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Short answer
CORSIA (Carbon Offsetting and Reduction Scheme for International Aviation) is an ICAO market-based measure under Annex 16, Volume IV designed to stabilize net CO2 emissions from international flights. Aeroplane operators emitting over 10,000 tonnes of CO2 annually must monitor fuel use, report verified emissions, and offset emissions growth exceeding 85% of 2019 levels.
Definition and scope
The Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA) is an international regulatory framework adopted by the International Civil Aviation Organization (ICAO) under Resolution A39-3 (updated in A41-22). Formally codified in Annex 16, Volume IV to the Chicago Convention, its Second Edition took effect on 31 July 2023 and became applicable on 1 January 2024.
CORSIA governs international flights between participating ICAO Member States via a route-based approach. Domestic aviation is excluded because domestic emissions fall under national Nationally Determined Contributions (NDCs) under the Paris Agreement. In regional jurisdictions, CORSIA coordinates with local mechanisms; under Directive (EU) 2023/958, the EU ETS governs intra-European flights while CORSIA covers flights connecting European Economic Area (EEA) states to third countries.
Applicability thresholds from Annex 16, Volume IV include:
- Emissions threshold: Commercial and general aviation operators emitting >10,000 metric tonnes of CO2 per year on international routes.
- Aircraft weight: Aeroplanes with a maximum certificated take-off mass (MTOW) >5,700 kg.
- Exemptions: Humanitarian, medical evacuation, and firefighting operations are exempt.
How it works or how it is used in practice
CORSIA operates through a cyclical architecture comprising monitoring, baseline offsetting, alternative fuels, and unit surrender.
Monitoring, reporting, and verification (MRV)
In force since 1 January 2019, the MRV system mandates that covered operators maintain an approved Emissions Monitoring Plan (EMP). Fuel use is measured via approved Annex 16 methods (Method A, Method B, Block-on/Block-off, Fuel Uplift, or the CERT tool). Operators submit an annual Emissions Report (ER) to their national authority, such as the Federal Aviation Administration under the U.S. CORSIA MRV Program (88 FR 58433, OMB No. 2120-0790). Reports require third-party verification by an accredited body under ISO 14065, supporting rigorous carbon accounting across flight networks.
Baseline calculation and offsetting obligations
Operators offset sectoral growth exceeding an established baseline across three phases:
- Pilot Phase (2021–2023): Voluntary; baseline adjusted to 2019 emissions due to COVID-19 disruptions.
- First Phase (2024–2026): Voluntary; baseline set at 85% of 2019 international emissions under Resolution A41-22.
- Second Phase (2027–2035): Mandatory for ICAO Member States (exempting LDCs, SIDS, and small aviation states); baseline remains 85% of 2019 emissions.
At the end of each three-year compliance cycle, operators calculate offsetting obligations by multiplying covered emissions by the Sectoral Growth Factor.
CORSIA eligible fuels (CEF)
Operators reduce offsetting requirements through CORSIA Eligible Fuels (CEF) under Annex 16, Volume IV:
- CORSIA Sustainable Aviation Fuels (SAF): Drop-in fuels produced from biogenic feedstocks or waste streams.
- CORSIA Lower Carbon Aviation Fuels (LCAF): Fossil fuels produced via certified low-emission refinery processes.
CEFs must achieve ≥10% life-cycle GHG reductions relative to baseline jet fuel (89 gCO2e/MJ). Life cycle emissions combine core LCA and induced land-use change (ILUC) values, certified by approved schemes per the CORSIA Default Life Cycle Emissions Values (Ninth Edition, November 2026). This boundary modeling mirrors standard life cycle inventory protocols.
Eligible emissions units
Remaining obligations are satisfied by surrendering CORSIA Eligible Emissions Units approved by the ICAO Council following Technical Advisory Body (TAB) review. Units must include Host Country Letters of Authorization and Article 6 corresponding adjustments to avoid double counting against Paris Agreement accounts.
Types or related concepts
The table below summarizes the primary CORSIA compliance pathways and their regulatory criteria:
| Pathway | Operational Role | Regulatory Basis | Core Requirement | Limits & Scope |
|---|---|---|---|---|
| CORSIA MRV | Fuel burn and emissions monitoring | ICAO Annex 16, Vol. IV; 88 FR 58433 | Annual third-party verified emissions report | Applies to operators >10,000 t CO2/yr and >5,700 kg MTOW |
| Phased Offsetting | Sectoral emissions capping | ICAO Resolutions A39-3 and A41-22 | Surrender units exceeding 85% of 2019 baseline | Mandatory starting 2027; exempts LDCs and SIDS |
| CORSIA SAF | Direct in-sector biogenic fuel abatement | Annex 16, Vol. IV, Sec. 3.3; ICAO CEF (2026) | ≥10% life-cycle GHG cut vs 89 gCO2e/MJ baseline | Requires approved Sustainability Certification Scheme |
| CORSIA LCAF | Low-emission conventional refinery fuel | ICAO Council CEF Rules (2022) | ≥10% refinery upstream GHG cut vs baseline | Subject to strict chain-of-custody tracking |
| Emissions Units | Out-of-sector offset cancellation | TAB Criteria; ICAO Eligible Units (2026) | Cancellation in approved registry with Article 6 authorization | Restricted to Council-approved crediting programs |
Where it matters for labs, clinics or supply decisions
CORSIA frameworks influence laboratory workflows, aerospace engineering, and institutional purchasing:
Aerospace testing and fuel qualification
Institutes active in aerospace engineering conduct fuel qualification trials under ASTM D7566 and ASTM D1655. Laboratories evaluate viscosity, freeze point, flash point, and combustor thermal stability to ensure alternative fuel blends maintain stringent aviation safety margins without compromising flight systems.
Analytical carbon verification
Chemical testing laboratories verify biogenic fuel fractions using stable isotope ratio mass spectrometry (δ13C) and radiocarbon dating (ASTM D6866). These assays confirm renewable content in co-processed refinery streams and validate life-cycle GHG accounting models.
Institutional procurement and emissions accounting
Organizations reporting carbon footprints classify air travel within Scope 1, 2, and 3 emissions categories. When institutions measure institutional or conference travel emissions, CORSIA MRV datasets provide certified flight-level fuel burn data. Procurement managers utilizing SAF book-and-claim agreements rely on ICAO-approved SCS certificates to prevent double claiming.
Common misunderstandings
- CORSIA regulates domestic flights: CORSIA applies exclusively to international routes between participating states; domestic flights are governed by national NDCs under the Paris Agreement.
- CORSIA requires zero gross aircraft emissions: The scheme stabilizes net sector emissions above 85% of 2019 levels through offsets and lower-carbon fuels, rather than mandating zero gross tailpipe emissions.
- Any voluntary carbon credit is accepted: Only carbon offset units from programs evaluated by the Technical Advisory Body (TAB) and approved by the ICAO Council with Article 6 adjustments qualify.
- All alternative fuels automatically qualify: Fuels must demonstrate at least a 10% life-cycle GHG reduction against the 89 gCO2e/MJ baseline and hold certification from an approved scheme.
- Private flight departments are fully exempt: Operators emitting >10,000 tonnes of CO2 annually on international routes using aircraft >5,700 kg MTOW must comply with MRV obligations regardless of corporate structure.
Frequently asked questions
What is CORSIA?
CORSIA is a market-based measure established by ICAO under Annex 16, Volume IV. It requires international aeroplane operators emitting over 10,000 tonnes of CO2 annually to monitor emissions and offset growth exceeding 85% of 2019 baseline levels.
How is the CORSIA baseline calculated for 2024 to 2035?
Under ICAO Assembly Resolution A41-22, the baseline for Phase 1 (2024–2026) and Phase 2 (2027–2035) is set at 85% of 2019 international aviation emissions.
How do Sustainable Aviation Fuels reduce offsetting requirements?
Operators burning CORSIA Eligible Fuels deduct verified life-cycle greenhouse gas reductions directly from their total emissions, reducing the quantity of offset units required for surrender.
How do the EU ETS and CORSIA interact?
Under Directive (EU) 2023/958, the EU ETS covers flights within the European Economic Area, while CORSIA covers international flights between EEA states and participating third countries.
Which operators are exempt from CORSIA?
CORSIA exempts operators emitting 10,000 tonnes or less of CO2 per year, aeroplanes with an MTOW of 5,700 kg or less, and humanitarian, medical evacuation, and firefighting flights.
Sources
- International Civil Aviation Organization (ICAO). (2024). Annex 16 to the Convention on International Civil Aviation: Environmental Protection — Volume IV: Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA). Second Edition, applicable 1 January 2024. URL: https://www.icao.int/CORSIA/sarps-annex-16-volume-iv. (Read November 11, 2026).
- International Civil Aviation Organization (ICAO). (2026). CORSIA Eligible Fuels: Default Life Cycle Emissions Values and Sustainability Certification Schemes. Ninth Edition, November 2026. URL: https://www.icao.int/CORSIA/corsia-eligible-fuels. (Read November 11, 2026).
- International Civil Aviation Organization (ICAO). (2026). CORSIA Eligible Emissions Units and Technical Advisory Body (TAB) Criteria. April 2026 Edition. URL: https://www.icao.int/CORSIA/corsia-eligible-emissions-units. (Read November 11, 2026).
- Federal Aviation Administration (FAA). (2023). Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA) Monitoring, Reporting, and Verification (MRV) Program. Notice of OMB Clearance Renewal, 88 FR 58433, Docket No. FAA-2022-1711. URL: https://www.federalregister.gov/documents/2023/08/25/2023-18319/agency-information-collection-activities-requests-for-comments-clearance-of-renewed-approval-of. (Read November 11, 2026).
- European Parliament and Council of the European Union. (2023). Directive (EU) 2023/958 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. Official Journal of the European Union, L 130/115. URL: https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX%3A32023L0958. (Read November 11, 2026).
