Rising acid levels at sea a serious threat

Michael Richardson, Straits Times 8 Jun 09;

MOST of us live and work on land. So we tend to forget that oceans cover more than 70 per cent of the earth and play a vital role in regulating the climate.

For centuries, humans have used the sea as a convenient dumping ground, even as they have intensified their harvesting of fish and other marine products. Vast amounts of waste have been tipped into the sea, which has been treated as an inexhaustible rubbish dump.

It might be so for normal trash. But 70 national academies of science, from both developed and developing countries, recently joined forces to warn that the massive release into the atmosphere of carbon dioxide (CO2), the main global warming gas, is raising acid levels at sea, 'with potentially profound consequences for marine plants and animals, especially those that require calcium carbonate to grow and survive, and other species that rely on these for food'.

The joint statement, issued on June 1, is intended to persuade international negotiators crafting a new framework to combat global warming to treat ocean acidification as one of the world's most important climate change challenges.

When CO2 is absorbed in sea water, it forms carbonic acid, making the water more acidic. Not only that, it reduces the availability of carbonate ions, which many creatures use to build shells and skeletons out of calcium carbonate. As a result, organisms such as plankton, algae, corals and molluscs struggle to build or maintain their protective or supportive structures.

Some scientists reckon that the oceans have absorbed as much as 50 per cent of the CO2 released by human activity over the past 200 years. The national science academies, in their joint statement, took a more conservative view, saying that approximately 25 per cent of the CO2 had been absorbed by the sea.

Still, there is no disagreement among mainstream scientists on the significance of what is happening and why. France's National Centre for Scientific Research, which is in the midst of a major study of ocean acidification with 26 partners, calculates that more than 25 million tonnes of CO2 dissolve in sea water every day, making the oceans a giant natural sink. If that were not so, the amount of CO2 in the atmosphere would be far greater.

If recent trends in CO2 emissions continue, computer projections suggest that by 2050, concentrations of the gas in the atmosphere will be more than double pre-industrial levels and the oceans will be more acidic than they have been for tens of million of years.

The current rate of change is much more rapid than at any time over the past 65 million years. Scientists say that these changes in ocean chemistry would be irreversible for many thousands of years, while the biological consequences could last much longer.

The acid level of the world's oceans is not consistent across the globe. However, no region is expected to escape the impact and South-east Asia is expected to be among the regions hardest hit.

Marine food supplies, already threatened by pollution and over-harvesting, are likely to be reduced, adversely affecting food security, as well as human health and well-being, in places dependent on fish protein.

A study published last month by the World Wide Fund For Nature looked at the future of the coasts, reefs and seas of Indonesia, the Philippines, Malaysia, Papua New Guinea, the Solomon Islands and Timor Leste. These countries form the so-called Coral Triangle. Although just 1 per cent of the earth's surface, this zone includes 30 per cent of the world's coral reefs, 76 per cent of its reef-building coral species and more than 35 per cent of the coral reef fish species. The zone is a breeding ground for many fish, including tuna, and sustains the lives of more than 100 million people.

The study said that the Coral Triangle and its resources were imperilled by rising ocean temperature, acidity and sea level. It warned that as poverty increased, tens of millions of coastal dwellers would migrate to already crowded cities and urban slums.

The national science academies have reinforced this sombre outlook, saying that tropical waters will suffer rapid declines in the carbonate ions important for coral reef construction.

Calling for cuts in global CO2 emissions of at least 50 per cent below 1990 levels by 2050, the academies said that without such cuts coral reefs may dissolve globally by the end of the century and other parts of the marine food chain would be unable to adapt.

Another development climate scientists are watching with concern is whether the oceans will reach the point where they are so saturated in CO2 that they will be unable to absorb as much of the gas as now, leaving more of it in the atmosphere to intensify global warming.

The writer is a visiting senior research fellow at the Institute of Southeast Asian Studies.