I hear a lot of comments from skeptics concerning ocean acidification. The gist of the complaints is that the ocean is not turning acid, therefore these claims are all false. Once again, the problem is a result of a lack of understanding. No one is saying the ocean is turned into an acid. Acidification refers to it become less base.
If you need a refresher, the pH scale goes from 0 to 14. Pure water is at 7, completely neutral. Less than 7 is acidic and more than 7 is base. A change in one number is a factor of 10. So, a pH of 9 is ten times more base than a pH of 8. The ocean has had an average pH of about 8.2 for the last 300 million years. In recent years that has changed to 8.1. That is a change of 25% in the acidity of sea water. In other words, it has moved in the direction of the acids, but is still a base.
This change in the pH is caused by the absorption of carbon dioxide in the air, which creates carbonic acid. As the level of CO2 in the atmosphere increases, the ocean absorbs more of it. This is both good and bad. When the ocean takes CO2 out of the air, it slows global warming down. That's good. But, the formation of carbonic acid lowers the ocean's pH and that's bad.
A lower pH puts many forms of sea life at risk. Shellfish are possibly the most vulnerable due to how easily their shells dissolve in acid. A more acidic (less base) ocean makes it more difficult for them to build strong shells. Obviously, coral reefs are also at risk. But, a lower pH will also interfere with other forms of sea life. In fact, it is estimated a lower ocean pH will cost us about $1 trillion every year by the year 2100. I obtained that figure from an excellent source of information on ocean acidification, the paleohistory of ocean acidification and the biological, physical and economic costs associated with acidification.
Now, we have enough sensors we can monitor the oceans, with some gaps, at nearly real time. Read this article in Scientific American about the efforts, or this one on LiveScience.com.