Jet fuel alternatives must be agreed to realise UK’s ‘net zero’ aviation ambitions, says report

Addressing the challenges of reducing the climate impact of aviation requires global coordination, according to a new report by The Royal Society and supported by academic expertise from Manchester Metropolitan University.

The Net zero aviation fuels: resource requirements and environmental impacts report warns there is no single, clear, sustainable alternative to jet fuel able to support flying on a scale equivalent to present day use.

While each fuel type has advantages and drawbacks, the findings underscore the challenges of decarbonising aviation, especially when resources are likely to be in global demand for a range of ‘net-zero’ objectives.

The report also identifies significant research requirements in scaling up net zero fuels, from storage and handling, to environmental impacts including CO2 and non-CO2 emissions

The findings are backed by research from David Lee, Professor of Atmospheric Science at Manchester Metropolitan University, who provided the academic expertise around the climate impact of global aviation emissions in the report.

Professor Lee said: “Our research shows that current alternatives to jet fuel will continue to have negative effects on our climate. However, there is hope that these effects might be considerably smaller if the independent modelling experiments, laboratory studies and testing needed to quantify this can be carried out.

“Ultimately we explain how, with more knowledge and research, it might be possible to reduce the effects of jet fuel on the environment both through careful aircraft and engine designs and improved operations.”

The report explores these resource availability challenges, as well as 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).

Sustainable fuels

Professor Graham Hutchings FRS, Regius Professor of Chemistry at Cardiff University, and chair of the report working group, said: “Research and innovation are vital tools for the delivery of net zero. 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 policy makers to understand the future resource implications of today’s policy and R&D decisions and to support international dialogue on this global technology transition.”

Global aviation CO2 emissions were approximately 1,000 million tonnes per year in 2018/19, representing 2.4% of global emissions, dropping in 2020 to 600 million tonnes and increasing in 2021 to 720 million tonnes. UK aviation (international and domestic) accounted for 8% of UK greenhouse gas emissions in 2019.

The UK has committed to scale up manufacturing of sustainable aviation fuels (SAFs) and make domestic flying ‘net zero ‘by 2040, but aviation is growing globally, and is one of a number of sectors needing to decarbonise.

While alternative aviation fuels will likely have an increased cost, persisting with traditional kerosene jet fuel is likely to become increasingly expensive as decarbonisation in other sectors accelerates, the report notes.

Life Cycle Assessment

Life cycle assessment of the fuel options in the report considered their environmental impacts including emissions beyond CO2 from fuel production to pump, or fuel production to exhaust (known as wake). However, accounting for emissions and environmental impacts depends in part on the assumptions made and availability of data 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.

Research will also be important 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 there are significant uncertainties over this.

Wider considerations, including the development of new airframes to permit hydrogen or ammonia storage, the refuelling infrastructure, and safe refuelling and storage protocols would also need to be investigated and adopted globally.

Professor Marcelle McManus, Director of the Institute for Sustainability at the University of Bath and a working group member, said: “How fossil fuel alternatives are produced is critical, as is how we measure their sustainability across the entire cycle of their use.

“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.”