This New Scientist article imagines what would happen to the Earth if all the people disappeared.

"Imagine that all the people on Earth - all 6.5 billion of us and counting - could be spirited away tomorrow. . . . Left once more to its own devices, Nature would begin to reclaim the planet, as fields and pastures reverted to prairies and forest, the air and water cleansed themselves of pollutants, and roads and cities crumbled back to dust."