Imagine a massive network of machines scrubbing the Earth’s atmosphere to remove carbon dioxide from the sky. Such a scenario is seen as a possible solution for taking the environmentally threatening greenhouse gas out of the air we breathe. But the idea has been dismissed by some because of the enormous cost of the technique. But Fulton Schools Professor Klaus Lackner, a leader in the new carbon-capture technologies, says the costs are coming down to a point where large-scale carbon dioxide removal can become a viable option.