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.