Why don't we consider the last "planet's gonna die" scare when dealing with this one?

Considering at least a 5,000 year chain of disaster predictions by alarmists of one flavor or another i am surprised anyone still listens to them. i mean in that extended period of time not one single the sky is falling disaster prediction has ever come true. Now we have had lots of disasters over that period, but none of the ones that actually happened were predicted in advance.