This new mechanism could have "large climate effects", according to the researchers who discovered it. The trouble is nobody knows whether the effect will speed up global warming or slow it down, the magazine warns.

The Earth is shaded by clouds, which help to moderate global warming. The new findings will add to concerns over how little we know about the processes by which they form, and how they are influenced by human activity. Clouds are already the biggest uncertainty in forecasting the pace of climate change, the magazine says.

New Scientist recalls that clouds are made up of droplets that form when water vapor condenses on solid particles, mostly of sea salt, suspended in the air. The droplets grow and collide, coalescing to form drops large enough to fall as rain.

In clean air, this process of droplet formation is slowed down by organic films that grow naturally on the surface of sea salt particles. Because these layers are hydrophobic and so obstruct the take-up of water by the particles, they act as a natural brake on cloud formation and rainfall.

But in studies at the Rutherford Appleton Laboratory in Oxfordshire, UK, Katherine Thompson of Birkbeck, University of London and colleagues measured for the first time how natural and man-made oxidants in the atmosphere attack these organic layers, the magazine added.

They pumped fine sprays of seawater and oleic acid into a metal chamber, and then introduced ozone. Using Raman spectrometry, the researchers could see how ozone´s oxidizing effect either destroyed the organic layer of oleic acid around single sea salt particles, or converted it into a more water-soluble layer.

The resulting droplets that formed grew by more than a fifth as a result, New Scientist explains.

One possibility is that with droplets growing more quickly, there could be more clouds. This would shade the planet"s surface and help moderate global warming. Equally likely is that faster droplet growth could mean that clouds produce rain more quickly, and so dissipate sooner.

That would lead to a less cloudy world and faster warming, Tompson warns.

By: Prena-Latina