page_title: Retreat of glaciers since 1850
section_title: Himalayas and Central Asia
hierarchical_section_title: Retreat of glaciers since 1850 / Middle latitude glaciers / Northern hemisphere – Eurasia / Himalayas and Central Asia
caption_attribution_description: English: This image shows the termini of the glaciers in the Bhutan-Himalaya. Glacial lakes have been rapidly forming on the surface of the debris-covered glaciers in this region during the last few decades. USGS researchers have found a strong correlation between increasing temperatures and glacial retreat in this region. According to a joint press release issued by NASA and the U.S. Geological Survey, the great majority of the world’s glaciers appear to be declining at rates equal to or greater than long-established trends. This image from the ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) instrument aboard NASA’s Terra satellite shows the termini of the glaciers in the Bhutan-Himalaya. Glacial lakes have been rapidly forming on the surface of the debris-covered glaciers in this region during the last few decades. According to Jeffrey Kargel, a USGS scientist, glaciers in the Himalaya are wasting at alarming and accelerating rates, as indicated by comparisons of satellite and historic data, and as shown by the widespread, rapid growth of lakes on the glacier surfaces. According to a 2001 report by the Intergovernmental Panel on Climate Change, scientists estimate that surface temperatures could rise by 1.4°C to 5.8°C by the end of the century. The researchers have found a strong correlation between increasing temperatures and glacier retreat. Français&#160;: Image de l'instrument ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) embarqué à bord du satellite Terra de la NASA montrant l'extrémité des glaciers hymalayens du Bhoutan. Depuis quelques décennies, des lacs glaciaires se forment rapidement sur la surface couverte de débris de ces glaciers. Les scientifiques de l'USGS (United States Geological Survey) ont montré une forte corrélation entre la montée des températures et le retrait des glaciers dans la région. En Himalaya, les glaciers reculent a une vitesse alarmante et de plus en plus importante, ce qui est établi par la comparaison des données actuelles et historiques, ainsi que par la multiplication et la croissance rapide des lacs de surface de ces glaciers, selon Jeffrey Kargel, de l'USGS. La grande majorité des glaciers du monde reculent a une vitesse supérieure aux anciennes tendances. Ce recul est fortement corrélé avec l'augmentation des températures. Selon le rapport de 2001 du GIEC (Groupe International sur le Changement Climatique), la température de surface du globe terrestre devrait augmenter de 1.4 à 5.8°C d'ici la fin de ce siècle.
context_page_description: The retreat of glaciers since 1850 affects the availability of fresh water for irrigation and domestic use, mountain recreation, animals and plants that depend on glacier-melt, and, in the longer term, the level of the oceans. Studied by glaciologists, the temporal coincidence of glacier retreat with the measured increase of atmospheric greenhouse gases is often cited as an evidentiary underpinning of global warming. Mid-latitude mountain ranges such as the Himalayas, Rockies, Alps, Cascades, and the southern Andes, as well as isolated tropical summits such as Mount Kilimanjaro in Africa, are showing some of the largest proportionate glacial losses.
  Glacier mass balance is the key determinant of the health of a glacier. If the amount of frozen precipitation in the accumulation zone exceeds the quantity of glacial ice lost due to melting or in the ablation zone a glacier will advance; if the accumulation is less than the ablation, the glacier will retreat. Glaciers in retreat will have negative mass balances, and if they do not find an equilibrium between accumulation and ablation, will eventually disappear.
context_section_description: The Himalayas and other mountain chains of central Asia support large glaciated regions. An estimated 15,000 glaciers can be found in the greater Himalayas, with double that number in the Hindu Kush and Karakoram and Tien Shan ranges, and comprise the largest glaciated region outside the poles. These glaciers provide critical water supplies to arid countries such as Mongolia, western China, Pakistan, Afghanistan and India. As with glaciers worldwide, those of the greater Himalayan region are experiencing a decline in mass, and researchers claim that between the early 1970s and early 2000s, there had been a 9 percent reduction in ice mass. Change in temperature has led to melting and the formation and expansion of glacial lakes which could cause an increase in the number of glacial lake outburst floods (GLOFs). If the present trends persist the ice mass will gradually be reduced, and will affect the availability of water resources, though water loss is not expected to cause problems for many decades.
  In the Wakhan Corridor of Afghanistan 28 of 30 glaciers examined retreated significantly between 1976–2003, with an average retreat of 11 m (36 ft) per year.  One of these glaciers, the Zemestan Glacier, retreated 460 m (1,510 ft) during this period, not quite 10% of its 5.2 km (3.2 mi) length. In examining 612 glaciers in China between 1950 and 1970, 53% of the glaciers studied were retreating. After 1990, 95% of these glaciers were measured to be retreating, indicating that retreat of these glaciers was becoming more widespread. Glaciers in the Mount Everest region of the Himalayas are all in a state of retreat.  The Rongbuk Glacier, draining the north side of Mount Everest into Tibet, has been retreating 20 m (66 ft) per year. In the Khumbu region of Nepal along the front of the main Himalaya of 15 glaciers examined from 1976–2007 all retreated significantly and the average retreat was 28 m (92 ft) per year. The most famous of these, the Khumbu Glacier, retreated at a rate of 18 m (59 ft) per year from 1976–2007. In India, the Gangotri Glacier retreated 1,147 m (3,763 ft) between the years 1936 and 1996 with 850 m (2,790 ft) of that retreat occurring in the last 25 years of the 20th century. However, the glacier is still over 30 km (19 mi) long. In Sikkim, 26 glaciers examined between the years 1976 and 2005 were retreating at an average rate of 13.02 m (42.7 ft) per year.  
  Overall, glaciers in the Greater Himalayan region that have been studied are retreating an average of between 18 and 20 m (59 and 66 ft) annually. The only region in the Greater Himalaya that has seen glacial advances is in the Karakoram Range and only in the highest elevation glaciers, but this has been attributed possibly increased precipitation as well as to the correlating glacial surges, where the glacier tongue advances due to pressure build up from snow and ice accumulation further up the glacier. Between the years 1997 and 2001, 68 km (42 mi) long Biafo Glacier thickened 10 to 25 m (33 to 82 ft) mid-glacier, however it did not advance.
  With the retreat of glaciers in the Himalayas, a number of glacial lakes have been created. A growing concern is the potential for GLOFs researchers estimate 21 glacial lakes in Nepal and 24 in Bhutan pose hazards to human populations should their terminal moraines fail. One glacial lake identified as potentially hazardous is Bhutan's Raphstreng Tsho, which measured 1.6 km (0.99 mi) long, 0.96 km (0.60 mi) wide and 80 m (260 ft) deep in 1986. By 1995 the lake had swollen to a length of  1.94 km (1.21 mi), 1.13 km (0.70 mi) in width and a depth of 107 m (351 ft). In 1994 a GLOF from Luggye Tsho, a glacial lake adjacent to Raphstreng Tsho, killed 23 people downstream.
  Glaciers in the Ak-shirak Range in Kyrgyzstan experienced a slight loss between 1943 and 1977 and an accelerated loss of 20% of their remaining mass between 1977 and 2001. In the Tien Shan mountains, which Kyrgyzstan shares with China and Kazakhstan, studies in the northern areas of that mountain range show that the glaciers that help supply water to 
caption: This NASA image shows the formation of numerous glacial lakes at the termini of receding glaciers in Bhutan-Himalaya.
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