4.1 - Emissions quantification method
Why and how to account for an organisation's emissions?
Accounting is defined as the process of collecting and processing the various data required to carry out a Bilan Carbone®.
As a reminder, each emission source of the organisation that must be accounted for is estimated as follows:
Emission from a source = Activity data x emission factor = result ± uncertainty
The emissions that must be accounted for in a Bilan Carbone® are the emissions of the following gases, predominantly retained under the Kyoto Protocol:
Carbon dioxide, CO₂
Methane, CH₄
Nitrous oxide, N₂O
Sulphur hexafluoride, SF₆
Hydrofluorocarbons, HFC
Perfluorocarbons, PFC
Nitrogen trifluoride, NF₃, not included in the Kyoto Protocol
🔎 These gases are conventionally taken into account within the main standards, notably within the regulatory GES assessment, the CSRD, the ISO 14064-1 standard and the GHG Protocol (NF₃ is not mandatory for the latter).
However, a Bilan Carbone® must also include other GHGs (if these are emitted by the organisation and data allows), notably water vapour (H₂O) related to aircraft condensation trails where they exist, as well as other GHGs sometimes used as refrigerants, in fire extinguishers or in certain industrial processes (chlorofluorocarbons, bromofluorocarbons, etc.).
A quantity of GHGs is expressed in a single unit, the "tonne of CO₂ equivalent" or tCO₂e (or possibly kgCO₂e, depending on the order of magnitude of the emissions). A conversion must therefore be carried out when different GHGs are emitted. The conversion is performed as follows: the various GHGs emitted are considered, and each quantity of GHG is multiplied by the 100-year global warming potential (GWP-100) of the GHG in question.
These GWP-100 values are ratios: the radiative forcing associated with a given quantity of CO₂ over a period of 100 years is divided by the radiative forcing associated with the same quantity of the GHG in question over the same period.
In the figure above, it can be observed that different GHGs have very different radiative forcings that evolve over time. Some GHGs, such as CF₄ or SF₆, remain in the atmosphere almost indefinitely and therefore have a high radiative forcing for thousands of years. Others, such as methane, have a radiative forcing that decreases significantly over the years (notably due to their lifetime coming to an end).
These GWP-100 values are regularly updated by the IPCC based on various scientific studies.
The emissions from all identified emission sources must be accounted for in the Bilan Carbone®.
Given the statistical nature of emission factors and sometimes also of activity data, the accounting of an organisation's GHG emissions remains an estimate, associated with an uncertainty inherent to the use of activity data and emission factors. In certain specific cases, and at the discretion of the organisation, it may also measure certain emissions, provided that the associated uncertainty is specified. Emissions from certain combustion processes can, for example, be measured using sensors.
In order to obtain the most accurate and precise estimate possible, the organisation's objective should be to minimise the uncertainties associated with emissions.
Each emission source must then be integrated within one of the Bilan Carbone® categories. The definitions of the categories, the emission sources they include, and the key accounting principles associated with them are detailed in the Appendix.
🔎 For more practical information and examples, organisations are invited to consult the Plan Carbone Général, a reference operational guide that compiles:
Commonly useful data
Data collection methods
Commonly useful emission factors
Explanations on the practical calculation of uncertainties
Other practical advice on carbon accounting
Sector-specific recommendations
Do you have a question about the content? Consult the FAQ. The method is evolving and therefore subject to change (clarifications, additions): find the change log here.
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