August 26, 2004  ·  Richard Posner

Good comments, and mostly supportive though some skeptical along the lines of climate models are complex, climate science is uncertain, the experts may be wrong. All true; but reading the skeptical literature, I am reminded of the debates in the 1960s over the effects of cigarette smoking on human health. The evidence for serious ill effects was already very strong, but there were skeptics, some financed by the tobacco industry, who said such things as: the evidence is statistical, the mechanism by which nicotine and tars cause changes in lung tissue, etc. is not well understood, and in short we can’t be certain that there are these effects–the implication being that we should do nothing. Similar points are made today, often by energy companies or persons in their pay, and similarly insinuating that, given uncertainty, we should do nothing.

That is a non sequitur. We rarely have the luxury of being able to act on certainties; you’d be a fool if, credibly informed that unless you had an operation to repair an aneurysm you had a 99 percent chance of dying within a week, you responded that you only act when you’re certain. In my last posting, I speculated that a 1 percent chance of criminal punishment might deter certain copyright violations, and I didn’t mean that only the irrational would be deterred.

What would be irrational would be to conclude, from the fact that a minority of scientists deride global warming fears, that we should ignore the problem. Indeed, if you look at their grounds for skepticism, you may become more alarmed about global warming rather than less so. Because what you will learn is that their skepticism is based mainly on the existence of profound uncertainties about climate, and those uncertainties cut both ways and by doing so imply added rather than diminished risk. For example, skeptics point out that in the earth’s prehistory there have been periods (one roughly 10,000 years ago) in which the concentration of carbon dioxide in the atmosphere spiked, even though cavemen didn’t drive SUVs. Yes, and if one of those non-human-induced spikes coincided with our human-induced spiking, we’ll be in real trouble.

I mentioned in passing, in the preceding posting, risk aversion. If you would rather pay $100 certain than run a 1 percent risk of a $9,999 loss, even though the expected cost of such a risk is only $99.99, then you’re risk averse (think of the $100 as an insurance premium). The greater the variance in possible outcomes, the more upset the risk averse are likely to be. The more uncertainty there is about climate, the greater the variance in possible consequences of increasing the atmospheric concentration of carbon dioxide (and of other greenhouse gases, such as methane, which is even more heat-retentive than carbon dioxide, and is being released into the atmosphere in increased quantity because of the melting of the Alaskan and Siberian permafrost–and you can see what a dangerous feedback effect is possible as more methane in the atmosphere raises surface temperatures which melts more permafrost releasing more methane…). So people who are risk averse, and that is most of us when we are facing potential disaster on the scale that global warming might inflict, will not be reassured by people who ground their global warming skepticism in nothing solider than a reminder that other things besides human activity affect climate; those other things seem as likely to exacerbate the effects of human activity as to offset them.

  • George

    Risk aversity is non-linear. It doesn’t scale between micro and macro issues, between the 10 people close to you that you will NEVER wish to see dead, and the 10,000+ in a far-off country that you feel unhappy about, but won’t change your breakfast choices to save.

    I insure my house. I attempt to reduce my premiums. This does not mean
    I calculate the relative risks of lift failure and planecrash for every lift journey or plane journey.

    Nor does it say what my level of concern is about greenhouse,

    How do you aggregate these kinds of non-linear, non-correlating things to achieve a consensus, or even a reliable measure of community concern?

  • Pakooka

    Judge Posner,

    If you have a strong belief that 1) global warming is a problem 2) mankind is responsible for a substantial protion of that warming, then be my guest and support Kyoto, etc.

    But you’re really not making the case. The smoking example is highly tendentious, science can control for other risk factors, and zero-in on the risk smoking actually entails.

    With smoking we can compare the average smoking person to the average non-smoking person. Maybe you can tell me where we can compare our world to an non-industrialized world. That, Posner, is impossible, and your bogus comparison to smoking falls flat on its face. The proper analogy would be if there was a single person on the planet and he had to try to figure out if smoking negatively effected his/her health.

