section_path: Hydrology/Glaciers
section_name: Glaciers
paragraph_text: Glaciers
  
  The great ranges of central Asia, including the Himalayas, contain the third-largest deposit of ice and snow in the world, after Antarctica and the Arctic. Some even refer to this region as the "Third Pole". The Himalayan range encompasses about 15,000 glaciers, which store about 12,000 km (2,900 cu mi), or 3600–4400 Gt (10 kg) of fresh water. Its glaciers include the Gangotri and Yamunotri (Uttarakhand) and Khumbu glaciers (Mount Everest region), Langtang glacier (Langtang region), and Zemu (Sikkim).
  
  Owing to the mountains' latitude near the Tropic of Cancer, the permanent snow line is among the highest in the world, at typically around 5,500 m (18,000 ft). In contrast, equatorial mountains in New Guinea, the Rwenzoris, and Colombia have a snow line some 900 m (2,950 ft) lower. The higher regions of the Himalayas are snowbound throughout the year, in spite of their proximity to the tropics, and they form the sources of several large perennial rivers.
  
  In recent years, scientists have monitored a notable increase in the rate of glacier retreat across the region as a result of climate change. For example, glacial lakes have been forming rapidly on the surface of debris-covered glaciers in the Bhutan Himalaya during the last few decades. Studies have measured an approximately 13% overall decrease in glacial coverage in the Himalayas over the last 40–50 years. Local conditions play a large role in glacial retreat, however, and glacial loss can vary locally from a few m/yr to 61 m/yr. A marked acceleration in glacial mass loss has also been observed since 1975, from about 5–13 Gt/yr to 16–24 Gt/yr. Although the effect of this will not be known for many years, it potentially could mean disaster for the hundreds of millions of people who rely on the glaciers to feed the rivers during the dry seasons. The global climate change will affect the water resources and livelihoods of the Greater Himalayan region.