TThe maritime sector may only account for about 3 % of total greenhouse gas (GHG) emissions, but regulations such as those of the International Maritime Organization and the EU Emissions Trading System (EU ETS) attempt to mitigate its impact. The goal of the system  emissions trading system (ETS) of the EU is reduce carbon emissions in the industry by requiring companies to have a permit for every tonne of CO2 they emit. The EU ETS works on the principle of "cap and trade. It sets a cap on the total amount of certain greenhouse gases that can be emitted by operators covered by the scheme. The cap is lowered over time, so overall emissions are falling. Within the limit, operators buy or receive emission quotas, which they can trade with each other as needed.