The Wilson Center Policy Briefs are a series of short analyses of critical global issues facing the next administration that will run until inauguration day.

We live in a world that is different from that inhabited by our ancestors in many profound ways. Among the most important changes is that, for the first time, almost half of the world’s people live in cities. According to the United Nations, in 2008 the global urban population surpassed half of the world’s population of 6.7 billion compared with 13 percent a century ago and 3 percent a century before that. This trend will require profound changes in the way the U.S. government addresses everything from development policy to international security.

The populations of cities will continue to grow at an accelerating pace for at least the first half of the 21st century, with the number of large cities increasing as well. Not only are such urban giants as Delhi, Dhaka, Jakarta, and Mexico City exploding to absorb up to 30 million residents and more – threatening to overtake the entire population of Canada – but more than 500 cities will have more than a million residents within a decade. Already, just over 700 urban centers are home to a half – million or more residents. Thus, in a little over a century, human beings have gone from being rural animals to urban ones.

Global population growth will continue to concentrate in urban centers of the developing world, which will become home to more than two billion new residents over the next two decades. In other words, 100 million people a year – a number that is on the scale of the population of Mexico – will be moving from rural areas to cities each year for the next 20 years. On average, the world’s urban population is growing by three million people – more or less the size of Cape Town – each week. China has been expanding its cities at a rate of one new Chicago every month for the past dozen years. Increasingly, such growth is proportionately less a consequence of migration and more a result of natural population growth within cities. Thus, the relative weight of cities on the planet will continue to grow even in the unlikely event that policies can be devised to keep people “down on the farm.”

Download the full policy brief from the Wilson Center.

Sources: UNFPA, UN Population Division.