> For example, 8 degrees of warming would be much worse than 4 degrees of warming

You should review where you got those figures and whether they are representative enough of current scientific consensus regarding the most likely scenarios.

As fas as I know and assuming that current pledges are fulfilled, most plausible estimations tend to be around 2 or at most 3 degrees of warming above pre-industrial levels (we are already well over 1°C).

While it is clear that this increase in temperatures will have severe consequences, I fail to see how it would lead anywhere near the civilization collapse that you seem so confident in predicting.

See for example: https://www.nature.com/articles/s41586-022-04553-z.epdf

("Realization of Paris Agreement pledges may limit warming just below 2 °C", Nature)