NGOs, as well as several governments, have consistently been sceptical towards the inclusion of sinks as CDM projects. The main reasons were fear of oversupply, that such projects cannot guarantee permanent storage of carbon, and that the methods of accounting for carbon storage in biomass are complex and still under development. Consequently, two separate carbon currencies (temporary CERs and long-term CERs) were created for such projects. Such credits cannot be imported to the European Union's Emission Trading Scheme. The lack of demand for such projects have resulted in very limited supply: Currently (21 July 2008), only one sinks project has been registered under CDM.