In their new book After the Spike , demographers Dean Spears and Michael Geruso make the counterintuitive case for worrying less about overpopulation and more about depopulation. Comparing it to climate change, they say population shrinkage is coming and once it starts it could be hard to stop. The highest number of births the planet has ever seen was in 2012, when 146 million children were born. The global population has continued to increase since then, even though the birth rate has fallen,