Scientists say a proposal to fight global warming by dumping iron into Antarctic waters would not do much good.

Some researchers had suggested that iron dumping would lead to a reduction of carbon dioxide in the atmosphere by promoting growth of microscopic algae that consume the gas.Carbon dioxide and other gases in the atmosphere trap energy that radiates away from Earth - the "greenhouse effect" that keeps the globe warmer than if the energy escaped into space.

Many scientists believe that increases in these gases will cause further global warming, disrupting agriculture and causing flooding.

The new study, in today's issue of the British journal Nature, suggests that even if the iron dumping did spur algae growth over 100 years of continuous Antarctic dumping, the resulting reduction in atmospheric carbon dioxide would be about 10 percent, give or take 5 percent.

If that is true, the dumping "would not significantly reduce the atmospheric carbon dioxide content," the authors concluded.

Too little water would be available for storing more carbon dioxide, said Tsung-Hung Peng of the Oak Ridge National Laboratory in Oak Ridge, Tenn., who did the study with Wallace Broecker of Columbia University's Lamont-Doherty Geological Observatory in Palisades, N.Y.

The study used computer simulations to determine how much Antarctic water would get a chance to store the gas.

Jorge Sarmiento, a researcher at Princeton University's Atmospheric and Oceanic Sciences Program, said his simulations suggest the carbon dioxide reductions might be larger. But he agreed that "this is not likely to be a significant contributor to mitigating increases in carbon dioxide."