The SuperFreakonomics Global-Warming Fact Quiz

By the time you finish this blog post, you will understand why we differ from our critics in our conclusions.

As we write in SuperFreakonomics, there are many misconceptions about the facts surrounding global warming. Take the following true/false quiz to test your knowledge of the science, economics, and technology of global warming.

Global-warming science questions:

1. The Earth has gotten substantially warmer over the past 100 years.


2. Even if we were to immediately and permanently stabilize our carbon emissions at the current levels, or even cut these emissions substantially, climate models predict that Earth will continue to get warmer for decades.


3. When Mt. Pinatubo erupted in 1991, it spewed millions of tons of sulfur dioxide into the stratosphere. Scientists believe that the haze generated by the eruption reflected some of the Sun’s light, causing the Earth’s temperature to temporarily drop as a consequence.


4. Because the half-life of sulfur dioxide in the stratosphere is relatively short (on the order of one year), the cooling effects of the Mt. Pinatubo eruption faded within a few years.


5. Dark surfaces absorb more sunlight than light surfaces. Thus, all else equal, light surfaces cause less global warming because more of the sunlight that strikes these surfaces is reflected back into space.


6. Clouds, which are white or gray, are lighter in color than the oceans, which are blue.


The correct answer to all six of these questions, we believe, is “TRUE.” You can see our chapter on global warming (pp. 165-209) and particularly the endnotes (pp. 247-256) for citations and elaboration. It is our impression that none of the six scientific statements above is at all controversial among climate scientists. I do not believe that any of our global-warming critics would quibble with any of these facts.

And just to be perfectly clear, despite all the bluster that has surrounded our chapter on global warming, these are the six scientific facts that are critical to our analysis of geo-engineering in that chapter, a point I will expand upon below. We document many other interesting facts in the chapter, but these are the only ones that are central to our argument.

It is simply not the case that criticisms of the geo-engineering solutions that we highlight in the chapter arise because we get the scientific facts wrong, unless the critics think that any of the six statements above are false.

So let’s move on to the economic issues surrounding global warming, and let’s see if that is where we differ from the critics in our assumptions.

Global warming economics questions:

1. If the Earth’s warming leads to global catastrophe, that would be a really bad outcome.


2. Even when there is enormous uncertainty about the likelihood of future cataclysms, it makes sense to invest now in finding ways to avoid such cataclysms.


3. Economists estimate that the costs of reducing carbon emissions are likely to be upwards of $1 trillion per year.


The correct answer to all three of these economic questions is “TRUE.” These are the three key economic facts that are critical to the arguments in our chapter. The first question doesn’t require any further explanation. The answer to the second question has been hammered home by Martin Weitzman‘s work in the area, which we cite in SuperFreakonomics, as well as a newer paper that Weitzman has written. The third fact is based on the analysis of Nicholas Stern. These cost estimates are obviously highly speculative, but the true cost of reducing carbon emissions is likely to be within two orders of magnitude of this number.

As far as I know, none of our critics would disagree with any of these three economic facts about global warming. Indeed, Paul Krugman‘s attack of our chapter largely focuses on the misconception that we do not agree with fact No. 2, when clearly we do. Somehow Krugman has come to the conclusion that we are in favor of inaction, missing the main point of the chapter, which is that we think immediate and aggressive action is warranted, in the form of investment in (or implementation of) geoengineering solutions. Perhaps Krugman does not consider those steps taking action.

So if there is no disagreement on either the six key scientific facts or the three key economic facts, where is the disagreement coming from?

Perhaps it is coming from a lack of agreement over technological facts.

Global warming technological questions:

1. There exists an engineering design that provides a means of delivering enough sulfur dioxide to the stratosphere on a continuous basis to effectively cool the Earth. The estimated cost of building and implementing this technology is a few hundred million dollars.


2. There exists an engineering design that provides a means of increasing oceanic cloud cover by seeding such clouds with salt-water that is sprayed into the air by a fleet of solar powered dinghies. The estimated cost of building and implementing this technology is a few hundred million dollars.


The answer to these questions is once again “TRUE.” As we describe in SuperFreakonomics, the Seattle-based company Intellectual Ventures has designs for both a “stratoshield” (No. 1) and the cloud-seeding project (No. 2).

I don’t see how the critics could argue with the answers to those two questions. They might argue that the technology won’t work as Intellectual Ventures hopes it will, but there is no arguing with the fact that Intellectual Ventures has the blueprints to try to build these contraptions, and could have them up and working within a year or two.

With all of this as preamble, let’s get to the fundamental question we try to answer in the chapter:

If we need to cool the Earth in a hurry, what is the best way to do it?

