I think it's really naïve to realize that climate change is an existential threat to many species, but not connect that we are part of the ecosystem which is being put in danger. You are experiencing survivorship bias.
Even if we don't go extinct. It's still an existential threat to our way of life. Which is also a totally valid interpretation of the phrase.
> You are experiencing survivorship bias
Ex ante survivorship is literally the delineation between existential and not.
> Even if we don't go extinct. It's still an existential threat to our way of life
You see why this comes across as bullshit, though. It’s needlessly redefining a word to seem more punchy. We have plenty of perils we massively mobilize against without imagining they’ll exterminate the human species.