Double counting risks and incomplete documentation in global accounting of emissions reductions from SAF

5th August, 2025

The environmental integrity of using SAF to reduce emissions from aviation is at risk if the current regulatory reporting system is not improved or properly implemented. In a new report, AEF identifies potential risks of double claiming and a lack of transparency in the way that emissions reductions are traced through the complex international chain of custody.

The most pressing concerns are:

1. Double claiming: If an airline reports Scope 1 reductions while a corporate buyer claims the same SAF usage under Scope 3 (under SBTi for example), total carbon savings may be overstated.
2. Double claiming:  International flight Scope 1 reductions are excluded from national inventories (NDCs), yet the same reductions could appear under Scope 3 claims in corporate inventories.
3. Risks of regulatory overload as potentially thousands of SAF claims are due to hit national regulators in the next few years.
4. Systems for tracking emissions savings – particularly across borders – are not fully developed or aligned, with overlapping frameworks, and incomplete paperwork trails.
5. Potential for consumers and corporate buyers to be confused about the nature of the multitude of emissions savings claimed by actors across a complex international value chain.
6. The absence of clear ICAO guidance to states on how to account for SAF and meet UNFCCC reporting requirements. These need to be fixed before adopting Book and claim systems.
   

AEF, with the help of the Sustainable Energy Systems Research Centre at the University of Bath, has mapped out the full international carbon accounting journey associated with so-called Sustainable Aviation Fuels. 

AEF wanted to better understand the journey of where claims of emissions reductions from using SAF are accounted for – whether at source where waste oils and residues from agriculture are used to produce feedstock for biofuels, or whether it is when the fuel is produced in a refinery, or when it is burnt on an aeroplane. Carbon accounting methods are often selected by the need to attach responsibility for emissions to a particular actor within the supply chain, but with a variety of methods to do this, the research found multiple potential points where competing actors could count that emissions reduction for their own inventory. This could be through a country’s national level carbon inventory, by the fuel producers and suppliers under a mandate, by airlines and airports under compliance schemes, or through voluntary corporate carbon reduction initiatives.

SAF has been suggested as one of the key pathways for reducing emissions, however it is not a low carbon fuel. It still produces as much CO₂ when combusted as kerosene. The emissions savings come from the fact that rather than using fossil CO₂ which has been stored away from the atmosphere for millions of years, it uses CO₂ already in the atmosphere as part of its production process. This theoretical “closed loop” could produce a 70% emissions saving across the lifecycle of the fuel, but these emissions savings need to be constantly assessed in the real world and not merely assumed. 

While a number of robust legal frameworks do exist, the report highlighted the immense complexity of these interwoven systems across multiple geographies. AEF found one of the biggest concerns was that regulators and verifiers may become overloaded as a significant increase in the number of claims is expected in the next few years. Of particular concern is the incomplete systems of documentation which should prove that an emissions reduction has only been claimed once. For example, the Refuel EU SAF mandate requires that ‘Proof of compliance’ certificates should be used only once to show that an emissions saving has been “banked”, however the system for producing these certificates has faced teething troubles. At the same time, there are multiple competing national registries (which list the batch number and blend of any SAF which has been sold on the market), and an EU-wide registry has faced delays. The compliance module of the global airline trade association IATA’s registry is not yet fully operational. These registries do not all measure carbon savings in the same way – there are thought to be about 60 different blends of SAF and feedstocks and multiple methodologies for calculating emissions savings.

A further concern relates to a number of voluntary schemes which may lead consumers or corporate to become confused about the nature of where the emissions saving takes place. Heathrow Airport for example is currently running a scheme to incentivise airlines to buy SAF with a goal of ensuring that 3% of fuel at the airport is SAF, but transparency is needed regarding how that is calculated and enforced in the wider carbon accounting framework. There are also multiple schemes where corporate travellers can claim Scope 3 emissions reductions in voluntary carbon market schemes (VCMs), but these same emissions savings may be claimed by airlines under their Scope 1 responsibilities. Airlines can also trade SAF certificates through a so-called “Book and claim” system, which works a bit like the renewables market, where companies can pay for SAF to be used somewhere in the global supply chain, but that might not actually be delivered to the aircraft they operate.

Tim Johnson, AEF’s Director, said:

Consumers would be right to be confused about these complex global supply chains and to worry that when an airline says SAF has been used in its operations, whether that has led to an actual carbon saving somewhere in the system. These global supply chains are fiendishly complex and risk running ahead of our ability to ensure real-world emissions savings.”