25 February 2005 Science Magazine
A review by Kenneth R. Foster

Catastrophe Risk and Response
by Richard A. Posner
Oxford University Press, New York, 2004. 332 pp. $28, 16.99. ISBN 0-19-517813-0.

In this fine book, U.S. federal judge and public intellectual Richard A. Posner worries about events of very low probability but very high impact, such as possible human extinction. These are catastrophes of a different order than the usual hurricanes and floods that are subject to a growing academic literature on risk management (1).

Case in point: a high-velocity collision of a 2-kilometer asteroid with Earth might kill a billion people, whereas a 10-kilometer asteroid might extinguish our species. Even a 75-meter rock could release energy equivalent to a 100-megaton nuclear weapon, enough to obliterate a city. Thousands of such near-Earth objects are thought to exist. Some estimates place the yearly death toll averaged over megayears at 1500--more than the current annual number of fatalities from airline crashes.

Other potential catastrophes that Posner discusses include global climate change that leads to a sudden change in the Gulf Stream, (devastating agriculture in Western Europe) and widespread death from bioterrorism. Some of the threats border on science fiction, for example, the "gray goo" of a nanotechnology gone wild and the "strangelet scenario" of a high-energy physics experiment gone awry. But the interest in this book lies not in its doomsday scenarios, but in Posner's finely reasoned discussion, which reflects more legal and economic sophistication than is commonly found in the highly polarized debates on these issues. The 47 pages of references to legal, economic, and scientific papers show that he has done his homework on the subject.

Natural event with an impact.There is little doubt that a collision with an asteroid 10 kilometers in diameter, such as the one that hit the Yucatan 65 million years ago, would lead to the death of much of the world's population.

For example, in a fine lawyerly analysis, Posner finds that experts who argue that human activity is causing global warming are more credible than naysayers who argue that it is not. He takes apart arguments of "doomsters" such as Paul Ehrlich, with their overly pessimistic predictions of environmental catastrophe, and technological optimists who minimize potential hazards of new technologies, such as John Maddox, former editor of Nature, and science journalist Gregg Easterbrook. He worries about legal justifications for "extreme measures," including curtailment of civil liberties and torture, in the fight against terrorism. He is less disturbed by the limited restrictions adopted by the United States since September 2001 than by the likely political consequences of another major terrorist attack. Posner might not be right, but his arguments have weight.

Relying on the dismal science for guidance, Posner monetarizes the anticipated costs of catastrophes and possible remediation strategies. Increased efforts to locate space rocks on collision course with Earth would be cost-effective, he finds.

Cost-benefit analysis is less supportive of caps on greenhouse gas emissions, as required by the Kyoto Protocol. The costs, particularly to the United States and other developed countries, would be huge in the short term while the benefits would accrue only in the very long run--unless, of course, a trigger point were reached that suddenly redirected the Gulf Stream. Expressed in terms of present value, Posner finds the costs to far outweigh the benefits. (By the same reasoning, the present value of a $1 million lottery award payable as a 20-year annuity is much less than $1 million). Posner favors, instead, a tax on carbon emissions to force the development of new technologies for clean fuels and economic methods to sequester carbon from the environment.

But cost-benefit analysis can only take one so far, given the extreme uncertainties surrounding the risks he considers. And for some risks, biological or nuclear terrorism for example, the likelihood of tragedy seems so high that cost-benefit analysis would not be needed to justify taking strenuous practical measures to counter them.

Posner will infuriate many scientists whom, he writes, have an "attitude gap created by the different goals, and resulting different mindsets, of science on the one hand and public policy on the other. The scientist qua scientist wants to increase scientific knowledge, not make the world safer--especially from science."

The strangelet scenario is a case in point. Shortly before a new high-energy accelerator was to begin operation at Brookhaven National Laboratory, a physicist raised concerns that a high-energy collision might trigger a runaway reaction that would quickly transform Earth into a 100-meter lump of inert matter. The lab director took the ethically dubious step of appointing an evaluation panel of physicists, all of whom had professional interests in seeing the experiments go forward. Posner dismisses as non sequiturs the various public statements by physicists intended to reassure the public of the improbability of the strangelet scenario. Seeing few economic benefits and a likely small but in fact unknown probability of disaster, he argues that high-energy research should be supported by universities rather than the government and that it should be brought under a strict regulatory umbrella.

This view, voiced by a judge with obviously high intelligence and sophistication, serves as a clear warning that scientists must pay attention to the social as well as to the technical dimensions of technological risk--and develop a better understanding of how nonscientists will interpret their pronouncements on the subject. Posner's perspective, very different from those held by most scientists, is a welcome addition to considerations of catastrophic risks.