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.
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.
The precise level for carbon neutral growth is set at the average of emissions in 2019-2020 (ICAO Assembly, 2016b, paragraph 11). When the ICAO Assembly set this target in 2013, the organisation and airlines anticipated 2020 CO2 emissions to be approximately 682-775 Mt (ICAO, 2013b). However, due to COVID-19 international aviation emissions will be much lower than this level.
IATA has requested that the ICAO Council take 2019 emissions as the baseline to avoid that airlines face higher obligation requirements than previously expected. At the time of writing, however, it is uncertain what decision ICAO will take with regards to the baseline for the target of carbon neutral growth. This CAT assessment rates the target based on the 2019 baseline, but also provides a baseline composed of average emissions in 2019 and 2020 baseline as a reference point. To determine this latter baseline, we assumed 2020 emissions are 60% lower than those in 2019.
To calculate 2019 emissions, we extrapolated emissions from 2017, the last year for which data is available, using an average of the 2014-2017 growth rate. Considering economic conditions, we expect emissions in 2018 and 2019 to resemble the same growth rates as in previous years, when growth rates fluctuated between 3-6% and have therefore used an average rather than the growth rate of 2017 – which was at the high end of the range.
As of 1 January 2019, all ICAO Member States that had aircraft operators undertaking international flights are required to implement a CORSIA Monitoring Reporting and Verification (MRV) system (ICAO, 2018). This system allows ICAO to collect data on CO2 emissions from international aviation on an annual basis; establish the baseline for carbon neutral growth; and compare emissions in future years to the baseline. ICAO’s data on international aviation emissions in 2019 is not publicly available and may differ from our estimate. We will update our assessment as more data becomes available.
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. 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.