The change is virtually imperceptible to humans, but it's a different story for some marine animals that build shells. Shell building creatures rely on an excess of dissolved calcium carbonate in the oceans, built up from millenniums of rock erosion on land. More and more of this raw material for shells is being diverted to, in effect, neutralize the acid, leaving less dissolved carbonates for shell-builders to use.
Ocean acidification could harm coral reefs by taking up mineral aragonite in seawater that the small animals use to build the elaborate structures that are home to fish and protect coasts from storm surges.
To be sure, the reaction to rising acidity isn't the same with all species. Researchers at the Woods Hole Oceanographic Institution (WHOI) subjected 18 species of shellfish to varying degrees of CO2-induced acidity in seawater in special tanks. They exposed the water to varying levels of CO2, selected from among the Intergovernmental Panel on Climate Change's emissions scenarios. Unexpectedly seven species, including lobsters, shrimp, and clams, actually built thicker shells.
“Some organisms were very sensitive,” Anne Cohen, a researcher at WHOI who took part in the study, said. "But there were a couple that didn’t respond to CO2 or didn’t respond till it was sky-high – about 2,800 parts per million. We’re not expecting to see that anytime soon.” One of the seven stoics was coral.
The team cautions that the animals were well fed and were not subject to any other environmental stresses. So the results don't shed much light on the synergystic effects acidification might have on the seven survivors. That's for another round of experiments. Still, “we can’t assume that elevated CO2 causes a proportionate decline in calcification of all calcifying organisms,” says Cohen.
No complex computer models here
The science behind the ocean acidification process is far more straightforward than climate science – needing little more than a high-school grasp of chemistry to understand, says Richard Feeley, a researchers at NOAA's Pacific Marine Environmental Laboratory in Seattle, Wash.