Oceans are one of the world’s most important carbon sinks. They have helped to keep global warming at bay. But as increased CO2 turns the oceans more acidic, climate scientists realize that global warming is not the only problem they face.
 | Coral Reef - Before and AfterThe photo on the left shows a healthy, protected coral reef off Papua New Guinea. Click on the photo to see the effects of coral bleaching off the coast of Belize (Photos: Reuters) |
Drop a piece of chalk in a glass of vinegar, watch it dissolve, and you'll get an idea of what unchecked carbon dioxide emissions might do to marine life. In fact, scientists now believe that marine species and ecosystems could be among the first casualties of man-made carbon dioxide emissions.
Were it not for the oceans, global warming would have been a lot more pronounced by now. About a third of all man-made carbon dioxide emissions have ended up in the Earth's oceans, which are, along with rainforests, the most important carbon sinks on the planet. But this service has a price: the more CO2 the oceans soak up, the more acidic they become.
When carbon dioxide combines with water, carbonic acid is formed and hydrogen ions are released - a chemical process that increases the ocean's acidity. As a result of increasing CO2 concentrations, ocean surfaces are now 30 percent more acidic than they were before the Industrial Revolution, and probably more acidic than at anytime in the last 20 million years.
The acid test
If carbon emissions grow unchecked, the UN's Intergovernmental Panel on Climate Change (IPCC) says that oceanic acidity could increase further by up to 150 percent from pre-industrial levels until the end of this century.
 | Picture Gallery (click the image to start)See how biodiversity protects against the impacts of climate change (Photo: Reuters) |
This spells trouble for small marine species - mollusks, crustaceans, algae, and plankton - that build their skeletons or shells out of calcium carbonate. Lower pH levels, a measurement for acidity, would disrupt their growth, or worse, dissolve the shells right off their backs. And since these organisms provide the basis of marine food chains, their migration or disappearance could have devastating impacts on larger species.
If, for example, the tiny, swimming sea snails known as pteropods vanish, even whales would suffer. "Pteropods are prey for many species from salmon to whales," says Scott Doney, a senior scientist at the U.S.-based Woods Hole Oceanographic Institution. "Their demise will likely have significant consequences."
Scientists now call ocean acidification "the other half of the CO2 problem" - not the one heating up our atmosphere, but rather the one unfolding below the waves. Researchers fear that increasing acidification could destroy what is left of the world's coral reefs and the very base of marine food chains by the end of this century.
Coral grief
Combined with over-fishing and pollution, acidification threatens the coral reefs all over the world. In many reefs, scientists have already observed the phenomena of "coral bleaching." This occurs when colorful, symbiotic algae cannot survive on their coral hosts because the water is too warm, polluted, or acidic. Once the algae goes, the coral's white skeleton beneath is exposed.
Acidification also disrupts coral calcification, the process that creates reefs. In a December 2007 issue of Science, a team of researchers projected that by century's end, most waters could be too acidic for most coral to grow.
In 2008, Australian scientists found that coralline algae, which glue the reef together and help coral larvae settle successfully, were highly sensitive to increased CO2. "These may die on reefs such as those in the southern Great Barrier Reef before year 2050," study leader Ken Anthony said.
If the IPCC's more dire scenarios for CO2 concentrations and warming come to pass, few existing coral reefs will survive by the end of the century. "The loss of tropical corals would have profound negative impacts, because they support some of the most diverse and rich ecosystems on the planet," says Scott Doney.
The decline of shallow-water reefs would affect millions of people, since these natural structures are essential to supporting local fisheries and tourism, and provide coastal protection from storms. According to the Nature Conservancy, reefs produce up to 375 billion U.S. dollars in "goods and services" each year.
Southeast Asia's vital "Coral Triangle" could disappear by the end of the century, predicted conservation group WWF in 2009, decimating coastal economies and food supplies, and sparking civil unrest and forced migration.
Such predictions are bound to get the attention of policymakers. According to Carol Turley, a scientist at the Plymouth Marine Laboratory in Britain and lead author of the most-recent IPCC assessment, awareness of the acidification issue has increased "hugely" over the last five years.
"The issue of ocean acidification is a very powerful argument for reducing CO2 emissions, but I don't think that it is really used enough," says Turley. "It is reaching climate mitigation policymakers at the international level, but there is still a long way to go."
editor: Valdis Wish
last updated: August 20, 2009
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