Coral reefs around the world are disappearing and the culprit here is carbon dioxide.
Silently and steadily, a tragedy is unfolding beneath the ocean's waves: Coral reefs around the world are disappearing. According to some projections, there could be few, if any, left by the end of the century.
This dire and credible prediction has shocked many marine scientists, who had not realised how close to the tipping point coral reefs are. The news is especially disheartening because 2008 is the International Year of the Reef.
The culprit here is carbon dioxide, the greenhouse gas that is responsible for global warming and that also is turning our oceans into an acid bath. Remember your mother's warning that too much Coke would dissolve your teeth? Well, too much acid in the oceans prevents corals from growing their calciferous skeletons. In a December Science magazine article, researchers reported results of models in which they simulated the effects of carbon dioxide emissions over the next century. By 2050, the projections revealed, oceans will be too acidic for coral reefs to grow.
In terms of biodiversity, coral reefs are the rain forests of the ocean. Reefs are home to between 1 million and 9 million species. Nobody knows the exact number. That's one of the goals of the Census of Marine Life being conducted by a network of researchers from more than 50 nations. If reefs disappear, at least half the species that live on them also might go extinct.
Here's the problem. When carbon dioxide enters the ocean, it reacts with water to form carbonic acid. A few other chemical steps ensue, with the outcome that fewer carbonate ions are available for biological systems. Corals are not the only organisms that suffer. All shell-forming marine creatures are adversely affected.
Taking a human analogy, it would be as if your bones could no longer keep growing. We are seeing the effects of ocean acidification. Today, the concentration of carbon dioxide in the Earth's atmosphere is more than 380 parts per million. That's more than at any time during the last 20 million years.
About 25 per cent of this carbon dioxide ends up being absorbed by the oceans. As carbon dioxide levels have risen during the industrial era, the average pH level in the ocean, an indicator of acidity, has dropped by 0.1 pH unit. That might not sound like much, but evidence from Antarctic ice cores shows that the global average is lower than at any time over almost half a million years. As the Science article notes, changes in atmospheric carbon dioxide over the last century "are 2 or 3 orders of magnitude higher than most of the changes seen in the past 420,000 years."
Until recently, many ocean scientists had imagined that as global temperatures rise, corals might begin to adapt. But acidification is a far more serious problem to these inherently delicate organisms. The best-case scenario from the Intergovernmental Panel on Climate Change, which tracks global warming, predicts that carbon dioxide concentrations in the atmosphere will rise to 450 ppm this century unless we change our consumption of fossil fuels quickly. Most models predict a rise to at least 500 ppm if we don't change our consumption habits. That will spell disaster for coral reefs.
Besides being enclaves of biodiversity, coral reefs perform other important functions. In Asia, coral reef-based fisheries provide one-quarter of the fish that help to feed a billion people. They are also critical mechanisms for protection throughout the Earth's tropical regions. Without coral reef barriers, coastal areas will become vulnerable to hurricanes.
Finally, many developing nations rely on reef tourism as a crucial part of their economies. Brainless, immobile and with only the most primitive nervous systems, coral polyps have built some of the most magnificent structures on our planet. They protect us, feed us and astound us with their beauty. Now they need our help - and time is running out.
