How do you think the world will end?

Well, the reason I started a thread like this is because I saw Terminator 3 a few weeks ago and it spurred my interest in post-apocalyptic fiction and theories of how the apocalypse will happen.

I've been reading stuff about how the world is going to end in '2012' and how many different religions or cultues (like American Indians) have said something is going to happen on 12/21/12.

This is the type of shit I read when I'm bored at work
 
If there is no 'apocalypse' like how we imagine it (Nukes, etc), the Sun will turn into a red giant in a few billion years and swallow the Earth.
 
The world itself will not end (until the Sun expands). The human race will make eventually make the environment no longer capable of sustaining human life. Our race will go extinct, after which the world will recover from bearing our destructive existence.
 
The fundamental problem is overpopulation, which we are making worse by curing diseases. Diseases are nature's way of population control.

Mass starvation or mass epidemics. Take your pick.
 
I was having a discussion with my friend at the bar on Wednesday night about how we could harness the power of fusion to power the world and he was all 'The problem with fusion is this: If you fuck it up, you blow up the world'