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CORSIA
What aircraft operators need to know about offsetting emissions from international flights
A comprehensive guide to CORSIA for UK and European aircraft operators
CORSIA introduced a global framework for managing emissions growth from international aviation, requiring operators to offset emissions above an agreed baseline. This guide explains how the scheme works, which credits count towards compliance, and how it is being implemented in the UK.
What is CORSIA?
CORSIA stands for the Carbon Offsetting and Reduction Scheme for International Aviation, a global scheme run by the International Civil Aviation Organization (ICAO). It requires aircraft operators to offset carbon emissions from international flights above an agreed baseline.
First market-based measure for a single industry
Adopted in 2016, it was the first market-based measure created for a single industry. Emissions from international flights are not attributed to any one country under the Paris Agreement, which is why ICAO administers a separate scheme for them and why domestic flights fall outside it.
Every operator in scope moves through the same sequence each year, reporting emissions to its regulator, receiving an offsetting requirement and meeting it through eligible credits, fuels, or a combination of both.
Operators above the size thresholds have reported their annual CO2 emissions from international flights since 2019, with each report independently verified before it reaches the regulator.
Offsetting only applies above an agreed baseline, which ICAO set at 85% of 2019 emissions in 2022, replacing an earlier measure distorted by the drop in air traffic during the pandemic.
ICAO publishes an annual Sector Growth Factor based on emissions across international aviation. During the current phase of the scheme, that factor is used to calculate operators' offsetting obligations against their covered emissions.
Applying the sector growth factor to an operator's verified emissions produces the volume it must offset, which the regulator then confirms to the operator.
Operators meet their offsetting requirement through cancelled eligible emissions units, CORSIA-eligible fuels, or a combination of the two.
Obligations are settled in three-year blocks, so emissions from 2024 to 2026 form the first compliance period, with the units covering them due to be cancelled by January 2028.
Who CORSIA applies to
Operators are assessed based on the volume of emissions they produce and the routes they fly. The latter changes in 2027, when the scheme becomes mandatory for most ICAO member states.
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Size thresholds
Operators come into scope above 10,000 tonnes of CO2 a year from international flights, using aircrafts over 5,700kg maximum take-off mass.
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Types of operator
Passenger operators are not the only ones in scope, with cargo carriers, business aviation and private operators also covered.
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Which flights are covered
Only flights between two participating states currently count. From 2027, all international flights are covered except those involving exempt states.
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UK operators
Where an air operator certificate was issued determines which country's rules apply, and which regulator oversees compliance.
Exemptions
Humanitarian, medical and firefighting flights are excluded. New operators get three years before obligations begin, and least developed countries, small island developing states and landlocked developing countries are exempt unless they opt in.
Why CORSIA matters for aircraft operators
The CORSIA phases
CORSIA Eligible Emissions Units (EEUs)
Not every carbon credit can be used for CORSIA compliance. Units have to come from a programme ICAO has approved and meet several further tests before they count.
See our CORSIA carbon creditsWhat is an EEU?
A CORSIA Eligible Emissions Unit, or EEU, is a carbon credit that ICAO has approved for use towards CORSIA compliance. One unit represents one tonne of CO2 reduced or removed outside the aviation sector.
Eligibility criteria
- The unit comes from an emissions unit programme ICAO has approved
- The underlying activity started its first crediting period in 2016 or later
- The activity type is one ICAO permits, as some methodologies are excluded
- The reduction falls within an eligible vintage
- The host country has authorised the unit for use towards CORSIA
Approved programmes
ICAO assesses and approves emissions-unit programmes, alongside eligibility requirements such as vintages and activity types, for each compliance period separately. The current list is published by ICAO and reviewed annually.
Corresponding adjustments and Article 6
Host countries authorise units for CORSIA by making a corresponding adjustment to their own emissions account, which prevents the same reduction being claimed twice. Without it, a credit sits outside the scheme regardless of its quality.
The mechanism sits within Article 6 of the Paris Agreement, which governs how emissions reductions transfer between countries.
CORSIA-eligible fuels
CORSIA-eligible fuels cover sustainable aviation fuel made from renewable or waste feedstocks, and lower carbon aviation fuel, which is conventional jet fuel produced with a lower carbon intensity.
Using either lowers the volume an operator has to offset, providing a second route to compliance alongside credits.
