A Discussion on the Viability of ‘Sustainable’ Aviation Fuels

On January 8th, 2025, close to two hundred gathered for a webinar, “Sustainable Aviation Fuels: Can They Meet 2050 Climate Goals?” The webinar, designed for policymakers and the public, can be viewed here.

The program was cosponsored by the Institute for Policy Studies, Sierra Club Massachusetts, and several other organizations concerned about the climate impact of expanding aviation, especially private jet travel. The speakers were independent researchers with no funding or affiliation with the aviation and ethanol industries.

The speakers were:

Neil Rasmussen: an MIT-trained engineer with a 36-year career in power systems and energy efficiency. He’s the founder and Chief Technology Officer of American Power conversion corporation and is a member of the governing board of MIT, where he serves on committees related to energy and climate.

Dan Lashof: senior fellow at the World Resource Institute where he served as director of WRI US for the last seven years and coordinated WRI’s work in the US across climate, energy, food, forest, water, and the Sustainable Cities programs. He oversaw the U.S. Climate Team, which aims to catalyze and support just and equitable climate action by the federal government, states, cities, and businesses while promoting U.S. Climate leadership internationally.

Chuck Collins: senior scholar at the Institute for Policy Studies and co-author of the report, “Sustainable Alternatives to Jet Fuels: Promising Solution or Industry Hype?” Collins directs the Program on Inequality and the Common Good where he co-edits Inequality.org.

Are Sustainable Aviation Fuels (SAFs) the Answer?

The aviation industry has set ambitious targets for reaching net carbon zero by 2050, even with projections of substantial global growth in air travel. Their ability to attain this goal depends entirely on what the industry calls “sustainable aviation fuels,” or alternatives to kerosene-based jet fuels with their substantial carbon emissions impact. 

This webinar aimed to provide an independent perspective on these possibilities. “We need to bring the same skepticism to claims about ‘sustainable aviation fuels’ that we do when we see advertising for ‘natural foods.’ A closer inspection of the ingredients is required,” said Chuck Collins.

In November 2024, there was the first 100 percent SAF-powered transatlantic flight by a commercial airline, Virgin Atlantic 100. The aircraft flew from London Heathrow to New York’s JFK International Airport, powered entirely by biogenic animal and crop residues and a retrofitted engine. 

The webinar worked to address four fundamental questions about alternative fuels:

1. Is it scientifically possible to create sustainable alternatives to kerosene-based jet fuels?
2. And what are the trade-offs in terms of land use and competing decarbonization needs?
3. What is realistically scalable at the pace of climate change?
4. What will it cost and who will pay? What are other investment trade-offs to achieve greenhouse gas emission reductions?

Is It Technologically Possible to Create Alternatives?

Neil Rasmussen reviewed each of the aircraft fuel technologies that could be feasible alternatives to petroleum fuel. These included electric (battery-based), hydrogen, and synthetic fuels.

In response to hopes about green electric aviation, Rasmussen pointed out that “the core problem with batteries is they weigh twenty times the weight of jet fuel for the same energy. And there’s no known way to increase this density because these batteries are based on lithium. And if you look at the periodic table, there’s no lighter metallic element than lithium. So there’s no way to make any lighter battery.  Therefore, batteries will never replace fuel for long haul flights.”

Rasmussen noted that current plans for SAF are based on biofuel based on crops such as corn or soybean oil and that a single passenger jet would require 36,000 acres of cropland per year, a use of land that would displace food production. He explained that SAF of this type is not zero-emissions, but only achieves approximately 64% reduction in greenhouse gasses. However, if SAF is made on cleared forest, as is a current practice, then SAF makes little sense as it generates over 60% more GHG than fossil jet fuel. 

He suggests that synthetic fuel is the greenest approach to low carbon aviation, but depends on technologies not yet invented. Also, synthetic SAF requires huge amounts of electricity, and cannot be low carbon until the electric system is completely decarbonized, which is certainly not going to happen by 2050 and may not happen for decades after, if ever.

Rasmussen’s assessment is that low greenhouse gas aviation is “not going to be possible without a lot of unknown technological breakthroughs. And certainly not by 2050. It’s not going to support long-haul aviation in the way that people imagine.”

