Higher load factors and less premium-class seating could make air travel far more efficient, according to a University of Oxford study.

Aviation is widely recognised as a hard-to-abate sector. Although there are mandates in place for the use of sustainable aviation fuels and much research into hydrogen-powered and electric aircraft – as well as other designs and technologies including blended wing aircraft – much of these remain in the early stages.

In an international study led by the university, researchers set out to discover what impact could be made to reducing aviation’s carbon emissions by simply using planes more efficiently. For instance, this could be by ensuring they aren’t flying with empty seats by scaling back on premium-class seating and replacing older, inefficient aircraft models with more modern ones.

Milan Klöwer, Natural Environment Research Council independent research fellow at the University of Oxford, said: “Aviation is responsible for 2-3% of global CO₂, but its contribution to global warming is about 4% when secondary effects like condensation trails (which trap heat) are factored in. This impact is dominated by rich people flying frequently, often long-haul in business and first class or even private.”

For their study, the research team assessed carbon dioxide efficiency across 27.5 million flights in 2023 using data from Airline Data, International Civil Aviation Organisation and the International Air Transport Association.

Klöwer said: “Efficiency in aviation is often thought of as an engineering challenge: how much thrust an engine generates for a given amount of jet fuel. But operational efficiency – the amount of passenger-kilometres per unit of CO₂ emitted – has received far less attention.”

The results show wide variation in emissions, ranging from 32 to 890 grams of carbon dioxide per passenger kilometre depending on the route, and from 60 to 360 grams depending on the aircraft model.

The most efficient flights – below 100 grams per passenger-kilometre – are particularly found on high-volume routes.

The differences in efficiencies, according to the researchers, can be explained by the share of occupied seats, the aircraft models used on a route (with Boeing 787 Dreamliner and Airbus 320neo found to be the most efficient) and the cabin layout, especially the space allocated for business and first class.

The conclusion drawn is that operating all routes at their demonstrated optimum could cut emissions by 10.7%.

They also calculated that for all flight routes – by airline, aircraft model and airport – the efficiency gains could reduce aviation’s climate impact by more than half.

To illustrate the potential of the efficiency gains that could be made, they modelled a few hypothetical scenarios – for instance, the impact of an all-economy cabin layout. 

Klöwer said: “Business and first class seats are up to five times more CO₂-intensive than economy seating because they occupy far more space per passenger. Operating all aircraft at the manufacturer’s maximum seating capacity would reduce global aircraft emissions by between 26% and 57%.”

Based on their findings, the researchers are calling for new policies and changes to current policies to accelerate efficiency gains in aviation.

Their study – Large carbon dioxide emissions avoidance potential in improved commercial air transport efficiency – has been published in the journal Nature. 

Earlier this month, US aerospace manufacturer Natilus unveiled a double-decker version of its Horizon blended-wing aircraft that it claims will enter commercial service in the early 2030s.