CORSIA 2027: What the Next Phase Means for Aviation Emissions Reporting and Verification
As four major aviation markets enter CORSIA's offsetting framework, international airlines face a broader regulatory landscape. What changes in 2027, and what remains essential for emissions reporting and independent verification?
International aviation is approaching an important regulatory transition.
On December 31, 2026, the first phase of the Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA) comes to an end. Its second phase begins on January 1, 2027, introducing a different framework for determining which States participate in the scheme's offsetting requirements.
The significance extends beyond a change in regulatory dates.
Brazil, China, India and the Russian Federation are included in the 2027 participation framework, expanding the number of participating States from 130 in 2026 to 134 in 2027.
According to projections published by the International Civil Aviation Organization (ICAO), CORSIA's coverage could increase from approximately 59% of international aviation CO₂ emissions in 2026 to approximately 86% from 2027.
For aircraft operators serving international markets, this is a substantial development.
It raises two distinct questions: How will expanded offsetting coverage affect their international routes? And are their existing emissions monitoring, reporting and verification processes prepared to support compliance as the framework evolves?
Understanding the difference between these obligations is essential.
Four Major Aviation Markets Enter the 2027 Framework
CORSIA was established by ICAO as a global market-based measure to address CO₂ emissions from international aviation.
Its implementation has been structured in three phases: a pilot phase from 2021 to 2023, a first phase from 2024 to 2026, and a second phase extending from 2027 through 2035.
During the pilot and first phases, State participation in CORSIA's offsetting framework was voluntary.
Beginning in 2027, participation is determined through criteria based on international aviation activity, with provisions for voluntary participation and exemptions for certain categories of States.
Four countries are particularly significant to this transition:
Brazil, a major aviation market connecting South America with North America, Europe and other international destinations.
China, one of the world's largest aviation markets, with extensive international passenger and cargo operations.
India, a major international aviation market with growing long-haul connectivity.
The Russian Federation, a geographically extensive aviation market connecting international routes across Europe and Asia.
Their inclusion expands the number of State pairs potentially subject to CORSIA offsetting requirements.
The importance of this development is not simply the addition of four countries. It is the volume of international aviation activity associated with these markets.
ICAO projects that the expansion could bring approximately 86% of international aviation CO₂ emissions within CORSIA's offsetting coverage from 2027, compared with approximately 59% in 2026.
These figures are projections of the scheme's coverage, not measurements of emissions reductions or the percentage of emissions that airlines will be required to offset.
What Does This Mean for Airlines?
CORSIA operates through two related but distinct mechanisms.
The first is Monitoring, Reporting and Verification (MRV).
Qualifying aircraft operators must monitor CO₂ emissions from their international operations, prepare annual emissions reports and obtain independent third-party verification.
These obligations continue regardless of the transition from the first phase to the second.
The second is emissions offsetting.
Under CORSIA, the international routes subject to offsetting requirements are determined in part by the participating States at either end of a flight.
Generally, flights between two participating States fall within the offsetting framework, while flights involving a non-participating State do not generate CORSIA offsetting obligations, although they may still be subject to emissions monitoring and reporting.
For example, international flights between Canada and China may become subject to CORSIA offsetting coverage in 2027 because both countries are included in the participating State framework.
This does not mean that every tonne of emissions from those flights must be offset. Actual obligations depend on the scheme's calculation methodology, applicable provisions and the operator's circumstances.
An international flight can therefore be subject to emissions reporting without generating an offsetting obligation.
For airline compliance and sustainability teams, understanding this distinction is essential when assessing the implications of the 2027 transition.
Why the Expansion Matters
The increase from 130 to 134 participating States may appear modest.
But participation numbers alone do not capture the significance of the change.
Because CORSIA's offsetting framework operates through participating State pairs, the inclusion of countries with substantial international aviation activity can affect a much larger share of global aviation emissions.
ICAO's projected increase in coverage from approximately 59% to 86% illustrates this effect.
For airlines operating across multiple international markets, a larger proportion of their route network may now fall within the scheme's offsetting framework.
This creates a practical need to examine route coverage, understand applicable offsetting requirements and distinguish those obligations from the emissions reporting processes already in place.
It also reinforces the importance of reliable emissions information.
The effectiveness of any reporting or offsetting framework depends on the accuracy, consistency and traceability of the data used to determine emissions.
The 2027 Transition Does Not End Existing Reporting Obligations
One point deserves particular attention.
December 31, 2026, marks the conclusion of CORSIA's first phase, not the deadline for completing emissions reporting or verification.
Annual reporting and verification for emissions generated during 2026 continue into 2027 under the applicable ICAO reporting timetable and administering-State requirements.
The transition to a new phase does not replace the existing MRV framework.
For qualifying operators, emissions monitoring, annual reporting and independent verification remain ongoing responsibilities.
