CORSIA

Executive Summary

The Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA) is the operative reference for any airline sustainability or compliance officer, corporate travel manager, ESG counsel, voluntary carbon market participant, or aviation regulator whose work depends on a structural understanding of how international aviation CO₂ emissions are governed in the 2026 climate regulation stack. Operated by the International Civil Aviation Organization (ICAO), a specialised agency of the United Nations headquartered in Montreal and established under the Chicago Convention on International Civil Aviation of 7 December 1944, CORSIA was adopted by ICAO Assembly Resolution A39-3 in October 2016 as the global market-based measure to address the residual emissions gap from international aviation that the “basket of measures” (aircraft technology, operational improvements, sustainable aviation fuel) could not eliminate. Its operational architecture is set out in the ICAO Standards and Recommended Practices (SARPs) in Annex 16 Volume IV (Environmental Protection — Carbon Offsetting and Reduction Scheme for International Aviation), with the 2nd Edition becoming applicable on 1 January 2024 and supported by the Environmental Technical Manual (Doc 9501) Volume IV.

The scheme's structural distinction from every other carbon programme on the GreenCalculus standards library is twofold. First, it is the world's first — and in 2026 still the only — sectoral global market-based mechanism for greenhouse gas emissions: the EU Emissions Trading System, the UK ETS, the California Cap-and-Trade Program, the Korea ETS, the New Zealand ETS, and the Chinese national ETS are all jurisdictional rather than sectoral; the IMO Net-Zero Framework adopted in April 2025 is the closest sectoral analogue but is not yet fully operational. Second, it is a compliance market hybrid: the offsetting obligation is mandatory for airlines flying between participating States, but the underlying credit eligibility filter (the CORSIA Eligible Emissions Units architecture under the ICAO Technical Advisory Body) overlaps substantively with the voluntary carbon market — the same Verra VCS, Gold Standard, ACR, CAR, ART TREES, and Global Carbon Council programmes that supply voluntary buyers also supply CORSIA-compliant credits, subject to the additional vintage restrictions, methodology exclusions, and host-country Letter of Authorization (LoA) requirements that distinguish CORSIA-eligible vintages from generic VCM credits.

Phase 1 (2024–2026) operates under voluntary state participation with mandatory airline offsetting for flights between participating States; Phase 2 (2027–2035) becomes mandatory for ICAO Member States above a 2018 RTK threshold, with the limited exemptions for Least Developed Countries (LDCs), Small Island Developing States (SIDS), and Landlocked Developing Countries (LLDCs). The 2024 baseline of 85 percent of 2019 emissions for participating State pairs was set at 305,522,071 tonnes against actual 2024 emissions of 361,159,641 tonnes, producing the first non-zero Sector's Growth Factor in the scheme's history at 0.15405257 — a substantively material number meaning that every airline operator with international flights on covered State pairs in 2024 carries a calculable offsetting obligation. The 2024 SGF is applied uniformly to all operators' covered emissions (under the 100 percent sectoral / 0 percent individual operator weighting that applies until 2032; from 2033 the blend shifts to 85 percent sectoral / 15 percent individual), with reductions available for verified use of CORSIA Eligible Fuels.

The credit instrument is the CORSIA Eligible Emissions Unit (EEU). Each EEU represents one tonne of CO₂ emission reductions or removals from a project activity registered under an ICAO-approved emissions unit programme and meeting the additional CORSIA-specific requirements: activity start no earlier than 1 January 2016; emissions reductions occurring within the 1 January 2021 to 31 December 2026 window for Phase 1 eligibility; host-country Letter of Authorization enabling the Paris Agreement Article 6.2 Corresponding Adjustment to prevent double-counting against the host country's NDC; and compliance with programme-specific scope exclusions for project types, methodologies, and renewable-energy capacity caps. Six programmes are fully approved for Phase 1 in 2026: the American Carbon Registry (ACR), ART TREES, Climate Action Reserve (CAR), Global Carbon Council (GCC), Gold Standard, and Verra VCS. The Phase 1 cancellation deadline is 31 January 2028.

The single most operationally consequential feature of the 2024–2026 CORSIA market in 2026 is the supply scarcity created by the Letter of Authorization bottleneck. As of late 2025, only one issuance of CORSIA Eligible EEUs had occurred — from a project in Guyana under the ART TREES programme in February 2024, with 7.14 million vintage 2021 credits issued and IATA-estimated Phase 1 demand between 64 and 162 million tonnes. The gap is structural: ICAO approval of a programme certifies that the programme's methodology and registry infrastructure meet the CORSIA Emissions Unit Eligibility Criteria, but the host country government must independently issue an LoA authorising specific credit volumes for CORSIA use and report the Corresponding Adjustment to the UNFCCC. The LoA decision is sovereign; ICAO cannot compel it. The scarcity dynamic has reshaped Phase 1 procurement strategy: airlines with material 2024–2026 obligations are negotiating forward purchase agreements, multi-year offtake arrangements, and direct engagement with host country governments to accelerate LoA issuance ahead of the January 2028 deadline.

The interaction with the EU Emissions Trading System is the highest-confusion topic in aviation carbon compliance and the section most searched by European airline sustainability teams. The operative architecture under the EU ETS Directive 2003/87/EC as amended by Directive (EU) 2023/958 (aviation revision under the Fit for 55 package) and the implementing decisions of the Dutch Emissions Authority (NEa) and other Competent Authorities is: intra-EEA flights are covered exclusively by the EU ETS and excluded from the CORSIA offsetting obligation for European aircraft operators; flights from the EEA to CORSIA-participating third countries are covered by CORSIA only (during the “stop-the-clock” derogation period); flights from the EEA to non-CORSIA-participating third countries fall in a regulatory gap that the European Commission was due to address in its July 2026 CORSIA assessment. That assessment, published with a legislative proposal on 17 July 2026, found CORSIA not yet strong enough; the proposal keeps the current scope for 2027 and 2028 and, from 2029, extends the EU ETS to departures to airports within 5,000 km of Frankfurt. The Parliament and Council are still negotiating it. The outcome is the single most important regulatory variable for European aviation through 2027–2030.

The 2025–2026 CORSIA Landscape

The international aviation climate regime in 2026 is materially different from the regime that existed at CORSIA adoption in October 2016 or even at the start of the Pilot Phase on 1 January 2021. The shift in baseline architecture following Resolution A41-22 in October 2022, the first non-zero Sector's Growth Factor determination in late 2025, the October 2024 ICAO Council approval of four additional emissions unit programmes (Gold Standard, Verra, CAR, GCC) bringing the Phase 1 EEU list to six, the November 2025 update to CORSIA Eligible Fuel default LCA values and feedstock list, the October 2025 ICAO Council approval of Phase 2 EEU programmes covering the 2027–2029 compliance period, and the operationalisation of Paris Agreement Article 6.2 through cooperative approaches that include host-country LoAs for CORSIA use have collectively reshaped the operating environment for airline compliance teams, voluntary carbon market participants, and corporate travel managers.

The implication for any 2026 CORSIA user is that the scheme has shifted decisively from the Pilot Phase posture (zero SGF, no actual offsetting obligations, small CEF volumes, single approved EEU programme with material LoA-backed supply) to a Phase 1 operational regime (non-zero SGF generating real obligations, six approved EEU programmes with active supply pipelines, materially scaling CEF volumes, January 2028 cancellation deadline). The 2024–2026 compliance period is the first operational test of CORSIA at material scale, and the Phase 2 expansion from 1 January 2027 will dramatically increase scheme coverage as participation becomes mandatory.

What CORSIA Is — and What It Is Not

CORSIA is a sectoral global market-based measure for CO₂ emissions from international civil aviation. It defines, in operational detail, the obligations that airline operators incur on flights between participating ICAO Member States, the methodology by which those obligations are quantified, the eligibility criteria for emissions units that may be used to discharge those obligations, the sustainability criteria for fuels that may reduce those obligations, and the monitoring, reporting and verification framework that underpins all of the above. Its contribution to the international climate regulation stack is the sectoral compliance regime for an emissions source that sits outside the Paris Agreement's NDC architecture by virtue of the Chicago Convention.

What CORSIA is, in summary: a sectoral global market-based mechanism for international aviation CO₂ emissions; the world's first — and in 2026 still the only — operational sectoral GHG compliance scheme; a programme operated by ICAO under SARPs in Annex 16 Volume IV with supporting Environmental Technical Manual (Doc 9501) Volume IV guidance; a hybrid compliance-and-voluntary-market instrument in the sense that the offsetting obligation is mandatory but the underlying credit eligibility filter overlaps the voluntary carbon market; a CO₂-only scheme that does not address non-CO₂ radiative forcing; a covered-route scheme that applies only to international flights between participating States and explicitly excludes domestic aviation; a three-phase architecture (Pilot 2021–2023, Phase 1 2024–2026, Phase 2 2027–2035) with progressively expanding coverage; and a sector-decarbonisation instrument intended to be one component of a “basket of measures” alongside aircraft technology improvements, operational efficiency gains, and CORSIA Eligible Fuel deployment.

What CORSIA is not is equally important and frequently misunderstood:

• It is not a cap-and-trade scheme. CORSIA does not impose a cap on aviation emissions, does not allocate allowances, and does not operate an allowance market. Operators offset emissions above the baseline through cancellation of EEUs; emissions below the baseline carry no obligation. This is the structural distinction from the EU ETS, which is a cap-and-trade scheme with declining allowance volumes and a carbon price set by allowance market clearing.
• It is not a corporate GHG accounting standard. CORSIA EEU cancellation by an airline operator does not reduce that operator's Scope 1 emissions under the GHG Protocol Corporate Standard or ISO 14064-1. The operator's actual fuel-combustion CO₂ emissions remain in its inventory; the cancelled EEUs represent an offsetting action that is separately disclosed.
• It is not a target-setting framework. CORSIA does not require any specific level of corporate ambition, science-based pathway alignment, or absolute reduction commitment. The SBTi Corporate Net-Zero Standard and the SBTi Aviation Sectoral Decarbonization Approach address this layer; CORSIA is the sectoral compliance mechanism that operates parallel to, not in substitution for, science-based target frameworks.
• It is not a net-zero scheme. An airline operator that complies with CORSIA — cancels EEUs equal to its calculated offsetting obligation — has not achieved net-zero in any meaningful technical sense. ICAO's 2050 long-term aspirational goal (LTAG) of net-zero carbon emissions from international aviation, adopted at the 41st Assembly in October 2022, is a sector-level aspiration that CORSIA contributes to but does not alone deliver. The basket of measures — especially the scaling of CORSIA Eligible Fuels and the development of next-generation aircraft technology — is the substantive decarbonisation pathway; CORSIA addresses the residual emissions that the basket cannot eliminate.
• It is not a domestic aviation scheme. CORSIA covers only international flights (flights between two different States). Domestic aviation falls under each State's NDC and any applicable national or sub-national jurisdiction's emissions regulation. A flight from Singapore to Kuala Lumpur is international and potentially CORSIA-covered (subject to State pair participation); a flight from Singapore to anywhere in Singapore is not (and Singapore being a city-state does not generate domestic flights of consequence; the example is illustrative).
• It is not a non-CO₂ radiative forcing scheme. Aviation's climate impact includes substantial non-CO₂ effects: NO_x emissions at altitude producing ozone and reducing methane; water vapour producing contrails and contrail-induced cirrus; soot and sulphate aerosols affecting cloud properties. The IPCC AR6 Working Group I assessment characterises aviation's effective radiative forcing as approximately three times its CO₂-only forcing on the standard global-warming-potential basis, with substantial uncertainty. CORSIA addresses only the CO₂ component. The EU is moving to address non-CO₂ effects through MRV requirements from 2025 under the EU ETS Directive amendments; CORSIA has no equivalent.
• It is not a guarantee of any particular environmental outcome. CORSIA delivers offsetting through EEU cancellation; the EEUs represent project-level emission reductions or removals registered under approved programmes. The environmental integrity of CORSIA compliance depends on the integrity of those programmes, the rigour of the methodology layer, the host-country LoA architecture, and the third-party verification of project performance — not on the existence of the CORSIA scheme itself.
• It is not a Paris Agreement instrument. CORSIA was adopted under ICAO Assembly authority pursuant to the Chicago Convention, not under the UNFCCC or the Paris Agreement. The two regimes intersect at the Article 6 Corresponding Adjustment architecture: CORSIA EEUs require host-country LoAs and Corresponding Adjustments to prevent double-counting against host country NDCs. But CORSIA itself is an ICAO instrument, governed by ICAO Assembly Resolutions and SARPs, not by COP decisions.

