International Aviation

To keep the Paris Agreement 1.5˚C temperature goal within reach, it is imperative that global CO₂ emissions reach net zero around 2050. The Paris Agreement requires countries to peak global emissions as soon as possible and to achieve a balance between GHG emission sources and sinks of removals in the second half of this century (Article 4(1)). Further, the Paris Agreement requires developed countries to set economy-wide emission reduction targets and developing nations to work towards those (Article 4(4)) (UNFCCC, 2015). The Agreement does not explicitly exclude emissions from international aviation, nor does it provide a role for ICAO to address these emissions (Dehon, 2021). The CAT therefore understands that governments must include international aviation in their NDC targets.

In addition, at ICAO’s 41st Assembly in 2022, member states agreed to a long-term aspirational goal (LTAG) of net zero CO₂ emissions from international aviation by 2050 (ICAO Assembly, 2022a). The Assembly Resolution urges states to contribute to this goal and to submit voluntary action plans, while it tasks the ICAO Council to take a coordination role (ICAO Assembly, 2022a; Mithal & Rutherford, 2023).

Just four jurisdictions are responsible for a quarter of international aviation emissions. These are the EU27 (10.4% in 2019), the United States (7.9% in 2019), China (4.4% in 2019) and the United Kingdom (3.9% in 2019) (Graver et al., 2020). Japan, the United Arab Emirates, and India are other important players: each was responsible for 2–3% of global CO₂ emissions from international aviation in 2019. Within the European Union, Germany, France, and Spain have the highest emissions from international aviation (Graver et al., 2020).

While some countries have started addressing emissions from international aviation, there is wide variation in how governments define ‘international aviation.’ The United Kingdom, for instance, covers emissions from all outgoing flights in its sixth carbon budget, but does not include emissions from incoming flights. The US net zero GHG aviation goal does not cover all outgoing and/or incoming flights, but rather covers emissions from flights operated by American airlines between two countries. For instance, if American Airlines flies between London and Paris, the emissions from that flight are covered, but if British Airways flies from New York to London, the emissions from that flight are not included in the US goal.

The EU and its 27 member states include international aviation in their NDC for 2030 (Germany and the European Commission, 2020). The Union’s climate neutrality target, however, does not explicitly cover emissions from international aviation.

Despite efforts from the European Commission and the European Parliament to reform the EU ETS and introduce a tax on kerosene and quota for SAF, the EU still has very limited measures in place to reduce emissions from international aviation.

EU ETS Directive

The EU Emission Trading Scheme (EU ETS) is limited in scope, covering only flights in the European Economic Area (EEA), i.e. 27 EU member states, Norway, Liechtenstein, and Iceland. Flights from the EEA to Switzerland and the United Kingdom fall under the EU ETS, while flights from these two countries to the EEA are covered by the Swiss and UK ETS, respectively.

The EU ETS originally covered all international flights to and from the EEA. However, to allow the continuation of developing a global approach to limiting emissions from international aviation through ICAO, the EU “stopped the clock” in April 2013, limiting EU ETS coverage to flights taking off and landing within the EEA (European Parliament and Council, 2013). The EU ETS was revised in 2021 and 2022. During the last revision round, the EU ETS was expanded to cover flights between the EEA and the EU’s outermost regions (e.g. Guadeloupe, Canary Islands, Madeira), unless these flights connect to the Member State to which the outermost region belongs (European Commission & European Parliament, 2023a). This means that a flight from Tenerife to Madrid is not covered by the EU ETS, but a flight from Tenerife to Paris is.

While the European Parliament pushed for expanding the scope to include all international flights departing from the EU, the suspension on including flights outside the EEA will remain in place until at least 2026 (European Commission & European Parliament, 2023a). In that year, the Commission will prepare a report assessing the environmental integrity of CORSIA. In addition, the Commission will develop a legislative proposal to expand the EU ETS scope if the ICAO Assembly does not strengthen CORSIA in line with the long-term global aspirational goal by the end of 2025, or CORSIA continues to cover less than 70% of international aviation emissions.

The decision not to extend the EU ETS’ scope to all flights departing from EEA countries is a missed opportunity. As discussed in the section on CORSIA, the offsetting scheme suffers from several limitations and is unlikely to deliver real emission reductions. An assessment, commissioned by the European Commission in 2020, found that the EU ETS, if extended to all international flights leaving the EEA, would deliver greater emission reductions than CORSIA, which has limited participation (ICF Consulting et al., 2020).

