Emissions - who is trading what?

Source: Parliamentary Library
"Since the United Nations Framework Convention on Climate Change and the Kyoto Protocol to that Convention, came into force in 2005, emissions trading has been the preferred approach for any international efforts to control, and eventually reduce, greenhouse gas emissions. Several emission trading schemes are already in operation in different regions and countries, and others at the planning stage. This background note provides the reader with a brief overview of emissions trading, the types of trading schemes and an examination of existing and proposed schemes."