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Scientists are considering a plan to combat climate change by dumping millions of tons of iron into the ocean to alter its chemical make-up.

They believe the iron could act as a “fertiliser”, promoting the growth of tons of plankton that would soak up carbon dioxide from the surrounding sea water. When the plankton died, their bodies would sink into the deepest waters and sediments, where the carbon would be locked up indefinitely.

The theory, known as “ocean fertilisation”, has long caused controversy among marine scientists, many of whom doubted that it could work. This week leading researchers will meet at the Woods Hole Oceanographic Institution in Massachusetts for a scientific conference to discuss the idea.

The renewed interest follows experiments by Planktos, an American firm, which seeded the Pacific ocean with 100 tons of iron particles, creating a bloom of plankton earlier this year.

“Researchers have carried out a dozen other scientific trials and some have shown interesting results,” said Dr Ken Buesseler, a scientist at Woods Hole.

Two years ago he led an expedition that dumped iron fertiliser into parts of the Pacific and measured the impact on plankton. He found that iron fertilisation did cause a surge in plankton, but there were big variations in the amount that eventually got locked into the sea bed.

In one area about half the plankton sank into the “twilight zone” where their carbon was locked away, but in others this fell to just a few per cent. “Ocean fertilisation needs a lot more research, but if there is a chance that we could use it to cut atmospheric carbon we have to look at it,” said Buesseler.

Buesseler and Scott Doney, a colleague, are hosting the Woods Hole conference which will bring leading scientists together with Planktos and other commercial companies.

Russ George, chief executive of Planktos, said adding a single ton of iron could remove as much as 100,000 tons of dissolved CO2 from the oceans. “Historic increases in atmospheric carbon dioxide levels have changed ocean chemistry and reduced iron availability. Replacing iron artificially on a large scale could promote the growth of enough plankton to completely combat climate change,” George said.

Dr David Santillo, a senior scientist at the Greenpeace research laboratories at Exeter University, said iron fertilisation was a foolish idea. “There is no proof that the plankton blooms result in carbon being locked into sediments,” he said. “Adding iron on such a scale will also damage natural ecosystems.”

The Woods Hole conference comes amid increased anxiety over climate change. Tomorrow Ban Ki-moon, the United Nations secretary-general, will convene the largest meeting of world leaders on climate change at a UN general assembly.

It will be followed by a meeting in Washington on Thursday and Friday, convened by President George W Bush, for the leading economies to discuss energy security and climate change.

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