Every day, marine stratocumulus clouds cover about one-third of the world's oceans, mostly around the tropics.
Clouds form when water vapour clings to dust or other particles in the air, creating droplets. Seeding clouds with tiny salt particles would enable more droplets to form, making the clouds whiter and therefore more reflective. Stephen Salter and John Latham believe that boosting reflectivity, or albedo, in just 3 per cent of marine stratocumulus clouds would reflect enough sunlight to curb global warming.
In order to achieve this they have designed GPS-steered wind- powered boats that would cruise the tropical latitudes, churning up salt spray.
Until the concept is tested, neither is exactly sure how many ships would be needed to mitigate global warming.
"Maybe between 5,000 and 30,000," says Salter.
Latham initially raised the notion in a 1990 paper.
"The article went down like a lead balloon," he says.
But in the past two years the concept has gained currency again. The attractiveness of the idea is that it can easily be fine-tuned. "If we tried it and there was some deleterious effect, we could switch it off, and within four or five days all evidence would have disappeared," Latham says.
One worry is that although the tiny salt particles released by evaporating sea mist are perfect for marine stratocumulus cloud formation, they are too small to create rain clouds.
Purists, however, argue that we have interfered enough with climate as it is.
