First he tried giant whisks. Now he is proposing a fleet of yachts that sprays water droplets into the clouds as the way to damp down global warming. The droplets, says engineer Stephen Salter of the University of Edinburgh, UK, will boost the whiteness of low-altitude clouds so that they reflect more sunlight back into space.
In a paper presented at a climate-change conference in Edinburgh last week, Salter says that chimneys mounted on a fleet of 500 £1 million sprayer yachts would cancel a year's worth of global warming from carbon dioxide emissions over their 20-year lifetime.
Instead of sails, the yachts will be propelled by spinning vertical cylinders known as Flettner rotors. The rotors, which were used to successfully cross the Atlantic in the 1920s, will double as chimneys for the water droplets. As the remotely controlled vessels move through the water, the motion will drive propeller-shaped turbines that will generate electricity to power the water sprayers. The form the sprayers will take has yet to be decided, but Salter is investigating the use of a centrifuge or ultrasonic atomiser, like the nebulisers used for dispensing asthma drugs.
The idea builds on a system proposed by Salter three years ago for rainmaking whisk-shaped wind turbines (New Scientist, 25 May 2002, p 20).
Though water vapour can itself cause greenhouse warming, Salter is aiming for an evaporation rate of 90 cubic metres per second, compared to a natural global rate of 12 million cubic metres per second.