Cirium Launches First Annual Airline Emissions Ranking

DALLAS — Cirium, the global aviation analytics company best known for its on-time performance (OTP) rankings, has launched its first Annual Flight Emissions Review, offering the most comprehensive and independently assured ranking of airline CO₂ emissions to date. Airways attended the virtual media briefing held this morning, when Cirium shared its emissions ranking.

For the first time, airlines are being publicly compared using consistent, flight-specific data, with calculations powered by Cirium’s proprietary EmeraldSky platform. The methodology, which has been independently assured to the highest international standard (ISAE 3000) by PwC, is being hailed as one of the most accurate public datasets on airline emissions currently available.

“This isn’t just another carbon calculator,” said Jeremy Bowen, CEO of Cirium, during the briefing. “The Flight Emissions Review sets a new standard for accuracy, giving operators, financiers, and travelers trusted, actionable insights to support sustainable decision-making.”

Methodology: Beyond Averages to Flight-Level Precision

Kevin O’Toole, Cirium’s Chief Strategy Officer, emphasized the uniqueness of the methodology, which moves away from traditional averages and instead calculates emissions at the individual flight level.

Unlike conventional models that estimate emissions based on average aircraft types and distances, Cirium’s approach factors in:

• The exact aircraft used, including its age, engine configuration, and any modifications.
• Real flight paths, including taxi times, takeoff, en route performance, descent, and taxi to the gate, measured in intervals as short as seven to eight seconds.
• Aircraft seat configurations, accounting for actual cabin layouts rather than generic multipliers for business or economy seats.

This granular modeling, cross-validated with airline data and extensive U.S. fuel burn statistics, enables unprecedented accuracy in estimating fuel consumption and emissions on a seat-by-seat and route-by-route basis.

“One-size-fits-all models can differ from real emissions by as much as 20%,” O’Toole noted. “We can now confidently differentiate the environmental impact of specific flights and aircraft types.”

Global Rankings: The Leaders in Efficiency

Mike Malik, Cirium’s Chief Marketing Officer, revealed the 2024 global rankings based on emissions intensity, measured as grams of CO₂ per Available Seat Kilometer (ASK)—a metric that captures what airlines can directly control: aircraft efficiency, seat density, and route optimization.

Top 3 Airlines with Lowest Emissions per ASK:

1. Wizz Air (53.9g CO₂ per ASK)
2. Frontier Airlines (Denver, USA)
3. Pegasus Airlines (Turkey)

Wizz Air, for example, increased flights by 4% while holding emissions per ASK flat, demonstrating the impact of newer, high-density fleets. The airline’s average aircraft age is just over five years.

Cirium also ranked the top 10 largest airlines globally by emissions efficiency, with Ryanair, Southwest Airlines, and Delta Air Lines topping the ranks.

Regional Highlights

Within North America, Frontier Airlines emerged as the most efficient carrier, followed by Flair Airlines and Spirit Airlines. In Western Europe, Wizz Air continued to dominate, while Scoot, VietJet Air, and Lion Air led the way in Southeast Asia.

In Latin America, smaller carriers like Sky Airlines and JetSMART led in emissions efficiency, driven by modern fleets and high seat utilization.

Cirium also analyzed interregional routes, with French Bee ranking as the most efficient carrier on North Atlantic flights and ZIPAIR Tokyo leading the Transpacific category.

Year-over-Year Emissions Long-Haul Improvements

One of the most striking aspects of the review is its analysis of specific long-haul routes that achieved the most significant year-over-year reductions in CO₂ emissions.

Key examples include:

• LATAM Airlines’ Lima–Mexico City route saw a 27.5% emissions reduction after switching from Boeing 767s to more efficient Airbus A320neo aircraft.
• British Airways improved its London Heathrow–Philadelphia route emissions by 21.5% by upgrading from Boeing 777s to Airbus A350s.
• Jetstar’s Brisbane–Denpasar route saw a 20.2% reduction thanks to fleet modernization.

Similar shifts were observed in medium- and short-haul routes, underscoring the importance of matching aircraft types to route lengths and optimizing seating configurations to maximize efficiency.

What Drives Efficiency?

Cirium’s analysis confirmed that the most significant factors in reducing airline emissions are:

• Fleet modernization: Newer aircraft outperform older models.
• Higher seat density: Typically, more seats per aircraft result in lower emissions per passenger.
• Route optimization: Airlines that tweak their routes and minimize taxi times can achieve further reductions.

The study deliberately excluded Sustainable Aviation Fuels (SAF) from the 2024 analysis due to their currently minimal contribution, representing only 0.53% of global aviation fuel usage. Cirium plans to include SAF credits in future editions once adoption scales meaningfully.

Q&A Highlights: Comparing Cirium to Industry Standards

During the Q&A session, I asked how Cirium’s methodology compares to established international calculators, such as the ICAO Carbon Emissions Calculator, IATA’s CO2 Connect, EPA benchmarks, and OECD datasets, particularly in terms of granularity, data sources, and transparency.

Kevin O’Toole explained that Cirium’s approach is significantly more detailed than many existing calculators. For instance, ICAO’s methodology broadly classifies aircraft without accounting for operational variations between individual aircraft.

“They average emissions across entire aircraft classes, sometimes including aircraft that are parked in the desert,” O’Toole said. “That level of aggregation hides the critical differences between specific flights and aircraft.”

IATA’s CO2 Connect is a step closer, he noted, as it incorporates airline-supplied fuel burn data, but it often averages those values. It does not track emissions at the granular, phase-of-flight level that Cirium employs.

O’Toole emphasized that Cirium’s flight-specific modeling captures real-world variables, such as taxi times, wind patterns, and load factors, which are frequently oversimplified or excluded in other calculators. “You see every single flight in our system. You can distinguish between going westbound versus eastbound on transatlantic routes because we account for headwinds and tailwinds,” he said.

Cirium’s system is also fully transparent about its data sources, leveraging EmeraldSky’s real-time flight tracking and operational datasets, many of which are already utilized by regulators such as the European Commission.

“We didn’t set out to replace the world’s standards,” O’Toole clarified. “But we realized we needed to put a stake in the ground. If you can’t differentiate between flights, aircraft, and even seats, it’s impossible to make truly sustainable choices.”

The full report will be available on Cirium’s website starting tomorrow.