Why CORSIA Exists

The international climate regime in the years leading up to 2016 had a structural gap. The Paris Agreement, adopted at COP21 in Paris on 12 December 2015, operationalised national mitigation commitments through Nationally Determined Contributions (NDCs) submitted by every Party. The NDC architecture worked well for emissions occurring within national territories — domestic industry, agriculture, buildings, surface transport, electricity generation. It worked considerably less well for two emission sources whose jurisdiction is internationally contested: international aviation and international shipping. The Chicago Convention on International Civil Aviation, signed in Chicago on 7 December 1944 and entered into force in 1947, vests jurisdiction over international civil aviation in ICAO — not in the State of departure, not in the State of arrival, not in the State of operator registration, not in the UNFCCC. Article 1 of the Convention reserves to each State complete and exclusive sovereignty over the airspace above its territory, but international flights cross multiple sovereignties and the regulatory framework for international air transport (safety, security, environmental protection) is set by ICAO Assembly Resolutions and the SARPs adopted under Article 37.

The implication for the Paris Agreement architecture is that international aviation emissions cannot straightforwardly be assigned to any State's NDC. An emission produced by a Singapore Airlines flight between London and Singapore is not the United Kingdom's emission (the UK did not produce it through any in-territory activity), not Singapore's emission (Singapore did not produce it either, though the operator is Singaporean), and not the emission of any of the intermediate overflight States. The conventional UNFCCC accounting approach — international “bunker fuels” reported separately in national inventories but not counted toward NDC compliance — left international aviation emissions in a regulatory limbo. In 2016, with international aviation responsible for approximately 2.5 percent of global CO₂ emissions and growing at 3–5 percent annually, this limbo was unsustainable.

ICAO's response was to develop a sectoral instrument that would operate within the UNFCCC framework conceptually — addressing climate change — but under ICAO authority procedurally. The development pathway ran from the 2010 ICAO Assembly Resolution A37-19 (which set a sectoral aspirational goal of carbon-neutral growth from 2020) through the 2013 Assembly Resolution A38-18 (which committed to develop a global market-based measure) to the October 2016 Assembly Resolution A39-3, which adopted CORSIA. The 2016 Resolution established the CORSIA framework with a Pilot Phase from 2021 to 2023, a First Phase from 2024 to 2026, and a Second Phase from 2027 to 2035; in 2022, the 41st Assembly Resolution A41-22 was adopted following the first periodic review of CORSIA by the ICAO Council, including the substantive change of the baseline from the original 2019–2020 average to 85 percent of 2019 emissions for the First and Second Phases.

The 2022 Assembly also adopted the long-term aspirational goal (LTAG) of net-zero carbon emissions from international aviation by 2050 (Resolution A41-21), recognising that carbon-neutral growth from 2020 — the original CORSIA objective — was insufficient for Paris Agreement temperature alignment. The 2050 net-zero LTAG repositioned CORSIA from being the primary international aviation climate instrument to being one component of a sector decarbonisation strategy that also includes large-scale SAF deployment under the CORSIA Eligible Fuels framework, next-generation aircraft technology development, operational efficiency improvements, and (potentially) the development of non-drop-in fuels such as hydrogen and electric propulsion for shorter routes.

Governance and Legislative History

CORSIA is governed by ICAO through its established institutional architecture: the ICAO Assembly (the supreme governing body of ICAO, comprising all 193 Member States, meeting every three years and adopting Resolutions that bind Member State conduct); the ICAO Council (a 36-member governing body elected by the Assembly with continuous oversight responsibility); the Committee on Aviation Environmental Protection (CAEP, the principal technical advisory body for environmental matters with sub-groups for fuels, emissions, MRV, and methodological questions); the Technical Advisory Body (TAB, the dedicated body for CORSIA Eligible Emissions Units assessment); and the ICAO Secretariat (operational management of CORSIA implementation, registry coordination, and Member State engagement). The SARPs framework operates under Article 37 of the Chicago Convention, which establishes the international standards regime.

Methodology and rule development for CORSIA operates through public consultation processes, expert panel review under CAEP and TAB, ICAO Council approval, and Assembly endorsement of substantive changes. The principal documents in the CORSIA layer are: Annex 16 Volume IV (the SARPs themselves — the binding requirements on Member States); the Environmental Technical Manual (Doc 9501) Volume IV (operational guidance supporting the SARPs); the CORSIA Implementation Elements (a set of documents directly referenced in the SARPs, covering State pairs, EEUs, CEF, certification schemes, sustainability criteria, default LCA values, etc.); the TAB Reports and the document “Clarification of TAB's criteria interpretation contained in TAB Reports” (the operational guidance on EEU eligibility interpretation); and the CORSIA Central Registry rules and implementation procedures.

The publication history:

CORSIA Architecture — The Three-Layer Structure

The CORSIA scheme operates through a three-layer architecture that distinguishes it from every other carbon programme on the GreenCalculus standards library. Layer 1 is the SARPs layer — the binding ICAO Standards and Recommended Practices that define what States and aircraft operators must do. Layer 2 is the CORSIA Eligible Fuels (CEF) framework — the SAF/LCAF crediting layer that operates at the fuel-supply level. Layer 3 is the CORSIA Eligible Emissions Units (EEU) layer — the offset quality filter that determines which carbon credits from voluntary market programmes may be used to discharge CORSIA offsetting obligations. The three layers are operationally distinct, governed by different bodies within ICAO, and produce different compliance instruments.

The architectural significance of the three-layer structure is that an airline operator's CORSIA compliance touches all three layers but the compliance touchpoints differ. At Layer 1, the operator complies with MRV obligations, reports its AOER, engages a third-party verifier, and ultimately cancels EEUs equal to its calculated offsetting obligation. At Layer 2, the operator may (optionally) procure and use CORSIA Eligible Fuels, claim the lifecycle emissions reduction against the 89 gCO₂e/MJ jet kerosene baseline, document the use through SCS-certified evidence, and reduce its offsetting obligation accordingly. At Layer 3, the operator (or its procurement partners) sources EEUs from ICAO-approved programmes meeting the EEU-specific eligibility requirements (vintage, methodology scope, host-country LoA, Corresponding Adjustment status) and cancels them through the operator's account on the relevant programme registry by the compliance deadline.

The structural distinction from voluntary carbon market participation is that CORSIA imposes mandatory cancellation; the underlying credit eligibility filter is more restrictive than voluntary market eligibility (vintage windows, methodology exclusions, LoA requirements); and the compliance is monitored by the State of Attribution acting as the regulator, with non-compliance generating consequences under national law implementing the SARPs. The corresponding implication for procurement is that CORSIA-eligible EEUs typically command a price premium over generic voluntary market credits from the same programmes, reflecting the additional eligibility requirements and the supply scarcity created by the LoA bottleneck.

Scope — Which Flights and Which Operators

The CORSIA route coverage rule is at once simple in concept and operationally complex in practice. The simple rule: CORSIA covers CO₂ emissions from international flights between two ICAO Member States that both participate in CORSIA in the relevant year. The operational complexity: identifying which State pairs are subject to offsetting obligations requires reference to the ICAO document “CORSIA States for Chapter 3 State Pairs”, which is updated annually by the ICAO Council and which currently (Edition 6 for 2026) lists 130 participating States. A flight from a participating State to another participating State is covered; a flight from a participating State to a non-participating State is not; a domestic flight (between two aerodromes in the same State) is never covered.

The operator coverage rule is governed by the 10,000-tonne threshold: aircraft operators with annual CO₂ emissions from international flights greater than 10,000 tonnes (from aeroplanes with a maximum take-off mass exceeding 5,700 kg) are subject to CORSIA MRV obligations. Below this threshold, operators are exempted from MRV and from offsetting obligations. This produces a structural exclusion from CORSIA scope for: most business aviation (typical business jet operators do not exceed 10,000 tonnes annual international CO₂); helicopter operators (excluded by aircraft type and rarely operating internationally at scale); aircraft below 5,700 kg MTOW; regional carriers with predominantly domestic operations.

The State pair logic in detail:

• Flight from participating State A to participating State B: covered; emissions reported by operators; offsetting obligation applied via SGF.
• Flight from participating State A to non-participating State C: not covered for offsetting obligation; MRV may still apply if the operator is above the threshold and the operator's State of Attribution requires reporting of total international emissions.
• Flight from non-participating State C to participating State A: not covered; same MRV qualification.
• Flight from non-participating State C to non-participating State D: not covered.
• Domestic flight within any State: never covered (falls under State NDC and national law).

The State of Attribution concept governs which State holds the regulatory relationship with each operator. The State of Attribution is, for most operators, the State of the Operator (the State where the operator is registered for operating purposes), but rules differ in edge cases involving multinational operations and wet-lease arrangements. The State of Attribution: receives the AOER; engages the third-party verifier oversight; calculates the operator's offsetting obligation by applying the SGF to the operator's covered emissions; communicates the obligation to the operator; oversees EEU cancellation by the compliance deadline; and reports aggregate data to ICAO. The State of Attribution's effectiveness in implementing CORSIA varies substantially across the 130 participating States, with EU Member States, the United States, Canada, the United Kingdom, Australia, and Japan having the most operationally mature implementation frameworks.

The 2024 coverage produced offsetting obligations for approximately 80 percent of international RTKs. The Phase 2 expansion from 1 January 2027, with mandatory participation for States above the 2018 RTK threshold, will expand coverage to approximately 85+ percent of international RTKs — the residual being predominantly LDCs, SIDS, and LLDCs that retain exemptions, plus the small share of operators below the 10,000-tonne threshold.

The Baseline and Offsetting Obligation Calculation

The CORSIA offsetting obligation calculation is the operationally critical mechanic of the scheme — the single piece of the architecture that every airline compliance team must understand in detail. The calculation operates in three stages: (1) the sectoral baseline and Sector's Growth Factor determination by ICAO; (2) the individual operator's covered emissions calculation by the State of Attribution; (3) the individual operator's offsetting obligation as the product of covered emissions and the applicable growth factor blend, less verified CORSIA Eligible Fuel reduction claims.

Stage 1 — The sectoral baseline and SGF

The sectoral baseline is calculated by ICAO as 85 percent of total 2019 CO₂ emissions for State pairs subject to offsetting requirements in the given year. The “State pairs subject to offsetting requirements” concept is dynamic: the baseline is recalculated each year based on which State pairs are participating that year. For 2024, the baseline was 305,522,071 tonnes; for 2025 and 2026, the baseline is similarly calculated against 85 percent of the 2019 emissions for that year's participating State pairs.

The Sector's Growth Factor (SGF) is calculated by ICAO as:

SGF_y = (SE_y − SE_B,y) / SE_y

Where:
  SE_y = Total sectoral CO₂ emissions for State pairs subject to offsetting requirements in year y
  SE_B,y = 85% of total annual sectoral CO₂ emissions for State pairs subject to offsetting requirements in 2019, in year y

For 2024, the calculation produced:

SE₂₀₂₄ = 361,159,641 tCO₂
SE_B,2024 = 305,522,071 tCO₂ (the baseline)

SGF₂₀₂₄ = (361,159,641 − 305,522,071) / 361,159,641
        = 55,637,570 / 361,159,641
        = 0.15405257

The 2024 SGF of 0.15405257 means that, of every tonne of CO₂ emitted by an aircraft operator on a covered State pair flight in 2024, approximately 15.4 percent must be offset through EEU cancellation. The remaining 84.6 percent is implicitly within the baseline (the “carbon-neutral growth from 2020” framing on the post-amendment 85-percent-of-2019 basis).

