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Tradable pollution permits

Weigh permits against a tax as a way of cutting pollution

Key terms
Tradable pollution permit
A tradable pollution permit allows a firm to emit a set quantity of pollution, and firms can buy and sell these permits among themselves.
Pollution charge
A pollution charge is a tax imposed on the quantity of pollution that a firm emits.

A permit scheme sets the total that may be emitted

The UK Emissions Trading Scheme works on the cap and trade principle: a cap is set on the total amount of certain greenhouse gases that the sectors it covers can emit. Within the cap, participants receive free allowances or buy them at auction or from each other. The cap is reduced over time, so total emissions must fall. It covers energy-intensive industry, power generation, aviation and maritime activity.

Cutting the cap in a permit marketVertical axis: Price of a permit. Horizontal axis: Permits. S1: a vertical line. S2: a vertical line. D: a downward-sloping line. D meets S1, at price P1 and Cap 1 on the horizontal axis. D meets S2, at price P2 and Cap 2 on the horizontal axis.Cap 1P1Cap 2P2S1S2D
The cap fixes how many permits exist, so their supply is a vertical line. Cutting the cap from S1 to S2 leaves firms competing for fewer permits, so the price of a permit rises from P1 to P2.