Summary of Externalities and Public Policy

## Introduction Externalities occur when an economic agent’s action affects the welfare of others without compensation. Policy and regulation are the practical tools governments and societies use to manage externalities when private negotiation fails or is infeasible. This material focuses on market-based policies, regulation tools, property-rights approaches, and political economy considerations relevant to externalities and pollution control. > **Definition:** An externality is an uncompensated impact of one person’s actions on the well-being of a bystander. ## Types of Externalities (Quick recap) - **Negative externalities:** activities that impose costs on others (e.g. car exhaust, cigarette smoke, factory pollution, loud stereos). - **Positive externalities:** activities that provide benefits to others (e.g. immunisations, restored historic buildings, research spillovers). > **Definition:** A negative externality is when the private cost of producing a good is lower than the social cost. A positive externality is when the private benefit is lower than the social benefit. ## When private solutions may work ### Coase Theorem and bargaining - **Coase Theorem:** If private parties can bargain without cost, they can reach efficient allocations regardless of initial property rights. - Practical limitations: transaction costs, many affected parties, asymmetric information, and enforcement problems. > **Definition:** The Coase Theorem states that if people can bargain without cost they can always reach an agreement in which resources are allocated efficiently. ### Other private solutions - **Social norms and moral behaviour:** voluntary restraint or community pressure. - **Charities and NGOs:** organisations (e.g. Greenpeace) can internalise some externalities via campaigns or direct action. - **Contracts and social agreements:** firms or neighbours may form agreements to limit nuisances. ## Government responses when private solutions fail Two broad government approaches: 1. **Command-and-control regulation** (direct regulation of behaviour) 2. **Market-based policies** (Pigovian taxes, tradable permits) ### Command-and-control regulation - Examples: limits on emissions per facility, mandatory technology standards, bans (e.g. forbidding certain pollutants). - Strengths: clear, direct, easier to enforce in some cases. - Weaknesses: often inefficient because they treat firms identically even if costs of abatement differ. ### Market-based policies - Aim: align private incentives with social efficiency at lower cost. - Two main instruments: **Pigovian taxes** and **tradable pollution permits**. > **Definition:** A Pigovian tax is a tax enacted to correct the effects of a negative externality by equating the private marginal cost to the social marginal cost. #### Pigovian taxes - Tax rate ideally equals the marginal external damage at the socially optimal output level. - Incentive effect: firms reduce pollution until their marginal abatement cost equals the tax. - Distribution effect: government collects revenue; can be used to reduce distortionary taxes or fund abatement. Mathematical intuition (simple): if private marginal cost is $MC_{p}(q)$ and marginal external damage is $MD(q)$, then a Pigovian tax $t$ should satisfy $$t = MD(q^*)$$ so that firms face private marginal cost $MC_{p}(q) + t$ equal to social marginal cost. #### Tradable pollution permits (cap-and-trade) - The government issues a fixed quantity of permits (a cap) and allows firms to trade them. - A market for permits establishes a price for the right to pollute. - Efficient outcome: firms with low abatement cost sell permits to firms with high abatement cost. > **Definition:** Tradable pollution permits are government-issued allowances that permit the holder to emit a specified amount of pollution and can be traded voluntarily. Equivalence note: Under certain conditions (fixed cap and competitive permit market), tradable permits can achieve the same al