> energy source Algae based bio fuels sounds promising. > replace plastics If we stop using oil for fuel, there's plenty left for plastics. Oh, and carbon fi

> energy source Algae based bio fuels sounds promising. > replace plastics If we stop using oil for fuel, there's plenty left for plastics. Oh, and carbon fibre is promising. > What are you going to feed your 20 billion? Food. There's plenty of unused room for it, and even then, there's hydroponics. Solve desalination, or hook up a cheap abundant energy source to what we already have, and there's even more room.