Environment, Ocean Science and the Natural World

Decarbonization, emissions and alternative fuels glossary

Where naval architecture, regulation, and climate science meet: the EEDI, EEXI, and CII efficiency measures, the IMO Net-Zero Framework with its GHG Fuel Intensity standard and well-to-wake accounting against the 93.3 gCO2eq/MJ reference, and regional measures (EU ETS, MRV, FuelEU Maritime, UK ETS). Covers the alternative-fuel slate (LNG, methanol, ammonia, hydrogen, biofuels), wind assist, the Poseidon Principles, and the Sea Cargo Charter.

186 defined terms.

A

Abatement Cost: Cost per ton of emissions avoided.
Additionality: Requirement that a project would not have occurred without the carbon scheme.
AER (Annual Efficiency Ratio): Carbon intensity metric used in early shipping efficiency reporting.
Air Lubrication System (ALS): System reducing hull friction via injected air bubbles.
Alternative Fuel: Fuel other than conventional fuel oil, including LNG, methanol, ammonia, and hydrogen.
Ammonia (fuel): Carbon-free alternative fuel addressed by IGF/IGC future amendments.
Annex VI MARPOL: IMO regulations on air pollution from ships.
AOSI (Alternative Outsourced Shipping Initiative): Not standard.
AP Moller-Maersk Decarbonization Strategy: Carrier strategy to deploy methanol-fueled ships.
Asia Clean Fuel Index: Generic index for clean marine fuel pricing in Asia.

B

Battery-Hybrid Vessel: Vessel combining engines with battery systems.
Bio-LNG: Liquefied biomethane used as drop-in fuel for LNG ships.
Biofuel (Marine): Fuel derived from biomass such as FAME or HVO blended with marine fuel.
Biomass-to-Liquid (BTL): Synthetic fuel from biomass via gasification.
Blue Ammonia: Ammonia produced from natural gas with CCS.
Blue Hydrogen: Hydrogen from fossil sources combined with carbon capture and storage.
Boil-off gas (BOG): Vapor from LNG cargo or fuel tanks managed by reliquefaction or use.
Bunker Adjustment Factor (BAF): Surcharge linked to bunker fuel prices.
Bunker Delivery Note (BDN): Required under MARPOL Annex VI Regulation 18.
Business-as-Usual Scenario (BAU): Reference emissions trajectory without new policies.

C

California Air Resources Board (CARB): US state regulator addressing port and at-berth emissions.
Carbon Border Adjustment Mechanism (CBAM): EU mechanism pricing imported carbon-intensive goods.
Carbon Capture and Storage (CCS): Capture of CO2 from sources and storage in geological formations.
Carbon Capture on Board (OCC): Onboard CO2 capture systems for ships.
Carbon Credit: Tradable unit representing one ton of CO2 equivalent reduced.
Carbon Intensity Indicator (CII): Operational indicator under MARPOL Annex VI Chapter 4.
Carbon Offsetting: Use of credits to compensate for emissions.
Carbon Pricing: Policy assigning a cost to greenhouse gas emissions.
CCAI (Calculated Carbon Aromaticity Index): Ignition quality indicator for marine fuels.
Cetane Number: Ignition quality indicator for diesel-type fuels.
Clarksons Green Transition: Industry analytics on alternative-fuel orderbook.
CleanShipping Index: Voluntary index ranking ships on environmental performance.
CO2 Equivalent (CO2e): Unit normalizing greenhouse gases by their global warming potential.
CO2 Slip: Reduced carbon efficiency from incomplete combustion in dual-fuel engines.
Cold Ironing: Onshore power supply enabling ships to shut down engines in port.
Container Throughput Carbon Intensity: Emissions per TEU moved.
Conversion Tonnage Reduction Coefficient (j): Capacity reduction parameter for ice class in EEDI.
Cooperation Mechanism Article 6: Paris Agreement mechanism enabling internationally transferred mitigation outcomes.
Corsia Aviation Parallel: Comparative framework with shipping not directly applicable but conceptually similar.
CR (Cargo Volume Reduction): Adjustment factor in EEDI for capacity-related corrections.

