Unfortunately, the more of them there are, the warmer the planet. This is because they're actually made of tiny ice crystals which trap heat in the atmosphere.
They're not the root cause of the climate change (that would be CO2) but it's been realised that, by dispersing enough of them, we could balance out all the warming effect we've had so far....
It was David Mitchell of the Reno Desert Research Institute that suggested the original cloud-busting idea back in 2009. Now Trudo Storelvmo and his team from Yale University have used climate modelling to test the idea. By adding powdered bismuth triiodide into the layer of the atmosphere where cirrus form, it greatly reduced their occurrence. Done on a global scale it would wipe out the 0.8 degrees C of man-made warming made so far.
Unfortunately, if you get the concentration wrong (always possible in something as dynamic and complex as the real atmosphere), it would have the opposite effect. Not good.
Even if we did understand enough about the atmosphere to safely achieve the effect we wanted safely: a) We'd have to continue doing it year after year; b) It wouldn't make climate change go away. It would just continue building (as CO2 levels keep increasing) until our efforts we're cancelled out; c) Ocean acidification, which could have disastrous effects on marine life, would continue to increase unabated.
So much for that idea then.
[Source: New Scientist 26th Jan 2013]
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