Transport emissions are usually a significant part of a company's Scope 3 footprint, and customers, investors and regulators increasingly expect them to be reported on a consistent method. Two references now anchor the field: the GLEC Framework from the Smart Freight Centre and the international standard ISO 14083:2023.
The core calculation
At its simplest, freight emissions for a leg are:
Emissions = transport activity (tonne-km) × emission intensity (g CO₂e per tonne-km)
Transport activity is the cargo mass multiplied by the distance travelled. Emission intensity depends on mode, vehicle or vessel type, load factor, empty running and fuel. A full shipment's footprint is the sum of its legs, including hub and terminal operations.
Typical intensities differ by roughly an order of magnitude between modes: ocean container shipping is among the lowest per tonne-km, road is higher, and air freight is far higher. Our route planner shows an indicative CO₂e per tonne for ocean and air using representative intensities; it is a screening estimate, not a report.
Well-to-wheel versus tank-to-wheel
- Tank-to-wheel (TTW) counts emissions from burning fuel in the vehicle or vessel.
- Well-to-tank (WTT) counts emissions from producing and delivering that fuel.
- Well-to-wheel (WTW) is the sum, and is the basis required by ISO 14083 and the GLEC Framework.
The distinction matters more as fuels change. Some alternative fuels cut tailpipe emissions but carry high upstream emissions, and vice versa.
Data hierarchy
Both frameworks encourage moving from generic to specific data:
- Default values by mode and vehicle type, useful for screening and small flows.
- Modelled values using carrier or trade-lane averages.
- Primary data from carriers: actual fuel consumption allocated to your cargo.
Reports should state which data type was used for each leg. For ocean freight, carriers increasingly publish lane-level intensities calculated to recognised methods.
The regulatory backdrop for shipping
- IMO: the 2023 IMO Strategy on Reduction of GHG Emissions from Ships targets net-zero emissions from international shipping by or around 2050, with indicative checkpoints of at least a 20% reduction by 2030 (striving for 30%) and 70% by 2040 (striving for 80%), compared with 2008. Existing measures include the Carbon Intensity Indicator (CII) rating for ships.
- EU Emissions Trading System: shipping entered the EU ETS from 2024, with shipping companies surrendering allowances for 40% of verified 2024 emissions, 70% for 2025 and 100% from 2026 emissions, for voyages within, into and out of the EU (50% of extra-EU voyages).
- FuelEU Maritime: since January 2025, FuelEU Maritime limits the greenhouse gas intensity of energy used on board ships calling at EU ports, tightening over time.
Carriers pass part of these costs to shippers through surcharges, so emissions increasingly show up on freight invoices as well as in sustainability reports.
Practical steps for shippers
- Adopt ISO 14083 / GLEC as your method, and report WTW CO₂e.
- Collect shipment data consistently: weight, origin and destination points, mode per leg.
- Ask carriers and forwarders for primary or lane-level data, and record which data type you used.
- Model the trade-offs: mode shift from air to ocean or sea-air, consolidation to raise load factors, and routing choices. See air freight chargeable weight and density and FCL vs LCL.
- Budget for regulatory surcharges on EU-related lanes.
Frequently asked questions
What is ISO 14083?
ISO 14083:2023 is the international standard for quantifying and reporting greenhouse gas emissions from transport chain operations, covering freight and passenger transport across all modes and hubs, on a well-to-wheel basis.
How does the GLEC Framework relate to ISO 14083?
The GLEC Framework, developed by the Smart Freight Centre with industry, is the practical methodology and guidance for logistics emissions accounting. It is aligned with ISO 14083 and provides default values and implementation guidance.
Does the EU ETS apply to container shipping?
Yes. Since 2024, shipping companies must surrender EU allowances for emissions from voyages within the EU and for half of emissions on voyages into or out of the EU, phased in from 40% of 2024 emissions to 100% of 2026 emissions.
References
- Smart Freight Centre, GLEC Framework for Logistics Emissions Accounting.
- International Organization for Standardization, ISO 14083:2023.
- IMO, 2023 IMO Strategy on Reduction of GHG Emissions from Ships.
- European Commission, Reducing emissions from the shipping sector (EU ETS).
- European Commission, FuelEU Maritime.
Prepared by the Apex Ocean Lines industry experts and editorial team, checked against the sources cited. Short forms link to our shipping glossary.