(Photograph) - A micro-organism that lives in oceans may have a dramatic effect on global warming, Aisling Irwin writes.

Scientists at the Southampton Oceanography centre are modelling the micro-organisms, called coccolithophores, to test their contribution to the greenhouse effect.

Coccolithophores live in the surface waters of the ocean. Like all phytoplankton, they absorb carbon dioxide from the water to photosynthesise. The ocean replenishes its stocks by absorbing carbon dioxide from the atmosphere.

This reduces the greenhouse effect, which is caused by carbon dioxide and other molecules in the atmosphere preventing heat escaping from the earth.

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But coccolithophores have other effects. They build up shells of calcium carbonate using bicarbonate dissolved in the surface water. This has a paradoxical effect. Removing carbon in the form of bicarbonate alters the carbon balance of the ocean surface, with the net effect that there is a surge in the carbon dioxide concentration in the water, and then in the atmosphere.

"We are setting out to put figures on this," says Toby Tyrrell, research fellow. "It is thought to be very significant. It is important on a global timescale and it could be making the greenhouse effect worse."

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The scientists, led by Patrick Holligan, will build up a computer model of these effects. Eventually, they hope the model will contribute to a global picture of the activities of coccolithophores. From there, their effects can be put into major ocean-atmosphere models of global warming. But before they can do this the scientists have to incorporate other myriad influences that coccolithophores may have on global warming.

For example, coccolithophores shed their carbon-containing shells which then set off on other journeys. Some go back to being bicarbonates in the ocean; some sink into the deep water and reemerge in thousands of years; others sink and become marine sediments.

Coccolithophores also affect cloud formation. They produce dimethyl sulphide, which gets into the atmosphere and causes cloud to condense around it. The amount of cloud affects the amount of light that reaches the ocean surface and therefore the extent to which it heats up. Any light that does reach the ocean surface has to contend with coccolithophore blooms, which reflect light and therefore reduce the extent to which it can heat up the waters.