How does one estimate the probability of doom from either of those things with any sort of reliability, given that they would be one off (future historical) events? Where's the science in predicting the future of civilization?
Since you asked, here’s some (old) science predicting the future (current state) of civilization:
In 1980, the American Petroleum Institute correctly predicted the current environmental crisis would happen now.
From the report:
"Timescale for significant impact, very roughly 50 years"
"1°C Rise (2005): Barely noticeable"
"2.5°C Rise (2038): Major economic consequences, Strong regional dependence"
"5°C Rise (2067): Globally Catastrophic effects"
They also predict that climate problems will cause global economic growth to halt in about 2025.
There’s no reason to think the trend lines in the report are suddenly incorrect. In fact, current events are well within the error bars of their model.
Averting it requires billions of people to agree to change course, and so far our leaders are doing nothing to make that happen.
Of course, much progress has been made in climate modeling since then, and now we’re more sure we’re screwed. On the other hand, since the report is 40 years old, it’s trivial to go back and confirm their predictions were correct so far.
That's a climate prediction with future predictions on what they expect to happen to civilization. But since it's not 2025, we can't say whether economic growth will halt. 2067 is the predicted doomsday year.
Of course if we overlay that with Kurzweil's singularity in 2045, then all bets are off. To the extent we take such predictions seriously.