New companies say pulling carbon dioxide straight from the air could solve global warming and provide an infinite source of gasoline. Really?

FORTUNE -- What if scientists could transform coal-fired power plants from giant carbon dioxide emitters into giant carbon sinks? Some say that they can, and will. Graciela Chichilnisky, a founder of Global Thermostat, admits it's hard to believe: "The more energy the less the emissions—it's mind boggling."

Global Thermostat and at least two competitors say they can pull carbon dioxide straight from the air, potentially at costs low enough to solve global warming and provide an infinite source of gas by using the CO2 to feed algae. Chichilnisky summarizes her company's business model this way: "Take CO2 from the air and turn it into cash." More