Clouds Could Clear Way To Saving Planet
February 10 2005
Earth looks as if it is about to overheat. Temperatures are rising, ice sheets are melting and all the evidence points towards a greenhouse future. But what if we could reduce the planet's temperature? Would that give us some time to wean ourselves off fossil fuels and find alternative sources of energy?
This is what a group of eminent atmospheric physicists and an engineer are proposing, and they have come up with an idea to halt the Earth's warming.
Using nothing more than salt water and wind power, they have designed a device that will increase the reflectivity of some of the Earth's clouds, bouncing more incoming sunlight back into space. They argue that this natural heat shield could be turned on and off at will, giving us a vital extra few decades to sort out the mess we are in. (image right from The Engineer Online)
John Latham, an atmospheric physicist based at the National Center for Atmospheric Research in Colorado, first came up with the idea about 15 years ago.
"I outlined my idea in Nature, but at that time there wasn't a strong awareness of the global warming problem and so there wasn't a big response," he says.
But more recently, the idea of a greenhouse world has become a dinner-party conversation topic and suddenly everyone is interested in ways of preventing the Earth from turning into a sauna. Together with colleagues, Latham has resurrected the idea and this time people are starting to take it seriously.Clouds come in different colours, shapes and sizes and occur at various altitudes; not just any old cloud will do. An increase in the high-level, wispy, cirrus clouds would actually have the opposite of the desired effect: making the Earth warmer as they trap more heat in. (image left from enchantedlearning.com, click image for detail)
It turns out that the low-level, lumpy grey clouds, known as stratocumulus, are the best for the job, bouncing sunlight back into space, off their bright, shiny tops. (image right from private-pilot-ground-school.com)
Which is all very well, but how do you go about making stratocumulus cloud more reflective?
Stephen Salter, the innovative Edinburgh University engineer, (known best for his invention of Salter's duck - the 300-tonne floating canister designed to drive a generator from the motion of bobbing up and down on waves) thinks he has the key. (image left of Professor Salter, from nek.no)
"We need to atomise seawater and throw tiny droplets into the air," he says. The idea is that this fine mist of sea-spray evaporates, leaving tiny particles of sea salt that get sucked up into marine stratocumulus clouds on rising currents of air.
These little particles act as centres for extra droplets to form. "Clouds become more reflective if you increase the number of droplets in them," explains Latham. A bonus of filling the clouds with smaller droplets is that they tend to last for longer, reflecting more sunlight back into space, before they disperse.