Climate change has never struck me as an existential risk. Certainly it is a major problem. But it's slow moving. Slow moving problems are way more soluble than fast moving problems. (For comparison, a hostile AI takeoff theoretically could wipe out humanity in a few minutes given the proper means.) The worst case scenario from climate change itself seems to be a small population of humans living in an artificial habitat in 1000 years. And of course there is a broad spectrum of other outcomes from there. If, for example, we master interplanetary colonization quickly by our effort to get to Mars, this would greatly minimize the impact since we could adapt the technologies used to survive on Mars.
The biggest argument in favor of climate change being a true existential risk is if the conflicts it would spawn would result in a global war.
The biggest argument in favor of climate change being a true existential risk is if the conflicts it would spawn would result in a global war.