Pathway to decarbonise US aviation sector with biofuel identified

Around 45,000 planes fly across the US daily, carrying some 1.7 million passengers, making it the single largest contributor to aviation carbon dioxide emissions globally and responsible for more than a quarter of all emissions from flying.

The new 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 across the US – land that often lays fallow or is poor in soil quality – would provide enough biomass feedstock to meet the liquid fuel demands of the country’s aviation sector fully from biofuels.

“We demonstrate that it is within reach for the United States to decarbonise 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.

“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.”

In the study, the researchers used climate and economic modelling to assess where energy crops used for biojet fuels could be grown sustainably using criteria that evaluates both environmental and economic performance.

After identifying where the best lands for growth were located, the team then looked at whether growing energy crop feedstocks on these lands would have detrimental effects on the surrounding climate or soil moisture before quantifying the amount of biojet fuel that would be produced.

“The current way we produce sustainable jet fuel is very land inefficient and not on a large scale,” said Nathan Parker, one of the study’s authors.

“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 financial returns for the existing uses for the lands were also benchmarked as some were already in use for pasture land or growing corn, soy and various other crops. It found that 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 Aragon. “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. Biojet fuels derived from miscanthus could meet the 30 billion gallons per year target, at an average cost of $4.10/gallon (£3.5/gallon).