Greenhouse gas emissions trading

System that imposes restrictions on the aggregate amount of greenhouse gas pollutants that a party (e.g. owner of coal-fired power plant) may emit from its facility. It is a mechanism through which emitters buy emissions reduction units from or sell emission reduction units to other emitters or third parties. The buyers and sellers under this system may be buying or selling for compliance purposes (i.e., because they are emitters who are "short" or "long" credits) or may be buying or selling for financial speculation.