For decades, MayDay parades in Moscow have taken place under clear blue skies, aircraft having deposited dry ice, silver iodide and cement powder to disperse clouds.

Cloud-seeding is a technique to enhance rainfall by introducing particles - often silver iodide crystals - into cloud systems, to help condense water vapor into raindrops.

Physicist Jerome Kasparian, of the University of Geneva, said: "the laser can run continuously, you can aim it well, and you don't disperse huge amounts of silver iodide in the atmosphere."