Timothy Lenton, a climate scientist at the University of Exeter, argues that such pollution could trigger wider instability in the monsoon.

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The Gang Avoidance Project in Lenton gives out advice followed up by workshops in which parents and children are encouraged to talk to each other and the police, project bosses said.

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Similarly sobering conclusions are reached in the second paper, by Tim Lenton of the University of East Anglia and Naomi Vaughan of the Tyndall Centre for Climate Change Research, and published in Atmospheric Chemistry and Physics Discussions.

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Dr Hamilton and Mr Lenton think otherwise.

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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.

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