Emissions and efficiency

Global commercial aviation released between 892 and 936 million tonnes of carbon dioxide in 2019, accounting for approximately 4% of the world’s net human-driven effective radiative forcing. This research analyses 27,451,887 flights operated between 26,156 bi-directional city pairs in 2023. These flights transported over 3.5 billion passengers over a total distance of 43,314,099,618 kilometres, resulting in emissions of 577,968,750 tonnes of carbon dioxide. The findings indicate a wide variation in efficiency, ranging from 32 to 890 grams of carbon dioxide per revenue passenger kilometre (RPK) across different routes.

The United States is responsible for 25% of global emissions (144.6 million tonnes), with an average weighted efficiency per RPK that is 14.3% higher than the global average. China follows as the second-largest emitter with 49.7 million tonnes and an average efficiency of 88.6 grams of carbon dioxide per RPK. Together, the 20 highest-emitting countries account for 74.9% of global air passenger transport emissions. Efficiency is found to be lowest in Africa, Australia, and Norway, while the highest efficiencies are observed in Brazil, India, and Southeast Asia. Larger airports and airlines generally demonstrate higher efficiency, with a strong correlation between RPK and total emissions.

Efficiency improvement potentials

The research identifies significant potential for emissions reductions through three primary strategies: operating only the most efficient aircraft, adopting all-economy class configurations, and increasing load factors. Observed aircraft model efficiency varies considerably; the most efficient models include the Boeing 787-900 (55.4g CO2 per RPK) and the Airbus A320neo (61.4g CO2 per RPK). If the global fleet were replaced with the Boeing 787-9 for long-haul and the Airbus A321neo for short-to-medium-haul flights, fuel savings of between 25% and 28% could be achieved.

Switching to an all-economy layout would allow airlines to carry between 26% and 57% more passengers, equivalent to a theoretical reduction in fuel use of the same magnitude. Furthermore, increasing the average passenger load factor from the 2023 level of 78.9% to 95% would further reduce emissions by 16.1%. Combined, these measures could theoretically reduce current fuel consumption by more than half. Analysis of 13,666 city pairs suggests that simply operating these routes using the most efficient configuration currently in use would reduce emissions by 10.7%.

Conclusions

As aviation continues to grow, efficiency gains become increasingly relevant for climate change mitigation. The replacement of Jet A1 with sustainable aviation fuels (SAF) does not eliminate non-carbon dioxide components, making fuel-use minimisation strategies preferable. The research highlights that while airlines often claim fuel savings are in their economic interest, many continue to operate older aircraft with low load factors or high proportions of premium-class seating. New policies and corrections, such as efficiency-based landing fees or carbon dioxide intensity caps, are recommended to accelerate efficiency gains. Current climate policies often focus on SAF adoption, but efficiency-focused measures offer a swift way to reduce fuel use without necessarily limiting transport capacity.

Methods

The efficiency model used in this study considers distance, aircraft type, and payload (including passenger and cargo weight). Data were derived from multiple sources, including AirlineData (T100I), ICAO Traffic by Flight Stage, and IATA World Air Transport Statistics. Fuel consumption is calculated for each individual flight using a physical aircraft performance model that accounts for takeoff weight and flight distance. Total fuel burn is then allocated to individual passengers and converted to carbon dioxide emissions based on a factor of 3.16. The model accounts for three levels of granularity in load factors, ranging from airline-aircraft-city pair averages to global category fallbacks.

Validation checks

The dataset covers approximately 83% of RPK and 82% of passengers compared to ICAO data, with gaps likely related to charter operators. Consistency analysis shows that the model’s load factor estimates for major airlines like Ryanair, Lufthansa, and American Airlines are within 10% of their reported figures. While validating emission intensities is challenging due to variable reporting standards, the model provides a robust framework for comparing operational efficiency across the global aviation system.

CO2 intensity cap model

A carbon dioxide intensity cap model was developed to illustrate how emissions would fall if flights were required to operate at mandated maximum intensities. Capping every flight’s intensity at the current industry average (the medium cap model) would save approximately 8.6% of emissions, or 50 million tonnes of carbon dioxide. A higher cap model, requiring the highest industry standards, could save up to 34.6% of emissions, representing 200 million tonnes of carbon dioxide. These scenarios demonstrate the considerable potential for policy-driven efficiency improvements.