As part of the negotiations for the offsetting scheme, governments have decided to make the first part of CORSIA from 2021 until 2026 voluntary. The aviation industry is encouraging all countries to volunteer for the scheme as early as possible. As of 24 July 2019, 81 states representing 76% of international aviation activity have done so. While emissions from all international flights must be reported to states, only emissions from flights between volunteering countries will be subject to offsetting initially.
Who volunteers for CORSIA

There are a number of reasons why states should volunteer to participate in the initial stages of CORSIA. Firstly, taking the political decision to volunteer sends a strong signal to the rest of the world that the state is willing to show climate leadership. It also increases the effectiveness of the scheme by ensuring that more flights are covered. However, there are other more practical benefits to volunteering. With more states participating, the demand for offsets will grow, driving investment in developing countries where many of the offset projects are located. Volunteering also allows both states and airlines to gain early experience of carbon trading, while the costs of the scheme are low.
See the full list of CORSIA volunteers here:
CORSIA and the EU ETS
CORSIA is a global scheme, in comparison with the regional scope of the European Union emissions trading system (EU ETS). As a result, CORSIA will result in a greater CO2 reduction in international aviation overall than EU ETS.
The EU has been instrumental in the adoption of CORSIA, so it is crucial that it implements CORSIA on the basis of the required agreements.
If the EU were to exclude international flights within the European Economic Area (EEA), or subject international flights to both EU ETS and CORSIA, this would give the wrong signal to other groups of countries that they could also detract from CORSIA by implementing regional or bilateral agreements. Such arrangements may not offer the same environmental benefits as CORSIA and the EU ETS, and would result in a patchwork of regulatory measures. All parties are seeking to avoid this situation through the adoption of a global ICAO mechanism.