. . . Every 20 years or so the Chicken Littles of the world move the end of the world back 20 years or so and the "science" is settled on the matter on the cause of the week.
Forecasting doom and gloom timelines is an art - disaster has to be close enough to worry people, but far enough in the future that they'll forget your prediction when time is up.
It's harder now with the internet to count on people forgetting - for example, for some years Rush Limbaugh's page was counting down Algore's disaster timeline; based on Algore's global warming disaster prediction, we all were wiped out several years ago.
And then of course some people claimed that the Mayan calendar predicted the end of the world in 2011. Oops - it was just the Mayan calendar rolling over.