1. AI being used in a malicious way 2. Global warming
I'm not sure about the third one. What do you think?
2. Inter-generational discounting (you can't make the next generation care about what you cared about) driving a lack of upkeep for essential yet invisible infrastructure.
3. Threats from space: Coronal mass ejection, cometary impact, meteor impact.
IMHO neither AI nor Global warming are as much a threat to human civilization. They could really suck, but they're not going to send us back to the bronze age or extinct us. We're pretty damn clever and resilient.
Biology used in the service of war/terrorism
Rent seeking of the elite
2. Greed
3. Tolerating corruption
2. Nuclear war
I can't think of a credible third.
2. Climate change
3. Giving power to stupid people