Environmental policy instruments: a pollution tax and a legal limit on the same diagram
The best level of pollution is not zero
Governments can cut pollution two ways. Regulation sets a legal limit on how much pollution is allowed, backed by law. A market instrument, such as a tax, puts a price on each unit of pollution and lets firms choose how much to cut. Pick a tool, set the tax or the limit and see where each one lands on the same diagram, and why the best outcome stops short of cutting every last unit.
Pollution taxTax: $0/unit
Marginal abatement cost must equal marginal benefit of abatement
UNTAXED EQUILIBRIUM
$0Optimal ($50)$100
Deadweight loss
$2,000
Net social benefit
$0
Taxes and tradeable permits let firms self-select: those who can reduce pollution cheaply do so, while high-cost firms pay the tax or buy permits. The result is cost-effective abatement—society reaches the target at minimum total cost. Subsidies for clean technology can work similarly, though they risk encouraging entry by less-efficient firms just to claim the subsidy. The innovation incentive is key: a firm paying a tax saves money by inventing cleaner processes, whereas a firm meeting a fixed standard has no economic reason to exceed it. Carbon leakage remains the Achilles heel—if permits only apply domestically, energy-intensive production moves offshore and global emissions barely budge.
Know This
Regulation sets a legal limit on pollution; a tax puts a price on it. Either way, the best amount of abatement is where the cost of cutting one more unit equals the benefit it brings. The optimal tax equals the marginal external cost at that efficient quantity, and the optimal limit allows that same amount of pollution, which is never zero pollution, because the last units of abatement cost more than the damage they prevent.