OK, yes, building larger-molecule more-useful-stuff will take more energy, and I'll go with the first approximation that it's a similar quantity of energy re-in

OK, yes, building larger-molecule more-useful-stuff will take more energy, and I'll go with the first approximation that it's a similar quantity of energy re-input (some useful things less, some more). And yes, all that product will take substantial volume. Thx for clarifying. That said, it still seems an extremely useful measure, even if we keep using only single-digit percentages for long-use plastics instead of hydrocarbon fuels. Let's assume that for the next century or so a bunch of applications will continue to require the convenience and energy-density of liquid hydrocarbons. In order to avoid extracting more and further increasing CO2 levels, we'll have to input significant energy to reconstitute them from CO2. Obviously, inputting that energy from more fossil fuels defeats the purpose, but using renewables will work; and now they are even cheaper energy inputs. The result would be a cycle of newly fabricated hydrocarbon fuels, which can be custom-optimised for each application. No new CO2 would enter the atmosphere and the existing levels would be reduced by the amount of hydrocarbon fuels (and plastics, etc.) fabricated and in existence throughout the entire chain of existence, fabrication, storage, distribution, transport, in-vehicle, right up to the moment it is burned. With cheaper renewable energy inputs and optimized custom fabrication, it would likely get cheaper than the existing drill/pump/transport/refine process. And, it's permanently sustainable, and as liquid hydrocarbon fuel use declines, custom production can be converted to storable materials.