https://science.nasa.gov/earth/explore/the-ocean-and-climate...

Has a pretty good overview. But in brief: Changes in biosphere due to heat and decreasing pH balance due to increased CO2 can leave species unable to adapt fast enough causing deaths.

It can also cause adaptations to go haywire like temperature dependent sex determination where the ratio of male to females in eggs is set by ambient temperatures, skewing breeding population gender too much in one direction.