The Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA) was adopted by the Assembly of the International Civil Aviation Organization (ICAO) in October 2016 to address greenhouse gas emissions from international civil aviation, a sector excluded from the Paris Agreement's national accounting. It complements operational, technological, and sustainable aviation fuel measures within ICAO's "basket of measures" aimed at carbon-neutral growth.
Under CORSIA, aircraft operators on covered international routes must monitor, report, and verify (MRV) their CO2 emissions annually. When emissions on a route-pair exceed the agreed baseline, operators must cancel an equivalent volume of eligible emissions units (offset credits) or claim reductions from CORSIA-eligible sustainable aviation fuels.
The scheme runs in phases:
- Pilot phase: 2021–2023
- First phase: 2024–2026 (both voluntary)
- Second phase: 2027–2035 (mandatory for most ICAO member states, with exemptions for least developed countries, small island developing states, landlocked developing countries, and states with very low aviation activity)
The baseline was originally set as the average of 2019 and 2020 emissions, but in 2020 the ICAO Council revised the pilot-phase baseline to 2019 levels only, after the COVID-19 collapse in air traffic would otherwise have produced an artificially low benchmark and disproportionate offsetting obligations. From 2024 onward the baseline is 85% of 2019 CO2 emissions.
CORSIA's Technical Advisory Body (TAB) assesses which carbon-crediting programs and unit types qualify. Eligible programs have included the American Carbon Registry, Climate Action Reserve, the Architecture for REDD+ Transactions, and others, subject to periodic review.
Critics — including civil-society groups and some climate economists — argue that offsetting allows continued absolute emissions growth, that credit quality is uneven, and that the scheme is weaker than including aviation in domestic emissions trading systems such as the EU ETS, which continues to cover intra-EEA flights in parallel with CORSIA.
Example
In 2022, during the pilot phase, participating airlines including those from the United States, Japan, and the United Kingdom began reporting verified international CO2 emissions to ICAO under CORSIA MRV requirements.
Frequently asked questions
Participation is voluntary during the pilot phase (2021–2023) and first phase (2024–2026), then mandatory from 2027 for most ICAO member states, with exemptions for least developed countries, small island developing states, landlocked developing countries, and states with very low international aviation activity.
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