Well, it's a matter of opinion which one is the root cause.
My take is that if you remove nuclear/biological war out of the picture somehow, climate change is not an existential risk. If you remove the latter then the former is still an existential risk (and there are unfortunately a lot of other possible sources of geopolitical instability). So the fundamental source of risk if the former. But it's a matter of opinion.
Conventional or chemical warfare, even on a global scale, are definitely not existential risks though. And like I said, probably not even nuclear. Biological... that I could see leading to extinction.
My take is that if you remove nuclear/biological war out of the picture somehow, climate change is not an existential risk. If you remove the latter then the former is still an existential risk (and there are unfortunately a lot of other possible sources of geopolitical instability). So the fundamental source of risk if the former. But it's a matter of opinion.
Conventional or chemical warfare, even on a global scale, are definitely not existential risks though. And like I said, probably not even nuclear. Biological... that I could see leading to extinction.