A.1 Note on uncertainty in collected data
The calculation of carbon emissions is based on the following formula:
Activity data × Emission factor = CO₂e
The data collected and entered into Carbulator may be subject to inaccuracies related to their reliability. These uncertainties in data quality can arise from various sources, such as human error, estimates, extrapolations, or partial information. This uncertainty affects the reliability and accuracy of the final carbon footprint results and must therefore be taken into account when interpreting them.
Accordingly, and in line with the «Méthode QuantiGES» de l’Ademe – Guide méthodologique 3ème version uncertainty related to collected activity data must be taken into account, based on the following breakdown:
- 70% Estimated data (or expert judgement)
- 30% Extrapolated data (rough calculations or extrapolations)
- 15% Secondary data (precise calculations or extrapolations)
- 5% Primary data (measurements or invoices)
To avoid requiring users to manually calculate uncertainty for each data point they enter, a median uncertainty value of 30% has been adopted. This rate is automatically applied to all activity data entered into Carbulator.
A.2 Note on uncertainty in emission factors
The calculation of carbon emissions is based on the following formula:
Activity data × Emission factor = CO₂e
The emission factors used in these calculations are sourced from various official databases, such as ADEME’s Base Empreinte. However, these factors inherently involve a degree of uncertainty, corresponding to a margin of error in the coefficients used to convert activity data (such as energy consumption or kilometres travelled) into greenhouse gas emissions. This uncertainty arises from potential variations linked to approximations, as well as geographical, technological, or temporal differences, and from the limitations of the scientific methods used to establish these factors.
A.3 Note on the Overall Uncertainty of the Carbon Footprint
In fine, l’incertitude totale d’un bilan carbone ne correspond pas à une simple moyenne des imprécisions Ultimately, the total uncertainty of a carbon footprint is not simply the average of the uncertainties associated with the data and emission factors. It results from a specific calculation: for each category, the uncertainty related to the activity data and that related to the emission factor are combined, then weighted according to the category’s actual share of total emissions.
- An item with high uncertainty but a low carbon weight has little impact on the final result.
- Conversely, a high-weight item (e.g., purchases, fixed assets, electricity outside Europe) amplifies the overall uncertainty.
- Two cumulative sources of uncertainty (e.g., estimated volume + low-quality emission factor) multiply each other’s effect.
The final result therefore reflects the actual influence of each item on the emissions inventory, rather than a crude average. This approach provides a structured estimate, with a normal margin of variation, without calling into question the order of magnitude of the calculated emissions.
«Méthode QuantiGES» de l’Ademe – Guide méthodologique 3ème version https://librairie.ademe.fr/ged/6768/guide_impact_ges__final_2022.pdf