Summary
Details
- Global
The rules are mandatory for all ships above 5,000 gross tonnage engaged in international voyages.
Exceptions include:
Smaller vessels below threshold.
Certain ship types with limited applicability.
Temporary exemptions under specific operational conditions
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What’s Required
The IMO Carbon Intensity Rules represent a hybrid technical and operational regulatory regime under Annex VI of the MARPOL Convention. They introduce a dual-layer compliance architecture combining:
A technical efficiency requirement (EEXI) is applied once per vessel.
An operational carbon performance system (CII) is applied annually.
These measures apply to international shipping vessels above 5,000 gross tonnage, which collectively account for the majority of maritime emissions.
1. Energy Efficiency Existing Ship Index (EEXI)
The EEXI is a design-based metric that evaluates the technical energy efficiency of existing vessels.
Shipowners must:
Calculate the vessel’s attained EEXI based on design parameters such as engine power, fuel consumption and ship capacity.
Compare the attained EEXI against a required EEXI threshold determined by vessel type and size.
Where vessels do not meet required thresholds, operators must implement technical modifications, including:
Engine power limitation (EPL) or shaft power limitation (ShaPoLi).
Propulsion system upgrades.
Hull and propeller optimization.
Compliance must be verified through classification societies and documented in an International Energy Efficiency Certificate.
EEXI is a one-time compliance requirement, but it establishes a baseline for vessel efficiency.
2. Carbon Intensity Indicator (CII) Framework
The CII introduces a dynamic, operational performance metric requiring ships to measure and improve emissions intensity annually.
The CII is calculated as:
Grams of CO2 emitted per cargo-carrying capacity and distance travelled.
This creates a transport work-based emissions intensity metric, linking emissions performance to actual operational activity.
Each vessel receives an annual rating from:
A (major superior performance).
B (minor superior performance).
C (moderate performance).
D (minor inferior performance).
E (inferior performance).
Ships must achieve a rating of C or better to remain compliant.
3. Annual Reporting and Data Collection
Ship operators must collect and report fuel consumption and operational data under the IMO Data Collection System.
Required data includes:
Fuel consumption by type.
Distance travelled.
Hours underway.
Cargo capacity utilization.
This data is submitted annually to flag states and verified by classification societies.
The reported data is used to calculate the vessel’s CII rating and assess compliance.
4. Corrective Action and Compliance Plans
If a vessel receives a D rating for three consecutive years or an E rating in a single year, it is considered non-compliant.
In such cases, shipowners must develop and implement a Corrective Action Plan as part of the Ship Energy Efficiency Management Plan (SEEMP).
This plan must include:
Operational measures such as speed optimization and route planning.
Technical upgrades to improve efficiency.
Fuel switching strategies, including the use of lower-carbon fuels.
The corrective plan must be approved by the vessel’s flag state or recognised organisation.
5. Progressive Tightening of Targets
The IMO has established a trajectory of increasing stringency for CII requirements.
Annual reduction factors are applied to required CII thresholds, meaning that:
Ships must continuously improve carbon intensity performance.
Compliance becomes progressively more demanding over time.
This creates a ratcheting regulatory mechanism, aligning with long-term decarbonization goals for the maritime sector.
6. Integration with Broader IMO Decarbonization Strategy
The CII and EEXI frameworks operate within the IMO’s broader strategy to reduce greenhouse gas emissions from shipping.
They interact with:
Future market-based measures (such as carbon pricing mechanisms under discussion).
Fuel standards targeting lifecycle emissions of marine fuels.
Energy efficiency design standards for new vessels.
This positions the CII regime as an intermediate compliance layer within a larger regulatory trajectory.
Important Deadlines
Entry into force: January 2023
First CII reporting year: 2023
Annual compliance cycle: ongoing
Progressive tightening of CII thresholds: annually through 2030
Alignment with IMO decarbonization targets:
2030: significant reduction in carbon intensity
2050: net-zero emissions ambition for international shipping
Current Status
The IMO Carbon Intensity Rules are fully in force and globally applicable under MARPOL Annex VI.
All applicable vessels engaged in international trade must comply.
Regulators and classification societies are actively verifying compliance and enforcing reporting requirements.
Penalties for Non-Compliance
Enforcement occurs through flag states and port state control regimes.
Penalties may include:
Detention of vessels in port.
Withdrawal or suspension of certification.
Fines and administrative sanctions.
Restrictions on vessel operations.
Persistent non-compliance may result in loss of commercial viability due to the inability to operate in regulated markets.
Examples of Known Violations
Observed compliance risks include:
Failure to achieve required CII ratings due to operational inefficiencies.
Inadequate data collection systems lead to inaccurate reporting.
Delayed implementation of corrective action plans.
Overreliance on speed reduction without structural efficiency improvements.
These issues can lead to regulatory intervention and operational constraints.
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