CORSIA Explained: The Best 2026 Guide to Aviation Carbon Offsets

Updated September 18, 2026 · 12 min read

CORSIA — the Carbon Offsetting and Reduction Scheme for International Aviation — is the world’s first global market-based climate scheme for a single industry. Run by ICAO, the UN’s aviation body, CORSIA requires airlines to offset the growth in CO₂ emissions from international flights above an agreed baseline. In 2026 the scheme sits at a critical turning point: its first proper phase (2024–2026) is ending, the mandatory second phase starts in 2027, and airlines are discovering that the carbon credits they are legally required to buy are in dangerously short supply. This guide explains how CORSIA works, who it covers, what the credits cost, and why critics argue it is not enough.

What is CORSIA and why does it exist?

International aviation was left out of the Paris Agreement because emissions from a flight between two countries belong to neither of them cleanly. Responsibility was handed instead to the International Civil Aviation Organization (ICAO), which adopted CORSIA in 2016 as its answer. The scheme’s official goal is carbon-neutral growth: aviation can keep expanding, but any CO₂ growth above the baseline must be neutralised with carbon credits or reduced with cleaner fuels.

The stakes are significant. According to IATA, without CORSIA the CO₂ footprint of international aviation would grow from just over 600 million tonnes in 2019 to almost 900 million tonnes by 2035. CORSIA is designed to cap that net growth while longer-term solutions — sustainable aviation fuel, hydrogen, batteries — mature. For the bigger picture of which nations emit the most, see our breakdown of aviation emissions by country.

One crucial limitation to understand up front: CORSIA only addresses CO₂. The warming from contrails and nitrogen oxides — which roughly doubles aviation’s climate impact — sits entirely outside the scheme. We cover that gap in detail in our guide to aviation non-CO2 effects.

A short history: from Kyoto to the 2025 Assembly

CORSIA took two decades to arrive. The 1997 Kyoto Protocol explicitly asked ICAO to deal with international aviation emissions, but progress stalled until the EU lost patience and pulled foreign airlines into its own Emissions Trading System in 2012 — triggering a trade backlash from the US, China and India. The compromise was a global scheme instead: ICAO’s 2016 Assembly adopted CORSIA with support from 191 states, and the first monitoring obligations began in 2019.

Since then the scheme has been repeatedly stress-tested. COVID-19 wiped out the intended 2019–2020 baseline and forced the switch to 2019 values, later tightened to 85% of 2019. The 2022 Assembly paired CORSIA with a long-term aspirational goal of net-zero international aviation by 2050, and the 2025 Assembly reaffirmed the framework — over familiar objections from a handful of states — while leaving the hard questions of credit supply and post-2035 design to future reviews.

How CORSIA works: the 85% baseline

CORSIA’s mechanics are simple in outline. Each year, ICAO calculates the total CO₂ emitted by international flights between participating states. Any emissions above the baseline — set at 85% of 2019 emissions from 2024 onward — become the sector’s collective offsetting obligation, distributed among airlines in proportion to their emissions.

Airlines meet the obligation by buying and cancelling CORSIA Eligible Emissions Units (EEUs) — carbon credits from programmes vetted by ICAO’s Technical Advisory Body — or by claiming reductions from CORSIA-eligible fuels. Every operator above 10,000 tonnes of CO₂ per year on international routes must monitor, report and verify its fuel burn under a standard MRV framework, even if its state has not yet joined the offsetting phase.

The choice of an 85% baseline matters. The original plan used average 2019–2020 emissions, but the pandemic collapse of 2020 would have produced an artificially low bar. ICAO first switched to 2019 alone for the pilot phase, then tightened the reference to 85% of 2019 from 2024 — meaning airlines started owing offsets sooner, as traffic recovered past that threshold.

CORSIA phases: pilot, Phase 1 and Phase 2

CORSIA rolls out in three stages, moving from voluntary to mandatory participation.

