We could also scale synthetic fuel made from atmospheric carbon, we’ve had the tech for decades after all, it’s just a lot more expensive than stealing it from the ground. While algae might be easier, i have doubts as to plant based biofuel owing largely to the land and water use required to scale up to the levels we need. I don’t doubt that with greenhouses and desalination it could be done, but labor, capital, and effort wise i would expect algae or chemical systhasis to come out on top.

Problem is that either way it takes more energy to make than it receives, which when we constantly burn oil for power is a net loss, but at the same time it’s the only long term solution for applications like long term flight.