In the worst case scenario for global warming, at least the bulk of the human population fails to survive the confluence of its negative effects that come together in a "perfect storm"!
There is no best case scenario; because, we blew past that in 1979 when the OPEC oil crisis failed to wake us up to what the World Climate Conference revealed about climate change. It's, also, the year that Alaskans reported the melting of their permafrost. If we had pursued developing and expanding renewable energy technology half as diligently as we did in oil discovery and extraction methods, then we'd have been able to mitigate the situation by now.
As it stands now, we know if we keep burning fossil fuels at the current rate then the worst case scenario will happen sooner rather than later. To the degree we reduce our emissions, we can delay the inevitable. But, stop it we cannot-- unless we stabilize the atmospheric levels of greenhouse gases, which is highly unlikely due to the collective short comings of the human condition.
My personal guess is that we will eventually experience another 6 degrees Celsius of temperature increase before atmospheric levels stabilize. By then, the Four Horsemen of the Apocalypse aka Conquest, War, Famine, and Death will have curtailed our ability to further destroy our biosphere.
Note: The Lord our God promised not to destroy mankind with another flood; but, he never promised to keep us from destroying ourselves.
Conclusion: Each person must decide how to best protect their loved ones in our tenuous future. Logic would dictate that a stringent internationally cooperative approach would be best (which is the opposite of what most hierarchical thinkers support). At the personal level, one choice might be to avoid further procreation and to support environmental action groups. [Also, avoid wasting any time or energy on global warming deniers (they're so full of reactionary fear that you'll only entrench them even deeper than they already are -- they can't be helped, only pitied).]
Serious Effects of Global Warming:
Search: Global Warming Facts