The Carbon Offsetting and Reduction Scheme for International Aviation is the world’s first global sectoral climate agreement, administered by the International Civil Aviation Organization under Annex 16 of the Chicago Convention. It is not a voluntary framework — it is a compliance instrument with the force of international law for signatory states. Its emissions unit eligibility criteria define the quality standard that offset credits must meet to discharge a regulatory obligation. From 2024, credits used in CORSIA Phase 1 must carry corresponding adjustments: host country consent that the emission reduction has been transferred out of the national NDC. The Sovereign Portfolio is the 360° Impact Portfolio product that addresses this requirement directly.
CORSIA was adopted by the 191 ICAO member states in 2016 and entered its pilot phase in 2021. It is a market-based measure requiring international airlines to offset the growth in their CO₂ emissions above 2019 baseline levels. The scheme operates in three phases: pilot (2021–2023), first phase (2024–2026), and second phase (2027–2035). Participation in the pilot and first phases is voluntary for states; from 2027, most states are required to participate.
For airlines operating international routes, CORSIA creates a hard compliance obligation: they must calculate their CO₂ emissions above the baseline, and purchase and cancel eligible emissions units (carbon credits) to cover that excess. The units must meet the CORSIA Emissions Unit Eligibility Criteria — a set of programme-level and credit-level requirements that define what a CORSIA-compliant offset looks like. Gold Standard and Verra are both CORSIA-eligible programmes, though not every credit from those registries is automatically CORSIA-eligible: vintage, the specific crediting methodology, and from 2024 the corresponding adjustments requirement all affect eligibility.
The relevance of CORSIA extends beyond the airline industry. Any company with a significant air travel footprint in scope 3 category 6 (business travel), or with operations in the aviation supply chain, will increasingly find that its sustainability reporting and credit quality decisions intersect with CORSIA requirements. More broadly, CORSIA’s corresponding adjustments requirement — the condition introduced for Phase 1 credits from 2024 — represents the most advanced real-world implementation of host-country double-counting prevention currently in operation. It is the compliance-grade precedent for what the voluntary market is moving toward.
CORSIA eligibility is assessed at programme level. The eleven design elements define the institutional architecture a crediting programme must have in place. Gold Standard and Verra satisfy all eleven. The assessment operates analogously to the ICVCM’s CCP-Approved process, providing a scalable quality signal across all credits issued by eligible programmes.
Programmes must have quantification methodologies publicly disclosed, alongside a documented process for developing further methodologies. Both existing and future methodologies must be transparent and publicly available.
The programme must define and publicly disclose which types of activities, sectors, and geographies are eligible. The eligibility criteria for each project category must be published.
Documented procedures for how credits are issued, retired or cancelled, whether and how discounting applies, and the length and renewability of crediting periods. All publicly disclosed.
Units individually identified with serial numbers, tracked through issuance to transfer or cancellation via a secure registry. Clearly identified owners. Linkages to other registries and data exchange standards publicly disclosed.
The underlying attributes and property aspects of a credit unit must be defined and the transfer process publicly documented. This establishes the legal basis for ownership transfer that an airline needs to demonstrate compliance.
Standards, procedures, and accreditation requirements for validators and verifiers must be in place and publicly disclosed. This is the institutional quality assurance for the project-level verification function.
Public disclosure of who is responsible for administration and how decisions are made. Governance accountability is the institutional equivalent of the ICVCM’s CCP 1 (Effective Governance).
Public disclosure of what information is available to stakeholders, local consultation requirements, public comment provisions, and how comments are considered. Conduct of public comment periods required.
Safeguards to address environmental and social risks must be in place and publicly disclosed. This corresponds to ICVCM CCP 9 (Sustainable Development Benefits and Safeguards) and ISO 14068-1 §11.3(b).
The programme must publicly disclose its sustainable development criteria, how it contributes to a country’s stated sustainable development priorities, and provisions for monitoring, reporting, and verification of SD contributions. Directly aligned with ISO 14068-1 §11.3(c).
The programme must provide information on how it addresses double counting in the context of evolving national and international carbon market regimes. This includes double issuance prevention, double use prevention, and — critically — double claiming between buyers and host country NDCs. This is the programme-level basis for the credit-level Criterion 7 requirement below.
