CORSIA Phase 1: what changes from 2024 to 2026
CORSIA Phase 1 runs from 2024 to 2026. It follows the 2021 to 2023 pilot phase and remains voluntary at state level, but it is the live compliance period shaping aviation offset demand now. This guide explains what changes during Phase 1 and what airlines, brokers and carbon project developers shoul
CORSIA Phase 1 runs from 2024 to 2026. It follows the 2021 to 2023 pilot phase and remains voluntary at state level, but it is the live compliance period shaping aviation offset demand now. This guide explains what changes during Phase 1 and what airlines, brokers and carbon project developers should watch.
CORSIA timeline overview
ICAO describes CORSIA in three phases: the pilot phase from 2021 to 2023, the first phase from 2024 to 2026, and the second phase from 2027 to 2035. The pilot and first phases are voluntary for states. From 2027, participation is determined using ICAO criteria based on aviation activity, with exemptions for certain states.
| Period | Years | Status | Why it matters |
|---|---|---|---|
| Pilot phase | 2021 to 2023 | Voluntary | First operational compliance period |
| Phase 1 | 2024 to 2026 | Voluntary | Current phase, with eligible units approved for this period |
| Phase 2 | 2027 to 2035 | Broader participation under ICAO criteria | Potentially larger compliance demand |
How many states participate in Phase 1?
ICAO publishes annual documents showing the states participating in CORSIA and the state pairs subject to offsetting requirements for a given year. As of 2026, ICAO says 130 states participate in CORSIA.
Participation matters because CORSIA applies to state pairs. A covered international flight between two participating states may be subject to offsetting requirements, while a route involving a non-participating state may be treated differently under the scheme.
What changed from the pilot phase?
Phase 1 is not a completely new scheme. It continues the monitoring, reporting, verification and offsetting architecture of CORSIA. The key change is that the scheme moves beyond the pilot phase and into the 2024 to 2026 compliance period, with updated eligible emissions unit approvals and annual participating-state documentation.
For airlines, the practical work remains data quality, verified emissions reporting, route coverage, obligation calculation and eligible unit procurement. For carbon market participants, the practical work is understanding which units qualify for the 2024 to 2026 compliance period.
Monitoring, reporting and verification
Aircraft operators covered by CORSIA monitor fuel use and calculate CO2 emissions for covered international flights. They submit verified emissions reports through the state to which they are attributed. Verification is not optional paperwork. It is the basis for calculating obligations and maintaining confidence in the scheme.
Airlines should maintain clear evidence trails for fuel data, route categorisation, emissions calculations, verification statements and any subsequent emissions unit cancellation.
Offset obligations
CORSIA offset obligations are calculated by states based on the scheme rules. Operators then meet final offsetting requirements by cancelling CORSIA eligible emissions units for the relevant compliance period. Buying units in advance may help with procurement planning, but only eligible units can be used for compliance.
What airlines should prepare now
Route coverage mapping: identify which international routes are covered for each year.
MRV controls: make emissions monitoring, reporting and verification repeatable and auditable.
Eligible unit procurement: check ICAO eligibility documents before purchasing credits for compliance.
Article 6 documentation: understand host country authorisation and corresponding adjustment requirements where relevant.
Public claim governance: distinguish compliance cancellation from broader carbon neutral or net zero marketing claims.
What suppliers and brokers should understand
CORSIA Phase 1 creates demand for a specific type of carbon market product: units that are eligible for the 2024 to 2026 compliance period. Brokers and project developers need to be precise about eligibility claims. A vague "CORSIA-ready" label is not enough. Buyers need evidence that the units fall inside ICAO's approved scope.
Sources cited
Key takeaway
CORSIA Phase 1 is the current 2024 to 2026 phase. It is still voluntary at state level, but it is operationally important because it determines live airline compliance demand, eligible unit procurement and the transition toward the broader second phase from 2027.