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What is sustainable aviation fuel? Some believe it is the key to a more environmentally friendly airline industry.

Flying isn’t great for the environment – it’s just a fact. It is carbon-intensive to get a giant aeroplane off the ground and keep it in the sky for hours. But United Airlines, along with all members of the International Air Transport Association, is committed to having a carbon-neutral operation by 2050.

What distinguishes United is that it has no plans to use carbon offsets – a fancy way of saying it will not pay to plant trees and claim credit for reducing emissions in this way – on its way there. Instead, the airline plans to rely heavily on sustainable aviation fuel, an alternative to traditional petroleum-based jet power that is more environmentally friendly to produce.

“United has, today, 40% of all of the announced fuel agreements for SAF globally and last year we consumed less than 0.1% of our total fuel supply as SAF, so there’s just not enough,”

“The airline industry is well aware of its predicament. They don’t need to be persuaded. They only have a few tools; they can do fuel efficiency, but they’ve been doing it for a long time “Julio Friedmann, chief scientist at Carbon Direct and a former professor at Columbia University, agreed. “They can make sustainable fuels, but they don’t currently deliver in terms of carbon intensity, volume, or price. They’re working on it really hard, but they’re not there.”

What is sustainable aviation fuel made of?
Sustainable aviation fuel refers to jet fuel made from sources other than traditional drilled oil.

It can be made from plants, recycled cooking oil, or a variety of other sources.

“It is composed of reprocessed waste lipids and fats. Tallow and used cooking oil are reprocessed into biokerosene, a jet fuel that can be blended with regular jet fuel at a ratio of up to 50% “Samuel Engel, vice president at the consulting firm ICF, agreed. “It has been effective, but its scalability is limited. You can’t run an airline on French fries.”

Other sustainable aviation fuel alternatives, according to Nathan Parker, an assistant professor at Arizona State University’s School of Sustainability, include wood-, grass-, or municipal waste-based fuels, as well as other products that are still being developed.

Riley from United also stated that she sees great promise in evolving technology that could one day allow for the direct capture of atmospheric carbon dioxide, which would then be converted into aviation fuel.

“The best SAF, that third generation, is this power to liquid, where you still have tailpipe emissions but you vacuum it out of the atmosphere to convert back into jet fuel,” she said.

Is sustainable aviation fuel actually sustainable?
It’s difficult. Even sustainable aviation fuel emits carbon dioxide into the atmosphere during its combustion cycle at nearly the same rate as traditional fossil fuel. The difference from petroleum-based jet fuel, experts say, is where that carbon comes from and how quickly it can be recaptured into a new fuel source as part of the production and refining process.

“In most cases, the carbon reduction is not actually being sucked out of the atmosphere. It’s something that’s relative,” said Nik Pavlenko, fuel programme lead at the International Council on Clean Transportation. “A lot of SAFs, pretty much all of them, are net emitters in absolute terms.”

Even so, Parker noted, the carbon emission and capture cycle can occur much more quickly with sustainable aviation fuel than with traditional fossil fuels.

In other words, plant-based aviation fuels (or direct carbon capture experimental fuels) offset their own carbon emissions as part of their production process. Sustainable aviation fuel production typically captures carbon that’s currently in the atmosphere. Then, the fuel itself releases carbon dioxide again during flight, but it’s recaptured when another batch of SAF is produced.

In the case of plant-based jet fuels, for example, carbon dioxide is captured during the normal plant-growing process.

One snag Parker pointed out is that municipal waste- and cooking oil-based fuels are releasing new carbon dioxide into the atmosphere, but he said it still may be more environmentally friendly than the alternatives for their disposal.

When can I take a sustainable aviation fuel-powered flight?
It’s probably going to be a while.

“This is legitimately difficult,” Friedmann admitted. “Nonetheless, I believe we will see a significant increase in fuel volumes with low carbon intensities. Incentives such as the Inflation Reduction Act have been created “for long-term aviation fuel production in the U.S.

According to Pavlenko, the European Union has pledged to make 5% of the continent’s aviation fuel supply sustainable by the end of the decade, and 20% by 2035.

But, he said, it will be a “steep slope” to get there.

“There is little hope for large-scale deployment of sustainable aviation fuel in the absence of public policy. Even the cheapest one costs roughly twice as much as fossil fuel “Pavlenko explained. “Airlines are price conscious… They are not going to shift one of their largest costs to a more expensive option.”

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