The green role of whitecaps

May 18, 2001

The white horses that cascade from breaking waves play a role in determining global climate.

A study has found that as the brilliant, foaming products of wave crests reflect sunlight, they reduce the amount of solar radiation hitting the surface of the ocean. This affects ocean currents, the atmosphere and the entire climate system.

Robert Frouin and Sam Iacobellis, of the Scripps Institution of Oceanography at the University of California, San Diego, United States, and Pierre-Yves Deschamps, of the Laboratoire d'Optique Atmospherique, France, found that the effect varied in different parts of the world.

In research published in Geophysical Research Letters , the scientists report that while the global average of reflected solar radiation measured 0.03 watts per square metre, this rose to 0.7 watts per square metre in the Indian Ocean.

They discovered that whitecaps seem to have the greatest impact in the Arabian Sea, where skies are often clear and wind speeds great.

In some regions, the effect can be much more substantial in determining the local climate.

"Our estimate of global radiative forcing by oceanic whitecaps is small, yet not negligible compared with the direct forcing by some greenhouse gases and anthropogenic aerosols," Frouin said.

White horses are part of the climate-change equation: greenhouse warming could change wind speeds, which would affect wave cresting, change the amount of reflected radiation and ultimately alter temperature.

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