Emission Factors and Data Sources in Carbon Accounting

The emissions from the same diesel vehicle can look different depending on whether you use the VTT Lipasto, DEFRA, or IEA factor. Differences are typically a few percent, but in Scope 3 spend-based calculations, the choice of source can swing the result by ±30%. This article covers the key emission factor sources and the appropriate use case for each.

What Is an Emission Factor and Why Does the Source Matter

An emission factor is a number that tells you how many kilograms of CO2 equivalent are produced per unit of activity. The activity unit can be a litre of fuel, a kilowatt-hour of electricity, a kilometre driven, a euro spent, or a kilogram of goods.

The formula is always the same: activity quantity × emission factor = emissions.

The choice of source affects the result for three reasons. Different sources have different boundaries (does the factor include, for example, the production of the fuel, or only combustion?). Different sources use different GWP values (AR5 vs AR6). Different sources are updated at different frequencies, and an outdated factor can be 20–40% off, particularly for electricity.

For this reason, every factor must be documented: source, publication year, version, and GWP time horizon (typically 100 years). This is also the first thing a verifier checks.

Main Sources and Their Use Cases

Summarised as a practical selection guide:

Source	Use Case	Update Frequency
Lipasto (VTT)	Finnish road, water, rail, and air transport	Annual
AIB residual mix	Electricity, market-based Scope 2	Annual
IEA Emissions Factors	Location-based electricity, international benchmarking	Annual
DEFRA	General-purpose: fuels, transport, business travel, waste	Annual
EXIOBASE	Scope 3 spend-based, sector-level emission intensities	Every 1–3 years
Ecoinvent	Product-level LCA, ISO 14067	Regular releases

Most organisation-level calculations use a combination of three or four sources. This is acceptable, provided the combination is documented.

Lipasto (VTT): Finnish Transport Emission Factors

The Lipasto database maintained by VTT is the standard Finnish source for transport emission factors. It covers road transport (passenger cars, vans, lorries, buses), rail transport, maritime transport, and machinery.

Particularly suited for:

Calculating emissions from domestic road transport
Machinery and equipment (excavators, forklifts)
Domestic freight and passenger transport

Limitations: Lipasto factors are optimised for Finnish conditions (driving conditions, vehicle fleet). For international transport or cross-country comparisons, DEFRA or IEA is more appropriate.

AIB and IEA: Electricity Emission Factors

Different factors are used for electricity depending on whether the location-based or market-based method is applied. For more detail, see the Scope 2 article.

AIB (Association of Issuing Bodies) publishes annual European residual mix factors by country. This is the residual factor used in market-based calculations for the portion of consumption not covered by guarantees of origin. Finland’s residual mix is typically 200–350 g CO2/kWh.

IEA Emissions Factors provides country-level location-based factors and international benchmarks. This is typically used to support location-based calculations and when a national source is not available.

Finland’s national electricity emission factor is published annually by the Finnish Energy authority (Energiateollisuus ry). This is typically the primary source for location-based calculations in Finland.

For district heating, supplier-specific factors are requested directly from the heat company. Alternatively, the averages published by Energiateollisuus can be used.

DEFRA: General-Purpose Source

The GHG Reporting Conversion Factors published by the UK’s Department for Environment, Food and Rural Affairs (DEFRA) is the best-known general-purpose emission factor source. It is updated annually and covers fuels, transport, business travel, waste, water, and many other categories.

Strengths:

Annual updates with a transparent methodology
Comprehensive: tens of thousands of factors across different activities
English-language and widely cited internationally

Practical note: the factors are built for UK conditions (the electricity factor is not Finland’s factor). Use DEFRA for fuels and general operations; use AIB or IEA for electricity.

EXIOBASE and Other Input-Output Databases

In Scope 3 spend-based calculations, the activity unit is euros: how many euros have been spent in a given product or service category. The factor comes from an input-output database that describes the average emission intensity of sectors per unit of economic output.

EXIOBASE is the most commonly used research-grade source. It contains factors for approximately 200 sectors across multiple countries.

Strengths:

Enables Scope 3 calculation even when activity-based data is unavailable
Covers all sectors and value chain categories

Limitations:

Accuracy is lower than activity-based calculation, since averages do not differentiate between suppliers
Price fluctuations (inflation, currency) affect the factor
Best used for the first year’s calculation or as a supplement, not as a permanent solution

Practical recommendation: use spend-based for the initial Scope 3 calculation, then progressively shift to activity-based calculation in the most significant categories as supplier data improves.

Ecoinvent is another widely used LCA database, employed particularly in product-level calculations (ISO 14067) and EPD work. It contains thousands of unit process emission factors for raw materials and processes. Its use requires a licence and suitable software, and it is typically a consultant’s tool rather than an end-user choice for organisation-level calculations.

How to Document Your Choices for the Report

For each emission source, record at a minimum the following information, for the verifier and for use in subsequent years:

Activity name (e.g. “diesel vehicles, own fleet”)
Activity quantity and unit (e.g. “4,500 litres”)
Emission factor used (e.g. “2.67 kg CO2e/litre”)
Factor source (e.g. “DEFRA 2025”)
Factor version or publication year
GWP values used (typically IPCC AR6, 100-year GWP)
Assumptions and estimates (if the factor had to be approximated)

This table is often the most important appendix to a calculation. It is the foundation for verification, year-on-year comparability, and future updates to the calculation.

Create a single table listing every emission source (e.g. diesel vehicles, district heating, flights) along with the emission factor source and year used. This is the verifier’s first question.

Choosing the Factor Year: A Practical Rule

The most common question in carbon accounting is which year’s factor to use. The practical rule is:

Fuels and transport. Use the factor from the same year as the reporting period. If the reporting period is 2025 and the DEFRA 2025 factor has not yet been published at the time of calculation, use the most recent available version and note the exception.

Electricity and district heating. Use the factor from the same year. Energiateollisuus ry typically publishes Finland’s electricity factor around June of the following year. The AIB residual mix is also published retrospectively.

Spend-based factors. EXIOBASE does not update annually. Use the most recent available version and record the price base year (e.g. EXIOBASE 3.8, reference year 2019) so that future comparability is maintained.

GWP values. Use IPCC AR6 100-year GWP for newer calculations. If comparing to earlier years that used AR5, note the difference in the report appendix.

The year selection is documented so that the following year’s calculation can be built on the same basis. If a source is updated and the organisation wishes to switch to the new version, the comparison years are recalculated to maintain comparability.

Frequently Asked Questions

Where do I get Finland’s electricity emission factor?

The location-based factor is published annually by Energiateollisuus ry. The market-based residual mix is published by AIB as a European reference. For international use, IEA Emissions Factors is appropriate.

Can different sources be used in the same calculation?

Yes, and this is the norm. Lipasto for transport, AIB for electricity, DEFRA for other fuels and general categories. Every choice is documented.

What is the difference between spend-based and activity-based calculation?

Activity-based uses physical units (litres, kilometres, kilograms). Spend-based uses euros and sector-level factors. Activity-based is more accurate; spend-based is more practical when physical data is not available.

How often are the factors updated?

DEFRA, Lipasto, AIB, and IEA update annually. EXIOBASE updates every 1–3 years. Ecoinvent is published on a regular release cycle.

Do you have to use the latest version?

For a given reporting period, you typically use the best available factor for that year. If a factor for the previous reporting period has not yet been published, use the preceding year’s version and record the choice. Verifiers accept this practice when it is documented.

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