When the human population on the earth drops from 7 billion to 1 billion in the coming century, there will be plenty of city downsizing.

James Lovelock:

"Our main task, should the earth continue to heat, is to adapt and learn how to survive," he said. "We're unlikely to become extinct by global heating, but we may be cut back to one billion people or less."

That's approximately a seventh the world's current population.