As of 1 January 2026, 130 states participate in the voluntary phases — including recent joiners such as Vietnam — covering the large majority of international traffic. Notable holdouts include China, India and Russia, which are expected to fall under the scheme only when Phase 2 makes participation mandatory in 2027.

Eligible carbon credits and the supply crunch

Not every carbon credit qualifies. ICAO approves specific crediting programmes — and specific vintages within them — as CORSIA-eligible, and for Phase 1 adds a further hurdle: the credit’s host country must issue a Letter of Authorization applying a "corresponding adjustment", so the emission reduction is not counted twice (once by the country, once by the airline). If the difference between credits and offsets is fuzzy, start with our explainer on carbon offset vs carbon credit.

That double-counting safeguard is good climate accounting — and the main reason supply has collapsed. Very few governments have been willing to give up credits they may need for their own Paris Agreement targets. By early 2026 only a handful of host countries — roughly seven to ten, led by Guyana — had issued the required authorizations.

The squeeze has already forced regulators to blink. In 2026 the European Commission proposed dropping its additional quality criteria for Phase 1 credits, easing what EU-based airlines may buy — a pragmatic concession that campaigners read as a warning sign about the scheme’s integrity.

What CORSIA credits cost in 2026

For now, CORSIA compliance is cheap by climate-policy standards. Fastmarkets assessed CORSIA Phase 1 credits at $11.60 per tonne of CO₂ in July 2026. Compare that with the EU Emissions Trading System, where allowances have traded several times higher — our guide to carbon credit prices explains why the two markets behave so differently.

Even at the high end, offsetting remains far cheaper for airlines than switching fuels — which is precisely the criticism most often levelled at the scheme. A low carbon price neutralises emissions on paper without changing how aircraft actually fly. Whether the underlying projects deliver real, additional reductions is a separate and heavily debated question; see our analysis of the carbon footprint of air travel for how offsetting fits into a flight’s true climate cost.

Where sustainable aviation fuel fits in

Offsetting is only one of two compliance routes. Airlines can also reduce their CORSIA obligation by burning CORSIA-eligible fuels — sustainable aviation fuels (SAF) and lower-carbon aviation fuels certified against ICAO’s sustainability criteria, which require at least a 10% lifecycle emissions reduction versus fossil jet fuel (in practice most certified SAF pathways deliver far more).

The catch is volume. SAF was well under 1% of global jet fuel in 2025, so fuel-based compliance remains marginal in Phase 1. That is expected to shift through the 2030s as production scales and mandates such as ReFuelEU tighten. For the technology and economics, see our full explainer on sustainable aviation fuel.

How airlines comply, step by step

Behind the headline numbers sits a detailed compliance machine. Every airline flying international routes — even from states not yet participating in offsetting — follows the same annual cycle under CORSIA’s monitoring, reporting and verification (MRV) rules:

• Monitor. The operator tracks fuel burn on every international flight, using an approved monitoring method set out in its Emissions Monitoring Plan.
• Report. By 30 April each year, it submits a verified emissions report for the previous calendar year to its national authority, which forwards aggregated data to ICAO.
• Verify. An accredited independent verification body checks the report before submission — the same third-party model used in the EU ETS.
• Offset. At the end of each phase, ICAO informs each operator of its final offsetting requirement. The airline then buys eligible credits and cancels them in the relevant registry, proving the retirement in an Emissions Unit Cancellation Report.

Two design choices soften the burden on smaller players. Operators emitting under 10,000 tonnes of CO₂ per year on international routes are exempt outright, as are humanitarian, medical and firefighting flights. And during Phase 1 the obligation is calculated almost entirely on a sectoral basis — each airline offsets in proportion to the industry’s collective growth rather than its own — before Phase 2 gradually shifts the formula toward each operator’s individual emissions growth.

