Carbon dioxide is only part of the story
Carbon dioxide comes to mind first when aviation’s climate impact is calculated, because it is directly proportional to the kerosene burned and straightforward to compute. Yet a significant share of aircraft climate impact comes from non-CO2 mechanisms. Nitrogen oxides emitted at altitude alter atmospheric chemistry; water vapour in the exhaust forms condensation trails under the right humidity and temperature conditions, which can develop into cirrus cloud; particulate emissions both seed that cloud formation and affect local air quality. Some of these effects are short-lived but strong, which makes comparing them with carbon dioxide on a single scale difficult.
Is SAF really zero-emission?
Sustainable aviation fuels still produce carbon dioxide when burned in the engine; the gain lies in the fuel’s life cycle, not at the exhaust. The feedstock of a biomass or waste-derived fuel may have drawn carbon from the atmosphere while growing, and in synthetic fuels the carbon may have been captured directly from air or from an industrial source. The net benefit only appears once the whole chain — feedstock production, conversion and distribution — is accounted for. The phrase “zero-emission fuel” is therefore technically wrong; the right question is how much reduction a particular production pathway delivers across its life cycle. SAF also does not automatically remove non-CO2 effects such as nitrogen oxides and contrails, although lower particulate content can reduce contrail formation on some pathways, depending on fuel composition.
Where the measurement happens: engine, flight, airport
Aviation emissions cannot be assessed at a single scale. At engine level, combustor conditions determine how emissions form. At flight level, altitude and power setting change both the total released and where in the atmosphere the effect occurs. At airport level, the landing and take-off cycle governs local air quality. Prof. Dr. Yasin Şöhret’s work spans all three scales, including a study of the environmental and economic aspects of aircraft emissions at Antalya International Airport and an analysis of how air pollution from commercial flights in Turkey changed during the COVID-19 period.
Life-cycle and enviroeconomic assessment
The environmental performance of a technology cannot be measured by its emissions at the point of use alone. Life-cycle assessment accounts for every stage from feedstock production through manufacturing, use and maintenance, making a genuine comparison of alternatives possible. Adding a monetary value for environmental impact — the enviroeconomic approach — also makes the cost dimension of engineering decisions visible. Şöhret’s work includes life-cycle assessments of the maintenance process of a training aircraft and of a piston-prop engine, alongside enviroeconomic analyses of turbofan and turboprop engines.
Where the standards are set
International standards on aviation’s environmental impact are prepared within the Committee on Aviation Environmental Protection (CAEP) of the International Civil Aviation Organization, a United Nations agency. Noise and emission certification criteria, fuel efficiency standards and carbon offsetting mechanisms are all shaped in that framework. Prof. Dr. Yasin Şöhret has served on this committee on behalf of the Republic of Türkiye since 2023.
