by Andrew Woodcock in London

THE oceans' ability to act as a "carbon sink" soaking up greenhouse gases appears to be decreasing, research shows, leading to new fears about global warming.

[1]Measurements of the North Atlantic taken by British scientists over the decade from the mid-1990s to 2005 show the level of carbon dioxide in its waters fell by about half over that time.

One of the authors of the study, published on Saturday in a paper for the Journal of Geophysical Research, said the change may have been triggered by climate change and may also accelerate the process by leaving more CO2 in the atmosphere.

Natural processes mean the amount of CO2 in the atmosphere is reduced when the gas dissolves into the waters of the oceans which cover much of the surface of the earth, turning them into vast "sinks" storing the carbon safely.

But the new study suggests the amount of carbon dioxide entering the oceans is declining, possibly because warmer global weather has heated the water near the surface.

Professor Andrew Watson, of the school of environmental sciences at the University of East Anglia, said there was no known means to artificially reverse the change.

As the 90,000 measurements, taken automatically by merchant ships as they criss-crossed the Atlantic, had been gathered for only a decade, it was too early to be certain whether they reflected a natural variation in CO2 levels or a man-made trend which could be expected to continue, Professor Watson cautioned.

He acknowledged that the processes driving the change were not yet known with certainty. "To be perfectly honest, we don't know," he told BBC radio. "We suspect that it is climactically driven, that the sink is much more sensitive to changes in climate than we expected.

"Therefore, if you have a series of relatively warm winters, the ocean surface doesn't cool quite so much, you don't get so much subsurface water formed and so the CO2 is not being taken down into the deep water."

He warned that the process may fuel climate change.

"It will be a positive feedback, because if the oceans take up less CO2 then CO2 will go up faster in the atmosphere and that will increase the global warming."

There have been proposals to increase the oceans' capacity to absorb CO2 by "fertilizing" them with iron or by building a network of millions of pipes to circulate water from deeper levels far below the surface.

But Professor Watson warned this would have little effect.

Another proposal to alter the weather has been made by US and Israeli scientists, who have revealed plans to weaken hurricanes and steer them off course to prevent tragedies such as Hurricane Katrina. The $US41 billion of damage done to New Orleans in 2005 has spurred two rival teams of climate experts to step up their efforts to enable people to play God with the weather.

Under a scheme proposed by the Massachusetts Institute of Technology, aircraft would drop soot into the near-freezing cloud at the top of a hurricane, causing it to warm up and so reduce wind speeds. Computer simulations of the forces at work in the most violent storms have shown that even small changes can affect their paths - enabling them to be diverted from big cities.

Last month scientists at the Hebrew University of Jerusalem said they had simulated the effect of sowing clouds with microscopic dust to cool the hurricane's base, also weakening it.

Press Association; Telegraph, London
Copyright © 2007. The Sydney Morning Herald.