Re:End of the world
Every scientifically valid model of global warming indicates that it will not cause significant increases in sea levels for a few centuries, at least (the nature of the Antartic ice cap, which is the crux of the matter, may be such that even a 50 degree increase in global temperature would take millenia to have an effect).
Precipitation patterns are more difficult to predict, but the development of new technologies are making irregular rainfall more a matter of monetary costs than of catastrophe (at least in developed nations...).
And yet, there is a looming crisis point. Even today, conflict in the Islamic world is threatening a series of limited nuclear/biological/chemical wars. Within twenty years, indications are that China will make a play for dominance, and America will either fight them or sink into a secondary role (which has it's own implications). In fifty years we will have "solved" the human genome, a crisis point that we cannot fully imagine. In a century...but we'll never make it that far.
How sudden do you want your apocalypse? I give humanity another thirty years at the outside.