In October 2021 United Airlines CEO Scott Kirby stood* in front of his peers at the IATA Annual General Meeting and declared that the industry had to “do the right thing” when it came to pursuing sustainable aviation fuels (SAFs). Part of that plan called for skipping soy, corn, and palm oil as the feedstock for those fuels. Two years later – and faced with the opportunity to realize a major price break on its commitment for SAF consumption – the “right thing” looks rather different. United is part of an industry consortium calling for corn-based ethanol blends to receive tax credits as SAFs. And it seems they’re going to get their way.
In trying to explain this shift in policy, an United spokesperson shared United’s view that the existing ethanol-as-a-fuel market will erode as ground vehicles shift to electrification. The airline sees potential to capture that supply, to the tune of billions of gallons annually, for SAF production. The carrier believes, “Having a ready available supply, as well as existing infrastructure to transport the fuel, lifts some of the biggest obstacles our industry faces to scale SAF.”
It seems that United is willing to settle for increased supply, even if the SAFs don’t really meet the core goal of broad emissions reductions. And United is not alone in this position.
Burning SAFs means there are emissions in the sky. As Dan Rutherford of the ICCT explains, “Engine out CO2 from burning SAF is essentially identical to Jet A.” But on an overall lifecycle level, he continues, “the good SAFs sequester carbon during their production (e.g. CO2 absorbed when growing miscanthus) that offset their emissions when burned.” Which differs significantly from the common message that burning SAF results in no emissions at altitude.
In the case of ethanol-based fuels, the environmental impact goes beyond just emissions. Growing the corn typically requires significant application of fertilizer and massive quantities of fresh water. It also potentially diverts farmland from producing food. Allocating federal subsidies to this version of SAFs effectively means paying farmers to pollute on the ground, and also contributing to higher grocery prices.
Moreover, this type of subsidy is supposed to be a short-term play, helping to achieve critical mass so the free market will take over and support production. That farmers still depend on these subsidies for ethanol-based fuel on the ground is a good indication it won’t work for SAFs, either.
Other SAF plays raise more questions
Southwest Airlines recently announced a deal for 680 million gallons of SAFs to be acquired over 20 years from USA BioEnergy. Thanks to the magic of blending that SAF with traditional fuel, however, the company claims it can deliver 2.6 billion gallons of “net-zero fuel.” That would be the equivalent of about 15 months of Southwest’s average consumption today, spread across two decades. But there are questions about how viable those numbers are.
Emissions are measured in carbon dioxide equivalent per megajoule (g CO2e/MJ), with JET A typically coming in at 85-95 grams, of which about 73 is attributable to the combustion (See Page 3 of this ICCT working paper). USA BioEnergy says its fuels reduce emissions 80% over traditional fossil fuels. Southwest, however, is saying that the company’s product does not just reduce emissions, but actually goes negative.
Rather than dropping the CO2e/MJ down below 20 grams in line with the 80% reduction described by USA BioEnergy, a Southwest spokesperson says the carrier will receive SAF from BioEnergy with carbon intensity of -375g eCO2/MJ.
BioEnergy’s proposed pathway appears similar to one that can get into single digits, assuming the feed stock truly is wood waste (and not new growth for the process). The company also plans to add carbon capture in the process, further reducing CO2e/MJ below zero. But getting negative at that significant a level is highly unlikely. And the fuel won’t be available in any volume until 2028, so it is hard to know for sure.
From frying pan to flying
Virgin Atlantic hosted a 100% SAF-fueled transatlantic flight in November 2023, the first of any commercial aircraft. It was described as a stunt by naysayers and a snapshot of the future by supporters.
Making that flight happen required 70 tons of fuel on board. The SAF used was a unique dual blend; 88% HEFA (Hydroprocessed Esters and Fatty Acids) supplied by AirBP and 12% SAK (Synthetic Aromatic Kerosene) supplied by Virent, a subsidiary of Marathon Petroleum Corporation. Virgin Atlantic explains that the HEFA comes from recycling waste oil, while the SAK is extracted from plant sugars and necessary in 100% SAF blends to give the fuel the required aromatics for engine function.
And while no one is suggesting that the industry is ready to transition to the new fuel today, there are many, many unanswered questions about just how much used oil is available on the market. Some are even claiming unused oil is even being (illegally) imported as used to take advantage of the blending tax credits.
Virgin Atlantic is no stranger to special SAF flights. The carrier also ran one in 2008, with a 747 carrying a 20% blend of 20-percent mix of biofuel derived from coconut and babassu oil in one fuel tank. Many of the same concerns were also raised then and remain valid today. Though, much like 15 years ago, a lot of the talk at this event was around pushing production of SAFs forward so the airlines could buy it.
Picking the right feedstocks makes a HUGE difference for SAFs
In June 2017 delegates to IATA’s Annual General Meeting in Cancun unanimously approved a resolution on the deployment of SAF. In it, they called for constructive government policies, and committing to only use fuels which conserve ecological balance and avoid depletion of natural resources. In theory that was what Kirby reiterated in 2021.
The carbon intensity of producing and processing corn into ethanol and, eventually, a Jet A replacement negates many of the benefits promised, which is why Kirby opposed it two years ago. United says the company will take advantage of existing production volumes, so the net ecological impact is relatively limited (i.e. existing farming subsidies continue, but it won’t drive conversion of more farmland to corn to grab the funding). Which is only a small solace.
Plus, that’s not necessarily the case for all feedstocks (or even a guarantee with corn-based ethanol in the USA). Palm oil, one of other sources Kirby spoke against, is a popular play in Southeast Asia. But growing it often comes at the cost of clearcutting old growth forests in the region. That is decidedly not carbon neutral on any lifecycle basis.
Where to go from here?
So, how does the industry scale up from the 70 tons of used cooking oil to be able to regularly fill fuel tanks on planes? The short answer is that it simply cannot. There’s not enough used oil to be processed. Nor is there enough corn being grown. Or any of the other agricultural feedstocks in play. Which is not to say that more cannot be grown, but the net zero impact comes from reducing the overall lifecycle emissions. Increasing agricultural loads to grow fuel won’t (or at least shouldn’t) meet those targets. And even if society were willing to accept that tradeoff, eventually there would be insufficient arable land to both grow fuel stocks and food for humans.
Which is not to say that SAFs are inherently bad. They can be part of the process, part of the path towards reducing aviation-related emissions. But it will be nearly impossible to meet IATA’s expectation that 65% of the emissions cuts on the path to Net Zero by 2050 will come from SAFs with the current feedstocks. That’s a problem for the industry.
*Technically he was seated at the time, as it was a panel discussion, but this reads better.
More on SAFs and the feedstock challenges:
- This ‘climate-friendly’ fuel comes with an astronomical cancer risk
- Net Zero by 2050: IATA’s major commitment and challenges
- United Airlines appoints Oscar the Grouch as Chief Trash Officer
- airBaltic offers passenger SAF purchase option (that doesn’t entirely suck)
- Revealed: more than 90% of rainforest carbon offsets by biggest certifier are worthless, analysis shows
- The Great Cash-for-Carbon Hustle
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