What is the Carbon Intensity Indicator (CII)?
Learing more about the CII as part of the IMO Data Collection System.
In the maritime industry, the Carbon Intensity Indicator (CII) is a metric introduced by the International Maritime Organization (IMO) as part of its broader strategy to reduce greenhouse gas (GHG) emissions from shipping. It is part of the IMO’s Energy Efficiency Existing Ship Index (EEXI) and the Carbon Intensity of International Shipping (CII) measures introduced under the IMO’s 2020 strategy for reducing carbon emissions in the maritime sector.
The CII is designed to measure how much carbon dioxide (CO₂) emissions are produced per unit of transport work, usually in terms of grams of CO₂ per ton-mile (gCO₂/mt NM). It aims to quantify the efficiency of a vessel in terms of carbon emissions relative to the cargo it is carrying and the distance traveled.
How is the CII calculated in the maritime industry?
The CII is typically calculated based on the following formula:
CII = Annual CO2 Emissions (gCO2) / Annual transport Work (mt x NM)
Where:
- Annual CO₂ Emissions: The total carbon emissions produced by the vessel in a given year. This includes emissions from the main engines and auxiliary engines, which are responsible for the propulsion and the power generation on the ship.
- Annual Transport Work: This is the total amount of transport work done by the vessel over the year, calculated as:
Transport Work (mt x NM) = Cargo (mt) x distance (NM)
The value represents the number of ton miles a vessel has traveled, i.e., the amount of cargo it has carried multiplied by the distance it has sailed.
Key points of the maritime CII
- Efficiency Focus: A lower CII value indicates that the ship is more efficient in terms of carbon emissions per ton of cargo transported over a certain distance. It reflects both the ship’s fuel consumption and cargo carrying capacity.
- Compliance and Targets: The IMO has set specific targets for the CII to help reduce carbon emissions from the maritime industry. For example, existing ships (those already in operation) must meet annual reduction thresholds to achieve the long-term decarbonization goals. These targets become progressively more stringent in the years ahead.
- Voyage Data: To calculate the CII for each ship, operators need to track and report detailed voyage data, including fuel consumption and the distance traveled during the year, along with the cargo carried. This data is typically submitted via the IMO Data Collection System (DCS).
Implications and Future of CII in the Maritime Industry
- Decarbonization: The introduction of the CII metric is a major step toward reducing the maritime sector’s carbon footprint. The shipping industry contributes around 2-3% of global CO₂ emissions, so improving energy efficiency and reducing emissions is critical to global climate goals.
- Shipowners’ Response: Shipowners and operators are expected to modify their operations to improve the CII of their vessels, either by adopting cleaner fuels, improving operational efficiency (e.g., speed optimization, hull cleaning, and energy-saving devices), or retrofitting ships with more efficient technologies.
- Compliance and Ratings: Starting in 2023, vessels will be assigned an annual CII rating (A to E) based on their calculated carbon intensity. Ships that do not meet the required CII targets will be required to improve their performance in the following year.
The CII is part of a broader initiative by the IMO to reduce greenhouse gas emissions from shipping, with a target of reducing the total annual GHG emissions from international shipping by at least 50% by 2050, compared to 2008 levels.
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