Current Discussion in UNFCCC and other international framework


1. Context of the introduction of CORSIA

Mitigation of GHG emission from the international civil aviation sector has been led by the International Civil Aviation Organization (ICAO), a specialized agency of the United Nations. ICAO has been elaborating countermeasures and international rules for GHG emissions reduction in the sector.

In 2010, at the 37th session of the ICAO Assembly adopted its international aviation sector's "Global reduction target goals" of 1) improving the efficiency of fuel economy in 2% annually and 2) stabilizing its global CO2 emissions at 2020 levels (so-called "carbon neutral growth from 2020"). Furthermore, in order to achieve these goals, the assembly also resolved to elaborate and implement the following four measures (referred to as "Basket of Measures"): 1) Introduction of new aircraft technology, 2) Operational improvements, 3) Efforts to utilize alternative fuels, and 4) Market-Based Measures (MBM).

"Carbon neutral growth from 2020" cannot be fully achieved by only implementing Non-MBM measures ((1), (2) and (3) above). Introduction of Global Market-Based Measures (GMBM) was adopted in the 39th session of the ICAO Assembly in 2016, to play a complementary role to other Non-MBM measures to reduce CO2 emissions from international aviation. Specific requirements of the GMBM were adopted in the resolution, and it was named as "Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA)".

The CORSIA will be operationalized by 2021 and aircraft operators will be required to purchase emissions units to offset their CO2 emissions along with defined offsetting requirements. Regarding the obligation to offset, allocation of CO2 emissions of international flights from 2020 onwards according to emissions at the early stage of each business operator are planned, but after 2030 an allocation reflecting the CO2 emissions of each company will be allocated.

2. CO2 emissions and reduction measures in the international aviation sector

According to the IPCC's Fifth Assessment Report (AR5), international and domestic aviation account for approximately 2% of anthropogenic global CO2 emissions and international aviation is responsible for approximately 1.3% of global CO2 emissions. The Committee on Aviation Environmental Protection (CAEP) of ICAO estimates that CO2 emissions from the aviation sector will grow somewhere between 2.8 to 3.9 times by 2040 compared to 2010 levels due to traffic growth if measures are not taken.

The figure below shows a forecast of CO2 emissions increase, and achievement of carbon neutral growth from 2020 by implementation of CO2 emissions reduction measures.

forecast of CO2 emissions increase, and achievement of carbon neutral growth
[Adapted from ICAO]

3. Timeline for CORSIA implementation and participating states

Timeline for CORSIA implementation and participating states

CORSIA will be implemented in phases, from 2021 to 2026 (2021-2023: pilot phase; 2024-2026: phase 1) ICAO Member States may participate voluntarily by declaring their willingness to participate; from 2027 to 2035 (phase 2) all ICAO Member States are required to participate, with the exception of exempted countries such as Least Developed Countries. The implementation schedule and details of countries eligible to participate can be found in Chapter 3 of Annex 16 to the Convention on International Civil Aviation.

List of participating states

As of 16 November 2022, 118 countries have expressed their willingness to participate in CORSIA; a list of countries that have voluntarily joined, as approved by the ICAO Council, can be found here.

4. Flight routes subject to the scheme

CORSIA shall be applied to all aircraft operators on the same routes between States (route‐based approach). A route will be subject to the scheme if both States connecting routes are participating in CORSIA. A route will not be subject to the scheme if one or both of States connecting the route are not participating in CORSIA. Details of regulated flight routes are available from Chapter 3 of Annex 16 to the Convention on International Civil Aviation.

5. Calculation of offsetting requirements and MRV system

Calculation of offsetting requirements for operators

In the early stages of the system, allocation of offsetting requirements will be based according to the growth rate of CO2 emissions in the international aviation sector from 2020. After 2030 however, an amount of CO2 emissions reduction by each operator is scheduled to gradually shift allocation reflecting the growth rate.

  Pilot phase First phase Second phase
2021 - 2023 2024 - 2026 2027 - 2029 2030 - 2035
Participating countries ICAO Member States may join voluntarily by declaring their willingness to participate. All ICAO Member States are required to participate, with the exception of countries subject to exemptions*.
Offsetting requirements Countries choose one of the following calculation methods
(i) Annual emissions x sector growth factor
(ii) 2020 emissions x sector growth factor
Annual emissions x [(X-100%) x sector growth factor + X% x individual company growth factor].
Baseline CO2 emissions in 2019 85% of CO2 emissions in 2019
Routes subject to offset Routes between countries that voluntarily participated. Routes between countries that have voluntarily participated and obligated countries (excluding small emitting countries, least developed countries, etc.)
  • * With the exception of Least Developed Countries/Small Island Developing States/Inland Developing States, countries are required to participate if the country's paid tonne-kilometres as of 2018 is at least 0.5% or until the cumulative share reaches 90%, with the CORSIA participating countries listed in order of largest paid tonne-kilometres.
  • * Sector growth factor = total annual CO2 emissions on the flight routes covered - sector baseline emissions (the share of the sector growth factor for the period 2021-2032 is 100%, for the period 2033-2035 is 85%, resolved at the 41st Plenary).
  • * Individual company growth factor = annual CO2 emissions of individual companies on the flight routes covered - individual company baseline emissions ('sector growth factor' percentage for 2033-2035 is 15%, resolved at the 41st Plenary).

