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More acidic seas pose new threat, scientists warn
The escalating level of carbon dioxide in the atmosphere is making the world's oceans more acidic, government and independent scientists say. They warn that, by the end of the century, the trend could devastate coral reefs and creatures that underpin the sea's food web.
Although scientists and some politicians have just begun to focus on the question of ocean acidification, they describe it as one of the most pressing environmental threats facing Earth.
"It's just been an absolute time bomb that's gone off both in the scientific community and ultimately, in our public policymaking," said Rep. Jay Inslee, D-Wash., who received a two-hour briefing in May with five other House members. "It's another example of when you put gigatons of carbon dioxide into the atmosphere, you have these results none of us would have predicted."
Thomas Lovejoy, president of the H. John Heinz III Center for Science, Economics and the Environment, has rewritten his new book's paperback version to highlight the threat of ocean acidification. "It's the single most profound environmental change I've learned about in my entire career," he said last week.
A coalition of federal and university scientists will issue a report today describing how carbon-dioxide emissions are, in the words of a press release from the National Center for Atmospheric Research (NCAR) and the National Oceanic and Atmospheric Administration, "dramatically altering ocean chemistry and threatening corals and other marine organisms that secrete skeletal structures."
For decades, scientists have viewed the ocean's absorption of carbon dioxide as an environmental plus, because it mitigates the effects of global warming. But by taking up one-third of the atmosphere's carbon dioxide — much of which stems from exhaust from automobiles, power plants and other industrial sources — the ocean is transforming its pH level.
The pH level, measured in "units," is a calculation of the balance of a liquid's acidity and alkalinity. The lower a liquid's pH number, the higher its acidity; the higher the number, the more alkaline it is. The pH level for the world's oceans was stable between 1000 and 1800 but has dropped 0.1 unit since the Industrial Revolution, according to Christopher Langdon, a University of Miami marine-biology professor.
Scientists expect ocean pH levels to drop by an additional 0.3 units by 2100, which could seriously damage marine creatures that need calcium carbonate to build shells and skeletons. Once absorbed in seawater, carbon dioxide forms carbonic acid and lowers the ocean's pH, making it harder for corals, plankton and tiny marine snails [called pteropods] to form body parts.
Ken Caldeira, a chemical oceanographer at Stanford University who briefed lawmakers along with NCAR marine ecologist Joan Kleypas, said the ocean is more acid than it has been for "many millions of years."
"What we're doing in the next decade will affect our oceans for millions of years," Caldeira said. "CO2 [carbon-dioxide] levels are going up extremely rapidly, and it's overwhelming our marine systems."
Hugo Loaiciga, a geography professor at the University of California, Santa Barbara, is one of the few academics who question the phenomenon. Loaiciga, a groundwater hydrologist, published a paper in the May edition of the American Geophysical Union's journal that suggested the ocean might not become so acidic because enough carbonate material will help restore equilibrium.
Loaiciga wrote that although seawater in certain regions may become more acidic over time, "on a global scale and over the time scales considered [hundreds of years], there would not be accentuated changes in either seawater salinity or acidity from the rising concentration of atmospheric CO2."
Two dozen scientists have written a response questioning this assumption, since it would take thousands of years for such material to reach the ocean from land. "The paper by Loaiciga ignores decades of scholarship, presents inappropriate calculations and draws erroneous conclusions that simply do not apply to real ocean," they wrote. They added that unless carbon-dioxide levels in the atmosphere stabilize soon, the seas would soon exceed the Environmental Protection Agency's recommended acidity limits.
Langdon, who conducted an experiment between 1996 and 2003 in Columbia University's Biosphere 2 lab in Tucson, Ariz., concluded corals grew half as fast in aquariums when exposed to the level of carbon dioxide that will exist by 2050. Coupled with the higher sea temperatures that climate change produces, Langdon said, corals might not be able to survive by the end of the century.
"It's going to be on a global scale and it's also chronic," Langdon said of ocean acidification. "These organisms probably don't have the adaptive ability to respond to this new onslaught."
Stanford University marine biologist Robert Dunbar has studied the effect of increased carbon dioxide on coral reefs in Israel and Australia's Great Barrier Reef. "What we found in Israel was the community is dissolving," Dunbar said.
Plankton and marine snails are critical to sustaining species such as salmon, redfish, mackerel and baleen whales.
"These are groups everyone depends on, and if their numbers go down, there are going to be reverberations throughout the food chain," said John Guinotte, a marine biologist at the Marine Conservation Biology Institute. "When I see marine snails' shells dissolving while they're alive, that's spooky to me."
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