The air was thin as a group of scientists trudged through snow near the peak of the Dagu Glacier in southwestern China on a gloomy June morning. It was quiet up there, 3 miles above sea level, except for the sound of running water — a constant reminder of the ice melting right beneath their feet.

As they trekked upwards, oxygen canisters tucked into their fleece jackets, porters walked alongside carrying thick rolls of white fabric. The researchers planned to spread those sheets across more than 4,300 square feet (400 square meters) of the mountain. The film was designed to reflect the sun’s rays back into the atmosphere, effectively shielding the glacier from the heat and hopefully preserving some of its ice.