Producing sustainable aviation fuel (SAF) to supply the United Kingdom’s net zero aviation goals would require enormous quantities of UK agricultural land or renewable electricity to keep flying at today’s levels, a briefing by the UK science academy, the Royal Society, has warned.
The Royal Society is a Fellowship of many of the world’s most eminent scientists and is the oldest scientific academy. The Society’s fundamental purpose, reflected in its founding Charters of the 1660s, is to recognize, promote, and support excellence in science and to encourage the development and use of science for the benefit of humanity.
Moreover, Society has played a part in some of the most fundamental, significant, and life-changing discoveries in scientific history. Royal Society scientists continue to make outstanding scientific contributions in many research areas. Its priorities include promoting excellence in science, supporting international collaboration, and demonstrating the importance of science to everyone.
The “Net zero aviation fuels: Resource requirements and environmental impacts report” warn that no single, clear, sustainable alternative to jet fuel can support flying on a scale equivalent to present-day use.
The report explores these resource availability challenges, likely costs, life-cycle impacts, infrastructure requirements, and outstanding research questions across four fuel types: Green hydrogen, biofuels (energy crops and waste), ammonia, and synthetic fuels (eFuels).
It estimates that meeting UK aviation demand entirely with energy crops would require around half of UK agricultural land. While producing sufficient green hydrogen fuel would need up to 3.4 times the UK’s 2020 renewable (wind and solar) electricity generation. While each fuel type has advantages and drawbacks, the findings underscore the challenges of decarbonizing aviation, especially when resources are likely to be in global demand for a range of net-zero objectives.
The report also identifies essential research requirements in scaling up net zero fuels, from storage and handling to environmental impact, including CO2 and non-CO2 emissions. Addressing these challenges requires global coordination, particularly for navigating the transition period between current and future-generation aircraft.
“Research and innovation are vital tools for the delivery of net zero,” said Professor Graham Hutchings FRS, Regius Professor of Chemistry, Cardiff University, and chair of the report working group. “But we need to be very clear about the strengths, limitations, and challenges that must be addressed and overcome if we are to scale up the required new technologies in a few short decades.
“This briefing tries to pull together those realities, to allow policymakers to understand the future resource implications of today’s policy and R&D decisions and to support international dialogue on this global technology transition.”
Net zero aviation goals need global adoption
Global aviation CO2 emissions were approximately 1 billion tons per year in 2018/19, representing 2.4% of global emissions, dropping in 2020 to 600 million tons and increasing in 2021 to 720 million tons. UK aviation (international and domestic) accounted for 8% of UK greenhouse gas emissions in 2019.
The United Kingdom has committed to scaling up the manufacturing of SAFs and making domestic flying net zero by 2040, but aviation is growing globally and is one of several sectors needing to decarbonize.
While alternative aviation fuels will likely have an increased cost, persisting with traditional kerosene jet fuel is likely to become increasingly expensive as decarbonization in other sectors accelerates, the report notes.
Life cycle assessment of the fuel options in the report considered their environmental impact, including emissions beyond CO2 from fuel production to pump or fuel production to exhaust (known as a wake). However, accounting for emissions and ecological effects depends partly on the assumptions made and data available on their use and production.
Despite increasing investment in ammonia and hydrogen fuels, data on emissions are limited in the public domain—in part because of the immaturity of these technologies—so these projections will need to be continually updated as engine data from laboratory and real-world testing develops.
The research will also be essential to understand the impact of non-CO2 emissions from jet engines and the formation of contrails, which currently contribute significantly to warming by aviation globally. Alternative fuels may reduce these effects, but significant uncertainties exist.
Broader considerations would also need to be investigated and adopted globally, including developing new airframes to permit hydrogen or ammonia storage, the refueling infrastructure, and safe refueling and storage protocols.
“How fossil fuel alternatives are produced is critical, as is how we measure their sustainability across the entire cycle of their use,” said Professor Marcelle McManus, director of the Institute for Sustainability of the University of Bath, and a working group member.
“We need consistency, and we need to apply this globally because adopting any of these new technologies will create demands and pressures for land, renewable energy, or other products that may have knock-on environmental or economic effects.”
Air traffic growth is inevitable
Aviation contributes to global warming, including through the emissions of carbon dioxide and the formation of contrails high up in the atmosphere. Globally, save for the few years of the pandemic. Air travel is expected to continue to grow in the future, increasing the impact on climate change unless close-to-net-zero forms of flying can be developed or any residual emissions offset by removals.
Suppose low carbon emission jet fuels are to have a strong positive impact on the UK’s Road to Net Zero. In that case, it is crucial that the alternative fuels adopted genuinely benefit the fight against the climate crisis and do not cause unacceptable collateral ecological damage.
What are the options for net zero aviation fuels? The report looks at four alternative fuels: hydrogen, ammonia, synthetic fuels (eFuels), and biofuels, and examines each option against:
• Equivalent resources that would be required for that option to replace fossil jet fuel;
• Life cycle analysis and non-CO2 environmental impacts;
• Likely costs;
• Modifications or replacements needed to implement the option;
• Advantages and challenges, as there is no single simple answer to decarbonizing aviation
The main conclusions from the net zero aviation report have been:
• Availability and accessibility of sustainable feedstock for all options is a crucial challenge;
• Further R&D will be needed in the development of the efficient production, storage, and use of green hydrogen, ammonia, and eFuels;
• Further development of LCAs (life cycle assessments) of all alternative aviation fuels is required, which will be critical in clarifying emissions across the entire cycle and highlighting key mitigation opportunities;
• R&D is required to understand and mitigate the non-CO2 climate impacts of all the alternative fuel options;
• A holistic approach to alternative fuel, engine, and airframe development will be needed;
• Considerations will have to be made on handling multiple technologies in the airport and aircraft;
• Staff and crew will need specialized training on handling alternative fuels, and the public will need to be informed about the safety concerns within the airport and aircraft. (Story and photos courtesy of The Royal Society, Sevenstorm Juhaszimrus/Pexels)