Ocean acidification: Climate change’s evil twin

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    FIVE YEARS ago, during the 11th International Coral Reef Symposium (ICRS) held in Fort Lauderdale, Florida, Dr. Simon Donner of the University of British Columbia embarked on a metaphor for climate change.

    “The climate is like this big ship. We are all on this big ship and the problem is once you hit the brakes it takes a long time for the ship to actually slow down and stop,” the climatologist says. “In our case the ship is the Titanic and we are going to hit the iceberg. It is going to be almost impossible for us not to hit the iceberg at this point.

    What we need to do is everything we can to put the brakes on, to slow the ship down and – to hope for the corals to help us – move the iceberg a little bit. The time for emission reductions isn’t so much now, it was 20 years ago.”

    The same concern was echoed by Janice Lough of the Australian Institute of Marine Science at last year’s ICRS at Cairns, Australia. Over the past century, she said, global temperatures have warmed by 0.7°C and those of the surface tropical oceans by 0.5°C.

    “Tropical coral reef waters are already significantly warmer than they were and the rate of warming is accelerating,” Dr. Lough pointed out. “With or without drastic curtailment of greenhouse gas emissions we are facing, for the foreseeable future, changes in the physical environment of present-day coral reefs.”

    Coral bleaching has been cited as one of consequences of the raising of baseline temperatures in the oceans.

    “If the current trends persist, 20 years from now roughly 50 per cent of reefs globally will experience severe bleaching in most years, and this number could jump to more than 95 per cent in 50 years,” says undersecretary of Commerce for Oceans and Atmosphere and National Oceanic and Atmospheric Administration (NOAA) Administrator Dr. Jane Lubchenco.

    But what most marine scientists around the world are concerned most of is ocean acidification, global warming’s evil twin. “Carbon dioxide in the atmosphere eventually finds its way to and dissolves in the oceans, causing the water to become ‘acidic’… reducing the ability of the coral reefs to deposit calcium carbonate or calcify,” explained Dr. Edgardo Gomez, the founding director of the University of the Philippines Marine Science Institute.

    Scientists say not all of the carbon dioxide emitted by human industrial activities remains in the atmosphere.

    Between 25% and 50% of these emissions over the industrial period have been absorbed by the world’s oceans, preventing atmospheric carbon dioxide buildup from becoming worse. But this atmospheric benefit comes at a considerable price.

    “As a result, the sea water becomes more acidic and the concentration of carbonate ions decreases,” explains Forest Rohwer, author of Coral Reefs in the Microbial Seas. “Carbonate ions are required by corals, crustose coralline algae, and other marine organisms for building their skeletons and shells.

    The increasing ocean acidifi cation that lies ahead will affect even the most remote coral reef ecosystems.”

    Experts claim the average pH (the concentration of hydrogen ions in a solution) of the ocean has already decreased about 0.1 pH unit from pre-industrial values, a shift that corresponds to a 30 percent increase in the concentration of hydrogen ions and a decrease in carbonate ions.

    “This has decreased the rate at which reef-building corals build their skeletons (their rate of calcifi cation) by 20 percent,” Rohwer writes.

    Ocean pH is projected to decrease another 0.3 to 0.4 pH units by the end of this century. This much change in pH is predicted to reduce coral calcification rates to 40-60 percent of normal. “This is a momentous change,” Rohwer notes.

    “Imagine dripping hydrochloric acid onto chalk,” says André Freiwald of the University of Erlangen-Nuremberg, one of the authors of a study that appeared in the professional journal Frontiers in Ecology and the Environment.

    “The chalk would disintegrate immediately; the corals could face a similar fate.” Will it happen soon? “Two hundred years ago, the amount of carbon dioxide in the ocean was around 200 ppm (parts per million).

    Now it is nearly 400 ppm. If people continue their business as usual, the United Nations’ Intergovernmental Panel for Climate Change… predicts that it will be more than 500 ppm at the end of the century,” said Dr. Gomez, who is the chair of the World Bank Coral Reef Targeted Research and Capacity Building for Management Program.

    The acidification, Dr. Gomez added, may be gradual but would happen simultaneously all over the world. He warned that it would be worse than the acidifi cation of agricultural lands due to the use of chemical fertilizers.

    “Land is more manageable. With the use of organic fertilizer and chemicals, land can easily recover. But once the ocean becomes acidic, it would take millions of years to bring back their natural (state).”

    The current acidification may be worse than during four major mass extinctions in history when natural pulses of carbon from asteroid impacts and volcanic eruptions caused global temperatures to soar, according to a study which appeared in the journal Science.

    The international team of researchers from the United States, Great Britain, Spain, Germany and the Netherlands examined hundreds of paleoceanographic studies, including fossils wedged in seafloor sediment from millions of years ago.

    They found only one time in history that came close to what scientists are seeing today in terms of ocean life die-off – a mysterious period known as the Paleocene-Eocene Thermal Maximum about 56 million years ago.

    “We know that life during past ocean acidification events was not wiped out – new species evolved to replace those that died off,” wrote lead author Dr. Barbel Honisch, a paleoceanographer at Columbia University’s Lamont-Doherty Earth Observatory.

    “But if industrial carbon emissions continue at the current pace, we may lose organisms we care about – coral reefs, oysters, salmon.” Dr. Honisch and colleagues said the current rate of ocean acidification is at least 10 times faster than it was 56 million years ago.

    “The geological record suggests that the current acidification is potentially unparalleled in at least the last 300 million years of Earth history, and raises the possibility that we are entering an unknown territory of marine ecosystem change,” said co-author Dr. Andy Ridgwell of Bristol University.

    The effects of acidifi cation can be more dramatic, as observed by a natural longterm “experiment” in the Mediterranean. Just offshore from Italy are thriving communities on non-reef-building corals, beneficial low-growing algae, and abundant sea urchins. Scattered in the region are underwater volcanic vents that release enough carbon dioxide to lower the local pH by 0.2 to 0.4 pH units.

    “In these islands of acidity, the community is dramatically altered,” writes Rohwer. “There are far fewer sea urchins, the algae are mostly large seaweeds, and there are no corals. Might similar changes be in store for other coral communities as ocean acidifi cation continues?”

    The Philippines has around 26,000 square kilometers of coral reef area, the second largest in Southeast Asia.

    Some 500 species of stony corals are known to occur, 12 of which are considered endemic. Today, poor coral cover is found in 40 percent of the country’s reefs, while areas with excellent cover have steadily declined to less than 5 percent from 2000 to 2004.

    “Despite considerable improvements in coral reef management, the country’s coral reefs remain under threat,” said Dr. Theresa Mundita S. Lim, the director of the Protected Areas and Wildlife Bureau.

    “The situation will get worse but it’s not too late tostave off disaster,” Dr. Gomez said. “The government should  take concrete steps to reduce fossil fuel use and unnecessary production of greenhouse gases, stop deforestation, and switch to alternative sources of energy like geothermal, wind power, solar power, even nuclear power. Using hybrid cars will also help.”

    What about you? Reef specialist Meaghan Johnson of the Nature Conservancy said individuals can make a difference. “Anything we can do to reduce stress on coral reefs is a step in the right direction, and there is definitely a role for the public,” she pointed out.

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