Life cycle assessment (LCA) framework definitions

Disclaimer: This list of relevant terms aims to provide a simple explanation of typical words and phrases used in the consideration of sustainability criteria and life cycle assessments of alternative marine fuels, as agreed by members of the Global Industry Alliance to Support Low Carbon Shipping (Low Carbon GIA). However, no representation or warranty, express or implied, is made as to its accuracy or completeness. It is a non-exhaustive list and the terms as explained are in no way to be considered “agreed definitions” from an IMO perspective, and do not imply the expression of any opinion whatsoever on the part of the IMO. For definitions, refer to ISO 14040/44 as appropriate.

Term: Life Cycle Assessment (LCA)

This is a standardised framework (set out in ISO 14040/44) that allows compilation and evaluation of the inputs, outputs, and the potential environmental impacts of a product system throughout its life cycle. LCA is based on four main phases:

  1. Goal and scope definition
  2. Inventory analysis
  3. Impact assessment
  4. Interpretation
Term: System Boundary

The system boundary determines which entities (unit processes) are inside the system and which are outside by demarcating the boundaries between the studied product system and the surrounding economy and the environment. It essentially determines which life cycle/supply chain stages and processes are included in the assessment. The system boundaries need to be in accordance with the goal and scope of the study.

The broader the system boundary, the more processes that directly and indirectly contribute to the system will be considered. For example, in a “cradle-to-grave” study, the system boundaries include all the processes from the extraction of all the raw resources to the intended point of use of the delivered product and its disposal, while in a “cradle-to-gate” study, the system boundaries end at the gate of the factory where the studied product is produced.

Term: Life Cycle Inventory (LCI)

This is a phase of the Life Cycle Assessment study. The LCI analysis involves the collection, compilation, and quantification of all inputs (resources, materials, semi-products and products) and outputs (emissions, waste and valuable products) for the product system under study.

Term: Functional Unit

The functional unit (FU) provides a reference to which the input and output flows from the LCI are normalized. The functional unit defines and quantifies the aspects of the reference product’s function by generally answering the questions “what?”, “how much?”, “for how long/how many times?”, “where” and “how well?”.

For example, the functional unit for fuels could be ‘1 MJ of delivered energy’, and hence the output flow for emissions related to global warming potential could be scaled to the functional unit and expressed in gCO2e/MJ.

Term: Multifunctional processes

Processes in the product system that delivers more than one output or service of which not all are used by the reference flow of the study. Multifunctional processes are a challenge in LCA. In order to solve multifunctionality issues, the ISO standard presents a hierarchy of solutions, which should be applied in the following order:

  • Subdivision of Unit Process
  • System expansion
  • Allocation
Term: Subdivision of Unit Process

Subdivision of Unit Process is an approach to solve multifunctional processes. The aim of this approach is to increase the resolution of the modelling by dividing the multifunctional unit process into minor units to investigate whether it is possible to separate the production of the product from the production of the co-product, and if so, exclude the subprocesses that provide the additional functions from the product system. If this approach fails to solve the multifunctionality problem, system expansion should be applied.

Term: System expansion

System expansion is another approach to solve multifunctional processes.

System expansion enables the comparison of two systems by adding another not provided function or subtracting not required function(s) substituting them with the ones that are superseded or replaced. For example, for a comparison of two processes, system expansion means expanding the second process with the most likely alternative way of providing the secondary function of the first process (see example below).

Term: Allocation

Allocation is another approach to solve multifunctional processes, and distribute environmental impacts (e.g., emissions) between two or more products resulting from a process or product system.

Allocation can be done by mass, energy, and economic value of the resulting products. Essentially, this method focuses on the individual product unit, which is assigned a share of the overall environmental impact, rather than considering the system as a whole. The inputs and outputs of the system are partitioned between its different products or functions in a way that reflects the underlying physical (or economical) relationships between them.

For example, consider a process (Process AB) which produces Product A and Product B, with a ratio of 1:4, in terms of energy used. The impact of Process AB is 10. Applying allocation, the share of impact allocated of Product A would be 2, and the one of Product B would be 8.

Term: Life Cycle Impact Assessment (LCIA)

The Life Cycle Impact Assessment (LCIA) phase translates the physical flows and interventions of the product system defined in the life cycle inventory, into impacts (environmental impact scores) on the environment using LCIA methods based on environmental science.

Term: Impact Category

As per ISO 14040, the impact category is the class representing environmental issues of concern to which life cycle inventory analysis results may be assigned. In other words, an impact category combines multiple factors that cause the same impact on the environment into a single environmental effect.

For example, carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) among others lead to the greenhouse effect and can be converted into a single unit (e.g., kg CO2e) that translates into one impact category (e.g., climate change).

Term: Impact Indicator

As per ISO 14040, the impact indicator is a quantifiable representation of an impact category. It may also be known as an “impact metric” or “impact category indicator”.

For example, for climate change (an impact category), the related impact indicator (global warming potential) is expressed in kg CO2e.

Examples of impact indicators can be found in the tables below.

Term: Sustainability Criteria

Sustainability criteria are parameters for the production processes (including extraction and cultivation) and quality of those processes that must be met to obtain a sustainability status or certification. Often sustainability criteria will consist of multiple impact categories against which a product lifecycle impacts will be assessed.

Sustainability criteria: Impact categories and indicator

Damage to human health

Impact Category
Impact Indicator
Impact Category: Human toxicity
Impact Indicator: Human Toxicity Potential (HTP)

Human toxicity potential indicates the toxicity impacts to humans posed by the system processes (waste/pollutant/emissions).

