Same product, different carbon number: how to choose the emission factor

Two firms make the exact same product and publish their carbon footprints — one says 4, the other says 11 kg CO₂e. Which one is lying? Often neither. The difference lies not in the number itself, but in the choice of emission factor behind it. This is the least understood yet most decisive point in carbon accounting.

What an emission factor is, and why it varies

The basis of carbon accounting is simple: emissions = activity data × emission factor. Use 1,000 kWh of electricity, multiply it by a factor. The catch: there is no single “the factor.” For the same activity it varies by:

• Source: IEA, DEFRA, EPA, IPCC and national sources (ETKB in Turkey) give different values for the same thing.
• Geography: The electricity factor depends on a country’s energy mix; a coal-heavy grid and a renewable-heavy grid can differ by several times.
• Year: A grid gets cleaner or dirtier each year; an old factor doesn’t reflect today.
• Boundary: Does the factor cover only combustion, or also fuel extraction and transport (well-to-tank)?
• Basis: Net (NCV) or gross (GCV) calorific value? Location-based or market-based?

A single wrong choice — wrong country, stale year, missing boundary — skews the result systematically. And you can do it with no bad intent at all.

”Looking low” is easy

Here is the subtle form of greenwashing: not an outright lie, but picking the factor that suits you best. A firm choosing the source that yields the lowest number, the most favourable year, or the narrowest boundary can technically produce a low figure “based on a source.” The number isn’t fake — but the choice isn’t defensible. When an auditor or EU customs asks “why this factor?”, a figure with no answer collapses.

What a defensible calculation requires

The right path is not to pick the “nicest number” but the most representative factor, shown transparently:

1. Hierarchy: Supplier/site-specific real data first; then a national/regional factor; default (IPCC) factor only as a last resort.
2. Representativeness: The correct country and the most recent year available.
3. Consistency: Keep boundary and basis (NCV/GCV, location/market) the same across years.
4. Provenance: Report each factor’s source, year, geography and unit.

How we do it

At RecoChainAI a carbon result never travels alone; it carries the provenance of the emission factor it used — source, year, country and unit. The calculation is deterministic: the same input and the same factor always yield the same result, and that result is sealed in a cryptographic receipt. So our number is one we can say “came from here” — one an auditor can trace step by step.

What decides the carbon truth is not the figure you publish, but the factor choice behind it. We make that choice visible and defensible — because a carbon number you cannot defend is riskier than none at all.