Carbon capture and storage (CCS)

The process of capturing carbon dioxide formed during fuel production processes and storing it so that it is not emitted into the atmosphere.

Carbon capture and utilisation (CCU)

The process of capturing carbon dioxide to be recycled for further usage. CCU will typically involve CCS.


A general term referring to the reduction and control of manmade GHG emissions. In shipping decarbonisation is used to describe both (short term) vessel efficiency measures and (mid to long term) zero carbon fuel solutions. Zero-Carbon Fuel Monitor focuses only on zero carbon fuel solutions.

Direct Air Capture (DAC)

The process of removing a stream of Carbon Dioxide from ambient air, typically using technology to filter and chemically absorb carbon dioxide. In combination with carbon storage it can result in a net-negative carbon dioxide balance in the atmosphere.

Electrofuels (e-fuels)

Zero carbon fuels produced using renewable electricity.


The process of using a DC current to drive a chemical reaction. Electrolysis of water is used to decompose the water molecules into separate streams of hydrogen and oxygen.

Greenhouse Gas (GHG)

A gas that traps heat in the earth’s atmosphere. Whilst carbon dioxide is the dominant GHG for shipping, GHGs include a basket of six gases:
• Carbon dioxide (CO2)
• Methane (CH4)
• Nitrous oxide (N2O)
• Hydrofluorocarbons (HFCs)
• Perfluorocarbons (PFCs),
• Sulphur hexafluoride (SF6)
• Nitrogen trifluoride (NF3)

Just transition

A just transition seeks to ensure that the substantial benefits of a green economy transition are shared widely, while also supporting those who stand to lose economically – be they countries, regions, industries, communities, workers or consumers.

Lifecycle emissions

The total GHG emissions of a fuel across every stage in the supply chain: resource, production, bunkering, onboard storage and propulsion. Often described as ‘well to wake’ meaning the sum of upstream (‘well to tank’) emissions and operational (‘tank to wake’) emissions.

Lifecycle emissions assessment (LCA)

A method for measurement of lifecycle emissions.

Natural gas with Carbon Capture and Storage fuels (blue fuels)

A fuel produced using natural gas from which carbon dioxide emissions are captured and stored never to be released to the atmosphere. Natural gas with CCS could be net zero if the capture and storage is sufficiently effective.
Hydrogen and synthetic non-carbon fuels (ammonia) can also be (e.g. when combustion of a fossil fuel is used with CCS (Carbon Capture and Storage)), which could make the fuel net- zero if the capture and storage is sufficiently effective.

Net zero

A state in which all the greenhouse gases released into the atmosphere balanced by an equivalent quantity of GHGs removed from the atmosphere. A fuel is considered net zero if the total supply chain GHG emissions across the lifecycle of the fuel are balanced by equivalent GHG removals (see lifecycle emissions). See comparison of selected fuels below.


Generic term for the nitrogen oxides most responsible for air pollution, nitric oxide (NO) and nitrogen dioxide (NO2). Whilst nitrous oxide (N2O) not included in NOx, but it is a GHG.

Steam methane reforming (SMR)

The process of reacting hydrocarbons with water to generate a stream of hydrogen and carbon monoxide. SMR with natural gas as the feedstock is typically coupled with water-gas shift reaction to produce additional hydrogen and a stream of carbon dioxide.


While not intended as an exhaustive list, sustainability in maritime transport entails, among other features, the ability to provide transportation infrastructure and services that are safe, socially inclusive, accessible, reliable, affordable, fuel-efficient, environmentally friendly, low-carbon and resilient to shocks and disruptions including those caused by climate change and natural disasters.

Sustainable biomass-derived fuels

A fuel that is derived from biomass, i.e. plant or algae material or animal waste. Because the production of biomass takes carbon dioxide out of the atmosphere in equivalent quantity to that emitted in combustion, it is considered net zero. However, GHGs emitted in upstream processes (e.g. land-use, harvesting, processing/refining, transport) generally cause small net positive carbon emissions.

Zero carbon fuel

Fuel that does not use carbon in production or have a carbon molecule in its chemical structure. For the purposes of Zero-Carbon Fuel Monitor we also include fuels that generate close to zero carbon emissions, which can be considered negligible relative to the magnitude of the emissions reduction goals set by global agencies.

Zero emissions vessel (ZEV)

Vessels, with operational emissions containing zero or negligible GHGs. A ZEV may release other pollutants, so we also require a ZEV to comply with other relevant air emissions regulations (for example NOx). However, Emissions generated in the fuel supply chain (upstream emissions) may not be zero or negligible.