A. manmade catastrophe.
B. celestial disaster--meteor, gammaray burst, rogue planet, supernova.
C. god commits suicide by cop.
The world (assuming you mean human civilization) will likely end in a comet impact if we don't do it to ourselves first. Climate change will have a major impact in the next several hundred years but it unlikely to be a human extinction event.
The universe will end in something called "the big rip"