The recent EU ETS reforms resulted in a gradual phase-out of free allowances for airlines, although so-called sustainable aviation (SAF) allowances will be allocated for free until 2030 (European Commission & European Parliament, 2023a). In 2024, 25% of all allowances will be auctioned, in 2025 50% and from 2026 onwards a 100%. This could provide airlines with a stronger economic incentive to reduce emissions on inter-EEA flights. While free allowances are phased out, the EU will distribute 20 million free SAF allowances between 2024 and 2030. These are meant to bridge the price gap between SAF and standard jet fuel. Only airlines that invest in SAF are eligible to receive SAF allowances.

MRV of non-CO₂ GHG forcers from aviation

The revised EU ETS Directive introduces a requirement for aircraft operators to report on the non-CO₂ effects from aviation, starting in 2025 (European Commission & European Parliament, 2023a). Implementation of the non-CO₂ monitoring, reporting, and verification (MRV) can help to increase understanding of aviation’s non-CO₂ climate impacts, which are estimated to contribute to two-thirds of aviation’s radiative forcing (Lee et al., 2021), and mitigation measures to address them.

The EU ETS agreement adopted in 2022 specified that the non-CO₂ MRV requirement would apply to all flights arriving at and departing from the EEA. However, the Commission later decided that only flights within the EEA and to the United Kingdom and Switzerland would be covered in the first two years (T&E, 2024). This means that only one-third of Europe’s non-CO₂ aviation impact falls within the MRV framework’s scope.

Based on a review of the MRV results, which is to be published by the end of 2027, the European Commission may develop a legislative proposal to expand the scope of the EU ETS to cover the non-CO₂ forcers from aviation (European Commission & European Parliament, 2023a).

Kerosene tax

As part of the ongoing proposal to revise the Energy Taxation Directive, the Commission proposed implementing a tax on kerosene used on intra-EU private and commercial flights (European Commission, 2021). Such a tax would be gradually implemented to reach a minimum rate of 10.75 EUR/GJ in 2033.

However, in September 2024, a leaked draft proposal showed that the EU Member States are considering exempting aviation and maritime fuels from a minimum EU tax rate for another twenty years (Abnett, 2021)

Quota for the use of SAF

The EU defines SAF to include biofuels, advanced biofuels, and synthetic fuels. The ReFuelEU Directive requires fuel suppliers to supply minimum shares of SAF at EU airports, starting at 2% in 2025, rising to 6% in 2030, and 70% in 2050 (European Commission & European Parliament, 2023b). Synthetic fuels must account for at least 0.7% of SAF in 2030 and 35% of SAF in 2050.

This quota for the use of SAF is an important policy lever and the ReFuelEU Directive can help to spur demand and supply of sustainable aviation fuels. However, the quota falls short of what global benchmarks show is necessary for the aviation sector to be aligned with a 1.5ºC trajectory. By 2030, SAF should account for 10–15% of global aviation fuel supply, rising to 100% by 2050 (Boehm et al., 2023; IEA, 2023b; UNFCCC, 2021). Governments in the Global North should aim for an even more ambitious SAF uptake. Raising ambition in the EU and other wealthy, high-emitting countries allows for more moderate uptake in countries in the Global South.

Although the EU’s SAF quota will help scale up the use of SAF, the large share of biofuels from unsustainable feedstocks it allows for is problematic. Biofuel production has a range of potential negative sustainability implications, including deforestation, biodiversity loss, and food insecurity (Ahmed et al., 2021; Calvin et al., 2020; Clarke et al., 2022; Hanssen et al., 2022; Hof et al., 2018; Kline et al., 2015). It also directly competes for land dedicated for biological carbon dioxide removals (Becken et al., 2023), making it more difficult to neutralise economy-wide residual emissions. For a more detailed discussion on biofuel and synthetic SAF, see the section on Mitigation options.

The change in leadership following the UK's July 2024 general election offers an opportunity for the new administration to set a more ambitious course on aviation emissions in line with the Paris Agreement. It remains to be seen whether it will take up this opportunity.

The previous UK government had announced in 2021 that it would include emissions from international aviation and shipping in its sixth carbon budget for the period 2033–2037, but inclusion of these sectors had not yet been legislated by August 2024 (BEIS, 2021). Emissions from international aviation cover outgoing flights only.

While the 2019 Climate Change Act does not specifically mention emissions from international bunkers, the UK government stated that these emissions are included in the net zero target for 2050, which was set on an economy-wide basis (BEIS, 2021).

