A climate solution or just a blimp in the air?
Scientists who are working on various concepts for 'geo-engineering' the climate are almost comically eager to stress that they are not trying to come up with a substitute for reducing carbon dioxide emissions, the main cause of man-made global warming. They are just researching back-up systems that we might need if the reductions don't happen fast enough.
'It's hard to imagine a situation except a dire emergency where this will be used, but in order to have that conversation sensibly we need to provide some evidence-based research,' Dr Matt Watson of Bristol University said recently. He is planning to test the feasibility of an 'artificial volcano' that injects sulphur dioxide into the stratosphere in order to cool the planet's surface.
Nobel Prize-winning scientist Paul Crutzen, who suggested this method of cooling the planet five years ago, pointed out that big volcanic explosions inject millions of tonnes of sulphur dioxide into the stratosphere, where they remain on average for a couple of years. During that time, they reflect enough incoming sunlight to lower the temperature at the surface.
The Mount Pinatubo explosion in the Philippines in 1991 put enough sulphur dioxide in the upper atmosphere to lower the average global temperature by half a degree Celsius for two years. No mass extinction or famine ensued.
We cannot assume that there would be no negative side-effects, however, which is why some scientists have been urging that we carry out small-scale experiments to learn more about the process.
That is the goal of a three-year project called Stratospheric Particle Injection for Climate Engineering (Spice), which is being supported by British universities. The first phase involves testing a blimp that will lift a reinforced hosepipe to an altitude of one kilometre and spray water into the air. It's purely about delivery methods: will a balloon tethered to the ground be stable enough to support such a length of hose?
If it passes that test, then the long process begins of scaling up to a blimp big enough to support a 20-kilometre hose, for that is the height at which the sulphate particles must be dispersed. A blimp big enough to do that would be the size of a football stadium, and researchers estimate that it would take about 20 of them, moored over the ocean, to cool the planet by 2 degrees. It could cost, they think, up to US$75 billion, but that would look affordable to a government in a panic - the kind of panic that would occur if the planet got 2 degrees hotter.
This is the first time that a geo-engineering idea has moved into the real world, and it is bound to attract some very hostile attention. Can geo-engineering avert catastrophe? Nobody really knows, and that's the point.
Gwynne Dyer is a London-based independent journalist