🌏 What Will Really Decarbonise Aviation? Hydrogen, SAFs & Policy
Published 5 months ago • 8 min read
Hey Reader 😊
Welcome to the October edition of Circular Digest.
I'm excited to share the final part of the 3 part series, written by Meghan Fitzpatrick. This month's deep dive we take a deeper look into a carbon-intensive and hard-to-abate sector, aviation, and explore how it can be decarbonised. ⬇️
Circular Roundup
Strategy: How can different types of companies increase the circularity of their value chain? Google is a tech company, tech is what they know best. They've created CircularNet, an open-source machine learning and AI tool, which helps recycling facilities increase the accuracy of sorting. Misidentification of waste leads to contamination that lowers the economic and environmental value of recycling and can reduce efficiency and profitability. Google used WBCSD’s CTI Enabling Solution methodology to assess CircularNet’s circularity impact and how it is contributing to Google's own sustainability goals.
CircularNet key features. Source: WBCSD
Policy: UK plastic waste exports to developing countries rose 84% in a year, data shows. Total plastic waste exports remained relatively high in the first half of 2024 and 2025, at 319,407 and 317,647 tonnes respectively. The percentage of UK plastic waste going directly to non-OECD countries was 20% of total plastic waste exports in 2025, up from 11% in 2024. The UK is part of them “high ambition” coalition of nations calling for the treaty to include binding obligations on reducing plastic production and consumption. However, campaigners are are calling for the UK to follow the EU and ban exports to non-OECD countries. They also want to close a loophole that makes it cheaper to export plastic waste rather than recycle it in the UK.
Strategy: This year's New York Climate Week heavily featured companies implementing circular strategies to offer consumers sutainable choices, increase cost effectiveness and of course reduce climate impacts. In a pilot program in Aarhus, Denmark, ~55 Mastercard merchants added a 5-krone/70-cent USD fee to coffee purchases at cafés after noticing disposable cups littered on the streets. Customers can return the plastic-lidded paper cups to vending machines placed around the city and tap their Mastercard to get the fee refunded. Successful circular programmes prioritise convenience!
Action This 💡
Biobased plastics can cut GHGs but still drive land-use change, biodiversity loss, and pollution. When considering substitution from fossil-based plastic:
Eliminate it entirely if the plastic isn’t needed
If biobased, ensure it’s also compostable (no they are not the same thing!)
Check that feedstocks are responsibly sourced
Reimagining Sectors: Aviation
With Meghan Fitzpatrick
Before I start this piece I wanted to flag that decarbonising the aviation sector is no straightforward task. Go to the Smart Picks section for a more holistic view regarding aviation's complicated road to decarbonisation.
It has been estimated that aviation is responsible for 2.5% of global, energy-related, CO₂ emissions per year (roughly one billion tonnes CO₂/yr) (a fraction higher than global shipping). This equates to roughly the emissions of Japan, the world’s third-largest economy.
This doesn’t account for its non-CO₂ impacts (NOx, water vapour, contrails and aerosols). If its non-CO₂ emissions are accounted for, it has been estimated that aviation could be responsible for 4% of already observed human-induced warming. But safe to say, most conversations around decarbonising aviation don't pay much attention to these highly impactful emissions.
Current warming and cooling effects of aviation.
The International Air Transport Association (IATA) has created a strategy to reach net zero emissions by 2050.
From the IATA’s perspective, Sustainable Aviation Fuels (SAFs) are the foundation of their strategy. Their 2021 targets to reach net zero emissions by 2050 heavily rely on SAFs. However decarbonising aviation is likely to require a combined approach. SAFs and other solutions will require major steps in technology and innovation (e.g. electrifying planes for long-haul journeys) but while these technologies mature, the sector felt something had to be done.
IATA's plan to Fly Net Zero by 2050. Source: IATA
Enter CORSIA. What is CORSIA?
An international carbon trading (offsetting) scheme adopted in 2016 which aims to mitigate the impact of international flying by aiming to keep CO₂ emissions at 2019 levels.
It offers the ability to purchase and cancel ‘emissions units' to offset emissions that are above 85% of 2019’s aviation emissions. This is done using ‘CORSIA-eligible fuels’ or by buying carbon credits called Eligible Emissions Units (EEUs) that are generated from projects that reduce CO₂ emissions.
The scheme has been voluntary since its inception in 2016, but will become mandatory in 2027.
Has the scheme been successful?
This depends on your general view of the ability for offsets/credits to actually address emissions. This piece is not aimed to be a debate on the efficacy of credits, this again is a huge topic on its own. However, there have been an increasing number of bodies arguing that CORSIA has structural flaws that make it fundamentally not fit for purpose. Reasons include CORSIA's focus on 'carbon-neutral growth' not absolute reductions, offsetting, not reducing, emissions (and no cap on overall emissions), low scope of participation (it will only be mandatory for 34 countries that have a percentage share of global aviation above 0.5% and are not classed as developing) and not including non-CO₂ impacts of aviation.
So if offsetting isn’t going to be our silver bullet, what other options do we have for this sector?
What are the alternatives?
