Revealed: how aviation emissions could be halved without cutting journeys

Climate-heating emissions from aviation could be slashed in half – without reducing passenger journeys – by getting rid of premium seats, ensuring flights are near full and using the most efficient aircraft, according to analysis.

These efficiency measures could be far more effective in tackling the fast-growing carbon footprint of flying than pledges to use “sustainable” fuels or controversial carbon offsets, the researchers said. They believe their study, which analysed more than 27m commercial flights out of approximately 35m in 2023, is the first to assess the variation in operational efficiency of flights across the globe.

The amount of carbon dioxide per kilometre flown has been falling as aircraft become gradually more fuel efficient. However, the growth in the number of flights has far outstripped this, meaning the emissions helping to fuel the climate crisis are rising. Aviation’s carbon dioxide emissions could double or even triple by 2050, according to experts.

The new analysis found that more polluting flights were common from airports in the US and Australia, particularly smaller ones, as well as in parts of Africa and the Middle East. Airports in India, Brazil and south-east Asia were dominated by less polluting flights.

Atlanta and New York were among the airports with the least efficient flights overall, almost 50% worse than the airports running the most efficient flights, such as Abu Dhabi and Madrid.

The UN’s aviation body, Icao, is relying on an “unambitious and problematic” offsetting scheme, called Corsia, to cut emissions. But it has yet to require any airline to use a carbon credit. Icao was recently accused of having been captured by the industry. The EU has set a 2030 target for airlines to use 6% sustainable aviation fuel, made from waste cooking oil or produced using electricity, but the supply of these fuels is limited and expensive.

“We are currently stuck with a global situation where there is no hope that aviation will reduce its emissions,” said Prof Stefan Gössling, at Linnaeus University in Sweden and who led the research. In contrast, he said all-economy-seat planes, 95% flight occupancy and using today’s most efficient aircraft could cut fuel use and therefore emissions by 50-75%. “That is huge,” he said, adding that it would also mean far less sustainable fuel would be needed to make flying near emissions free in the future.

“I always thought air transport was already very efficient, and that is also what airlines like to tell people,” Gössling said. “But, in reality, it’s very inefficient because of the three factors: using old aircraft, transporting people [in premium seats] with lots of space, and often having aircraft that are not really fully loaded.” In 2023, the average “load factor” – seat occupancy – was almost 80%.

The study, published in the journal Communications Earth & Environment, examined the efficiency of flights between 26,000 pairs of cities, based on the CO₂ emitted per kilometre per passenger. The analysis involved 3.5 billion passengers who flew a combined distance of 6.8tn km, equivalent to 145 return journeys to the sun. The flights caused 577m tonnes of CO₂ emissions, equivalent to the annual emissions of Germany.

The research found that the US, which is responsible for a quarter of all aviation emissions, had flights that were 14% more polluting than the global average. China, the second biggest aviation polluter, had flight efficiencies slightly above the global average, while the UK, the world’s third biggest aviation polluter, had efficiencies slightly below the average of 84.4g of CO₂ per passenger kilometre.

The emissions on specific routes varied enormously. The most efficient route was from Milan, Italy, to Incheon airport near Seoul, South Korea (31.6g CO₂/pkm). Modern, full planes with fewer premium seats are largely the reason for more efficient flights. The least efficient route was in Papua New Guinea, with the second worst from Ironwood airport to Minneapolis/St Paul in the US (805g CO₂/pkm).

“While airlines often claim that fuel savings are in their own economic interest, the reality is that many airlines continue to fly with old aircraft, low load factors, or growing shares of premium-class seating,” the researchers said.

Gössling said replacing premium seats with denser economy seating was probably the most important factor. Overall, first and business class passengers are responsible for more than three times the emissions of economy passengers, he said, and up to 13 times more in the most spacious premium cabins.

Policies to implement greater efficiency could include softer options, such as requiring airlines to disclose an efficiency rating for each route, Gössling said: “Just as with white appliances, you wouldn’t want to fly with an airline that is rated F.”

Market-based policies could involve airports charging higher landing fees for more polluting aircraft, which also worsen the air quality of local communities, he said. Finally, regulation could ban the most polluting aircraft, as has already happened in places for the noisiest planes.

The potential improvements in efficiency set out in the study, such as replacing older, more polluting planes, would involve costs, and the aviation industry already runs on low profit margins. But Gössling argued the aviation industry had got stuck in a business model that focuses on growing passenger numbers to increase profit.

Instead, he said, it could run fewer, fuller flights with higher ticket prices. He said many flights were only taken because they were so cheap: “We know that a lot of air transport demand is induced. If you increase the cost, people would just choose a different type of holiday.”

Marie Owens Thomsen, the senior vice-president of sustainability at the International Air Transport Association, the trade association for the world’s airlines, said: “Airlines have a strong self-interest to reduce fuel burn and maximise load factors. However, supply-chain failures have caused an aircraft order backlog of over 5,000 planes.” She said real progress in cutting aviation emissions lay in deploying SAF, Corsia, and modernising air routes.

Globally, flying is dominated by rich passengers, with just 1% of the world’s population responsible for 50% of aviation emissions. Only about 10% of people fly at all each year and only 4% fly abroad. Even in richer nations such as the US and Germany, only about a half and a third of people respectively take flights.

A spokesperson for ICAO said its analysis determined that operational improvements could deliver 4-11% of the carbon emission reductions needed to reach net zero, with cleaner fuel delivering over half, and innovative technologies the rest. ICAO is encouraging accelerated action by its 193 member states, he said, and welcomed all research providing new insights.