The eight credit integrity assessment criteria define the quality conditions that individual emissions units must meet. They are substantively aligned with the ICVCM Core Carbon Principles, and where they address the same principle they are consistent with ISO 14068-1 §11.2. A credit that satisfies all eight CORSIA criteria satisfies the ICVCM CCPs and ISO 14068-1 credit requirements simultaneously.
Criterion 1 — Additionality
Credits must represent emissions reductions or carbon sequestration that are additional: they exceed any reductions required by law, regulation, or legally binding mandate, and exceed what would otherwise occur in a conservative business-as-usual scenario. Programmes must demonstrate that they have procedures to assess or test for additionality. Where programmes pre-define certain activities as automatically additional via a positive list, they must provide clear evidence of how additionality was determined and publish the criteria used.
Aligns with: ICVCM CCP 5 · ISO 14068-1 §11.2(b)
Criterion 2 — Credible baseline
Credits must be based on a realistic, defensible, and conservative baseline estimation of emissions — the level of emissions that would have occurred without the project. Baselines and underlying assumptions must be publicly disclosed. A speculative or inflated baseline overstates the emissions reduction and produces credits that do not represent genuine climate benefit.
Aligns with: ICVCM CCP 7 · ISO 14068-1 §11.2(c)
Criterion 3 — Quantified, monitored, reported, and verified
Emissions reductions must be calculated conservatively and transparently, based on accurate measurements and approved quantification protocols. Monitoring must occur at specified intervals throughout the crediting period. Reductions must be verified by an accredited, independent third-party verification body. Ex-post verification is required before credit issuance; programmes that issue credits before reductions have been verified are not CORSIA-eligible. Transparent measurement and reporting is non-negotiable.
Aligns with: ICVCM CCP 4 & 7 · ISO 14068-1 §11.2 (ex-post rule) & §11.3(f)
Criterion 4 — Clear and transparent chain of custody
Each credit must carry an identification number tracked from issuance through to transfer or cancellation via a registry system. The chain of custody must be verifiable at any point. This is the technical infrastructure that makes serial numbers meaningful: without it, a serial number is merely an identifier rather than an auditable chain of title.
Aligns with: ICVCM CCP 2 · ISO 14068-1 §11.3(g) · ISO 14068-1 §11.4(e)
Criterion 5 — Permanence
Credits must represent emissions reductions, avoidance, or carbon sequestration that are permanent. Where there is a risk of reversal, either such credits are excluded or mitigation measures are in place to monitor, mitigate, and compensate any material non-permanence event. This applies with particular force to nature-based solutions and land use projects, where fire, disease, and land use change create ongoing reversal risk.
Aligns with: ICVCM CCP 6 · ISO 14068-1 §11.2(d)
Criterion 6 — Leakage assessment and mitigation
Credits must be generated from projects that do not cause emissions to materially increase elsewhere. Programmes must have an established process for assessing and mitigating leakage. Leakage deductions must be reflected in the credits issued.
Aligns with: ICVCM CCP 5 (leakage component) · ISO 14068-1 §11.3(g) · DEFRA Good Quality — Avoiding leakage
Criterion 7 — Only counted once
Measures must be in place to prevent three distinct forms of double counting. Double issuance: more than one unit issued for the same emission or reduction. Double use: the same unit used twice, for example by duplication across registries. Double claiming: the same reduction counted by both the purchasing airline and the host country of the project towards its nationally determined contribution. Eligible programmes are required to demonstrate that host countries agree to account for transferred units such that double claiming between the airline and the host country does not occur.
Aligns with: ICVCM CCP 8 · ISO 14068-1 §11.1 (CA note) · ISO 14068-1 §11.3(g)
Criterion 8 — Do no net harm
Credits must represent reductions from projects that do no net harm. Projects must not violate local, regional, national, or international regulations or obligations. Programmes must demonstrate compliance with social and environmental safeguards and publicly disclose which institutions, processes, and procedures are used to implement, monitor, and enforce them. This is the social licence requirement that sits alongside the carbon accounting requirements.
