Aviation is among the hardest sectors to decarbonise, with sustainable fuels and novel propulsion still years from scale. A study co-led by the University of Oxford, published in Nature Communications Earth and Environment, argues that enormous cuts are available now: analysing more than 27 million commercial flights from 2023, covering 26,000 city pairs and nearly 3.5 billion passengers, the researchers found some routes emit almost 900 grams of CO2 per passenger-kilometre, nearly 30 times the most efficient at around 30 grams.
Against a 2023 global average of 84.4 grams per passenger-kilometre, the study identifies three practical levers: operating only the most fuel-efficient aircraft, replacing premium cabins with all-economy layouts, and raising passenger loads to 95 per cent from the current average of 79. Fleet replacement with the most efficient long-haul and short-haul models alone would save 25 to 28 per cent of fuel, while denser seating and fuller aircraft would add substantially more.
Combined, the three strategies could reduce global aviation emissions by 50 to 75 per cent without cutting a single flight, and around 11 per cent is achievable immediately simply by deploying the most efficient aircraft airlines already own more strategically across existing routes. The authors argue for policies that reward efficiency, shaping both airline fleet decisions and passenger choices while longer-term technological fixes mature.