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Don't rely on plankton to save the planet
16 February 2002
From New Scientist Print Edition.
Nicola Jones, Hawaii

Encouraging plankton growth in the ocean has been touted by some as a promising way to remove carbon dioxide from the atmosphere. Its opponents fear that it will damage the marine ecosystem, and now a computer model shows that the trick would also be remarkably inefficient.

Adding iron to patches of ocean can make plankton bloom temporarily. The microscopic organisms suck up dissolved carbon dioxide from the water, which in turn is replaced by carbon dioxide from the air. As plankton die and settle on the ocean floor, their carbon is supposedly locked up in the seabed.

Jorge Sarmiento from Princeton and his colleagues developed a complex computer model to analyse how factors such as ocean chemistry and water circulation would affect the process if 160,000 square kilometres of ocean were seeded with iron for a month. They found that 100 years later only between 2 and 11 per cent of the extra carbon that was originally taken up by plankton had actually been removed from the atmosphere.

In their scenario, which covers an area 10 times as big as the largest experiment of this kind ever proposed, fertilising the ocean removes 1 million tonnes of carbon from the atmosphere—just 0.2 per cent of the carbon dioxide humankind spews out each month.

Rough estimates in the past have predicted similarly disappointing results. "[These are] newer and better models," says Sallie Chisholm, an environmental engineer from the Massachusetts Institute of Technology. "But the take-home message is the same. Ocean fertilisation is not the answer to global warming."

From issue 2330 of New Scientist magazine, 16 February 2002, page 16

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