Global Warming--Posner's Response to Comments

I cannot do justice to the 102 comments that my post evoked, but I will try to respond to the recurrent themes in them. One comment suggests the use of the "minimax" (meaning, in this context, minimizing the maximum loss) decision rule to guide response to the risk of abrupt global warming, since no probability can be assigned to that risk. This raises the interesting and important question of how if at all to adapt cost-benefit analysis to risks that cannot be quantified. The problem with minimax is that it provides no definite guidance. I prefer, as argued in my book Catastrophe: Risk and Response (2004), to retain as much of the structure of cost-benefit analysis as possible in situations where the probability of a catastrophe cannot be quantified. In the case of abrupt global warming, this means trying to quantify the loss should such warming occur and the cost of averting the loss, and then see whether the probability implied by assuming that incurring the cost would be cost-justified is reasonable. So suppose a loss of $1 trillion could be averted at a cost of $100 billion. That cost would be worth incurring (ignoring a number of refinements and qualifications that would be necessary in a rigorous analysis) if the probability of the catastrophe were at least 10 percent. The question would then be whether 10 percent was in the probability ballpark--assuming we could estimate the ballpark, though not the location of the ball. I agree with the suggestion that prizes are a good way of motivating research; recently Al Gore teamed with the British billionaire Richard Branson to offer a $25 prize for the development of a workable method of removing carbon dioxide from the atmosphere. Most of the comments, as I expected, are in a state of denial about global warming. (Indeed, as I would have expected, one of them denies that cigarette smoking has been shown to have adverse health effects.) To many conservatives, global warming is a red flag. The global warming skeptics point out that there are natural climate fluctuations, that anticapitalists are enthusiastic beaters of the drum for action against global warming, and that global warming would have good effects on agriculture in northern climes. These points are correct, but do not support the skeptical position. The existence of natural climate fluctuations increases the risk from human-caused global warming, because increased atmospheric concentrations of carbon dioxide increase the amplitude of the fluctuations. The fact that the motives of some of the people who are worried about global warming are political is irrelevant to the scientific issues, not only because scientists use apolitical methods of testing their hypotheses, but also because there are politics on both sides of the global warming debate: if leftwingers exaggerate the danger of global warming, rightwingers belittle them excessively. As for improving agricultural yields in northern climes, the transitional costs of relocating agriculture from (at present) tropical to arctic climes would be immense. Nor would improvements in agricultural yields respond to the effects of inundation of low-lying land areas, the migration of tropical diseases to temperate climates, the effects of increasingly violent weather, and the possible deflection of the Gulf Stream, causing Europe's climate to become Siberian. It is also untrue that a 7 degree Fahrenheit increase in average global temperatures by the end of the century is a "worst case" prediction. That would imply a degree of certainty that we clearly do not have. And it is untrue that warming and cooling in millennia prior to the Industrial Revolution were unrelated to human activity. Substantial deforestation through burning, releasing large quantities of carbon dioxide into the atmosphere, began with the invention of agriculture some 8,000 years ago, and periods of reforestation (e.g., after the Black Death reduced the European population by a third) are correlated with global cooling. So at least the paleoclimatologist William Ruddiman argues, and I do not sense that the skeptics have read his work. Some of the skeptics believe that Becker and I are part of a leftwing conspiracy to foist a false belief in global warming on the world. Anyone familiar with our work would know that we are conservatives. What is true and important is that there is considerable uncertainty about predictions of climate change. The climatologists' consensus may prove incorrect. What is striking however is the thinning of the ranks of the dissenters over time. Many of the skeptical commenters appear to have visceral rather than a reasoned hostility to the idea that global warming is a problem that might require costly solutions. They and are not impartial readers of the scientific evidence. One commenter describes global warming as "another cult religion just like Marxism or Lysenkoism." But neither Marx nor Lysenko ever commanded a scientific consensus for their views. But I do agree with this otherwise rather intemperate commenter that Paul Ehrlich's The Population Bomb was total nonsense--and I have so said in my book Public Intellectuals. One comment questions how heavy gasoline taxes could reduce our reliance on imported oil, since the cost of production of Middle Eastern oil is lower than that of oil produced in the United States. Depending on how stiff the taxes were, however, our total consumption of oil would fall, including consumption of foreign oil, though the mix would indeed shift (as I said in my post) toward imported oil. Another effect would therefore be to conserve our own oil--it would remain in the ground, available for future pumping, and a check on the behavior of foreign producers, such as threats by Iran to embargo oil. Our dependence on foreign oil would diminish in still another sense: the incomes of the foreign oil producers would fall, reducing those countries' geopolitical influence, including influence over us. We would be less dependent on their political whims.

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