The other day my dad saw a TV show where scientists said that the last Ice Age started very quickly. What happened was Greenland's ice suddenly melted, and the Gulf Stream, which is nearby, stopped. Then Europe froze over and weather went really bad throughout the world, for example North Africa dried up seemingly overnight.
I haven't had a dream exactly about that but it's one of the things that we could realistically expect to happen. That would also cause a rise in sea level, a very fast one, and all the ports would be underwater.
I'll tell you if I get more details about this today.