Cap and trade

For instance, in New York State:

Under a cap and trade program, the state would set an industry-wide "cap" on carbon dioxide emissions, lower than the current amount, and then give each power plant a target and a deadline. Companies that reduce emissions further than required could then "trade" emission credits with companies who cannot meet their goals. The concept, used with some success in the national Clean Air Act to reduce smog and acid rain emissions, is designed to reduce costs for the regulated businesses. (source: New York Sun)

See: greenhouse gas, global warming