The world's population is expected to reach seven billion soon, placing an ever greater strain on limited resources.
There are some countries, however, facing the opposite problem. South Korea once had one of the highest birthrates, but now the population is ageing at an unprecedented rate.
With the workforce ageing so quickly, Korea's economy is slowing, and the government remains at a loss on how to provide for its seniors.
Al Jazeera's Steve Chao reports from Seoul, South Korea, for our special series, Crowded Planet.