We've never been as certain that things are going to change so radically.
Millenarianism of some kind is a natural state in human nature and affairs. The sense of an ending is innate. But the difference between previous Armageddon hysterias and us is that now the concern is truly global, and based on a generally (if not universally) agreed system of thought and deduction - science.
For a long time, there has been too much competition and not enough co-operation in the recipe for human progress. In fact, co-operation is our defining human characteristic, far more so than competition. Civilisation has always needed a specific balance of competition and co-operation. But old habits die hard, and industrial capitalism definitely forced more primitive competition into the mix at exactly the same time when the added productivity it delivered provided the opportunity for more co-operation. This 'decision' of history to take the wrong fork in the road lead to the planet-threatening excesses of Consumerism. And now we know, with the benefit of hindsight - another difference between us and almost every other generation of human history - that we are stuffed if we don't do something fast.
I think that amounts to a unique dilemma in human history.