To some entrepreneurs, the icy seas between Australia and Antarctica could become a money spinner by engineering nature to soak up carbon dioxide (CO2) and then selling carbon credits worth millions.

To some scientists and many nations, though, the concept of using nature to mop up mankind's excess CO2 to fight global warming is fraught with risk and uncertainty.

An analysis by an Australian body has urged caution and says more research is crucial before commercial ventures are allowed to fertilize oceans.

"I don't think the scientific community has even sat down and made a list of things we need to check before we feel this would be a low-risk endeavor," said one of the Australian report's authors, Tom Trull.

"We never even designed measurement programs to look at ecological change and the risks," said Trull of the Antarctic Climate and Ecosystems Cooperative Research Center.

Scientists say sprinkling the ocean surface with trace amounts of iron over thousands of square kilometers promotes blooms of tiny phytoplankton, which soak up CO2 in the marine plants. When the phytoplankton die, they drift to the ocean depths, along with the carbon locked inside their cells where it is potentially stored for decades.

Firms eyeing this natural carbon sink hope to commercialize it to yield carbon credits. But no one knows exactly how much carbon can be captured and stored in this way, for how long or the risks to ocean ecosystems from such large-scale geo-engineering. Some fear such schemes could change species composition in the oceans, increase acidity and cause oxygen depletion.

(China Daily via Agencies December 16, 2008)