US airlines increased fuel efficiency by 3 per cent between 2016 and 2018, but industry wide carbon emissions still rose by more than 7 per cent , according to a report from the International Council on Clean Transportation.

Time reports that the increase in emissions was due to growth in air travel.

The report said airlines could improve fuel efficiency by buying newer planes and filling more seats on flights.

“We are heading off an emissions cliff right now. This is becoming even more urgent,” said report co-author Dan Rutherford.

Overall, air travel accounts for 2.5 per cent of global carbon emissions. Airline industry officials defended their efforts to reduce their carbon footprint.

“The fact is that the US airline industry is a green economic engine,” said Airlines for America spokesman Carter Yang.

“When you look at the bigger picture, the US carriers transported 42 per cent more passengers and cargo in 2018 than in 2000, and we did it with just a 3 per cent increase in total emissions.”

The report cited Frontier as the most fuel-efficient US airline, and JetBlue as the least efficient.