pianotuna, the answer to your question is at least half of us starve. Most if not all plastic replacements have to be grown, and you need fertilizer to grow it, if you need big crops. This takes you back to Haber and natural gas, or syngas made from oil or coal.
I wish I could find who said: "If it can't be grown, it has to be mined". The quote is wrong, even most foods grown depend on mining (drilling).
When people started agriculture, and then the industrial revolution, we went down a path from which there is no return.
Read about the Club of Rome, their predictions are probably right, their timing is wrong. Farmers, Biologists, Engineers and others have found plenty of just in time solutions, but past performance is no guarantee of future results. I am always surprised how much my degrees in Biology and Petroleum Engineering overlap.
