizenry to sacrifice… the agnostics grumble that human activity accounts for just 2 percent of global carbon-dioxide emissions, with the remainder generated by natural processes like plant decay.” This sentence makes a conspiracy theory out of nothing! Take a look at this figure from the Energy Information Administration: it shows that, yes, human generation of CO2 is dwarfed by natural processes like plant decay. But it also shows that natural processes balance each other out: plant decay generates massive amounts of CO2, and plant growth takes in massive amounts of CO2 via photosynthesis. What you’re left with is a completely plausible story in which human activity slowly increases atmospheric concentrations of CO2 from pre-industrial concentrations of about 285ppm (parts per million) to current concentrations of about 385ppm that are going up by about 2ppm per year.

This sort of misleading skepticism exists throughout the chapter, and it does a disservice to climate science, to economists like me who work on climate change, to academic work in general, and to the general public that will have to live with the impacts of climate policy down the road. Since you don’t do climate economics I’m guessing that the chapter was written by Dubner without much if any input from you, but the book still has your name on it and I hope you will consider reading more of my comments—or just talking to any random climate scientist at Chicago or elsewhere—and think seriously about making a statement to correct the inaccuracies in the book. It would not be hard for you to move the public discussion in a thoughtful direction instead of in the conspiratorial direction suggested by the book.

PS. The book has a quote from climate scientist Ken Caldeira (“carbon dioxide is not the right villain in this fight”) that is directly contradicted by a quote on Caldeira’s own website, and now Caldeira is saying this about your book: “If you talk all day, and somebody picks a half dozen quotes without providing context because they want to make a provocative and controversial chapter, there is not much you can do.” I know it would be easy for you to ignore all this, but I hope you decide to confront it.

yoram bauman

From: Steven Levitt
To: Yoram Bauman


By the way I really like your book and jotted a short blurb, I just need to remember to send it. Nicely done. Remind me if I forget.

I don’t understand your comment below. Why does it matter if natural processes are in balance or not? CO2 is Co2! The source doesn’t matter. If we could cut CO2 emissions a little bit overall, whether through natural sources or others, the effect would be the same. It is not saying that cutting human emissions isn’t the right way to do it, but it is a surprising fact and one worth mentioning.

On the Caldiera references, he worked closely with us and read the chapter twice giving detailed comments before it went to print, so I don’t even know what to say about that. Please visit our blog later today or tomorrow to get the full story behind the Caldiera quote to Romm. [Update: Their post is here.]

As far as I know, every fact or claim we make in that chapter is backed up by citations in the end notes, or is specifically attributed to a particular leading scientist based on our interviews with them. If you can find a counter-example, or more than one, I’d be eager to see them. It wasn’t like we just went out and made stuff up. Maybe there is disaggrement among climate scientists about the facts, but so far little of the push back we have been getting is on facts (including, as far as I can tell, your CO2 comment).

Also, I haven’t looked at the chapter for a while, but our main point isn’t that the earth isn’t getting warmer, and honestly, for our arguments we don’t even care why. All we are saying in the end is this: if the earth is getting warmer, is the better solution one that

a) costs 1.5 trillion dollars, doesn’t work for 50 years, somehow requires all humans to change their behavior sharply, and may not work anyway, or

b) one that costs $200 million, could be built tomorrow, would start working right away, and can be stopped and
reversed within a year if we don’t like the results.

I think I would start by choosing “b,” and only use “a” if I had to.

From: Yoram Bauman
To: Steven Levitt

Hi Steve, and thanks for taking the time to respond (and for your kind words about my book 🙂

1) I will wait for your post about Caldeira, my apologies for jumping the gun.

2) My perspective is that you are probably correct that there are few factual errors in the book (I’ll wait for the footnotes and let you know if I find any errors 🙂 but that you are ignoring the overall thrust of the chapter, which is terribly misleading.

It’s not factually incorrect to write that “agnostics… grumble that human activity accounts for just 2 percent of global carbon-dioxide emissions”, or to give big play to media stories from the 1970s about “global cooling”, or to write that Lowell Wood says that global sea level will rise 1.5 feet by 2100, or to write that Weitzman says (more or less) that “the future holds a 5 percent chance of a terrible-case scenario—a rise of more than 10 degrees Celcius”, or to divide the world into “true believers [who] bemoan the desecration of our earthly Eden” and “heretics [who] point out that this Eden… once became so naturally thick with methane smog that it was rendered nearly lifeless”…

…but all of these statements collectively give a terribly misleading perspective:

* Yes there are agnostics who “grumble that human activity accounts for just 2 percent of global carbon-dioxide emissions”, but this is not a reason to doubt the theory of anthropogenic climate change. The book makes it sound like YOU are among the agnostics, and this is bad.

