August 27, 2004  ·  Richard Posner

The following description of a recent conference on the world’s worst ills, featuring several economists who had been awarded the Nobel Prize in economics, enables me to sink global-warming skeptics and academic public intellectuals with only one salvo.

“An international panel of economists brought together to rank the world’s worst ills ended a weeklong conference in Copenhagen Saturday by listing HIV/AIDS, hunger, trade barriers and malaria as the world’s most pressing problems while relegating global warming to the near-bottom of the list. The eight economists at the Copenhagen Consensus � among them Nobel laureates Robert Fogel, Douglass North and Vernon Smith � were invited by maverick environmentalist Bjorn Lomborg to spend a hypothetical $50 billion in ways that would produce the most results. The panel unanimously gave HIV/AIDS top priority and recommended spending $27 billion to fight it, saying that although the costs were ‘considerable, they are tiny in relation to what can be gained.’ The issue deemed second in importance, malnutrition, was allocated $12 billion. The panel ranked trade liberalization third but allocated no funds to expand it. Fourth-ranked malaria received $13 billion.”

Each of these illuminati was paid $30,000 to attend the conference.

The AIDS epidemic is serious, but it does not threaten to destroy civilization; it is also readily controllable, without medical intervention, by avoidance of promiscuous sex. Malnutrition and malaria are serious problems too, but one effect of eliminating them would be to cause a population surge, which would in turn increase global warming, because added population means added energy demands (met primarily by burning fossil fuels) and added food demands (met in part by deforestation). Unlike AIDS, malnutrition, and malaria, global warming, especially if abrupt, could terminate civilization.

As I mentioned in a previous posting, the global climate equilibrium is fragile. In a period (known as the “Younger Dryas”) of only about a decade some 11,000 or 12,000 years ago, the earth’s temperature rose by 14 degrees Fahrenheit. The climate was very cold (it was the end of the last ice age) when the surge started, so no harm to human beings was done (rather the contrary); but imagine a similar surge today. Suppose the ice sheets that cover Greenland and Antarctica melted, raising ocean levels to the point at which most coastal regions, including many of the world�s largest cities, would be inundated. Or if the dilution of salt in the North Atlantic as a result of the melting of the north polar ice cap, the ice of which is largely salt free, diverted the Gulf Stream away from the continent of Europe. The dense salty water of the North Atlantic blocks the Atlantic currents from carrying warm water from the South Atlantic due north to the Arctic, instead deflecting the warm water east to Europe. That warm-water current is the Gulf Stream. If reduced salinity in the North Atlantic allowed the Gulf Stream to return to its natural northward path, the climate of the entire European continent would become like that of Siberia, and Europe�s agriculture would be destroyed.

Worse is possible. I mentioned in a previous posting the possibility of a runaway methane greenhouse effect, and here I add that it might be augmented by the effect of higher atmospheric temperatures in increasing the amount of water vapor in the atmosphere, because water vapor is another greenhouse gas. It is even conceivable that because increased rainstorms mean more clouds, and some clouds prevent sunlight from reaching the earth without blocking the heat reflected from the earth�s surface, global warming could (paradoxically) precipitate a new ice age�or worse. Falling temperatures might cause more precipitation to take the form of snow rather than rain, leading to a further drop in surface temperatures and creating more ice, which reflects sunlight better than seawater and earth (both of which are darker than ice) do. Surface temperatures might fall so far as to engender a return to �snowball earth.” The snowball-earth hypothesis is that 600 million years ago, and maybe at earlier times as well, the earth, including the equatorial regions, was for a time entirely covered by a layer of ice several kilometers thick except where the tips of volcanoes peeped through.

The hypothesis is controversial. It is unclear whether the conditions required for the initiation of snowball earth were ever present, and whether current or foreseeable conditions could cause such initiation. What is suggestive about the example is the ominous tipping or feedback effect that it illustrates (the domain of chaos theory). A relatively small change, such as an increase in rainfall caused by global warming, or an increase in the fraction of precipitation that takes the form of snow rather than rain, could trigger a drastic temperature spiral. The runaway greenhouse effect involving methane illustrates the same process in reverse, and, as in the rainfall example, one spiral can trigger the opposite spiral; that is the essence of a chaotic system.