D

DCS (IMO Data Collection System): Mandatory fuel oil consumption data reporting since 2019.
Default Emission Factor: Standardized factor used when measured data are unavailable.
Demonstration Project: Pilot project for new fuels or technologies.
DESS (Dual-fuel Engine Slow Speed): Slow-speed dual-fuel marine engine.
Direct Air Capture (DAC): Extraction of CO2 directly from ambient air.
DME (Dimethyl Ether): Cleaner-burning fuel evaluated for marine use.
DNV ETO (Energy Transition Outlook): DNV annual scenario analysis of the energy transition.
DSME / Hanwha Ocean LNG Carriers: Builders supplying LNG carriers and dual-fuel vessels.
Dual-fuel engine: Engine running on both liquid and gaseous fuels (e.g., WinGD X-DF).

E

E-Fuel: Synthetic fuel produced from renewable electricity and CO2 or N2.
E-Methane: Synthetic methane from renewable hydrogen and CO2.
E-Methanol: Methanol synthesized from green hydrogen and captured CO2.
EATSPA: Generic emissions abatement service term; not standard.
EEDI (Energy Efficiency Design Index): Mandatory IMO design efficiency metric for new ships.
EEOI (Energy Efficiency Operational Indicator): Voluntary IMO operational efficiency metric.
EEXI (Energy Efficiency Existing Ship Index): IMO design efficiency metric for existing ships.
Electrofuel: See E-Fuel.
Emission Control Area (ECA): Sea area with stricter SOx, NOx, or PM controls.
Emission Factor: Mass of emissions per unit of activity or fuel.
Emission Trading System (ETS): Cap-and-trade system for greenhouse gas emissions.
Energy Density (Fuel): Energy per unit mass or volume of a fuel.
Energy Efficiency Management Plan (SEEMP): Ship-specific plan for operational efficiency.
Environmental Ship Index (ESI): Voluntary index used by ports to reward cleaner ships.
EU ETS for Shipping: Extension of the EU emissions trading system to maritime CO2 emissions from 2024.
EU MRV: EU Regulation 2015/757 on monitoring, reporting, and verification of CO2 emissions from shipping.

F

FAME (Fatty Acid Methyl Esters): First-generation biodiesel often blended for marine use.
FCEV Hybrid Vessel: Vessel using fuel cells and batteries.
Fischer-Tropsch Synthesis: Process converting syngas to liquid hydrocarbons.
Flag State Implementation (Energy): Flag state enforcement of energy and emissions rules.
Fleet Modernization: Replacement and upgrading of vessels for efficiency.
Flettner rotor: Wind-assisted propulsion using Magnus effect.
Fuel Cell: Device converting fuel and oxidant directly to electricity.
Fuel Consumption Data Collection (DCS): IMO data reporting system.
Fuel EU Maritime: EU regulation limiting GHG intensity of marine fuels from 2025.
Fuel Switching: Operational change between fuels on the same voyage.

G

Gas carrier: Vessel for liquefied gases such as LNG, LPG, ethane, or ethylene.
GFI (Greenhouse Gas Fuel Intensity): IMO Net-Zero Framework metric (gCO2e/MJ) covering well-to-wake emissions.
GHG Strategy 2023 (IMO): Revised IMO strategy targeting net-zero emissions around 2050.
Global Warming Potential (GWP): Relative warming impact of a gas, usually over 100 years.
Green Ammonia: Ammonia produced from renewable hydrogen via the Haber-Bosch process.
Green Corridor: Shipping route along which zero-emission options are scaled up.
Green Hydrogen: Hydrogen produced via electrolysis using renewable electricity.
Green Methanol: Methanol produced from renewable feedstocks.

H

Haber-Bosch Process: Industrial synthesis of ammonia from nitrogen and hydrogen.
Heavy fuel oil (HFO): Residual marine fuel, RMG 380, ISO 8217.
Hot Ironing: Generation of vessel power while berthed; antithesis of cold ironing.
Hybrid Propulsion: Combination of multiple propulsion sources for efficiency.
Hydrogen Combustion Engine: Internal combustion engine running on hydrogen.
Hydrogen Fuel Cell: Electrochemical device producing electricity from hydrogen.
Hydrotreated Vegetable Oil (HVO): Renewable diesel often used as drop-in marine fuel.

