It does not even matter whether there is evidence that the risk is likely to increase or not. Plus, it is arguable unknowable what the current risk may be now or in a few years time (plus, do you really trust NK's safety in chain of command and equipment?). Regardless, no matter how unlikely the event is to occur the magnitude or the event is so unbelievably massive that is something to be worthy of worrying about.
It all comes downs to understanding that despite a extremely low probability of occurring, some events are so earth shattering, you cannot discount it by its probability of happening.
On September 10th there was no evidence an attack on New York City was particularly likely (apart from in the minds of the terrorists). But September 11th came along and changed the West and Middle East for decades.