    To properly account for global warming attributable to manking we would need to either 1) have confidence in our understanding of climate 2) have many different worlds to compare, as is the case with smoking studies (comparing mortality rates of average smoker to average non-smoker). Neither of these, of course, is a reality, Mr. Posner.

    Your argument is that because global warming could be really, really bad, and because mankind’s actions may be driving a substantial portion of that warning, that we must take action to prevent global warming. This argument rests on a number of shaky, ultimately unprovable conclusions:

    1) That global warming would negatively affect humanity, taken as a whole. Russia, for example, might be positively benefitted by global warming.

    2) That global warming is largely driven by human activity.

    3) That the benefits of global warming prevention outweigh the costs (factoring in expected value, risk, all that stuff).

    Your argument is this in a nutshell: Global warming could be really, really bad, and we could be causing it. We must do something. I’d agree as long as that “something” was justifiable from an ecomonic perpsective. Kyoto, in my mind, is not.

    Where’s the pragmatism, Judge?



  • Macneil Shonle

    Thank you for this post! :-) You’ve said it all quite well and I think I can see how I can explain this to my skeptical friend who otherwise seems intelligent.

  • Heidi

    I’m not sure, exactly, why it is that Judge Posner has to accept Kyoto. The step in this semi-logical train that goes from “we should do something” to “that something should be Kyoto” seems to be missing. Has Judge Posner come out in favor of Kyoto somewhere besides here?

    And of course the other steps in the logical train are not provable, in the mathematical sense. Science never proves things in the mathematical sense. Instead, science tries to see how likely things are, so that you can infer a conclusion. For instance, electromagnetic attraction has never been proven. Instead, it has been tested under an array of circumstances, and results consistent with our theory have repeatedly been found. This is not proof. This is inference. Maybe it will all change tomorrow — and there have been instances where the basic “law” that everyone accepted has been found to be incomplete or even wrong — but we can infer, with great likelihood, that certain things are true.

    The problem with the global warming debate is that the inferences are not as strong as those with respect to, say, gravity. But because the possible results are of more than academic interest, it behooves us to pay attention, even if we are skeptical about the chain of inference.

  • Karl

    This skeptic isn’t saying we shouldn’t do anything. I’m saying that the possibility that warming exists and that it’s human-caused is far below 99%, and while it stays that way it’s folly to shoot human progress and inovation in the foot (re: sign Kyoto). Drive less, carpool, buy a hybrid…I support that. I’d support a widescale shift in our power production to advanced nuclear power systems such as the Integral Fast Reactor (a ‘Renewable Energy Source’ in every sense of the word, that had it’s funding cut by President Clinton due to fear mongering).

    In the end, I’m suprised that no one sees the (albeit somewhat nebulous) corollary between this topic and copyright. The CTEA was pushed through by a fearful extremist minority, resulting in a loss of freedom and ability to inovate on the part of the whole population.


  • Matthew Saroff

    There is a 2×2 matrix of possibilities with regards to human generated global warming.

    Either it exists, or it doesn’t.

    Either we take action, or we don’t.

    The two “best” cases are “Doesn’t exist-Take no action” and “Exists-Take” action.

    The two “Worst” cases are “Exists-Take no action” and “Doesn’t Exist-Take Action”.

    Our concern is about the down side, so we can ignore the “best” cases for this argument, and compare the “worst” cases.

    If we take action against a non-existent threat, we waste a lot of money.

    If we forgo action against serious threat, we have a disaster.

    The “safe” thing to do, even without 100% certainty, is to act as if human generated global warming exists, because mass starvation and extinction, juxtaposed with rising oceans, is REALLY bad.

  • Karl

    If we take the “safe” route, we don’t just waste a lot of money…we risk damning the potential of industry and progress for mankind and set an awful precedent for future decision making. Oh, not to mention the whole risk of losing our faith in science and truth by turning our entire belief system into a better safe than sorry ethic.

