The search for guilt-free flight may have been sidetracked by an extensive study that concluded that “there is no clear or single net-zero alternative to jet fuel.”
The four most viable alternatives “offer some carbon savings but are not ideal,” according to the review by the Royal Society academy of scientists.
Replacing jet fuel with biomass, for example, would require half of the UK’s farmland just to maintain current passenger levels.
But the government is planning for levels to soar 70% by 2050, which will mean an additional 200 million passengers.
Switching to sustainable fuel is key to its “jet zero” strategy to green aviation, which it touts as a plan to deliver “guilt-free flights.”
Flying is responsible for 8% of UK emissions and around 2.4% globally, and releases other forms of pollution as well.
The lack of alternatives makes carbon-intensive industry one of the hardest to decarbonise as the world works to achieve net zero emissions by 2050.
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“The requirements for a jet fuel alternative to kerosene is energy density, it must be sufficient to sustain short and long-haul flights, it must be produced on a global scale, it must be cost-effective, and it must be deployable by 2050,” he said. Professor Graham Hutchings, chair of the report working group.
Other options, such as hydrogen, ammonia, and synthetic fuels, require a massive increase in renewable energy production, or are expensive or require substantial modifications to existing aircraft.
Producing enough green hydrogen, which is created by splitting water molecules into oxygen and hydrogen with renewablely generated electricity, would require more than doubling or tripling the UK’s renewable capacity.
A biomass fuel can be used in the same aircraft engine, but there are questions about its sustainability.
Suitable crops could be rapeseed, fast-growing poplars and miscanthus, the Royal Society said.
But because of the amount of land it would take to grow them, there has been increasing interest in using bio-waste like used cooking oil.
The UK is “highly dependent” on the import of biofuel feedstocks, known as feedstocks, with 423m liters of used cooking oil imported from China in 2021 alone.
Converting waste from the 250 million liters of vegetable oil produced in the UK would produce just 0.3-0.6% of the UK’s annual jet fuel needs.
The government wants five “sustainable aviation fuel” (SAF) plants under construction by 2025.
A Department of Transportation spokesman said its SAF program 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 make sure there is no impact on food crops.”
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The Royal Society report did not consider battery-powered aircraft as it is “unlikely they have been developed to deliver the power density required for most commercial flights in the time scale available to reach net zero.” by 2050″.
A spokesman for Airlines UK, the industry trade body, said “there is no magic bullet”.
“But by modernizing airspace to make flights more efficient, by introducing new zero-emission technology like hydrogen planes, and by increasing the use of sustainable aviation fuels this decade, it can be done.”
Cait Hewitt, policy director for the campaign group Aviation Environment Federation, said the “elephant in the room” is “the need to fly less.”
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