Aligns with: ICVCM CCP 9 · ISO 14068-1 §11.3(b) · SBTi CNZ v2.0 §1.8
From 2024, credits used in CORSIA Phase 1 must carry corresponding adjustments. This is the most significant development in voluntary and compliance carbon markets since the ICVCM CCPs were published, and it creates a clear quality tier above standard voluntary credits.
What corresponding adjustments are
When an airline purchases and cancels a carbon credit to meet its CORSIA obligation, that emission reduction has effectively been transferred from the host country to the airline. Without a corresponding adjustment, both the airline and the host country government could count the same reduction — the airline as a CORSIA compliance unit, the host country towards its NDC. Corresponding adjustments are the mechanism by which the host country government formally acknowledges the transfer and adjusts its NDC accounting accordingly. The result is that the reduction is counted once and once only in the global accounting system.
The Paris Agreement basis
Corresponding adjustments are rooted in Article 6 of the Paris Agreement, specifically paragraphs 2 and 4. Article 6.4 establishes the international carbon market mechanism under which ITMOS (Internationally Transferred Mitigation Outcomes) are issued with sovereign CA authorisation. ISO 14068-1 §11.1 notes CAs as the mechanism for avoiding double counting between private entities and governments. CORSIA Phase 1 has operationalised this requirement: credits used from 2024 must carry CAs from the host country.
What this means for credit supply
Not all credits on CORSIA-eligible programmes (Gold Standard, Verra) carry corresponding adjustments. CAs require host country engagement and agreement to adjust the NDC — a process that adds complexity and cost to project development. In practice, the CA requirement has segmented the voluntary carbon market into two tiers: standard voluntary credits (without CAs) and CA-backed credits. CA-backed credits command a premium and are in shorter supply. For CORSIA compliance buyers, only CA-backed credits satisfy the Phase 1 requirement.
The voluntary market direction of travel
CORSIA’s CA requirement is the compliance-grade implementation of a principle that the voluntary market is converging on independently. ISO 14068-1 §11.1 notes CAs as the mechanism for government double-counting avoidance. The VCMI Claims Code and SBTi v2.0 do not currently require CAs for voluntary contribution claims, but the direction of travel — as NDC accounting matures and host countries increasingly account for voluntary transfers — is toward CAs becoming the de facto standard for high-integrity voluntary credits as well. The CA tier is not just for compliance buyers today: it represents the quality frontier that the broader market is moving toward.
The primary CORSIA audience is international airlines. For airlines registered in participating states, CORSIA creates a hard compliance obligation: calculate emissions above the 2019 baseline and cancel eligible units to cover the excess. Failure to comply creates regulatory exposure under national aviation law. This is a direct procurement obligation for airline sustainability and compliance teams, not a voluntary enhancement.
The secondary audience is broader. Any company making a voluntary carbon neutrality claim or BVCM contribution claim while simultaneously operating in, adjacent to, or in the supply chain of the aviation sector will find that sophisticated stakeholders increasingly expect CORSIA-compatible credit quality. More specifically: companies whose scope 3 category 6 (business travel) or scope 3 category 4 (upstream transport) includes significant aviation emissions may find that their sustainability advisers, investors, or assurance providers raise the CA question in the context of an ISO 14068-1 neutrality claim.
The deepest relevance is structural: CORSIA represents the most advanced real-world implementation of Article 6 corresponding adjustments currently operating at scale. It is the compliance precedent for what high-integrity voluntary markets are converging toward. A company that today understands CORSIA, understands CAs, and has sourced CA-backed credits is positioned ahead of the voluntary market development curve rather than responding to it after it becomes the expected standard.
The Sovereign Portfolio is the 360° Impact Portfolio product for buyers who require CA-backed credits: CORSIA compliance buyers, organisations seeking the strongest available double-counting protection, and clients positioning ahead of voluntary market CA convergence.
Sovereign authorisation
Each credit carries a corresponding adjustment from the host country government. The host country has formally adjusted its NDC to account for the transfer. The reduction is counted once, globally.
Compliance grade
Credits satisfy all eight CORSIA credit integrity criteria and carry the CAs required for Phase 1 compliance from 2024. CORSIA eligibility confirmation is provided in the disclosure pack.