    You’re essentially making this decision into a neuvo Pascal’s wager, and I don’t think we want governments to function that way.

    I can see it now…”Well, it’s ‘safer’ to believe in God, so weekly mandated Church service for everyone…well, unless they didn’t go to church much back in 1990…”


  • Rob

    You naysayers are all missing the point. If there is global warming, it’s not a question of it just getting bit hotter in the summers (maybe 120 in Dallas instead of 110) and the oceans rising a few feet. It’s a question of this planet turning itself into a Venusian hellhole with daytime highs above the melting point of lead. THAT’S the scenario we want to avoid at all costs. If we set up some sort of self-reinforcing feedback loop that incinerates the planet because we were too dumb to figure out how it worked before we pushed the big red button, boy won’t we have fried egg on our faces.

    Let’s see: damn the potential of industry and progress for mankind, or avoid maybe making the planet uninhabitable because we don’t know what we’re doing. Hmm, which would I choose?

  • A.J.

    Judge Posner,

    I always enjoy and respect your comments. I am not a trained economist or mathematician. Could you explain your comments using “six sigma”. I understand many companies use six sigma to reduce the probability of accidents or failures. For example, in the nuclear industry, calculations are performed on safety systems to determine the probability of core meltdown or release of radiation into the atmosphere in the next 500,000 or 1,000,000 millions. Why is that significant? Why do we concern ourselves with what could happen in 500,000 or 1,000,000 million years. I’d appreciate if you could help shed some light. Again, I really appreciate your comments, Judge Posner.


  • Matt

    I don’t doubt that we are increasing global warming with greenhouse gases, though I don’t think anyone really knows how much of our current warming is caused by us.

    I quite doubt that any efforts to fix this problem globally are going to do more good than harm. We don’t know whether the best answer to global warming is “save money to build dikes later” or “seed the blue ocean to grow more plankton” or “raise taxes on industry until CO2 emissions are in the ‘right’ range”.

    My guess is attempts to find a global political solution to this problem are going to be based on what makes the best headlines and appeases the most active interest groups, and not what provides the most benefit at the least cost. See Lomborg’s argument that Kyoto would have cost billions a year for almost no real reduction in global warming.

    A policy like Kyoto would do more than just waste money to no effect; secondary effects in the developing world will mean more poverty, more misery, and at the margin, more death. To say that the stakes are apocalypse on one hand and a little wasted money on the other is to ignore the importance of technology and economic growth for the truly poor people of the world.

  • Jeff Licquia

    Matthew, your decision matrix is incomplete, because it’s not clear that anything we do will have enough of an effect. Thus, there’s an “it works/doesn’t work” axis to consider.

    Many people are concerned about the “exists/take action/doesn’t work” scenario. Could we have done something different that enhances our ability to survive the inevitable global warming, instead of wasting time trying to prevent it? (I’m not saying this is the right way to think about the problem, just pointing out a flaw in your decision matrix.)

    Regarding Venusian disaster: where’s the science for that? Global flooding, extinction, changes in agricultural suitability–ok, I’ve seen that. Daytime highs over the melting point of lead, though? Isn’t this just another example of the pseudo-science people are throwing around just because it sounds good?

  • Macneil

    To those who think environmentalists are making up science: What do you think is the reason they would want to do it?

    I can understand how tabacoo companies would lie about the dangers of smoking, and I can understand how oil companies want to keep getting a free ride, but I see no incentive for people to make up climate change science. I’ve never seen an explaination behind this “conspiracy.” Frankly, I think those who claim climate change isn’t a problem just have no concern for future generations, and when given the choice of making wise decisions versus making more money in the short-term, they’ll always pick the short-term gains.

    That’s one good use of government, because, on ballance, the industry is basically set up to greatly reward short term thinking and discounts majorly the values from long-term planning.

  • realish

    Yes, Palooka, global warming wouldn’t be so bad because Russia will become more pleasant.

    The level of debate on this, even among this hyper-educated crowd, is amazing.

