Scientists urge caution in CO2 capture schemes

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SINGAPORE — To some entrepreneurs, the wild and icy seas between Australia and Antarctica could become a money spinner by engineering nature to soak up carbon dioxide and then selling carbon credits worth millions of dollars.

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 a leading Australian research body has urged caution and says more research is crucial before commercial ventures are allowed to fertilize oceans on a large scale and over many years to capture CO2.

“I don’t think the scientific community has even sat down and made a list of the things we need to check before we feel comfortable that this would be a low-risk endeavour,” said one of the report’s authors, Tom Trull.

“We never even designed measurement programs to look at ecological change and the risks,” said Trull, Ocean Control of Carbon Dioxide program leader at the Antarctic Climate and Ecosystems Cooperative Research Centre in Hobart.

Scientists say sprinkling the ocean surface with trace amounts of iron or releasing other nutrients over many thousands of square kilometres promotes blooms of tiny phytoplankton, which soak up carbon dioxide 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 or centuries in sediments on the ocean floor.

Firms eyeing this natural carbon sink hope to commercialize it to yield carbon credits to help industries offset their emissions.

The problem is 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 scientists fear such schemes could change species composition in the oceans, increase acidity or cause oxygen depletion in some areas, even promote the release of another powerful greenhouse gas, nitrous oxide.

“Ocean fertilization may cause changes in marine ecosystem structure and biodiversity, and may have other undesirable effects,” says the ACE CRC position analysis on ocean fertilization science and policy, soon to be publicly released.

“While controlled iron fertilization experiments have shown an increase in phytoplankton growth, and a temporary increase in drawdown of atmospheric CO2, it is uncertain whether this would increase carbon transfer into the deep ocean over the longer-term,” it says.

It also says the potential for negative impacts is expected to increase with the scale and duration of fertilization. There are doubts that any damaging effects could be detected in time.

“It is very important to recognise that if deleterious effects increase with scale and duration of fertilization, detection of these cumulative effects may not be possible until the damage is already done,” said John Cullen, professor of oceanography at Dalhousie University. “It is extremely important to look at the ecological risks of this kind of activity.”

Oceans soak up vast amounts of CO2 emitted by nature or through burning of fossil fuels and deforestation and the Southern Ocean plays the greatest role of all the oceans.

But much of the Southern Ocean is depleted of iron and experiments have shown even small amounts of the nutrient can trigger phytoplankton blooms that can last for up to two months.

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