International shipping contributes roughly 2.5–3% of global CO2 emissions. A layered framework of IMO mandatory measures and EU regulations now governs operational and design-phase carbon intensity for commercial vessels. For seafarers, the most immediate impacts are the administrative requirements that bridge and engine teams must meet — accurate fuel and voyage records feed directly into compliance calculations.
The instruments below are listed in order of their practical proximity to shipboard operations. The SEEMP, EEXI, and CII are mandatory under MARPOL Annex VI; EU ETS and FuelEU are EU law applying to operators in European trade.
SEEMP
— Ship Energy Efficiency Management PlanIn force: 1 January 2013 (Part III from 1 January 2023)
Mandatory under MARPOL Annex VI Regulation 22. Required for all ships ≥ 400 GT.
Key provisions
·Part I — energy efficiency operational plan: describes how the company and ship will reduce fuel consumption (speed optimisation, trim, weather routing, hull maintenance, etc.).
·Part II — data collection plan for the IMO DCS: specifies which fuel types, consumption measurement methods, and voyage data will be reported annually.
·Part III — CII implementation plan (mandatory from 1 January 2023): documents the ship's current CII rating, target rating, and the technical and operational measures to achieve it; reviewed annually.
·The SEEMP must be kept on board and produced on request by port state control.
Practical notes
Flag-state verified. A ship without a SEEMP (or with an unapproved Part III) is liable to deficiency and detention. The plan is ship-specific, not fleet-wide.
EEXI
— Energy Efficiency Existing Ship IndexIn force: 1 November 2022 (first IAPP survey)
One-off technical standard for existing ships ≥ 400 GT. Analogous to the EEDI for new builds.
Key provisions
·Computed at the design-stage-equivalent level using the ship's installed power, speed, and capacity — not measured from operational data.
·Each ship's attained EEXI must not exceed the required EEXI (set per ship type and size by IMO).
·Non-compliant ships must take technical measures: Engine Power Limitation (EPL) is the most common — a shaft power limiter or software limit that caps maximum continuous rating.
·Verified at the first annual, intermediate, or renewal survey of the IAPP certificate after 1 November 2022 and confirmed by an EEXI Technical File.
·A Statement of Compliance (SoC) for EEXI is issued by the flag or recognised organisation and is distinct from the IAPP certificate.
Practical notes
EEXI is a one-time check; once the SoC is issued, the ship does not need to recalculate unless major conversion. Unlike CII, EEXI does not change year-on-year.
CII
— Carbon Intensity IndicatorIn force: 1 January 2023
Annual operational rating for ships ≥ 5,000 GT engaged in international voyages.
Key provisions
·Expressed as grams of CO2 per deadweight-tonne per nautical mile (AER) or, for some ship types, per capacity-tonne-mile (cgDIST).
·Rated A (best) to E (worst) against required CII thresholds, which tighten each year: 2% reduction per year 2023–2026 vs the 2019 baseline, with further tightening to 2030.
·A rating of D for two consecutive years, or E for one year, requires a corrective action plan endorsed into the SEEMP Part III and submitted to the flag state.
·Rating is calculated from DCS-reported fuel consumption and distance sailed; verified annually by a recognised organisation.
·A CII Statement of Compliance is endorsed on the SEEMP. The rating must also appear in the Ship Energy Efficiency Certificate (SEEC).
·Practical impact: CII rating is increasingly referenced in charterparty clauses, loan covenants, and vessel valuations.
Practical notes
CII applies only to actual operational performance. A ship with a good EEXI can still receive a poor CII if it operates inefficiently. Bridge and engine teams record fuel per grade and cargo/distance per voyage to feed the DCS submission.
DCS
— IMO Data Collection SystemIn force: 1 March 2018
Fuel-consumption reporting for all ships ≥ 5,000 GT on international voyages.
Key provisions
·Owners report annual fuel consumption per fuel type (HFO, MDO, LNG, methanol, etc.), hours underway, distance sailed, and cargo carried (dwt × nm or passengers × nm) to the flag state.
·Flag state verifies and issues a Statement of Compliance for DCS; IMO aggregates data into a public IMO DCS database.
·Data covers the preceding calendar year; reporting deadline is typically within five months of year-end.
·The DCS feeds into CII calculation and into IMO's broader GHG emissions monitoring framework.
Practical notes
A similar but separate EU MRV (Monitoring, Reporting, Verification) system applies in EU waters — it has somewhat different scope and is verified by an EU-accredited verifier. Both must be maintained in parallel for most operators.
