Picture of the day: Why living on top of one another is a growing concern

(Reuters)

In Shanghai, the world's most populated city in China, the planet's most populated country, this photograph of a residential building not only captures a snapshot of daily life in a metropolis filled with more than 23 million people.

The stacks of uniform apartments, seemingly endless, serve as a reminder of the challenges the planet faces when the world's population reaches seven billion as of tomorrow.

The figure, calculated by the United Nations Population Fund, is among several startling facts to emerge this week; the earth's present population is double what it was 50 years ago, seven times higher than it was 200 years ago, and it could grow to 15 billion by 2100.