Military jets and transport planes play a key role in global defense, but their operations consume large amounts of fossil fuel. From combat missions to routine training, the environmental footprint of military aviation is significant. Despite this, emissions from military aircraft are rarely included in national climate reports.
Aircraft release not only carbon dioxide (CO₂) but also soot, nitrogen oxides, water vapor, and sulfur compounds. These pollutants affect the climate, air quality, human health, and ecosystems. Contrails and cirrus clouds formed by military jets can have a warming effect similar to the CO₂ emissions from commercial flights.
Recently, the UK government announced plans to purchase 12 F-35A fighter jets. Some of these jets will focus on addressing a pilot training backlog. While this move is driven by defense needs and international commitments, it also has environmental consequences. More training flights mean higher fuel use and greater emissions. Fighter jets consume fuel at much higher rates than commercial aircraft.
The impact of aviation on climate goes beyond CO₂. Aircraft engine emissions influence atmospheric chemistry and cloud formation. Any strategy to reduce military aviation’s climate effect must account for both CO₂ and non-CO₂ emissions.
Sustainable aviation fuel (SAF) offers a promising solution. When produced from waste oils or residues, hydroprocessed esters and fatty acids (HEFA) fuels can lower life-cycle CO₂ emissions by 50–70% compared to fossil jet fuel. Advanced synthetic fuels, called power-to-liquid (PtL) e-fuels, may reduce emissions by more than 80%, though they are not yet widely available.
SAFs also produce fewer soot particles, reducing the formation of contrails and cirrus clouds. This could significantly lower aviation’s total climate impact. While SAFs are not yet certified as standalone fuels, blends of up to 50% with conventional jet fuel are approved for both civil and military aviation.
The F-35 jet provides a clear example of SAF’s potential. A single F-35 sortie can burn up to five tonnes of jet fuel in one hour, an amount a diesel car would consume over its entire lifetime in just a few hours. The F-35 is already certified to use blends of conventional kerosene and SAF up to 50%, with no engine modifications needed. The Norwegian Air Force successfully flew F-35s on 40% SAF blends in early 2025.
For military training flights, SAF could make a measurable difference. A 50% HEFA blend could reduce CO₂ emissions per flight by roughly one-third. Targeting flights that are likely to produce persistent contrails, such as high-altitude training in humid conditions, could maximize the climate benefit of limited SAF supplies.
Despite technical readiness, the main challenges are fuel availability and cost. Widespread adoption of SAF in military aviation will require scaling production and managing expenses. Still, SAF remains the most practical near-term option to reduce emissions while maintaining operational readiness.
The UK’s purchase of additional F-35A jets will address pilot training gaps, but it will also increase emissions. Using sustainable aviation fuels in these jets can substantially reduce their environmental impact. While SAFs will not make military aviation climate neutral, they represent a meaningful step toward lowering emissions and supporting sustainable defense operations.
As conflicts and climate change are closely linked, reducing the carbon footprint of military aviation is both an environmental and strategic priority. SAF adoption could help balance defense needs with climate responsibilities, providing a feasible path toward greener military aviation.
