I wouldn't put a number out here, but the purpose is simply to suggest that if we clean up the process, as we know we can do today, it will become more energy-intensive.
Of course, my original premise was that it doesn't make any difference whether it's more energy-intensive, because we will never run out of energy. We just run out of some of the forms of materials we use—or we may—but we have always stopped using energy sources not because of running out of them, but because there was a better technology and a better source. We didn't stop using coal to heat our houses because we were running out of coal. It was a whole lot easier to put an oil burner in, or an electric.