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The Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA)

In 2019 global aviation emitted around 1 billion tonnes of CO2 emissions, and flying is estimated to have contributed around 4% to global warming to date. In spite of its impact, a large part of the industry (international flights) are not part of any country's carbon budget. This means that they are not included in reduction and offsetting plans in the same way as domestic flights. 

It is essential that a system is created to measure and reduce emissions from international flight, which is why CORSIA (the Carbon Offsetting and Reduction Scheme for International Aviation) was developed. 

CORSIA is an agreement created by the International Civil Aviation Organization (ICAO), the UN agency helping countries to share their skies for their mutual benefit. Under CORSIA, airline operators with annual emissions greater than 10,000 tonnes of CO2 are required to 1. report their emissions from international flights every year, and 2. buy carbon credits to offset the rise in their CO2 output compared to 2019 levels.

​Who participates in CORSIA?

From 2027, CORSIA will apply to all ICAO member states, but for now, it is voluntary. In the current phase, member states decide whether or not to participate, rather than individual airline operators. 

There are three phases to the plan:

  • Pilot phase (2021-2023) - Voluntary 

  • First phase (2024-2026) - Voluntary

  • Second phase (2027 onwards) - Participation will be determined based on 2018 Revenue Tonne Kilometer (RTK) data.

A map of the countries participating in CORSIA in 2024
Source: IATA

Who/what’s not included:

  • Emissions from domestic flights (who contribute ⅓ of aviation emissions!)

  • Aircrafts with a Maximum take-off weight (MTOW) of less than 5.7 metric tons (small private jets) 

  • Operators whose total annual CO2 emissions from international aviation are below or equal to 10,000 tonnes

  • Aircraft operated by the police, military, custom or the State

  • Humanitarian, medical and firefighting flights

How much of their emissions do eligible airlines need to offset under CORSIA?

CORSIA doesn’t require airlines to offset all their emissions, but rather focuses on their growth, measured against their 2019 emissions. In any year in which an airlines emissions surpass 2019 numbers, they must offset the difference between the two. 

For example, if a participating airline emitted 38.2 million tonnes of CO2 in 2019, and 38.9 million tonnes in 2021 (the first year of phase 1) they would have had to purchase CORSIA credits for 0.7 million tonnes from their total emissions that year. 

If, in 2022, their emissions dropped to 38.1 million tonnes, they would not have to purchase any credits for 2022. 

Benefits of CORSIA 

Aviation is a major contributor to global emissions and is growing rapidly. The demand for flights quadrupled between 1990 and 2019, and, despite a dip in 2020 and 2021 following the COVID-19 pandemic, we are now back to year-on year growth.   

Just 10% of people fly in an average year (Gössling, S., & Humpe, A., 2020), leaving massive potential for industry expansion as more people are able to afford flying. Many countries have started to regulate the growth of domestic flights, with some banning short haul flights below a certain distance to encourage other methods of travel, but international flights don’t face the same pressure. CORSIA aims to fill that gap and discourage growth at the expense of the planet.

Which offsetting projects are eligible?

The criteria for CORSIA eligible offsets have a lot of similarities with rules set by other carbon offset certification bodies. 


The offsetting activity must be ‘additional’ to business-as-usual. 


There must be a permanent reduction of emissions that cannot be reversed. 

No leakage 

Activity related to offsetting shouldn’t result in unintended increases in emissions elsewhere. 


All projects must have a baseline to represent what would have happened without the project. They must use accurate measurements and valid protocols to quantify emissions reductions and must be audited independently. 


Programs will need to demonstrate that they have procedures in place to track units and to avoid emissions reductions being counted more than once.

Social and environmental harm 

Safeguards should be in place to address potential environmental and social risks.

Even with strict guidelines for project eligibility, CORSIA has not been able to escape accusations of greenwashing, along with other criticisms. 

Criticisms of CORSIA

Carbon offsetting is not a replacement for emissions reductions, and shouldn’t be used to facilitate unsustainable growth, but we’ve seen CORSIA referred to as a path to carbon neutral growth. 

Until low carbon options exist for the aviation sector, reducing the number of flights should remain a priority. If CORSIA is used to placate the public while the industry (and industry emissions) continue to grow, is it better than ‘greenwashing? 

Many climate activists have strong views about CORSIA, as they think it distracts from real solutions and from the need to reduce the number of flights. Another criticism is the timeline. Considering how hard other sectors are working to lower our chances of passing 1.5 ° C of warming, aviation could do more, and faster. 

Part of the issue is that since flight emissions fell heavily in 2020 during the height of the COVID pandemic, it will be a while before they bounce back to the 2019 rates, let alone pass them. Some estimates suggest it could take until 2026 before airlines are passing their 2019 emissions. As a result, most are still not compensating for any emissions through CORSIA. 

Our thoughts

While it is encouraging to see money from such a high impact industry funding credible climate solutions, CORSIA is not the magic bullet that will ‘solve’ aviation’s climate impact. What’s most urgently needed is to slow industry growth and reduce emissions, meaning it is vital to avoid a pay-to-play scenario, where airlines can let their emissions increase unchecked as long as they can afford CORSIA requirements.


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