The quest for guilt-free flying may have been blown off course by a large-scale study that concluded that “there is not a clear single net-zero alternative to jet fuel.”
According to a review by the Royal Society’s academy of scientists, the four most viable alternatives “offer some carbon savings but are not ideal”.
For example, replacing jet fuel with biomass would require half the UK’s agricultural land to sustain current levels of passenger numbers.
But the government plans to increase the level by 70% by 2050, which means an additional 200 million passengers.
The shift to sustainable fuel is key to the ‘jet zero’ strategy to make aviation green, which it touts as a plan to offer ‘guilt-free flying’.
Flying accounts for 8% of UK emissions and around 2.4% globally, as well as releasing other forms of pollution.
The lack of alternatives makes the carbon-intensive industry one of the hardest to decarbonise as the world moves towards net-zero emissions by 2050.
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“The requirements for the alternative to jet fuel, kerosene, are energy density, it must be sufficient to sustain short- and long-haul flights, it must be produced on a global scale, it must be competitively priced and it must be deployable by 2050.” said Professor Graham Hutchings, chair of the report’s working group.
Other options, such as hydrogen, ammonia, and synthetic fuels, require massive increases in renewable energy production, are expensive, or require significant modifications to existing aircraft.
Producing enough green hydrogen – which is created by splitting water molecules into oxygen and hydrogen using electricity generated from renewable sources – would require more than doubling or tripling the UK’s renewable capacity.
Biomass fuel can be used in the same aircraft engine, but there are concerns about its durability.
Canola, fast-growing poplars and miscanthus may be suitable crops, the Royal Society said.
But because of how much land would be needed to grow them, there is growing interest in using bio-waste, such as used cooking oil.
The UK is “highly dependent” on imported biofuel feedstocks, known as feedstocks, with 423 million liters of used cooking oil imported from China alone in 2021.
Recycling the waste from 250 million liters of UK-produced vegetable oil would provide just 0.3 to 0.6% of the UK’s annual jet fuel needs.
The government wants five “sustainable aviation fuel” (SAF) factories to be built by 2025.
A Department for Transport spokesman said the SAF program is “one of the most comprehensive in the world”.
“Our Jet Zero Strategy outlines how we can achieve net zero emissions from aviation in the UK by 2050, without directly reducing aviation demand.
“Sustainable aviation fuels and hydrogen are key elements of this, and we will ensure that food crops are not impacted.”
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The Royal Society report does not consider battery-powered aircraft as “these are unlikely to be developed to deliver the energy density required for most commercial flights on the available time scale to reach net zero by 2050”.
A spokesperson for Airlines UK, an industry trade body, said there was “no magic bullet”.
“But by modernizing the airspace to make flying more efficient, by introducing new zero-emission technology such as hydrogen aircraft, and by increasing the use of sustainable aviation fuels this decade, it can be achieved.”
Cait Hewitt, director of policy at the Aviation Environment Federation group, said having an “elephant in the room” was “needing less flying”.
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