Some organisms may tolerate a certain amount of change, but thinner shells will make others more vulnerable to damage or predators. Some organisms might also tolerate acidification of internal fluids to a point, yet even so many will expend more energy to maintain their optimal acid-base balance or will struggle to supply their body with oxygen and to sustain cellular functions vital to life. The extra expense of coping with acidification may make them more prone to dying. These stresses will be particularly severe for deep-sea animals, which have adapted to an extremely stable environment. And even if animals survive, the stresses will sap energy they would otherwise use for growth and reproduction.
We would probably see the effects of ocean acidification first in animal groups that have finely tuned environmental ranges, particularly those already “living on the edge” such as coral reefs, which have already suffered widespread bleaching and death from warming ocean temperatures. Less appreciated are effects on massive communities of tiny animals that live in the ocean’s midlevels. These creatures migrate en masse to the surface layer at night to feed yet sink to deep water during the daytime to avoid predators. In so doing, they form a critical link between the warm, oxygenated surface layer and the cold, oxygen-depleted waters of the deep, as well as a critical link in the oceanwide food chain.
Increased acidity and expanding zones of low oxygen in some regions may force these midwater organisms into shallower waters where they would be more exposed to predators. And if, as expected, the zones of low oxygen expand and intensify, many of these migrators could die. Together these effects could slice through this daily, migratory lifeline between shallow and deep waters—an outcome that could impact society’s ocean fisheries.
How well marine life can adapt to rapid acidification remains an open question, but there is real reason for concern. Ocean life has weathered large environmental perturbations during the earth’s history, just barely; some 250 million years ago massive volcanism is thought to have caused ocean acidification and other factors that left 90 percent of marine species dead.
Although man-made climate change will be much milder, strong and immediate action to stabilize CO2 levels is essential to minimize our disruption of ocean chemistry and ecosystems. We can no longer deny our role in global climate change. Now is the time for serious discussion among science, business and political leaders about ways to minimize our impact on our air and water, to set limits on the effects of our fossil-fuel use, and to plan how to adapt to coming change.
Note: This article was originally printed with the title, "The Other CO2 Problem".