In July 2022, the previous administration also presented its Jet Zero strategy, which is to bring the UK aviation sector to ‘net zero’ by 2050. However, in this context, ‘net zero’ does not mean net zero, and eliminating the negative climate impacts of aviation by 2050, but rather allowing for an increase in emissions that needs to be offset through the UK ETS, CORSIA, and other offsetting mechanisms outside the aviation sector. Although non-CO₂ emissions and impacts contribute to an estimated two-thirds of aviation’s radiative forcing (Lee et al., 2021), the Jet Zero strategy does not set clear targets for their elimination. It remains to be seen how the new UK government will amend or build upon this strategy.

No demand reduction measures

The previous UK government believed that the UK can achieve “Jet Zero” without government interventions to limit growth in aviation demand (Department for Transport, 2022). The Jet Zero envisaged that demand could grow by 70% between 2021 and 2050. This runs directly counter to the advice of the UK Climate Change Committee (CCC), which stated that no net expansion in airport capacity should be permitted, and passenger growth should be limited to a maximum of 25% above 2018 levels (CCC, 2020).

The new government has also confirmed that it is not opposed to expanding airport capacity, subject to a series of tests including consistency with the UK’s climate obligations (Burford, 2024). Given the advice from the CCC, it seems clear that no net airport expansion can pass this test, and the UK government should be unequivocal in opposing airport expansion, and instead develop strategies to manage and reduce demand for aviation.

UK ETS and CORSIA

The previous UK government expected that the UK ETS and CORSIA, together, could reduce emissions of flights departing the UK by around 25% by 2050 (Department for Transport, 2022), which seems an optimistic estimate: as explained in the section on CORSIA, the scheme is highly unlikely to drive any significant CO₂ reductions from aviation. The UK ETS covers domestic flights and flights to the EEA, but these are only responsible for about one-quarter of emissions from flights departing from UK airports, with the vast majority of emissions generated on flights to countries outside Europe (Department for Transport, 2022; Finch, 2024)

The UK government is in the process of assessing feedback on how to include CORSIA in the UK ETS that they received during a consultation period in the second quarter of 2024 (Gualandi, 2024b). The government is considering a penalty system to enforce compliance with CORSIA.

GHG removals

The UK government further plans to offset emissions through greenhouse gas removals, including direct air capture (DAC), a technology that is not yet mature, and has a highly uncertain abatement potential (Fuss et al., 2018; Jeffery et al., 2020).

There is limited global potential for capturing CO₂ from the atmosphere and permanently storing it (Fuss et al., 2018; Jeffery et al., 2020). This limited potential should be reserved to balance out residual emissions to achieve net zero global emissions, rather than to facilitate a stark increase in aviation sector emissions in one of the world’s wealthiest countries.

SAF mandate

The UK government also expects SAF to play an important role and commits to have at least 10% SAF in the UK fuel mix by 2030, rising to 22% by 2040 (UK Department for Transport, 2024). The new government confirmed this commitment, and introduced a SAF mandate that will require UK jet fuel demand to be met by 2% SAF in 2025, 10% in 2030, and 22% in 2040 (Department for Transport, 2024). There will also be a revenue certainty mechanism to provide confidence to investors seeking to build SAF plants to meet UK demand.

The level of SAF rollout envisaged by the UK government is at the lower end of what global benchmarks deem as necessary for the aviation sector to be aligned with a 1.5ºC trajectory. By 2030, SAF should account for 10–15% of global aviation fuel supply (Boehm et al., 2023; IEA, 2023b; UNFCCC, 2021). Governments in the Global North should aim for an even more ambitious SAF uptake. Raising ambition in the UK and other wealthy, high-emitting countries allows for more moderate uptake in countries in the Global South.

While 10% is at the lower end of global benchmarks, it will be challenging for the government to achieve this level of SAF without worsening other sustainability issues. The UK government also allows for synthetic SAF and requires that by 2040, 3.5% of all jet fuel in the UK comes from low-carbon electricity (UK Department for Transport, 2024) However, especially in the short term, most SAF will be biofuels.

The UK government’s sustainability criteria for SAF allow biofuels made from used cooking oil, forestry residues, and recycled plastics. Given the limited availability of these bio-resources, it is questionable whether the UK can reach its 10% SAF goal by 2030, without exacerbating other sustainability issues (see also the section on Mitigation options). The absence of demand measures only compound these issues.

