That's right, but then you have to capture it from atmospheric concentrations (430ppm) rather than directly from a waste gas stream at a much higher concentrati

That's right, but then you have to capture it from atmospheric concentrations (430ppm) rather than directly from a waste gas stream at a much higher concentration. It can be done but the economics don't look good right now. Possible very cheap solar energy in desert regions can change that a bit. Australia have been trying but they didn't get very far with it yet, granted there is still room for solar to get cheaper again.