Question: Can you refine carbon dioxide into a source of energy for our machines and tech?

Hywel Owen answered on 14 Jun 2012:

In principle you can, but what matters is how much energy goes into separating the carbon atoms from the oxygen atoms. If more energy goes into separating them than you get back when you recombine them (by burning the carbon with the oxygen), then what was the point?

Some biofuels have this problem. Converting corn (maize) crops into diesel for cars sounds attractive because it looks like the sun is doing the job of converting the CO2 in the air into burnable fuel in the corn. But you also have to harvest the corn, and then convert it into diesel fuel. Right now, we use petrol pumped out the ground to do that, and it can take more petrol energy to make the corn fuel than you get when you finally burn it. You might as well have burned the petrol, and saved yourself all that bother, and a bit of CO2 emissions. Even if some biofuels do give out more energy than they take to make, it might still be a bad idea because of all the effort involved.