Tropical glaciers are rapidly receding, and nowhere are they thinning faster, relative to their size, than in the Andes, whose ice caps shrank by nearly a third between 2000 and 2016. Glaciers are vital resources for communities in these arid regions, and their accelerated retreat, caused by warming temperatures, threatens not only the livelihood of indigenous farmers but also the entire agricultural and hydroelectric sector from Chile to Bolivia. High-altitude lagoons risk overflow as glaciers melt, but flooding will be followed by drought in the coming years. Densely populated cities such as