The level of human toxicity potential will depend on estimates of environmental fate (i.e., the destiny of each waste/pollutant/emission after release into the environment) and human exposure (i.e., the extent to which each waste/pollutant/emission is exposed to humans).

HTP may be further divided into cancer and non-cancer effects.

Impact Category: Ionizing radiation
Impact Indicator: Ionizing Radiation Potential (IRP)

Ionizing radiation potential is an impact indicator for all emissions of radioactive elements, which have potentially carcinogenic effects.

For most fuels, this impact indicator is not likely to be of significant relevance unless nuclear power is included within the system/fuel value chain under consideration.

Impact Category: Ozone depletion
Impact Indicator: Ozone Depletion Potential (ODP)

Ozone depletion refers to the destruction of the protective ozone layer in the polar regions of the Earth’s stratosphere brought about by the interaction of certain gaseous emissions (e.g., CFCs) with NOx and UV radiation.

For most fuels, this impact indicator is not likely to be of significant relevance.

Impact Category: Photochemical Ozone Formation
Impact Indicator: Photochemical Ozone Formation Potential (POFP)

Photochemical ozone formation occurs due to the release of meta-stable volatile organic compounds which, in the presence of UV radiation and NOx, give rise to a series of photochemical reactions that ultimately lead to the formation of ozone and other secondary pollutants at ground level. These can have a negative impact on human health.

Impact Category: Particulate Matter Formation
Impact Indicator: Particulate Matter Formation Potential (PMFP)

Particulate matter formation refers to the release of fine particulates at ground level, which can have a negative impact on human health.

Damage to ecosystem health

Impact Category
Impact Indicator
Impact Category: Acidification
Impact Indicator: Acidification Potential (AP)

Acidification potential quantifies the potentially damaging effects of acidic atmospheric depositions (i.e., rain, sleet, snow) as a result of the natural hydration of acidic gaseous emissions (e.g., SOx, NOx) in the atmosphere.

Impact Category: Eco-toxicity
Impact Indicator: Eco-toxicity Potential (ETP)

Eco-toxicity potential indicates the eco-toxicity impacts to ecosystems posed by the system processes (waste/pollutant/emissions).

The level of eco-toxicity potential will depend on estimates of environmental fate (i.e., the destiny of each waste/pollutant/emission after release into the environment) and ecosystem exposure (i.e., the extent to which each waste/pollutant/emission is exposed to the ecosystem).

ETP may be further divided by different ecosystems e.g., freshwater, marine water, freshwater sediment, marine water sediment, and soil.

Impact Category: Eutrophication
Impact Indicator: Eutrophication Potential (EP)

Eutrophication is the impact of cumulative fertilization or excess supply of nutrients on land or aquatic environments, in particular nitrogen and phosphorous, leading to increased plant/algae growth and bacterial use of oxygen, which in turn leads to oxygen starvation and loss of aquatic biomass across all food chain levels.

Impact Category: Global Warming
Impact Indicator: Global Warming Potential (GWP)

Global warming potential indicates the potential of a greenhouse gas to trap extra heat in the atmosphere over time. The enhanced heat trapping in the atmosphere (i.e., the “greenhouse effect”) is caused by the absorption of infrared radiation by a given gas.

The GWP also depends on the atmospheric lifetime of a gas, and the time horizon considered (for example, GWP20 is based on the energy absorbed over 20 years, whereas GWP100 is based on the energy absorbed over 100 years). As reference, the GWP of carbon dioxide is 1.

Each greenhouse gas has a specific global warming potential which is used to calculate the CO2-equivalent (CO2e) by multiplying the mass of gas emitted by its GWP.

Impact Category: Land use change (LUC)
Impact Indicator: Land Use

Land use, as an impact indicator, refers to all degradative land use, and takes into account the length of time over which such use is sustained, and the degree to which the land can be restored to its original condition after the use has ceased.

This impact indicator, along with the associated impact indicators direct land use change (DLUC) and indirect land use change (ILUC), are likely to be of most relevance to first generation biofuels, due to land use in the cultivation of biomass feedstock.

Land use change refers to a change in the use or management of land by humans, which may lead to a change in land cover (physical elements which cover the land surface e.g. crops, trees, lakes, cities).

Direct land use change occurs when land is converted from a native ecosystem into land used for agricultural production or between shifts in crops on currently productive land.

Indirect land use change refers to the conversion of agricultural land, originally used for production of food and feed, to use for the cultivation of energy crops/biomass. The impact of this land use change will depend on the area of land conversion and where the conversion occurs.

Resource availability

Impact Category
Impact Indicator
Impact Category: Abiotic (resource) depletion
Impact Indicator: Abiotic Depletion Potential (ADP)

Abiotic depletion describes the cumulative extraction of non-living (abiotic), non-renewable resources such as fossil fuels, minerals, clay, and peat. It can be divided into ADP, elements, referring to the cumulative use of non-fuel and non-living natural resources, such as metals and minerals, each weighted according to its relative scarcity, and ADP, fossil, referring to the cumulative use of fuel resources (fossil and fissile).

Impact Category: Water depletion
Impact Indicator: Water Use

Water use, as an impact indicator, quantifies the water withdrawal-to-availability ratio of the system under consideration. ‘Withdrawal’ refers to all off-stream water use which excludes water extracted and subsequently returned to the environment unpolluted, e.g., cooling water.

This impact indicator is likely to be of most relevance to first generation biofuels, due to water use in the cultivation of biomass feedstock but may also have relevance for other fuel pathways depending on the process used.