Our answer to that question follows directly from the three sets of facts I presented above. Reducing carbon emissions is not a great way of cooling the Earth in a hurry for two key reasons: (1) even if we cut carbon emissions today, the Earth will continue warming for decades; and (2) reducing carbon emissions is expensive, with a price tag of at least $1 trillion per year. (There is a third problem with reducing carbon emissions, which is that it requires worldwide behavioral change, which will be hard to achieve. But even beyond that, carbon mitigation is not a great solution to the question posed above. There might be other significant benefits tor reducing carbon emissions — addressing ocean acidification, for instance.)

A much better approach, we conclude, is geoengineering. The scientific evidence suggests that either the stratoshield or increased oceanic clouds would have a large and immediate impact on cooling the Earth, unlike carbon-emission reductions. The cost of these solutions is trivial compared to the cost of lowering carbon emissions — literally thousands of times cheaper! Perhaps best of all, if something goes wrong and we decide we don’t like the results of the stratoshield or the oceanic clouds, we can stop the programs immediately and any effects will quickly disappear. These two geo-engineering solutions are completely reversible. Given the huge costs of global cataclysm and how cheap the solut
ions are, it would be crazy not to move forward with geoengineering research in order to have these solutions ready to go in case we decide we need to cool the Earth.

Why then, are our our conclusions so radically different from those of our critics? The answer:

We are answering a different question than our critics.

Our question, at noted above, is what is the cheapest, fastest way to quickly cool the Earth. Like every question we tackle in Freakonomics and SuperFreakonomics, we approach the question like economists, using data and logic to conclude that the answer to that question is geo-engineering. Not coincidentally, almost every economist who has asked the same question has come to the same conclusion, including Martin Weitzman and the economists at the Copenhagen Consensus.

But that is not the question that Al Gore and the climate scientists are trying to answer. The sorts of questions they tend to ask are “What is the ‘right’ amount of carbon to emit?” or “Is it moral for this generation to put carbon into the air when future generations will pay the price?” or “What are the responsibilities of humankind to the planet?”

Unlike the question that we are asking — How can we most efficiently cool the Earth fast? — the types of questions that environmentalists are trying to answer mix together both scientific issues and moral/ethical issues. If you have any doubts about this, watch Al Gore’s movie, in which he says explicitly that reducing carbon emissions is not a political issue, but a moral issue.

That is why someone like Ken Caldeira can agree with the facts presented in our chapter, say that the chapter is written in good faith, but still disagree with the conclusion that geoengineering is the answer. It is because the question Ken Caldeira is trying to answer is not the question we are trying to answer. The same is true of our critics. But instead of just making this simple point — that we are asking different questions — the critics have either intentionally or unintentionally confused the issues by making all sorts of extraneous arguments.

I do not mean to imply that the question we answer in the book is the most important question. It may be that the questions that environmentalists are trying to ask are more important and more interesting, but that certainly does not mean that we don’t want to know the answer to our question, a question that the environmentalists don’t bother to ask very often because they are focused on their more philosophical questions.

So for all the blogosphere shouting against our chapter, I have to be honest and say that I just don’t get it. I can’t understand why any environmentalist who really cares about the Earth’s future could say with a straight face that geoengineering doesn’t deserve a seat at the table as the global-warming debate heats up.


I like the geo-engineering solution. But I was reading that one of the biggest problems with global warming is not actually the warming itself, but global climate change. So some places will get cooler, some hotter, and so on. The problem with this is that economies aren't prepared for an abrupt change in climate. Some places just aren't prepared for rain, some aren't prepared for a lack of water, and so on.

Couldn't this cost even more?

And would we be able to control geo-engineering so that climate keeps more or less consistent?

What can you tell us about that?



The question isn't whether geoengineering deserves a seat at the table - everyone agrees it is worth researching. The question is whether it is worthwhile to expend resources to reduce carbon emissions immediately while this research is being conducted. Your critics seem to say, "Yes, it certainly is." As far as I gather from this blog post, you are saying, "No, it isn't." To accuse your critics of failing to "approach the questions like economists" is extremely disingenuous. There is a substantive economic question here about whether geoengineering type solutions and reducing carbon emissions are substitutes or complements. You have failed to engage with your critics who argue that they are complements.


Dr. Levitt,

Unfortunately for you guys, the environmentalists could care less about logic and reason. Their only interest appears to be in sensationalizing their issue. It reminds me a bit of organized religion.

"You will be damned if you don't do what we want you to do".

I have made my peace with attempting to get through to people on this subject.

I am a finance guy, so I'm pretty much evil anyway.

Good luck.


