To be honest, I've read a bit about the acidification of the oceans and much of it goes right over my head, but the basic thrust of it is that increased CO2 in the oceans leads to increased production of carbolic acid which changes the oceans pH slightly and since corals are particularly sensitive to pH it may be wiping them out.
From what I can tell, this is still somewhat speculative, but most everyone agrees on the fundamentals that increased CO2 in the water results in increased carbolic acid resulting in lower ocean pH and that corals are sensitive to this.
I personally don't know if this is part of the reason for dying reefs or not, but it sounds much more plausible to me than a 1 degree shift in temperature over a 100 year period.
Of course you mean carbonic acid (H2 CO3.) not carbolic acid (C6 H5 OH.)