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What Is the Optimal Level of Pollution?

On a theoretical plane, the question has not been properly answered. Its neglect may be partly explained by its seeming obviousness. And though the answer is indeed obvious once it is correctly stated, it is not the answer one gleans from a reading of the relevant literature. Other factors have probably contributed to its neglect. One is the altogether commendable concern now growing among economic specialists, particularly in the United States, about practical methods for stemming rising levels of air and water pollution. Another reason is that, in theoretical discussions much attention is given to what I have called (1965) "external diseconomies internal to the industry," or to the ''activity," the phenomenon associated chiefly with the names of Allen Young and Frank Knight (1924), whose contributions are summarized in the classic Ellis and Fellner paper (1943). The "external diseconomy" here springs from nothing less familiar than the eventually diminishing returns to a variable factor arising from the fixity of other factors. Whereas in the case of agriculture-the scarce factor, land, is assumed properly priced-that is, by reference to the difference between the average and marginal product of labor-the resulting competitive supply curve is also the correct marginal cost curve of grain, and the perfectly competitive output is therefore the optimal output. Where, instead, the scarce factor is some common property such as a road or a fishing area, it is not priced at all. The competitive supply curve of the good produced on, or with, this common property factor is only an average curve, one that excludes rent to the scarce factor. Consequently, the competitive equilibrium (of traffic or output) exceeds optimality. Restriction of one's attention to these external diseconomies that are internal to the industry, and therefore also to the theme of an unpriced scarce factor, suggests that the optimum external diseconomy to be borne by the industry (and by society) is that associated with the optimal output