As an engineer, I have some doubts as to truthfulness of the Geoengineering Technological questions you pose above. I have no doubt they have some fancy renderings, ( which they do, nicely contained in their white paper on the subject) But, renderings and white papers do not constitute a final design, and that "few hundred million dollars" is at best a +-50% estimate.

So, does a concept exist? yes. Does a Design exist? No. It would probably take a few tens of millions of dollars to get to the final design, never mind the first prototype.


It would also be good if you added a Scientific Question 1.5: The vast majority of the Earth's warming over the past 100 years is due to human release of greenhouse gases to the atmosphere. (Answer: true)


Hey, I got one for the authors:

The argument apparently advanced by this chapter will be used by the fossil fuel lobby to hem and haw over potentially dire known consequences of their product:



Without having read the chapter I hesitate to ask this, but are you asking the right question? You say that it might not be the most important question, and I think you may be right.

As to why environmentalists wouldn't want geoengineering to have a seat at the table, I can think of two reasons:

1.) They've been advocating for decades that there are no shortcuts, that we have to behave more responsibly in order to save our planet. Geoengineering could suddenly prove this untrue -- we could continue indulging ourselves at the planet's expense, but we wouldn't have to worry about at least global warming.

2.) More importantly, there's a really good chance it's not the best solution -- either morally or economically -- to our environmental problems in the long-run. Geoengineering seems like it might be a good band-aid -- we can halt global warming for a couple decades while we wait for the carbon in the atmosphere to dissipate -- but seems unlikely to solve all of our problems in the long run. If we don't slow down the rate of pollution b/c we can just make the earth cooler with more oceanic cloud cover, it most likely means that we won't dramatically cut pollution and will face more problems with ocean acidification and such in the future. Not to mention that geoengineering will probably continue to get more expensive as we add carbon to the atmosphere while the cost of reducing carbon emissions will likely continue to get cheaper after we've done so and developed alternative technologies.

In short: yes, you're thinking like an economist when answer the the question. But maybe that's the problem. Maybe that's what people are objecting to.



the ideas in the book are fascinaing from an innovation point of view, but the goal is to bring earth back to normal not to keep altering it.


I'm not certain Dr. Krugman has disagree with any of the points you make here. The way I read his criticism, and I commented to this effect on his blog earlier today, is that he is concerned that your contrarian approach will take the wind out of the sails of cap and trade, providing the conservative media with ammunition to attack it. This greatly concerns me since I agree with you that honest and free discussion is of utmost importance. I don't see much difference between Dr. Krugman's opinion on this subject and those in the Bush administration who stifled debate on certain issues where they believed they had the correct answer. If one does indeed have the correct solution, it should withstand debate. Now I realize there are people on both side who debate dishonestly, but if we allow those people to control the debate by not having it, then we've all already lost no matter what our position.



Good work on the response.

I have to ask the question is this collusion between you and all the bloggers, with the theory that any press is good press so should be a boon to Superfreakonomics sales? That would be a great economics experiement but I guess you would have to control against something Superfreakonomics-ese that had less pre-press release (maybe Freakonomics because I do not think that had as much fanfare before being released). For instance now I am checking out blogs I have never checked out before, so perhaps this maybe a case of you scrath my back I scratch yours, however unintentional it maybe.

It also reminds of what Steven Landsburg lays out int he Armchair Economist about the simliarities between Religion and Evironmentalism. I just re-read it and this argument has the hallmark ideas incorporated in that chapter.

Anyways guys you have made a strong defense of Superfreakonomics, but I may have to wait until a friend buys it because that would be a lower carbon emitting activitiy then both of us buying a copy.



I think the most frustrating thing about this chapter was that your entire book discussed unintended consequences and somehow, you managed to write an entire chapter about geoengineering without mentioning the fact that nobody has any idea what the unintended consequences of that would be. That was the part of the chapter I found to be intellectually dishonest, not anything else.


Steven, what's you've gotten yourselves mixed up in is rhetorical trench warfare. It's the same phenomenon in the abortion debate, which is why you should be familiar with it.

You and I may be swayed effectively by reason, but that doesn't work on everybody the same way. Sometimes, if persuasion is the goal (persuading people to care about the atmosphere, or that abortion is right/wrong), then rationality is not seen as the best tool by many people. To use rational argument is to give ground to those who are more convincing with inflammatory or mesmerizing statements.

So think about it: what are you trying to accomplish with your "different questions"? You are trying to arrive at an evidence-based, rationally correct solution to a problem. But that is not what many others are hoping to accomplish. They are trying to MOVE MINDS. That's what's wrong with your chapter from many people's standpoint. They are employing a tool to move minds that can be more effective than a rational argument. And when a rational argument is presented such as yours, it nullifies some of the effectiveness of their tool. Their persuasiveness loses it's power when the sort of people who would be persuaded by it start hearing seemingly conflicting information.

