科学美国人60秒:Urban Growth Defines This Century

More than half of the world's seven billion people live in cities, 54 percent to be specific, or 3.9 billion people. That's according to new figures released by the United Nations on July 10th.
 
Cities in China, India and Nigeria, the world’s first, second and seventh most populous countries, are expected to grow the most by 2050.
 
India alone will add more than 400 million people to its cities, or the equivalent of 20 Mumbais, just in the next three decades. By 2030, New Delhi is likely to have 36 million residents.
 
How these cities in Asia and elsewhere grow and get built will determine how humanity fares in the 21st century. Housing, energy and transportation are all major challenges, whether in sprawling megacities or relatively small towns of a million or so inhabitants.
 
The health and environmental consequences of wasteful infrastructures could be devastating. Cities are now responsible for more than 70 percent of the greenhouse gases causing global warming, which has impacts on everything from growing food to water supplies. And most at risk from sea level rise are all those folks in coastal cities. The future is urban—for better or worse.
 
—David Biello