4.1 - Method for quantifying emissions
Why and how to account for the organization's emissions?
The accounting is defined as the process of collecting and using the various data necessary to carry out a Bilan Carbone®.
Emissions that must be mandatorily accounted for in a Bilan Carbone® are the emissions of the following gases, mostly included under the Kyoto Protocol :
Carbon dioxide, CO₂
Methane, CH₄
Nitrous oxide, N₂O
Sulfur hexafluoride, SF₆
The hydrofluorocarbons, HFCs
The perfluorocarbons, PFCs
Nitrogen trifluoride, NF₃, not included in the Kyoto Protocol
🔎 These gases are classically taken into account within the main standards, notably within the regulatory GHG 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 organization and data allow), notably water vapor (H₂O) related to aircraft contrails when present, 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). Therefore a conversion must be made if different GHGs are emitted. The conversion is done 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 quantity of CO₂ over a 100-year period is divided by the radiative forcing associated with the same quantity 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, like CF₄ or SF, remain almost indefinitely in the atmosphere and therefore have a high radiative forcing for thousands of years. Others, like methane, have a radiative forcing that decreases significantly over the years (notably due to their finite lifetime).
Emissions from all identified emission sources must be accounted for in the Bilan Carbone®.
Due to the statistical nature of emission factors and sometimes activity data as well, the accounting of an organization's GHG emissions remains an estimate, associated with an uncertainty inherent to the use of activity data and emission factors. In certain particular cases, and at the organization's discretion, it may also measure certain emissions, provided that 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 organization's objective should be to minimize the uncertainties associated with the emissions.
Each emission source must then fit 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 Appendix.
🔎 For more concrete information and practical examples, organizations are invited to consult the General Carbon Plan, a reference operational guide that 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
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.
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