Two simple trends are driving these concerns. The world has more people than ever, and more of those people than ever are breaking out of abject poverty and competing in a global market for goods and resources.
The human population passed 7 billion last year, and the U.N. projects it will top 9.3 billion by 2050. Most of the growth is occurring in Asia, where the population is on track to balloon 40 percent, to 8 billion, by midcentury.
An even bigger human accomplishment, and cause for worry, is the rise of the middle class. It's expected to nearly triple in the next two decades, to 4.9 billion people in 2030 from 1.8 billion today, according to the Organization for Economic Cooperation & Development. The Global Footprint Network, which developed a resource-accounting tool for countries, puts it this way: At current consumption rates, we'll need two Earths by 2030.
For more, see Bloomberg