"But in your perishing you will shine brightly, fired by the strength of the God who brought you to this land and for some special purpose gave you dominion over this land and over the red man. Your destiny is a mystery to us, for we do not understand when the buffalo are all slaughtered, the wild horses are tamed, the secret corners of the forest heavy with the scent of many men, and the view of the ripe hills blotted by talking wires. Where is the thicket? Gone. Where is the eagle? Gone. And what is it to say good bye to the swift pony and the hunt? The end of living and the beginning of survival...."
The Drowned World, by J.G. Ballard: in the late 21st century the ice caps have melted, iguanas and alligators inhabit a drowned London and humanity has retreated toward the poles. Kind of a dull story that reads like a post-apocalypse Heart of Darkness, but very visionary considering it was written in 1962.
Wolf and Iron, by Gordon R. Dickson: A man and a wolf band together to survive in an America devastated by financial collapse.
Earth Abides, by George R. Stewart: civilization is destroyed by a plague, and humans have reverted to tribes that survive by scavenging from the old civilization or Paleolithic-style hunter-gathering.
The Sheep Look Up, by John Brunner: set in a corporate-controlled U.S. with a devastated environment. William Gibson said of this novel: "No one except possibly the late John Brunner, in his brilliant novel 'The Sheep Look Up', has ever described anything in science fiction that is remotely like the reality of 2007 as we know it."
To the commenter below who accused you of being Malthusian: anyone who thinks that on a planet with an exploding population of nearly 7 billion people (compared to say 1.5 billion in 1890), supported by ecosystems and climate that are in disarray, new technology can prevent a large die-off is, shall we say, optimistic.
In general, I agree that SF serves a useful function by imagining the dark side of technological progress, which in our present situation seems much more prophetic than the more sterile, utopian visions of more celebrated authors.