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In the first part of our series on the decarbonization of aviation, SQUAKE’s research team published an overview of the leading climate actions of authorities and the current state of GHG emissions in the aviation sector. This chapter will focus on several of the primary carbon, and other GHG, calculation frameworks and methodologies used in the aviation industry.
Besides the global air transport industry’s resolution to achieve net-zero carbon emissions by 2050 and the negative sentiment of consumers because of the environmental impact of flying, there are also some laws that require airlines to report their greenhouse gas emissions.
Some countries within the EU, as well as the EU itself, have already introduced penalties for airlines not reporting and reducing carbon emissions. For example, Romania fines between EUR ~14K and EUR ~20.5K for false reporting of carbon emissions. The EU fines EUR 100 per ton of carbon not reported. Finally, Germany fines EUR 470 per tonne of carbon which was not reduced according to the CORSIA guidelines. Most of the reports necessary to comply can be built by the methodologies that will be introduced in this article.
There are two main approaches to the creation of frameworks, namely: historic and scientific. The landmark approach takes into account the consumed fuel and extrapolates it to the current state, while the scientific method uses physics and mathematics to forecast emissions.
There are multiple methodologies to choose from when it comes to calculating the carbon emissions caused by flight operations:
IATA (International Air Transport Association) is an international non-governmental organization.
Although there are several ways of calculating the carbon emissions of a flight, airlines participating in the IATA offset program use a methodology based on IATA’s Recommended Practice developed and approved by airlines in 2022. That methodology allows airlines to use their own historic data on fuel burned, passenger and cargo weights, seat configurations, and load factors. This generates the most accurate calculation of carbon emissions per passenger that has been developed based on secondary data*. IATA has set forth accurate and standardized practices for sectoral GHG calculation, which is revised by Quality Assurance Standard (QAS).
ICAO (International Civil Aviation Organization) is an agency of the United Nations that establishes international standards for civil aviation and coordinates their development in order to improve safety and efficiency in the industry.
ICAO authorities created a standard for ICAO members to calculate aviation’s carbon emissions. Doing so, the agency aims at supporting more transparency by understanding the emissions of any flying activity and communicating it to relevant stakeholders (passengers, shareholders, employees, regulators…). ICAO’s methodology combines the in the graph above-mentioned factors (number of passengers, total number of seats, freight weight, and fuel burn) with verified airline operational historic data which makes the calculation even more accurate. As the whole methodology is based on actual fuel consumption, as well as the weight of freight and the total number of occupied seats, it allows for precise emission estimations.
ICAO also developed a publicly available carbon emission calculator. The ICAO has established a technique to determine the carbon emissions from air travel. The technique takes into consideration a number of variables, including aircraft types, route-specific statistics, passenger load factors, and cargo carried, by applying the best publicly available industry data. The ICAO Carbon Emissions Calculator enables travelers to raise awareness of the emissions generated by flights.
The GHG Protocol specializes in reporting business travel-related CO2 emissions. Per this framework, to calculate the carbon emissions of a flight, the total distance of said flight is multiplied by an emission factor and the number of passengers. This calculation methodology has been deemed inaccurate by most of the airline industry but still proved to be valuable for businesses and individuals who wish to gain transparency about their emissions. The reason why the GHG Protocol is assumed to be inaccurate is due to the fact that a lot of factors are not taken into account. Namely, booking class, aircraft model or type, and whether the flight type is domestic or international.
The GLEC framework is usually not used for the carbon calculations of passenger airlines; it is rather used for cargo and logistics. However, it can be applied to that industry segment too when the number of passengers on a flight is known. The calculation steps are quite similar to those within the IATA methodology. All default factors for carbon emissions are taken using averages from the IATA members’ available data. Default values are provided for both IATA and DIN EN 16258** methodologies, which allows companies to see the differences between these values and choose which methodology they prefer to use for their end clients. Generally speaking, the GLEC framework for air travel provides instructions that offer using either IATA or DIN EN 16258 methodologies.
Various government environmental agencies in countries such as France, the UK, and Germany also developed their own frameworks based, for example, on domestic flight information, or on the country of arrival or departure of international flights.
Nevertheless, all the above-mentioned approaches use historical data, instead of scientific and mathematical-based approaches. One of the most known frameworks that are based on the scientific method was developed by the Chalmers University of Technology. The TU Chalmers has developed a more scientific and mathematical-based methodology to estimate the CO2 emissions per trip:
Scientific approaches are models based on assumptions and, therefore, less precise than calculations with actual, historical data. The main purpose of applying this methodology is to gain research insights. Scientific approaches are rarely used in practice and have limitations, namely: a time-consuming process, rare possibility to access datasets, and formal revision times, which can take up to half a year in the scientific community.
Last but not least, the place in the framework list is taken by private companies such as the data businesses RDC Aviation or Cirium. A more precise computation may be achieved thanks to RDC Aviation and Cirium’s extensive database of airlines, aircraft, engine types, and seating arrangements. Such companies have access to primary databases of various airlines and airports, which also allows them to make secondary estimates. RDC’s methodology applies airline-specific seat arrangements enabling emissions to be ascribed on a per seat, per person, or per cabin/seat basis, more precisely showing the variation in emissions per passenger. Cirium’s approach is closely related to RDC’s one. However, in addition to the historic CO2 emissions, Cirium makes forecasts of the CO2 emissions in the coming months and years, so that companies will be able to estimate emissions in advance.
Which framework is the most appropriate for the airline industry? It depends on the purpose it is used for. When companies have simple reporting requirements to track their emissions, the GHG protocol provides a simple framework that is sufficient for that aim. The GLEC framework was developed for logistics and is therefore applied by cargo airlines. ICAO and IATA consider international standards, while country-specific frameworks are more precise for the respective region — however, not applicable to the whole industry. Scientific approaches are mathematical calculations used for research purposes rather than in practice. Frameworks developed by private companies such as RDC Aviation and Cirium are data-driven and have a high level of accuracy, but accessibility comes at a cost.
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