Scientists sometimes scoff at modern rainmaking – seeding clouds with crystals to induce precipitation – as a 21st-century version of the ancient tribal rain dance. But their scepticism has not discouraged the increasing use of “weather modification” technology, mainly to increase rainfall but also to take the sting out of damaging storms, particularly hail showers.

Sixty years after US researchers first attempted to wring rainfall from clouds by scattering dry ice and silver iodide crystals from aircraft, it remains impossible to produce unequivocal scientific evidence that weather modification works, says the US National Academy of Sciences in a recent report.