Mountains matter—that’s the message from the United Nations for International Mountain Day, observed on December 11. More than half the world’s population relies on mountains for fresh water, food, and clean energy. When mountain ecosystems are threatened by climate change and land degradation, it endangers not just plants and animals, but also the people who depend on mountains to survive. Here at Mount Kilimanjaro, viewed from Chyulu Hills National Park in neighboring Kenya, the peak’s shrinking glaciers and ice fields are being closely monitored by scientists.