It won't be limitless. There is a limit to how much biofuel you can grow and process in a year; there hasn't been a limit to how much fossil fuels have been pulled out of the ground up until now. Admittedly, biofuels do put out
greenhouse gas emissions, but it's the ones that are pulled out of the ground that are the big problem. Greenhouse gas emissions were in a natural state up until 1900 or so. What got burned, even whale oil, was going to decompose and have some of it end up in the atmosphere as
CO2 anyway.
Even fossil fuel use is not out of the question,
as long as you can offset that carbon by planting trees or burying biochar. But humanity hasn't done that. They have cut down more trees to make way for low carbon sequestering field crops. They have depleted soil carbon and replaced a carbon-based food web with nutrients that are derived from chemical processes that use fossil fuel.
If we could put saline water wastelands (look up Loving county, TX) to use growing salt-water algae to make biofuels, it would be a positive step.
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