“Over the past 300 million years, ocean pH has been slightly basic, averaging about 8.2. Today, it is around 8.1, a drop of 0.1 pH units, representing a 25-percent increase in acidity over the past two centuries” (4)
http://centerforoceansolutions.org/climate/wp-content/uploads/2009/12/Acid_pH_graph.jpg
http://www.publichealthnewswire.org/wp-content/uploads/2012/06/smokestacks.jpg