CORSIA Phase 1: what changes from 2024 to 2026
CORSIA (Carbon Offsetting and Reduction Scheme for International Aviation) Phase 1 runs from 2024 to 2026.
CORSIA (Carbon Offsetting and Reduction Scheme for International Aviation) Phase 1 runs from 2024 to 2026. For the wider scheme route map, use the CORSIA aviation carbon market guide. Phase 1 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 (International Civil Aviation Organization) 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.
Why Phase 1 matters commercially
Phase 1 matters because it turns CORSIA from an early implementation topic into a live procurement, reporting and governance issue. Airlines need to understand covered routes, expected obligations, eligible unit supply and the timing of cancellation. Brokers need to avoid overstating eligibility. Project developers need to understand whether their programme, vintage, host-country treatment and methodology are likely to fit aviation demand.
The commercial risk is not only price. It is also usability. A buyer can spend money on a carbon credit and later discover that it does not meet the exact CORSIA scope needed for the compliance period. That makes eligibility evidence part of procurement due diligence, not a nice-to-have document.
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 (monitoring, reporting and verification) 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.
Phase 1 operating checklist
| Workstream | What to check | Why it matters |
|---|---|---|
| Route scope | Participating states and covered state pairs for each year. | Offset obligations depend on which routes are covered. |
| Emissions data | Fuel data, calculation method, verifier evidence and reporting deadlines. | Weak MRV (monitoring, reporting and verification) creates compliance risk. |
| Unit eligibility | Programme, vintage, methodology, compliance period and scope limitations. | Not every credit from an approved programme is usable. |
| Procurement timing | Expected demand, eligible supply and cancellation deadlines. | Late buying can create price and delivery risk. |
| Claims review | Whether public wording separates CORSIA compliance from voluntary climate claims. | Compliance cancellation does not automatically support broad carbon neutral 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.
Good documentation should show the programme name, project identifier, vintage, serial number range where available, methodology, host-country status, compliance period, registry status and any restrictions attached to the programme approval. If a buyer cannot trace those details, the unit should not be treated as safely usable for CORSIA.
What changes after Phase 1
Phase 1 is important partly because it is the bridge into the broader second phase. From 2027, CORSIA is expected to apply more widely under ICAO's participation criteria, which could change the scale and timing of demand for eligible units. The exact market effect will depend on aviation growth, participating state coverage, eligible supply, airline procurement strategies and how Article 6 documentation develops.
That is why Phase 1 should be treated as a learning period, not a side issue. Airlines that build stronger monitoring, reporting, verification and procurement controls now should be better prepared for Phase 2. Project developers and brokers that can document eligibility cleanly may also be better placed if demand becomes more selective.
Read this article alongside the CORSIA aviation carbon market guide, eligible carbon credits guide and CORSIA vs EU ETS comparison.
CORSIA Phase 1 FAQ
Is Phase 1 mandatory?
Participation remains voluntary at state level during Phase 1, but operators on covered routes between participating states still need to follow the relevant monitoring, reporting and offsetting rules.
Why does Phase 1 matter if it is voluntary?
It matters because it is the current operational period, it shapes eligible unit demand and it gives airlines, brokers and project developers a live compliance framework before the broader second phase.
What should buyers check first?
Buyers should check the latest ICAO participating state and eligible emissions unit documents, then confirm vintage, programme, scope and cancellation requirements.
Phase 1 is a market test
CORSIA Phase 1 is not just a compliance period. It is also a test of whether airlines, registries, crediting programmes and host countries can handle the practical details of international aviation offsetting. The volumes may be smaller than later phases, but the operational lessons are important.
Airlines need to understand which emissions are covered, which units are eligible, how claims should be documented and when compliance deadlines fall. Credit suppliers need to understand whether their units meet the relevant eligibility criteria and whether host-country authorisation affects demand. Host countries need to decide how international use interacts with their own climate targets. That makes Phase 1 a signalling period. The market will be watching not only how many credits are used, but which credits are trusted and whether the compliance process runs smoothly.
Useful source links
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.