The transition to sustainable aviation fuel (SAF) would require the use of 50 per cent of the UK’s agricultural land, the Royal Society has found.
Scientists have not been able to find a single clear alternative to jet fuel that would help the aviation industry achieve net zero.
Currently, the UK aviation sector consumes 12.3 million tonnes of jet fuel a year and produces 8 per cent of the country’s greenhouse gas emissions. However, it is considered a hard-to-abate sector due to a lack of technologically mature alternatives to jet-fuelled engines.
Made from waste materials or by-products such as household waste, industrial gases or used cooking oil, SAFs have often been considered as the most efficient option, as they can achieve greenhouse gas emissions savings of more than 70 per cent compared to conventional fossil jet fuels.
Nonetheless, the authors of a report published by the Royal Society have found that replacing jet fuel with biomass, or SAF, would require the use of huge tracts of land – approximately 50 per cent of the available agricultural land in the UK.
Meanwhile, alternatives including hydrogen, ammonia and synthetic fuels would require a massive increase in renewable energy production.
“The requirements for an alternative to jet fuel, to kerosene, are that its energy density has to be sufficient to sustain short and long-haul flights, it must be produced globally at scale, it must be cost-competitive and it must be implementable by 2050,” said Professor Graham Hutchings, chair of the report’s working group.
In order to achieve the International Civil Aviation Organisation’s goal of reaching net zero carbon emissions by 2050, the UK has been heavily investing in SAF research. As part of this effort, the government awarded five SAF projects a share of the £165m Advanced Fuels Fund.
Together, the initiatives are expected to produce over 300,000 tonnes of SAF a year – enough to fly to the Moon and back an estimated 60 times – and slash CO2 emissions by an average of 200,000 tonnes each year, which would be the equivalent of taking 100,000 cars off the road.
However, the environmental and social impacts highlighted by the Royal Society might have an impact on this sector.
The authors of the report warned that the UK is “highly reliant” on importing raw material for biofuel, known as feedstocks, with 423 million litres of used cooking oil imported from China alone in 2021.
In contrast, converting waste from the 250 million litres of vegetable oil produced in the UK would produce only 0.3 to 0.6 per cent of the UK’s annual jet fuel needs.
The authors suggest researching rapeseed, fast-growing poplar trees and miscanthus as energy-providing crops.
In contrast, other research has focused on facilitating green hydrogen planes. Although green hydrogen has been hailed as one of the solutions that will enable the UK to reach net neutrality, the amount needed to maintain current passenger levels would require more than doubling or tripling the UK’s renewable capacity, according to the Royal Society.
It would also mean the development of new aircraft and airport infrastructure to store and transport fuel as well as new training and safety regimes.
A similar effort would be necessary to run planes with ammonia, a fuel made using hydrogen.
“With all of these fuels we need to have new supply chains, new resources and at the scale we need, this is not going to come without difficulties,” said Professor Marcelle McManus of the University of Bath.
“How and where they’re produced will have significant impacts on their impact and their cost.”
The report also said that replacing kerosene may not completely stop planes from warming the Earth’s climate. It is thought that up to two-thirds of the climate-warming effect from aviation comes from non-CO2 sources like contrails, though there is a wide degree of uncertainty about this.
A spokesperson from the Department for Transport said: “The UK’s Sustainable Aviation Fuels programme is one of the most comprehensive in the world.
“Our Jet Zero Strategy sets out how we can achieve net zero emissions from UK aviation by 2050, without directly limiting demand for aviation. Sustainable aviation fuels and hydrogen are key elements of this, and we will ensure that there is no impact on food crops.”
A spokesperson for Airlines UK, the industry’s trade body, added: “There is no magic bullet, but by modernising airspace to make flying more efficient, by introducing new zero-emission technology like hydrogen aircraft and by upscaling the use of sustainable aviation fuels this decade, it can be achieved.
“Critically, the UK does have sufficient feedstocks for sustainable fuels, which would be drawn initially from household, commercial, agricultural and forestry waste and waste industrial gases – and do not compete with food crops.”
Cait Hewitt, policy director at Aviation Environment Federation, which campaigns on aviation’s environmental impacts, said: “The elephant in the room here is, of course, the need to fly less.
“One area that would really benefit now from some Government-funded research is how to deliver better standards of living, continued connectivity for businesses, and sustainable employment for the aviation workforce without the continued growth of flying.
“Tax cuts for domestic tourism and leisure and promotion of alternatives to in-person business flights would be good places to start.”
The Climate Change Committee, which advises the Government on how to reach net zero, said in its sixth carbon budget that passenger demand should not rise more than 25 per cent by 2050 from its pre-pandemic levels.
The UK was one of the first countries to include curbing aviation emissions in their climate targets in 2021 and helped launch the International Aviation Climate Ambition Coalition at COP26. That same year, British Airways sourced SAF to cover the requirements for all its flights between London, Glasgow and Edinburgh during the COP26 climate conference.
Sign up to the E&T News e-mail to get great stories like this delivered to your inbox every day.