apocapricious

An apocalyptic feeling or prediction that is characterized by or subject to whim; someone who issues predictions of a future apocalypse who is both impulsive and unpredictable.

"You know, the British doomsayer James Lovelock has some good ideas about climate change and global warming, but his ideas about breeding pairs of humans surviving in an uninhabited and desolate Arctic is completely over the top and apocapricious!"

-- Overheard at a pub in Cornwall, England