If you don’t understand that climate change does NOT threaten our existence I can’t make it any clearer than that.
What would convince you that it does threaten our existence?
How could it?
Increased sea level wipes out current coastal cities, destroying the global economy.
Increased heat causes current crop rotations to fail, while happening too fast for ready transition to the new ones to accommodate the volume of agriculture we need.
Shifting of climate zones causes "circle of life" in multiple regions to fail, eliminating most pollinating species, leading to further crop failure, dying off of fish in major zones, and other food sources.
Climate zone changes also move disease-born insects into regions where the animal life has no antibodies for them, potentially destroying the livestock that feeds many of us, whether chickens, pigs, or cows.
Avian flu and swine flu variants arrive, but with collapse of economy, CDC doesn't have the resources to construct a good counter to one or more such things.
Since you asked.
Also: "existential" for many people does not mean extinction of humanity, "merely" extinction of our current level of "civilization," which this could do all too easily.
Again, Ward, what would convince you that this is a threat that is worth considering action to prevent?