Green Aviation Fuel Math Fails to Add Up, Warn Scientists
Scientists and aviation experts have issued a stark warning that sustainable aviation fuels (SAFs) cannot be produced quickly enough or in sufficient volumes to keep pace with projected global air traffic growth. A new report reveals that even under the most optimistic scenarios, aviation emissions are unlikely to fall significantly by 2050.
The Scale of the Challenge
Aviation currently accounts for between 2 and 3 per cent of global CO2 emissions, a share that continues to rise with increasing air travel. SAFs, which include biofuels from agricultural waste and synthetic fuels made from hydrogen and captured carbon dioxide, are considered the most promising technology to replace fossil kerosene. However, the report from Aéro Décarbo and The Shift Project highlights fundamental production constraints.
BioSAF faces limitations due to finite sustainable biomass availability, with land, water, and competition from food production restricting how much biological material can be diverted to fuel. "Expanding biofuel production also risks creating additional pressure on biodiversity and water resources," the report states.
The Electricity Dilemma
E-SAF, the synthetic alternative, presents a different but equally daunting problem. Replacing all global kerosene consumption with synthetic fuel would require approximately 10,000 terawatt-hours of electricity annually – roughly one third of current global electricity production. Loïc Bonifacio, vice-president of Aéro Décarbo and co-author of the report, explained: "The limit isn't on a biological factor but rather the amount of electricity."
Even with ambitious SAF deployment projections from the Air Transport Action Group, the industry's own global body, aviation would still consume about the same amount of fossil kerosene in 2050 as it does today. "Even in this scenario, there are not enough SAF to fulfil aviation's demand, because the growth of the traffic is too high for the technological progress," Mr Bonifacio said.
Emissions Projections and Alternative Paths
The report projects that emissions would peak around 2030 before falling to just 9 per cent below current levels by mid-century – far short of Paris Agreement requirements. Alternative approaches come with significant trade-offs:
- Weakening sustainability standards to unlock more biomass would damage biodiversity and food systems.
- Diverting clean electricity from other sectors to power e-SAF production would simply shift emissions elsewhere, as electric vehicles and industry can use the same power far more efficiently.
The Only Viable Solution: Flying Less
The report concludes that the only workable path is reducing air traffic while SAF capacity builds. "To reduce emissions we need to reduce fossil fuels consumption. However as long as SAF aren't here in quantities large enough, to reduce fossil fuels consumption, air traffic must degrow," Mr Bonifacio explained.
A pathway compatible with limiting warming to 1.7 degrees would require global air traffic to fall by at least 15 per cent within the next five years – roughly back to 2010s levels. A 1.5-degree trajectory would require a 60 per cent cut by 2035.
"In practice, it means we need to discuss how much we globally use aviation and what regulations we want to put in place," Mr Bonifacio said. "A sustainable use of aviation, in our optimistic scenario, would be around 1,000 km per year and per person, around the globe."
Addressing Inequality in Air Travel
The report notes that in 2018, only 11 per cent of the global population flew at all, with 1 per cent responsible for half of commercial aviation's emissions. Moderating growth need not mean the end of affordable air travel, but the authors suggest that airport expansions, particularly in wealthier countries where flying is already widespread, should be paused until SAF capacity can support them.
"We don’t prescribe which measures should be taken, but we can legitimately question airports extensions projects, or publicity for air travels, in such a context of both climate change and geopolitical matters surrounding fossil fuels supply," Mr Bonifacio concluded.
