IF the world is going to sharply reduce the amount of carbon dioxide pumped into the atmosphere by midcentury, then many businesses will have to go carbon neutral, bringing their net emissions of the greenhouse gas to zero. GREEN GIANTS Algae, which have a high energy value per pound and consume carbon dioxide, are being cultivated at a biofuel demonstration facility run by the Solena Group in Alicante, Spain. Related Dot Earth: Making Fuel From Air - Some Details (February 19, 2008) But some could go even further by removing more CO2 than they produce. Instead of carbon neutral, how about carbon negative? In academic and industrial labs worldwide, researchers are working on technologies to reach that goal. Success could create the ultimate green business