Air transport is the mode of freight transport with the highest emissions per unit of cargo moved. According to the GLEC Framework v3.1, emissions associated with air transport range between 500 and 700 grams of CO₂ equivalent per tonne-kilometre, a value significantly higher than all other transport modes. This figure can be explained by a combination of factors: the high energy intensity required for flight, the exclusive use of fossil fuels such as Jet A-1, and the low specific weight of the goods transported—typically high-value, perishable cargo moved in relatively small load units.
Less than 1% of global tonne-kilometres (Eurostat) is transported by air, yet despite this marginal share of total volumes, the environmental impact of aviation remains substantial precisely because of its very high emissions per unit transported. This leads to an apparent paradox: a mode used very little in terms of tonne-kilometres nonetheless contributes significantly to logistics-sector emissions.
It is also useful to distinguish between domestic and international flights: the share of freight moved on domestic flights is minimal, so it is reasonable to assume that almost all of that 1% refers to international traffic.
From an emissions perspective, this distinction further complicates the allocation of impacts. Adding to this is an important methodological aspect: around 80% of air freight travels in the belly hold of passenger flights, often representing a marginal use of available cargo capacity and not significantly influencing the aircraft’s total load, which would fly anyway for passenger transport. The weight of freight is generally negligible compared to the total weight of the aircraft, including passengers and baggage, making it difficult to precisely quantify the specific impact of cargo alone in aviation.
At global level, air cargo generates roughly 5% of logistics-sector emissions, which itself accounts for about 8% of global greenhouse gas (GHG) emissions (GLEC Framework v3.1; Smart Freight Centre).
Several international strategies have been introduced to tackle this challenge. Among these, the inclusion of air transport in the EU Emissions Trading System (EU ETS) is a key regulatory lever, aimed at encouraging lower-impact practices through economic incentives. In parallel, the adoption of Sustainable Aviation Fuels (SAF) is considered one of the main pathways to decarbonizing the sector. However, widespread uptake is still hindered by high production costs (up to three times higher than Jet A-1), limited volumes and restricted availability at major airport hubs.
Another innovative instrument is the Book & Claim mechanism, described in specific Smart Freight Centre publications dedicated to aviation. This system allows the certification of SAF use even when the fuel is not physically used on the flight to which the credit is attributed, overcoming certain logistical barriers in distribution. Although consistent with the GLEC Framework approach, Book & Claim is covered in separate technical documents on market-based measures.
An often underrated factor is the role of so-called belly freight, i.e., cargo transported in the hold of passenger aircraft. This practice is logistically efficient because it enables unused space—otherwise occupied only by baggage or ancillary passenger equipment—to be leveraged for freight transport, without the need for dedicated cargo flights.
From an environmental standpoint, belly freight generally results in lower emissions compared to dedicated cargo operations, precisely because it makes use of passenger flights that would operate anyway. Emissions attributed to this type of cargo are therefore “shared” rather than “additional,” and freight benefits marginally in terms of climate impact.
However, current reporting methods based on tonne-kilometre metrics may not fully capture this reality. Future methodological standards should therefore distinguish more clearly between shared and additional emissions, recognizing the environmental efficiency of belly freight compared to dedicated cargo flights.
In conclusion, although air freight represents only a small share of total volumes, its environmental impact is significant and calls for targeted action. Instruments such as the EU ETS, SAF adoption and Book & Claim offer promising avenues, but their effectiveness will depend on large-scale
deployment and methodological improvements in emissions reporting. Greater recognition of belly freight and better differentiation between shared and additional emissions will be essential for a more accurate evaluation and to encourage climate-efficient logistics practices.
