Blue Mars — Kim Stanley Robinson

The red planet is no more. Now green and verdant, Mars has been dramatically transformed from a desert world into one where humans can flourish. But as Mars reaches its final transformation, Earth is in peril. A great flood threatens an already overpopulated and polluted planet, and Mars, its last hope, may find itself facing a population explosion or an interplanetary war. Meanwhile, the First Hundred settlers of Mars are being pulled into a fierce new struggle between the Reds, a group devoted to preserving Mars in its desert state, and the Green "terraformers." Soon the human drama at the center of this breathtaking epic explodes in political upheaval, leading to new explorations into the solar system and to choices that will decide the ultimate fate of Mother Earth.