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in 1973]] The retreat of Glaciers since 1850, worldwide and rapid, 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 Glaciologist s, the temporal coincidence of ''glacier retreat'' with the measured increase of atmospheric Greenhouse Gas es is often cited as an evidentiary underpinning of Anthropogenic (human-caused) Global Warming . Mid-latitude mountain ranges such as the Himalayas , Alps , Rocky Mountains , Cascade Range , and the southern Andes , as well as isolated tropical summits such as Mount Kilimanjaro in Africa , are showing some of the largest proportionate glacial loss. The Little Ice Age was a period from about 1550 to 1850 when the world experienced relatively cooler temperatures compared to the present. Subsequently, until about 1940, glaciers around the world retreated as the climate warmed. Glacial retreat slowed and even reversed, in many cases, between 1950 and 1980 as a slight Global Cooling occurred. However, since 1980 a significant global warming has led to glacier retreat becoming increasingly rapid and ubiquitous, so much so that some glaciers have disappeared altogether, and the existence of a great number of the remaining glaciers of the world is threatened. In locations such as the Andes of South America and Himalayas in Asia , the demise of glaciers in these regions will have potential impact on water supplies. The retreat of mountain glaciers, notably in western North America , Asia, the Alps, Indonesia and Africa, and tropical and subtropical regions of South America, has been used to provide qualitative evidence for the rise in global temperatures since the late 19th century. The recent substantial retreat and an acceleration of the rate of retreat since 1995 of a number of key Outlet Glacier s of the Greenland and West Antarctic Ice Sheet s, may foreshadow a Rise In Sea Level , having a potentially dramatic effect on coastal regions worldwide. GLACIER MASS BALANCE and NSIDC . The increasing downward trend in the late 1980s is symptomatic of the increased rate and number of retreating glaciers.]] See Also: Glacier mass balance Crucial to the survival of a glacier is its mass balance, the difference between Accumulation and ablation (melting and Sublimation ). Climate Change may cause variations in both temperature and snowfall, causing changes in mass balance. A glacier with a sustained negative balance is out of equilibrium and will retreat. A glacier with sustained positive balance is also out of equilibrium, and will advance to reestablish equilibrium. Currently, there are a few advancing glaciers, although their modest growth rates suggest that they are not far from equilibrium. Glacier retreat results in the loss of the low-elevation region of the glacier. Since higher elevations are cooler, the disappearance of the lowest portion of the glacier reduces overall ablation, thereby increasing mass balance and potentially reestablishing equilibrium. However, if the mass balance of a significant portion of the accumulation zone of the glacier is negative, it is in disequilibrium with the climate and will melt away without a colder climate and or an increase in frozen precipitation. The key symptom of a glacier in disequilibrium is thinning along the entire length of the glacier. For example, Easton Glacier (see below) will likely shrink to half its size, but at a slowing rate of reduction, and stabilize at that size, despite the warmer temperature, over a few decades. However, the Grinnell Glacier (pictured above) will shrink at an increasing rate until it disappears. The difference is that the upper section of Easton Glacier remains healthy and snow covered, while even the upper section of the Grinnell Glacier is bare, is melting and has thinned. Small glaciers with minimal altitude gain are most likely to fall into disequilibrium with the climate. Methods for measuring glacier retreat include staking Terminus Location , Global Positioning mapping, Aerial Mapping , and laser Altimetry . MID-LATITUDE GLACIERS Mid-latitude glaciers are located either between the Tropic of Cancer and the Arctic Circle , or between the Tropic of Capricorn and the Antarctic Circle . These two regions support glacier ice from mountain glaciers, valley glaciers and even smaller icecaps, which are usually located in higher mountainous regions. All of these glaciers are located in mountain ranges, notably the Himalayas ; the Alps ; Rocky Mountains and Pacific Coast Range s of North America; the Patagonia n Andes in South America; and mountain ranges in the island nation of New Zealand . Glaciers in these latitudes are more widespread and tend to be more massive the closer they are located to the polar regions. These glaciers are the most widely studied over the past 150 years. As is true with the glaciers located in the tropical zone, virtually all the glaciers in the mid-latitudes are in a state of negative mass balance and are retreating. Eastern hemisphere The World Glacier Monitoring Service reports on changes in the terminus, or lower-elevation end, of glaciers from around the world every five years. In