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New climate change signal: oceans turning acidic

Climate change is driving talks to curb greenhouse gas emissions in Copenhagen, but scientists warn that rising CO2 is turning oceans more acidic.

By Peter N. SpottsStaff writer / December 9, 2009

A gam of Minke whales pass icebergs in the Southern Ocean off the Australian Antarctic Territory in this December 2007 file photo.

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COPENHAGEN, DENMARK -- Forget "climategate" and arguments over whether the Earth is really warming. If you need a simple, non-controversial scientific reason to support curtailing greenhouse gas emissions, stop looking skyward and look at the pH of the oceans.

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At least that's the argument Jeffrey Short made Tuesday at the global climate change summit in Copenhagen. Dr. Short, the Pacific science director for Oceana, an environmental group working to protect the world's oceans, says that regardless of the impact on climate, the billions of tons of carbon-dioxide (CO2) that human activity pumps out every year is making oceans more acidic.

That's threatening fisheries that millions rely on for food and livelihoods. Already some shellfish, from commercially important crabs, clams, and mussels to tiny creatures called pteropods (dubbed the "potato chips of the ocean" for the important rung they occupy near the bottom of the marine food chain), are showing the effects of ocean acidification. Coral reefs, important nurseries for commercial fish species, are also being threatened.

The damage to the oceans should be enough on its own to push policy makers to sign a global agreement to reduce CO2 emissions, "even if carbon dioxide didn't do anything to warm the atmosphere," says Short, who spent more than 30 years as a marine scientist at the National Oceanic and Atmospheric Administration (NOAA) before entering the policy arena.

Ocean acidification refers to the effect CO2 has on seawater as the oceans take up the gas. The world's oceans absorb roughly 25 percent of the CO2 humans release into the atmosphere each year. That CO2 reacts with seawater to form small but increasing amounts of carbonic acid.

Shellfish as canaries in the coal mine

The change is virtually imperceptible to humans, but it's a different story for some marine animals that build shells. Shell building creatures rely on an excess of dissolved calcium carbonate in the oceans, built up from millenniums of rock erosion on land. More and more of this raw material for shells is being diverted to, in effect, neutralize the acid, leaving less dissolved carbonates for shell-builders to use.

Ocean acidification could harm coral reefs by taking up mineral aragonite in seawater that the small animals use to build the elaborate structures that are home to fish and protect coasts from storm surges.

To be sure, the reaction to rising acidity isn't the same with all species. Researchers at the Woods Hole Oceanographic Institution (WHOI) subjected 18 species of shellfish to varying degrees of CO2-induced acidity in seawater in special tanks. They exposed the water to varying levels of CO2, selected from among the Intergovernmental Panel on Climate Change's emissions scenarios. Unexpectedly seven species, including lobsters, shrimp, and clams, actually built thicker shells.

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