Not only will coastal areas be inundated but previously relatively temperate areas will suffer from regular inundation, storm damage, and/or droughts, or possibly all of the above in alternation.
This is already happening in Europe, California, Australia, and elsewhere. And we haven't even had significant sea level rise yet.
Anyone who doesn't understand what this means for developed countries - never mind rest-of-world - isn't thinking straight.
Miami and Venice, as two easy examples, are already suffering annually recurring issues from higher sea levels than they were previously accustomed to.
Perhaps the framing needs tweaking. It is inaccurate to say "if we don't fix climate change, it will end humanity". But "unmitigated climate change could spell the end of the world as we know it. Do you like the world as it currently is, or do you wanna roll the dice and risk apocalypse/Mad Max/ etc?" is completely plausible.
Is there a semantic and ontological difference between "er'rybody gonna die!" and "[almost] er'rybody might die!"? Of course. Is there a difference in terms of expectation value of human quality of life in the future? Not a very big one if you ask me.
So are sleeping volcanoes and space asteroids
The point is that the "end of the world as we know it" has already happened in history, more than a few times already.
I'm sure either we stop it or not that things are going to be vastly different after .
But it doesn't mean is gonna be worse
They're not even remotely comparable.
It will devastate part of the population. Climate change is just an inevitable change. To cope with the change, certain portion of people will be sacrificed and certain people's position will be leveraged. So the view depends on the perspective. If you looking at humanity as every one together and equally, then it is apocalyptic. There is little hope that we can sustain. If you are looking at human civilization as something carried on by elites (as we always have), then such changes may even be welcomed -- all the reason that one need be prepared.