Procurement is handled either directly with carbon project developers, or through brokers and traders operating in the market. Units are transferred between registry accounts and cancelled once they are used for compliance.
Operators typically approach procurement in one of four ways.
Purchasing units that have already been issued, which meets an immediate offsetting requirement but offers no protection against price movements or limited availability.
Contracting for units to be delivered at a future date, which fixes price and volume in advance of a compliance deadline.
Securing supply across more than one compliance period, which spreads exposure instead of concentrating it in a single buying window.
Buying units alone does not complete compliance. Compliance is met at retirement, when the unit is permanently cancelled in an approved registry and can no longer be used.
Route selection is determined by an operator's confidence in its future obligation and its appetite for price exposure. Because eligible supply is finite, timing and pricing are equally significant, and operators procuring close to a deadline compete for a narrowing pool of units.
At SmartestEnergy, we help operators source and deliver eligible units with certainty. To find out more, take a look at our CORSIA carbon credits and aviation trading page.
CORSIA in UK law
The UK has implemented CORSIA in stages. Monitoring and reporting were introduced through The Air Navigation (CORSIA) Order 2021, which is enforced by the Environment Agency, with offsetting for the 2021 scheme year added by amendment. The order covering offsetting from Phase 1 onwards has not yet been made.
The proposed penalty
The government has consulted on a civil penalty of £100, adjusted for inflation, for every unit an operator fails to cancel on time. This remains a proposal until the legislation is made.
CORSIA and the UK ETS
Flights from the UK to the EEA, and from Great Britain to Switzerland, currently sit within both CORSIA and the UK Emissions Trading Scheme (UK ETS), raising the prospect of the same emissions being charged twice.
The consultation set out two options, either applying the UK ETS alone on those routes, or allowing both to apply with operators compensated for their CORSIA costs.
Which rules apply on which route
| Route | Scheme |
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Domestic flight |
UK ETS |
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Flight from the UK to the EU |
CORSIA and UK ETS |
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Long-haul flight to a participating state |
CORSIA |
Speak to a CORSIA expert
CORSIA compliance depends on securing eligible units at the right time. Speak to our experts to understand your obligation and plan procurement around it.
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Meet us at Aviation Carbon
We are excited to exhibit at this year's Aviation Carbon, a major UK event focused on aviation decarbonisation.
Come and meet our trading team to explore how we are providing support for airlines across global aviation carbon markets, with our CORSIA carbon credits and aviation trading solutions.
Date: 30th November - 2nd December 2026Venue: London Heathrow Marriott HotelFrequently asked questions
What does CORSIA stand for?
The Carbon Offsetting and Reduction Scheme for International Aviation. Administered by ICAO, it requires operators to offset emissions from international flights above an agreed baseline.
Is CORSIA mandatory?
Participation has been voluntary for states so far, though compulsory for operators once their state volunteers. From 2027, it becomes mandatory for most ICAO member states.
Which operators does CORSIA apply to?
Operators producing more than 10,000 tonnes of CO2 a year from international flights, using aircrafts above 5,700kg. Cargo, business and private operators are included.
What is the CORSIA baseline?
The level above which offsetting applies, set at 85% of 2019 international aviation emissions until the scheme ends in 2035.
How do operators calculate their CORSIA baseline?
They do not. ICAO publishes a sector growth factor, and applying it to an operator's verified emissions produces the volume it must offset.
What makes a carbon credit CORSIA-eligible?
It must come from an ICAO-approved programme, start its first crediting period in 2016 or later, be a permitted activity type, fall within an eligible vintage, and carry host country authorisation.
Does CORSIA apply to domestic flights?
No. Domestic emissions are counted within each country's Paris Agreement commitments, and in the UK they fall under the UK ETS.
Can operators buy CORSIA credits on a forward basis?
Yes. Forward contracting fixes price and volume ahead of a deadline, though units must still be cancelled in an approved registry to count.
When is the Phase 1 compliance deadline?
January 2028, covering emissions from 2024 to 2026.
What happens if an operator does not comply with the CORSIA scheme in the UK?
The UK has consulted on a penalty of £100 per unit not cancelled on time. This remains a proposal until the offsetting legislation is made.
Does CORSIA replace the UK ETS?
No. Both apply, and flights from the UK to the European Economic Area currently engage each of them.