Topic: Ten Ways the World Could End

[sam]

Despite what you may think, the universe is not necessarily a friendly place. Sure, things here on Earth have been pretty stable over the past few millennia, allowing human civilization to gain a foothold. But that could change at any time. Disaster lurks everywhere, from the deepest reaches of space to the very bowels of our planet. We've recruited nine prominent Canadian scientists (and one science fiction writer) and asked them to imagine how they think the world might end. We bring you The Quirks & Quarks Guide to the End of the World -- it's cataclysmically fun!

http://www.cbc.ca/quirks/archives/08-09/qq-2008-12-06.html

[Clive]

I think the asteroid scenario is the most likely in the shorter term.  Followed by the super volcano.