Stage 2 — The operator's covered emissions

The State of Attribution calculates each operator's covered emissions as the sum of the operator's monitored, reported, and verified CO₂ emissions on flights between participating State pairs in the year, drawing on the operator's AOER and applying the route attribution rules in Annex 16 Volume IV. This produces a single tonne-of-CO₂ figure per operator per year.

Stage 3 — The operator's offsetting obligation

The operator's offsetting obligation in year y is calculated as:

OOR_y(operator) = OE_y(operator) × [α_y × SGF_y + (1 − α_y) × IGF_y(operator)] − FCR_y(operator)

Where:
  OOR = Operator Offsetting Requirement (tCO₂)
  OE = Operator's covered emissions on participating State pairs (tCO₂)
  α = Sectoral weighting (1.00 through 2032; 0.85 from 2033)
  SGF = Sector's Growth Factor (as calculated in Stage 1)
  IGF = Individual Operator Growth Factor (zero weighted until 2033)
  FCR = Fuel Claim Reduction from verified CORSIA Eligible Fuel use

Through the Phase 1 (2024–2026) and the first two years of Phase 2 (2027–2032), the α weighting is 1.00 — meaning the obligation is calculated purely on the sectoral growth factor, with no individual operator growth factor contribution. This design choice prioritises competitive neutrality across operators: a fast-growing carrier and a slow-growing carrier face the same growth-factor multiplier per tonne of emissions. From 2033, the blend shifts to 85 percent sectoral / 15 percent individual operator, introducing a modest accountability mechanism for each operator's own growth trajectory.

The Fuel Claim Reduction (FCR) is the operator's claim under Layer 2 (the CEF framework): verified use of CORSIA Eligible Fuels reduces the operator's offsetting obligation. The detailed FCR calculation is set out in §10 below; conceptually, each tonne of jet fuel replaced by CEF with X percent lifecycle reduction against the 89 gCO₂e/MJ baseline produces a creditable reduction of X percent of the emissions attributable to that fuel volume.

Worked Example — An Individual Operator's 2024 Offsetting Obligation

The 2024 SGF's impact on a real airline's offsetting obligation is the single most operationally consequential calculation in the CORSIA architecture. The worked example below illustrates the magnitude across three SAF-blend scenarios. The numbers are stipulated for instructional purposes; the example is hypothetical and not the operational values for any specific real-world airline.

Operator profile

“Aerolíneas Meridional” (hypothetical) — a mid-size international carrier with operations between South American hub airports and destinations in North America, Europe, and the Caribbean. All home-country State pairs are CORSIA Phase 1 participating States. Phase 1 reporting covers all 2024 international RTKs.

2024 emissions and fuel data

Total 2024 international fuel burn: 1,275,000 tonnes Jet A
CO₂ emission factor (jet kerosene, IPCC default): 3.16 tCO₂/t fuel
Total 2024 international CO₂ emissions: 4,029,000 tCO₂

Of which, on covered State pairs (94% of routes): 3,787,260 tCO₂
Of which, on non-covered State pairs (6%): 241,740 tCO₂ (excluded from OOR)

State of Attribution: Hypothetical CORSIA-participating State
Operator qualifies for CORSIA (above 10,000 t threshold): Yes (substantially)

Stage 1 application of 2024 SGF

SGF₂₀₂₄: 0.15405257
Sectoral weighting α₂₀₂₄: 1.00 (no individual weighting)

Gross offsetting obligation (before FCR):
  = 3,787,260 × 0.15405257
  = 583,425 tCO₂

Three SAF-blend scenarios for 2024 FCR claim

Scenario A — No SAF use (pure fossil fleet).

CEF volume: 0 tonnes
FCR₂₀₂₄: 0 tCO₂

Net 2024 offsetting obligation:
  = 583,425 − 0
  = 583,425 tCO₂
  ≈ 583,425 EEUs to cancel by 31 January 2028 (for 2024 alone)

Scenario B — ReFuelEU-mandated 2% SAF blend (HEFA from used cooking oil).

CEF volume: 25,500 t (2% of fleet fuel)
Conventional jet fuel CI (CORSIA baseline): 89 gCO₂e/MJ
HEFA-UCO CORSIA default LCA core value (illustrative): 13.9 gCO₂e/MJ
Lifecycle reduction: 89 − 13.9 = 75.1 gCO₂e/MJ
Percentage reduction vs baseline: 75.1 / 89 = 84.4%

Avoided CO₂ from CEF use:
  = 25,500 t SAF × 3.16 tCO₂/t × 84.4%
  = 68,002 tCO₂

Coverage adjustment (94% covered routes):
  FCR₂₀₂₄ applicable to covered emissions:
  = 68,002 × 0.94
  = 63,922 tCO₂

Net 2024 offsetting obligation:
  = 583,425 − 63,922
  = 519,503 tCO₂
  ≈ 519,503 EEUs to cancel

Scenario C — Aggressive 8% SAF blend (mix of HEFA-UCO and emerging pathways averaging 80% lifecycle reduction).

CEF volume: 102,000 t (8% of fleet fuel)
Average CEF lifecycle reduction: 80%

Avoided CO₂ from CEF use:
  = 102,000 t SAF × 3.16 tCO₂/t × 80%
  = 257,856 tCO₂

Coverage adjustment (94% covered routes):
  FCR₂₀₂₄ applicable to covered emissions:
  = 257,856 × 0.94
  = 242,385 tCO₂

Net 2024 offsetting obligation:
  = 583,425 − 242,385
  = 341,040 tCO₂
  ≈ 341,040 EEUs to cancel

Three-scenario summary and cost implication

Difference Scenario A vs Scenario C (EEU obligation):
  = 583,425 − 341,040
  = 242,385 tCO₂ avoided EEU cancellation

Difference Scenario A vs Scenario C (EEU cost at $22/t):
  = $12,835,350 − $7,502,880
  = $5,332,470

SAF cost premium (Scenario C):
  102,000 t SAF × ($1,800/t premium over jet kerosene at $900/t)
  = 102,000 × $1,800
  = $183,600,000

Net economic comparison (2024 alone, illustrative):
  Scenario C SAF premium of $183.6M vs $5.3M EEU saving
  = economic gap of approximately $178M against SAF
  …but SAF carries parallel ReFuelEU compliance value
  …and EU ETS allowance savings on intra-EEA flights
  …and brand/sustainability narrative value

Three-year Phase 1 aggregate obligation (illustrative)

If the 2024 SGF and emissions pattern recur with modest growth through 2025 and 2026 (illustrative assumption of 4% annual emissions growth and proportionally higher SGFs of 0.18 and 0.21 respectively, with no SAF use), the Phase 1 cumulative obligation for Aerolíneas Meridional in Scenario A would be approximately:

2024 OOR: 583,425 tCO₂
2025 OOR (illustrative): ~709,134 tCO₂
2026 OOR (illustrative): ~860,000 tCO₂

Phase 1 cumulative obligation: ~2,152,559 tCO₂
  ≈ 2.15 million EEUs to cancel by 31 January 2028

CORSIA Eligible Fuels (CEF) Under CORSIA

The CORSIA Eligible Fuels framework is Layer 2 of the CORSIA architecture — the fuel-supply crediting layer that operates parallel to the EEU offset layer. CEF includes CORSIA Sustainable Aviation Fuels (SAF) and CORSIA Lower Carbon Aviation Fuels (LCAF), both required to meet the CORSIA sustainability criteria across 14 themes; 49 feedstocks are currently recognised in the framework as of the November 2025 update. The framework is operationally documented through five principal ICAO documents: the CORSIA Eligibility Framework and Requirements for Sustainability Certification Schemes (4th Ed., June 2025); CORSIA Approved Sustainability Certification Schemes (3rd Ed., October 2024); CORSIA Sustainability Criteria for CORSIA Eligible Fuels (June 2025); CORSIA Default Life Cycle Emissions Values for CORSIA Eligible Fuels (June 2025, with November 2025 amendments); CORSIA Methodology for Calculating Actual Life Cycle Emissions Values.

The 89 gCO₂e/MJ baseline and the 10% minimum reduction

CORSIA establishes conventional aviation fuel (jet kerosene) at a baseline carbon intensity of 89 gCO₂e/MJ, a well-to-wake lifecycle value. To qualify as a CORSIA Eligible Fuel, a candidate fuel must deliver at least 10 percent lifecycle emissions reduction against this baseline — producing a maximum lifecycle CI of 80.1 gCO₂e/MJ. The 10 percent threshold is intentionally less stringent than the corresponding thresholds under parallel SAF mandates (the EU ReFuelEU Aviation Regulation requires 65 percent reduction for eligible SAF; the US Inflation Reduction Act 45Z credit tiers operate at 50 percent and above), allowing CORSIA to credit a broader set of pathways including LCAF (lower-carbon aviation fuel based on fossil feedstocks with reduced upstream emissions) alongside higher-reduction SAF pathways.

Default LCA values versus actual LCA values

The CORSIA Default Life Cycle Emissions Values document provides default core lifecycle values for approved feedstock/conversion-process/region combinations. Operators using CEF may apply the default value applicable to the specific feedstock and pathway, or may submit an Actual LCA Value calculation under the CORSIA Methodology for Calculating Actual Life Cycle Emissions Values. The default values are typically conservative (slightly higher CI than a well-executed actual LCA), trading precision for procedural simplicity. The November 2025 update approved new feedstocks and added refined default core LCA values for several pathway combinations.

The 14 sustainability themes

The CORSIA Sustainability Criteria for CORSIA Eligible Fuels document operationalises the requirement that CEF meet a broad sustainability standard beyond the GHG outcome alone. The 14 themes cover: GHG reductions (the lifecycle reduction threshold and ILUC accounting); carbon stock (preservation of high-carbon land); water (water use efficiency and water quality protection); soil (soil health); air (air pollutant emissions); conservation (biodiversity protection); waste and chemicals; human and labour rights; land use rights and land use; water use rights; local and social development; food security; ILUC (Induced Land Use Change emissions explicitly included in the LCA); other indirect effects. Each theme has defined criteria that the feedstock supply chain must satisfy, evidenced through the Approved Sustainability Certification Scheme.

SAF pathway taxonomy

The principal SAF pathways approved under ASTM D7566 and recognised by CORSIA include: HEFA (Hydroprocessed Esters and Fatty Acids) — the dominant operational pathway in 2026, using used cooking oil, tallow, animal fats, and oilseed crops; FT (Fischer-Tropsch) — using biomass gasification; ATJ (Alcohol-to-Jet) — using ethanol or other alcohols; SIP (Synthesized Iso-Paraffins) from hydroprocessed fermented sugars; CHJ (Catalytic Hydrothermolysis Jet); HC-HEFA-SPK (Hydroprocessed Hydrocarbons from Algae). The default core LCA values vary substantially across pathways and feedstocks: HEFA from used cooking oil typically delivers ~75–85 percent lifecycle reduction; HEFA from tallow ~80 percent; HEFA from soy or rapeseed substantially lower due to ILUC, and in some cases below the 10 percent threshold; FT from forest residues typically >85 percent; ATJ-Isobutanol from sugarcane ~50–70 percent.

