Carbon Intensity Indicator

The Carbon Intensity Indicator is one of the IMO's key measures for reducing greenhouse-gas emissions from existing ships. Introduced under MARPOL Annex VI, it addresses how a ship is actually operated, in contrast to design-based measures. In simple terms it relates the carbon dioxide a ship emits to the transport work it performs (the cargo carried over the distance sailed in a year) to give a figure for how much carbon is emitted to move a unit of cargo a unit of distance. The lower the carbon intensity, the more efficient the ship.

Each applicable ship calculates its attained carbon intensity every year from its fuel consumption and voyage data, and this is compared against a required value that becomes progressively more demanding over time. On this basis the ship is assigned an operational rating from A to E, where A is the best and E the worst. A ship rated D for three consecutive years, or E in a single year, must develop a corrective action plan showing how it will bring its rating back into an acceptable band, which creates ongoing pressure to improve.

Because the CII is operational, it can be influenced by how the ship is run, not only by its hardware. Measures such as slow steaming, optimising trim, keeping the hull and propeller clean, better voyage and weather routing, and reducing time spent waiting at anchor all improve a ship's carbon intensity. The mechanism has been debated within the industry, partly because the rating can be affected by trading patterns and time spent idle that are outside a ship operator's full control, and it continues to be reviewed and refined. Alongside the design-focused EEXI and EEDI, the CII is central to the IMO's strategy to cut shipping's carbon emissions, and it increasingly features in charter negotiations and financing decisions.