Cap and Trade vs Marketable Permit
Cap and Trade and Marketable Permit are two Environmental Economics concepts in AP Economics that students often mix up. Cap and trade is a system that limits total pollution and lets firms buy and sell permits to emit within that cap. A marketable permit is a tradable allowance to emit a set quantity of pollution, issued under a cap, that a firm can buy or sell instead of abating. Here is how they compare side by side.
The government sets a cap and issues tradable permits; firms that cut emissions cheaply can sell permits to those that can't. It puts a market price on pollution and achieves a target at the lowest total cost, addressing a negative externality.
The regulator decides the total quantity of emissions, issues exactly that many permits, and either auctions them or hands them out; from then on the permits trade like any other asset. A firm compares the market price with its own marginal abatement cost: below the price it cuts and sells the spare permit, above the price it buys. Trading therefore drives every firm's marginal abatement cost to the same level, which is the cheapest route to the cap. The contrast with an emissions tax is the standard exam point: permits fix the quantity of pollution and let the price adjust, while a tax fixes the price and lets the quantity adjust, so when abatement costs are uncertain you get certainty about the environmental outcome or certainty about the cost, never both.
Cap and Trade vs Marketable Permit: The System Versus the Unit It Trades
| Cap and Trade | Marketable Permit | |
|---|---|---|
| What the term names | The whole regulatory design | One tradable unit created inside that design |
| Level it operates at | The market as a whole, fixing the total | A single firm's holdings |
| Quantity involved | Fixed at the cap and unaffected by trading | Varies firm by firm as permits change hands |
| How it first reaches firms | A design choice between auctioning and granting free | Received or bought, then resold if abating is cheaper |
| Price attached to it | The system carries no price of its own | Trades at the marginal abatement cost the cap implies |
| Where else the term turns up | Almost always about pollution | Also fishing quotas and tradable development rights |
| If trading were banned | The design collapses into a fixed quota per firm | The permit becomes a non-transferable allowance |
The permit is the unit of account; the cap is what makes it worth anything
Cap and trade names the rules, and a marketable permit is the object those rules create, much as a stock exchange is not itself a share. Suppose two plants would each emit 15 tons, a regulator caps total emissions at 20 tons, and each plant receives 10 permits worth one ton apiece. Plant Low's cost of removing the next ton after a tons is 2a; Plant High's after h tons is 8h. Held to 10 permits with no trading allowed, each cuts 5 tons, costing Low 25 and High 100, or 125 between them. Let the permits trade and the two equalize marginal cost: 2a equals 8h with a plus h equal to 10 gives 8 tons from Low, 2 from High, and a market clearing price of 16. Low now emits 7 while holding 10 permits, so it sells 3; High emits 13 while holding 10, so it buys 3, at 16 each. Low pays 64 in abatement less 48 of permit income, or 16, against 25 before. High pays 16 in abatement plus 48 for permits, or 64, against 100 before. Both gain, by 9 and 36, and the same 10 tons come out for 80 rather than 125.
Who receives the permits changes who pays, never who abates
Rerun that cap with a lopsided handout: Plant Low gets 2 permits and Plant High gets 18. Neither cost curve moved, so the equilibrium does not move either. Low still removes 8 tons, High still removes 2, the price is still 16, and total abatement cost is still 80. Only the direction of the money changed. Low emits 7 while holding 2 permits, so it buys 5 for 80; High emits 13 while holding 18, so it sells 5 for 80. Low's net bill jumps to 144, and High collects more from selling permits than it spends abating, finishing 64 ahead. Auction all 20 permits instead and each plant buys what it emits, 7 and 13, paying 112 and 208 for public revenue of 320, while the real resource cost of abatement sits unchanged at 80. This independence of the environmental outcome from the initial handout holds when the permit market is competitive and firms' decisions do not turn on their wealth, and it is a close cousin of /glossary/coase-theorem. The practical reading matters for essays: giving permits away free is not a softer cap. It is the identical cap with the scarcity value handed to incumbents instead of the public.
Frequently asked questions
Is a marketable permit the same thing as cap and trade?
No, one is the unit and the other is the system. Cap and trade describes the whole arrangement: a regulator fixes total allowable emissions, issues allowances adding up to that total, and lets firms buy and sell them. A marketable permit is one of those allowances, sitting in a single firm's hands, that can be sold to a firm whose abatement costs are higher. Every cap and trade program uses marketable permits, though permits also appear in schemes with no economy wide cap.
Does it matter whether permits are auctioned or given away free?
Not for emissions or for total abatement cost, so long as the permit market is competitive. The permit price and each firm's abatement decision follow from the cap and the cost curves, not from who happened to receive the allowances. What the choice settles is who captures the scarcity value the cap creates: an auction routes it to the public purse, while free allocation hands it to the firms already emitting.
Are marketable permits used for anything besides pollution?
Yes, the same design appears wherever a regulator wants to cap use of a shared resource and let a market decide who uses it. Individual transferable quotas in fisheries give each vessel a share of an allowable catch that can be bought and sold. Tradable development rights let a landowner sell the right to build. In each case the permit manufactures excludability for a resource that had none, which is the fix /micro/market-failure describes for shared resources.
Live Externalities graph. Drag the curves, or open the full version.
Related comparisons
Get AP Econ exam tips in your inbox
Occasional emails with study tips, new interactive graphs, and exam-season reminders. Free, no spam.
No spam. Unsubscribe anytime. Read our privacy policy.
Keep track of what you have studied
A free EconLearn account adds progress tracking, your quiz history, and achievements. Studying here is free either way, and there is nothing to pay for as a student.
Create a free accountAlready have one? Sign in
Last updated