The ETS was adopted in 2003 and came into force in 2005. It covers all EU states plus Iceland, Liechtenstein and Norway. It mainly covers carbon dioxide (CO2) but also other greenhouse gases such as methane and nitrous oxide from energy intensive industries such as electricity and heat generation, oil refineries and production of various metals and chemicals, as well as aviation. From 2024, the ETS will apply to maritime shipping. T&E explains how this will work and what it will mean.