their 1995–2000 edition, they noted the terminal point variations of glaciers across the Alps. Over the five-year period from 1995 to 2000, 103 of 110 glaciers examined in Switzerland , 95 of 99 glaciers in Austria , all 69 glaciers in Italy , and all 6 glaciers in France were in retreat. French glaciers experienced a sharp retreat in the years 1942–53 followed by advances up to 1980, and then further retreat beginning in 1982. As an example, since 1870 the Argentière Glacier and Mont Blanc Glacier have receded by 1,150 (3,800 ft) and 1,400 m (4,600 ft), respectively. The largest glacier in France, the Mer De Glace , which is 11 km (7 miles) long and 400 m (1,300 ft) thick, has lost 8.3% of its length, or 1 km (0.6 miles), in 130 years, and thinned by 27%, or 150 m (500 ft), in the midsection of the glacier since 1907. The Bossons Glacier in Chamonix , France, has retreated 1,200 m (3,900 ft) from extents observed in the early 20th century. In 2005, of 91 Swiss glaciers studied, 84 retreated from where their terminal points had been in 2004 and the remaining 7 showed no change. Other researchers have found that glaciers across the Alps appear to be retreating at a faster rate than a few decades ago. In 2006, the Swiss Glacier survey of 85 glaciers found 84 retreating and 1 advancing. The Trift Glacier had retreated over 500 m (1,600 ft) just in the three years of 2003 to 2005, which is 10% of its total length. The Grosser Aletsch Glacier , the largest glacier in Switzerland, has retreated 2,600 m (8,500 ft) since 1880. This rate of retreat has also increased since 1980, with 30%, or 800 m (2,600 ft), of the total retreat occurring in the last 20% of the time period. Similarly, of the glaciers in the Italian Alps, only about a third were in retreat in 1980, while by 1999, 89% of these glaciers were retreating. In 2005, the Italian Glacier Commission found that 123 galciers were retreating, 1 advancing and 6 stationary. Repeat photography of glaciers in the alps provides clear evidence that glaciers in this region have retreated significantly in the past several decades. Morteratsch Glacier , Switzerland is one key example. The yearly measurements of the length changes started in 1878. The overall retreat from 1878 to 1998 accounts for a total of 2 km with a mean annual retreat rate of approximately 17 m/y. This long-term average was markedly surpassed in recent years receding 30 m/y from 1999–2005. One major concern which has in the past had great impact on lives and property is the death and destruction from a Glacial Lake Outburst Flood (GLOF). Glaciers stockpile rock and soil that has been carved from mountainsides at their terminal end. These debris piles often form dams that impound water behind them and form glacial lakes as the glaciers melt and retreat from their maximum extents. These Terminal Moraine s are frequently unstable and have been known to burst if overfilled or displaced by earthquakes, landslides or avalanches. If a glacier has a rapid melting cycle during warmer months, the terminal moraine may not be strong enough to continue to impound the rising water behind it, leading to a massive localized flood. This is an increasing risk due to the creation and expansion of glacial lakes resulting from glacier retreat. Past floods have been deadly and have resulted in enormous property damage. Towns and villages in steep, narrow valleys that are downstream from glacial lakes are at the greatest risk. In 1892 a GLOF released some 200,000 m³ (260,000 yd³) of water from the lake of the Glacier de Tête Rousse, resulting in the deaths of 200 people in the French town of Saint Gervais. GLOFs have been known to occur in every region of the world where glaciers are located. Continued glacier retreat is expected to create and expand glacial lakes, increasing the danger of future GLOFs. Though the glaciers of the Alps have received more attention from glaciologists than in other areas of Europe, research indicates that throughout most of Europe, glaciers are rapidly retreating. In the Kebnekaise Mountains of northern Sweden , a study of 16 glaciers between 1990 and 2001 found that 14 glaciers were retreating, one was advancing and one was stable. During the 20th century, glaciers in Norway retreated overall with brief periods of advance around 1910, 1925 and in the 1990s. In the 1990s, 11 of 25 Norwegian glaciers observed had advanced due to several consecutive winters with above normal precipitation. However, following several consecutive years of little winter precipitation since 2000, and record warmth during the summers of 2002 and 2003, Norwegian glaciers have decreased significantly since the 1990s. By 2005 only 1 of the 25 glaciers monitored in Norway was advancing, two were stationary and 22 were retreating. In 2006 glacier mass balances were very negative in Norway and of the 26 glaciers examined, 24 were retreating with one statinary and one advancing. The Norweigan Engabreen Glacier has retreated 185 m (603 ft) since 1999, while the Brenndalsbreen and RembesdalsskÃ¥ka glaciers have retreated 276 m (905 ft) and 250 m (820 ft), respectively, since 2000. The