All other frameworks satisfied
CA-backed credits from Gold Standard and Verra satisfy ICVCM CCPs, ISO 14068-1 §11, DEFRA Good Quality, and VCMI credit due diligence requirements simultaneously. The disclosure pack covers all frameworks.
Model disclosure for illustrative purposes only. CORSIA compliance verification is the airline’s regulatory responsibility. Legal review recommended before use in a compliance filing or published disclosure.
CORSIA compliance is the airline’s regulatory responsibility. The Sovereign Portfolio supplies the credits and documentation that support that compliance; it does not verify or warrant compliance on the airline’s behalf. The following summarises the process positions for Sovereign Portfolio transactions.
Credits sourced from CORSIA-eligible programmes (Gold Standard, Verra) satisfying all programme design elements and the eight credit integrity criteria. CCP-Approved status provides independently assessed quality confirmation. All credits are ex-post, vintage-confirmed, and methodology-referenced.
Each Sovereign Portfolio credit carries host country CA documentation confirming that the mitigation outcome has been transferred out of the host country NDC. CA confirmation is verified at point of sourcing and recorded in the disclosure pack alongside the credit serial numbers.
Credits retired on the Gold Standard Impact Registry or Verra Registry in the client’s legal entity name. CORSIA eligibility status noted on the retirement certificate. Serial numbers and direct registry link provided in the disclosure pack within 14 working days.
The disclosure pack for Sovereign Portfolio transactions includes a CORSIA eligibility section confirming: programme eligibility, vintage compliance, CA status per credit, and CORSIA Phase 1 criteria satisfaction. Structured to support the airline’s own CORSIA reporting obligations.
CORSIA is the only compliance instrument in the seven-framework library. The six voluntary frameworks address credit quality, neutrality disclosure, UK regulatory compliance, claim language, portfolio construction, and the science-based transition pathway.
Integrity Council for the Voluntary Carbon Market · 2023
The voluntary market equivalent of CORSIA’s credit integrity criteria. Substantively aligned on all eight CORSIA criteria. CCP-Approved status of Gold Standard and Verra provides the programme-level quality assurance that satisfies both CORSIA and the voluntary frameworks simultaneously.
International Organization for Standardization · 2023
§11.1 of ISO 14068-1 notes corresponding adjustments as the mechanism for avoiding double counting between private entities and governments — the same principle CORSIA Criterion 7c operationalises. CA-backed credits satisfy both the CORSIA requirement and the §11.1 note simultaneously.
Voluntary Carbon Markets Integrity Initiative · 2023
The VCMI Claims Code does not currently require CAs for voluntary contribution claims. An airline using Sovereign Portfolio credits for CORSIA compliance may simultaneously make a VCMI-conformant contribution claim using the same credits, with the CA status representing a quality enhancement above the minimum required.
UK Government · SECR Guidance · 2019
DEFRA does not address corresponding adjustments or CORSIA. CA-backed credits satisfy all seven DEFRA Good Quality criteria by virtue of their programme eligibility, and go substantially beyond them on double-counting protection. UK companies with CORSIA exposure satisfy DEFRA as a baseline.
University of Oxford · Smith School · 2024
The Oxford Principles address portfolio composition and the shift toward durable removals. CORSIA does not distinguish project types by removal vs. avoidance. An airline seeking both CORSIA compliance and Oxford Principles alignment would source CA-backed credits from projects that also satisfy the Oxford durability progression.
Science Based Targets initiative · Consultation draft Nov 2025
SBTi v2.0 explicitly states that CAs do not apply under its Mitigation Impact Contribution framing. However, an airline with SBTi targets making both a CORSIA compliance purchase and an SBTi-aligned BVCM contribution would benefit from CA-backed credits for the CORSIA element, with standard voluntary credits potentially sufficient for the SBTi contribution element.
The Sovereign Portfolio supplies CA-backed credits from CORSIA-eligible Gold Standard and Verra programmes, with host country corresponding adjustment documentation, CORSIA Phase 1 eligibility confirmation, and a full ISO 14068-1 disclosure pack. The 30-minute discovery call is the starting point — for CORSIA compliance buyers and for voluntary buyers seeking the highest available double-counting protection.