Public bad

A public bad, in economics, is the symmetric of a public good. Air pollution is the most obvious example since it is non-excludable and non-rival, and negatively affects welfare.

Whereas public goods are typically under-provided by decentralized decision making (the market), public bad will generally be over-provided, since the parties generating the public bad do not account for the negative effects (or externality) imposed on others. One possibility to mitigate the existence of public bad is the intervention of a third party, typically the state.

In "green economics", it is a good that produces socially undesirable results (or an externality in standard economics). Most "green economists" advise measuring such impacts back to the present from the seventh generation. Thus in the golf course example, both the recreation and the negative impacts from deforestation, associated habitat and biodiversity loss, and pesticide toxicity would be estimated across those generations and some amortization applied to determine whether the golf course was a public benefit or a public bad from the point of view of that seventh generation.