When it comes to climate change, almost all the attention is on the air. What's happening to the water, however, is just as worrying -- although for the moment it may be slightly more manageable.
Here's the problem in a seashell: As the oceans absorb about a quarter of the carbon dioxide released by fossil-fuel burning, the pH level in the underwater world is falling, creating the marine version of climate change. Ocean acidification is rising at its fastest pace in 300 million years, according to scientists.
The most obvious effects have been on oysters, clams, coral and other sea-dwelling creatures with hard parts, because more acidic water contains less of the calcium carbonate essential for shell- and skeleton-building. But there are also implications for the land-based creatures known as humans.
It's not just the Pacific oyster farmers who are finding high pH levels make it hard for larvae to form, or the clam fishermen in Maine who discover that the clams on the bottom of their buckets can be crushed by the weight of a full load, or even the 123.3 million Americans who live near or on the coasts. Oceans cover more than two-thirds of the earth, and changes to the marine ecosystem will have profound effects on the planet.
Stopping acidification, like stopping climate change, requires first and foremost a worldwide reduction in greenhouse-gas emissions. That's the bad news. Coming to an international agreement about the best way to do that is hard.
Unlike with climate change, however, local action can make a real difference against acidification. This is because in many coastal regions where shellfish and coral reefs are at risk, an already bad situation is being made worse by localized air and water pollution, such as acid rain from coal-burning; effluent from big farms, pulp mills and sewage systems; and storm runoff from urban pavement. This means that existing anti-pollution laws can address some of the problem.
States have the authority under the U.S. Clean Water Act, for instance, to set standards for water quality, and they can use that authority to strengthen local limits on the kinds of pollution that most contribute to acidification hot spots. Coastal states and cities can also maximize the amount of land covered in vegetation (rather than asphalt or concrete), so that when it rains the water filters through soil and doesn't easily wash urban pollution into the sea. States can also qualify for federal funding for acidification research in their estuaries.
Such research can hardly happen fast enough. It's still not known, for instance, exactly to what extent acidification is to blame for the decline of coral reefs. And if the chemical change in the ocean makes it harder for sea snails and other pteropods to survive, will that also threaten the wild salmon and other big fish that eat them?
Better monitoring of acidification would help scientists learn how much it varies from place to place and what makes the difference. This calls for continuous readings, because pH levels shift throughout the day and from season to season. Engineers are designing new measuring devices that can be left in the water, and it looks like monitoring will eventually be done in a standardized way throughout the world.
In the meantime, researchers are finding small ways to give local populations of shellfish their best chance to survive -- depositing crushed shells in the mudflats where clams live, for instance, to neutralize the sediment, or planting sea grass in shellfish habitats to absorb CO2. Such strategies, like pollution control, are worthwhile if only to help keep shellfish populations as robust as possible in the short term, perhaps giving natural selection the opportunity to breed strains better suited to a lower-pH world.
These efforts also give humans more time to learn about ocean acidification. And maybe they will help their political leaders better understand the urgency of international cooperation on limiting greenhouse gas emissions.
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