Open Source vs Proprietary Emission Factors

When calculating a carbon footprint the accuracy of your activity data is only half the story. The other half is the emission factor that converts litres or pounds into kilograms of CO₂e. Choose the wrong factor set and the most meticulous meter readings will still produce shaky numbers. That is where the “open-source versus proprietary” debate flares up. Should you stick with freely available libraries such as the UK Government’s GHG Conversion Factors, or licence a commercial database such as ecoinvent or GaBi?

Below is a framework finance-sustainability teams can use to decide which route best fits their budget, audit expectations and reporting scope.

1 Understand what “open source” really means

Open-source factor sets are publicly released under permissive licences. The 2025 UK Government conversion factors, for example, are available under the Open Government Licence v3.0, allowing free use and redistribution as long as you cite the source. The US EPA’s Emission Factors Hub follows a similar model, providing annual updates that anyone can download and apply. These datasets cover common activities: fuel combustion, purchased electricity, basic transport modes, and include clear methodology papers.

Crucially, “open source” does not imply lower quality. Government and inter-governmental libraries usually undergo peer review and public consultation. What they sometimes lack is deep sector coverage or cradle-to-grave life-cycle details.

2 Know what you pay for with proprietary data

Proprietary factor databases charge annual licence fees: ecoinvent’s corporate licence starts at around CHF 4,500 per year. In return they offer:

• Breadth and granularity – tens of thousands of processes across energy, chemicals, agriculture and more.
• Regular updates beyond headline revisions – some providers issue quarterly patches.
• Life-cycle inventory depth – cradle-to-gate factors for specific materials or technologies.
• Technical support – analysts who can explain boundaries or help integrate factors into LCA tools.

If you design products, compare production methods or need Environmental Product Declarations, this depth can be indispensable. For a service-heavy company with modest Scope 1 and Scope 2 emissions, the extra granularity may add cost without material benefit.

3 Transparency versus black-box risk

Audit-readiness hinges on evidence. Open-source libraries publish underlying methodology papers, version histories and change logs. The 2025 UK set lists every major adjustment, from updated grid intensity to revised refrigerant factors, on a single PDF. Proprietary vendors usually summarise changes but keep raw calculations behind paywalls. If an auditor asks you to show the arithmetic that produced a factor, you may need to request a letter of representation from the vendor.

Ask three transparency questions before you sign any licence:

Can I share the factor value in my public report?

Does the licence allow me to give auditors full visibility?

Is a public methodology document available on request?

If the answer to any question is “no”, budget extra time (and cost) for the assurance process.

4 Licence terms and downstream users

Open-source factors impose few restrictions. Proprietary licences often limit how and where you can use or redistribute data. For example, sub-licensing ecoinvent data through a SaaS platform demands a specific tool-provider agreement. If your finance system shares carbon calculations with suppliers or customers, confirm that your licence permits downstream disclosure. Otherwise, you risk breach of contract or expensive upgrade fees just when your Scope 3 engagement programme gains momentum.

5 Coverage gaps and hybrid strategies

No single factor library covers everything. Typical gaps include:

• Emerging technologies (e-fuels, green hydrogen).
• Niche geographies (small island grids).
• Supplier-specific data (intensity factors or product LCAs).

A hybrid strategy solves this. Use open-source factors as the default backbone. Layer proprietary factors where the open set lacks detail or where materiality demands precision: often in purchased goods, capital goods and complex logistics. Emitrics’ factor engine lets users assign a hierarchy: open-source default → proprietary override → supplier-specific factor. The platform then applies the most granular available factor automatically, keeping evidence linked to each transaction.

6 Cost-benefit calculus

Before paying for data, calculate the financial impact of greater accuracy:

• Investor perception – does improved factor precision move the footprint enough to influence ESG ratings or borrowing costs?
• Customer demands – are key buyers asking for product-level LCAs that only proprietary libraries supply?
• Internal decision-making – will better visibility change capital-allocation or procurement choices?

If the answer to all three is “no”, start with open-source and revisit the discussion annually.

7 Governance and version control

Whether you choose open or proprietary, rigorous governance is non-negotiable:

• Freeze the factor set per reporting year so numbers remain comparable across quarters.
• Store publication dates, GWP basis and boundaries alongside each factor.
• Track overrides – note when a proprietary or supplier factor replaces the open default.

Tools such as Emitrics automate these controls, but a structured spreadsheet can work for lean teams.

Common pitfalls and how to avoid them

• Assuming price equals quality – many proprietary sets draw heavily on open data, adding modelling rather than primary measurement.
• Ignoring licence fine print – sub-licensing restrictions can derail supplier-facing dashboards.
• Mixing factor bases – combining AR4, AR5 and AR6 GWPs without adjustment skews totals.
• Delaying decisions until audit time – factor provenance questions are easiest to answer when evidence is captured at source.

Quick wins you can action this week

• Download the 2025 UK conversion factors and log the Open Government Licence details in your evidence archive.
• Request a sample dataset and draft licence from your preferred proprietary provider; compare coverage side by side.
• Add a “Factor Source” column to your emissions spreadsheet, noting whether each line is open, proprietary or supplier-specific.

Conclusion

Choosing between open-source and proprietary emission factors is not an either-or dilemma but a strategic trade-off between transparency, coverage and cost. Open libraries deliver audit-friendly documentation at zero licence fee, while proprietary databases unlock deeper sector detail and support complex product analyses. Map your material categories, assess stakeholder expectations and adopt a hybrid hierarchy that balances rigour with budget discipline. Get the governance right and you can trust whichever factor sits behind each tonne.

Emitrics integrates both open and proprietary libraries, applies the right factor automatically and stores the audit trail in one place, so you focus on reduction, not reconciliation.