Briksdalsbreen glacier retreated 96 m (314 ft) in 2004 alone—the largest annual retreat recorded for this glacier since monitoring began in 1900. This figure was exceeded in 2006 with five glaciers retreating over 100 m from the fall of 2005 to the fall of 2006. Four outlets from the Jostedalsbreen ice cap, Kjenndalsbreen, Brenndalsbreen, Briksdalsbreen and Bergsetbreen had a frontal retreat of more than 100 metres. GrÃ¥fjellsbrea, an outlet from Folgefonna, had a retreat of almost 100 metres. Overall, from 1999 to 2005, Briksdalsbreen retreated 336 m (1102 ft) image shows the formation of numerous glacial lakes at the termini of receding glaciers in Bhutan - Himalaya .]] The Himalayas and other mountain chains of central Asia support large regions that are glaciated. These glaciers provide critical water supplies to arid countries such as Mongolia , western China , Pakistan and Afghanistan . As is true with other glaciers worldwide, the glaciers of Asia are experiencing a rapid decline in mass. The loss of these glaciers would have a tremendous impact on the ecosystem of the region. A WWF report concluded that 67% of all Himalayan glaciers are retreating. 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 Khumbu Glacier , which is one of the main routes to the base of Mount Everest, has retreated 5 km (3.1 miles) since 1953. The Rongbuk Glacier , draining the north side of Mount Everest into Tibet , has been retreating 20 m (65 ft) per year. In India the Gangotri Glacier , which is a significant source of water for the Ganges River , retreated 34 m (111 ft) per year between 1970 and 1996, and has averaged a loss of 30 m (100 ft) per year since 2000. With the retreat of glaciers in the Himalayas, a number of glacial lakes have been created. A growing concern is the potential for Glacial Lake Outburst Floods—researchers estimate 20 glacial lakes in Nepal and 24 in Bhutan pose hazards to human populations should their terminal moraine dams fail. One glacial lake identified as potentially hazardous is Bhutan's Raphstreng Tsho, which measured 1.6 km (0.99 mile) long, 0.96 km (0.59 mile) wide and was 80 m (262 ft) deep in 1986. By 1995 the lake had swollen to be 1.94 km (1.20 mile) long, 1.13 km (0.70 mile) wide 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 potions of that mountain range show that the glaciers that help supply water to this arid region have been losing nearly two cubic km (0.47 mile³) of ice per year between 1955 and 2000. The University Of Oxford study also reported that an average of 1.28% of the volume of these glaciers had been lost per year between 1974 and 1990. To the south of the Tien Shan, the Pamirs mountain range located primarily in Tajikistan has many thousands of glaciers, all of which are in a general state of retreat. During the 20th century, the glaciers of Tajikistan lost 20 km³ (4.8 mile³) of ice. The 70 km (43 mile) long Fedchenko Glacier , which is the largest in Tajikistan and the largest non-polar glacier on Earth, lost 1.4% of its length, or 1 km (0.6 mile), 2 km³ (0.5 mile³) of its mass, and the glaciated area was reduced by 11 km&2 (4.2 mile&2) during the 20th century. Similarly, the neighboring Skogatch Glacier lost 8% of its total mass between 1969 and 1986. The country of Tajikistan and neighboring countries of the Pamir Range are highly dependent upon glacial runoff to ensure river flow during droughts and the dry seasons experienced every year. The continued demise of glacier ice will result in a short-term increase, followed by a long-term decrease in glacial melt water flowing into rivers and streams. have continued to retreat rapidly in recent years. Notice the larger terminal lakes, the retreat of the white ice (ice free of moraine cover), and the higher moraine walls due to ice thinning. ]] In New Zealand the mountain glaciers have been in general retreat since 1890, with an acceleration of this retreat since 1920. Most of the glaciers have thinned measurably and have reduced in size, and the snow accumulation zones have risen in elevation as the 20th century progressed. During the period 1971–75, Ivory Glacier receded 30 m (98 ft) at the glacial terminus, and about 26% of the surface area of the glacier was lost over the same period. Since 1980 numerous small glacial lakes were created behind the new terminal moraines of several of these glaciers. Glaciers such as Classen, Godley and Douglas now all have new glacial lakes below their terminal locations due to the glacial retreat over the past 20 years. Satellite imagery indicates that these lakes are continuing to expand. There has been significant and ongoing ice volume losses on the largest New Zealand glaciers, including Tasman, Ivory, Classen, Mueller, Maud, Hooker, Grey, Godley, Ramsay, Murchison, Therma, Volta and Douglas Glaciers. The retreat of these glaciers has been marked by expanding proglacial lakes and terminus region thinning. Several glaciers, notably the much visited Fox and Franz Josef Glacier s in New Zealand, have periodically advanced, especially during the 1990s, but the scale of these advances is small when compared to 20th-century retreat. Both