I

IMO 2020 Sulphur Cap: Limit of 0.50 percent sulfur in marine fuel outside ECAs.
IMO MEPC: Marine Environment Protection Committee setting environmental rules.
IMO Net-Zero Framework: Adopted 2025 mid-term measure combining mandatory GFI standard with economic measure.
Initial GHG Strategy 2018 (IMO): First IMO climate strategy, since revised in 2023.
Inland AIS Emissions Estimation: Use of AIS to estimate inland waterway emissions.
Internal Carbon Price: Company-set carbon price used in investment decisions.
ISO 14001 (Maritime): Environmental management system standard.
ISO 8217: International standard for marine fuel oil specifications.

J

Joint Industry Project (JIP): Collaborative project on shared technical challenges.
Just Transition: Equitable transition framework for affected workers and communities.

K

KW/T (Kilowatt per Ton): Indicator of installed power per ton of deadweight.

L

Lifecycle Assessment (LCA): Evaluation of environmental impacts across a product life cycle.
LNG Bunkering: Process of supplying liquefied natural gas as marine fuel.
LNG Fuel: Liquefied natural gas used as ship fuel.
Low Carbon Fuel Standard: Policy requiring fuel suppliers to reduce carbon intensity.
Low Sulphur Fuel Oil (LSFO): Marine fuel with 0.50 percent sulfur maximum.
LR Fuel Tracker: Lloyd's Register tool monitoring alternative-fuel ship orders.

M

MARPOL Annex VI Chapter 4: Energy efficiency provisions including EEDI and SEEMP.
Mass Flow Meter (MFM): Bunkering meter used in Singapore and elsewhere for accurate measurement.
Master GHG Database: Industry datasets compiling reported ship emissions.
MEPC 80: 80th session of the Marine Environment Protection Committee, adopting the 2023 GHG Strategy.
MEPC 83: 83rd session, adopting the 2025 IMO Net-Zero Framework as draft MARPOL amendments.
Methane Slip: Unburned methane emissions from dual-fuel LNG engines.
Methanol Bunkering: Supply of methanol as marine fuel.
Methanol Fuel: Methanol (CH3OH) used as a marine fuel with potential for renewable production.
MGO (Marine Gas Oil): Distillate marine fuel meeting ISO 8217 grades DMA/DMZ.
MSC Decarbonization Roadmap: Carrier-specific transition plan.

N

Natural Gas Slip: Methane emissions from gas-fueled engines.
Net Zero: State where anthropogenic GHG emissions are balanced by removals.
NETs (Negative Emissions Technologies): Technologies removing CO2 from the atmosphere.
NOx Tier I/II/III: IMO NOx emission limits for marine diesel engines under MARPOL Annex VI.
NOZE (Net Zero Emissions Vessel): Vessel achieving net-zero across the value chain.

O

Onboard Carbon Capture: CO2 capture from ship engine exhausts.
Onshore Power Supply (OPS): Electrical supply to ships at berth, also called cold ironing.
OPCC (Operational Performance Carbon Capture): Operational on-board CCS performance.
Operational Efficiency: Operational measures such as slow steaming improving energy use.
Optimization (Voyage): Routing and trim optimization for fuel savings.

P

Paris Agreement: 2015 UNFCCC agreement to limit warming well below 2 degrees Celsius.
PEM Fuel Cell: Proton exchange membrane fuel cell.
Pilot Fuel: Small amount of conventional fuel igniting alternative fuel in dual-fuel engines.
Poseidon Principles: Framework for integrating climate considerations into ship finance.
Poseidon Principles for Marine Insurance: Analogous initiative for marine insurers.
Power Take-Off / Take-In (PTO/PTI): Shaft generator-motor arrangements.
Pre-Combustion Capture: CO2 capture before fuel combustion.
Pre-Treatment (Ammonia Bunkering): Necessary processing for safe ammonia bunkering.
Project-Based Mechanism: Carbon market mechanism crediting emission reductions from projects.

