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This reminds me of a story that I can only half remember (by Grant Morrison maybe?), where in the far future humanity, with a population even greater than ours today, has coalesced into a few immense towering city-states, protected by bubbles. The majority of the earth was allowed to return to its natural, wild state, with humanity carefully visiting the "outside" for recreation. It was a peaceful, prosperous future.
Source: Vital Signs 2010, article by Margarita Yatsevich