GLEC Framework vs ISO 14083:2023 — how they fit together, and what you have to choose between

The framing of “GLEC versus ISO 14083” is the wrong one. GLEC and ISO 14083 are not alternatives. They sit on top of each other. ISO 14083:2023 is the methodology standard — it tells you how to allocate a transshipment between two legs, what an empty-mileage policy must look like, how to define a data quality tier, what counts as primary data. GLEC is the emission factor table — it tells you the actual number of grams of CO₂e per tonne-kilometre to multiply by. You almost always use them together. The interesting question is what you swap if you put GLEC factors under a different methodology, or what changes if you keep the methodology and swap the factor table.

I read both documents for a living. I also read the GHG Protocol Corporate Value Chain (Scope 3) Standard, which is the older methodology framework that ISO 14083 partially supersedes for the transport-chain sub-problem. The way these three things fit together is not obvious from the marketing material on any of their websites. So here is the map.

What ISO 14083:2023 actually specifies

ISO 14083:2023 is titled “Quantification and reporting of greenhouse gas emissions arising from transport chain operations.” It is a methodology standard, published by the International Organization for Standardization, and the structural cousin of ISO 14064 (organisational GHG accounting) and ISO 14067 (product carbon footprint). The full text is on iso.org/standard/78864.html.

The clauses that drive most practical decisions on a calculator build:

• §5.3 Hub and transshipment allocation. When a shipment passes through a container terminal or air cargo facility, the standard tells you how to allocate the per-handling emissions between the upstream and downstream leg, and how to treat hub-internal moves. The default is to attribute hub emissions to the leg that initiated the handling, with secondary allocation to throughput-weighted shipments.
• §6.2 Empty-mileage policy. ISO 14083 requires that empty-mileage be embedded in the per-tonne-km factor by default, with explicit declaration if the operator is claiming a Tier 2 adjustment using their own empty-running data. The policy is that the laden and empty legs of a round trip are treated as one closed system for allocation purposes, not two independent journeys.
• §7.1 Multimodal leg allocation. When a shipment moves on a sea–road combination, the standard specifies how distance, mass, and emissions are allocated per leg. The default is per-leg attribution with no fungibility — each leg gets its own emission factor, its own data quality tier, its own line in the disclosure.
• §8.1–8.4 Data quality tier definitions. This is the largest single contribution of ISO 14083 to the freight accounting field. The standard defines four tiers of data quality (default factor, modelled, secondary primary, and primary), specifies what evidence is required for each, and requires that the tier be declared per leg in the disclosure.
• §9 WTW / TTW / WTT boundary. The standard defines well-to-wake, tank-to-wake, and well-to-tank as the three reporting boundaries, with WTW as the default headline figure. CSRD and CDP both reference this clause.

What ISO 14083 does not do: it does not give you a single emission factor for a single mode. It defines what a factor must look like — what unit it is in, what boundary it covers, what data quality tier it represents — but it does not publish the numbers. That is on purpose. ISO methodology standards generally avoid publishing factor tables because factor tables go stale on a different cadence from methodology.

What GLEC Framework v3.2 actually specifies

GLEC Framework v3.2 (Smart Freight Centre, 2023, with a v4 draft circulating since late 2025) is the factor table. The full text is on the Smart Freight Centre site. What you get when you open the document:

• Per-mode emission factor tables. Container ship by TEU class (after the v3.2 segmentation split). Articulated truck by gross combined weight band. Belly cargo by long-haul vs short-haul. Rail electrified vs diesel. Inland waterway by vessel class. Each row has WTW, TTW, and WTT values in g CO₂e per tonne-km.
• Engine-type breakouts. LNG marine factors split by high-pressure dual-fuel, low-pressure dual-fuel, and steam turbine (the methane-slip-driven revision I covered in the v3.2 changes post).
• Hub and transshipment line items. A new addition in v3.2 — per-handling factors for container yard, air cargo terminal, rail-truck transfer, with electrification grade adjustments.
• Methodology cross-reference. The framework text refers explicitly to ISO 14083 throughout. The position GLEC takes is that its factor tables are designed to be used under ISO 14083 methodology, and the framework document is structured so the pairing drops in without methodology gymnastics.

What GLEC does not do: it does not invent its own data quality tier definition, it does not invent its own allocation rules, it does not invent its own WTW/TTW boundary. All of that is borrowed from ISO 14083 (and from the GHG Protocol where ISO 14083 is silent). The GLEC document is, in honest terms, a factor table with a methodology bibliography.

Where they overlap

One area: the WTW / TTW / WTT boundary definition. Both documents define these boundaries the same way and use them the same way. The GLEC factor tables are published with all three values; ISO 14083 specifies which of the three goes in which disclosure. There is no conflict here, just a clean handoff — GLEC reports the numbers, ISO 14083 says which number to report.