The probability of abrupt global warming that would precipitate the disasters that I have described is unknown, but presumably small; yet economists know that to figure the expected cost of some risk, you must consider the consequences if a risk materializes, and not just the low probability that it will materialize. This point was missed by the “Copenhagen Consensus.” Nor is there any indication that the participants had studied the relevant science or conducted any cost-benefit analyses in deciding how to allocate their hypothetical $50 billion. Nor, I believe, were any of the economists experts in the economics of climate change. Economics is a large field, and the fact that one has received a Nobel Prize for work in economic history (Fogel), experimental economics (Smith), or the history of institutions (North) is no warrant of competence to opine on the economics of climate change.

  • Craig

    Judge Posner:

    Your article in the New York Times is now up. You may want to link to it:


  • Karl

    Judge Posner,

    As a skeptic, I’d hardly consider myself ‘sunk’ after reading your piece here. Just because these three bright individuals got it wrong, doesn’t mean the entire anti-Kyoto crowd is up a creek. These three got it wrong, and I’m sad to see it, because I used to work for Professor Fogel, and he is amazingly gifted at creating, testing and analyzing hypotheses. I’d be interested to see some of their thought processes that lead to the conclusions they drew.

    I can surmise a guess…why is AIDS the worst crisis? Because, the one thing that must happen for the survival of man…the most basic and essential thing, is procreation. And the act of procreation is where AIDS strikes. To claim that one can avoid AIDS by avoiding ‘promiscuous’ sex is not a legitimate claim when significant portions of the populations of some African countries are HIV positive. Use a condom�sure, great advice, but if we all took it every time it’d be a fast track to extinction.


  • Dylan

    Anyone who followed the Copenhagen Consensus process throughout would know that each issue considered was the subject of a paper by a supposed expert in that particular field, and that expert did perform cost-benefit analyses. The final panel merely compared, critiqued, and chose among these papers.

    AIDS was chosen because the cost/benefit analysis was overwhelmingly in its favor. A few dollars save a lot of lives, which are worth a lot of money. I seem to recall no one took the global warming numbers seriously, partly because the predicted growth in green house gasses was tied to unserious estimates of third world economic growth (although I could be confusing it with remembered criticism of an earlier paper).

    In any case, if global warming is a problem, it will require vastly more than $50 billion to do anything about it. A couple of orders of magnitude more is not unthinkable.

  • Fred Blasdel

    If reduced salinity in the North Atlantic allowed the Gulf Stream to return to its natural northward path, the climate of the entire European continent would become like that of Siberia, and Europe�s agriculture would be destroyed.

    Emphasis Mine

    If the earth’s natural machinations cause will cause us to go extinct, there’s not much we can do about it. Our influence is but a drop in the bucket.

  • James Robertson

    The fact that temperatures have fallen and risen precipitously many times in the past – clearly without human intervention – doesn’t ring some alarm bells with you? It doesn’t tell you that we understand very little about global climate at this point in time? It doesn’t tell you that temperature variations – even extreme ones – are quite possible with or without people?

  • Dylan

    I was indeed misrembering. The problem was a highly unrealistic discount rate. I’ve briefly summarized the results and provided links (for Economist subscribers) to the Consensus summaries at my blog.

  • Palooka

    Judge Posner,

    Human activity causing global warming to rise, triggering a global, civilization-shattering event is a ridiculous what if scenario. If we’re going to spend hundreds of billions of dollars every year to possibly reduce the slim-to-none possibility of the events you speak of, then what else shall we spend equal somes preventing? Meteor strikes?
    Alien invasion? Does society have to spend enormous sums of money on every possible earth-shattering event? Because that’s a long list, Mr. Posner.

    For society to expend the resources which something like Kyoto demands, there should be better than highly improbable what if science fiction. The fact that climate changes occur abruptly without industrialization is troubling, but we have no idea how, exactly, Kyoto would effect this equation. Your response is that anything’s worth a try when the future of the world’s at stake.

    You agree there is a possibility of an alien invasion which destroys civiliation, right? Well, then what prevents society from expending vast sums of money preparing for this doomsday event?

    What possibility is great enough to justify attention? 1%? .0001%? .000001%?



  • Lindsay

    Dear Judge Posner,

    It may be instructive to recall Aaron Wildavsky’s argument, in his book ‘Searching for Safety’. Wildavsky argued that, in general, there are two responses to risk – ‘anticipation’ and ‘resilience’. The former involves seeking to identify harms in advance, and take preventative action to avoid them. Although I have not read any specific recommendations from you on this page, I gather that you would propose, in response to threats such as terrorism of various kinds, or global warming – perhaps even (as suggested by another commentator) alien invasion.

