4.1 - Emissions quantification method
Why and how shall the organisation account for its emissions?
The accounting is defined as the process of collecting and using the various data necessary 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
Emissions to be mandatorily accounted for in a Bilan Carbone® are the emissions of the following gases, mostly retained within the Kyoto Protocol :
Carbon dioxide, CO₂
Methane, CH₄
Nitrous oxide, N₂O
Sulphur hexafluoride, SF₆
The hydrofluorocarbons, HFCs
The perfluorocarbons, PFCs
Nitrogen trifluoride, NF₃, not included in the Kyoto Protocol
🔎 These gases are conventionally taken into account within the main standards, notably within the Regulatory GHG Assessment, the CSRD, ISO 14064-1 and the GHG Protocol (NF₃ is not mandatory for the latter).
By contrast, a Bilan Carbone® must also include other GHGs (if these are emitted by the organisation and if data allow), notably water vapour (H₂O) related to aircraft contrails when they occur, but also 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 CO₂ equivalent" or tCO₂e (or possibly kgCO₂e, depending on the order of magnitude of emissions). A conversion must therefore be performed if different GHGs are emitted. The conversion is carried out as follows: the different emitted GHGs 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-100s are ratios: the radiative forcing associated with a certain amount of CO₂ over a 100-year period is divided by the radiative forcing associated with the same amount of the GHG in question over the same period.
In the figure above, we observe that different GHGs have very different radiative forcings which evolve over time. Some GHGs, such as CF₄ or SF₆, remain virtually indefinitely in the atmosphere 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 finite lifetime).
These GWP-100s are regularly updated by the IPCC based on various scientific studies.
Emissions from all identified emission sources must be accounted for in the Bilan Carbone®.
Because of the statistical nature of emission factors and sometimes also of activity data, the accounting of an organisation's GHG emissions remains a estimate, associated with an uncertainty inherent to the use of activity data and emission factors. In certain particular cases, and at the organisation's discretion, it may also measure certain emissions, provided the associated uncertainty is specified. Emissions from some 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 main accounting principles associated are detailed in Annex.
🔎 For more concrete information and practical examples, organisations are invited to consult the General Carbon Plan, an operational reference guide which lists:
Data usually useful
Their collection methods
Emission factors usually useful
Explanations on the concrete calculation of uncertainties
Other practical advice on carbon accounting
Sector-specific recommendations
All information on the operational boundary is documented and Do you have a comprehension question?Consult the FAQ . The method is living and therefore likely to evolve (clarifications, additions): find the.
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