What CORSIA means for ticket prices and travellers

For passengers, the honest answer is: very little, so far. At roughly $12 per tonne of CO₂ and with only emissions above 85% of 2019 levels in scope, CORSIA’s cost per ticket works out to cents on a short-haul hop and at most a few dollars on a long-haul flight. Airlines have absorbed it without visible fare changes, which is exactly why campaigners argue the scheme sends no meaningful price signal.

That could change after 2027. Mandatory participation, growing traffic and a constrained credit market pulling prices toward the $60 scenario would push CORSIA costs into the same territory as the EU ETS on some routes — still small relative to fuel, but no longer invisible. Travellers who want to understand — or shrink — their own share of aviation’s footprint can start with our guide to the carbon footprint of air travel.

It is also worth separating CORSIA from the voluntary offset checkbox many airlines show at booking. Those retail offsets are a separate, unregulated purchase; CORSIA is a regulatory obligation on the airline itself, with vetted credits and third-party verification. The quality bar — whatever its flaws — is considerably higher.

CORSIA vs the EU ETS

Europe runs its own, stricter carbon market for aviation — and the coexistence of the two systems is one of the most contested issues in aviation climate policy.

The EU applies its ETS to intra-European flying and CORSIA to extra-European routes, pending an assessment of whether CORSIA is strong enough to justify keeping it that way. A 2026 review is feeding an expected 2027 decision — if Brussels judges CORSIA too weak, long-haul flights touching Europe could be pulled back into the ETS, a move airlines fiercely oppose.

Does CORSIA actually work? The criticisms

Environmental groups have never been enthusiastic. The core objections:

• It offsets rather than reduces. Transport & Environment argues CORSIA does nothing to cut jet fuel demand; Greenpeace called it "a timid step in the right direction".
• Partial coverage. Domestic aviation is excluded, and with exemptions and the 85% baseline the scheme is expected to address only around a quarter of international aviation emissions through 2035.
• Credit quality risk. The scheme’s integrity depends entirely on ICAO’s programme vetting — and the 2026 EU move to relax additional quality criteria shows how supply pressure can erode standards.
• No price signal on flying. At roughly $12 per tonne, CORSIA adds only cents to a ticket — too little to change airline economics or passenger behaviour.

Defenders reply that CORSIA is the only instrument that exists at global scale, that its MRV framework has forced every major airline to measure emissions rigorously for the first time, and that corresponding adjustments make its credits more credible than most of the voluntary market. Both things can be true: a real institutional achievement, and not remotely sufficient on its own.

What happens next: 2027 and beyond

Three dates now define the scheme’s trajectory. In 2027, Phase 2 begins and participation becomes mandatory for nearly all ICAO states, pulling in China, India and Russia and roughly doubling covered traffic. On 31 January 2028, the first true test arrives: airlines must have cancelled enough eligible credits to cover their entire 2024–2026 obligation — against a market that today holds a fraction of the required supply. And through 2035, the current framework runs to its scheduled end, with ICAO reviews every three years determining whether the baseline tightens.

Watch the supply side most closely. Either dozens more host countries start issuing Letters of Authorization, or prices spike toward the $60 scenario, or ICAO loosens eligibility — each path carries very different consequences for the scheme’s credibility.

Related guides: Are Carbon Offsets Effective, EU ETS Aviation Explained: The Best 2026 Guide to Airline Carbon Costs and Aviation and Carbon Emissions.

Frequently Asked Questions

Sources

• ICAO. Carbon Offsetting and Reduction Scheme for International Aviation. icao.int
• IATA (2026). CORSIA fact sheet and participation status. iata.org
• Sylvera (2026). CORSIA Phase 1 pricing: what airlines need to know. sylvera.com
• Fastmarkets (2026). CORSIA Phase 1 carbon credit price assessment. fastmarkets.com
• ESG News (2026). EU eases CORSIA carbon credit rules amid supply crunch. esgnews.com
• Wikipedia. Carbon Offsetting and Reduction Scheme for International Aviation. en.wikipedia.org

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