海角大神

Oceans' rising聽acid聽levels have emerged as one of the biggest threats to coral reefs, acting as the "osteoporosis of the sea" and threatening everything from food security to tourism to livelihoods, the head of a U.S. scientific agency said Monday.

The speed by which the聽oceans'聽acid聽levels has risen caught scientists off-guard, with the problem now considered to be climate change's "equally evil twin," National聽Oceanic聽and Atmospheric Administration chief Jane Lubchenco told The Associated Press.

"We've got sort of the perfect storm of stressors from multiple places really hammering reefs around the world," said Lubchenco, who was in Australia to speak at the International Coral Reef Symposium in the northeast city of Cairns, near the Great Barrier Reef. "It's a very serious situation."

Oceans聽absorb excess carbon dioxide in the atmosphere, increasing sea聽acidity. Scientists are worried about how that increase will affect sea life, particularly reefs, as higher聽acid聽levels make it tough for coral skeletons to form. Lubchenco likened聽ocean聽acidification to osteoporosis 鈥� a bone-thinning disease 鈥� because researchers are concerned it will lead to the deterioration of reefs.

Scientists initially assumed that the carbon dioxide absorbed by the water would be sufficiently diluted as theoceans聽mixed shallow and deeper waters. But most of the carbon dioxide and the subsequent chemical changes are being concentrated in surface waters, Lubchenco said.

"And those surface waters are changing much more rapidly than initial calculations have suggested," she said. "It's yet another reason to be very seriously concerned about the amount of carbon dioxide that is in the atmosphere now and the additional amount we continue to put out."

Higher聽acidity聽levels are especially problematic for creatures such as oysters, because聽acid聽slows the growth of their shells. Experiments have shown other animals, such as clown fish, also suffer. In a study that mimicked the level of聽acidity聽scientists expect by the end of the century, clown fish began swimming toward predators, instead of away from them, because their sense of smell had been dulled.

"We're just beginning to uncover many of the ways in which the changing chemistry of聽oceans聽affects lots of behaviors," Lubchenco said. "So salmon not being able to find their natal streams because their sense of smell was impaired, that's a very real possibility."

The potential impact of all of this is huge, Lubchenco said. Coral reefs attract critical tourism dollars and protect fragile coastlines from threats such as tsunamis. Seafood is the primary source of protein for many people around the world. Already, some oyster farmers have blamed higher聽acidity聽levels for a decrease in stocks.

Some attempts to address the problem are already under way. Instruments that measure changing聽acid聽levels in the water have been installed in some areas to warn oyster growers when to stop the flow of聽ocean聽water to their hatcheries.

But that is only a short-term solution, Lubchenco said. The most critical element, she said, is reducing carbon emissions.

"The carbon dioxide that we have put in the atmosphere will continue to be absorbed by聽oceans聽for decades," she said. "It is going to be a long time before we can stabilize and turn around the direction of change simply because it's a big atmosphere and it's a big聽ocean."