Scientists call it the third pole — but when it comes to clear and present threats from climate change, it may rank first. The high-altitude glaciers of the Himalayas and the Tibetan Plateau — which cover parts of India, Pakistan, Nepal, Bhutan and China — are the water tower of Asia. When the ice thaws and the snow melts every spring, the glaciers birth the great rivers of the region, the mightiest river system in the world: the Ganges, the Indus, the Brahmaputra, the Mekong, the Yellow, the Yangtze. Together, these rivers give material and spiritual sustenance to 3 billion people, nearly half of the world's population — and all are nursed by Himalayan ice.