The US committed to net-zero GHG emissions from the US aviation sector by 2050 (FAA, 2021). This goal covers CO₂, N₂O, and CH₄ emissions but not other climate impacts from aviation such as cirrus trails.

The US government uses a limited definition of international aviation, which leaves out a substantial share of emissions from international flights departing from US airports. The government defines the ‘US aviation sector’ as:

1. Domestic aviation (i.e. flights departing and arriving in the US and its overseas territories);
2. Flights operated by US airlines between two countries (e.g. a flight from London to Paris by American Airlines would be covered, but a flight from the US to the UK operated by British Airways would not); and
3. Emissions from US airports, for instance from ground operations.

The US government proposes measures to reduce emissions from aviation, but with a strong focus on domestic flights. In its SAF Grand Challenge Roadmap, the US government sets the goal of scaling up the production and use of SAF from 19m to 11bn litres per year by 2030 (US Government, 2022). By 2050, SAF should account for 100% of domestic aviation fuel demand.

The 2022 Inflation Reduction Act (IRA) includes provisions to spur the aviation industry to develop and adopt sustainable fuel technologies (The White House, 2023). The Sustainable Aviation Fuel Credit incentivises the sale or use of aviation fuel: SAF that reduce lifecycle GHG emissions by at least 50% compared to petroleum-based jet fuel are eligible for a tax credit of USD 0.33 per litre. This credit is progressive; it increases for each percent that emissions reductions exceeds 50% (U.S. Department of Energy, 2022). The IRA also provides almost USD 300m in grants to develop and deploy projects related to sustainable aviation fuel and low-emission aviation technologies (The White House, 2023).

The US government recognises that offsetting may be needed to bring the aviation sector to net zero, but provides no further details (FAA, 2021). Although the US participates in CORSIA, and the first phase of this scheme started in 2024, the US government has not yet started to implement CORSIA into national law (Gualandi, 2024b).

We have not identified any commitments or policies related to international aviation.

In the UK, the aviation industry committed to net zero CO₂ emissions by 2050, in line with the UK government targets (Sustainable Aviation, 2019). The industry, like the UK government, does not see any need for demand measures.

According to the UK industry’s Decarbonisation Roadmap (Sustainable Aviation, 2019), the UK could accommodate an increase in passenger numbers of 70% in the next three decades, but acknowledges that new technologies, operational improvements, and SAF would not be able to keep up with this increase in demand. Rather, the EU ETS, CORSIA, and carbon removal measures would be key in bringing UK aviation emissions to net zero.

The UK's aviation industry commits to make use of natural and technology-based carbon removals, but neither of these are solutions to depend on. Natural carbon removals, such as sequestration in forests, bring a high risk of impermanence: the sequestered carbon will be released back into the atmosphere within years to centuries, negating any benefits of sequestration in the first place. The potential for natural carbon removals is limited. Its limited potential is needed to balance out residual global emissions; it is questionable whether this solution should be used to ‘neutralise’ a stark increase in emissions growth in the world’s wealthiest nations.

The European aviation industry has drafted a pathway to net zero CO₂ emissions from aviation by 2050 (NLR - Royal Netherlands Aerospace Centre & SEO Amsterdam Economics, 2021). The pathway is ambitious, but fails to discuss the financial contributions that can be made by the aviation industry.

The European aviation industry’s pathway foresees a major role for sustainable aviation fuels and hydrogen: by 2050, these two technologies, including their impact on demand, would reduce BAU emissions by 67% (NLR - Royal Netherlands Aerospace Centre & SEO Amsterdam Economics, 2021). Improved kerosene technologies, air traffic management, and operational measures would account for the reduction of another 23%, while economic measures would contribute to a reduction of 10% below BAU.

The European aviation industry calls for financial incentives, including subsidies, to scale up the use of SAF. At the same time, Airlines 4 Europe (A4E), one of the main groups behind the net zero pathway, argues against a kerosene tax (A4E, 2023). A4E states that such a tax “would be a setback for the decarbonisation efforts of the European aviation industry and jeopardise our global competitiveness” (A4E, 2023).

It is problematic for the aviation industry to expect that public resources will be used to scale up SAF and implement other decarbonisation measures, without discussing how the industry itself can contribute. A kerosene tax could raise funds for SAF development. It could also help decrease emissions from short- and medium-distance flights, as lower-carbon modes of transport would become economically more attractive if a tax were implemented.

In February 2022, European countries and aviation industry groups signed the Toulouse Declaration, reaffirming their commitment to net zero carbon from international aviation by 2050 (ACI Europe, 2022).