It's not acid rain, but dissolution of CO2 into oceanic water creating carbonic acid. This carbonic acid dissolves the materials many marine organisms use to construct their homes and shells.

So anthropogenic CO2 (we know it's anthropogenic because of satellite measurements showing seasonal variations around population centers) caused anthropogenic climate change. Even if an unknown effect serves to counteract the massive greenhouse effect of all of our CO2, temperature is only one effect of climate change. There is also changing ocean currents due to meltwater changing salinity and temperature of the ocean, shifting of precipitation to other regions creating droughts and floods, the aforementioned acidification, etc.