* Yes there were media stories in the 1970s about global cooling, but your chapter implicitly compares those media stories with the current scientific consensus on climate change: “These days, of course, the threat is the opposite. The earth is no longer thought to be too cool but rather too warm.” In my opinion this is snarky and the only purpose is to cast doubt on the current scientific consensus. This is bad.

* Yes it is possible that Lowell Wood says that global sea level will rise 1.5 feet by 2100 (I wasn’t there, I don’t know what he said!), but this is not what the IPCC says. By writing about it you are making it sound like it IS the scientific consensus, and this is bad. PS. Admittedly, the IPCC estimate on sea level rise issue is something that almost nobody reports correctly. The 2007 IPCC estimates present a range “excluding future rapid dynamical changes in ice flow” (IPCC WG1 Summary, Table SPM3, p. 13), which is very different from saying that these dynamical changes will be zero. Elaboration comes from IPCC FAQ 10.2: “Recent satellite and in situ observations of ice streams behind disintegrating ice shelves highlight some rapid reactions of ice sheet systems. This raises new concern about the overall stability of the West Antarctic Ice Sheet, the collapse of which would trigger another five to six metres of sea level rise. While these streams appear buttressed by the shelves in front of them, it is currently unknown whether a reduction or failure of this buttressing of relatively limited areas of the ice sheet could actually trigger a widespread discharge of many ice streams and hence a destabilisation of the entire West Antarctic Ice Sheet. Ice sheet models are only beginning to capture such small-scale dynamical processes that involve complicated interactions with the glacier bed and the ocean at the perimeter of the ice sheet. Therefore, no quantitative information is available from the current generation of ice sheet models as to the likelihood or timing of such an event.”

* Yes Weitzman says (more or less) that “the future holds a 5 percent chance of a terrible-case scenario—a rise of more than 10 degrees Celcius”, but you’re making it sound like Weitzman is arguing that there’s a 95 percent change of an outcome that is not a “worldwide catastrophe”. My belief is that this is a misleading read of Weitzman, and if you don’t believe me you should ask Weitzman if he’s happy with how you’ve described his research. (Actually, heck, you’re probably busy elsewhere, so I’ll ask Weitzman and let you know what he says.) [Update: We had a nice email conversation with Weitzman, I asked him if he thought the book was a misleading representation of his views… and he basically said No. He didn’t exactly come out and say it was fine, but… plus one for Levitt, and minus one for me.]

* Yes the earth’s climate has changed a lot even before humans, and I’ll assume your story about the methane fog is correct; but you’re clearing giving the impression that the “true believers” are wrong and that the “heretics” are right. This is not factually incorrect but it is terribly misleading and makes it seem like you are casting doubt on the current scientific consensus.

So that’s my two cents: Your chapter pains me not because it’s factually incorrect but because it clearly gives a misleading impression of the scientific consensus on climate change. I am reminded of your quorum on global warming that your blog colleagues were kind enough to invite me to participate in. There’s nothing factually wrong in there, but it is terribly misleading that the two scientists you quote are BOTH skeptics. What are the odds of that? Probably a billion to one, so my unavoidable conclusion is that you are deliberately trying to cast doubt on the scientific consensus. I don’t mind if you do this in a straightforward way by getting involved in climate research, but to do it via insinuations is in my opinion a disservice to to climate science, to economists like me who work on climate change, to academic work in general, and to the general public that will have to live with the impacts of climate policy down the road.

PS. I do not know enough to get involved in the debate on geo-engineering; my beef with your writing is elsewhere.


From: Steven Levitt
To: Yoram Bauman


It is funny that both you and Krugman interpreted our weitzman cite as evidence we were skeptics! We took it the other way — if there is a 5% chance of catastrophe, yikes!! — we better do something. Weitzman must be an outlier in thinking that the chance of catastrophe is that high. (for the record, I am getting roughly an equal number of criticisms like yours from people who are on the other side saying we are too accepting of the current global warming thinking!)

So our point on Weitzman was that this _is_ a big deal.

I do think also that there is something to be said for raising some skepticism about the current climate models and predictions…they are stated and restated as if they are fact, when in practice I suspect, and good scientists agree, that there is enormous uncertainty and things we cannot or at least could not know.

Probably, though, our message on geoengineering would have come through better if we had written the chapter

thanks for your time and insights they are very useful.


From: Yoram Bauman
To: Steven Levitt

Right-o. Good luck in dealing with the firestorm, and I think the more times you can emphasize that you are not casting doubt on the scientific consensus on climate change the better it will be for all of us 🙂

PS. Yes there’s a lot of uncertainty (e.g., about sea level rise), but the scientific consensus does include a high degree of certainty about some basic points that are still disputed in the media and by politicians, i.e., that “Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations” (IPCC 2007).