SYDNEY - Rising carbon dioxide emissions are making the world's oceans more acidic, particularly closer to the poles, heralding disaster for marine life, a major UN report on climate change impacts says. Harvey Marchant, Australian lead author on polar regions for the report, the second of four this year by the UN climate panel, said research showed a high take-up of carbon dioxide by polar oceans was producing marked changes in several species.

The report, released in Brussels on Friday, carries the toughest UN warning yet about the impacts of global warming. Marchant, a former head of biology at the Australian Antarctic Division, said in Canberra that Southern Ocean species were more susceptible because cold waters absorb more carbon dioxide than warmer waters.

"Carbon dioxide emissions into the atmosphere continue to rise, putting a greater strain on the world's oceans which are being forced to absorb more of these emissions than ever before and with potentially catastrophic effects," he said. "Many important planktonic species such as pteropods, or sea snails, and some algae and single-celled animals rely on calcium carbonate for their shells to develop," he said. "The more carbon dioxide taken up by the ocean the more acidic it becomes, inhibiting calcium carbonate formation and leaving these species vulnerable."

Changes could also affect the chemistry of dissolved nutrients, potentially causing large-scale changes in marine ecosystems with a knock-on effect to other larger species, such as fish and squid that rely on these organisms to survive. Other recent reports say corals and molluscs are also being affected by increasingly acidic oceans, disrupting the processing of calcium carbonate for their skeletons and shells.

Marchant said that it was not known how long it would take for these effects to be reversed.

A report by the Royal Society in 2005 said there appeared to be no practical way to remove the additional carbon dioxide from oceans after it had been absorbed, nor any realistic way to reverse its widespread chemical and biological effects. It would take many thousands of years for natural processes to remove the excess gas and return to a level close to their pre-industrial state, it said.

The first report by the UN's Intergovernmental Panel on Climate Change, released on February 2, said it was "very likely" human activities were heating the planet. It predicted more severe rains, melting glaciers, droughts, heatwaves and rising sea levels, particularly if ice sheets in Antarctica or Greenland thaw.

The IPCC report said present carbon dioxide levels of about 380 parts per million far exceed the natural range of the past 650,000 years. The gas has risen from about 280 ppm since pre-industrial times and concentrations are set to grow rapidly in the next 50 years unless the world curbs its increasing appetite for fossil fuels.

(Planet Ark, 10/04/2007)