Once again Joel Schwartz nails it on air pollution issues, this time in the venerable Washington Post.
The EPA attributes well over 90 percent of the benefits of its clean air programs to improvements in human health. Thus, a key policy question is whether EPA’s health-benefit claims are credible. . . . The most serious claim about air pollution is that it prematurely kills tens of thousands of Americans each year. This claim is based on small statistical correlations between pollution levels and risk of death. But correlation doesn’t necessarily mean causation, as demonstrated recently by a number of embarrassing reversals of conventional medical wisdom. The air pollution–mortality claim deserves even greater skepticism. First, it is based on the same unreliable correlation methods that have led medical authorities astray in other areas. Second, even though pollution is weakly correlated with higher premature mortality on average, it seems to protect against death in about one-third of cities. How could pollution kill people in some cities and save them in others? More likely, both results are chance correlations rather than real effects. Third, in laboratory experiments, researchers have been unable to kill animals by exposing them to air pollution at levels many times greater than ever occur in the United States.