ECO101H1 Chap.6 Externalities and Efficiency
Externalities and Efficiency
Start With the Person Outside the Transaction
A private market records the benefits and costs that guide buyers and sellers. An externality arises when an activity also changes the welfare of someone outside that decision and the effect is not incorporated into the decision-maker’s incentives. The useful diagnostic is to identify that person and the relevant additional effect.
A pollution complaint, for example, concerns damage beyond the producer’s private resource costs. A beneficial spillover concerns gains beyond those counted by the purchaser.
The distinction is marginal. Ask what one more unit does, not merely whether the entire activity has a large benefit or a large cost.
Private equilibrium can be internally consistent while socially inefficient because the additional unpriced effect changes whether the next unit should occur.
A high total benefit does not justify indefinite expansion, and a harmful side effect does not alone establish that all production should stop.
Translate the Omitted Effect Into a Curve
Marginal social cost equals marginal private cost plus marginal external cost. Marginal social benefit equals marginal private benefit plus marginal external benefit.
These relations say which side of a market diagram needs adjustment. For an external production cost without a benefit spillover, social cost lies above private cost. For an external consumption benefit without a cost spillover, social benefit lies above private benefit.
Locate the affected curve before discussing whether the private market produces too much or too little.
The efficient quantity equates marginal social benefit and marginal social cost, where the usual conditions support that crossing as the maximum of net benefits. A corrective tax can make a decision-maker face an omitted marginal cost. A subsidy can recognize an omitted marginal benefit.
The size matters: a correction that pushes activity beyond the efficient quantity can create a new loss. Identify the relevant marginal effect at the efficient quantity instead of treating any intervention as automatically helpful.
Choose the Amount of Cleanup and Its Allocation
Pollution control contains two separate problems.
One is how much aggregate pollution should remain after comparing its marginal benefits and social costs. The other is which firms should undertake the required abatement. Firms may face very different costs of eliminating a ton of emissions.
Imposing identical emissions limits can therefore achieve a target at a higher total cleanup cost than a policy that allows firms to rearrange who reduces pollution.
Tradable permits hold an aggregate emissions entitlement while allowing transfers between firms. A firm that can clean up cheaply can reduce its emissions and sell permits.
A firm with expensive cleanup can buy those permits while still respecting the total cap. Trading is valuable because a reallocation can replace expensive abatement with cheaper abatement. The transfer payment divides the gain between firms; it is not an additional physical cost of cleaning the air.
Check Incentives and the Conditions for Agreement
An initially free permit still has value.
Emitting uses an entitlement that could otherwise be sold, so the permit’s market price is an opportunity cost. The initial distribution affects who receives valuable rights, but it does not make the use of those rights economically free. A numerical comparison should distinguish tons emitted, tons reduced, abatement expenditure and payments for permits.
Combining them without labels can count a transfer twice or confuse a cap with a reduction target.
Private bargaining offers another possible response when rights and low transaction costs allow the affected parties to reach agreement. This possibility is conditional. Identifying an efficient agreement does not prove that organizing all relevant participants is cheap or that monitoring is easy.
The concluding policy comparison should state the aggregate target, the allocation of cleanup and the transaction conditions that support the predicted savings.
What this chapter covers
- 01
External Costs
- 02
External Benefits
- 03
Social Marginal Curves
- 04
Corrective Taxes
- 05
Tradable Permits
- 06
Abatement Costs
- 07
Private Bargaining
Worked example · free
Equal Emissions Versus Tradable Permits
- 2The equal limit requires reductions of 175 and 75 tons. Resource costs are 175×8=1400 and 75×4=300, totaling 1700.
- 2Let the low-cost firm abate all 200 tons. The high-cost firm then needs to abate only 50 tons to keep combined emissions at 250.
- 2Trading gives cleanup cost 200×4+50×8=1200, so the saving is 1700−1200=500 for the same 250-ton reduction.
Key terms
- Externality
- An unpriced effect of an activity on someone outside the private market decision.
- Marginal External Cost
- The additional harm to others caused by one more unit of an activity, beyond the private cost counted by its decision-maker.
- Marginal Social Benefit
- The additional benefit to all affected people, combining private benefit and any external benefit.
- Abatement
- A reduction in pollution emissions relative to the initial or otherwise specified level.
- Tradable Permit
- A transferable entitlement to emit a specified amount, carrying an opportunity cost when used rather than sold.
- Transaction Costs
- The costs of organizing, negotiating or carrying out exchanges or agreements that can obstruct otherwise beneficial bargaining.
Externalities and Efficiency FAQ
Does efficiency require eliminating all pollution?
No. The efficiency comparison concerns the marginal benefits and marginal social costs of emissions. Zero pollution follows only when that comparison supports the boundary; it is not implied by the word pollution.
Why is an emissions cap different from an abatement target?
A cap states how much pollution may remain. Abatement is the reduction from initial emissions. With initial emissions of 500 and a cap of 250, the required reduction is 250.
Does a free permit eliminate the cost of emitting?
No. A usable permit could be sold, so exercising it sacrifices that sale opportunity. Its market value influences the emit-versus-abate decision even when the firm paid nothing to receive it.
Can a subsidy produce too much of a beneficial activity?
Yes. Benefits may be positive while further units cost more than their social benefits. An oversized subsidy can move quantity beyond the efficient comparison instead of merely correcting the omitted benefit.
Why might private bargaining fail to resolve a spillover?
Agreement can be costly to arrange, implement or enforce. The efficiency argument for bargaining assumes suitable conditions, including low transaction costs, rather than guaranteeing a successful agreement in every real setting.
Exam move
For each externality, write the affected outsider and the missing marginal effect before drawing curves. In pollution problems, maintain a quantity ledger for initial emissions, final emissions and reductions. Compare total resource costs only after verifying that competing policies achieve the same aggregate target.
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