The hub and transshipment line item in GLEC v3.2 §9.1 explicitly references ISO 14083 §5.3 for the allocation rule it expects to be used with. So even where GLEC publishes a number, the methodology stays in ISO 14083’s lane.

Where GLEC has factors but ISO 14083 has no methodology line

One gap worth flagging. ISO 14083 is silent on the right way to handle aviation radiative forcing. The standard treats CO₂e as the reporting unit and does not require a non-CO₂ multiplier for high-altitude aviation effects. GLEC v3.2 inherits that silence and publishes belly-cargo factors without a radiative-forcing uplift. The IPCC AR6 working group has put the effective radiative-forcing multiplier between 1.7x and 3x depending on altitude and contrail conditions, but neither framework mandates that you apply it.

The practical effect: if you use GLEC factors under ISO 14083 methodology and disclose to CSRD or CDP, your aviation numbers are CO₂-only and footnoted as such. Some shipper-side carbon teams ask for a parallel radiative-forcing-included number; you can produce that, but you cannot claim ISO 14083 alignment for it. It is a parallel disclosure.

Where ISO 14083 has methodology but GLEC has no factor

And on the other side: ISO 14083 §6.2 defines the empty-mileage policy, but it expects the calculator to use a factor that has empty-running embedded. If you decide to use a primary-data Tier 3 factor — say, the actual fuel burn on the specific trip with the carrier’s telematics data — you may need to derive a per-tonne-km figure from primary fuel data, and GLEC does not give you a closed-form for that. You are deriving the number yourself, under the methodology rules in ISO 14083 §6 and §7. That is fine — ISO 14083 explicitly contemplates this case — but it is a place where the GLEC table stops being the source of truth and the methodology starts doing the work.

Worked example: same shipment, two methodology stacks

Take a shipment with two legs and a hub. Twenty tonnes from Shanghai to Munich, routed as Shanghai-Rotterdam on a 14,000 TEU ULCV container ship (19,600 km), then Rotterdam-Munich on an articulated truck >32 t (890 km), with a transshipment hop in Rotterdam (one TEU handling).

Stack one: GLEC v3.2 factors + ISO 14083:2023 methodology.

• Sea leg: 19,600 km × 20 t × 7.6 g/tkm (GLEC v3.2 container ship 8,000+ TEU) = 2,979,200 g, or 2,979 kg CO₂e.
• Hub: 1 TEU handling, GLEC v3.2 hub factor for an electrified container yard = ~3.5 kg CO₂e.
• Road leg: 890 km × 20 t × 62 g/tkm (GLEC v3.2 articulated >32 t after v3.2 lane-utilisation adjustment) = 1,103,600 g, or 1,104 kg CO₂e.
• Total, three-line disclosure: 4,086 kg CO₂e WTW. Three lines on the disclosure (sea, hub, road), each tagged with the data quality tier per ISO 14083 §8 — all Tier 1 in this example.

Stack two: GLEC v3.2 factors + GHG Protocol Corporate Value Chain methodology.

• Sea leg: same factor, same arithmetic = 2,979 kg CO₂e.
• Hub: GHG Protocol Scope 3 Category 4 guidance does not require a separate transshipment line. The 3.5 kg is either bundled into the sea-leg disclosure or omitted entirely — depends on the operator’s policy and is allowed either way.
• Road leg: same factor, same arithmetic = 1,104 kg CO₂e.
• Total, two-line disclosure: ~4,083 kg CO₂e WTW. Two lines on the disclosure, no per-leg data quality tier requirement (the GHG Protocol uses a single Quality Score per emissions category instead of per-leg tiers).

The total moves by about 3 kg on a 4,086 kg shipment — less than 0.1%. The numerical impact of changing the methodology stack while keeping the factor table constant is tiny on a single shipment. So why does anyone care?

Two reasons. First, scale. A 0.1% change on a single shipment compounds across a 50,000-shipment portfolio if the hub line gets dropped consistently — you under-disclose by 1–3% of total freight emissions, which is exactly the size of the gap the v3.2 hub breakout was designed to fix. Second, audit trail. Three lines with three data quality tier declarations holds up under CSRD assurance more cleanly than two bundled lines with a single Quality Score. The auditor can trace the factor, the distance, the mass, and the tier per leg. That is what the “assurance-ready” pitch on ISO 14083 actually buys you.

What does it cost you to switch methodology only?

If you have an existing calculator on GLEC factors and GHG Protocol methodology, what does it cost to move to GLEC factors and ISO 14083 methodology?