In a crowded room that may or may not be about to go up in flames, they are frantically trying to yell "FIRE!" and you're deploying a smoke detector. And the way they see it is that if anyone stops to check your smoke detector when they could be racing for the exit, you are dangerous.



Steve, you did it again. You failed to state that man is unequivocally the cause of warming and that we must immediately cease all carbon emissions. You really must hate the planet.

So, how we gonna get these guys to stop emitting carbon?

Think we can do it with these?

Doubt it, but maybe a little. Physics seems to be getting in the way:

Very few of us so-called "deniers" really deny that climate change is occurring. Speaking for myself, I am unequivocally certain that climate change is occurring. I am just as certain, however, that some sort of cost-effective technology like geoengineering, will arise to counter warming and I am just as certain that SUV's of one sort or another are with us to stay. Not too crazy at the thought of a constant dousing of sulfur dioxide, though, nor at the thought of tampering with such large, complex systems as the weather.

I am old enough to remember when Mt. Pinatubo blew her top and I have fond memories of two years or so of absolutely wonderful weather. The Earth adjusts itself very nicely, technology or not.



You have failed to engage with your critics who argue that they are complements [not substitutes].

— Jason

Gotch'er back on this one Dr. Leavitt:

Complements: an increase in need (demand) for one increases the need (demand) for the other, ceteris paribus.

Substitutes: an increase in need (demand) for one DEcreases the need (demand) for the other, ceteris paribus.

If geo-engineering solutions are pursued for the warming problem, it decreases the need (demand) for carbon mitigation.


'The question is whether it is worthwhile to expend resources to reduce carbon emissions immediately while this research is being conducted. Your critics seem to say, “Yes, it certainly is.” As far as I gather from this blog post, you are saying, “No, it isn't.”'

@Jason. Where did he say that? Nowhere. Nowhere has it been said "Geo-engineering is the one thing we should focus on, or is the only solution." Stop trying to find something to be indignant about.

Geoff Deane

Feel free to direct readers to the Intellectual Ventures Laboratory blog site, where more information can be found on the Stratoshield and the Salter Sink:


Finally, a clear summary of the debate! There is still a significant doubt in my mind, however, whether these are good solutions. Is it really a good idea to disperse massive amounts of sulfur into the atmosphere? The unintended consequences -- the bread and butter of the field of Freakonomics -- could well be enormous. I don't know the answer to this question; my engineering expertise has little to do with chemistry and biochemistry. Still, I would like to see Levitt and Dubner bring their perspective to this aspect of the issue.


But, renderings and white papers do not constitute a final design, and that “few hundred million dollars” is at best a +-50% estimate.

— Aaron

Ergo: worst case scenario: $999 Million + 50% = approx. $1.5 Billion.

Ergo: worser than worst cast scenario (implementing sulphur dioxide AND seawater) = approx. $3 billion

Dr. Levitt's estimate of cost of carbon mitigation: $1 trillion

Factor in a NEGATIVE 2 order of magnitude margin of error: $10 Billion

$10 Billion > $3 Billion

Which makes geo-engineering at least 3 times less expensive than mitigation.


To use a somewhat tired analogy, it's the same reason no piece of religious scripture could be questioned in the middle ages: once part of it is questioned, the precedent is set that questioning it is okay, which is very dangerous for any dogma.

A lot of people in the global warming movement want to join the club without studying the controversies and complexities. They feel safe doing so because they have confidence in the principle that they will always be able to use the arguement from intimidation to avoid accounting for their ignorance, implying that you don't know what you're talking about if you disagree with anything they say.

You agree with them fundamentally, but have questioned a key part of the movement's orthodoxy: that the solution is entirely for there to be less interference, not a different or counter modification. A rational person, even if he disagrees, will see that you're fundamentally on the same page and won't be threatened by you.

But it isn't a logical structure for many people in this movement, it's a huge singular emotional zeal. They can't counter logically, or try to consolodate, the minor questions because there is no logical structure in their mind, just a huge certainty that people who disagree are "deniers" who will be labeled as such. You've threatened their territory, and boy are they barking.



Very well put, and I see that the detractors here stil don't grasp the concepts. I think your layout was an excellent attempt to cut through the clutter being thrown around. For anyone that really wants to see, it's in there. It won't be long and these sorts of (the lock-minded) people will be labeled crusaders.

Felix - there's no such thing as "normal" in a complex system.