The Carbon Intensity Indicator (CII) is a rating system for ships that the International Maritime Organization (IMO) developed. This will be a mandatory measure under MARPOL Annex VI, which came into force on the 1st January 2023.

The measure will impact all cargo, RoPax and cruise vessels above 5,000 gross tonnage (GT) and trading internationally.

The CII determines the annual reduction factor needed to continuously improve the ship's operational carbon intensity within a specific rating level. The actual annual operational CII achieved will need to be documented and verified against the required annual operational CII.

This will then enable the operational carbon intensity rating to be determined on a scale of A, B, C, D or E, indicating a major superior, minor superior, moderate, minor inferior, or inferior performance level. The performance level will need to be recorded in the ship's Ship Energy Efficiency Management Plan (SEEMP). A ship rated D or E for three consecutive years will need to submit a corrective action plan to show how the required index rating (C or above) will be obtained.

This short-term measure aims to achieve the carbon intensity reduction aims of the IMO's initial GHG emissions strategy.