In 1968, Paul R. Ehrlich wrote a book called The Population Bomb, in which he predicted an explosive rise in the world's population would outstrip the world's food supply, causing unprecedented famine and conflict over resources. Well, it's 42 years later, and his prediction did not come to pass. Instead, the world's population is beginning to stabilize. Check this video from The Economist:
Dr. Ehrlich made predictions based on extrapolating the statistics of the day, without a deep understanding of the underlying processes behind the statistics. And indeed, some of those underlying processes weren't clear to anyone until a couple of decades later.
If you are wondering why the population is stabilizing, it may be because people realize that they are now living longer and can therefore delay child-bearing: take a look at this data.
Anyway, the global emergency of the 1960's was pollution, the 1970's was population, and now it's climate change. Shall this, too, pass?