Is climate change seriously considered to be an existential risk? It seems to 1st order climate change would just move population densities, to 2nd order there might be net less or net more land and ag resources after the climate change, and either 2nd or 3rd order, the rate of hurricanes and other weather storms is changed.

It doesn't seem to me that something which reduces human population from 6 billion to 2 billion should be considered an existential threat. A threat, yes, an expense we would prefer not to tolerate, perhaps. But a game ender? Not the way I play.