5 to 8 degrees is probably the death of the biosphere with only extremophiles left.
But not human life.
Could humans survive this? Probably yes - we are resourceful and adaptable. But probably with a vastly smaller population and with a type of civilization radically different to our own.
Yes, but it didn't become that this fast.
> Could humans survive this? Probably yes - we are resourceful and adaptable.
No, and we're not.
I agree that 5-8C warming will lead to mass death through war, famine. But why would Siberia be too hot for habitation for the remaining population (whether that's 100 or 500 million people)?
When permafrost melts, it turns into a bog. Over decades and centuries, many of those bogs would dry out, but most of Siberia will be one great big morass for generations after it melts.