Fifty-six million years ago, a surge of carbon dioxide in the atmosphere raised the acidity of the world’s oceans substantially. Many single-celled organisms, and most likely larger creatures farther up the food chain, went extinct.

The carbon dioxide that humans are pumping into the atmosphere now is causing a similar acidification effect — only 10 times faster.

In a study published today in the journal Science, researchers compared the current rates of ocean change to other major acidification events going back 300 million years, and what they found is shocking: never in that long period did the ocean pH fall as rapidly as it is falling right now (lower pH means higher acidity). Ocean pH has already dropped 0.1 units to 8.1 — it is a logarithmic scale, meaning the drop represents about a 30 percent change in acidity. Within another hundred years, it could drop to 7.8.

At this level, coral, mollusks, and many other creatures will be unlikely to survive. Increased CO2 entering the oceans depletes the carbonate ions that these animals need to make their shells and reefs.

The new study, led by Bärbel Hönisch of Columbia University’s Lamont-Doherty Earth Observatory, found that only the event 56 million years ago, known […]