By Michael Christie
The carbon dioxide spewed into the atmosphere by factories, cars and power plants is not just raising temperatures. It is also causing what scientists call "ocean acidification" as around 25 percent of the excess CO2 is absorbed by the seas.
The threat to hard-bodied marine organisms, such as coral reefs already struggling with warming waters, is alarming, and possibly quite imminent, marine scientists gathered this week for a coral reef conference in Fort Lauderdale, Florida, said.
"The threshold for (corals) could be approached by the middle of this century ... when they'll reach a point where they may no longer be able to reproduce themselves as fast as they're being destroyed," said Chris Langdon, am associate professor at the University of Miami's Rosenstiel School of Marine and Atmospheric Science.
"It's not going to be instant. They're not going to disappear that year. It may take another 50 or 100 years."
It was only recently that scientists woke up to the fact that global warming would reduce the pH value of the oceans due to a chemical reaction of water with CO2. The pH scale is a measure of alkalinity or acidity, with 7 being neutral.
The pH value of the oceans has been around 8.2 for hundreds of thousands of years, but since the start of the industrial age in 1800, it has dropped by 0.1.
The U.N.'s Intergovernmental Panel of Climate Change projects it will drop further to 7.8 by the end of the century and some scientists fear the fall could be more precipitous.
A recent study of a natural CO2 vent in the waters off Italy suggests calcifying organisms, like coral, cannot exist in conditions where pH values go below 7.6, said Maoz Fine of Israel's Interuniversity Institute for Marine Science.
"It's like tossing a tooth into a glass of Coke," Fine told reporters at the conference in Fort Lauderdale.
Where pH values dropped to 7.6 at the vent there was a "complete shift from calcifying organisms to none," he said. "It was really quite dramatic, it was very obvious. You don't have to be a specialist to see it."
Stone-hard corals became soft as a sea anemone as their skeletons slowly dissolved in the acidic waters, he said.
Coral specimens had managed to survive without their skeletons in benign laboratory conditions for up to two years, Fine said. But in their natural environment they would be vulnerable to predators, like parrot fish, and suffer increased damage from threats like storms.
Entire reefs would eventually collapse as they lost the mortar holding them together, scientists said.
The threat of ocean acidification is not as immediate to coral as the danger posed by bleaching, which occurs when environmental stresses, like heat, break down the symbiotic relationship between coral polyps and the unicellular algae that give them color.
But it would likely be much harder for coral to adapt to, and would affect coral all over the planet, said Langdon.
Researcher Simon Donner of the University of British Colombia said it was far too late already for the world to avoid climate change.
What coral scientists needed to do was develop ways to help coral reefs adapt to a changing environment so as to buy them another 40 of 60 years of existence before hoped-for cuts in industrial pollution begin to have an impact.
"The climate is like this big ship. In our case the ship's the Titanic and we're going to hit the iceberg. It's almost impossible for us not to hit the iceberg," Donner said.
"What we need to do is everything we can to put the brakes on, to slow the ship down, and then do whatever we can -- hopefully the coral will help us with this -- to move the iceberg a little bit."
(Editing by Jane Sutton and Sandra Maler)