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.
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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鈥攋ust 0.2 per cent of the carbon
dioxide humankind spews out each month.
Rough estimates in the past have predicted similarly disappointing results.
鈥淸These are] newer and better models,鈥� says Sallie Chisholm, an environmental
engineer from the Massachusetts Institute of Technology. 鈥淏ut the take-home
message is the same. Ocean fertilisation is not the answer to global warming.鈥�
