Decarbonization of US aviation sector ‘within reach’: study

Planting grass on unused agricultural lands could provide the U.S. with enough biomass feedstock to meet the liquid fuel demands of the country’s aviation sector, a new study has found.

Such a strategy could pave the way toward the full decarbonization of U.S. aviation fuel by swapping conventional jet fuel with sustainably generated biofuels, according to the study, published on Monday in Nature Sustainability. 

Researchers explained that feedstock for these biofuels would be produced by planting a type of grass called miscanthus across 23.2 million hectares, or 57.3 million acres — roughly the size of Wyoming.

The grass would grow on what the authors described as “existing marginal agricultural lands” — or land that is poor in soil quality or often lays fallow.

Cultivating miscanthus in such spaces could provide enough biomass to meet the U.S. aviation sector’s liquid fuel needs, which are expected to reach 30 billion gallons per year by 2040, according to the study.

“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,” co-author Nazli Uludere Aragon, a recent PhD recipient from Arizona State University’s geography program, said in a statement.

“If we are serious about getting to net zero greenhouse gas emissions, we need to deal with emissions from air travel,” added Uludere Aragon, who is now a postdoctoral fellow at the Environmental Defense Fund.

“Finding alternative, more sustainable liquid fuel sources for aviation is key to this,” she said.

To draw their conclusions, Uludere Aragon and her colleagues said they analyzed a combination of hydro-climate, ecosystem and economic models, as well as land assessments, to determine where and under what conditions crops could be grown sustainably for biojet fuels.

After identifying where optimal marginal agriculture lands already existed in the U.S., they explored whether the right energy crops could thrive in these spots without additional water, according to the study.

They also looked at whether feedstock cultivation could have negative impacts on the surrounding climate or soil moisture and examined the potential yields of both miscanthus and a second type of grass, switchgrass.

Lastly, the scientists said they quantified the amount and cost of biojet fuel that could be generated and distributed nationwide at scale.

“The current way we produce sustainable jet fuel is very land inefficient and not on a large scale,” co-author Nathan Parker, an assistant professor at Arizona State’s School of Sustainability, said in a statement.

“There are very limited ways that aviation could become low carbon emitting with a correspondingly low climate impact,” he continued.

The cultivation of miscanthus on these swaths of existing marginal farmlands “is feasible and can get the aviation industry to be carbon neutral through agriculture,” according to Parker.

Miscanthus ended up being the more promising feedstock, as fuels derived from this type of grass could meet the 30 billion gallons per year target at an average cost of $4.10 per gallon, the researchers found.

While this is a higher average price than that of conventional jet fuel — which is usually about $2 per gallon — the scientists concluded that this was a reasonable threshold when accounting for the potential to curb emissions.

In addition, the authors noted, 2022 jet fuel prices have varied from $2 to $5 per gallon due to fluctuations in supply and demand — demonstrating that prices above $4 per gallon are well within this range.

Another key strategy was to prove that a switch to growing miscanthus would be more profitable than the existing use of the land in each area, according to the authors.

“These lands we identified are owned and operated by real people for different agricultural uses,” Uludere Aragon said.

“The cost-effective biofuel potential from biomass feedstocks is influenced largely by the opportunity cost of alternative land uses,” she added.