April 5, 2016 — Tiny, thin-shelled oysters; crumbling coral reefs; fish unable to make sense of odors; decimated plankton populations. Those are some of the nightmare scenarios conjured by the prospect of a rapidly acidifying ocean caused by unchecked carbon dioxide emissions from fossil fuel burning.
Here’s the chemistry: when carbon dioxide and water mix, they form a weak acid, called carbonic acid. Add enough carbon dioxide, and the pH, or acidity, of the water will start to change. Of course, the ocean is a big place with a lot of water, and it naturally contains other chemicals that can help stabilize the pH.
On the other hand, the ocean has absorbed more than a quarter of all human-produced carbon dioxide since the industrial revolution. The result: globally, the pH of the ocean has dropped by an average of 0.1 pH units. That may not sound like much but, since the pH scale is logarithmic, it translates to a 25 to 30 percent increase in acidity. And, as ocean water becomes more acidic, the carbonate that many animals use to build their calcium skeletons and shells becomes scarcer.