SAF supply scaling

Total CORSIA-certified SAF production in 2024 was 181,263 tonnes, against total global jet fuel consumption of approximately 300 million tonnes — a SAF share of approximately 0.06 percent. The supply gap is structural and the central operational risk to the 2050 net-zero LTAG: even at aggressive announced expansion rates, 2026 SAF production capacity is expected to deliver low single-digit percent of total fleet fuel by the late 2020s. The CORSIA framework is positioned to credit SAF use, not to mandate it; the mandate function is performed by parallel jurisdictional instruments — most notably the EU ReFuelEU Aviation Regulation (EU) 2023/2405 requiring 2 percent SAF by 2025, 6 percent by 2030, 20 percent by 2035, 34 percent by 2040, 42 percent by 2045, and 70 percent by 2050, the UK SAF Mandate, and the US Sustainable Aviation Fuel Grand Challenge.

SAF Book and Claim versus physical SAF

The CORSIA framework permits a Book and Claim approach for SAF accounting: an airline operator may purchase SAF certificates (representing SAF produced and delivered to a different fuel system) without physically uplifting the SAF on its own aircraft. The Book and Claim mechanism enables SAF use at airports where physical SAF supply is unavailable while preserving the GHG reduction claim. Book and Claim is operationally important during the supply-constrained phase: SAF production is concentrated in a small number of refineries (predominantly in Northern Europe, the US Gulf Coast, and Singapore), but offsetting obligations apply across the global participating-State route network.

Interaction with ReFuelEU Aviation

The interaction with ReFuelEU is the most operationally consequential parallel regulation for European-operating carriers. ReFuelEU requires jet fuel suppliers operating in the EU to ensure that the fuel supplied at EU airports contains the mandated minimum share of SAF, with eligible SAF requiring a minimum of 65 percent GHG emissions reductions. CORSIA accepts SAF at the 10 percent threshold but the EU airport SAF must additionally meet the 65 percent threshold. A SAF batch certified under both frameworks must satisfy the higher EU threshold; double-claiming (using the same SAF batch under both ReFuelEU and CORSIA) is constrained by the CORSIA MRV requirement that operators confirm CEF batches have not been used in other schemes, and by the ReFuelEU framework's own anti-double-counting provisions.

CORSIA Eligible Emissions Units — The Offset Quality Filter

CORSIA Eligible Emissions Units (EEUs) are the offset instruments that airline operators cancel to discharge their offsetting obligations. The EEU eligibility filter is operationalised through Layer 3 of the architecture: the ICAO Technical Advisory Body (TAB) assesses voluntary carbon market programmes against the CORSIA Emissions Unit Eligibility Criteria; the ICAO Council approves programme eligibility based on TAB recommendations; the approved programmes appear in the ICAO document “CORSIA Eligible Emissions Units” with programme-specific scope of eligibility, terms of eligibility, and exclusions.

The six EEU quality criteria

The CORSIA Emissions Unit Eligibility Criteria document (March 2019) establishes six core criteria that emissions units must satisfy:

1. Real. Emission reductions or removals must be physical outcomes that have actually occurred, not modelled outcomes alone. The project activity must be implemented and operational.
2. Additional. Reductions must be additional to what would have occurred without the carbon finance — the project would not have happened or would not have happened at the same scale without the carbon revenue.
3. Verifiable. Reductions must be quantified and validated/verified by an independent third-party body operating under recognised assurance standards.
4. Permanent. Reductions must be permanent (irreversible) or, where reversal is possible (land-use storage), the project must address reversal risk through buffer provisions or risk-mitigation measures.
5. Unique. Reductions must not be double-counted — the same tonne of emission reduction cannot be claimed by multiple parties or against multiple obligations. This is the criterion that drives the Article 6 Corresponding Adjustment requirement.
6. Conservative. Where uncertainty exists, the quantification must err on the side of caution to ensure that issued credits are not overstated.

Programme-level assessment

The TAB conducts the assessment at the programme level — not at the individual project level. A programme that passes TAB assessment and receives ICAO Council approval is then authorised to certify EEUs for CORSIA use, subject to programme-specific scope of eligibility, terms of eligibility, and any project-type or methodology exclusions the Council imposes. The programme's own validation and verification processes apply to individual projects under that programme; CORSIA does not duplicate the project-level certification.

Current approved programme list (Phase 1, 2024–2026)

Vintage restrictions

The Phase 1 vintage restrictions are operationally critical:

• The project activity must have started its first crediting period on or after 1 January 2016
• The emissions reductions or removals must have occurred between 1 January 2021 and 31 December 2026 for Phase 1 eligibility
• For Pilot Phase eligibility (2021–2023 compliance, now closed), the relevant emission reduction window was 1 January 2016 to 31 December 2020

The vintage restrictions exclude legacy CDM-era credits, pre-2021 vintage voluntary market credits, and credits from project activities that started crediting periods before 2016. The implication is that a substantial volume of generic voluntary market credits from approved programmes are not CORSIA-eligible because of vintage; the available CORSIA-eligible supply pool is materially smaller than the total pool of credits from the same programmes.

The Letter of Authorization (LoA) and Corresponding Adjustment requirement

The structural choke point in Phase 1 EEU supply is the host-country LoA requirement. A credit can be issued by an ICAO-approved registry but still fall short of full CORSIA eligibility if the host country has not authorised its use for CORSIA purposes; the host country's issuance of an LoA and the parallel Corresponding Adjustment reporting to the UNFCCC are the operational substantiation of the “unique” quality criterion. Without an LoA, the same tonne could be double-counted — once by the airline against its CORSIA obligation, once by the host country against its NDC.

As of late 2025, only Guyana had issued CORSIA EEUs at material volume — 7.14 million ART TREES vintage 2021 credits in February 2024. Additional host countries (Honduras, Belize, Cambodia, others) have signalled intent to issue LoAs but the operational pipeline through early 2026 remained narrow. The scarcity drives the per-tonne price: the IATA-organised first Guyana procurement event in Q4 2024 sold ART TREES credits at $21.70 per tonne fixed-price auction, materially above generic ART TREES voluntary market pricing for the same vintages.

Monitoring, Reporting and Verification (MRV)

The CORSIA MRV framework is the operational backbone of the scheme — the mechanism by which aircraft operators' emissions are measured, reported, and verified consistently across the 130 participating States. The MRV framework is established in Annex 16 Volume IV, Part II, with detailed procedural guidance in the Environmental Technical Manual (Doc 9501) Volume IV. Compliance with the MRV framework is the precondition for participation in the offsetting regime: an operator that fails to monitor, report, or verify cannot validly calculate or discharge its offsetting obligation.

Fuel use monitoring methods

CORSIA permits five methods for fuel use monitoring, each with different precision and operational complexity:

1. Method A — Fuel uplift method. Fuel uplifted into the aircraft is measured at each refuelling event and recorded; the difference between uplifted fuel and remaining fuel at engine shutdown produces the fuel burn per flight.
2. Method B — Block-on / block-off fuel. Fuel quantity at engine start (block-on) and engine stop (block-off) is measured and the difference is the flight fuel burn.
3. Method C — Fuel allocation with block hours. Total fuel consumed by the fleet over the reporting period is allocated to individual flights based on block hours or other operational metrics. Simplified method for operators with limited per-flight measurement capability.
4. Method D — ICAO CORSIA CO₂ Estimation and Reporting Tool (CERT). A simplified estimation tool for smaller operators or specific flight types that do not have access to detailed fuel data; produces a conservative CO₂ estimate based on aircraft type, route, and operational characteristics.
5. Method E — Block hours method. Total block hours multiplied by aircraft-type-specific average fuel consumption.

Most major international carriers use Method A or Method B (the more precise methods); smaller operators may use Method D (CERT) or simpler alternatives. The State of Attribution approves the operator's Emissions Monitoring Plan (EMP), which specifies the chosen method and the operational implementation.

The Aeroplane Operator Emissions Report (AOER)

The AOER is the operator's annual emissions report submitted to the State of Attribution. The AOER includes: the operator's identification and contact details; the chosen fuel use monitoring method; the operator's fleet composition; emissions from international flights between participating State pairs (covered for CORSIA offsetting); emissions from international flights to/from non-participating States (relevant for MRV but not for offsetting); any verified CORSIA Eligible Fuel claims with supporting SCS certification; and the third-party verifier's opinion. The AOER submission deadline is typically 30 April of the year following the reporting year, with the third-party verification statement attached.

Compliance period structure

CORSIA operates on a three-year compliance period structure. The Pilot Phase compliance period (2021–2023) and the First Phase compliance period (2024–2026) each cover three calendar years. Operators monitor and verify emissions annually but discharge offsetting obligations on a compliance-period basis: the Phase 1 cumulative obligation (2024 + 2025 + 2026) must be cancelled by 31 January 2028. This structure permits operators to optimise EEU procurement timing within the compliance period — for example, deferring some cancellation to allow new EEU supply to come online after host-country LoA issuance.

Third-Party Verification Under CORSIA

CORSIA requires third-party verification of every AOER from aircraft operators above the 10,000-tonne threshold. The verification methodology operates under ISO 14064-3:2019 at reasonable assurance level, with CORSIA-specific procedural additions in the CORSIA-Verification document referenced in Annex 16 Volume IV.

Verifier accreditation

Third-party verifiers must be accredited as Validation and Verification Bodies under ISO 14065:2020 by a national accreditation body that is a member of the International Accreditation Forum (IAF). The accreditation must cover the GHG accounting scope and, for CORSIA work, must include CORSIA-specific scope verification under the ICAO Doc 9501 Volume IV procedures. The State of Attribution maintains oversight of verifier engagement; some States operate additional national-level approval requirements for verifiers operating in their jurisdiction.

What the verifier assesses

The CORSIA verification engagement assesses: the operator's EMP and its application; the fuel use monitoring method implementation and data quality; the route attribution and State pair classification; the emissions calculation and reporting; the CORSIA Eligible Fuel claim documentation and SCS certification (where claimed); the controls environment around the operator's monitoring and data systems; and the AOER's consistency with operational records (flight logs, fuel receipts, fleet data). The verification output is a Verification Statement — an unqualified opinion if the AOER materially complies with CORSIA requirements, or a qualified opinion / adverse opinion with specified findings if material deviations are identified.

CORSIA verification versus VCS/Gold Standard project verification

The distinction between CORSIA verification and project-level voluntary market verification is operationally important and frequently confused. CORSIA verification covers the airline operator's AOER (the emissions side of the CORSIA equation); voluntary market project verification covers the carbon credit project's monitored emission reductions (the credit-supply side). The same accredited body may perform both types of engagement (the ISO 14065 accreditation is the common foundation), but the engagement scope, the technical documentation reviewed, and the verification output are different. An airline operator's CORSIA-compliant Verification Statement does not transfer to the projects from which the operator subsequently sources EEUs; those projects must independently carry valid project-level verification statements from their respective programme's accredited verifiers.

State Action Plans and National Implementation

The CORSIA SARPs are binding on ICAO Member States under Article 37 of the Chicago Convention, but the operational implementation occurs through national civil aviation authorities (CAAs) and the legal frameworks each State adopts to discharge its SARPs obligations. The variation in national implementation quality and enforcement is substantial. EU Member States operate under the harmonised EU framework (the EU ETS Directive 2003/87/EC as amended by Directive (EU) 2023/958 implements CORSIA into EU law alongside the EU ETS); the United Kingdom operates under the equivalent UK legislative framework post-Brexit; the United States operates through the FAA and EPA jurisdictional split; Canada, Australia, Japan, and Singapore each have operationally mature frameworks; many other participating States are still building implementation capacity.

The State Action Plan concept is the structural mechanism by which States communicate their voluntary CORSIA implementation choices to ICAO. The Action Plan documents the State's implementation approach, the participating CAA, the operator-level reporting framework, the verifier engagement protocol, and the enforcement mechanism for non-compliance. State Action Plans are reviewed periodically and updates are submitted to ICAO.

The structural risk for operators is that a poorly-implemented State of Attribution may produce delays in offsetting obligation calculation, inconsistent verifier oversight, or weak enforcement of cancellation deadlines. Operators with a State of Attribution in a less-developed implementation jurisdiction must engage proactively with the national CAA to ensure timely receipt of the calculated obligation and operational coordination through the compliance cycle.

