The shipping industry, responsible for nearly 3% of global greenhouse gas (GHG) emissions, is under increasing scrutiny to adopt sustainable practices. The Carbon Intensity Indicator (CII), introduced by the International Maritime Organization (IMO), provides a standardized metric to measure and monitor a ship’s carbon emissions relative to its transport work. As IMO aims to reduce total GHG emissions from shipping by at least 50% by 2050 compared to 2008 levels, the CII has become a critical tool in the decarbonization journey.
The Concept of the Carbon Intensity Indicator (CII)
The Carbon Intensity Indicator measures the grams of CO₂ emitted per deadweight tonnage-nautical mile (gCO₂/dwt-nm), providing a straightforward metric for evaluating the environmental performance of a vessel. This value is then compared against predefined baselines to assign a rating from A (best) to E (worst). Ships rated D or E consecutively over three years are required to implement a corrective action plan under the supervision of their flag state.
The CII applies to ships 5,000 gross tonnage and above, accounting for approximately 85% of emissions from international shipping. It covers diverse vessel types, including bulk carriers, tankers, container ships, and cruise liners, making it a universal benchmark.
Methodology and Key Metrics
The CII is calculated annually based on three key parameters:
- Fuel Consumption: All types of fuel used by the ship, including heavy fuel oil (HFO), marine gas oil (MGO), and liquefied natural gas (LNG), are reported.
- Distance Traveled: The total nautical miles covered during the reporting period.
- Cargo or Passenger Load: The ship’s capacity utilization, measured in deadweight tons or passenger numbers.
By normalizing CO₂ emissions against transport work, the CII offers a fair comparison across vessel classes and sizes. For instance, a fully laden bulk carrier covering a long voyage may achieve a better CII rating than a partially loaded ship on a short route, emphasizing the importance of operational efficiency.
Credit: MarineDigital
Challenges in Implementing the CII
Accurate data collection is fundamental for reliable CII calculations, but this remains a challenge for many operators. Variations in fuel measurement techniques, voyage reporting, and load factors can lead to discrepancies. Real-time data monitoring systems, such as Automatic Identification Systems (AIS) and Electronic Logbooks, are becoming essential tools to address these gaps.
The CII indirectly incentivizes full-capacity voyages and minimal ballast operations, potentially limiting a vessel’s operational flexibility. For example, a tanker operating in spot markets may struggle to maintain a favorable CII due to unpredictable routes and loading conditions.
While the IMO sets global standards, enforcement varies significantly among regions. For example, the European Union’s Emissions Trading System (ETS) adds an additional layer of compliance, requiring shipowners operating in EU waters to pay for their emissions. Aligning regional frameworks with IMO regulations remains an ongoing challenge.
Case Studies: Real-World Impact of CII
Case Study: M/V Frontier Triumph The Frontier Triumph, a 180,000-dwt bulk carrier, achieved a significant improvement in its CII rating by implementing several measures:
- Installing energy-saving devices (ESDs) such as pre-swirl stators and rudder bulbs.
- Transitioning to low-sulfur fuel with optimized combustion properties.
- Adjusting operational speeds to balance voyage efficiency and fuel consumption.
These changes reduced the vessel’s carbon intensity by approximately 12%, moving it from a D rating to a B within two reporting periods.
Cruise ships face unique challenges due to high energy demands from onboard services such as HVAC systems, entertainment, and desalination. Carnival Corporation addressed these by:
- Retrofitting hybrid exhaust gas cleaning systems (scrubbers).
- Deploying cold ironing technology to utilize shore power while in port.
- Conducting crew training to optimize voyage planning and energy management.
These efforts enabled Carnival to maintain favorable CII ratings across its fleet despite the inherent challenges of the cruise segment.
Strategies to Improve CII Scores
Fuel-efficient navigation is one of the most effective ways to enhance CII performance. Voyage optimization tools, such as weather routing software, can minimize fuel consumption by avoiding adverse weather and current patterns. Speed management, often referred to as slow steaming, also plays a crucial role in reducing emissions.
Transitioning to cleaner fuels, such as LNG, biofuels, or methanol, can significantly lower a ship’s carbon footprint. For example, Maersk’s methanol-powered container ship, launched in 2023, demonstrated the feasibility of alternative fuels in achieving superior environmental performance.
Retrofitting older vessels with modern technologies is a cost-effective way to improve CII scores. Examples include:
- Air lubrication systems: Reduce hull resistance by creating a layer of bubbles beneath the vessel.
- Solar panels and wind-assist propulsion systems: Supplement energy needs with renewable sources.
- Propeller modifications: Improve thrust efficiency with optimized designs.
Effective implementation of operational improvements requires a well-trained crew. Continuous education on energy management systems and eco-friendly navigation practices can have a lasting impact on a vessel’s CII rating. Programs like Green Marine Europe offer certification and training to enhance environmental awareness among maritime professionals.
The Role of Digitalization and Future Prospects for the CII
Digitalization is a cornerstone of modern CII compliance strategies. Advanced analytics platforms provide actionable insights into fuel consumption patterns, voyage efficiency, and maintenance schedules. For instance, ABB Marine’s Energy Management System enables real-time monitoring and optimization, ensuring ships operate within their best CII range. Artificial intelligence (AI) is also being leveraged to predict future emissions scenarios, enabling proactive measures. For example, Kongsberg Digital’s Vessel Insight platform integrates AI-driven tools to help ship operators identify inefficiencies and improve their carbon performance.
The CII is not a static framework; it will evolve to reflect technological advancements and stricter environmental targets. The IMO has already signaled a possible shift towards absolute emissions reduction metrics, which could complement or replace relative indicators like the CII. This would require significant adjustments in how ships are designed, operated, and powered. Another area of development is the integration of lifecycle emissions into CII calculations, accounting for the carbon footprint of shipbuilding, fuel production, and eventual scrapping. This holistic approach would align the CII with broader sustainability goals.
The Carbon Intensity Indicator (CII) represents a critical step towards achieving the IMO’s decarbonization goals. By providing a transparent and standardized measure of carbon emissions per transport work, it enables ship operators to identify inefficiencies and implement targeted improvements. While challenges remain—such as data accuracy, regional inconsistencies, and operational constraints—innovative strategies and technologies are emerging to address these issues. From digital tools and alternative fuels to energy-efficient operations and crew training, the shipping industry has numerous pathways to optimize CII ratings. As the CII framework evolves, it will play an increasingly central role in maritime sustainability. By understanding and embracing this tool, the global fleet can transition towards a greener, more efficient future, aligning economic objectives with environmental responsibility.