What Makes an Airline 'Emissions-Efficient'? See the Top 10 Rankings

Skift

02-07-2025

Some airlines are becoming more efficient, but overall emissions are still growing as the sector grows. The bigger picture is how fast aviation is expanding, and what that means for the climate.
Wizz Air has been named the most emissions-efficient airline in a new climate ranking from aviation analytics firm Cirium. The Hungarian low-cost carrier emits around 54 grams of CO₂ per seat per kilometer, according to the review, which was verified by PwC and is the first of its kind in the industry.
That efficiency measure is driven by several key factors, starting with Wizz Air's relatively young fleet. The airline's planes average around four years old, and many are up to 25% more fuel-efficient than older aircraft.
Seat configuration plays a role too. Low-cost carriers typically cram more seats into each plane, which reduces emissions per passenger.
One often-overlooked detail: how long a plane spends taxiing on the ground. That process can at times account for as much as 20% of a flight's total emissions.
Cirium's ranking lists airlines that are moving to newer generation aircraft.
Total Greenhouse Gas Emissions Not Accounted For
However, the ranking does not account for total greenhouse gas emissions or the use of sustainable aviation fuel (SAF), which the industry says could cut a flight's carbon footprint by up to 80%.
Wizz Air, for example, is still one of Europe's most polluting airlines. It's also among the fastest-growing, with over 70 new planes on order.
Since 2019, Wizz Air's total emissions have nearly doubled, from 3,734,556 tonnes in 2019 to 7,962,308 tonnes in 2024, according to a report from Transport and Environment and the airline's own sustainability data.
Yvonne Moynihan, the group's ESG officer, previously told Skift that the rise in emissions is linked to the airline's rapid growth under its 'WIZZ500' strategy, which aims to double the fleet by 2033.
'This growth contributes to higher overall emissions,' she said. 'But we emphasize carbon intensity per passenger-kilometer as a more relevant metric for assessing environmental impact.'
Moynihan acknowledged that reducing emissions while expanding is a significant challenge and that deeper cuts will depend on scaling up SAF, which is still barely used across the industry.
'We are actively pursuing fleet renewal and operational efficiency,' she said. 'But broader reforms are needed across the industry to ensure success.'
Cirium excluded SAF from its 2024 analysis because it currently makes up just 0.53% of global aviation fuel use.
'SAF still emits CO₂,' said Jeremy Bowen, CEO of Cirium. 'But today it makes up a very small fraction of fuel use. In the future, if SAF use ramps up, it will be taken into account.'
How Airlines Ranked
Cirium ranked airlines by CO₂ emissions per seat per kilometer in grams.
Here are the top performers:
Wizz Air: 53.9 grams of CO₂ per seat per kilometer
Frontier Airlines: 54.4
Pegasus: 57.1
Volaris: 57.9
IndiGo: 58.2
Jetstar: 58.4
Spirit Airlines: 58.4
Scoot: 58.7
SunExpress: 59.4
Air India Express: 60.5
Another Cirium list looked at the largest airlines in the world by passengers. It then ranked them by emissions-efficiency.
Ryanair: 63 grams of CO₂ per seat per kilometer
Southwest Airlines: 68.9
Delta Air Lines: 74.4
American Airlines: 74.6
United Airlines: 75.4
Turkish Airlines: 76.9
China Southern: 78.2
Qatar Airways: 79.7
Air China: 83.3
Emirates: 84.9
Cirium told Skift that while the ranking allows for fair comparison between airlines of different sizes and fleet types, it doesn't capture the full picture, such as the total emissions growth of airlines or the climate impact of individual companies.
Skift's in-depth reporting on climate issues is made possible through the financial support of Intrepid Travel. This backing allows Skift to bring you high-quality journalism on one of the most important topics facing our planet today. Intrepid is not involved in any decisions made by Skift's editorial team.