Re: We need the technological progress...
"WE are doing exactly that. ... Distill it. Presto: Fuel from the atmosphere that virtually any petrol/gasoline engine can be run on."
Sorry, I guess I should have addressed that in my post. But it would have made a rather long post. The major problem with your somewhat utopian scenario is distillation. Making fermented corn mash into 190 proof whiskey -- which is what corn ethanol pretty much is -- takes a lot of energy. In the US, that's mostly done with natural gas which is abundant and pretty cheap. Cheap in North America. Not necessarily elsewhere. There have been a number of studies that conclude that the energy budget for corn ethanol is slightly positive in the best growing areas and actually negative in less favored areas. Bottom line -- after one takes into account fertilization, mechanized field work, harvesting, and conversion to fuel, corn ethanol is a relatively inexpensive way to convert natural gas to a liquid fuel. That's not a bad thing. But a replacement for fossil fuel it is not. (BTW petroleum from Alberta Oil shales is pretty much the same story. How to the get the hydrocarbons out of the shale? Steam heated by Natural gas.)
Can ethanol be distilled more cheaply? Maybe. Solar distillation MIGHT work. But I suspect only in lower latitudes. Almost certainly not here in Vermont where corn is grown, but making a crop is problematic some years because of the short growing season. By the time you got your mash fermented, you'd be trying to use solar heat with an eight hour day, a maximum sun angle of about 25 degrees and solar collectors likely covered with ice or snow. The only study I've seen says solar distillation of ethanol is not economic even in the tropics, but I'm not sure that's the final word.
How about ethanol from sugar cane? Maybe. I've never seen an energy budget for that. Maybe it'll work. But Sugar cane is a tropical crop and it won't grow well even in some parts of the tropics. It needs a LOT of water.
How about biofuel crops that don't require distillation? Maybe. I tried once to figure out if it was possible to grow enough oil palms to support modern air travel. My conclusion. Maybe, probably not. Too many unknowns to be sure. BTW, environmentalists loathe palm oil. I'm not sure I disagree. Endless rows of oil palm trees are not my idea of living in harmony with nature.
My point remains. We do not currently have the technologies to feed 7 or 8 o 10 million people and fuel a modern civilization. It might be a good idea to have those technologies in hand before we run out of fossil fuels.