Keep the cap fixed while allowing cheaper reductions.
A quota directly limits the permitted activity. Tradeable permits attach rights to a capped quantity, such as tonnes of emissions. Trading lets firms with lower reduction costs cut more and sell permits to firms with higher reduction costs. This can meet a given cap at lower cost, provided monitoring and trading work. It does not show that the chosen cap is socially optimal.
- Quota and cap
- A quota limits a specified activity over a period. An emissions cap is the total amount of a pollutant that covered firms may release.
- Permits and trading
- A permit gives the right to emit a stated amount. A firm that cuts its own emissions can sell spare permits to one that finds cuts more expensive. Both must still hold enough permits to cover their emissions.
- Limit
- Trading can meet the same cap with fewer resources spent on reduction. This does not prove the cap is the best one: that choice still needs a comparison of social benefits and costs.
Choose a workable cap
Quantity control
A quantity limit can give direct control over a measured activity with enforcement. It can be too tight or too loose if the social optimum is uncertain.
Monitoring
Measure the regulated pollutant, prevent invalid permits and check that actual emissions are covered. An announced cap is not proof of compliance.
Allocation
An auction sells permits to bidders; free allocation gives initial permits without charging for them. Either way, using a permit has an opportunity cost: the firm gives up what it could receive by selling it. This preserves an incentive to reduce emissions even for a permit received free.
Local harm
The same tonne can cause different local damage at different places. Unrestricted trading may need additional local rules rather than treating all emissions as equally harmful.
| Allocation of reductions | A cost at 2/tonne | B cost at 8/tonne | Total resource cost |
|---|---|---|---|
| A 2; B 2 | 4 | 16 | 20 |
| A 4; B 0 | 8 | 0 | 8 |
Worked example: Two firms facing the same total cap
Two firms together must cut four tonnes of emissions. Firm A can cut up to four tonnes at $2 each; firm B can do so at $8 each. Compare a two-tonne reduction by each with trading. Other effects and transaction costs are absent.
- A uniform two-tonne cut each costs A $4 and B $16: total resource cost $20.
- If A cuts all four tonnes and B cuts none, the same total reduction costs $8. The saving is $12.
- Starting from the equal allocation, A makes two extra cuts costing $4 and frees two permits. At a $5 permit price, it sells them to B for $10 and gains $6. B pays $10 instead of spending $16 on its own two cuts, also gaining $6.
- The $10 permit payment moves money from B to A; it is a transfer, not an extra resource saving. Their combined $12 gain matches the fall in reduction costs from $20 to $8.
- Trading changes who reduces emissions, not the total cap. Monitoring, valid permits and enforcement are needed; local damage differences may also matter.
Watch out for this
Permit trading lets firms ignore the emissions cap.
Firms may change how they comply, but each must hold enough valid permits for its regulated emissions.
Check your understanding
The cap is unchanged and permits move from a low-reduction-cost firm to a high-reduction-cost firm. What is the intended effect?
- The low-cost firm reduces more, potentially lowering total compliance cost.
- Total permitted emissions automatically increase.
- The cap becomes socially optimal merely because trading occurs.