Thank you for providing these links backing your claim, so far I haven't been able to disprove the numbers that have been used. I still feel like it could be made competitive somehow, I'll get back to shouting that biofuel is an option when I've found out how :)
I strongly recommend Vaclav Smil, Energy in World History and Energy and Civilization (along with many other books on resources). The "Burning Buried Sunshine" paper (Springer link above)describes human energy use relative to net primary production. As of the late 1990s humans wwere accounting for (using directly or indirectly) 20% of all net primary production, with other energy use roughly doubling that.
Whether or not remaining biological systems could survive on just 60% of plant life is a possibility, though the impacts would likely be large. Further growth in human energy consumption would obviously be limited.
I'd come across that independently, Smil also cites it.
