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UNDER THE RADAR| 4 March 2013

Geoengineering: Goldilocks effect to cloud seeding

Philip Ball

Get this climate techno-fix right, and the effect is dramatic, Get it wrong, though, and you make the problem worse. So how do you get this to work as planned?

It’s quite a promise. Using existing technology, we could engineer clouds “to cancel the entire warming caused by human activity from pre-industrial times to present day”. But cloud seeding, the latest of many geo-engineering proposals to mitigate climate change, has a drawback: get it only a bit wrong, and you make the problem worse.

That, however, has been the worry with proposed technical fixes to the climate all along. We could fire a fleet of little mirrors into an orbit around the Sun that locks them in place to deflect sunlight from the Earth. But if it goes wrong, we could be plunged into an ice age. Manipulating the clouds has been a popular idea with would-be geo-engineers, but these proposals face the fact that the climate effects of clouds are among the hardest parts of the climate system to understand and predict, so we can’t be too sure what the results will be.

The new suggestion examined by climate scientist Trude Storelvmo of Yale University and her co-workers targets the cirrus ice clouds that extend their thin and wispy tendrils in the upper troposphere, at altitudes of about 5-15 kilometres. The researchers say that these thin clouds are known with confidence to have a net warming effect on our planet, since their ice crystals re-emit infrared radiation absorbed from the sun-warmed surface back down towards ground. So if we can make cirrus thinner still, we’ll let out more heat and cool the globe.

Read more: BBC – Future – Science & Environment – Geoengineering: Goldilocks effect to cloud seeding.

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