A new study co-led by the University of Oxford has found that global aviation emissions could be reduced by 50 to 75% by flying only the most fuel-efficient aircraft models, switching to all-economy layouts, and increasing passenger loads to 95%.
The study was published in Nature Communications Earth & Environment and co-authored by Dr Milan Klöwer, a research fellow in the Department of Physics. It showed that a 10.7% reduction in global aviation emissions is achievable immediately, by using more efficient aircrafts on more strategic routes.
Data collected from Airline Data, International Civil Aviation Organization, and International Air Transport Association was used to analyse almost 27.5 million flights, transporting over 3.5 billion passengers over a total distance of over 43 billion kilometres – a distance equivalent to 145 return journeys to the sun. These flights emitted a total of 577 million tonnes of carbon dioxide. Business and first class seats were found to be up to five times more CO2-intensive than economy class seats.
20 countries accounted for 74.9% of global emissions from air passenger transport, with the United States, the highest, responsible for 25% of global aviation emissions. Efficiency was lowest in Africa, Australia, and Norway, and highest in Brazil, India, and Southeast Asia. Dr Klöwer told Cherwell that the least efficient airlines, according to his research, were United Airlines, Delta, and Air Algerie.
The study found that the most efficient aircraft model was the Boeing 787-900, and that replacing aircraft with models like the Boeing 787-900 for long-haul flights and the Airbus A321neo for medium and short-haul flights could result in fuel savings of 25 to 28%. Due to predicted “robust growth” of the industry over the next 20 years, the study called for serious changes to reduce fuel use without limiting air transport capacity.
Dr Klöwer told Cherwell that whilst aviation is only responsible for 2 to 3% of annual CO2 emissions, its contribution to global warming is at 4% higher due to secondary climate effects like condensation trails. Dr Klöwer told Cherwell: “this contribution to global warming is dominated by rich people flying excessively, often long-haul in business and first class or even private.”
The study highlighted that “aviation’s climate impact continues to grow, with little progress toward emission reductions aligned with global targets”. Factors affecting this growth include the expansion of airlines, airports, and the role of subsidies, as well as patterns of flight distribution and the influence of frequent fliers on demand generation. As demand growth has outpaced efficiency gains in the past, aviation emissions will continue to rise unless new technologies, including sustainable aviation fuels (SAF) become available on a large scale.
Concern was expressed over Airbus’ recent decision to delay work on hydrogen-electric aircraft, as well as the technical and economic barriers to e-fuel production and the cost and production limits to SAF. The researchers found it unlikely that the sector will decarbonise in line with global climate stabilisation objectives. Airlines have recognised that fuel savings are in their own economic interest, yet continue to fly with old aircraft, with many aircrafts operating for 25 years.
Four methods for optimising fuel consumption were suggested. The first was reforms to aircraft technology and design, improving the weight and aerodynamics of aircraft and optimising engine fuel efficiency. The second was research into alternative and new fuels that could help reduce CO2 emissions. The third was reforms to aviation operations and infrastructure: optimisation of flight routes, including altitude, air traffic control systems, dynamic scheduling, efficient ground handling, airport designs, and airport congestion.
The study strongly recommended increasing passenger load to reduce fuel consumption per passenger, the most efficient method being switching to economy class only seating configurations. The final recommendation was socio-economic and policy measures. Policies that targeted emissions, such as SAF fuel quotas, landing fees, air passenger duties, and emission trading could act as incentives for airlines to operate more efficiently.
Dr Klöwer told Cherwell that “the flight emissions from some celebrities…are often 10,000x higher than for an average person from a rich country”, and that private aviation will never be as efficient as commercial flights, and is many times worse for the climate than first class.
Dr Klöwer said: “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.”
