Definition of the sector
International aviation – which refers to flights that take off in one country and land in another – is generally not covered by countries’ NDCs. International aviation currently contributes 1.2% of global GHG emissions – or about 600 MtCO2 annually (IEA, 2019). Total aviation emissions – that is emissions from both international and domestic flights – contributed approximately 2.4% of total global CO2 emissions in 2018 (Graver, Zhang and Rutherford, 2019).
Our assessment is of international aviation only. GHG emissions from domestic aviation are considered as part of national totals and are included in the assessment of individual CAT countries.
Due to data availability, our analysis is limited to CO2 emissions. However, international aviation is also a source of non-CO2 emissions and impacts that contribute to global warming, including NOx and water vapour (H2O), which, when emitted at altitude, forms contrail cirrus (Owen, Lee and Lim, 2010). Contrail cirrus traps heat that is radiated from the Earth’s surface back to the atmosphere.
Historical CO2 emissions from 1990 to 2017 were taken from the IEA and emissions for 2018 to 2020 from ICAO’s CAEP (CAEP, 2021).In our 2020 assessment, we extrapolated emissions from 2017, the last year for which the IEA provided data, using an average of the 2014-2017 growth rate. In this assessment, we used data from ICAO’s CAEP for 2018, 2019 and 2020. CAEP estimates that annual CO2 emissions are around 30 Mt lower in this period than what the IEA provided.
The sector’s target is to achieve carbon neutral growth relative to 2020 levels. In other words, international aviation’s net CO2 emissions should remain constant at those levels. ICAO expects CORSIA to be the main measure to achieve carbon neutral growth and CORSIA’s baseline represents the basis of this goal (ICAO, 2020f).
When ICAO set the goal of carbon neutral growth in 2013 and established CORSIA in 2016, the organisation and airlines anticipated 2020 CO2 emissions to be approximately 682-775 Mt (ICAO, 2013b, ICAO Assembly, 2016b, paragraph 11). However, due to COVID-19 international aviation emissions will be much lower than this level.
In June 2020, the ICAO Council decided that 2019 emissions will form CORSIA’s baseline in the pilot phase (2021-2023) (ICAO, 2020d). In 2022, the ICAO Assembly will decide on the baseline for CORSIA’s first and second phase (ICAO, 2020d). As the baseline after 2023 is currently uncertain, this CAT assessment rates the target based on the 2019 baseline, but also provides a baseline composed of average emissions in 2019 and 2020 s a reference point.
Current policy projections
We based the pre-COVID current policy projections on the projections in ICAO’s Environmental Report of 2019 (ICAO, 2019b). As ICAO does not provide exact data points for future years, we extracted data points from the ‘optimistic technology improvements’ and the ‘low technology improvements’ trajectories for 2015 to 2050 with five-year intervals from the graphs in the report. For the years 2015-2017, the historical emissions used by ICAO are very close to historical emissions as provided by the IEA, so we did not need to harmonise the data.
We also developed two scenarios to evaluate the impacts of COVID-19 on international aviation emissions. The assumptions related to the impacts of COVID-19 are explained in the current policies section. To assess the impact on emissions until 2030, we applied the growth rates using the ICAO’s optimistic and low technology scenarios.
We used these two scenarios, so we could develop an upper and lower bound for emission projections based on current policies. The Environmental Report does not explain what assumptions these scenarios consider.