Lifecycle assessment (LCA) framework definitions
Disclaimer: This interactive graphic 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. However, no representation or warranty, express or implied, is made as to its accuracy or completeness. The terms as defined 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.
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 lifecycle. There are four steps:
- Definition of goal and scope
- Inventory analysis
- Impact assessment
- Interpretation
The system boundary determines which entities (unit processes) are inside the system and which are outside. It essentially determines which lifecycle/supply chain stages and processes are included in the assessment and need to be in accordance with the goal and scope of the study.
Ideally, the boundary should be as broad as possible, thereby including all the processes that directly and indirectly contribute to the system under consideration, from the extraction of all the raw resources to the intended point of use of the delivered product.
The functional unit represents the reference product or service to which the input and output flows from the lifecycle inventory (LCI) are related.
For example, the functional unit for fuels could be e.g. ‘MJ of delivered energy’, and hence the output flow for emissions could be expressed with the unit: gCO2e/MJ.
This is a phase of the lifecycle assessment which involves the compilation and quantification of inputs and outputs for a product throughout its lifecycle.
This is the evaluation phase of the lifecycle assessment which aims to assess the magnitude and significance of the potential environmental impacts for a product system throughout the lifecycle of the product.
Sustainability criteria are parameters for the production process and quality of a process 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.
An established methodology to assess impacts e.g.
- EU Renewable Energy Directive (RED II)
- JEC (JRC-EUCAR-Concawe) Well to Wheels study
- GREET Model
- ICAO CORSIA carbon certification
An impact category combines multiple factors that cause the same impact on the environment into a single environmental effect.
For example, carbon dioxide (CO2) and methane (CH4) both 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). In LCA, impact categories represent the environmental issue of concern to which a lifecycle inventory analysis (LCIA) may be assigned.
An impact indicator may also be known as an “impact metric”. This provides a quantifiable representation of an impact category, which can result in numerical values, expressed in category-specific units.
For example, for climate change (an impact category), the related impact indicator (global warming potential) is expressed in kg CO2e.
Co-product allocation is a method to 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.
System expansion is a method to distribute environmental impacts (e.g. emissions) between two or more products resulting from a process or product system.
Let’s consider this with the figure below. In the system expansion approach, the entire impact of the system (Plant AB) is first calculated, and then the boundary of the multioutput system is expanded to include a set of alternative independent production pathways (Plant B) which are capable of producing outputs that are deemed to be “functionally equivalent” to the various co-products of interest (Product B’ being functionally equivalent to Product B). The impact assigned to one co-product (Product A) is finally calculated as the difference between the entire impact of the original multi-output process (Impact AB), and the sum of the impacts of the alternative independent pathways that produce functional equivalents of all the other co-products (Impact B’).
This approach is part of the consequential lifecycle assessment method that seeks to capture change in environmental impact as a consequence of a certain activity.
ISO 14040 recommends the use of system expansion whenever possible.
Sustainability criteria: Impact categories and indicator
Damage to human health
Human toxicity potential indicates the toxicity risk 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 HTP.
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.
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.
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.
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
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.
Eco-toxicity potential indicates the toxicity risk 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.
Eutrophication is the impact of over-fertilisation 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.
Global warming potential indicates the potential of a greenhouse gas to trap extra heat in the atmosphere over time in relation to carbon dioxide. 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.
Each greenhouse gas has a specific global warming potential which is used to calculate the CO2-equivalent (CO2e).
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 land use change 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).
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
Abiotic depletion describes the over-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).
Cumulative energy demand is an impact metric that accounts for the total harvesting of renewable (i.e., solar, wind, water geopotential, tidal, and biomass energy) and non-renewable (i.e., fossil and fissile fuels) primary energy resources. Sometimes, non-renewable cumulative energy demand (Nr-CED) is considered as an impact indicator by itself.
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.
