There are many threats out there and the oddest thing is that we have not prepared for non of them.
Let's see, there are 7 billion people on Earth (and still counting) and current system doesn't even work for all of us.
We are using Earth's resources faster than it can re-produce them. We seek Infinite growth on a finite planet and the formula is not sustainable!
I don't think this system is going to last without some big changes.
http://www.theguardian.com/environment/ ... scientists
Also, notice how much natural disasters have caused and how little we have done to rebuild. In Haiti, people are still living in tents! And how was help for american's after big hurricanes? And there will be even more disasters in the future;
I think I don't have to tell you what global warming's effects would/will be. Very big problems for food industry, more storms, rise of sea level, unstable weather/season cycle.. And our system that doen't work even now is going to adapt to that?