[avmich]

We don't have reliable data that an advanced civilization of our level (yes, we're advanced comparing to many our ancestors) goes extinct. Particularly for reasons like this. So we naturally not sure. On the other hand, we see some examples of wonderful inventiveness - say, in time of a war, but also in time of great geographical discoveries, technology and science achievements etc. So for many it feels like an open question.

As for validity time scale, I'd like to see research myself.

[AstralStorm]

We have some examples. Just look at Petra and some Mayan cities... They fell because climate stopped spring people there - they ran out of water and fell to either starvation or disease.

Mostly they moved elsewhere, but on planet scale that would be much more problematic.