1. Anthropogenic Global Climate Change (sometimes referred to as "Global Warming")
2. Non-sustainable farming methods leading to draught and famine
3. Pollution/ecosystem damage
4. Nuclear War
5. Global financial calamity
6. Nuclear Reactor Disaster
7. Asteroids/Meteors/Comets
8. Large/Super-Volcano explosion, earthquakes, tsunamis and other natural disasters, both in their direct effects and indirect consequences.
9. War in general.
10. Deliberate killing of populations outside of officially declared wars.
11. Non-sustainable farming methods leading to emergence of unstoppable or almost unstoppable superbugs.
12. Other/hard-to-predict
13. Release of Biological War Pathogens (whether deliberate or not)
[etc.]