Three things. First, you have to add a hub line item to your data model. Most calculators that came up under GHG Protocol bundled hub emissions into the upstream leg; ISO 14083 expects it broken out. Second, you have to add a data quality tier per leg in your output schema. That is a per-line metadata change, and it propagates to anywhere the disclosure is consumed (CSRD assurance file, CDP submission, internal dashboard). Third, you have to write up a methodology disclosure that says “factors from GLEC v3.2, methodology from ISO 14083:2023” in plain language. That last bit sounds trivial but it is the most common audit-finding source I see — operators forget to declare the methodology framework and an auditor flags it.

Schema-wise: small change. Behavioural-wise: meaningful. The EcoFreight API ships the data quality tier in the response by default, which is the kind of detail you do not appreciate until you build a CDP submission and realise the C6.5a question requires it.

What does it cost you to switch factors only?

And on the other side — if you are on ISO 14083 methodology with a non-GLEC factor table (say, DEFRA, or an in-house factor table), what does it cost to switch to GLEC v3.2?

Mostly: per-shipment number changes. The methodology stays the same, the schema stays the same, the audit trail stays the same. What moves is the absolute value of the emissions per shipment, by amounts that depend on the lane and the prior factor source — typically 5–15% on UK road, 0–5% on European road, up to 10–12% on certain marine routes (especially LNG). If you migrate mid-cycle, you have to restate the prior period on the new factor base for year-on-year comparability. If you migrate at the start of a reporting year, you can disclose the change as a footnote and move on.

I covered the specific GLEC versus DEFRA factor delta in the GLEC vs DEFRA post, which is the more common factor-table migration question in practice.

The pairing most CSRD assurance providers expect

For what it is worth, the combination I see in clean CSRD assurance files through 2026 is:

• Methodology: ISO 14083:2023 with all the per-leg data quality tier declarations.
• Factor table: GLEC v3.2 (current edition), with version stamped per disclosure row.
• Boundary: WTW headline number, with TTW and WTT broken out in the underlying calculation but not necessarily in the public disclosure.
• Scope mapping: Scope 3 Category 4 (upstream transportation) for purchased freight services; Scope 1 for own-fleet road freight.

That pairing — GLEC factors under ISO 14083 methodology with the WTW headline — is what the EcoFreight calculator and API output by default. It is also what the methodology page on the site documents. You can override the factor source for UK-domestic disclosure (DEFRA available as a secondary table) but the methodology stack stays on ISO 14083 either way.

One honest caveat

ISO 14083:2023 is two years old. The standard is not yet uniformly implemented across the assurance market. I have seen audits in 2025 where an assurance provider applied ISO 14083 by the letter and audits in 2025 where the same provider treated GHG Protocol Quality Scores as interchangeable with ISO 14083 data quality tiers. The convergence on ISO 14083-by-default is happening through 2026 but it is not finished. If you have a specific assurance provider in mind, ask them which methodology stack they will mark cleanest. The honest answer most of them give in private is “ISO 14083 if you have it, GHG Protocol if you don’t, do not mix them on the same disclosure.” That advice has stayed stable for two years and I expect it to stay stable for at least another two.

Closing

GLEC is the factor table. ISO 14083 is the methodology. The right way to use them is together. The numerical difference between using GLEC factors under ISO 14083 versus GLEC factors under GHG Protocol is small on a single shipment and meaningful at portfolio scale. The methodology gives you the audit trail; the factor gives you the number. Skip either one and you are doing the calculation in half.

The deeper changelog on what specifically moved in GLEC v3.2 is in the v3.2 in detail post. The factor-by-factor comparison against UK DEFRA is in the GLEC vs DEFRA post. And the end-to-end calculation worked through three modes is in the worked examples post.

Sources

ISO 14083:2023 Quantification and reporting of greenhouse gas emissions arising from transport chain operations — iso.org/standard/78864.html. GLEC Framework v3.2, Smart Freight Centre, 2023 — smartfreightcentre.org. GHG Protocol Corporate Value Chain (Scope 3) Standard, World Resources Institute and WBCSD, 2011 with technical guidance updates through 2024 — ghgprotocol.org. IPCC AR6 Working Group I, Chapter 7, for the non-CO₂ aviation radiative-forcing multiplier range cited in this post. Section references throughout (§5.3, §6.2, §7.1, §8, §9) refer to ISO 14083:2023; section references §9.1 refer to GLEC v3.2 as published.

The EcoFreight calculator and EcoFreight freight emissions API default to GLEC v3.2 factors under ISO 14083:2023 methodology, with the data quality tier declared per leg in the response. The methodology changelog records every version bump in dated form. Methodology critique gets a response faster than feature requests — email the team if a number here looks wrong.