The researchers said the UK would need to sacrifice half its agricultural land or more than double its total renewable electricity supply to produce enough jet fuel to meet its ambitions for “jet zero”, or net zero flying.
A report published on Tuesday by the Royal Society argues that there is no single, clear, sustainable alternative to jet fuel that can support current levels of flying.
Scientists say that while the government and the aviation industry have set a 2050 target to offset emissions, there are still huge challenges related to the availability, cost and impact of alternative fuels, as well as the need for new types of aircraft and airport infrastructure around the world to enable most likely long-term solutions.
The researchers say significant further research and investment would be needed to answer questions about four types of fuels – green hydrogen (produced from water using renewable energy), biofuels (energy crops and waste), ammonia and synthetic fuels or e-fuels.
Producing enough biofuels would require around half the UK’s agricultural land, while other feedstocks such as municipal waste could only account for a “very small fraction” of jet fuel needs, they say.
Producing enough green hydrogen or ammonia to power future aircraft would require well over twice all of today’s UK renewable energy 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 more power than today’s UK.
The Royal Society said the findings highlight the challenges of decarbonising aviation and that there is still work to be done on the storage and handling of such fuels – as well as their actual environmental impact during production and in flight.
CO aviation2 accounted for 2.4% of global emissions in 2019. Aviation in the UK (both international and domestic) contributed 8% of the country’s greenhouse gas emissions.
Graham Hutchings, regius, professor of chemistry at Cardiff University and chair of the working group for the report, said: “We need to be very clear about the strengths, limitations and challenges that need to be addressed and overcome if we are to scale up the required new technologies in a few short decades.”
The report said more research is needed to understand how alternative fuels will affect contrails, which contribute significantly to the heating effect of aviation.
Sustainability would depend on how alternative fuels are produced, said Prof. Marcelle McManus, director of the Institute for Sustainable Development at the University of Bath. “We need consistency and we need to apply it globally because the adoption of any of these new technologies will create demand and pressure on land, renewable energy or other products that may have environmental or economic impacts.”
While airlines are looking for sustainable fuels to reduce CO emissions2 emissions by 70-80%, McManus said that for many different types of fuels labeled as sustainable, “definitely not the case” with the change.
Dr Guy Gratton, associate professor of aviation and environment at Cranfield University, said: “The term SAF (sustainable aviation fuel) is quite nebulous … not all have the same environmental impact.”
The government has said it will require airlines to use SAF for at least 10% of their fuel requirements by 2030. Gratton said that while this target could be met, the overall environmental benefits would be “a more complex issue”.
He said creating new fleets of radically different aircraft to power hydrogen planes would be extremely costly but doable, adding: “It seems reasonable to say that if we invest in research and infrastructure, we can come close to a massive reduction in emissions. towards the 2050 target.
A spokesperson for industry body Airlines UK said the sector was committed to going net zero by 2050. He said: “There is no magic bullet, but airspace modernization to make flying more efficient by introducing new zero emission technology such as hydrogen and this can be achieved by increasing the use of sustainable aviation fuels this decade.”
A spokesman said the sector was working closely with the government to “maximize both the environmental and huge economic opportunities of the transition to jet aircraft.”
A Virgin Atlantic Boeing 787 will fly from London to New York later this year, running solely on fuel made primarily from waste oils and fats, in the first-ever net-zero transatlantic flight.