The federal spending law passed in early July 2025, often called the One Big Beautiful Bill Act, significantly reduces federal funding for efforts to create renewable or sustainable types of fuel that can power aircraft over long distances while decreasing the damage aviation does to the global climate.

Aviation contributed about 2.5% of global carbon emissions in 2023. It’s particularly hard to reduce emissions from planes because there are few alternatives for large, portable quantities of energy-dense fuel. Electric batteries with enough energy to power an international flight, for instance, would be much larger and heavier than airplane fuel tanks.

One potential solution, which I work on as an aerospace engineer, is a category of fuel called “sustainable aviation fuel.” Unlike conventional jet fuel, which is refined from petroleum, sustainable aviation fuels are produced from renewable and waste resources such as used cooking oil, agricultural leftovers, algae, sewage, and trash. But they are similar enough to conventional jet fuels that they work in existing aircraft tanks and engines without any major modifications.

Prior to Donald Trump’s second term as president, the U.S. government had set some bold targets: by 2030, producing 3 billion gallons of this type of fuel every year, and by 2050, producing enough to fuel every U.S. commercial jet flight. But there’s a long journey ahead.

The earliest efforts to create sustainable aviation fuels relied on food crops—turning corn into ethanol or soybean oil into biodiesel. The raw........

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