The CORSIA calls for international aviation to address and offset its emissions through the reduction of emissions elsewhere—i.e., outside of the international aviation sector—using the concept of “emissions units”. One emissions unit represents one tonne of CO₂. Two main types of emissions units exist: “offset credits” from crediting mechanisms and “allowances” from emissions trading schemes.

Offsetting could be through the acquisition and redemption of emissions units, arising from different sources of emissions reductions achieved through mechanisms (e.g. UNFCCC’s Clean Development Mechanism), programs (e.g. REDD+) or projects (e.g. substituting coal-fired stoves with solar cookers).

The buying and selling of eligible emissions units happens through a carbon market. The carbon market is a commodity market with the underlying commodity being emissions units. Like any commodity market, it is driven by the law of supply (eligible emissions units offered from different sources) and demand (eligible emissions units purchased by aircraft operators to offset their international aviation emissions under the CORSIA).​

Implementation of the CORSIA will begin with a pilot phase from 2021 through 2023, followed by a first phase, from 2024 through 2026.

Participation in both of these early stages will be voluntary and the next phase from 2027 to 2035 would see all States on board. Some exemptions were accepted for Least Developed Countries (LDCs), Small Island Developing States (SIDS), Landlocked Developing Countries (LLDCs) and States with very low levels of international aviation activity.

It has taken a great deal of effort and understanding to reach this stage, and I want to applaud the spirit of consensus and compromise demonstrated by our Member States, industry and civil society. We now have practical agreement and consensus on this issue backed by a large number of States who will voluntarily participate in the GMBM—and from its outset. This will permit the CORSIA to serve as a positive and sustainable contributor to global greenhouse gas emissions reduction.

—ICAO Council President Dr. Olumuyiwa Benard Aliu

As of 29 September 2016, 64 states, representing more than 83.8% of international aviation activity, had indicated their intention to participate voluntarily in the global MBM scheme from its outset.

However, noted the International Coalition for Sustainable Aviation (ICSA)—the official environmental civil society observer at the global negotiations—the participating countries deleted key provisions from the text that would have align the ambitions of the MBM with the Paris Agreement’s aim of limiting global temperature rise to well below 2 degrees with best efforts to not exceed 1.5 degrees Celsius.

In a statement released after the ICAO announcement, ICSA said that while it recognized the agreement as a hard-fought political compromise to see that aviation contributes its fair share in the climate change fight, critical work remains to ensure environmental integrity and broad participation.

ICSA’s current analysis of the resolution text and the commitments from more than 60 countries to join the first phases of the GMBM suggests that the measure will cover an estimated three quarters of international aviation’s expected emissions growth between 2021 and 2035.

Although this falls short of ICAO’s own target of carbon neutral growth from 2020, the anticipated coverage would be 2.5 billion tons of CO₂ emissions—provided the emissions criteria to be elaborated allow only high quality carbon credits. Importantly, the integrity of the agreement’s emission reductions depend on rules not yet in place.

ICSA welcomes that more than 60 states have so far stated their intent to participate in the measure from the beginning. However, it is critical to expand coverage of the measure given the shortfall between what was agreed to at the assembly and the goal of stabilizing emissions at a 2020 level and the need for further action. ICSA urges ICAO member states to use the resolution’s review clause to ratchet up ambition over time. It is also important that states and regions, especially developed and fast-developing ones, adopt additional measures to mitigate aviation’s climate impact.

—ICSA

Last week, the International Council on Clean Transportation (ICCT) released a technical report analyzing emerging technologies to reduce new aircraft fuel burn. The study concludes that the rate of fuel efficiency improvement for new aircraft can be more than doubled through 2034, from about 1% today to 2.2% annually, by the adoption of cost effective technologies to improve engine efficiency, reduce aerodynamic drag, and trim aircraft empty weight. (Earlier post.)

ICAO’s decision to promote carbon offsets for some international flights doesn’t address the core problem. In the long run airlines need to decarbonize, not to pay others to do it for them. A host of new technologies to reduce aircraft emissions are under development today but need policy support. Since ICAO won’t provide that, other measures will be needed, starting with US EPA’s aircraft CO₂ standard next year.

—Dan Rutherford, aviation program director for the ICCT