Ocean acidification is the name given to the ongoing decrease in the pH of the Earth's oceans, caused by their uptake of atmospheric carbon dioxide. Between 1751 and 1994 surface ocean pH is estimated to have decreased from approximately 8.18 to 8.1. PH is a measure of the acidity or basicity of a solution. It approximates but is not equal to concentration of hydrogen ions expressed on a logarithmic scale. A low pH indicates a high concentration of hydrogen ions, while a high pH indicates a low concentration. A strong acid would be less than 1 on this scale. A recent study indicates the relative impact on future ocean acidification of different aspects of global climate change mitigation policies such as the year that global emissions peak.
The absorption of CO2 by water results in the formation of acid (carbonic acid) which is similar in concept to acid rain.
Although the natural absorption of CO2 by the world's oceans helps to mitigate the climatic effects of high CO2, it is believed that the resulting decrease in pH will have negative consequences, primarily for marine life used to a certain pH level that use CO2 to build carbonate shells. These span the food chain from autotrophs to heterotrophs and include organisms such as coccolithophores, corals, foraminifera, echinoderms, crustaceans and molluscs.
Aside from calcification, organisms may suffer other adverse effects, either directly as reproductive or physiological effects, or indirectly through negative impacts on food resources. Marine life will change as pH levels change. As of yet, there is no complete understanding of the overall effects.
In the Geophyswical Research Letters (VOL. 37, L15704, 5 PP., 2010), there is an article on the influence of environmental mitigation policy on ocean pH changes.
Relative to a scenario where CO2 emissions peak in 2016 and then decrease by 1% per year tend to lead to the same or current pH by 2100. No CO2 emission reduction leads to a decrease of global mean ocean surface pH to 7.67 to 7.81 in the same time frame.
If emissions are capped for example in 2016 and then reduced by 5% per year, ocean pH may be limited to a minimum of 8.02. This is still more acidic than the nineteenth century's pH level but better than the worse case projected in these computer simulations.
Unfortunately, the buffering capacity of the oceans is really not known, What is clear is that the ocean's pH is going down.
For further information: http://www.agu.org/pubs/crossref/2010/2010GL043181.shtml or http://en.wikipedia.org/wiki/Ocean_acidification