A new study co-led by the University of Oxford has found that global aviation emissions could be reduced by 50-75 percent through combining three strategies to boost efficiency: flying only the most fuel-efficient aircraft, switching to all-economy layouts, and increasing passenger loads.
Crucially, the study shows that around an 11 percent reduction in global aviation emissions is achievable immediately, by using the most efficient aircraft that airlines already have more strategically on routes they already fly.
Published today in Nature Communications Earth & Environment, the researchers analysed more than 27 million commercial flights in 2023, covering 26,000 city pairs and nearly 3.5 billion passengers.
This revealed enormous variability in emissions efficiency, with some routes producing nearly 900g of CO2 per kilometre for each paying passenger – almost 30 times higher than the most efficient, at around 30g of CO2 per kilometre.
“Our results clearly show that efficiency-focused policy could swiftly reduce aviation emissions by more than half, without reducing flight numbers or waiting for future fuels,” said co-author Dr Milan Klöwer, Department of Physics at the University of Oxford.
“These are tools that we can use right now.”
Globally, average aviation emissions were 84.4g of CO2 per kilometre for each paying passenger in 2023.
However, the study identifies three practical levers to reduce this figure: operating only the most fuel-efficient aircraft, removing premium-class seating to carry more passengers, and raising passenger loads to 95 percent.
The aircraft model alone was found to make a significant difference, with emissions ranging from 60-360g CO2 per kilometre for each passenger.
According to the analysis, replacing all aircraft with the most efficient models – the Boeing 787-9 (long-haul) and the Airbus A321neo (short and medium-haul) - would result in fuel savings of 25 to 28 percent.
Co-author Dr Milan Klöwer (Department of Physics, University of Oxford) said: “While economically and practically unfeasible to replace all older aircraft [in the] short term, this analysis shows the potential more efficient aircraft have in comparison to other efficiency gains.
“Realistically, this would be a long-term transition – one that could be promoted by policies that reward efficiency, so that the most efficient aircraft are favoured whenever replacement decisions are made.”
Seating configurations also matter, since business and first-class seats are up to five times more CO2-intense than economy class seats.
The researchers found that increasing passenger numbers to the maximum seating configuration for the most efficient aircraft would further reduce emissions by 22 to 57 percent.
In 2023, aircraft passenger occupancy ranged from 20 to 100 percent, with an average of 79 percent.
According to the analysis, increasing average occupancy to 95 percent would further reduce emissions by 16 percent.
If these three measures were applied globally, the study estimates that emissions could be reduced by between 50 and 75 percent – though this full reduction would require systemic changes.
Nevertheless, the analysis found that airlines could reduce emissions by around 11 percent right now by flying their most efficient aircraft on routes where they already operate.
Lead author Professor Stefan Gössling (Linnaeus University) said: “Efficiency-based policies have a great potential to curb aviation emissions, and can be in airlines’ own economic interest.
“However, the reality is that many airlines continue to fly with old aircraft, low passenger occupancies, and growing proportions of premium-class seating.”
The researchers suggest that efficiency improvements could be promoted using policy tools and market-based measures, such as emissions ratings for airlines, adjusted landing fees based on aircraft performance, and carbon intensity caps – drawing parallels to standards used in sectors like household appliances and vehicles.
The study was based on data from Airline Data, the International Civil Aviation Organization, and the International Air Transport Association.
This showed that the regions with the most inefficient flights were Africa, Oceania, the Middle East, Central Asia, and North America. The regions with the most efficient flights were Brazil, India, and Southeast Asia.