Ken Caldeira of Stanford University, another of the authors, reckons that it may be feasible to place sulphates in the stratosphere near the poles and thus cool the Earth in a place where global warming manifests itself most strongly, though that would scarcely please the Russians and the Canadians.

ECONOMIST: Global warming

Injecting sulphate particles into the stratosphere, for instance, would cool the Earth by reflecting more sunlight into space. (Nature has already shown that this concept can work, since volcanic eruptions that send sulphur-rich plumes into the stratosphere can temporarily alter the world's climate.) However, Dr Lenton notes that the method becomes less effective as the atmosphere becomes more saturated with particles.

ECONOMIST: Geo-engineering

Research can run far into the stratosphere, but it has a real-world component pulling it back to earth.

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This is because it takes years for the compounds to reach the ozone layer's home in the stratosphere, 15-50 kilometres (10-30 miles) above the earth.

ECONOMIST: Phew, the ozone layer may be saved

Finally, in a third set of simulations, they doubled the CO2 in the atmosphere, but added a layer of sulfate aerosols to the stratosphere, which would deflect about two per cent of incoming sunlight from the earth.

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The idea is to inject clouds of material into the stratosphere, creating a thin haze and deflecting some of the sun's rays away from the Earth, at least temporarily.

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