    We’re not talking about a slow, linear heat increase across the globe. We’re talking about an increase in highly variable, severe weather systems. Floods. Droughts. Typhoons. Heat waves. These things are already upon us, and they’re only going to get more common.

    And why this assumption that aggressive action on climate change will suppress innovation? What spurs more innovation than limits? (See: White Stripes) And why assume that all industrialization and innovation not only are, but must be, based on burning fossil fuels?

    What about innovations in energy efficiency, housing density, new fuels, alternative energy? If we had anything resembling a genuinely free market in this country, we would already be seeing action in these areas. As it is now, other countries are leaving us in the dust, and once our current system of propping up outmoded energy sources and behavior patterns collapses, we will rue that we didn’t move more aggressively into these markets.

  • Heidi

    I think the decision matrix mentioned is rather incomplete, and rather not a useful tool.

    It’s not just a question of existence. We also have to figure out what the effects are. And those are not agreed upon. They range from “gee, the artic circle is quite pleasant now that the permafrost has melted!” to “drat, the planet can no longer sustain life.” In between there is a near-continuum. Then, as pointed out, there’s a set of possible responses which range from “Mary had a little lamb, I’m not listening!” to the introduction of an Energy Gestapo.

    If we knew exactly what all these effects and responses were, and what the various (not necessarily quantifiable) costs were, we could figure out the optimum response. But we don’t, and we won’t, because despite all this argument, basically all we know with near-certainty is that the earth is a complex system with highly non-linear responses.

    Ah well. We’ll have to muddle about instead. That’s okay; we’re good at muddling. We have a lot of experience.

  • Palooka


    Thanks for your comments. I have not studied the topic of global warming extensively, so I reserve final judgment. But the arguments presented here (including, sadly, by the good judge) are just bogus. It amounts to nothing more than a global warming boogeyman–it could be really, really, really bad so let’s doing whatever we can despite our lack of knowledge and understanding. That’s scary and that’s a dangerous way for a government and a civilized people to act. We don’t know the effects of global warming, and we don’t know how much of global warming is attributable to mankind. Of course we can’t have a 100% level of certainty, but I don’t see anywhere even close to a 10% level of certainty among the scientific data.

    As I said, as long as we can be confident that our actions aren’t counter-productive, then some action is permissable. I just don’t see the urgency justified by any real data or knowledge, it’s all worst-case scenario boogeyman baloney. Yes, we could be invaded by aliens, so why don’t we prepare for that while we’re at it? Our world is one of scarcity, we must make our priorities with that in mind. We can always make thing safer and better, but the most basic premise of economics says we cannot do that–we must allocate our scarce resources to accomplish finite objectives. We can’t prepare for every far-fetched contingency, and, yes, scenarios like the “Venusian hellhole with daytime highs above the melting point of lead” mentioned by someone responding here really are ridiculous. My point is we can’t go lashing out at every paranoid fantasy (e.g. Venusian hellholes).

    BTW, to another reader, I never said that Judge Posner endorsed Kyoto, though I got that impression. I said to Judge that from my perspective Kyoto is unjustified.

    Best to all,


  • Eugene Keech

    The whole “chicken little” scare tactic of “the sky is falling” with global warming is a farce! Temperature increases of 2 to 4 degrees C by 2100 are consistently estimated by the scare merchants, and the Kyoto Protocol is repeatedly rammed down our throats as “needed NOW!” and frightening pictures of consequences if we don’t limit our CO2 emissions heavily.

    1. Kyoto restrictions on U.S. [or even heavier] would severely harm our economy to the point of costing MILLIONS of jobs, and give the benefits to red China to pick up and double or triple their production of CO2 [not limited by Kyoto]. So-no benefit, yet!

    2. The Kyoto treaty can only reduce temperature by 0.05 degrees to 0.07 degrees C by 2050 per estimates of top environmental scientists, including S. Fred Singer. That’s less than a quarter of a degree by 2100, so it won’t help at all.