CORSIA and the EU ETS — The Critical Overlap

The interaction between CORSIA and the EU Emissions Trading System for aviation is the single highest-confusion topic in aviation carbon compliance and the section most searched by European airline sustainability teams. The operative architecture is set out in the EU ETS Directive 2003/87/EC as amended by Directive (EU) 2023/958 (the aviation revision under the Fit for 55 package), with implementing decisions of the European Commission and the national Competent Authorities operationalising the rules.

The four route categories

The route coverage matrix for a European-operating carrier in 2026 is:

The avoidance of double charging

The structural design principle of the EU's CORSIA implementation is that no flight should be subject to both EU ETS surrender and CORSIA offsetting for the same emissions. The implementation in EU law operationalises this through the route-category split: intra-EEA is EU ETS only; extra-EEA to CORSIA-participating third countries is CORSIA only; the routes that would have been EU ETS-extra-EEA absent the derogation are deferred to CORSIA. The mechanism by which double charging is avoided is therefore the stop-the-clock derogation itself, not a netting calculation at the operator level.

The July 2026 Commission assessment and proposal

The EU ETS Directive required the European Commission to assess CORSIA's implementation by July 2026. It published the assessment with a legislative proposal on 17 July 2026. The Commission found that CORSIA had not yet been strengthened enough, but it did not propose covering all departing flights. Instead it proposed keeping today's scope for 2027 and 2028 and, from 2029, extending the EU ETS to departures from the EEA to airports within 5,000 km of Frankfurt, plus business-jet flights to and from the EEA, with a new CORSIA assessment in 2032. The proposal still needs the agreement of the European Parliament and the Council, so the final scope can change. Civil society and the SASHA Coalition want all departing flights covered; airline industry positions (A4A, A4E, IATA) generally favour CORSIA continuation. The decision will materially shape the 2027–2035 European aviation compliance environment.

Free allocation and full auctioning

Separate from the scope question, the EU ETS aviation rules implement a phased transition to full auctioning of aviation allowances. Free allocation to aircraft operators was reduced by 25 percent in 2024, by 50 percent in 2025, and is fully eliminated in 2026: from 1 January 2026, all aviation allowances are auctioned, with the cost of EU ETS surrender passed through to airline operators in full. This produces a substantial cost step-up for European-operating carriers on intra-EEA routes from 2026 onwards.

The non-CO₂ MRV pilot under EU ETS

From 1 January 2025, EU ETS aviation MRV expanded to include monitoring of non-CO₂ radiative forcing effects (NO_x, contrails, water vapour) for intra-EEA flights; from 2027, the scope extends to all flights to or from the EEA. The MRV pilot is the data-gathering precursor to potential future regulatory inclusion of non-CO₂ effects in the EU ETS scope. CORSIA has no equivalent — non-CO₂ effects remain outside CORSIA scope.

CORSIA and Article 6 of the Paris Agreement

The intersection between CORSIA and Article 6 of the Paris Agreement is operationally critical to the EEU eligibility architecture and is the source of the supply scarcity that defines the Phase 1 market. The Chicago Convention's jurisdictional reservation of international civil aviation to ICAO produces a structural challenge: a CORSIA EEU represents an emission reduction that occurred in a host country's territory; that host country has its own NDC under the Paris Agreement; without a Corresponding Adjustment, the same tonne of reduction could be claimed both by the airline against CORSIA and by the host country against its NDC — the “double-counting” problem that the unique quality criterion is designed to prevent.

The Article 6.2 Cooperative Approaches mechanism

Article 6.2 of the Paris Agreement permits Parties to engage in Cooperative Approaches involving the use of Internationally Transferred Mitigation Outcomes (ITMOs) for NDC purposes. The operational guidance for Article 6.2 was adopted at COP26 (Glasgow, November 2021) through Decision 2/CMA.3 and refined at COP27, COP28, and COP29. The mechanism requires the transferring Party (host country) to apply a Corresponding Adjustment to its NDC accounting when ITMOs are transferred to another Party or used for purposes other than NDC accounting — including CORSIA.

For CORSIA, the operational pathway is: the host country issues a Letter of Authorization (LoA) authorising specific EEU volumes for CORSIA use; the LoA is recorded on the relevant approved programme registry, which labels the credits “CORSIA Eligible”; the host country simultaneously reports the Corresponding Adjustment to the UNFCCC, recording the transfer for international tracking purposes. The credits become tradeable as CORSIA Eligible EEUs and may be cancelled by airlines against their offsetting obligations.

The Guyana precedent (February 2024)

Guyana's February 2024 issuance of 7.14 million ART TREES vintage 2021 jurisdictional REDD+ credits was the world's first Paris Agreement Corresponding Adjustment reported to the UNFCCC and the operational test case for the CORSIA EEU architecture. The Guyana approach: ART issued the credits to Guyana for verified 2021 performance under Guyana's national-scale REDD+ initiative; the Government of Guyana authorised the credits for a range of compliance and voluntary purposes under Article 6.2; the LoA enabled ART to label the credits as “CORSIA Eligible” on the public registry; the Corresponding Adjustment was reported to the UNFCCC. The first IATA-organised procurement event in Q4 2024 sold credits at $21.70 per tonne; further procurement events through 2025 have followed the same model.

The 2026 LoA bottleneck

The Guyana precedent demonstrated that the architecture works; the operational challenge is that few other host countries have issued LoAs at material volume. The IATA Joint Statement of 2025 urged additional host countries to issue LoAs; the ICAO State Letter of 25 July 2025 reinforced the appeal. The reasons for the slow LoA issuance vary by country: capacity constraints in NDC accounting infrastructure; political concerns about authorising international transfer of credits that could be counted against domestic mitigation; the absence of mature operational templates for Article 6.2 in many countries; and concerns about pricing and the long-term value of the credits. The bottleneck is the central operational risk for Phase 1 EEU supply through the January 2028 deadline.

The Article 6.4 Mechanism

Article 6.4 of the Paris Agreement establishes a UNFCCC-administered mechanism for centrally-recognised mitigation outcomes (Article 6.4 Emission Reductions, or A6.4ERs). The operational rules were adopted progressively through COP26 to COP29 (2021–2024); the Supervisory Body has operationalised standards for crediting methodologies through 2025; first A6.4ERs are anticipated through 2025–2026. The intersection with CORSIA is that the Paris Agreement Crediting Mechanism (PACM) under Article 6.4 has applied to TAB for CORSIA eligibility assessment in the 2026 cycle, alongside other emissions unit programmes. If approved, the Article 6.4 mechanism could become an additional EEU supply source for the Phase 2 (2027–2029) compliance period.

Interaction with the GHG Protocol

The interaction between CORSIA and the GHG Protocol Corporate Standard operates at two levels for airline operators and at a parallel level for non-airline corporate Scope 3 reporters.

For airline operators

• Airline Scope 1 inventory. An airline's CO₂ emissions from owned-aircraft fuel combustion are Scope 1 emissions under the GHG Protocol. CORSIA-related EEU cancellation does not reduce the Scope 1 inventory: the operator's actual combustion emissions remain in inventory; the cancelled EEUs are separately disclosed as offsetting actions. This is the same principle that applies to every other voluntary or compliance offsetting regime.
• Disclosure architecture. The airline discloses Scope 1 fuel combustion emissions in its corporate inventory; separately discloses CORSIA offsetting obligation, EEU procurement, and EEU cancellation; and (where applicable) discloses CORSIA Eligible Fuel use as a reduction lever distinct from the offsetting layer. The GHG Protocol Corporate Standard supports this multi-layer disclosure.
• Non-CO₂ radiative forcing. The GHG Protocol Corporate Standard's inventory boundary is the Kyoto basket of gases (CO₂, CH₄, N₂O, HFCs, PFCs, SF₆, NF₃). Aviation non-CO₂ radiative forcing (contrails, NO_x-induced ozone) is not in the Kyoto basket and is not formally part of the Corporate Standard inventory. Some airlines voluntarily disclose non-CO₂ radiative forcing alongside the Scope 1 inventory, using approaches based on IPCC AR6 effective radiative forcing values or industry-standard multipliers.

For non-airline corporate Scope 3 reporters

The GHG Protocol Scope 3 Standard requires corporates to disclose value-chain emissions across 15 categories. Aviation emissions appear in: Category 6 (Business Travel) for employee air travel on commercial carriers; Category 9 (Downstream Transportation) for freight movements. The interaction with CORSIA is structural and frequently misunderstood:

• Corporate Scope 3 Category 6 (business travel) emissions are not reduced by airline CORSIA compliance. A corporate that purchases business travel from an airline does not “take credit” for the airline's CORSIA EEU cancellations against its own Scope 3 inventory; the CORSIA-compliant airline still reports its actual Scope 1 emissions; the corporate buyer's Scope 3 emissions are calculated using emission factors derived from the airline's Scope 1 (not adjusted for the airline's offsetting).
• Corporate procurement of CORSIA-eligible offsets does not reduce inventory emissions. A corporate that voluntarily purchases and retires CORSIA-eligible EEUs (or any other offset credits) does not reduce its Scope 1, 2, or 3 inventory under the GHG Protocol. The retirements are disclosed separately as Beyond Value Chain Mitigation or analogous categories.
• Radiative forcing factor for Scope 3 aviation calculations. The GHG Protocol does not currently mandate a non-CO₂ radiative forcing multiplier for Scope 3 aviation emissions, but many corporates voluntarily apply a multiplier (typically 1.9–2.0× for non-CO₂ effects, drawing on IPCC AR6 values or industry guidance). The UK DEFRA emission factors include both CO₂-only and CO₂e-with-RFI variants for business travel; DEFRA datasets structure the choice explicitly.

Interaction with SBTi Aviation SDA

The Science Based Targets initiative (SBTi) operates an Aviation Sectoral Decarbonization Approach (SDA) that provides science-based target-setting guidance specifically for the aviation sector. The Aviation SDA establishes intensity-based reduction trajectories (grams CO₂ per Revenue Tonne Kilometre, or gCO₂/RTK) aligned with the global temperature-stabilisation pathway. The interaction with CORSIA is structurally distinct from the airline's CORSIA compliance:

• CORSIA EEU cancellations do not count toward SBTi reduction targets. SBTi reduction targets are measured against in-boundary Scope 1, 2, and 3 emissions; offset retirements are excluded from the reduction calculation. An airline with both a CORSIA obligation and an SBTi-validated target must satisfy CORSIA through EEU cancellation and separately progress against its SBTi target through value-chain decarbonisation (SAF, operational efficiency, fleet renewal).
• The SBTi Aviation SDA does not endorse CORSIA as a substitute for in-boundary reduction. The SDA explicitly positions science-based targets as a complement to, not a replacement for, sectoral compliance mechanisms. An airline that is CORSIA-compliant but has no SBTi target is not science-based-aligned; an airline that has an SBTi target but is non-compliant with CORSIA faces compliance enforcement separate from its SBTi commitments.
• SAF use counts under both frameworks. Verified CORSIA Eligible Fuel use reduces the CORSIA offsetting obligation (Layer 2 of CORSIA); the same SAF use also reduces the airline's Scope 1 emissions intensity and contributes to SBTi target progress. The dual counting is not double counting — the SAF physically reduces the operator's emissions, and that single reduction is reflected in both the CORSIA obligation and the SBTi performance.
• Beyond Value Chain Mitigation positioning. Airlines with SBTi Corporate Net-Zero Standard targets may use CORSIA-eligible credit retirements (beyond the mandatory compliance obligation) in the Beyond Value Chain Mitigation tier; this is the same architectural position that voluntary VCS and Gold Standard credits occupy. The SBTi readiness checklist integrates the aviation-specific considerations.