Land Use Trade-Offs 

Dan Lashof, of World Resources Institute, picked up from Rasmussen’s presentation by exploring more in depth the land use trade-offs. “Aviation is a genuinely hard to abate sector, perhaps the hardest to abate source of climate change that we have,” observed Lashof. “So it is worth thinking about what the options are.”

Lashof is “a little more optimistic about the potential to abate emissions from the aviation sector by 2050 with synthetic fuels and crop waste.” But he warned there is a “very high risk of taking the wrong course by using crop-based alternative fuels instead of truly sustainable fuels.”

According to the World Resources Institute, the production of 35 billion gallons of SAF, as is the Biden administration’s current goal, would require 114 million acres of corn — 20 percent more than the current, total land area of corn crops in the U.S. Lashof pointed out that growing soybeans for soybean oil for jet fuel would require four times the amount of land because yields from soy are much lower than yields from corn.

Lashof concluded that “it’s a really dumb idea to turn food into jet fuel. And the aviation industry is doing a lot of greenwashing. If you’ve flown anytime recently, you may have seen United [Airlines] has Oscar the Grouch, who’s talking all about how they’re using food waste, but the reality is they’re actually using virgin crops.” 

Scalability at the Pace of Climate Change

Collins was highly skeptical of the industry’s ability to scale up production.  In 2022, the U.S. produced just 15.8 million gallons of SAF (and an estimated 26 million in 2023). But to meet the Biden Administration’s 2030 target of 3 billion gallons a year would require a whopping 18,887 percent increase over the next six years. And to meet the 2050 target of 35 billion gallons, production would have to increase a whopping 227,400 percent over 2022 production levels. Collins underscored how the industry has abysmally failed to meet its own benchmarks since 2007.

In addition to the science and scalability questions, the other concerns are policy questions about land use and financial tradeoffs. “While it may be technologically possible to create alternate fuels for private jets, the public and policymakers should consider the tradeoffs in terms of government subsidies, land use changes, and competing decarbonization needs in other sectors,” said Collins.

Financial Trade-offs

Billions in taxpayer funds are already flowing to research and deployment of alternative fuels including allocations in the FAA Reauthorization bill at the end of 2024 that includes a growing investment in alternative jet fuels. The U.S. Treasury department recently issued new guidelines for the Sustainable Aviation Fuel (SAF) Credit, a provision of the 2022 Inflation Reduction Act.

There are finite resources for the transition to a post-fossil fuel economy in terms of taxpayer subsidies, land, agricultural crops, and carbon sinks, ways of naturally absorbing and sequestering greenhouse gases. Shouldn’t we prioritize decarbonizing agriculture, heating systems, and ground transport before we invest in alternative jet fuels? 

Conclusions

“It is a mistake to accept that aviation is going to grow without limit over the next hundred years as all these forecasts say,” said Neil Rasmussen at the conclusion of the webinar, “because it really is impractical to cut the greenhouse gases from aircraft as much as we had hoped. To reduce aviation emissions we need to cut aviation. And the smartest way to do that is get rid of all the short flights and do what China did and build up a high-speed rail system. Also, we need to stop using extremely inefficient aircraft such as private jets.”

“Based on our research, there is no scalable alternative to kerosene-based jet fuels that will move at the pace of climate change to offset these harms,” said Chuck Collins. 

NOTE: These are just a few of the points from the Webinar. We encourage you to watch the entire one-hour program to glean more key points. You can view the webinar on YouTube here.

Additional Resources:

• Alternatives to Jet Fuels: Promising Solution or Industry Hype? May, 14, 2024, co-author Chuck Collins, Institute for Policy Studies
• Under New Guidance, ‘Sustainable’ Aviation Fuel in the US Could Be Anything But, May 9, 2024, by Dan Lashof and Audrey Denvir, World Resources Institute
• The potential for private luxury jets with low climate impact, Jan 1, 2024, white paper by Neil Rasmussen
• How are airports ‘greenwashing’ their reputations? November 20, 2024, CBS News interview with Chuck Collins