Slate: According to technological optimists, in the next two or three decades, humanity will embark on a new era of possibility. Super-smart computers and other advances may even make certain types of less risky, large-scale climate actions a reality. Open any number of sci-fi books from the last few decades and you have an idea of how nanotechnology could make planetary-scale engineering possible. (Kim Stanley Robinson's work comes immediately to mind.) Maybe swarms of self-replicating photosynthetic nanobots...