Q

Quality Standard for Marine Fuel: ISO 8217 quality grades.
Quantitative Risk Assessment (QRA): Risk assessment used for new-fuel safety cases.

R

Reference Line (EEDI): Reference EEDI value against which design is compared.
Refrigerant CO2 Equivalent: GHG impact of refrigerant leaks.
Renewable Diesel: Drop-in diesel produced from biomass-derived oils.
Renewable Energy Certificate (REC): Tradable certificate for renewable electricity generation.
RFNBO (Renewable Fuel of Non-Biological Origin): EU category covering green hydrogen-derived fuels.
Right Whale Slow Zone: Speed restriction also reducing fuel use and emissions.
RINA Notation (GREEN PLUS): Class society environmental notation.
Rotor Sail: See Flettner Rotor.

S

Sail Cargo: Cargo movement powered partly by sails.
Scrubber: Exhaust gas cleaning system used as an equivalent under MARPOL Annex VI Regulation 4.
Sea Cargo Charter: Framework for charterers to align with IMO climate goals.
SEEMP Part I, II, III: Ship Energy Efficiency Management Plan parts for management, DCS, and CII under MARPOL Annex VI.
Selective Catalytic Reduction (SCR): NOx aftertreatment using urea/ammonia.
Shaft generator: Generator driven by main engine via PTO.
Slow Steaming: Operating below design speed to save fuel and reduce emissions.
Slow Steaming Index: Indicator of fleet-average operating speeds.
Smart Buoy (Bunkering): Floating bunkering installation, sometimes for LNG.
SOx Cap (Global): 0.50 percent sulfur cap on marine fuel.
SOx ECA Cap: 0.10 percent sulfur cap within Emission Control Areas.
SSI (Sustainable Shipping Initiative): Multi-stakeholder coalition on sustainable shipping.
Sulphur cap 2020: 0.50 percent global cap on fuel oil sulphur.
Synthetic Fuel: Fuel produced via chemical synthesis from feedstocks such as hydrogen and CO2.

T

Tank-to-Wake (TtW): Emissions accounting from fuel tank through combustion.
Tier III NOx: Strictest IMO NOx limit applying in NOx ECAs.
Total Carbon Footprint: Full carbon emissions associated with a voyage or company.
Toxicity (Ammonia Fuel): Safety concern requiring strict mitigation for ammonia bunkering.
Twin Hybrid Power Plant: Two engine sets sharing load for efficiency.
Twin Skeg Design: Hull design improving propulsive efficiency.

U

UK ETS: UK emissions trading scheme, with maritime inclusion under consideration.
UNFCCC: United Nations Framework Convention on Climate Change.
Urea Solution (AUS 40): Reductant used in SCR systems on marine engines.

V

Verified Emissions Report: Independently verified ship emissions report under EU MRV or IMO DCS.
Voyage Optimization Software: Routing and trim software reducing fuel use.

W

Wartsila Dual Fuel Engine: Family of dual-fuel medium-speed engines.
Waste heat recovery (WHR): Steam/power recovery from main engine exhaust.
Water Lubrication System: Friction reduction via water-injected layers.
Well-to-Tank (WtT): Emissions associated with fuel production and delivery to the ship.
Well-to-Wake (WtW): GHG accounting basis for GFI under MARPOL Annex VI Chapter 5.
Wind-Assisted Propulsion (WAP): Use of sails, rotors, or kites to supplement main engines.
WinGD X-DF Engine: Two-stroke dual-fuel engine running on LNG with pilot fuel.

X

X-DF Otto Cycle: Two-stroke gas engine cycle used by WinGD.
XGen Vessel: Generic term for next-generation low-emission vessel.

Y

Yara Birkeland: Pioneering autonomous battery-electric container ship.
Yield Loss (Refining): Fuel-quality consideration for ULSFO production.

Z

Zero Carbon Fuel: Fuel with no direct CO2 emissions at the point of use, such as ammonia or hydrogen.
Zero Emission Pilot Project: Demonstration project for zero-emission vessels.
Zero Emission Vessel (ZEV): Vessel with no greenhouse gas emissions from operation.
ZESTAs: Zero Emission Ship Technology Association advocating for zero-emission shipping.

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