The UK would have to devote half its farmland or more than double its total renewable electricity supply to make enough aviation fuel to meet its ambitions for “jet zero”, or net zero flying, scientists have said.
A report published on Tuesday by the Royal Society argues there is no single, clear, sustainable alternative to jet fuel that could support the current level of flying.
The scientists say that while the government and aviation industry have set a target of 2050 to balance out emissions, huge challenges remain around the availability, costs and impacts of alternative fuels, as well as the need for new types of planes and airport infrastructure around the world to allow the most probable long-term solutions.
Significant further research and investment would be needed, the scientists say, to address questions across four fuel types – green hydrogen (made from water using renewable energy), biofuels (energy crops and waste), ammonia and synthetic fuels or e-fuels.
Producing enough biofuels would require about half of UK agricultural land, while other feedstocks such as municipal waste could only contribute “a very small fraction” of the jet fuel requirements, they report.
Making sufficient green hydrogen or ammonia to power future planes would require well over double today’s entire UK renewable electricity generation capacity. E-fuels or synthetic fuels – which are made by capturing and converting carbon dioxide from the air – would require five to eight times today’s UK capacity.
The Royal Society said the findings underscored the challenges of decarbonising aviation, and much work remained to be done in how such fuels were stored and handled – as well as their actual environmental impacts in production and when used in flight.
Aviation’s CO2 accounted for 2.4% of global emissions in 2019. UK aviation (both international and domestic) caused 8% of the country’s greenhouse gas emissions.
Graham Hutchings, the regius professor of chemistry at Cardiff University and chair of the report working group, said: “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.”
The report said more research was needed to understand how alternative fuels would impact contrails, which contributes significantly to aviation’s heating effect.
Sustainability would depend on how fuel alternatives were produced, said Prof Marcelle McManus, a director of the Institute for Sustainability at University of Bath. “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.”
While airlines are looking to sustainable fuels to reduce CO2 emissions by 70-80%, McManus said that for a number of different fuels types labelled as sustainable that was “definitely not the case” that would result from a switch.
Dr Guy Gratton, the associate professor of aviation and the environment at Cranfield University, said: “The term SAF [sustainable aviation fuel] is quite nebulous … they don’t all have the same environmental footprint.”
The government has said it will mandate airlines to use SAFs for at least 10% of their fuel needs by 2030. Gratton said that while that target could be met, what the overall environmental benefits were would be “a more complex question”.
He said creating new fleets of radically different planes to run on hydrogen airliners would be hugely expensive but achievable, adding: “It does seem reasonable to say if we do get the investment in research and infrastructure we could get close to a massive reduction in emissions by the 2050 target.”
A Department for Transport spokesperson 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 the industry body Airlines UK said the sector was committed to achieving net zero by 2050. They said: “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.”
The spokesperson said the sector was working closely with government to “maximise both the environmental and huge economic opportunities from leading the jet zero transition”.
A Virgin Atlantic Boeing 787 will fly from London to New York later this year powered entirely by fuel made primarily from waste oils and fats, in what is being billed as the first ever net zero transatlantic flight.
