While most activity to get global warming under control focuses on the threatened system most humans are most familiar with—the atmosphere—researchers are warning of the far-reaching implications of climate change’s “evil twin”, ocean acidification.
“Since the industrial revolution, the waters that cover more than two-thirds of our planet’s surface have become increasingly hostile to their inhabitants,” with overfishing, plastic pollution, and warming waters making it “harder for marine life to survive,” Deutsche Welle reports. “But now, perhaps the biggest threat is also one of the most insidious effects of the carbon we pump into the atmosphere.”
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Acidification occurs because oceans absorb up to one-quarter of the carbon dioxide emissions humanity pumps into the atmosphere. “The CO2 reacts with the seawater to form carbonic acid. The more CO2 the ocean takes up, the more acidified it gets,” explained Ulf Riebesell of the GEOMAR Helmholtz Centre for Ocean Research in Kiel, Germany.
“Normal levels of CO2 reacting with seawater would present no problem,” DW notes. “But atmospheric levels of CO2 have not been normal for some time,” hitting successive record highs year after year.
“Acidification continues, but also the ocean loses what we call its buffer capacity,” Riebesell told the paper. “The more acidified it gets, the less CO2 it actually takes up,” leading to an acceleration in atmospheric warming.
What DW calls “healthy seawater” has a pH of 8.2 on a scale of acidity to alkalinity. That level has fallen to 8.1 since the dawn of the Industrial Revolution—and since pH is measured on a logarithmic scale, the seemingly small decline represents a 26% drop in alkalinity, enough to have a major impact on marine life.
For juvenile polar cod, for example, “what we’ve seen is that their survival has decreased by 50% if they’re exposed to even moderate increased CO2 concentrations,” Riebesell said. “The future populations of cod might be down to one quarter to one twelfth of their size today—which will have massive impact on cod fisheries.”
And the impacts go far beyond a single species. “The whole ecosystem responds to these changes,” explained GEOMAR researcher Allanah Paul. “A good example is calcifying organisms. When you lower the seawater pH, they have to use more energy to build their calcium cabinet shell, because these dissolve in seawater that has a lower pH.”
“These waters will become corrosive, meaning they will have conditions where calcium carbonate shells and skeletons just start to dissolve,” Riebesell added. “A lot of organisms will not be able to survive under those conditions in the Arctic and the Antarctic. Biodiversity will drop down strongly in the polar areas.”
If that’s a problem for corals, crustaceans, mollusks, and some types of plankton, it’s just as serious for species that depend on them for food or shelter. “And that includes people,” DW notes. “The oyster industry off the coast of the U.S. state of Oregon has already been hit by ocean acidification. And fish could be at risk, too—both from the direct effects of acidification on their development early in life, and from its effect on the species they prey on.”
The latest studies show ocean acidification moving 10 times faster than it has in the last 55 million years, far too swiftly for species to adapt. The scientists behind that research say drastic cuts in carbon emissions are the only way to slow the decline, but “even if the world manages to cut emissions in line with the Paris agreement goal of keeping global warming below 2.0°C (3.6°F), it may not be enough to stop further acidification,” DW notes.