1. Up to one half of the carbon dioxide (CO2) released by burning fossil fuels over the past 200 years has been absorbed by the world's oceans
2. Absorbed CO2 in seawater (H2O) forms carbonic acid (H2CO3), lowering the water's pH level and making it more acidic
3. This raises the hydrogen ion concentration in the water, and limits organisms' access to carbonate ions, which are needed to form hard parts
Ocean chemistry is changing because water absorbs extra CO2 from the air. The increasing concentration of CO2 [in the air] is making the oceans more acidic. This is likely to affect the capacity of organisms including molluscs, coral and plankton to form "hard parts" of calcium carbonate. It affects marine life, it affects coral, and that in turn could affect the amount of fish in the sea - and a billion people in the world depend on fish for their principal source of protein.
Concentrations in the atmosphere are now about 30% higher than in pre-industrial times; a proportion of this is absorbed by seawater, which results in rising concentrations of carbonic acid. As a result, the pH of seawater has fallen by about 0.1, and a further change of 0.3-0.4 is expected by the end of the century.
(BBC News, 12/14/09)
* Up to 50% of the CO2 released by burning fossil fuels over the past 200 years has been absorbed by the world's oceans
* This has lowered the pH value of seawater - the measure of acidity and alkalinity - by 0.1
* The vast majority of liquids lie between pH 0 (very acidic) and pH 14 (very alkaline); 7 is neutral
* Seawater is mildly alkaline with a "natural" pH of about 8.2
* The IPCC forecasts that ocean pH will fall by "between 0.14 and 0.35 units over the 21st Century, adding to the present fall of 0.1 units since pre-industrial times"