Dealing with climate change does not mean an end to air travel.

I’m honestly a big fan of airplanes. I’ve been fortunate enough to travel a fair amount over the last couple decades, and that wouldn’t have been possible without the ability to fly. In my ideal world, I think there would be a lot less air traffic, but I don’t think we should get rid of it entirely. Obviously, the rich and their flying habits must go, and a better world would be a somewhat slower world, in which people can actually take the time to travel by boat, by zeppelin, or by train. When it comes to that, we should also have much more high-speed rail for transportation across continents. Even so, there are times when the speed and versatility of airplanes and helicopters will be indispensable.

That said, the way we do air travel needs to change, just like everything else. It’s possible that if all other fossil fuel use stopped, maintaining current airplane usage would be fine, but that seems very unlikely, and given the greenhouse gas emissions and other pollution coming from fossil fuel extraction, we need that to end. Fortunately, a lot of people have been working hard on finding alternative ways to make things like jet fuel, and they’ve been having real success! The question, with this sort of thing, is how well it can scale up. It may be that we can create this stuff under certain conditions, but will that be worth the energy and resources invested? I’ve generally been assuming so. When my friend was working on this a while back, the company he was with was using sugar beets as their starting point, but there’s a lot of vegetable matter that could be turned into fuel, which means a lot of the “work” is being doing as the plant grows. While my assumptions and anecdotes may hold credibility to some of you, for the others, here’s some research claiming that we can have an aviation industry that runs on plant-based fuel:

New research published today in the journal Nature Sustainability shows a pathway toward full decarbonization of U.S. aviation fuel use by substituting conventional jet fuel with sustainably produced biofuels.

The study, led by a team of Arizona State University researchers, found that planting the grass miscanthus on 23.2 million hectares of existing marginal agricultural lands — land that often lies fallow or is poor in soil quality — across the United States would provide enough biomass feedstock to meet the liquid fuel demands of the U.S. aviation sector fully from biofuels, an amount expected to reach 30 billion gallons per year by 2040.

“We demonstrate that it is within reach for the United States to decarbonize the fuel used by commercial aviation, without having to wait for electrification of aircraft propulsion,” said Nazli Uludere Aragon, co-corresponding author on the study and a recent ASU geography PhD graduate.

“If we are serious about getting to net-zero greenhouse gas emissions, we need to deal with emissions from air travel, which are expected to grow under a business-as-usual scenario. Finding alternative, more sustainable liquid fuel sources for aviation is key to this.”

That caveat always looms over discussions of climate change, doesn’t it?

If we are serious about getting to net-zero greenhouse gas emissions…”

It doesn’t generally feel like the “we” that has the power is serious about much of anything beyond keeping or increasing their power. Still, this research is promising, and I appreciate the bredth of the work they did.

In the study, the researchers used an integrated framework of land assessments, hydro-climate modeling, ecosystem modeling and economic modeling to assess where and under what conditions across the United States energy crops used for biojet fuels could be grown sustainably using criteria that evaluate both environmental and economic performance.

The criteria were extensive. The team first identified and assessed where optimal marginal agriculture lands already existed in the U.S. They then assessed whether one could grow the right energy crops on the land without using additional water.

The team then analyzed whether growing energy-crop feedstocks on these lands would have detrimental effects on the surrounding climate or soil moisture and predicted the potential productivity of yields of two different grasses — miscanthus and switchgrass — as suitable biomass-energy feedstocks. Finally, the team quantified the amount and the cost of biojet fuel that would be produced and distributed nationwide at scale.

“The current way we produce sustainable jet fuel is very land-inefficient and not on a large scale,” said Nathan Parker, an author on the study and an assistant professor in the School of Sustainability. “There are very limited ways that aviation could become low carbon emitting with a correspondingly low climate impact, and this is one way we’ve shown that is feasible and can get the aviation industry to be carbon neutral through agriculture.”

The scientists emphasized that this integrated systems perspective was critical to the study. In the past, research around the potential of biofuels has largely consisted of isolated assessments that have not been well integrated, for example, overlooking key data on how altering the crop cover influences the surrounding climate.

“When you plant crops over strategically designed areas, the planting of these crops has an impact on the climate,” said Matei Georgescu, co-corresponding author of the study and associate professor in the School of Geographical Sciences and Urban Planning and director of the Urban Climate Research Center at ASU. “If there is a change in the underlying landscape, for example an increase or decrease in the amount of vegetation, there may be implications for local- to regional-scale climate, including more or less precipitation, or warmer or cooler temperatures.”

