Cap-and-trade

Emissions trading or cap and trade is a government-mandated, market-based approach to controlling pollution by providing economic incentives for achieving reductions in the emissions of pollutants. In contrast to command-and-control environmental regulations such as best available technology (BAT) standards and government subsidies, cap and trade schemes are a type of flexible environmental regulation that allows organizations to decide how best to meet policy targets. Various countries, states and groups of companies have adopted such trading systems, notably for mitigating climate change.

A central authority (usually a governmental body) allocates or sells a limited number of permits to discharge specific quantities of a specific pollutant per time period. Polluters are required to hold permits in amount equal to their emissions. Polluters that want to increase their emissions must buy permits from others willing to sell them.Financial derivatives of permits can also be traded on secondary markets.

In theory, polluters who can reduce emissions most cheaply will do so, achieving the emission reduction at the lowest cost to society. Cap and trade is meant to provide the private sector with the flexibility required to reduce emissions while stimulating technological innovation and economic growth.

There are active trading programs in several air pollutants. For greenhouse gases, which cause climate change, permit units are often called carbon credits. The largest greenhouse gases trading program is the European Union Emission Trading Scheme, which trades primarily in European Union Allowances (EUAs); the Californian scheme trades in California Carbon Allowances, the New Zealand scheme in New Zealand Units and the Australian scheme in Australian Units. The United States has a national market to reduce acid rain and several regional markets in nitrogen oxides.

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