The main alternatives to fossil jet fuel (currently available) for the aviation sector are:
Use of gaseous or liquid hydrogen propulsion aircraft - although Hydrogen fuels (e-fuels) are more inefficient- electricity-to-useful-energy efficiencies range from roughly 10% to 35%, there are less concerns around land use, biodiversity and deforestation than there are with biofuels and is seen by some as the most feasible way to displace large quantities of fossil fuels from aviation.
Producing jet fuel from SAFs which use renewable sources - despite their prioritisation from many industry associations, SAFs are not unproblematic: combustion processes, land-use change, demand competition.
Each alternative has a range of pros and cons, showing that decarbonising aviation is incredibly complex.
Pros and cons of alternative aviation fuel sources.
No matter which option we take, a massive scale-up of technology and the means to finance the transition for aviation is needed.
Hydrogen - the next frontier in aviation?
As we’ve seen hydrogen can be used to create synthetic e-fuels (such as e-kerosene) - sometimes referred to as ‘synthetic aviation fuels’, or a fuel source for propulsion.
Current progress in the sector:
Airbus has recently announced hydrogen fuel cell technology is the propulsion method for its first hydrogen-powered aircraft, ZEROe.
Ecojet, is the UK’s first zero-emission airline, aiming to use hydrogen fuel cells to power commercial flights with passengers on routes of up to 300 miles. As a new player in the field, Ecojet have experienced first hand the road blocks for this sector - i.e. regulation barriers.
ZeroAvia is developing full hydrogen-electric engines for existing commercial aircrafts sand is supplying hydrogen and electric propulsion component technologies for novel battery, hybrid and hydrogen-electric air transport applications.
H2Fly is developing the first qualified commercial hydrogen-electric powertrain system for aviation. The company is aiming to certify and operate its first commercial fuel cell system in aircrafts by the end of this decade.
"It is no longer a question of 'if' hydrogen will power future flights, but 'when'" - H2FLY founder, Josef Kallo
What do we need to get hydrogen off the ground?
To decarbonise this hard-to-abate sector, a favourable policy landscape must be created. The following policy recommendations are from Opportunity Green, a climate change NGO and the facilitator of the Skies and Seas Hydrogen-fuels Accelerator (SASHA) Coalition.
Upholding international legal obligations - National aviation policies must be consistent with States’ binding international legal obligations.
Increased ambition and pace of decarbonisation - States adopting a GHG pricing mechanism on international aviation emissions, designed to reduce climate impact while generating stable and predictable revenues to enhance resilience in climate vulnerable countries; Policies must also address non-CO₂ impacts (e.g. contrails, NOₓ); The International Civil Aviation Organisation's (ICAO) long-term aspirational goal must be underpinned by clear interim targets (2030/2040) to ensure credibility and progress in alignment with a Paris Agreement 1.5ºC pathway.
Establish governance mechanisms to ensure revenues from pricing mechanisms flow to climate action, adaptation, resilience, and capacity-building in climate vulnerable countries.
The SAF mandate does not go far enough in regulating for the use of green hydrogen fuels over others that do not have the same potential to lower emissions. Unless the ambition of the power-to-liquid submandate is raised, there is a risk that UK investment will continue to go towards what will ultimately be stranded assets. The same approach to incentivising the lowest emission fuels must also be taken when putting in place other mechanisms to drive the supply of alternative fuels for the sector.
Tax - Aviation currently pays no fuel tax nor any VAT (value added tax) in Europe, however various countries have brought in passenger taxes, which usually differentiate by distance and/or class. The UK's Air Passenger Duty (APD) is the highest in the world. The Global Solidarity Levies Task Force (a coalition of 9 countries) recently proposed a solidarity levy, a passenger tax on private jets, first class and business class tickets. The proceeds would support countries around the world experiencing the impacts of climate change.
Meghan has just started a position as a Research Assistant for the Climate Action100+ Initiative team within the Transition Pathway Initiative Centre, at the London School of Economics and Political Science (LSE). She has an undergraduate degree in Earth Sciences and a postgraduate degree in Climate Change Science and Policy from King's College London. She has professional experience in the non-profit sector, working at CDP for two years. Meghan worked as an assessor in CDP's ACT team - Accelerating the Low-Carbon Transition - assessing the highest emitting companies in sectors such as Oil and Gas and Electric Utilities. She is a skilled science communicator and has previously worked with the EU Commission on city sustainability projects, including the European Green Capital and Green Leaf Awards. Meghan has a keen interest in marine science, plastic pollution, renewable energy solutions and circular economy policy.
How to make climate-neutral aviation fly - The European aviation sector must substantially reduce climate impacts to reach net-zero goals. Based on rigorous assessments this article demonstrates that, from a technological standpoint, using electricity-based synthetic jet fuels and compensating climate impacts via direct air carbon capture and storage (DACCS) can enable climate-neutral aviation. However with continuous increasing air traffic, climate-neutral aviation will only fly if air traffic is reduced to limit the scale of the climate impacts to mitigate.
A cleaner future for flight - aviation needs a radical redesign -Efficiency and clean fuels won’t be enough. Governments and industry must experiment with other approaches to bring the climate impact of aviation close to zero.
What did you think of this edition of Circular Digest? If you have any thoughts, questions, or ideas for future content, reply to this email. 😊
See you next month!
Kayleigh
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