torsdag 3. januar 2019

Collapsing glaciers threaten Asia’s water supplies

The ‘third pole’ is the planet’s largest reservoir of ice and snow after the Arctic and Antarctic. It encompasses the Himalaya–Hindu Kush mountain ranges and the Tibetan Plateau. The region hosts the world’s 14 highest mountains and about 100,000 square kilometres of glaciers (an area the size of Iceland). Meltwater feeds ten great rivers, including the Indus, Brahmaputra, Ganges, Yellow and Yangtze, on which almost one-fifth of the world’s population depends.

Climate change threatens this vast frozen reservoir (see ‘Third pole warming’). For the past 50 years, glaciers in the Himalayas and Tibetan Plateau have been shrinking. Those in the Tian Shan mountains to the north have lost one-quarter of their mass, and might lose as much as half by mid-century. Their meltwater is expanding lakes. River flows at the start of summer peak earlier than they did 30 years ago. And weather patterns are shifting. A weaker Indian monsoon is reducing precipitation in the Himalayas and southern Tibetan Plateau; snow and rain are increasing in the northwestern Tibetan Plateau and Pamir Mountains.