Our power plants and cars have pumped so much carbon dioxide into the atmosphere that the oceans are becoming more acidic. Something like a quarter of our carbon dioxide pollution dissolves into the seas, where it reacts with water:

CO2 (aq) + H2\leftrightarrow H2CO3 \leftrightarrow HCO3 + H+ \leftrightarrow CO32− + 2 H+

Illustration by Perry Shirley
Illustration by Perry Shirley

Those leftover hydrogen ions at the right of the equation add up. The hydrogen ion concentration at the surface of the world’s oceans has increased by 26 percent since pre-industrial times, leading to a pH decline of 0.1. That might not sound like much, but it has been enough to kill off billions of farmed shellfish and punch holes in the shells of wild sea snails.

Shellfish and corals are especially vulnerable to ocean acidification because they rely on calcium carbonate to make their shells and skeletons. Ocean acidification increases concentrations of bicarbonate ions while decreasing concentrations of carbonate ions—and these animals need calcium carbonate to produce their protective body parts.

Fish, meanwhile, are thought to be suffering neurological effects of acidifying oceans, while vast mats of algae are expected to flourish.

The good news is that populations of animals naturally adapt to changes in their environments—and evolutionary changes to help some species cope with ocean acidification are already underway. The bad news is that changes in oceanic pH levels might be happening too quickly for animals to adapt, threatening scores of marine species with extinction.

I asked Ryan Kelly, an assistant professor at the University of Washington’s School of Marine and Environmental Affairs, and a coauthor of a recent BioScience paper about acidification that I wrote about for Pacific Standard, whether we could do anything to help species accelerate the rate with which they evolve needed adaptations.

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