Forget about warming. Ocean acidification will doom us first.

If you take pure water with a pH of 7 and let it sit for 24 it will absorb CO2 from the atmosphere and become more acidic. The amount of CO2 in the atmosphere is increasing and thus, so is the amount that water automatically acidifies.

I ran this experiment in a lab and it worked. Carbonic acid was formed and the water went down to I think 6.4 but this was several years ago so my number may be off.

The phenomena of water acidifying is easily provable and should be one of the scariest things on your mind.