Maritime emissions glossary
The terms used in the CII, the EU ETS, FuelEU Maritime, the UK ETS and the IMO Net-Zero Framework, in one or two sentences each.
Updated 2026-10-20
Attained CII
A ship's carbon intensity for a calendar year: CO₂ emitted divided by capacity and distance sailed, in grams of CO₂ per capacity-nautical mile. More
Required CII
The reference value for a ship's type and size, reduced by the Z factor for the year. It sits inside the C band: a ship rated C, B or A meets the requirement. More
CII rating
A, B, C, D or E, from the attained CII divided by the required CII and compared with the boundaries for the ship type. More
Z factor
The yearly reduction of the required CII below the 2019 reference: 5% in 2023 rising to 21.5% in 2030. More
Corrective action plan
The part of SEEMP Part III a ship needs after an E rating, or D three years running, showing how it will reach at least C. More
SEEMP
Ship Energy Efficiency Management Plan. Part I covers energy efficiency, Part II fuel data collection, Part III the CII plan. More
IMO DCS
The IMO Data Collection System: fuel, distance and hours reported each year to the Administration under MARPOL Annex VI regulation 27. More
Statement of Compliance
The document the Administration issues each year confirming the IMO DCS report and giving the CII rating, by 31 May. More
EEXI
Energy Efficiency Existing Ship Index: a one-off technical design rating, unlike the CII which is operational and yearly. More
EU ETS
The EU Emissions Trading System. Since 2024 shipping companies surrender allowances for ships of 5,000 GT and above calling at EU and EEA ports. More
EUA
EU Allowance: the right to emit one tonne of CO₂-equivalent under the EU ETS. More
MOHA
Maritime Operator Holding Account: the account in the Union Registry from which a shipping company surrenders allowances. More
Shipping company (EU ETS)
The ISM Document of Compliance holder, or an owner or manager that has taken on the EU ETS obligation by mandate. More
Phase-in
The share of emissions surrendered: 40% of 2024, 70% of 2025 and 100% from 2026. More
EU MRV
Regulation (EU) 2015/757: monitoring, reporting and verification of ship emissions, published each year by EMSA in THETIS-MRV. More
THETIS-MRV
EMSA's public register of each ship's verified fuel, CO₂ and distance on voyages to, from and within the EU and EEA. More
FuelEU Maritime
Regulation (EU) 2023/1805, limiting the well-to-wake greenhouse gas intensity of the energy ships use, from 2025. More
GHG intensity
Grams of CO₂-equivalent per megajoule of energy used on board, well-to-wake, as FuelEU Maritime measures it. More
Well-to-wake
Counting the emissions from producing and transporting a fuel (well-to-tank) as well as from using it on board (tank-to-wake). More
Compliance balance
Under FuelEU, the target minus the ship's GHG intensity, times the energy in scope. Negative is a deficit. More
FuelEU pooling
Ships combining their compliance balances for a year so that the pool as a whole complies (Article 21). More
FuelEU Document of Compliance
The document a ship must hold on board from 30 June showing it met FuelEU Maritime for the previous year. More
RFNBO
Renewable fuel of non-biological origin, such as e-methanol or e-ammonia. Counts double under FuelEU until 2033. More
Methane slip
Unburned methane released by LNG engines. Counted in the EU ETS from 2026 and in FuelEU from the start. More
UK ETS (maritime)
The UK Emissions Trading Scheme for ships of 5,000 GT and above on domestic voyages and in UK ports, from 1 July 2026. More
GFI
Greenhouse gas fuel intensity: the measure the draft IMO Net-Zero Framework would apply to all of a ship's energy from 2028. More
Remedial unit
In the draft IMO Net-Zero Framework, a unit bought to cover a GFI above the target. More
Poseidon Principles
A framework under which banks report how their shipping loans align with IMO decarbonisation trajectories. More
EU ETS, FuelEU, CII and UK ETS for each ship, from the public register or your own data.