CORSIA is the carbon market for international flights. It doesn’t cap airline emissions. Instead, it requires airlines to offset the growth in their international CO₂ emissions above a baseline, using carbon credits from approved programmes. It also decides which credits can be labelled “CORSIA-eligible”.
This page is part of our Learn section. It connects closely to Article 6 of the Paris Agreement.
What is CORSIA?
CORSIA stands for the Carbon Offsetting and Reduction Scheme for International Aviation. It was adopted by the International Civil Aviation Organization (ICAO) at its 39th Assembly on 6 October 2016 in MontrealSource 3. EASA describes its aim as stabilising CO₂ emissions from international aviation at 2020 levelsSource 2.
The phases and the baseline
CORSIA runs in three phases, each split into three-year compliance periodsSource 1:
Scrolls sideways to show every column.
| Phase | Years | Baseline |
|---|---|---|
| Pilot phase | 2021–2023 | 2019 emissions |
| First phase | 2024–2026 | 85% of 2019 emissions |
| Second phase | 2027–2029, 2030–2032, 2033–2035 | 85% of 2019 emissions |
As of Oct 2026
Source: GOV.UKSource 1. Offsetting applies only to emissions above the baseline. EASA reports that international aviation emissions did not reach 2019 levels by 2023, so there were no offsetting requirements during the pilot phaseSource 2. Participation is voluntary, state by state, and has grown from 88 states in 2021 to 129 in 2025Source 2.
Who has to comply?
An airline counts as an aeroplane operator under CORSIA if its annual CO₂ emissions from international flights, using aeroplanes over 5,700 kg maximum take-off mass, exceed 10,000 tonnesSource 1.
CORSIA does not apply to humanitarian, medical and firefighting flights, the international flights immediately before or after them, or flights by state aircraftSource 1. Operators must submit a verified annual emissions report to their regulator by 30 April for the previous yearSource 1.
How airlines meet their obligation
Airlines have two tools:
- Offsetting. They buy eligible emissions units equal to their offsetting obligation and cancel them in a registry approved by ICAOSource 1.
- CORSIA eligible fuels. Sustainable aviation fuel, or lower-carbon aviation fuel that meets CORSIA’s criteria, reduces an airline’s offsetting requirementSource 1.
Which carbon credits count?
Only units from programmes approved by the ICAO Council are eligibleSource 2, and an approval can exclude some types of credit. Programmes approved for the first phase (2024–2026) include Verra’s VCS, approved in December 2024Source 4, and Gold StandardSource 3. ACR also lists ICAO among the markets it servesSource 5.
First-phase credits need Article 6 authorisation
For the first phase, the rules are stricter than in the voluntary market. Verra credits with vintages from 2021 onward need an “Article 6 Authorized – International mitigation purposes” labelSource 4. That ties CORSIA to Article 6: under the Article 6.2 guidance, mitigation outcomes a country authorises for international mitigation purposes other than its NDC are ITMOs, and corresponding adjustments apply to all ITMOsSource 6.
The VCS approval also excluded some credit types, including large-scale renewable energy over 15 megawatts and cookstove projects under older methodologiesSource 4. See carbon credit vintage for why the year of a credit matters here.
What CORSIA means for travellers
CORSIA applies to airlines, not to passengers, and it covers only growth above the baseline. It is not a reason to skip thinking about your own flights. Fly less where you can, then offset what is left. Our flight emissions calculator estimates a trip’s footprint, and the offset section explains how to cover it with credits retired in your name.