[mc32]

A big difference now is the ease of mobility. A catastrophe in equatorial Africa a thousand years ago didn’t result in mass migration to Southern Africa. A catastrophe today will result in massive mobilization from one locale to another. The only example I can think of of mass migration was the steppes peoples but even that wasn’t that quick to happen.

[monocasa]

There's not a lot of great data from that time period, but another potential example is the bronze age collapse which was in part caused by a mass migration of "the sea peoples" into the great empires of the time.

The societal collapse so great that we forgot and had to reinvent writing after it had existed for millennia.

[ThomPete]

Mass migration over time though. Not civilization ending.

You should be more concerned about a meteor or giant vulcanic eruption than catastrophic climate change.