We can already see it happening with dramatically reduced insect populations, fish populations, bird populations, etc. Whats hard is to distinguish what is caused by the global temperature changes vs just general human habitat destruction, but the general decline of insect populations at certain equatorial belts in the last decade definitely hints towards a global influence from climate change.

If all we had to do were just relocate our coastal metros a few meters up after the polar ice melts and just proceed as usual with 3c hotter days on average it wouldn't be this severe of an existential threat. It is probably half of why its so hard to argue towards fixing - the real danger seems "impossible" to most people because they can't wrap their head around how delicate biomes can be and the domino effects our mass extinction event is causing.