The [accounting ](https://www.bilancarbone-methode.com/methode-bilan-carbone-r-en/appendices/glossary#comptabilisation)is defined as the process of collecting and using the various data necessary to carry out a Bilan Carbone®.
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As a reminder, each emission source of the organisation that must be accounted for is estimated as follows:
Emission from a source = [Activity data](https://www.bilancarbone-methode.com/methode-bilan-carbone-r-en/4-accounting/4.2-method-for-collecting-activity-data) x [emission factor](https://www.bilancarbone-methode.com/methode-bilan-carbone-r-en/4-accounting/4.3-method-for-selecting-emission-factors) = [result](https://www.bilancarbone-methode.com/methode-bilan-carbone-r-en/4-accounting/4.5-emission-profile) ± [higher](https://www.bilancarbone-methode.com/methode-bilan-carbone-r-en/4-accounting/4.4-method-for-estimating-uncertainties)
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The emissions to be **mandatorily** accounted for in a Bilan Carbone® are the emissions of the following gases, largely retained within the [Kyoto Protocol](https://www.bilancarbone-methode.com/methode-bilan-carbone-r-en/appendices/glossary#protocole-de-kyoto) :
* Carbon dioxide, CO₂
* Methane, CH₄
* Nitrous oxide, N₂O
* Sulphur hexafluoride, SF₆
* The [hydrofluorocarbons](https://www.bilancarbone-methode.com/methode-bilan-carbone-r-en/appendices/glossary#h), HFCs
* The [perfluorocarbons](https://www.bilancarbone-methode.com/methode-bilan-carbone-r-en/appendices/glossary#p), PFCs
* Nitrogen trifluoride, NF₃, not included in the Kyoto Protocol
> :mag\_right: *These gases are classically taken into account within the* [*main standards*](https://www.bilancarbone-methode.com/methode-bilan-carbone-r-en/appendices/bibliography#ressources-sur-la-comptabilisation)*, notably within the Regulatory GHG Assessment, the CSRD, the ISO 14064-1 standard and the GHG Protocol (NF₃ is not mandatory for the latter).*
Conversely, a Bilan Carbone® **shall also include** other GHGs (if these are emitted by the organisation and data allow), notably water vapour (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). A conversion must therefore be performed 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-100 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.
Figure 4.1: Radiative forcing (W/m²) over time (years) of one tonne of different GHGs, on a log-log scale. Source: D. Hauglustaine, LSCE
In the figure above, we observe that different GHGs have very different radiative forcings which evolve over time. Some GHGs, like CF₄ or SF₆[^1], 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 lifetime coming to an end).
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These GWP-100 are regularly updated by the [IPCC ](https://www.bilancarbone-methode.com/methode-bilan-carbone-r-en/appendices/bibliography#evolutions-climatiques)based on various scientific studies.
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Emissions from all [identified emission sources](https://www.bilancarbone-methode.com/methode-bilan-carbone-r-en/2-scope-of-the-approach/2.4-operational-boundary#identification-des-sources-demissions) shall be accounted for in the Bilan Carbone®.
Due to 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 [higher](https://www.bilancarbone-methode.com/methode-bilan-carbone-r-en/4-accounting/4.4-method-for-estimating-uncertainties) 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 shall be to **minimise the uncertainties** associated with emissions.
Each emission source must then be integrated within one of the [Bilan Carbone® categories](https://www.bilancarbone-methode.com/methode-bilan-carbone-r-en/4.5-emission-profile#profil-demission-au-format-bilan-carbone-r). The definitions of the categories, of the emission sources they include, and of the main accounting principles associated are detailed in [Annex](https://www.bilancarbone-methode.com/methode-bilan-carbone-r-en/appendices/appendices/appendix-1-main-accounting-principles-of-bilan-carbone-r).
> :mag\_right: *For more concrete information and practical examples, organisations are invited to consult the* [*General Carbon Plan*](https://www.bilancarbone-methode.com/methode-bilan-carbone-r-en/appendices/bibliography#plan-carbone-general)*, a reference operational 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*
***
*Do you have a comprehension question?* [*Consult the FAQ*](https://www.bilancarbone-methode.com/methode-bilan-carbone-r-en/appendices/faq)*. The method is living and therefore likely to evolve (clarifications, additions): find the* [*track of changes here*](https://www.bilancarbone-methode.com/methode-bilan-carbone-r-en/foreword/history-and-tracking-of-changes)*.*
[^1]:
