CORSIA stands for the Carbon Offsetting and Reduction Scheme for International Aviation. It is run through ICAO, the UN aviation body, and is designed to address growth in international aviation emissions that remains after operational efficiency, aircraft improvements and sustainable aviation fuel are considered.
It is not the same as the voluntary carbon market. Airlines cannot simply buy any credit and call it CORSIA compliance. They need CORSIA Eligible Emissions Units, usually shortened to EEUs, from programmes, vintages and activity types approved through ICAO's Technical Advisory Body process.
What CORSIA covers
CORSIA applies to international aviation, not domestic flights. The obligation sits with aircraft operators on routes covered by the scheme, and the final offsetting requirement depends on their reported emissions, route coverage and ICAO's growth-factor calculations.
The scheme has three broad operating stages: a pilot phase from 2021 to 2023, a first phase from 2024 to 2026, and a second phase from 2027 to 2035. Participation was voluntary in the earlier phases, with broader participation expected in the second phase subject to exemptions and state participation rules.
How the offsetting obligation is calculated
CORSIA does not offset every tonne of aviation CO2. It focuses on growth above a baseline. ICAO's post-pandemic baseline for CORSIA is tied to 85% of 2019 international aviation emissions. In practice, airlines monitor and report covered emissions, apply the relevant sector growth factor, and then use CORSIA Eligible Emissions Units to meet their cancellation obligation for the compliance period.
The result is an important distinction for developers and buyers: CORSIA demand is driven by aviation growth, covered routes and compliance rules, not by a company's broad net-zero claim. That makes CORSIA a more rule-bound buyer segment than many voluntary offset purchases.
Where sustainable aviation fuel fits
Sustainable aviation fuel and lower-carbon aviation fuels can reduce an operator's CORSIA offsetting requirement when they meet the scheme's sustainability and lifecycle-emissions rules. That means CORSIA demand is affected by more than passenger growth. Fuel uptake, route participation and policy enforcement all influence how many units airlines ultimately need.
Why CORSIA matters for carbon project developers
CORSIA eligibility can create a more valuable buyer route, especially when eligible supply is tight. But it also raises the bar. A project has to fit an approved programme and methodology scope, satisfy vintage and start-date conditions, avoid double claiming, and increasingly secure host-country authorisation with corresponding adjustment treatment for relevant vintages.
That is why a project can be excellent in voluntary-market terms and still not be CORSIA-eligible. The credit needs to fit the CORSIA rulebook, not just the buyer's impact preferences.
CORSIA versus EU ETS and voluntary offsets
Airlines may sit inside several carbon systems at once. EU ETS applies to certain aviation emissions in Europe. CORSIA applies through ICAO rules for international aviation. Voluntary offsetting is separate again and is used for brand, customer or net-zero claims rather than CORSIA compliance. The same airline may therefore buy different credit types for different purposes.
CORSIA is a moving eligibility target. Always confirm the latest ICAO eligibility documents before making investment or buyer claims.
Read the CORSIA eligible units guide →