The European Union was the only group of nations that seriously considered implementing it. A European quota system, limited to electricity producers and materials manufacturers, the two major sources of emissions, has been in place since 2005.
而在众多国家集团中，欧盟是唯一一个认真执行了该方案的。自 2005 年起，一个约束发电企业和原料生产企业这两大温室气体排放源的欧洲配额系统已经开始投入运作了。