Credit: Epanchincev Evgeniy/ITAR-TASS/Corbis

Advocates of carbon-trading schemes in the United States like to point to Europe's cap-and-trade program as a model worthy of emulation. The European Union's Emission Trading System, which has been in place since 2005, puts a price on carbon dioxide pollution for the purpose of inducing industry to cut emissions of greenhouse gases and reduce the effects of climate change. European governments set annual caps on total carbon dioxide emissions that may be produced by a group of energy-intensive industries. They then hand out a number of allowances to each company, allotting them on the basis of past emissions. Each allowance, called an EUA, permits the company to release a ton of carbon dioxide into the atmosphere. Companies whose emissions exceed their allowances for a given year must buy more; those with fewer emissions can sell their allowances.

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