Ocean acidification is the ongoing decrease in the pH of the Earth's oceans, caused by the uptake of atmospheric carbon dioxide (CO2) as water and air mix at the water’s surface. Oceans, rivers and lakes absorb roughly one third of human-created CO2 emissions (22 million tons) each day.
Before the industrial era began, the average pH at the ocean surface was about 8.2 (slightly basic; 7.0 is neutral). Current ocean pH is roughly 8.1. This drop of 0.1 pH units represents a 25% increase in acidity over the past 200 years. Stress on marine life due to acidification (lowering the pH) leads to dying or severely affected ecosystems.