The Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA) is a global, market-based mechanism adopted by the International Civil Aviation Organization (ICAO), a United Nations body, to address the growth in CO₂ emissions from international flights. It is a compliance framework, not a voluntary one, and is the first sector-specific global market-based measure for climate action.
The scheme was adopted by the 191 nations of the ICAO in October 2016. Its purpose is to achieve carbon-neutral growth for international aviation from 2020 onwards, solving the problem that international flight emissions fall outside the scope of national climate targets under the United Nations Framework Convention on Climate Change (UNFCCC) and the Paris Agreement.
CORSIA works by requiring aircraft operators to offset emissions that exceed a defined baseline. All operators with annual CO₂ emissions greater than 10,000 tonnes from international flights must monitor, report, and verify their emissions annually, starting from January 1, 2019. The scheme is implemented in phases: a Pilot Phase (2021–2023), a First Phase (2024–2026), and a mandatory Second Phase (2027–2035). Offsetting obligations are triggered when the sector's emissions growth exceeds the baseline. For the Pilot Phase, the baseline was 2019 emissions, but this was amended by the 41st ICAO Assembly in 2022 to be 85% of 2019 emissions for the period from 2024 to 2035. Airlines meet their obligation by purchasing and retiring CORSIA Eligible Emissions Units (EEUs), which are carbon credits from approved standards like Verra and Gold Standard.
The scheme is governed by the ICAO Standards and Recommended Practices (SARPs) contained in Annex 16, Volume IV to the Chicago Convention. CORSIA connects to the Paris Agreement through Article 6, which governs the international transfer of emission reductions, requiring a Corresponding Adjustment (CA) by the host country to prevent double counting of the offset credits. A recent change is the start of the First Phase in 2024, which has triggered the first real offsetting obligations due to the Sectoral Growth Factor (SGF) turning positive, and the ICAO Council's tightening of eligibility criteria for carbon crediting programs for Phase 2.