Well, for all those hundreds of millions it will indeed be existential (and I have read that a 4C Earth could only be able to host ~1 billion people, so the dea

Well, for all those hundreds of millions it will indeed be existential (and I have read that a 4C Earth could only be able to host ~1 billion people, so the deaths could be a lot more than "millions to hundreds of millions".) In any case, arguing about the technicalities of the word "existential" at this point denotes such a complete lack of empathy that it's not even worth it.