    The alternative, ‘resilent’ approach favoured by Wildavsky involves increasing ones’ capacity to respond to adverse circumstances as and when they arise. In the context of terrorism, this would presumably involve such measures as strengthening our emergency services to cope with a variety of scenarios and to be able to respond flexibly to surprise events, developing the capacity of our armed forces to retaliate against known terrorists. In the context of global warming, it would presumably involve the ability to evacuate and re-build cities, adapt our agriculture and fishing to a new climate, develop cooler (or warmer, or more waterproof) clothes. More realistically, there may be a time at which the evidence is sufficiently persuasive that we have to devote substantial resources to abrupt carbon reduction strategies–alternative fuels, reforestation, carbon sinks etc. I am not an expert on global warming, but for all I know, that time may be immanent.

    The case for a primarily ‘resilient’ rather than primarily ‘anticpatory’ response is along the following lines. As a previous comment pointed out, there is a long list of remote but high cost risks – we couldn’t possibly respond ex ante to all of them. Better to wait until they have materialised, then decide whether to invest our resources in fighting Al Quaeda or aliens (we now know that the former demands our attention and resources, at least for the time being, and we can fight that ‘war’ intelligently). Our powers of forecasting are such that the chances are that if we try to predict in advance which risks to counter, we are going to get it wrong a large amount of the time. Furthermore, as Wildavsky argues, richer IS safer, as seen by the response by developed versus developing countries to natural disasters etc. So there is an opportunity cost (even measured only in terms of safety, rather than in broader terms) of the reduction of human risk.

    Of course, I am open to the argument that the so-called global mega hazards we are talking about are such that ex post responses are impossible. Once the ‘snowball’ scenario has materialised it will be too late. But I feel that this particular case is yet to be made by you (Judge Posner) or by anyone else. I would be very interested to hear your response.

  • seobro

    Global warming will have a profound impact on human civilization. Consider the Chinese that are now increasing their consumption of coal to unequaled levels. The amount of carbon dioxide in the atmosphere will continue to increase.

    But I believe that the worst problem will be Hypercanes, a hybrid of a tornado and a hurricane. These mosters will completely destroy civilization. All we need is warm water.

  • Peter Rossi

    1 – You criticise the Copenhagen Consensus on the grounds that none of the economists were experts on climate change – in other words because they are commenting outside their field, their work carries less weight. Isn’t this exactly what you are doing?

    2 – In arguing that the conclusions of the Consenus were mistaken, you state: ‘Malnutrition and malaria are serious problems too, but one effect of eliminating them would be to cause a population surge, which would in turn increase global warming.’
    Surely you are not suggesting that it would better for malnutrition and malaria to go untreated? Perhaps I have misunderstood your point here or you need to clarify it.

  • Fuzzy

    All I can do is laugh. I can’t figure out whether this points out the inability of top economists to do simple math or the normal way economists spin numbers by assuming deficits are okay or if there was just a typo in the blog, but how can you spend $52 billion (27 + 13 + 12 = 52) when you were only given $50 billion to spend?

  • Gabriel

    “promiscuous” sex? How blatantly misinformed and prejudiced. People get infected by HIV mainly by having sex (once is all that is needed) and using drugs (once is all that is needed).

    Why is AIDS so important a human problem and why should so much money be allocated to minimizing the impact of this disease on humanity? When entire national populations are infected at rates of 10, 20, 30+%, the impact of this disease on the society is more than simple deaths. Even corporations are realizing that this disease needs to be stopped if these nations are going to build themselves out of their poverty. But i guess if we focus our resources on global warming instead, we won’t have to worry that these people have a nice environment in which to die.

  • Karl


    Posner has read Malthus. If we were to feed/medicate everyone, we wouldn’t be feeding anyone shortly.

  • Palooka

    Malthus, of course, has been proven wrong. Except with the notable sub-saharan Africa dilemma, where there is so little political and economic stability that the market can’t function to meet the increasing needs of humanity, as it has done across the globe.

    Interesting that you’d bring up Malthus, who environmentalists touted for years as the Mesiah. The coming population catastrophe. Yada, yada, yada, yada. Well, it never materialized. The nuts go back to the drawing board, and we’ve got another dime-a-dozen doomsday scenario–the looming global warming catastrophe.

