Environmental groups fear new US guidelines for sustainable aviation fuel (SAF) could promote widespread production of biofuels that may not actually be sustainable.

At issue are guidelines released on 15 December defining how fuel producers can determine which alternative fuels qualify for a new SAF tax credit.

Environmental groups have been urging the government not to allow a method known as “GREET”, which they say fails to fully account for a biofuel’s lifecycle emissions.

But they face a tough fight against powerful US industries, including airlines, which say the GREET method is credible and critical to helping them meet carbon-reduction goals. Lobby groups with ties to biofuel – like the National Corn Growers Association and Clean Fuels Alliance America – are aligned behind airlines.

Truckee Tahoe airport SFA usage

Source: Avfuel

The airline industry has embraced SAF as key to carbon-emission cuts, while critics question the fuels’ actual carbon benefits

“Our initial assessment is that this would be a blank check for fuels made from sugar cane, soybean and rapeseed – none of which are sustainable or consistent with Congress’ intent,” Environmental Defense Fund senior vice-president Mark Brownstein said on 15 December of the USA’s new tax guidance.

A 2022 US law grants fuel producers a $1.25-$1.75 tax credit per gallon for SAF deemed to have 50% less life-cycle carbon emissions than fossil-based jet fuel. The law defines qualifying fuels as those meeting definitions within ICAO’s Carbon Offsetting and Reduction Scheme for International Aviation. But the law also allows fuels meeting other “similar” methods as qualifying.

The 15 December guidance, issued by the Internal Revenue Service and US Department the Treasury, starts to define those other methods.

Specifically, the government says current GREET models to not satisfy SAF requirements. But it is developing a “modified GREET” model for SAF, to be completed in early 2024.

“Today’s announcement is welcome news for the aviation sector, as it will help to accelerate the production and availability of SAF and stimulate new investment,” says trade group Airlines for America. The GREET model “ensures that credible and up-to-date life-cycle emissions measurements of a wide range of SAF pathways can be made.”

United Airlines says, “The forthcoming updates to the GREET modelling will provide fuel producers, airlines and companies developing emerging sustainable technologies the clarity they need to leverage the best science available”.

But environmental groups had hoped the government would not allow GREET, which they say inadequately accounts for carbon emissions related to land-use changes. Such changes can involve land being converted into crop land for growing biofuel crops, and possibly leading to deforestation.

“Some SAF… uses raw materials whose sourcing and processing can cause deforestation and harm the climate,” adds the Environmental Defense Fund.

The International Council on Clean Transportation (ICCT) has firmly opposed use of GREET for SAF, saying the model’s treatment of land-use changes is in “contrast with real-world evidence”.

“Adopting GREET… could incentivise fuel pathways with uncertain [greenhouse gas emission] reduction benefits,” it has said.

But ICCT finds optimism in the government deciding to modify the GREET model rather than flatly accepting it.

“It is good to see the administration reaffirm rigorous environmental standards for SAFs,” ICCT aviation director Dan Rutherford said on 15 December. “Next step is to make sure that any accounting changes for agricultural practices are evidence-based, not speculative.” 

ICCT favours “an open and transparent process to ensure that any changes made to [GREET’s] inputs and assumptions [are] supported by scientific experts. Just adopting an industry wishlist could do real harm to the integrity of SAF markets.”

Story updated on 15 December to include comments from The International Council on Clean Transportation.