Interaction with CSRD / ESRS E1

For aviation-sector reporters in scope of the EU Corporate Sustainability Reporting Directive, disclosure of CORSIA obligations is required under the European Sustainability Reporting Standard E1 (Climate Change). The structural disclosure points:

• ESRS E1-1 (Transition plan for climate change mitigation). Aviation-sector reporters disclose their long-term decarbonisation strategy including CORSIA compliance, SAF deployment, fleet renewal, and operational efficiency. The CORSIA pathway is one component of the broader transition plan, not the totality of it.
• ESRS E1-3 (Actions and resources in relation to climate change policies). The CORSIA compliance programme is disclosed as an action: EEU procurement budget, SAF use targets, MRV system investments, third-party verification engagement costs. The financial substantiation is part of the climate-related financial effects disclosure.
• ESRS E1-5 (Energy consumption and mix). Aviation fuel consumption is disclosed with the CORSIA Eligible Fuel share separately identified; the fuel mix narrative covers conventional jet kerosene versus SAF and (where relevant) LCAF.
• ESRS E1-6 (Gross Scopes 1, 2, 3 and Total GHG emissions). The airline's Scope 1 inventory includes all fuel combustion emissions from owned aircraft (international, domestic, on-ground, etc.). CORSIA offsetting is not netted against the Scope 1 inventory under ESRS E1-6; the actual Scope 1 figure is disclosed before any offsetting is considered.
• ESRS E1-7 (GHG removals and GHG mitigation projects financed through carbon credits). Quantitative disclosure of CORSIA EEU procurement and cancellation, including programme (ART TREES, Verra VCS, Gold Standard, etc.), methodology, vintage, geographic distribution, ICVCM CCP status where applicable, and the discharge of the compliance obligation. CORSIA EEU cancellations are compliance offsets (not voluntary contributions); the disclosure clearly distinguishes the compliance-driven volume from any voluntary additional purchases.
• ESRS E1-9 (Anticipated financial effects from material physical and transition risks). The future Phase 2 expansion from 2027 and the CORSIA obligation trajectory through 2035 is disclosed as a quantified climate-related financial effect.

Non-airline corporates in scope of CSRD who report Scope 3 Category 6 (business travel) emissions disclose under ESRS E1-6 the aviation-related business travel emissions calculated using applicable emission factors. The corporate's ESRS E1-7 disclosure for any voluntary CORSIA-eligible credit purchases is distinct from the airline's own ESRS E1-7 compliance disclosure.

Interaction with Verra VCS, Gold Standard, ACR, CAR, ART TREES, GCC

The six ICAO-approved EEU programmes for Phase 1 each carry programme-specific scope of eligibility, methodology exclusions, and project-type restrictions for CORSIA use. The detailed treatment of each programme is referenced through the GreenCalculus standards library: Verra VCS and Gold Standard have dedicated reference pages; the remaining four (ACR, CAR, ART TREES, GCC) are smaller-volume programmes covered through their primary documentation.

Key 2026 procurement considerations across the six programmes:

• ART TREES dominates current supply. Guyana's February 2024 issuance under ART TREES remains the largest single CORSIA Phase 1 Eligible EEU pool; subsequent ART issuances from additional host countries (Honduras, Belize) are anticipated. ART TREES is exclusively jurisdictional REDD+; project-level forest credits are not in scope.
• Verra VCS offers the broadest project type coverage but project-type exclusions for CORSIA Phase 1 narrow the eligible pool from the total VCS universe; the specific methodology and project type exclusions are programme-specific and require reference to the ICAO “CORSIA Eligible Emissions Units” document for current scope.
• Gold Standard offers premium-priced cookstove, renewable energy, water purification credits with strong SD co-benefit substantiation; the Gold Standard CORSIA scope mirrors much of the broader Gold Standard portfolio with vintage and methodology restrictions.
• ACR and CAR carry strong US-domestic project pools with methane abatement, IFM, and ARR predominating; the project type concentration produces specific co-benefit and integrity profiles.
• GCC operates with a 15 MW renewable energy cap for Phase 1 and applies a 15 percent buffer deduction prior to issuing the C+ label for Phase 1; the buffer is a programme-specific safeguard against LoA revocation risk.

Defensible 2026 procurement diversifies across multiple programmes to manage supply concentration risk, host country LoA dependence, and methodology-specific integrity profiles. The procurement strategy must additionally address the timing risk: Phase 1 cancellation by 31 January 2028 with material supply emerging through 2026–2027.

Interaction with IPCC AR6 and the Non-CO₂ Radiative Forcing Question

The IPCC AR6 Working Group I assessment provides the operative scientific basis for CO₂-equivalent accounting through the GWP-100 values applied across the climate regulation stack. For aviation, the AR6 assessment also addresses the non-CO₂ radiative forcing effects that CORSIA does not cover. The non-CO₂ components include: NO_x emissions at altitude producing tropospheric ozone (a short-lived climate forcer) and reducing atmospheric methane (a partial offsetting cooling effect); water vapour emissions producing linear contrails and contrail cirrus (the largest non-CO₂ warming component on a global mean basis); soot and sulphate aerosol emissions affecting cloud properties.

The IPCC AR6 effective radiative forcing assessment for aviation places the non-CO₂ components at approximately 2× the CO₂-only forcing, with substantial uncertainty (the “low confidence” classification reflects the methodological challenges in characterising contrail forcing in particular). On a global mean basis, aviation's total effective radiative forcing is approximately 3× its CO₂-only forcing. The implication: a CORSIA scheme that fully offsets the CO₂ growth above the 85%-of-2019 baseline addresses only approximately one-third of aviation's climate impact on the AR6 ERF basis.

The methodological challenge is that contrail forcing in particular is highly route-, time-, and atmosphere-specific: contrails form at specific altitudes and atmospheric conditions, persist for hours to days under favourable conditions, and produce both warming (longwave trapping) and cooling (shortwave reflection) effects with the net being warming on average. Operational mitigation (contrail avoidance through flight planning adjustments) is technically feasible but is not currently incentivised by CORSIA. The EU ETS amendments include MRV provisions for non-CO₂ effects from 2025 (intra-EEA) and 2027 (extra-EEA) as a precursor to potential regulatory inclusion; CORSIA has no equivalent.

The corporate Scope 3 Category 6 implication: corporates with material business travel emissions face a choice between CO₂-only reporting (consistent with CORSIA's scope) and CO₂e-with-RFI reporting (incorporating non-CO₂ effects through a radiative forcing multiplier). Industry practice in 2026 is split; the SBTi Aviation SDA and major corporate sustainability reporting standards (CDP, GRI) generally accept either approach with disclosure of the methodology applied.

Corporate Buyer's Perspective — Purchasing CORSIA-Eligible Offsets Voluntarily

CORSIA-eligible EEUs are a credit instrument designed primarily for airline compliance use, but a parallel voluntary market exists where non-airline corporate buyers purchase CORSIA-eligible credits for voluntary climate claims. The structural attraction of CORSIA-eligible credits for voluntary buyers is the additional quality signal: a CORSIA-eligible credit has passed both the originating programme's certification (Verra VCS, Gold Standard, ART TREES, etc.) and the ICAO TAB assessment of programme alignment with the CORSIA Emissions Unit Eligibility Criteria, and the host-country LoA process with Corresponding Adjustment reporting. The triple-check produces a credit with stronger integrity substantiation than a generic voluntary market credit of the same vintage from the same programme.

The trade-off is price: CORSIA-eligible credits typically command a $5–$15 per tonne premium over generic voluntary market credits from the same programmes, reflecting the constrained supply pool, the compliance market demand, and the integrity signal. The 2024 IATA Guyana procurement event price of $21.70 per tonne for ART TREES Guyana credits substantially exceeds the typical $5–$15 range for generic ART TREES voluntary credits.

For corporate buyers using CORSIA-eligible credits voluntarily, the disclosure recommendations:

• Disclose the CORSIA-eligible status as a quality signal alongside the underlying programme certification
• Note that the buyer is using the credits voluntarily (not for compliance against CORSIA, since the buyer is not an airline subject to the obligation)
• Confirm whether the LoA-backed Corresponding Adjustment is appropriate for the buyer's use case — for purely voluntary corporate claims within the buyer country, the CA may not be required by the buyer's applicable claims framework, but its presence does not reduce the credit's validity
• Avoid implying that the buyer's voluntary use of CORSIA-eligible credits substitutes for the airline's own compliance obligation

Airline Operator Compliance Workflow

The defensible 2026 airline operator CORSIA compliance workflow integrates the MRV, CEF, EEU, and reporting layers into an 8-stage process:

1. Route determination and State pair classification. Identify all international flights operated in the reporting year; classify each flight by State pair against the ICAO “CORSIA States for Chapter 3 State Pairs” document; segment emissions by covered vs non-covered State pairs.
2. Operator threshold confirmation. Verify the operator is above the 10,000-tonne annual international CO₂ threshold (effectively automatic for any major carrier; relevant for smaller operators near the threshold).
3. Fuel monitoring method selection and EMP implementation. Confirm the approved fuel use monitoring method (typically Method A or Method B for major carriers); maintain the Emissions Monitoring Plan; operate the fuel data collection systems.
4. AOER preparation. Compile annual emissions report covering covered State pair emissions, non-covered international emissions, fleet composition, CEF use, and supporting documentation.
5. Third-party verifier engagement. Engage an ISO 14065-accredited verifier with CORSIA scope; the verifier conducts the verification engagement under ISO 14064-3 at reasonable assurance level; verification statement issued.
6. Offsetting obligation calculation receipt. The State of Attribution applies the published SGF to the operator's covered emissions, less any verified CEF reduction claim, and communicates the calculated offsetting obligation to the operator.
7. EEU procurement. Source EEUs from ICAO-approved programmes meeting Phase 1 vintage and LoA requirements; diversify across programmes and host countries; budget for the Phase 1 cancellation deadline of 31 January 2028.
8. Retirement and reporting. Cancel EEUs on the relevant programme registries against the CORSIA compliance use; the State of Attribution confirms cancellation; the operator's CORSIA compliance is documented; ESRS E1-7 disclosure for in-scope reporters.

SAF Compliance Workflow for Operators

An airline operator seeking to use CORSIA Eligible Fuel to reduce its offsetting obligation operates a parallel SAF compliance workflow:

1. SAF supplier qualification. Confirm the supplier is certified under an ICAO-approved Sustainability Certification Scheme (SCS) for the specific SAF batch; verify SCS-issued certificates for batch identity, feedstock, conversion process, production region.
2. CEF list verification. Confirm the feedstock is on the current ICAO CEF feedstock list (49 approved as of November 2025); verify the conversion process is an approved ASTM D7566 pathway; verify the production region is in scope.
3. Lifecycle emissions value selection. Apply the appropriate default LCA core value (with ILUC where applicable) from the ICAO CORSIA Default Life Cycle Emissions Values document, or submit an actual LCA calculation under the CORSIA Methodology for Calculating Actual Life Cycle Emissions Values for the specific batch.
4. Sustainability criteria evidence. Document SCS evidence that the SAF batch meets the 14 CORSIA Sustainability Criteria themes (GHG, carbon stock, water, soil, air, conservation, waste, labour, land use, water rights, social development, food security, ILUC, other indirect effects).
5. Physical or Book and Claim deployment. Document whether the SAF was physically uplifted by the operator (with chain-of-custody documentation) or claimed under Book and Claim (with mass balance documentation).
6. Anti-double-claiming attestation. Confirm the same CEF batch has not been claimed under another scheme (e.g. ReFuelEU compliance, UK SAF Mandate, voluntary corporate purchases by other buyers).
7. FCR calculation. Calculate the Fuel Claim Reduction as the avoided CO₂ emissions relative to the 89 gCO₂e/MJ jet kerosene baseline; apply the reduction against the operator's offsetting obligation per the FCR formula.
8. AOER inclusion and verification. Include the FCR claim in the AOER with supporting SCS documentation; the third-party verifier confirms the FCR claim as part of the AOER verification.

