Are people committing shirk when they say the world is ending?

Question

Are shaikh and other islamic scholar who keep saying the world going to end in 2019,2020,2050 etc in youtube or other sites committing shirk? In my opinion I think they are as far as I know only Allah knows when they world going to end or when's dajjal coming etc. So aren't they committing shirk by saying they know when the world going to end. I mean not even our Prophet Muhammad (SAW) knows about it. So how can they arrogantly claim the world ending in this year or that year or that going to happen etc.