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Statistical Insights: A new near-real-time global database on CO2 emissions from air transport

 

14 Mar 2022 - Air transport facilitates international trade and tourism and contributes to economic growth and job creation, but it also produces carbon dioxide (CO2) emissions that contribute to global warming. 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 Working Paper published today.

Aviation-related CO2 emissions are expected to increase rapidly after the COVID-19 pandemic, and these new statistics will help monitor changes as well as the impact of technology developments and policy measures to curb aviation-related CO2 emissions. They will help inform the debate on 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

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

S‌ource: IEA (2022), "Detailed CO2 estimates", IEA CO2 Emissions from Fuel Combustion Statistics: Greenhouse Gas Emissions from Energy (database), authors’ calculations.

 

…and are now rising again

Although the pandemic has had a big impact on international passenger travel, recent data suggests that emissions from air transport are now increasing (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.

The impact of the pandemic on air transport emissions can be seen clearly in the new OECD statistics. These are more frequent and timely than statistics from other sources: they are monthly, and estimates are published within three months. The Working Paper uses the OECD estimates to report on the rebound following the early stages of the COVID-19 pandemic. Looking ahead, the OECD database will make it possible to track future trends in aviation-related CO2 emissions after the COVID-19 pandemic, as well as the impact of developments in aircraft fleet technology and of environmental policies such as carbon taxation on CO2 emissions.

 

Figure 2. In December 2021, aviation-related CO2 emissions were significantly below their pre-pandemic level

CO2 emissions relative to the same month of 2019, January 2020- December 2021

In December 2021, aviation-related CO2 emissions were significantly below their pre-pandemic level - CO2 emissions relative to the same month of 2019, January 2020- December 2021

Source: OECD (2022), "Air and climate: Air Transport CO2 Emissions", OECD Environment Statistics (database), authors’ calculations. 

 

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- December 2021

In December 2021, CO2 emissions from domestic flights had returned to their pre-pandemic level, CO2 emissions relative to the same month of 2019, January 2020- December 2021

Source: OECD (2022), "Air and climate: Air Transport CO2 Emissions", OECD Environment Statistics (database), 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-December 2021

 International freight flights were largely unaffected by the pandemic, CO2 emissions relative to the same month of 2019, January 2020-December 2021

Note: The pattern is very similar for OECD countries
Source: OECD (2022), "Air and climate: Air Transport CO2 Emissions", OECD Environment Statistics (database), 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 Emission 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.

 

The measure explained

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 to 2018, the ICAO data relates to scheduled flights. From 2019 onwards, it is for flights actually taking place, 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 (Annex-I) countries; and with official 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? 

 

Further reading

  

 

@OECD_Stat

 

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