To account for these land-atmosphere interactions, the research team took outputs from their hydroclimate model to inform their ecosystem model. The team then evaluated the economic feasibility for farmers to grow these grasses.

Real-world solutions

For any uptake of an alternative-energy pathway, solutions need to make economic sense.

I get that they’re working within the world as it exists, and that makes perfect sense, but boy – “solutions need to make economic sense” is a phrase that makes me see red. So much about how our world is run right now makes zero economic sense, but exists anyway because it’s great for keeping money and power in the hands of the rich and powerful. Ian Danskin framed conservatism and capitalism as developed to protect the aristocracy from democracy, and if you look at the world through that lens, a lot of strange stuff starts to make more sense. Still, if something does “make economic sense” within the current paradigm, it seems likely that it would be at least as functional in the “ideal” scenario I discussed above.

The researchers, in their analysis, benchmarked the financial returns of the existing uses for the lands they identified — some already are used for growing corn, soy or various other crops, and others are being used as pasture — against those from cultivating either miscanthus or switchgrass as biomass feedstock.

Growing miscanthus or switchgrass needed to be more profitable to replace the existing use of the land in each area.

“These lands we identified are owned and operated by real people for different agricultural uses,” said Uludere Aragon, who is now a postdoctoral fellow at the Environmental Defense Fund. “The cost-effective biofuel potential from biomass feedstocks is influenced largely by the opportunity cost of alternative land uses.”

In the end, researchers found miscanthus to be the more promising feedstock and that biojet fuels derived from miscanthus can meet the 30 billion gallons/year target at an average cost of $4.10/gallon.

While this is higher than the average price for conventional jet fuel — typically about $2 per gallon — the team concluded it is reasonable when considering biojet’s potential to cut emissions. Notably, in 2022 jet fuel prices have varied from $2 to $5 per gallon (not to be confused with retail gasoline) due to changes in supply and demand, showing that prices above $4 per gallon are well within the range of possibility.

A template for the future

The researchers say that in finding further solutions to Earth’s climate crisis, it is important that the scientific community bridges disciplines and moves past incremental reductions in emissions. Rather, the researchers emphasize the importance of realistic solutions that scale.

“This was an interdisciplinary team with expertise from ecosystems sciences, climate modeling and atmospheric sciences and economics,” said Georgescu, who acknowledged this research was a culmination of eight years of modeling work and collaboration. “To truly address sustainability concerns, you need the expert skills of a spectrum of domains.

“As academics, we should remember economics drives people’s decisions on the ground. It is vitally important to find the circumstances when these decisions are also aligned with desirable environmental outcomes.”

The endless subsidies and wars propping up the fossil fuel industry, and the military-industrial complex, demonstrate that we have the ability to determine what is and is not “economical”, for all our leaders babble about “market forces”. Even so, there’s something cathartic about being able to point out that a huge number the changes we need are entirely feasible even within the system that’s resisting that change. At this point, I’m starting to wonder if I should just get a tattoo of this, but – the obstacles are social and political, not technical. There are absolutely technical challenges, and we’ll discover new problems as we work on new ways of doing things. All of that is to be expected, but none of it is why have failed to adequately address climate change.

We can do this. We can end fossil fuel use, and there’s no reason to think that doing so will result in anything other than a better standard of living for most of humanity. We just need to get around the money-hoarding doofuses that are currently in charge.

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  1. KG says

    Hmm, I’m sceptical. Has anyone grown and harvested Miscanthus on such a scale? If concentrated in large patches of monoculture (probably necessary to make it economic), what about pests, and fire risk? Is the US “need” for jet fuel, on a BAU trajectory, projected to plateau in 2040? Somehow, I doubt it. And what about the rest of the world? Can they all have Miscanthus-based air travel at US levels? Whatever, reducing the amount of air travel is going to make things easier. Personally, I haven’t flown since I retired in 2012, and not for non-work purposes since 1992.

  2. says

    I do not have answers to those questions, but in terms of scalability and the monoculture problem, it seems like if they’re basing these calculations on grasses, then this kind of thing could be done with lots of different kinds of plants, so it’ll probably depend on how much ecosystem health is prioritized.

    In terms of scale, as I said, I think we *should* reduce flying a great deal, and have high-speed rail be more the default, so I’m less concerned about meeting the current demand.

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