Choosing Emission Factors: IPCC 2006, DESNZ 2026, Türkiye Grid

Choosing an emission factor means getting four things right at once: the axis that matches the unit of your activity data, the country where the activity happens, the publication period that covers the inventory year, and the GWP (global warming potential) set behind the factor. For a site in Türkiye that usually means IPCC 2006 defaults for combustion, the ETKB consumption-point factor for purchased electricity, and mostly DESNZ for items such as freight and materials. Once the factor is chosen, the remaining job is to freeze the calculation together with it.

Four axes of factor selection

The most common error we see in verification is not a wrong number but a right number used in the wrong context: Turkish electricity calculated with the UK grid factor, a net-calorific-value factor multiplied by a gross value, a CO₂e figure labelled AR6 that was aggregated with AR5. What they share is that none of them throws an error in a spreadsheet.

IPCC 2006 defaults: the basis for combustion

For stationary combustion the reference is Volume 2 of the 2006 IPCC Guidelines. For natural gas, Table 1.2 gives a net calorific value of 48.0 TJ/Gg (confidence interval 46.5-50.4) and Table 1.4 a CO₂ factor of 56,100 kg/TJ (54,300-58,300). The Guidelines work on net calorific value (NCV) and state the gap plainly: for coal and oil the NCV is about 5% below the gross calorific value (GCV), and for most forms of natural gas about 10% below.

Turkish gas invoices show Sm³, the gross calorific value in kcal/Sm³ and kWh. The calorific value on the invoice is GCV, so it cannot be multiplied directly by the IPCC factor.

Example (hypothetical invoice): 100,000 Sm³, gross calorific value 9,155 kcal/Sm³, industrial site.

• Energy (GCV): 100,000 × 9,155 × 4.1868 kJ = 3.8330 TJ
• Conversion to NCV (IPCC's approximate 10% when the supplier gives no ratio): 3.4497 TJ
• CO₂: 3.4497 × 56,100 = 193,529 kg
• CH₄: 3.4497 × 1 kg/TJ × 27.0 = 93 kg CO₂e; N₂O: 3.4497 × 0.1 × 273 = 94 kg CO₂e
• Total: 193.72 tCO₂e

Skip the NCV conversion and the result is 215.2 t, 11% too high for the same invoice. If the supplier gives an NCV/GCV ratio, use it instead of the approximate 10% and record the choice in the calculation trail.

The choice of 27.0 for CH₄ is deliberate. The GHG Protocol GWP document says that methane from fossil fuel combustion should use the "non-fossil" value: the fuel's carbon is already counted in the CO₂ factor, so the fossil value (29.8) would double count. The fossil value is for fugitive sources such as oil and gas systems and coal mining, and for processes with fossil carbon.

DESNZ 2026: when to use it and what to watch

The UK Department for Energy Security and Net Zero (DESNZ) published its 2026 conversion factors on 11 June 2026. The flat file was revised on 31 July 2026 because some values with no data, including well-to-tank figures for certain hybrid, CNG and LPG cars and hotel stays in some countries, had been entered as 0. The full set was not revised. Record which file you downloaded and when.

The DESNZ set is useful where no official Turkish factor exists: road freight per tonne-km on a well-to-wheel basis, business travel per passenger-km, materials and waste disposal. Two limits apply.

The first is geography. DESNZ values reflect UK and European supply chains. The well-to-tank factor for natural gas, for example, includes the UK's LNG share. Used in a Turkish inventory, it is a geographic proxy and should be disclosed as one. For electricity it is not even a proxy: the DESNZ 2026 UK grid factor is 0.13096 kgCO₂e/kWh against ETKB's 2023 distribution consumption-point factor of 0.469. On 100,000 kWh, the gap between 13.1 t and 46.9 t is not a methodological choice; it is an error.

The second is boundary. According to the DESNZ methodology paper, waste disposal factors, landfill aside, only cover collection and delivery to the point of treatment or disposal. The emissions from the stack of the plant that incinerates your waste are not in the DESNZ combustion row; that row counts the truck journey.

GWP basis: AR4, AR5, AR6

A factor is published either per gas (kg CO₂, kg CH₄, kg N₂O) or as aggregated CO₂e. With per-gas factors you choose the GWP set. With an aggregated factor the publisher has already chosen, and you cannot undo it.

100-year values from the GHG Protocol GWP document of August 2024:

The document recommends using the latest values (AR6). The impact varies enormously by source. In the gas example above, the difference between AR4, AR5 and AR6 is under 2 kg, far below a thousandth of the total. A 10 kg SF₆ leak from switchgear, by contrast, is 228 tCO₂e with AR4, 235 with AR5 and 243 with AR6. In an inventory dominated by fugitive gases, the GWP set alone can move the total enough to trigger a base-year recalculation.

Table 1 of the DESNZ 2026 methodology paper lists which factor groups are on an AR4 basis and which on AR5. Most have moved to AR5; well-to-tank bioenergy factors are still AR4, and hotel stays are mixed by country. For refrigerants and process gases without an AR5 value, AR6 was used. If your inventory runs on AR6, you cannot "convert" an aggregated DESNZ CO₂e row to AR6, because the gas breakdown is not published. The right move is to record in the calculation trail and the report that the row is on an AR5 basis. The ETKB electricity factor, as published, does not state a GWP basis.