Non-Airline Corporate Exposure — Scope 3 Category 6 Business Travel

For non-airline corporates with material business travel programmes, CORSIA's operational consequence is indirect but real. The corporate travel manager's decisions interact with CORSIA at three points:

• Scope 3 Category 6 emission factor selection. The corporate calculates aviation business travel emissions using applicable emission factors. The factors typically reflect the airline industry's actual operations (fuel burn, RTK, passenger load factor) without any deduction for the airline's CORSIA offsetting. A corporate that “takes credit” for the airline's offsetting against its own Scope 3 inventory is misapplying the GHG Protocol.
• Sustainable travel programme decisions. Corporates with science-based targets (SBTi) or net-zero commitments operate sustainable travel programmes that may favour airlines with stronger CORSIA performance, higher SAF use, more efficient fleets, or substantive science-based commitments. The corporate's choice of carrier is downstream of the airline's CORSIA compliance but is influenced by it.
• Voluntary offset procurement. Corporates may voluntarily purchase and retire offsets equivalent to their business travel emissions; the offsets may include CORSIA-eligible credits, in which case the corporate's purchase contributes to the same supply pool that airlines draw from for compliance. The corporate's disclosure should make clear that its voluntary retirements are distinct from the airline's compliance obligation and from the corporate's Scope 3 inventory.

The GHG Protocol's answer to the “double-counting” concern in Scope 3 is consistent across all categories: the corporate's Scope 3 emissions are calculated from the corporate's perspective using applicable emission factors; the upstream actor's own compliance actions (including CORSIA compliance) do not reduce the corporate's Scope 3 inventory; voluntary offsetting by the corporate is disclosed separately.

Sector-Specific Notes

• Full-service carriers. Material CORSIA exposure on extra-EEA routes (for European carriers) and on long-haul international networks (for all FSCs). Higher per-RTK fuel burn on widebody fleets than on LCC narrowbody fleets; CORSIA obligation cost is correspondingly higher per RTK.
• Low-cost carriers (LCCs). European LCCs (Ryanair, easyJet, Wizz Air) have predominantly intra-EEA networks and therefore predominantly EU ETS exposure rather than CORSIA exposure. The 2026 free-allocation phase-out under the EU ETS is the dominant cost lever; CORSIA exposure on the smaller extra-EEA share is secondary.
• Cargo operators (FedEx, UPS, DHL, Cargolux). Heavy CORSIA exposure on international cargo networks; the operator-level obligation may be substantial. FedEx and UPS operate primarily on US-attributed routes; the US is a CORSIA participating State; cargo operators with global networks face the full CORSIA architecture.
• Business aviation. Below the 10,000-tonne threshold for most operators; effectively excluded from CORSIA. Increasing scrutiny on business aviation environmental performance through other channels (national regulation, voluntary commitments) but not through CORSIA.
• Helicopter and regional operators. Typically below the threshold or operating predominantly domestically; effectively excluded from CORSIA.
• Flag carriers in developing states. Differentiated treatment under Phase 2 for LDCs, SIDS, and LLDCs: exemption from mandatory participation, but the State may voluntarily participate. The implementation choices vary by State.

Common Misinterpretations

Common Compliance Failures

1. MRV data gaps. Incomplete fuel data on some routes (particularly wet-lease, code-share, and operationally complex routes); inconsistent State pair classification; missing CEF documentation. The verifier finding pattern most commonly produces qualified verification statements rather than adverse opinions, but qualified opinions delay AOER acceptance and downstream obligation calculation.
2. Fuel monitoring method inconsistency. Operators that switch fuel monitoring methods within the reporting period without adequate documentation; operators that apply different methods inconsistently across the fleet.
3. Vintage restriction violations. EEU procurement of credits with vintages outside the Phase 1 eligibility window (pre-2021 or post-2026 emission reductions; project activity starts pre-2016); typically a procurement-side error caught by registry checks but occasionally requiring retirement reversal.
4. Verifier qualification issues. Engagement of verifiers without specific CORSIA scope accreditation; finding scope conflicts with the State of Attribution's national requirements for verifier qualification.
5. State-level deadline misses. AOER submission delays; verification statement submission delays; offsetting obligation calculation delays. Frequently driven by the State of Attribution's capacity rather than operator failure.
6. Anti-double-claiming for SAF. The same SAF batch claimed under CORSIA, ReFuelEU, UK SAF Mandate, and/or voluntary corporate buyers; the chain-of-custody documentation must establish single-claim use.
7. LoA timing assumptions. Procurement plans that assume LoA-backed supply will be available without contractual safeguards if the LoA does not materialise; concentration risk in supply from a single host country.

What CORSIA Does Not Cover

• Domestic aviation. Falls under each State's NDC and national jurisdiction. The EU ETS, the UK ETS, the New Zealand ETS, the Korea ETS, and the Chinese national ETS variously cover domestic aviation.
• Non-CO₂ radiative forcing. NO_x-induced ozone, contrails and contrail cirrus, water vapour, soot, and sulphate aerosol effects. The EU ETS includes MRV provisions for non-CO₂ effects from 2025 (intra-EEA) and 2027 (extra-EEA); CORSIA has no equivalent.
• Surface transport to airports. Outside CORSIA scope; addressed by jurisdictional surface transport regulation.
• Aircraft manufacturing emissions. The Scope 3 upstream emissions of aircraft production are outside CORSIA; relevant to airline Scope 3 reporting but not to CORSIA compliance.
• Military aviation. Excluded from ICAO Annex 16 scope; subject to national defence-sector emissions reporting where applicable.
• State aircraft (government, police, customs, search-and-rescue). Excluded from CORSIA.
• Humanitarian, medical, and firefighting flights. Specific exemptions under Annex 16 Volume IV.
• Flights below 5,700 kg MTOW. Excluded by aircraft type.

Future Evolution — Phase 2 and the 2050 Trajectory

Five trajectories will shape CORSIA through the late 2020s and into the 2030s.

Phase 2 mandatory expansion from 2027. The shift from voluntary state participation to mandatory participation for ICAO Member States above the 2018 RTK threshold will expand CORSIA coverage from ~80 percent of international RTKs in Phase 1 to ~85+ percent in Phase 2. The expansion brings into scope several major aviation States that have not voluntarily participated, increases EEU demand correspondingly, and tests the operational maturity of the LoA / Corresponding Adjustment architecture at materially larger volume. The growth factor blend shifts to 85 percent sectoral / 15 percent individual operator from 2033, introducing a modest accountability mechanism for individual carrier growth.

The 2050 net-zero LTAG and the SAF scaling question. ICAO's 2050 long-term aspirational goal of net-zero carbon emissions from international aviation, adopted at the 41st Assembly in 2022, repositions CORSIA from being the primary instrument to being one component of a basket of measures. The basket relies heavily on SAF scaling to multiples of current supply — from approximately 0.06 percent of fleet fuel in 2024 to 30–50 percent or more by 2050 on most analyst pathways. The SAF supply gap is the central operational risk: even at aggressive announced expansion rates, the available SAF volume through the late 2020s and 2030s falls substantially short of pathway requirements. CORSIA's offsetting layer must therefore grow substantially in the 2030s to address the residual gap, with the implication that EEU demand could exceed 1 billion tonnes cumulatively by 2035.

The Article 6 CA resolution. The structural scarcity of CORSIA-eligible supply in 2026 reflects the slow LoA issuance pace by host countries. The 2027–2030 trajectory will be defined by whether the additional host countries (Honduras, Belize, Cambodia, Costa Rica, others) follow Guyana's precedent and whether the Article 6.4 mechanism becomes a material additional supply source through PACM. The IATA-coordinated procurement events demonstrate that demand exists at market-clearing prices; the supply-side response is the open question.

The EU ETS aviation scope trajectory (continued). The legislative process on the European Commission proposal of 17 July 2026 will decide the final scope; the proposal sits between covering all departing flights from the EEA (the SASHA Coalition position) and keeping the stop-the-clock derogation (the airline industry position). The decision materially affects European-operating carriers' total compliance cost, the EU ETS allowance market, and the precedent for non-EU jurisdictions considering parallel sectoral expansions. The outcome is the single most important regulatory variable for European aviation through 2027–2030.

The emerging competition between CORSIA and EU ETS as parallel compliance frameworks. The 2024–2026 architecture treats CORSIA and the EU ETS as complementary instruments operating on different route categories. The post-2026 trajectory may see this complementarity erode: if the EU ETS scope expands to all departing flights, the same routes will become subject to both regimes (with double-charging avoided through netting); if CORSIA Phase 2 mandatory expansion brings more non-EU States into the offsetting regime, the relative scope of the two systems may converge. The 2030s could see a hybrid regime in which carriers face EU ETS surrender for the carbon-price layer and CORSIA cancellation for the residual growth layer on every flight to or from the EEA.

The non-CO₂ radiative forcing inclusion question. The EU ETS non-CO₂ MRV pilot (intra-EEA from 2025; extra-EEA from 2027) is the precursor to potential regulatory inclusion of contrail forcing in compliance scope. The methodological challenge — contrails are highly route-, time-, and weather-specific — is substantial but not insurmountable; operational mitigation through flight planning adjustments is technically feasible. The 2030s trajectory may see the EU lead a regulatory inclusion of non-CO₂ effects, with ICAO either following at the sectoral level or facing a fragmenting regulatory landscape. CORSIA itself has no current pathway to non-CO₂ inclusion; the question may be decided at the EU level first.

Frequently Asked Questions

Sources and References

Every claim and methodological statement on this page reconciles to the primary sources below. Where the International Civil Aviation Organization, the UNFCCC, the European Commission, the European Parliament, the European Aviation Safety Agency (EASA), the International Air Transport Association (IATA), the Architecture for REDD+ Transactions, the Government of Guyana, or a national civil aviation authority has published a definitive document, the primary source is cited directly; secondary commentary is used only for interpretation of operational practice and market dynamics.

ICAO primary documentation

• International Civil Aviation Organization, Convention on International Civil Aviation (Chicago Convention), signed 7 December 1944, entered into force 4 April 1947.
• ICAO, Annex 16 to the Convention on International Civil Aviation, Volume IV — Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA), 2nd Edition, applicable 1 January 2024.
• ICAO, Environmental Technical Manual (Doc 9501) Volume IV — Procedures for Demonstrating Compliance with the Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA).
• ICAO Assembly Resolution A39-3 (October 2016) — Consolidated statement of continuing ICAO policies and practices related to environmental protection — Global Market-based Measure (MBM) scheme.
• ICAO Assembly Resolution A41-22 (October 2022) — Consolidated statement of continuing ICAO policies and practices related to environmental protection — Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA).
• ICAO Assembly Resolution A41-21 (October 2022) — Long-term aspirational goal (LTAG) for international aviation CO₂ emissions.

CORSIA Implementation Elements

• ICAO, CORSIA States for Chapter 3 State Pairs, Edition 6 (130 States participating in 2026); preceded by Editions 4 (126 States, 2024) and 5 (129 States, 2025).
• ICAO, CORSIA Emissions Unit Eligibility Criteria, March 2019.
• ICAO, CORSIA Eligible Emissions Units (consolidated list of approved programmes for the 2021–2023, 2024–2026, and 2027–2029 compliance periods).
• ICAO, CORSIA Eligibility Framework and Requirements for Sustainability Certification Schemes, Fourth Edition, June 2025.
• ICAO, CORSIA Approved Sustainability Certification Schemes, Third Edition, October 2024.
• ICAO, CORSIA Sustainability Criteria for CORSIA Eligible Fuels, June 2025 (Sixth Edition).
• ICAO, CORSIA Default Life Cycle Emissions Values for CORSIA Eligible Fuels, June 2025, with November 2025 amendments approving new feedstocks and default core LCA values.
• ICAO, CORSIA Methodology for Calculating Actual Life Cycle Emissions Values.
• ICAO, CORSIA CO₂ Estimation and Reporting Tool (CERT) — methodology and operational documentation.

