Tower snow gun in use. This piece of equipment is commonly found at ski resorts, where it produces extra snow to ensure a good ski-ing surface. A tower snow gun has two pumps, one for water and one for compressed air. Water droplets are sprayed as a fine mist into the compressed air. The water freezes rapidly and forms tiny crystals of snow that fall onto the slopes. To encourage the formation of crystals, a natural protein called Snowmax can be used to aid freezing in a process called nucleation. Climate change has been blamed for the lighter, shorter snow falls that have necessitated the use of tower snow guns. Photographed in the French Alps, France.