The airline industry spews about 800 megatons of CO2 into the atmosphere each year, roughly 2 percent of total greenhouse gas emissions. There is an increasingly need to decarbonize air travel, but that doesn’t mean that we’ll be cutting the cord on it anytime soon.

Air travel is imperative for global connectivity, with roughly 100,000 flights in transit every day carrying people and goods around the world. Aircrafts come with a lengthy list of qualifications, like the need to be lightweight, fuel efficient, reliable, cost effective, quickly refuelable, and able to fly long distances – it’s not so easy to change them.

The looming question that emerges is: Can flying ever truly be sustainable? Maybe it can, though biofuels are likely a near-term bridge to a future in which aircrafts are powered by hydrogen or even electricity. But none of these options come without their set of challenges.

Sustainable Aviation Fuel

November 2024 marked a milestone in the field of aviation. Virgin Atlantic’s Flight100, a Boeing 787, embarked on the world’s first transatlantic flight from London to New York powered entirely by biofuel – fuel derived from organic matter rather than fossil fuels.

The fuel, known in the industry as Sustainable Aviation fuel (SAF), is derived from renewable or recycled waste such as corn grain, oil seeds, algae, other fats, oils, and greases, agricultural residues and more. It boasts substantially fewer carbon emissions — up to 70 percent less than traditional jet fuel.

Parallel to the advancements in SAF, H2Fly’s hydrogen-powered four-seater aircraft took to the skies in Slovenia late last year.

“Alternatives for liquid fuels in aviation are largely hydrogen or electrical, but those technologies are nowhere near where we are with SAF,” says Andrew Chen, principal of aviation decarbonization at RMI. “The beauty of SAF is it’s a drop-in fuel,” so it can go into existing aircrafts, says Chen.

Read More: Airlines Prepare for Greener Future

What Does SAF Come From?

Flight100 set a record as the longest flight to use 100 percent SAF, challenging the current 50 percent SAF blending limit for commercial flights. Flight100’s liquid blend consists predominantly of material from waste fats, and a small portion of synthetic kerosene, a type of jet fuel made from plant sugars.

Although some SAF can be created through the utilization of already-available waste materials, a much larger portion will have to be manufactured. This can be done through growing feedstocks, the organic materials used to produce biodiesel – which can be environmentally taxing in itself.

“You need a lot of land to grow all those crops, there’s only so much waste material that you can make liquid fuels from. You don’t even have enough waste oils from all the world’s restaurants to power one airport,” says Lewis Fulton, director of the Energy Futures Program at the University of California Davis.

Aamir Shams, senior associate of climate aligned industries/aviation at RMI called out the steep competition for feedstocks among industries, and the necessity to explore new feedstocks that do not require land usage – such as algae and camelina.

SAF can also be created using electricity and carbon waste, which Fulton points to as the most feasible long-term option – as they don’t require nearly the land that biofuels do. That is, if they can be accessed at a reasonable price point.

“Then it becomes a question of whether you can get enough CO2 to support the volume that you need. CO2 is expensive,” says Fulton.

Read More: The Other Solar Power: How Scientists Are Making Fuel From Sunlight and Air

Shifting to Sustainable Travel

Biofuels are cheaper to produce, and the manufacturing infrastructure is already in place to do so, making them the near-term alternative that airlines are looking to. As of 2022, over 30 airlines have announced their plans to shift to SAF.

To use hydrogen in an aircraft, it needs to be stored as either a liquid or a gas.

Storing liquid hydrogen requires extremely low temperatures, which complicates its use, but by opting for liquid over pressurized gaseous hydrogen, H2Fly could double its fuel capacity and flying range.

Electric air travel struggles with the same limitations as it relates to flying range. Electric aircrafts already exist and are flying short-distance commercial routes, but Chen says the battery technology won’t be able to sustain medium to long haul flights until at least 2030.

Yet the energy efficiency of battery-powered aircrafts is distinctly advantageous – about 70 percent of the energy used to charge the battery can actually be utilized by the aircraft, whereas hydrogen and synthetic fuel hover at an efficiency of around 20 to 30 percent.

Read More: How the U.S. Could Have an All-Renewable Energy Grid

The Costs of Sustainable Flights

With SAF as the leading short-term prospect for an alternative jet fuel, governments, corporations, and airlines are scrambling to create an economic outcome that makes it feasible for the typical consumer.

Traditional kerosene jet fuel in the U.S. retails around $2.85 a gallon, while SAF hovers around $6.69 per gallon. The premium price stems from the scant availability of SAF, paired with the high costs of producing and blending the sustainable fuel.

Even with a prioritization on the cheaper fuels, projections indicate that by 2030, the shift to SAF could translate into an increase in ticket prices ranging from $3 to $14.

However, unlike the technological hurdles that come with hydrogen, “the challenge with SAF is not the technology, it’s the mandates,” says Orlando O. Spencer from OOS Group.

Government policies and shifts in carbon pricing and subsidies could play pivotal roles in narrowing this cost disparity. President Biden created tax credits for farmers using land to create biodiesel, and a target through the U.S. SAF Grand Challenge for the U.S. to produce 35 billion tons of SAF per year by 2050, with a near-term goal of 3 billion by 2030.

And while governments can stimulate production, corporations will need to contribute the bulk of the initial capital to support it. Governments worldwide have begun to recognize the importance of SAF, with mandates in the U.S., U.K., and EU aiming for a 10 percent SAF usage by 2030.

Read More: How to Save Planet Earth

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