MRV System

MRV system had implemented and applied to all ICAO member states whose aircraft operators undertakes international flights from January 1st, 2019 regardless of whether states are participating in CORSIA or not. The MRV system consists of following three components in order to collect data on international aviation CO2 emissions on an annual basis and compare emissions against the baseline emissions.

  • Monitoring: Data collection of fuel use on each flight and calculation of CO2 emissions.
  • Reporting: Reporting of emissions information between aircraft operators, States and ICAO.
  • Verification: Verification of reported emissions data to ensure completeness and to avoid misstatements.

To support reporting through the MRV system, the CORSIA CO2 Estimation and Reporting Tool (CERT) has been developed, which can be used by aircraft operators to monitor and report their CO2 emissions. It helps aircraft operators fulfil their monitoring and reporting requirements by filling in standardised emissions monitoring plans and emissions reporting templates. For further information on the MRV system, see chapter 2 in Annex 16 and for more information on the CORSIA CO2 Estimation and Reporting Tool (CERT), see here.

6. Eligibility of emissions units

Emissions units

Each aircraft operator shall meet their offsetting requirements under CORSIA by purchasing and cancelling eligible emissions units.

The specific types of emissions units and criteria (Emissions Unit Criteria: EUC) that can be used are listed in Table 1. These are determined by the Board in accordance with the CORSIA document “CORSIA Emissions Unit Eligibility Criteria” , which is developed on the basis of advice from the Technical Advisory Body (TAB) established by the Board. The emissions unit programmes determined up to January 2023 are listed in Table 2.

Table 1 CORSIA Eligibility criteria for qualifying emission units

Program Design Elements Carbon Offset Credit Integrity Assessment Criteria
A1. Clear Methodologies and Protocols, and their Development Process B1. Are additional.
A2. Scope Considerations B2. Are based on a realistic and credible baseline.
A3. Offset Credit Issuance and Retirement Procedures B3. Are quantified, monitored, reported, and verified.
A4. Identification and Tracking B4. Have a clear and transparent chain of custody.
A5. Legal Nature and Transfer of Units B5. Represent permanent emissions reductions.
A6. Validation and Verification procedures B6. Assess and mitigate against potential increase in emissions elsewhere.
A7. Program Governance B7. Are only counted once towards a mitigation obligation.
A8. Transparency and Public Participation Provisions B8. Do no net harm
A9. Safeguards System
A10. Sustainable Development Criteria
A11. Avoidance of Double Counting, Issuance and Claiming

Source ICAO “CORSIA Emissions Unit Eligibility Criteria”

Table 2 Determined emission unit programme (as of March 2022)

Name of Credit scheme Summary
American Carbon Registry (ACR) This was established in 1996 as the first voluntary GHG emissions registry in the USA; it manages and operates a registry of GHG emissions and develops voluntary certification standards and methodologies.
Architecture for REDD+ Transactions (ART) This is a mechanism for issuing credits by reducing emissions from deforestation and forest degradation in developing countries.
China GHG Voluntary Emission Reduction Program This is a voluntary programme established by the NDCR in 2012, with formal registry and trading commencing in January 2015.
Clean Development Mechanism (CDM) This is a mechanism whereby Annex I countries under the Kyoto Protocol are involved as investors, and credits are issued based on the emission reductions resulting from the implementation of emission reduction projects in non-Annex I countries where GHG emissions are not capped.
Climate Action Reserve (CAR) This is an offset registry initiated by the State of California in 2001.
Global Carbon Council (GCC) This is a voluntary carbon offset programme that helps companies diversify their sector economies by reducing their CO2 emissions and adopting low-carbon pathways.
The Gold Standard (GS) This is a certification standard that guarantees the quality of carbon credits, e.g. CDM.
Verified Carbon Standard (VCS) This is a credit certification scheme for the voluntary carbon market, established in 2005. It approves methodologies and projects and issues credits after providing rules and guidelines.

CORSIA Central Registry (CCR)

The CORSIA Central Registry (CCR) usually takes the form of an electronic database and records data on CO2 emissions and emission rights in order to track the implementation of CORSIA by participating countries and operators. With regard to the detailed rules, guidelines and guidance have been adopted to support the establishment of the registry. The adopted documents are listed in Table 3.

Implementation components of CORSIA

CORSIA (Annex 16 - Environmental Protection, Volume 4 - Carbon Offsetting and Reduction Scheme for International Aviation) was adopted by the ICAO Council in June 2018 as SARPs (Standards and Recommended Practices), adopted by the ICAO Council in June 2018.SARPs refer to globally uniform rules adopted by the ICAO Council, consisting of 'Standards' (Standards) that apply in principle to all Contracting Parties and SARPs are divided into 'Standards', which apply in principle to all Contracting Parties, and 'Recommended Practices', which should be applied uniformly to all Contracting Parties.

The implementation component of CORSIA consists of five implementation elements, the structure and rules of which are reflected in 14 institutional documents approved by the ICAO Council (see Table 3 below for details). These ICAO documents are directly referenced in Annex 16, Volume 4 and are integral to the implementation of CORSIA.

Table 3 CORSIA implementation components and relevant ICAO documents

CORSIA implementation components ICAO document
CORSIA States for Chapter 3 State Pairs 1. CORSIA States for Chapter 3 State Pairs
CORSIA CO2 Estimation and Reporting Tool 2. ICAO CORSIA CO2 Estimation and Reporting Tool
CORSIA Eligible fuels
CORSIA Applicable emission units
CORSIA Central Registry (CCR)