The Carbon Intensity Indicator (CII) is an operational measure introduced by the International Maritime Organization (IMO) to assess how efficiently a ship transports goods or passengers relative to its carbon dioxide emissions. Specifically, CII measures the grams of CO2 emitted per unit of cargo-carrying capacity (typically deadweight tonnage) per nautical mile sailed. It came into effect on January 1, 2023, as part of the IMO’s short-term greenhouse gas reduction strategy and applies to all ships of 5,000 gross tonnage and above engaged in international voyages.
The A-to-E Rating Scale
Each year, a vessel’s attained CII is calculated from its actual fuel consumption and voyage data, then compared against reference lines that tighten annually to drive continuous improvement. The result is a rating on a five-level scale: A (major superior), B (minor superior), C (moderate), D (minor inferior), and E (inferior). Vessels rated D for three consecutive years, or rated E in any single year, must submit a corrective action plan as part of their Ship Energy Efficiency Management Plan (SEEMP Part III). These plans must outline concrete measures to achieve at least a C rating in subsequent years.
Commercial Impact and Software Solutions
Beyond regulatory compliance, CII ratings increasingly affect a vessel’s commercial viability. Charterers and cargo owners — particularly those with their own environmental commitments — prefer to charter vessels with A or B ratings, creating a market premium for carbon-efficient ships and a penalty for poor performers. Some financial institutions are also considering CII ratings in lending decisions under the Poseidon Principles. Ship management software helps operators track and optimize their CII by collecting fuel consumption data, monitoring voyage efficiency in real time, modeling the impact of operational changes such as speed reduction or weather routing, and generating the annual reporting required for IMO Data Collection System (DCS) submissions.