Ocean acidification is decrease in the pH in our oceans caused when chemical substances like carbon dioxide (CO2), sulfur, or nitrogen mix with seawater. Ocean pH pH has dropped by slightly less than 0.1 units since industrial revolution and it is estimated that it will drop by a further 0.3 - 0.5 units by 2100, mainly because of carbon dioxide.
Ocean acidification has extremely negative results on some marine creatures like sea urchins, corals, and certain types of plankton as it decreases their ability to harness calcium carbonate which they need to harden their outer shells (exoskeletons). Importance of these creatures is highly important in marine food chain since they provide essential food and habitat to other species and they really represent the base of ocean ecosystems. Researcher Gretchen Hofmann recently said: "It's possible by 2050 they may not be able to make a shell anymore. If we lose these organisms, the impact on the food chain will be catastrophic.
Ocean acidification isn't making oceans significantly more acidic on global scale, but it significantly hurts coastal and shallow area and organisms that live in these areas. There are many factors contributing to acid rains such as farming, livestock husbandry and combustion of different fossil fuels. The most affected areas are usually downwind of coal power plants, on the eastern edges of North America, Europe, and south and east of Asia.
So not only our land hurts because of acid rains, but also our oceans and many marine organisms struggle to cope with increased acidity. And if current rates continue, by the end of this century acidity will be five times bigger than today, and this would really mean catastrophe.