For airlines reviewing their 2027 obligations, it is therefore important to consider both the upcoming offsetting framework and the reporting responsibilities associated with the preceding calendar year.
These are related compliance activities, but they follow different requirements and timelines.
Why Independent Verification Matters
An emissions report is the final output of a much larger process.
Behind each reported figure are flight records, fuel consumption data, monitoring methodologies, calculations and supporting documentation.
Independent verification examines whether reported emissions have been determined in accordance with applicable requirements and whether sufficient evidence supports the information presented.
That process may involve reviewing an operator's approved emissions monitoring plan, assessing the methods used to collect and calculate data, testing information against source records, and examining how inconsistencies or missing information have been addressed.
The challenge is not necessarily the complexity of an individual calculation.
It is the need to demonstrate that information is complete, consistent and traceable across the reporting period.
For airlines managing international flight networks, emissions information may originate from multiple systems, departments and operational processes.
Flight activity, fuel records and reporting datasets must ultimately support a coherent, verifiable account of annual emissions.
When discrepancies arise, resolving them can require coordination across operational, technical and environmental reporting functions.
This is why verification should not be regarded as an administrative step performed after reporting work is complete.
It is an integral part of the compliance process.
The Operational Questions Worth Addressing Before 2027
The transition to CORSIA's second phase provides an opportunity for operators to evaluate whether their existing reporting arrangements remain appropriate.
Several questions deserve attention.
Are emissions monitoring procedures consistently applied?
As flight networks and operational arrangements evolve, established methodologies must continue to reflect the activities being reported and the requirements of the approved monitoring plan.
Can reported figures be traced to supporting records?
The ability to reconcile emissions calculations with relevant flight and fuel information is essential to an effective verification process.
Are discrepancies identified early enough?
Incomplete records, inconsistent data or changes in reporting procedures can become more difficult to resolve once the reporting period has concluded.
Has the operator assessed the implications of the 2027 participation framework?
Changes in participating State pairs may affect which international routes fall within CORSIA's offsetting requirements.
Are independent verification arrangements in place for the next reporting cycle?
Engaging an appropriately accredited verification body at the right stage allows time to establish the verification scope, identify documentation requirements and address potential findings before applicable submission deadlines.
These considerations are not entirely new. They are fundamental elements of effective emissions reporting.
However, the transition into CORSIA's second phase makes this an appropriate moment to review them.
Beyond the Regulatory Transition
CORSIA's evolution also reflects a broader development in international aviation: environmental performance is increasingly managed through formalized measurement, reporting and independent assurance processes.
Airlines must maintain operational efficiency while responding to evolving environmental requirements.
Emissions information is therefore no longer simply a figure produced for an annual submission. It is part of a broader reporting discipline requiring coordination between technical operations, environmental management and regulatory compliance.
For organizations operating internationally, consistency is particularly important.
Monitoring methodologies must be understood. Supporting information must remain accessible. Reporting responsibilities must be clearly assigned.
Independent verification must be supported by evidence that can withstand scrutiny.
The importance of these practices extends beyond an individual regulatory milestone.
They establish a dependable foundation for responding to changing requirements without having to reconstruct the underlying information each time the framework evolves.
Preparing for What Comes Next
The beginning of CORSIA's second phase does not mean that every aviation operator suddenly faces the same new obligations.
Applicability depends on the operator, its international activities and the relevant provisions of the scheme.
Nor does January 2027 represent a reset of existing reporting responsibilities.
Qualifying operators must continue to monitor, report and independently verify their emissions while assessing the offsetting requirements applicable to their operations under the expanded framework.
For aviation organizations, the immediate priority is practical: understand what is changing, confirm what remains applicable and ensure that the processes supporting reporting and verification are ready.
As CORSIA expands, the challenge is not simply calculating aviation emissions. It is being able to substantiate them.
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Discuss Your CORSIA Verification Requirements
As CORSIA enters its second phase, qualifying aviation operators must maintain reliable emissions reporting and independent verification processes.
Zenith Net-Zero combines more than 25 years of aviation industry experience with specialized greenhouse gas verification expertise.
For a discussion about your organization's CORSIA verification requirements and upcoming reporting obligations, contact Nick Houseman, CEO of Zenith Net-Zero.
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Sources and Further Reading
International Civil Aviation Organization (ICAO). CORSIA States for Chapter 3 State Pairs, seventh edition, 2027. Official participating State lists and State-pair coverage.
ICAO. Environmental Report 2025, Chapter 6: Carbon Offsetting and Reduction Scheme for International Aviation. Historical and projected participation and emissions coverage.
ICAO. CORSIA Frequently Asked Questions. Phased implementation, State participation, MRV, offsetting and annual reporting requirements.
ICAO. CORSIA Central Registry: Information and Data for Transparency. Verification body information and emissions reporting data.
ICAO. CORSIA Implementation and Standardized Reporting Resources.
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