ICAO Council and Technical Advisory Body determinations

• ICAO Council determination, late 2025 — 2024 Sector's Growth Factor: 0.15405257; 2024 baseline: 305,522,071 tonnes CO₂; 2024 actual emissions for applicable State pairs: 361,159,641 tonnes CO₂.
• ICAO Council, October 2024 — Full approval of Gold Standard, Verra VCS, Climate Action Reserve, and Global Carbon Council to supply EEUs for Phase 1 (2024–2026 compliance period).
• ICAO Council, October 2025 — Approval of Phase 2 (2027–2029) EEU programme eligibility for ART TREES, Verra VCS, Gold Standard, and other programmes with scope specifications.
• ICAO Council, 19 November 2025 — Approval of new CEF feedstock classifications and default core LCA values; CEF feedstock list expanded to 49 approved feedstocks.
• ICAO Council, 27 June 2025 — Approval of CAEP/13 recommendations on CORSIA Eligible Fuels documents.
• ICAO Council, 28 October 2024 — Approval of amendments to three CORSIA Eligible Fuels documents and a new CORSIA Approved Sustainability Certification Scheme.
• ICAO Technical Advisory Body (TAB), Terms of Reference, Procedures, Work Programme and Timeline.
• ICAO TAB, Clarifications of TAB's Criteria Interpretation Contained in TAB Reports — consolidated TAB criteria interpretations.
• ICAO TAB, 2026 assessment cycle for Phase 2 (2027–2029) EEU programme applications, 9 February to 9 March 2026; 25 organisations submitted applications including the Paris Agreement Crediting Mechanism (PACM).
• ICAO State Letter, 25 July 2025 — ICAO communication to Member States urging host country issuance of Letters of Authorization.

EU regulatory documentation

• European Parliament and Council, Directive 2003/87/EC of 13 October 2003 establishing a system for greenhouse gas emission allowance trading within the Community, as amended.
• European Parliament and Council, Directive (EU) 2023/958 of 10 May 2023 amending Directive 2003/87/EC as regards aviation's contribution to the Union's economy-wide emission reduction target and the appropriate implementation of a global market-based measure.
• European Parliament and Council, Regulation (EU) 2023/2405 of 18 October 2023 on ensuring a level playing field for sustainable air transport (ReFuelEU Aviation).
• European Commission, communications and implementing decisions on CORSIA implementation through the EU ETS framework.
• EASA (European Union Aviation Safety Agency), European Aviation Environmental Report (EAER), and operational guidance on CORSIA implementation under EU law.
• Dutch Emissions Authority (NEa), Threshold and Reporting Obligation Guidance — 3rd Edition 2024–2026, and other implementing guidance for European aircraft operators.

Paris Agreement Article 6 documentation

• United Nations Framework Convention on Climate Change, Paris Agreement, adopted at COP21, 12 December 2015.
• UNFCCC, Decision 2/CMA.3 — Guidance on cooperative approaches referred to in Article 6, paragraph 2, of the Paris Agreement, adopted at COP26, Glasgow, November 2021.
• UNFCCC, Decision 3/CMA.3 — Rules, modalities and procedures for the mechanism established by Article 6, paragraph 4, of the Paris Agreement, adopted at COP26, Glasgow, November 2021.
• UNFCCC Article 6.4 Supervisory Body, methodology and registry rules adopted progressively through COP27 (Sharm El-Sheikh, 2022), COP28 (Dubai, 2023), and COP29 (Baku, 2024).

Approved EEU programme documentation

• Architecture for REDD+ Transactions (ART), The REDD+ Environmental Excellence Standard (TREES), current operative version; ART public registry recording the Guyana CORSIA Eligible issuance of 7.14 million vintage 2021 credits, February 2024.
• Verra, Verified Carbon Standard (VCS) Program Documents, Standard v4.5 (August 2024); CORSIA-scope methodology and project-type exclusions per ICAO Council determination.
• Gold Standard Foundation, Gold Standard for the Global Goals (GS4GG) v2.0 with 2024 amendments; CORSIA-scope methodology and project-type exclusions per ICAO Council determination.
• American Carbon Registry (ACR), The ACR Standard, current version; CORSIA-scope methodology determinations.
• Climate Action Reserve (CAR), Reserve Offset Program Manual, current version; CORSIA-scope methodology determinations.
• Global Carbon Council (GCC), GCC Programme Documents including the 15 percent buffer deduction and renewable energy 15 MW cap provisions for Phase 1 CORSIA-eligible C+ label.

Guyana Article 6 documentation

• Government of Guyana, Low Carbon Development Strategy (LCDS) documentation including LCDS 2030.
• Government of Guyana, Letter of Authorization for ART TREES vintage 2021 credits under Paris Agreement Article 6.2, February 2024.
• UNFCCC record of the world's first Paris Agreement Corresponding Adjustment for ART TREES vintage 2021 credits, reported by Guyana, February 2024.

IATA and industry documentation

• International Air Transport Association, CORSIA Fact Sheet, December 2025 edition.
• IATA, Joint Statement on CORSIA Eligible Emissions Units with 21 other signatories, 2025.
• IATA, press releases on Aviation Carbon Exchange (ACE) CORSIA EEU procurement events from Q4 2024 onwards, with the Government of Guyana, Mercuria, and Xpansiv.
• IATA, Lifecycle Analysis (LCA) and SAF Sustainability, May 2025 Chart of the Week.

GHG accounting reference standards

• World Resources Institute & World Business Council for Sustainable Development, The Greenhouse Gas Protocol: A Corporate Accounting and Reporting Standard, revised edition 2004.
• World Resources Institute & World Business Council for Sustainable Development, Corporate Value Chain (Scope 3) Accounting and Reporting Standard, 2011.
• International Organization for Standardization, ISO 14064-1:2018 Greenhouse gases — Part 1: Specification with guidance at the organization level for quantification and reporting of greenhouse gas emissions and removals.
• International Organization for Standardization, ISO 14064-3:2019 Greenhouse gases — Part 3: Specification with guidance for the verification and validation of greenhouse gas statements.
• International Organization for Standardization, ISO 14065:2020 General principles and requirements for bodies validating and verifying environmental information.
• Intergovernmental Panel on Climate Change, Sixth Assessment Report (AR6), Working Group I, Chapter 7 Supplementary Material, 2021. Aviation effective radiative forcing assessment and GWP-100 values.

Parallel target-setting and disclosure frameworks

• Science Based Targets initiative, Corporate Net-Zero Standard, 2021, with subsequent revisions through 2024 and 2025.
• Science Based Targets initiative, Aviation Sectoral Decarbonization Approach (SDA).
• Science Based Targets initiative, Beyond Value Chain Mitigation (BVCM) framework, 2023, updated 2024 and 2025.
• European Parliament and Council, Directive (EU) 2022/2464 (CSRD), as amended.
• European Financial Reporting Advisory Group, ESRS E1 Climate change, including E1-1 (transition plan), E1-3 (actions and resources), E1-5 (energy), E1-6 (gross GHG emissions), E1-7 (GHG removals and mitigation projects), E1-9 (financial effects).

ASTM and fuel certification standards

• ASTM International, ASTM D1655 Standard Specification for Aviation Turbine Fuels.
• ASTM International, ASTM D7566 Standard Specification for Aviation Turbine Fuel Containing Synthesized Hydrocarbons, with applicable Annexes for the approved SAF pathways (HEFA, FT, ATJ, SIP, CHJ, HC-HEFA-SPK).
• ASTM International, ASTM D4054 Standard Practice for Evaluation of New Aviation Turbine Fuels and Fuel Additives.

Civil society and analytical commentary

• SASHA Coalition, EU ETS Aviation 2026 Revision Position Paper.
• Transport & Environment, briefings on EU ETS aviation and CORSIA implementation.
• InfluenceMap, The EU Emissions Trading System for Aviation: New Lobbying Trends, 2025.
• Carbon Market Watch, analyses on EU ETS aviation and CORSIA price differentials.
• Sylvera, BeZero, Calyx Global, Renoster — carbon credit rating agency assessments of CORSIA-eligible methodologies and programmes.

Related GreenCalculus reference pages

• EU Emissions Trading System — the parallel compliance regime for European aviation; the critical overlap analysed in §15
• GHG Protocol Corporate Standard — the upstream organisational GHG accounting basis for airline Scope 1 and corporate Scope 3 reporters
• SBTi Corporate Net-Zero Standard — the science-based target framework and Aviation SDA
• Verra VCS — an approved CORSIA Phase 1 EEU programme
• Gold Standard — an approved CORSIA Phase 1 EEU programme
• CSRD ESRS E1 — the EU climate-disclosure regime including ESRS E1-7 carbon credit disclosure
• IPCC AR6 — the operative scientific basis for CO₂-equivalent accounting and aviation effective radiative forcing
• ISO 14064-3 — the verification methodology applied to CORSIA AOER engagements

What changed in this revision

Updated 13 May 2026. Initial publication. Reflects the operative state of CORSIA and the broader international aviation climate regime as of May 2026, incorporating: ICAO Annex 16 Volume IV (2nd Edition, applicable 1 January 2024); ICAO Environmental Technical Manual (Doc 9501) Volume IV; ICAO Assembly Resolution A41-22 (October 2022) including the 85 percent of 2019 baseline amendment, the 100 percent sectoral / 0 percent individual growth factor weighting through 2032, and the 85/15 blend from 2033; ICAO Assembly Resolution A41-21 (October 2022) adopting the 2050 long-term aspirational goal of net-zero international aviation; the ICAO Council determination of the 2024 Sector's Growth Factor (0.15405257) against the 2024 baseline (305,522,071 tonnes) and 2024 actual emissions (361,159,641 tonnes); the October 2024 ICAO Council approval of Gold Standard, Verra VCS, CAR, and GCC for Phase 1 EEU supply (the six fully-approved programmes for Phase 1: ACR, ART TREES, CAR, GCC, Gold Standard, Verra); the October 2025 ICAO Council approval of Phase 2 EEU programme eligibility through 2029; the November 2025 update to the CORSIA Eligible Fuel feedstock list (49 approved feedstocks) and default core LCA values; the June 2025 CORSIA Sustainability Criteria 6th Edition; the EU ETS Directive 2003/87/EC as amended by Directive (EU) 2023/958 and the ReFuelEU Aviation Regulation (EU) 2023/2405; the Paris Agreement Article 6.2 and 6.4 operationalisation through COP26 (Glasgow, 2021) to COP29 (Baku, 2024); the February 2024 Guyana issuance of the world's first CORSIA Phase 1 Eligible EEUs (7.14 million ART TREES vintage 2021 credits) and the world's first Paris Agreement Corresponding Adjustment reported to the UNFCCC; the IATA Aviation Carbon Exchange (ACE) procurement events from Q4 2024 onwards at the $21.70 per tonne price point; the SBTi Aviation SDA and Beyond Value Chain Mitigation framework; the GHG Protocol Corporate Standard and Scope 3 Standard treatment of airline Scope 1 and corporate Scope 3 Category 6 emissions; the CSRD ESRS E1 disclosure architecture for in-scope aviation-sector reporters; and the IPCC AR6 aviation effective radiative forcing assessment. Worked numerical example in §9 (Aerolíneas Meridional 2024 offsetting obligation across three SAF-blend scenarios) is hypothetical and stipulated for instructional purposes; not the operational values for any specific real-world airline. The five-method MRV taxonomy in §12 reflects the operative methodology under ICAO Annex 16 Volume IV; specific operator method selection at AOER preparation requires reference to the approved Emissions Monitoring Plan. The four-route CORSIA / EU ETS dual-compliance matrix in §15 reflects the operative architecture under Directive (EU) 2023/958 as of May 2026; the European Commission proposal of 17 July 2026 would extend the EU ETS to more extra-EEA routes from 2029 if adopted.