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. Requirements for participation in each phase are summarized as follows.

  Pilot phase
First phase
Second phase
Requirements for participation ICAO member states can voluntarily participate in the scheme. Applied to all States except those exempted from offsetting requirements*.

* The Second phase will be applied to all States that have an individual share of international aviation activities in RTKs in year 2018 above 0.5% of total RTKs or whose cumulative share in the list of States from the highest to the lowest amount of RTKs reaches 90% of total RTKs, except Least Developed Countries (LDCs), Small Island Developing States (SIDS) and Landlocked Developing Countries (LLDCs) unless they volunteer to participate in this phase.

List of participating states

As of August 2017, over 70 States intend to voluntarily participate in the global MBM scheme from its outset. The latest list of participants can be found in following ICAO website.

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.

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.

Calculation of offsetting requirements for operators

  Pilot phase First phase Second phase
2021 - 2023 2024 - 2026 2027 - 2029 2030 - 2035
Offsetting requirements State selects from two options below:
1) Annual emissions in a given year (i.e. 2021; 2022 and 2023) x Sector's growth factor
2) Annual emissions in 2020 x Sectoral growth factor
Annual emissions x [(X-100%) x Sector's growth factor + X% x Aircraft operator's growth factor]
  • * Sector's growth factor = Total emissions covered by CORSIA in the given year – Sectoral baseline emissions
  • * Aircraft operator's growth factor = Operator's emissions covered by CORSIA in the given year – Operator's baseline emissions
  • * Sectoral baseline emissions = Average of CO2 emissions in 2019 and 2020 with route-coverage by CORSIA
  • * Operator's baseline emissions = Average of an operator’s CO2 emissions in 2019 and 2020 with route-coverage by CORSIA
  • * Assembly Resolution A39-3 set the shares of individual approaches (referred as X) as follows: X = 20% for 2030-2032 and X = 70% for 2033-2035, but this figure will be final adjusted at the 2028 ICAO General Assembly.

MRV System

MRV system will be 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.
    Regarding detailed rules, MRV SARPs (Standards and Recommended Practices) and guidance on implementation will be developed and adopted by the Council by 2018 at the latest.

6. Eligibility of emissions units

Emissions units

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

Regarding eligible emissions units, SARPs (Standards and Recommended Practices) and guidance for Emissions Unit Criteria (EUC) will be developed and adopted by the Council by 2018 taking into account relevant developments in the article 6 of the Paris Agreement.


Registries usually take the form of electronic databases that record and track verified emissions data and/or emissions units, in order to assess state of performance of CORSIA by participating countries and operators.

Regarding detailed rules, policies and related guidance material to support the establishment of registries under the scheme, will be reviewed and adopted by the Council by 2018 at the latest.

7. Timeline for preparation for CORSIA Implementation

Review of detailed rules on MRV system, emissions credits, and registries will be promoted, after the approval by the ICAO Executive Board scheduled in 2018 and final consultation by member countries. The system operation will begin on January 1st, 2019 (Offsetting requirements will be applied to operators from 2021.)