This is a list of least carbon efficient power stations in selected countries. Lists were created by the WWF and lists the most polluting power stations in terms of the level of carbon dioxide produced per unit of electricity generated. In general lignite burning coal-fired power stations with subcritical boilers (in which bubbles form in contrast to the newer supercritical steam generator) emit the most. The Chinese national carbon trading scheme may follow the European Union Emission Trading Scheme in making such power stations uneconomic to run. However some companies such as NLC India Limited and Electricity Generation Company (Turkey) generate in countries without a carbon price. Lignite power stations built or retrofitted before 1995 often also emit local air pollution. In early 2021