Robinson, Kim Stanley: Blue Mars

The red planet is no more. Now green and verdant, Mars has been dramatically altered from a desolate world into one where humans can flourish. The First Hundred settlers 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. Meanwhile, Earth is in peril. A great flood threatens an already overcrowded and polluted planet. With Mars the last hope for the human race, the inhabitants of the red planet are heading toward a population explosion--or interplanetary war.