Current aviation roadmaps, which depend on replacing fossil kerosene with sustainable aviation fuel (SAF), would still push the sector past key planetary boundaries through 2050, a study in Nature Communications finds. Researchers at the University of Toulouse and partner institutions, led by Bastien Païs, report that every scenario they modeled breaches the climate change and biosphere integrity boundaries, while placing heavy demands on energy, land, freshwater and carbon dioxide (CO2) capture.
Companies buy SAF through airline programs and certificates tied to business travel, and supply is still growing, with North American production and policy moving at different speeds. For those buyers, the study's message is practical. A lifecycle emissions figure says little about the resources behind it.
How the Study Measured the Gap
The team tested roadmaps drawn from the International Civil Aviation Organization (ICAO), the Air Transport Action Group (ATAG) and the European Union's ReFuelEU Aviation mandates against the planetary boundaries framework, which sets limits on pressures such as climate change and biodiversity loss. Each boundary's safe operating space was split using two allocation methods, one based on aviation's economic weight and one on ethical grounds. The climate and biosphere breaches held under both. Nitrogen and phosphorus limits were exceeded only under the ethics-based method, and freshwater and ozone limits were respected.
The work assesses the sector as a whole and does not rank suppliers. It also leaves out aviation's non-CO2 effects, such as contrails, which the authors say means it understates the climate impact.
What Sits Behind a Carbon Score
Production pathways explain much of the spread. Biofuels tie a supplier to land and feedstock, while synthetic fuel, often called e-SAF, needs electricity to make hydrogen plus a source of captured carbon. The power source matters a great deal. In the study, e-fuel made with grid electricity carried freshwater impacts 131% higher than e-fuel made with renewable power. That gap deserves attention as synthetic jet fuel moves closer to commercial scale.
Buyers can ask suppliers to name the feedstock and pathway behind a claimed reduction, say whether the figure was measured or modeled, and for e-SAF, identify the electricity and carbon sources. Water figures mean more alongside the plant's location and supply. These are questions prompted by the research, not tests its authors ran.
Accounting Questions Run in Parallel
Cost and reporting already slow corporate demand. Findings released February 11 by the GBTA Foundation, part of the Global Business Travel Association (GBTA), an industry group, drew on 58 SAF-purchasing organizations and named uncertainty over accounting standards, cost sensitivity and limited internal readiness as barriers. A price premium is easier to defend when the environmental evidence and the reported claim both hold up, and state incentives can shift that math in some markets.
The authors conclude that fuel substitution alone cannot bring aviation within safe limits and call for pairing supply-side measures with policies that curb demand. For corporate buyers, that points toward weighing SAF purchases alongside travel policy.
