I think this global warming thing is crap. Our Earth changes naturally. At one point the Sahara desert (I believe it's that one) was not a desert, but full of life. Earth changed. We've had periods on earth where it's very hot (dinosaurs maybe?), and very cold (ice age).
Also, people are worried that cars will do this to us because what they put out destroys the ozone layer. First off, Volcanoes put out more stuff (has something to do with carbon, forget the exact term though) than we do...a lot more. I believe one volcano eruption is equal to about one year of what we put out...correct me if I'm wrong, but it's something like that. Considering volcanoes still exist, and the Earth is still doing quite well, I don't think it's going anywhere.
Not to mention, the ozone layer is known to have patterns...sometimes it's not as strong as other times.
So for global warming killing us...Hmm, no. Even if it was true and happened, we'd know far ahead of time and adapt.
As far as things like nuclear wars...well, that could happen.
I think it's silly to worry about this stuff. Just live for now, and face stuff when it comes.