Aviation's first global carbon compliance scheme is well underway. CORSIA's First Phase covers 2024 to 2026, and with the compliance deadline for Phase 1 retirements set for January 2028, airlines operating international routes between participating countries are now working through their obligations.
This blog covers what CORSIA Eligible Emissions Units (EEUs) are, what makes a credit eligible, and how airlines go about sourcing them.
What is an EEU?
According to ICAO, an EEU represents one metric ton of CO2 reduced or removed. Under CORSIA, an airline must cancel EEUs in a quantity equal to its total offsetting requirement for a given compliance period.
But not every carbon credit qualifies. To supply units to CORSIA, programs must be assessed and approved by ICAO's Technical Advisory Body (TAB) against two sets of criteria: Program Design Elements Criteria and Carbon Offset Credit Integrity Assessment Criteria. Both must be met to ensure the environmental and social integrity of the units.
Credits must also carry a Corresponding Adjustment (CA) from the host country, a Paris Agreement mechanism that ensures the same ton of CO2 isn't counted twice, once by the country toward its own climate targets and once by the airline.
Which programs are currently approved?
In October 2024, the ICAO Council granted full approval to four additional carbon standards for Phase 1, Gold Standard, Verra, Climate Action Reserve, and Global Carbon Council, joining ACR and ART TREES, which were already fully approved. The current approved list is published and regularly updated on the ICAO website.
Each program comes with methodology-level exclusions, meaning sourcing teams need to verify not just that a credit comes from an approved registry, but that the specific project type qualifies under CORSIA rules.
How does an airline actually source and retire EEUs?
Airlines measure and report their emissions, purchase eligible credits to offset emissions above the baseline, and retire those credits through approved registries to document compliance.
The obligation sits with the airline. Host countries, however, are not required to issue Corresponding Adjustments, which is optional for them and this creates a genuine scarcity dynamic. A credit can be issued by an approved registry but still fall short of full eligibility if the host country hasn't authorized its use for CORSIA purposes.
This gap between credits that have been issued and credits that are genuinely eligible is one of the more consequential nuances in CORSIA procurement today.
What this means for Phase 1 procurement?
IATA expects airlines to purchase upwards of 200 million EEUs for Phase 1 compliance by late 2027, at an estimated cost of $4-5 billion, rising to nearly 2 billion EEUs through to 2035.
For more on how CORSIA works, visit our CORSIA FAQ page here.