glaciers are currently more than 2.5 km shorter than a century ago. These large, rapidly flowing glaciers situated on steep slopes have been very reactive to small mass-balance changes. A few years of conditions favorable to glacier advance, such as increased snowfall and cooler temperatures, are rapidly echoed in a corresponding advance, followed by equally rapid retreat when those favorable conditions end. The glaciers that have been advancing in a few locations in New Zealand have been doing so due to a temporary weather change associated with El Niño , which has brought more precipitation and cloudier, cooler summers since 2002. Western hemisphere after melting away in 1990]] North American glaciers are primarily located along the spine of the Rocky Mountains in the United States and Canada, and the Pacific Coast Ranges extending from northern California to Alaska . While Greenland is geologically associated with North America, it is also a part of the Arctic region. Aside from the few Tidewater Glacier s such as Taku Glacier , that are in the advance stage of their tidewater glacier cycle prevalent along the coast of Alaska, virtually all the glaciers of North America are in a state of retreat. The observed retreat rate has increased rapidly since approximately 1980, and overall each decade since has seen greater rates of retreat than the preceding one. There are also small remnant glaciers scattered throughout the Sierra Nevada mountains of California and Nevada . The Cascade Range of western North America extends from southern British Columbia in Canada to northern California. Excepting Alaska, about half of the glacial area in the U.S. is contained in the more than 700 glaciers of the North Cascades , a portion of the range between the Canadian border and I-90 in central Washington . These glaciers store as much water as that contained in all the lakes and reservoirs in the rest of the state, and provide much of the stream and river flow in the dry summer months, approximating some 870,000 m³ (1,140,000 yd³). retreated 450 m from 1987 to 2005.]] As recently as 1975, many North Cascade glaciers were advancing due to cooler weather and increased precipitation that occurred from 1944 to 1976. However, by 1987 all the North Cascade glaciers were retreating, and the pace of the glacier retreat has increased each decade since the mid-1970s. Between 1984 and 2005, the North Cascade glaciers lost an average of more than 12.5 m in thickness and between 20% and 40% of their volume. Glaciologists researching the North Cascades glaciers have found that all 47 monitored glaciers are receding and that four glaciers—Spider Glacier, Lewis Glacier (pictured), Milk Lake Glacier, and David Glacier—have disappeared completely since 1985. The White Chuck Glacier (near Glacier Peak ) is a particularly dramatic example. The glacier shrank from 3.1 km&2 (1.19 miles&2) in 1958 to 0.9 km&2 (0.34 miles&2) in 2002. Similarly, the Boulder Glacier on the southeast flank of Mount Baker retreated 450 m (1,476 ft) from 1987 to 2005, leaving barren terrain behind. This retreat has occurred during a period of reduced winter snowfall and higher summer temperatures. In this region of the Cascades, winter snowpack has declined 25% since 1946, and summer temperatures have risen 0.7 °C (1.2 °F ) during the same period. The reduced snowpack has occurred despite a small increase in winter precipitation; thus, it reflects warmer winter temperatures leading to rainfall and melting on glaciers even during the winter. As Of 2005 , 67% of the North Cascade glaciers observed are in disequilibrium and will not survive the continuation of the present climate. These glaciers will eventually disappear unless temperatures fall and frozen precipitation increases. The remaining glaciers are expected to stabilize, unless the climate continues to warm, but will be much reduced in size. On the sheltered slopes of the highest peaks of Glacier National Park in Montana , its Eponymous glaciers are diminishing rapidly. The area of each glacier has been mapped by the National Park Service and the U.S. Geological Survey for decades. Comparing photographs taken in the mid-19th century with contemporary images provides ample evidence that the glaciers in the park have retreated notably since 1850. Repeat photography over the decades since clearly show that glaciers throughout the park such as Grinnell Glacier are all retreating. The larger glaciers are now approximately a third of their former size when first studied in 1850, and numerous smaller glaciers have disappeared completely. Only 27% of the 99 km&2 (38 miles&2) area of Glacier National Park covered by glaciers in 1850 remained covered by 1993. Researchers believe that by the year 2030, the vast majority of glacial ice in Glacier National Park will be gone unless current climate patterns reverse their course. Grinnell Glacier is just one of many glaciers in Glacier National Park that have been well documented by photographs for many decades. The photographs below clearly demonstrate the retreat of this glacier since 1938.
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