SINGAPORE, Dec 15 (Reuters) - 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 fertilise 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 Australian report's authors, Tom Trull.
"We never even designed measurement programmes to look at ecological change and the risks," said Trull, Ocean Control of Carbon Dioxide programme leader at the Antarctic Climate and Ecosystems Cooperative Research Centre (ACE CRC) 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 commercialise 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.
BLOOMING
"Ocean fertilisation may cause changes in marine ecosystem structure and biodiversity, and may have other undesirable effects," says the ACE CRC position analysis on ocean fertilisation science and policy, soon to be publicly released.
"While controlled iron fertilisation 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 fertilisation. 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 at Nova Scotia in Canada.
"It is extremely important to look at the ecological risks of this kind of activity," he said.
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.
Companies such as California-based Climos and Australia's Ocean Nourishment Corp are planning small-scale experiments to test their ocean carbon capture and sequestration projects.
Ocean Nourishment uses ammonia and urea, delivered via a marine pipeline to a region deficient in nitrogen, to boost phytoplankton growth and boost fish stocks. Climos uses iron and plans experiments in the Southern Ocean in 2010.
"Iron fertilization is no silver bullet for climate change -- which underscores the severity of the problem we have, and the urgency for immediate emissions reductions worldwide," Climos founder and CEO Dan Whaley told Reuters in an email interview.
But he said it was premature to judge iron fertilisation as dangerous.
"Phytoplankton are nature's way of sequestering CO2 to the deep ocean, where nearly 90 percent of earth's carbon lies. Further, most everything we put up in the air is going to the deep ocean eventually. The only question is how long it takes," he said.
Many nations, though, remain cautious and member states of two treaties that govern dumping of wastes at sea passed a non-binding resolution in October calling for ocean fertilisation operations to be allowed only for research.
Parties to the London Convention and related London Protocol, part of the International Maritime Organisation, signed the resolution that said member states were urged to use "utmost caution" to evaluate research proposals to ensure protection of marine life.
ABSORPTION LIMIT
Trull, who participated in the first ocean fertilisation experiment in 1999, one of a dozen since conducted globally, said commercial ventures would need to operate over huge areas of ocean for many years.
The ACE CRC report also says ocean fertilisation just using iron would likely hit an absorption limit of about 1 billion tonnes of carbon (3.7 billion tonnes of CO2) annually, or about 15 percent of mankind's total carbon emissions.
"That really puts the risk in context. We're talking about altering ecosystems of planetary scale for a benefit that won't actually relieve us from dealing with all the other issues, such as conservation or alternative energy generation."
Cullen of Dalhousie University said studies suggested that to sequester large amounts of carbon would require fertilisation of most of the Southern Ocean for long periods of time.
(Editing by Megan Goldin)
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