Algae will be a big part of any sustainable future. It absorbs carbon dioxide, like plants. It can survive in saltwater and wastewater, saving freshwater resources for human needs. It can be cultivated in shallow pools built and maintained in regions spare of farmable land. It grows quickly, needs little fertilizer and requires no pesticides. Algae can power cars, ships and planes, and feed cattle—as well as people. A good overview of the promise of algae innovation by Popular Science.