4 minute read

By Bram Groenewoud, with Daniel Clarke (Daniel.CLARKE@oecd.org) & Pierre-Alain Pionnier (Pierre-Alain.PIONNIER@oecd.org), Statistics and Data Directorate (OECD)

Air transport is vital for international trade, tourism and employment, but it also produces carbon dioxide (CO₂) emissions that contribute to global warming, and these emissions are expected to increase rapidly after the COVID-19 pandemic. The OECD has developed a new database using a near real-time data source from the International Civil Aviation Organisation (ICAO) to produce estimates of CO₂ emissions from air transport. The new estimates have global coverage and ensure a consistent allocation of CO₂ emissions across countries. The data and methods are described in a recently published OECD Working Paper. These new statistics will help monitor aviation emissions as well as the impact of technological developments and policy measures to curb them. They will help inform better policy actions for a low-carbon transition of air transport and the green economic recovery.

Emissions from air transport grew rapidly before the pandemic…  

Before the COVID-19 pandemic, air transport – particularly international passenger travel – was one of the fastest growing sources of global CO₂ emissions (Figure 1). In 2019, global CO₂ emissions from domestic and international aviation were roughly similar to the total energy-related CO₂ emissions of Japan and accounted for 5% of all energy-related CO₂ emissions from OECD countries.

Figure 1: Aviation-related CO₂ emissions have increased much faster than other energy-related CO₂ emissions in OECD countries

Aviation- and other energy-related CO₂ emissions in OECD countries, 1971-2019, 2010 = 100

Source: International Energy Agency, author’s calculations.

…and are now rising again

Although the pandemic had a significant negative impact on international passenger travel, recent data suggests that emissions from air transport are now increasing again (Figure 2). Moreover, projections by the International Transport Forum show that, in the absence of accelerated technological developments and more ambitious policy measures, aviation-related CO₂ emissions will increase by two and a half times between 2015 and 2050.

Figure 2: Aviation related CO₂ emissions are rising, though they remain below pre-pandemic levels

CO₂ emissions relative to the same month of 2019, January 2020-April 2022

The new database includes breakdowns into domestic and international flights and into passenger and freight flights. Distinguishing between domestic and international flights (Figure 3) is important because the demand for them does not grow at the same pace, and because governments have more policy levers to curb the CO₂ emissions from domestic flights than from international flights.

Figure 3: In December 2021, CO₂ emissions from domestic flights had returned to their pre-pandemic level, while CO₂ emissions from international flights remained lower

CO₂ emissions relative to the same month of 2019, January 2020-April 2022

Source: OECD database on Air Transport CO2 emissions, authors’ calculations.

Tracking freight flights separately allows us to use the database to monitor international trade developments in different countries and regions. CO₂ emissions from freight flights represent a very small share of total air transport emissions, but international freight flights were largely unaffected by the pandemic (Figure 4).

Figure 4: International freight flights were largely unaffected by the pandemic

CO₂ emissions relative to the same month of 2019, January 2020-April 2022

Note: The pattern is very similar for OECD countries. Source: OECD database on Air Transport CO2 emissions, authors’ calculations.

Use of the new estimates for environmental accounting

The System of Environmental Economic Accounting (SEEA) was endorsed as an international statistical standard by the UN Statistical Commission (UNSC) in 2012. It provides a way to relate air emissions to economic activities through the development of Air Emissions Accounts (AEAs). The UNSC has asked the UN Committee of Experts on Environmental Economic Accounting (UNCEEA), of which the OECD is a Bureau member, to scale up implementation of the SEEA by supporting capacity building in countries, developing methodological guidelines and compiling global databases.

The OECD’s new CO₂ emissions statistics for air transport contribute to the development and international compilation of AEAs according to SEEA methods. For example, they are a source for validation of national estimates and for the conversion between the inventories and national accounts bases of emissions reporting.

The AEAs are compiled on a residence basis. By contrast, the air emission inventories provided by the UN Framework Convention on Climate Change (UNFCCC) use a territory perspective. The new OECD database records emissions from air transport on both bases, so the information can be used both by compilers of UNFCCC inventories and those working on the AEAs.

How do we measure CO_2­ emissions from air transport?

The OECD estimates of CO₂ emissions from air transport are produced using information on individual flights and the specific type of aircraft used for each flight. The main source of information is air traffic data provided by the International Civil Aviation Organisation (ICAO), which includes most of the passenger and freight flights taking place around the world. For each flight, the ICAO database includes information on the departure and arrival airports, the operating airline, and the type of aircraft used. More than a thousand aircraft types are considered in this database. Up until 2018, the ICAO data relates to scheduled flights. From 2019 onwards, it extracts real-time flight data based on information from the Automatic Dependent Surveillance-Broadcast (ADS-B) system.

To estimate CO₂ emissions, the flight information provided by ICAO is linked with a CO₂ emissions calculator from the European Organisation for the Safety of Air Navigation (EUROCONTROL). Given an aircraft type equipped with a specific type and number of engines and a specific distance travelled, this tool calculates a flight trajectory, a quantity of fuel burnt and a quantity of CO₂ emitted.

The Working Paper assesses the quality of the estimates, comparing them with annual emissions reported in UNFCCC inventories, which are available for 43 countries; and with official Air Emission Accounts (AEAs), available for around 40 (mostly European) countries. Although these official statistical sources are only available with a delay and at lower frequencies than the new OECD estimates, the comparisons support the conclusion that the overall accuracy of the new estimates is high.

Where to find the underlying data?

Access the database

Further reading

• Clarke, D., et al. (2022), “CO2 Emissions from air transport: A near-real-time global database for policy analysis”, OECD Statistics Working Papers, No. 2022/04, OECD Publishing, Paris, https://doi.org/10.1787/ecc9f16b-en.