4.3 - Method for selecting emission factors
How to select the emission factors needed for accounting?
This subsection details what an emission factor is, how to choose or develop them from available information, and provides some examples of database (DB) of emission factors.
Emission factors
The emissions quantification method involves defining emission factors (EF) that convert an organization's activity data into tCO₂e. These EFs represent the average amount of GHG emitted per reference unit. They do not measure GHG emissions but estimate them. They typically take the following form:
By multiplying this EF by the number of kilograms of raw pitted apricots consumed by an organization, it will obtain the GHG emissions associated with that consumption. EFs are therefore essential to carbon accounting, but they must be handled with care.
Indeed, EFs are developed from assumptions and resulting studies. An EF covers a specific temporal, geographic and technical scope. For example, emission factors for the average French electricity mix apply only to France and vary by year. Therefore, one must always ensure to choose the EF best suited to the situation.
Selection of emission factors
Not all EFs are of equal quality, so they must be carefully chosen to achieve accurate. In general, the broader an EF's scope, the less precise it is, and vice versa.
Thus, when choosing EFs, the organization should:
Choose or develop EFs of the best possible quality, in accordance with the various criteria stated above.
Document and keep all EFs used, including notably their source, units and theuncertainty associated (all characteristics), related documents (DB documentation, sources used, etc.) and any other information deemed relevant, to ensure that these emission factors are traceable and comparable from year to year.
Balance efforts: Seeking or developing a very precise EF for an emission source is often resource-intensive. It is important to carefully select EFs for significant emission sources. Focusing on action and reduction of significant emissions is at the heart of the Bilan Carbone®.
Data collection matrix
This documentation of emission factors is carried out alongside the documentation on the activity data used, notably by indicating all this information within the data collection matrix, which allows assigning the corresponding AD and EFs.
The different types of emission factors
The various scenarios an organization will encounter when selecting emission factors are detailed below.
EFs from databases
A number of EFs are available in databases (DBs), some of which are listed in the following section.
🔎 The reference database for France is the Base Empreinte® of the French Environment and Energy Management Agency (ADEME, French Public Agency for Ecological Transition).
Here are a number of elements to consider, which should be taken into account by the organization in order to choose the best possible EF in a DB. These selection elements may be the responsibility of the organization or of the DB (but the organization is responsible for its choice of DB). When multiple EFs are available for the same emission source, the organization should refer to these elements to decide.
EFs developed by the organization
In the case where no EF is available for the considered emission source, or to improve the precision or representativeness of an EF, the organization can:
Approximate this emission source to another emission source that would be similar. This degrades the representativeness of the EF and will result in less precise quantification. The organization should therefore use a uncertainty higher than that of the chosen similar EF.
Develop its own emission factor for the considered emission source.
To develop an emission factor, the organization must carry out a relevant life cycle analysis (LCA) and use the "Climate Change" indicator. Note that it is necessary to follow the methodological recommendations for creating EFs from the DB most used by the organization to maintain consistency among the EFs used.
Following the LCA, the emission factor will in principle be as representative and precise as possible, because specific to the organization's emission source. Uncertainty stemming from the LCA must be associated with the obtained EF.
If this is not possible, the organization may develop its own EF from, for example, the different raw materials used to create the product (via their respective EFs) or from the carbon accounting of the product manufacturer. In the case of a product that requires machining, manufacturing or assembly phases, the organization may increase the EFs of the different raw materials by a certain percentage to account for additional emissions related to these phases. In all cases, it will be necessary to assign a high uncertainty rate to this EF.
EFs in monetary ratios
Some EFs are presented as values in kgCO₂e/k€ spent, which are notably offered by several DBs. They are called "Spend-based emission factors", or "Non-specific monetary ratios".
While they have the advantage of being usable for data easily accessible to the organization (the accounting activity data from the organization's standard accounting), these EFs have two major drawbacks in carbon accounting:
There are very few of them, and they are derived from averages over many products, and are therefore associated with very high uncertainties. They are also sensitive toRegarding the sub-item “Goods and materials in a spend-based approach”, in the case where the organisation would use spend-based ratios, it may adjust these spend-based ratios according to the and not always representative of the activity. For example, the monetary ratio "land transport" in kgCO2e/k€ can be used for any land vehicle in the same way, whereas cost is not representative of differences in GHG emissions from one vehicle to another.
They do not allow tracking the impact of actions from one assessment to another. With an assessment calculated from monetary ratios, the only decarbonization lever becomes reducing the amount of the expense. Yet responsible purchasing policies (local, sustainable purchases) are often more costly, which will lead to an increase in the assessment if these purchases are accounted for via monetary-ratio EFs.
An organization can create its own monetary ratio, for example based on the carbon accounting of its stakeholders. These EFs are called "Specific spend-based emission factors". However, even if the associated uncertainties are low (monetary ratio developed specifically for an emission source), this does not allow fine management of actions, because the only decarbonization lever becomes reducing the amount of the expense.
It is therefore strongly recommended to not resort to EFs "Monetary ratios". These EFs may possibly be used for the following emission sources:
Use of service activities and intellectual services (lawyers, consulting, etc.), but the organization will need to develop "Specific monetary ratio" EFs as it matures.
Non-significant emission sources, and for which data are difficult to access (example: small office supplies). The organization should nevertheless move away from monetary ratios for these emission sources as it matures.
In the event the organization uses monetary ratios, it can adjust these monetary ratios according to the inflation that applies to its purchases or rentals of goods and services.
Requirements for selecting emission factors
Here are different requirements to achieve in terms of EF selection for each of the 3 maturity levels.
Do you have a question about understanding? Consult the FAQ. The method is living and therefore likely to evolve (clarifications, additions): find the track of changes here.
Last updated