  • Peter

    I am sure Posner has at least heard of and no doubt read Malthus, and also read the numerous scholars who have proven Malthus wrong. Forgive the following sarcasm – Karl, are you saying that as long as you have read Malthus it is alright to withhold treatment of a population so as to induce some sort of unnecessary Malthusian population correction? Who are you to make that judgement? Would you prevent members of this population purchasing life saving drugs and treatment?

  • Karl

    Re: the Malthus comment, it was flippant. I was trying to say that the Judge’s comment echoed Malthus, I wasn’t trying to lend any credence to either.


  • Hal

    I don’t understand this snowball earth theory. It sounds crazy to me. How could global warming possible lead to an increase in snow accumulation? If things started to cool off so that snowfall increased, then we wouldn’t have global warming any more, we’d have global cooling. But that would be inconsistent with atmospheric CO2 levels near geological highs.

    More plausibly, any increase in cloud cover will serve to moderate the warming trend, acting as a negative feedback effect to stabilize the climate and avoid the most extreme negative predictions. Present climate models have difficulty with this phenomenon and it is an active area of research. It is exactly this sort of uncertainty which makes people hesitant to believe the dire warnings of disaster which you are offering here.

  • koreyel

    In my book HIV should not be Number 1 either.

    However in regards to this:

    “The AIDS epidemic … is also readily controllable, without medical intervention, by avoidance of promiscuous sex.”

    What role has promiscuous sex played in the success of the human species?

    How would human behavior differ today if those having a predilection for promiscuous sex been exterminated by a virus millennia ago?

    Is it possible for those with a predilection for promiscuous sex to alter their behavior? Or mightn’t one be about as successful at halting this behavior as one would be in urging dolphins to stop screwing each other wantonly?

    Which is all to say: that remark was a bit too flip.

  • Darko Hristov

    “Malnutrition and malaria are serious problems too, but one effect of eliminating them would be to cause a population surge, which would in turn increase global warming”
    What a fascistic point, and for a judge.

    You are on very thin ice here. An African could then say that you should stop fighting terrorism, because terrorism is reducing world population and so preventing global warming.

    God Save America With Such Judges.

  • Anonymous

    There seems to be a ridicule of people giving up their freedoms for federal security against terrorist threats, and I agree.
    We should not be scared into giving up our God-given liberties to our national government for protection against terrorism.

    However, on the flip side, there seems to be little concern over the idea of scaring people into giving up their freedoms
    (and massive amounts of money) for federal security against environmental threats. We have witnessed with our own eyes thousands of people killed
    from terrorist attacks; what we have with environmental studies, however, are merely hypothesizing, estimates, and predictions
    (that have been going on for decades and have never come true to the extent predicted, by the way).

    I strongly support littering fines, energy conservation, and personal stewardship of the environment. Let us not, however,
    allow a political figure to cater to hysterical emotions and allow us to cede our freedoms to tyranny to embark on a massive
    and vexing Gaia campaign any more than we would allow a political figure to overestimate the threat of terrorism.

  • Jeff Licquia

    Never be surprised when an economist proposes that one spend one’s money on enterprises that have a chance at success.

    Combating disease and mitigating hunger are solved problems. We have eradicated some diseases completely from the earth (polio, smallpox), and many countries in the world have reduced the problem of hunger to extremely low levels by historic standards.

    By contrast, global warming mediation will be hideously expensive by any stretch, with resulting benefits that are slim to none. Kyoto, as controversial as that is, is thought to be woefully inadequate at stopping global warming. Moreover, plausible theories exist that attribute nearly all global warming to natural causes, such as increases in solar output. Thus, we are spending an enormous amount for little gain that we have some (however small) reason to believe may be illusory.

    Also, before one can dismiss the economists, one must prove that one can spend $50 billion on the global warming problem and get a better bang for the buck than for the other things. That’s doable (say, on alternative fuels research), but it’s certainly not enough to slam-dunk the economists for foolishly ignoring the problem.

  • Alex Pinto

    Judge Posner

    I agree with you when you place the global warming and the demografic explosion as the world’s worst ills. Even without considering the hypothesis stated in your post of a sudden change in global climate equilibrium. In the last 15th days I visited the republique of Maldives which is the first country that will disappear if the oceans level keep raising at the same rhythm. As I read there, the oceans level is raising 10/15 mm/year. Considering that the highest point in Maldives is 2 m, this beautiful and unique country will disappear in 150/200 years!

    Alex Pinto (a portuguese follower of your posts)