EU-ETS
— EU Emissions Trading System for shippingIn force: 1 January 2024
Cap-and-trade carbon market extended to maritime transport; applies to vessels ≥ 5,000 GT calling EU/EEA ports.
Key provisions
·Shipping companies must surrender EU Allowances (EUAs) equal to a percentage of verified CO2 (and, from 2026, CH4 and N2O) emissions.
·Coverage by voyage type: 100% of emissions from intra-EU voyages (port-to-port within the EU); 50% for voyages between an EU port and a non-EU port (one leg).
·Phased percentage surrender: 40% of 2024 emissions due by September 2025; 70% of 2025 emissions; 100% of 2026 emissions onwards.
·Verified emissions data come from the existing EU MRV system. EUAs must be surrendered by 30 September each year.
·The Shipping Company (legal entity responsible for compliance) is determined by the ISM Document of Compliance holder.
Practical notes
Allowance costs flow through charterparty clauses. BIMCO has published standard ETS clauses allocating costs between owner and charterer. Non-surrender incurs a €100 per tonne excess-emissions penalty plus repayment obligation.
FuelEU
— FuelEU Maritime RegulationIn force: 1 January 2025
Annual GHG-intensity reduction obligation for ships ≥ 5,000 GT using EU ports; covers well-to-wake emissions.
Key provisions
·Requires the annual average GHG intensity of energy used on board to not exceed a declining limit: 2% reduction in 2025 (vs 2020 baseline), 6% in 2030, 14.5% in 2035, rising steeply to 80% by 2050.
·Well-to-wake accounting: includes upstream (production and supply chain) emissions for all fuels, not just tank-to-wake combustion.
·Pooling: ships can pool their compliance surplus/deficit across a fleet; banking of surpluses within a year is allowed.
·Renewable Fuels of Non-Biological Origin (RFNBOs — e-methanol, e-ammonia, e-hydrogen) receive a multiplier bonus: 2× credit applied to their GHG contribution until 2033.
·ONSHORE POWER SUPPLY (OPS): from 1 January 2030 passenger ships and container ships at EU ports must use shore power where available.
·Non-compliance incurs a FuelEU penalty of €2,400 per tonne of VLSFO equivalent of the GHG deficit.
Practical notes
FuelEU and EU ETS operate in parallel. Compliance with FuelEU does not automatically satisfy ETS obligations and vice versa. Verified by an EU MRV accredited verifier.
IMO-GHG-2023
— IMO 2023 GHG StrategyIn force: Adopted July 2023 at MEPC 80
Long-term decarbonisation ambition and mid-term measure roadmap for international shipping.
Key provisions
·Net-zero GHG emissions by or around 2050 — a strengthening of the 2018 strategy's '50% reduction by 2050' goal.
·Interim checkpoints: at least 20% reduction (striving for 30%) by 2030; at least 70% (striving for 80%) by 2040 vs 2008 baseline.
·Zero- and near-zero GHG fuels to represent at least 5% (striving for 10%) of the energy mix by 2030.
·Mid-term measures under negotiation at MEPC (81, 82, 83): basket of candidate measures includes a Global Fuel Standard (GFS) on GHG intensity and an economic measure (carbon levy or credit trading); targeted entry into force 2027.
·Technical and economic mid-term measures are expected to be finalised at MEPC 83 (April 2025 est.) and adopted for entry into force at MEPC 84–85.
Practical notes
The 2023 strategy is not directly enforceable — it sets the political framework for the binding measures under negotiation. However, it shapes port-state and flag-state planning, shipbuilding contracts, and long-term fuel-investment decisions across the industry.
Crew responsibilities
The Master and Chief Engineer bear primary responsibility for the accuracy of the data that flows into DCS and CII reporting. Per voyage, the bridge team records distance sailed and cargo carried (tonnes or passengers); the engine team records fuel consumed per grade. Chief Officers and Chief Engineers should be familiar with the SEEMP Part II and Part III and understand the CII correction factors that apply to their vessel type (e.g., ice navigation, port waiting on anchor, sea passage in adverse weather). A CII rating that falls to D or E has direct consequences for vessel employment and value — making it a commercial, not just compliance, matter.
See also
· MARPOL Annexes — Annex VI is the parent instrument for SEEMP, EEXI, and CII.
· SOLAS — construction and safety framework that interacts with decarbonisation retrofits.
· Charterparties — ETS and CII clauses increasingly appear in voyage and time CP forms.
· ITF & IBF — union position on just transition and crew welfare during decarbonisation.