The world's oceans absorb CO2. During this process, the CO2 changes the water's ph causing acidification which expedites destruction of coral reefs, calcareous plankton and all organisms whose skeletons or shells contain calcium carbonate.
Most of the affected biota resides near the surface of the water, where the greatest pH change would be expected to occur, but deep-ocean biota may be more sensitive to pH changes.
Scientists Ken Caldeira and Michael E Wickett of the Lawrence Livermore National Library created a model to what will happen to the ocean's PH if global carbon emissions continue at their current rate of growth.
They conclude: "We conclude that unabated CO2 emissions over the coming centuries may produce changes in ocean pH that are greater than any experienced in the past 300 Myr, with the possible exception of those resulting from rare, catastrophic events in Earth's history"
More: Anthropogenic carbon and ocean pH