Up in the Air: Analysing The Discrepancies in Airline Emissions Reporting

PACE feature image for analysing airline emission reporting . Image of aircraft with passengers disembarking

After a few years of staycations, it was wonderful to be able to travel again. It makes you realise what a luxury these getaways are. If the data around rate of recovery in airline traffic in 2023 is anything to go by, many people share the same view.

Airline travel is statistically one of the safest modes of transport, thanks to the assurance of global standards of engineering safety and standardised operating best practice.

However, when it comes to emissions and sustainability, the aviation industry has yet to adopt the same levels of standardisation in the way it reports its impact on the environment.

At PACE we have been analysing those airlines that have reported their actual carbon emissions data in recent years and our findings on what (or in most cases what has not) been reported make for a seriously challenging read.

A Patchwork of Data with Little Transparency

In a sector with so many safety standards one might assume there are similar standards for emissions reporting, but the reality is far from it. Airlines around the world employ a variety of metrics which creates a patchwork of data as diverse as the destinations served. While some extol transparency and have been reporting for many years, the majority have been at best inconsistent or at worst, not reporting at all. PACE analysed data published over the past decade and found that only 88 airlines reported in 2022, representing less than 5% of all of AOCs 1 flying that year, and significantly less than had reported in 2017, as illustrated in Table 1.

table 1 pace analysis of airlines reporting emission data since 2017 to 2022. The number of airlines reporting in 2017 was 108 and it has dropped to 88 in 2021 and 2022.


Table 1 – PACE analysis of Airlines reporting emissions data since 2017

Absolute Emissions

Total emissions is a headline figure that both airlines and their financiers are under scrutiny to publish2. These large and hard to contextualise numbers have often been presented as CO2 measured by weight, generated by fuel burned during flight. There is an evolution towards reflecting broader environmental impacts and including the CO2 equivalent (CO2e) of the spectrum of greenhouse gases defined in the Kyoto protocol. CO2e includes full lifecycle emissions including both mining the fuel (Well to Tank) and burning it in flight (Tank to Wake), with the two stages captured as an overall CO2e Well to Wake. Once this absolute weight value is calculated comparative analysis can be made across aircraft, portfolios and operators using Intensity Based Metrics, effectively allowing comparison on an ‘apples with apples’ basis (though the devil can be in the detail).

Two frequently used examples include:

  • ASK (Available Seat Kilometer) – this is a widely reported metric because information on available seats is available commercially. CO2 per ASK allows for comparison on a per seat basis, regardless of whether the seat is occupied or not. It is not a holistic measure – a regional jet with fewer seats is likely to have a higher CO2 per ASK than a larger aircraft with a higher seat density when in reality, if travelling the same route, the total CO2 emitted by the regional jet will be lower.
  • RPK (Revenue Passenger Kilometer) – where CO2 per ASK can disproportionately favour low-cost carriers who enjoy a double whammy of high seat capacity and younger aircraft, CO2 per RPK attributes the emissions to actual “bums on seats” (rather than potentially empty chairs) and can therefore be favoured by full-service carriers.

However this “carbon language” is still very new and has not typically been used by aviation, which instead publishes data around the volume of passengers carried, volume of cargo load and the seat/passenger ratios of distances flown. The terms “traffic” and “load factor” are more commonly used.

Journey to Standardisation

The absence of a standard framework in an industry that applies such high levels of standardisation elsewhere may be resolved by regulation eventually, but in the meantime is more likely to be driven by financial market forces. These place pressure on the airlines, and a criticism by those who do report is that they have to do so in a multitude of ways depending on who is doing the asking. A consequence illustrated by Table 2 is 22 different emissions and 15 different traffic metrics reported.

Emissions Scopes\ MetricsTraffic Scopes\ Metrics

Table 2 – PACE analysis of emissions and traffic metrics reported by Airlines since 2017

Traffic and Carbon in RTK (Revenue Tonne Kilometer)

The need to incorporate load factors into meaningful comparisons of carbon emissions across all airline business models is high. RTK based metrics, including traffic and carbon emissions, is finding increasing favour, such as CO2e WtW which measures the ultimate aircraft load regardless of payload type (passengers / belly cargo / dedicated cargo).

The implementation of reporting requirements in aviation may be boosted by the recently clarified EU Taxonomy, which is intended to support positive change and makes requirements for financiers clearer. The timing of the taxonomy coincides with a number of aviation representative groups that have been developing standardised frameworks for their members.  This month we have launched PACE Academy which includes highlights of the main reporting frameworks that apply to stakeholders in aviation, including TCFD, CSRD and SFDR.

Quarter 4 of this year should see formative discussions progressing beyond RTK towards what really matters – driving change quickly enough to achieve net zero by 2050 while maintaining the accessibility of air travel for all. We look forward to it.


Rob Neale is Chief Product Officer for PACE and Head of Innovation in Fexco’s Sustainability Platform Team. Rob has 18 years of experience designing digital value-exchange platforms for Banks, Leasing companies and FinTechs. PACE Academy is available on the PACE website and is a free resource providing education on key sustainability topics affecting aviation.





[1] AOCs = Air Operator Certificates are the approval granted by a civil aviation authority to airlines for commercial aviation use
[2] Airlines include total emissions as part of Scope 1 reporting while Financiers include the same figure as their Scope 3




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