Türkiye's grid factor and period selection

ETKB's Energy Efficiency and Environment Department publishes a separate information form each year, "Türkiye Electricity Generation and Electricity Consumption Point Emission Factors", intended for companies' scope 2 calculations. The factors are calculated with the IEA method, and the consumption-point value already includes transmission and distribution losses. Adding a loss percentage on top of the ETKB factor counts losses twice.

Units: tCO₂e/MWh. The "Türkiye National Electricity Grid Emission Factor" used for carbon credit projects is a separate document and does not belong in a corporate inventory.

The table raises the period question by itself: a year's factor arrives about two years later. A company closing its 2025 inventory today has no 2025 factor. Use the nearest past year (2023) and disclose that the factor period differs from the inventory year. That is not an estimate; it is a declared proxy. Do not mix up connection levels either: a plant fed from the high-voltage transmission grid uses 0.436, while most consumers supplied by a distribution company use 0.469.

Freezing the calculation: factors change, reports don't

Factors change. ETKB publishes a new year, DESNZ releases a new set every year, and occasionally a published file is corrected. None of this should silently alter a past report.

A concrete case: a 2024 inventory was calculated in mid-2025. The nearest published ETKB year at the time was 2022, at 0.478. In December 2025 the 2023 factor (0.469) came out. Recalculate the electricity line with the new factor and the result falls by 1.9%. The figure in the verifier's copy of the report no longer matches the system, and nothing anywhere flags it.

To prevent that, a completed calculation has to carry the factor value, set version, source document and GWP set inside it. A calculation with the new factor is opened as a separate run. The difference is a methodology change and an input to the base-year recalculation assessment; for companies with SBTi targets, clause C8.3 of V2.0 sets that threshold at 5% per scope.

Supplier-specific factors: when to move off the default

A secondary factor is an average. If your supplier has an actual, documented value, it is usually better. Two common cases:

Electricity, market-based scope 2. The market-based result multiplies consumption not covered by certificates by a supplier-specific factor. With 100,000 kWh consumed, 40,000 kWh of YEK-G (Türkiye's guarantee of origin) and a supplier factor of 0.3 kgCO₂e/kWh, market-based scope 2 is 18.0 t; the location-based result (with the 2022 factor) is reported separately at 47.8 t. The two are never added together. Falling back to the grid average when there is no supplier factor is an assumption, and the report should say so.

Purchased goods. A supplier's product carbon footprint is more representative than a DESNZ material factor or a spend-based factor. But a number that arrives without an evidence file, a stated boundary (cradle-to-gate or not), a reference year and a GWP basis is weaker than a secondary factor, because nobody can verify it.

Negative supplier factors, certificates without evidence and values with unclear units should be rejected. A system that stops the calculation in those cases is better than one that writes zero.

How Carbolyt handles it

In Carbolyt, factors come from the IPCC 2006, DESNZ 2026 and ETKB consumption-point sets. Each set is loaded with its source document, download date and document checksum, and cannot be edited once published. The calculation engine resolves the factor by activity type, country and period; if there is no factor for the inventory year it uses the nearest year and adds a factor-period warning to the result. If no factor is found, it stops instead of writing zero. For aggregated CO₂e factors, the factor's GWP basis is shown and a warning appears when it differs from the inventory's GWP set. More on the platform page.

Completed calculations are frozen: when a factor is updated, past reports stay the same, and every line opens with its formula, factor and source table. Suppliers can be sent a form they fill in without logging in; product footprint factors arrive with an evidence file and enter the calculation once approved. The publications and timelines behind the factors are on the regulation page, and you can request a demo to try it with your own invoices.

Frequently asked questions

Which factor applies to purchased electricity in Türkiye?

For a corporate inventory (location-based scope 2), the consumption-point emission factor published by Türkiye's Ministry of Energy and Natural Resources (ETKB). For 2023 it is 0.469 tCO₂e/MWh for consumers connected to the distribution grid and 0.436 for those connected to transmission. The national grid emission factor published for carbon credit projects is a different document and is not used in corporate inventories.

How much does the choice between AR5 and AR6 change an inventory?

It depends on the source. In natural gas combustion, CH₄ and N₂O are a tiny share of the total and the difference stays well under 0.1%. For fugitive gases the GWP is the multiplier itself: 10 kg of SF₆ is 228 tCO₂e with AR4, 235 with AR5 and 243 with AR6.

What if the factor for the inventory year has not been published yet?

Use the nearest published year and disclose it. ETKB published its 2023 factors on 26 December 2025, so anyone closing a 2025 inventory today has to use the 2023 value.

Should past reports change when a factor is updated?

No. A completed calculation should store the value and source of the factor it used and stay as it is. A calculation with the new factor is a new calculation, and the difference is assessed against the base-year recalculation threshold.

Sources

1. IPCC 2006 Guidelines, Volume 2, Chapter 1 Introduction (Tables 1.2 and 1.4)
2. DESNZ, Greenhouse gas reporting: conversion factors 2026
3. DESNZ, 2026 GHG conversion factors methodology paper (PDF)
4. ETKB, electricity generation and consumption emission factors (Turkish)
5. GHG Protocol, IPCC Global Warming Potential Values v2.0 (7 August 2024, PDF)

This article is for information and is not legal advice. Dates and rates reflect the official texts at the time of publication; check the current text before acting.