The fourth season of Torchwood explores this universe: One day, nobody dies. All across the world, nobody dies. And then the next day, and the next, and the next, people keep aging -- they get hurt and sick -- but they never die. The result: a population boom, overnight.
With all the extra people, resources are finite. It’s said that in four month's time, the human race will cease to be viable. But this can’t be a natural event – someone’s got to be behind it.