Over 12 percent of the world's land area is now officially protected, and that number has been rising fast, doubling just since 1990. You can see it in the right-most bars on the chart below. The rest of the chart breaks down the progress by types of regions.
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