Companies have a shortage, if their CO2 emissions exceed the rights they have received in a particular calendar year. This does not imply that they have to buy emission rights in the same calendar year. During part of the year, companies have rights on their emission accounts, which relate to two ‘emission years’. Companies can also 'borrow' emission rights, but if they do this, they will have to buy extra rights in later years. They can also ‘save’ emission rights so that they will require fewer emission rights in later years. Back to article