Correcting externalities
Economists have developed several tools to bring private incentives in line with social costs and benefits.
Pigouvian taxes
Economist Arthur Pigou proposed taxing activities with negative externalities by an amount equal to the external cost. This makes producers and buyers face the full social cost, so they choose the efficient quantity themselves. Carbon taxes, fuel duties, and taxes on plastic bags are examples.
Pigouvian subsidies
Activities with positive externalities can be subsidised by the amount of the external benefit. Subsidies for vaccination, education, research and development, and home insulation encourage more of these activities toward the efficient level.
Command-and-control regulation
Governments can directly limit externalities: emissions standards for cars, bans on certain chemicals, required safety equipment. Regulation is simple and certain but can be costly, because it does not let firms with cheaper ways to cut pollution do more of the cutting.
Cap-and-trade
A cap-and-trade system sets a total limit on emissions and issues tradable permits adding up to the cap. Firms that can cut emissions cheaply do so and sell spare permits; those with high costs buy them. The cap is met at lowest total cost. The EU Emissions Trading System and the US sulphur dioxide programme are examples.
Taxes versus permits
A tax fixes the price of pollution and lets the quantity adjust; a cap fixes the quantity and lets the price adjust. If the exact damage threshold matters, such as avoiding a tipping point, a cap gives certainty about quantity. If costs of cutting emissions are uncertain, a tax gives certainty about cost.
The Coase theorem
Ronald Coase argued that if property rights are clear and bargaining is cheap, the parties can negotiate an efficient outcome without government intervention, whoever holds the rights. If a factory has the right to pollute, residents can pay it to cut back; if residents have the right to clean air, the factory must pay them to pollute.
Limits of Coase
Coasean bargaining works poorly when there are many affected parties, high transaction costs, unclear rights, or free-riding: millions of people affected by air pollution cannot easily negotiate with thousands of firms. That is why government tools are usually needed for large-scale externalities.
Worked example
Two firms each emit 100 tonnes. Firm A can cut emissions for 20 dollars a tonne; Firm B for 60. The goal is to cut 100 tonnes total. Requiring each to cut 50 costs 50 x 20 + 50 x 60 = 4,000 dollars. With tradable permits, Firm A cuts all 100 for 2,000 dollars and sells permits to B, achieving the same reduction at half the cost.
Key takeaways
Pigouvian taxes make polluters face external costs; subsidies reward external benefits. Regulation is direct but can be costly. Cap-and-trade achieves a set reduction at lowest cost by letting firms trade permits. Taxes fix price; caps fix quantity. The Coase theorem shows bargaining can solve externalities when rights are clear and transaction costs are low, which is rare at large scale.
Flashcard
Tax equal to external cost
Check your understanding
Why can cap-and-trade achieve the same pollution cut more cheaply than requiring equal cuts from every firm?