Market Failure and the Environment — Externalities

Ordinary markets work well when the private cost a producer pays equals the full cost that production imposes on society. Environmental problems arise precisely because this equality often breaks down — a case economists call market failure.

Externality is the technical term for this gap: a cost (or benefit) of an economic activity that falls on a third party who is neither the buyer nor the seller in that transaction, and is therefore not reflected in the market price.

• A negative externality occurs when an activity imposes an uncompensated cost on others. The standard example: a factory that discharges untreated effluent into a river pays only its own private cost of production (raw materials, labour, capital) — but the pollution imposes a real cost on downstream villages (contaminated drinking water, harm to fishing, health costs) that the factory never pays for and that never enters its price. Because the factory's decision-making ignores this external cost, it has no market incentive to produce less pollution or invest in treatment — the market, left alone, produces more pollution than is socially desirable.
• A positive externality occurs the other way — an activity benefits third parties who pay nothing for it (for example, a farmer who plants trees provides shade and clean air that neighbours enjoy for free).

Tragedy of the commons: a related idea concerning common-pool resources — resources like open grazing land, common fisheries, or groundwater that are not owned by any single individual and can be used by anyone. Because no single user bears the full cost of their own overuse (each individual gains the full private benefit of using a bit more, while the cost of depletion is shared by everyone), every user has an incentive to use as much as possible before others do — leading to overexploitation and eventual depletion of a resource that would have been sustainable under limited, coordinated use. This is exactly why open-access forests, grazing lands and fisheries are especially vulnerable to environmental degradation compared to resources under clear ownership or regulation. …