From Longman Dictionary of Contemporary Englishdoomsayerdoom‧say‧er /ˈduːmˌseɪə $ -ər/ especially American English (also doomster British English) noun [countable] someone who says that bad things are going to happen
Examples from the Corpus
doomsayer• Doomsayers predict that one day California will tumble into the sea.• What these entities ultimately accomplish may be academic; but their mere existence should give doomsayers cause for hope.• Yet the place invariably confounds its doomsayers.• In short, it was a rout of the doomsayers and a vindication of the architects of Desert Storm.• When the Cats slipped to fifth in a tough Pac-10 race, the doomsayers fired up their engines.• Some of these doomsayers make good money from their false warnings. 