The world is not going to end - that must first be accepted before any of this has purpose. Rapture and Mayan Apocalypse notwithstanding, humans are going to have to find a way to survive the climate change they'll have forced upon the world.
Second assumption - humans aren't going to be able to prevent/reverse global warming. Bleak, but at the least, a scenario worth preparing for.
Now, my science to back this all up - the debate is useless without science. However, I'm not a climatologist, and other than a natural interest as a concerned citizen, my big focus is how people will react to this. Proactive doesn't seem to be a serious plan, and so I'm guessing people won't seriously react until the process is irreversible, and I'll be using this science (and the handy 'what if? at the bottom of the page) to speculate what humans will do when the sea level goes up 5 meters.
5 meters wipes out the area of the earth where currently ten percent of human lives. Minor climate change precipitates invasions and conflict (there is some speculation that this is part of the problem behind Darfur), and invasion and conflict, more often that not, beget further invasion and conflict. In this brave new century, with its drained petroleum, massive population growth, and shortage of land made only worse by the submergence of valuable, densely populated land, conflict on a large scale seems to be an inevitability.
Added to this mess, the climate change will produce, well, climate change, making land that is currently arable not, and adding an uncertainty to this conflict. Albuquerque, fantastic city at 5,000 feet that it is, stands a good chance of being unlivable. Migration will be huge, everywhere.
Survivability will be much easier to focus on the nation scale. Countries with lots of land, lots of varied land, and an average elevation of more than 20 meters will survive, especially if these countries already have economic resources. Coastal nations, poor nations, and nations that occupy a small area will suffer. Since there is a lot of overlap for those areas, global warming will create a sick irony, with the wealthy countries that caused global warming being the ones that survive.
There's more to be said, and there plenty here to be refuted. A tip of the hat to John Fleck, whose ideas and bleak musings are partly the inspiration, and partly (lets be overt) borrowed with hopeful future consent. The specifics of the endgame, the reshaping of the world during and after such a catastrophe as we seem to be plunging into, will be mused about more later. Or turned into fiction, which is perhaps a more appropriate venue.